Description of Operation. McQuay MicroTech II

Description of Operation

The following sections describe how the various zone (or space comfort) control unit processes function to maintain temperature, ventilation and pressure control. The “Operating States and Sequences” section provides an overall description of unit operation. The subsequent sections provide detailed descriptions of the various control processes and how the related set points and parameters affect them.

The related set points and parameters are listed at the beginning of each applicable sub-section. The default keypad programmable values are shown in italic letters.

Note: Not all the features covered in this section apply to all units depending on the specific unit options. The applicable items should be read and understood before making set point or control parameter changes.

Operating States and Sequences

About Operating States

Operating states define the current overall status of the rooftop unit. The operating state can be displayed and the unit operating condition can be quickly determined by viewing the UnitStatus= parameter in the System menu. Each operating state summarizes the following information: l l l l l l

Discharge and return/exhaust fan status

Outdoor air damper status

Return/exhaust airflow capacity

Heating system status

Cooling system status

Fan Operation Output status (MCB-BO3)

Table 28 shows the all the normal operating states and the

status information they summarize

Operating State Descriptions

The following sections describe each of the unit operating states.

Off

There are five different Off operating states. In any of the

Off operating states the unit is shut down. The fans are off and the outdoor air dampers are closed, any fan inlet vanes or VFD is driven to 0%. Cooling and heating are disabled.

The Fan Operation Output (MCB-BO3) is open.

The five different Off operating states are described in the following sections:

Off Unoc . Generally, the unit operating state is Off Unoc when it the unit is being scheduled on and off by a time clock function and the time schedule indicates an unoccupied period. Specifically, the operating state is Off Unoc when the

Occupancy= parameter indicates “Unocc” and none of the unoccupied unit operation functions are active. For details regarding the Occupancy=

parameter refer to “Occupancy” on page 46. For details regarding unoccupied unit operation

functions refer to “Unoccupied Control” on page 89.

Off Net . The unit operating state is Off Net when the Appl

Mode= parameter is set to “Off” via a network signal and the

Ctrl Mode= parameter is set to “Auto.” For detailed information regarding the Appl Mode= and Ctrl Mode= parame-

ter, refer to “Auto/Manual Operation” on page 45.

The unit operating state is also Off Net when the Emerg

Override= parameter in the Occupancy menu is set to “Off.”

Refer to “Emergency Override” on page 48.

Table 28: Operating States

Operating

State

Off

Startup

Recirc

Fan Only

Econo

Cooling

MWU

Heating

Min DAT

UnocEcon

UnocClg

Discharge/

Return Fans

Off

Off

On

On

On

On

On

On

On

On

On

Exhaust

Fan

Off

Off

Off

Cycling

Cycling

Cycling

Off

Cycling

Cycling

Cycling

Cycling

OA

Dampers

Closed

Closed

Closed

Minimum

Modulating

Minimum or

Open a

Closed

Minimum

Minimum

Modulating

Closed or

Open b

Closed

Return

Airflow

Capacity

0%

0%

Modulating

Modulating

Modulating

Modulating

Modulating

Modulating

Modulating

Modulating

Modulating

Exhaust

Airflow

Capacity

0%

0%

0%

Modulating

Modulating

Modulating

0%

Modulating

Modulating

Modulating

Modulating

Heat

Enabled

No

No

No

No

No

No

Yes

Yes

Yes

No

No

Mechanical

Cooling

Enabled

No

No

No

No

No

Yes

No

No

No

No

Yes

Fan Output

(MCB-BO3)

Open

Closed

Closed

Closed

Closed

Closed

Closed

Closed

Closed

Closed

Closed

UnocHtg On Off Modulating 0% Yes No Closed a.

When the OA Ambient= parameter indicates “Low”, the economizer outdoor air dampers is fully open; when the OA Ambient= parameter indicates “High”, the economizer outdoor air dampers are at Eff Min OA Pos= value.

b.

When the OA Ambient= parameter indicates “Low”, the outdoor air dampers are fully open; when the OA Ambient= parameter indicates

“High”, the outdoor air dampers are fully closed.

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Off Sw. The unit operating state is Off Sw when a field supplied and installed switch across terminals 101 and 104 on the unit field terminal block (TB2) is in the on or closed position (binary input MCB-BI2 on). Refer to “Manual Unit

Enable/Disable” in IM 696, MicroTech Applied Rooftop Unit

Controller .

Off Alm. The unit operating state is Off Alm when an active alarm of the “fault” type has a unit shut down. Refer to

“Alarm Monitoring” on page 51 for a description of “fault”

alarms.

Off Man. The unit operating state is Off Man when the Ctrl

Mode= parameter is set to “Off.” For detailed information regarding the Ctrl Mode=

parameter, refer to “Ctrl Mode” on page 45.

Startup

When a unit is commanded to start the unit always enters the

Startup operating state from the Off operating state. The unit remains in the Startup operating state for an adjustable time period defined by the Start Init= parameter in the Timer Settings menu (default value is 180 seconds) before entering the

Recirc operating state. During the Startup operating state the unit is prepared for startup. The fans remain off, the outdoor air dampers are driven closed, any fan inlet vanes are driven to a fixed 17% minimum position (VFD remains at 0% speed). Cooling and heating remain disabled. The Fan Operation Output (MCB-BO3) is closed.

For more information regarding the Startup operating state,

refer to “Startup Control” on page 64.

Recirc

Units with return air always enter the Recirc operating state after the completion of the Startup operating state. In the

Recirc operating state fans are started and operate while the outdoor air dampers remain closed. This allows temperature conditions throughout the unit and space to equalize before temperature control begins. Cooling and heating remain disabled. The Fan Operation Output (MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained. The unit remains in the

Recirc operating state until the Recirculate State Timer expires. This timer is adjustable from 2 to 60 minutes with the Recirculate= parameter in the Timer Settings menu.

Note: 100% outdoor air units do not transition through the

Recirc operating state.

For more information regarding the Recirc operating state,

refer to “Startup Control” on page 64.

Fan Only

The unit enters the Fan Only operating state during occupied operation when cooling and heating are either not required based unit heat/cool changeover function or are disabled.

During the Fan Only operating state, the outdoor air dampers are either 100% open on a 100% outdoor air unit or are controlled to the Eff Min OA Pos= parameter in the OA Damper menu. Cooling and heating operation is disabled. The Fan

Operation Output (MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained.

Econo

The unit enters the Econo operating state when cooling is required during occupied operation when economizer operation is enabled. During the Econo operating state, mechanical cooling and heating are disabled. The outdoor and return air dampers are modulated to maintain the discharge air temperature at the Eff Clg Spt= parameter in the Discharge

Cooling menu. The Fan Operation Output (MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained. Mechanical cooling and heating are disabled.

Note: 100% outdoor air units do not transition through the

Econo operating state.

For detailed information regarding economizer operation,

refer to “Economizer” on page 68.

Cooling

The unit enters the Cooling operating state during occupied operation when cooling is required and the economizer is either disabled, not present, or already fully opened. During the Cooling operating state, the outdoor air dampers are fully open if the unit is a 100% outdoor air unit or if economizer operation is enabled. The outdoor air dampers are controlled to the Eff Min OA Pos= parameter if economizer operation is disabled or not present. Mechanical cooling is supplied as required to maintain the Ctrl Temp= parameter at the Eff Clg

Spt= in the Zone Cooling menu. The Fan Operation Output

(MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained.

Heating is disabled.

For detailed information regarding the cooling operation,

refer to “Cooling: Multistage” on page 72 or “Cooling: Modulating” on page 77 as applicable.

MWU

When the unit transitions from unoccupied to occupied operation and heating is required to warm the Ctrl Temp= parameter up to the Eff Htg Spt= setting in the Zone Heating menu, the unit enters the MWU (Morning Warm-up) operating state after the Startup and Recirc operating states are complete.

The MWU operating state is similar to the Heating operating state except that the outdoor air dampers are held closed rather than controlled to the Eff Min OA Pos= parameter.

Once entering the MWU operating state, the unit remains there until either the Ctrl Temp= parameter warms up to the

Eff Htg Spt= setting in the Zone Heating menu or until a maximum morning warm-up time period expires. This time period is defined by the Max MWU= parameter in the Timer

Settings menu. The Fan Operation Output (MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained. Cooling is disabled.

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Note: 100% outdoor air units do not transition through the

MWU operating state.

For detailed information regarding morning warm-up heat-

ing operation, refer to “Heating: Multistage” on page 78, or

“Heating: Modulating” on page 80 as applicable.

Heating

The unit enters the Heating operating state when heating is required during occupied operation. During the Heating operating state, the outdoor air dampers are either 100% open if the unit is a 100% outdoor air unit or controlled to the

Eff Min OA Pos= parameter. Cooling is disabled. The Fan

Operation Output (MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained.

For detailed information regarding heating operation, refer

to “Heating: Multistage” on page 78, or “Heating: Modulating” on page 80 as applicable.

Min DAT

The unit enters the Min DAT operating state during occupied operation when neither cooling nor heating is required based on the Eff Clg Spt= and Eff Htg Spt= parameters in the Zone

Cooling and Zone Heating menus, but the discharge air temperature falls below the MinDAT Limit= parameter in the

Discharge Heating menu. The Min DAT operating state prevents cold discharge air temperatures during what would normally be the Fan Only operating state. During the Min

DAT operating state, the outdoor air dampers are either

100% open if the unit is a 100% outdoor air unit or are controlled to the Eff Min OA Pos= parameter. Cooling is disabled. The Fan Operation Output (MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained.

For detailed information regarding the Min DAT operating

state, refer to “Discharge Air Low Limit Control” on page 80

(multistage heat) or “Discharge Air Low Limit Control” on page 84 (modulating heat) as applicable.

UnocEcon

The unit enters the UnocEcon operating state if the outdoor air is suitable for free cooling when “purge” or unoccupied cooling (night setup) operation is required. During the UnocEcon operating state, the outdoor air dampers are modulated to maintain the discharge air temperature at the Eff Clg

Spt= parameter in the Discharge Cooling menu. Mechanical cooling is disabled. The Fan Operation Output (MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained. Heating is disabled.

Note: 100% outdoor air units do not transition through the

UnocEcon operating state

For detailed information regarding unoccupied economizer

operation, refer to “Unoccupied Cooling (Night Setup)” on page 90 and “Purge” on page 90.

UnocClg

The unit enters the UnocClg operating state when unoccupied cooling (night setup) operation is required and the economizer is either disabled, not present, or already fully opened. During the UnocClg operating state, the outdoor air dampers are fully open if the unit is a 100% outdoor air unit or if economizer operation is enabled. The outdoor air dampers are at 0% if economizer operation is disabled or not present. The Fan Operation Output (MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained. Heating is disabled.

For detailed information regarding the unoccupied cooling

operation, refer to “Unoccupied Cooling (Night Setup)” on page 90.

UnocHtg

The unit enters the UnocHtg operating state when unoccupied heating (night setback) operation is required. During the

UnocHtg operating state, the outdoor air dampers are closed.

The Fan Operation Output (MCB-BO3) is closed and in building pressure control applications, normal return fan capacity control is maintained. Cooling is disabled.

For detailed information regarding the unoccupied heating

operation, refer to “Unoccupied Heating (Night Setback)” on page 89.

UnocFanO

The UnocFanO operating state is not a “typical” operating state. If night set back operation is activated while the unit heating is disabled or if the unit is not equipped with heating equipment, the unit with enter the UnocFanO operating state in lieu of the UnocHtg operating state. Unit operation is the same as describe for the Fan Only operating state except that the outdoor air dampers are controlled as in the UnocHtg operating state.

The unit will also enter the UnocFanO operating state if cooling or heating are disable while in the UnocEcon, Unoc-

Clg or UnocHtg operating states. If entering the UnocFanO operating state from the UnocEcon or UnocClg operating state, the outdoor dampers are control as describe for the

UnocClg operating state.

For detailed information regarding the unoccupied heating or

cooling operation, refer to “Unoccupied Control” on page 89.

Man Ctrl

The unit enters the Man Ctrl operating state when the Manual Control= parameter in the Manual Control menu is set to

“Yes”. During manual operation, all the unit control functions are disabled and the main control board (MCB) outputs can be turned on and off manually by setting the parameters contained in the Manual Control menu.

For detailed information regarding manual unit control, refer

to “Manual Output Control” on page 59

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Figure 7: Operating State Sequence Chart

Operating State Sequence Chart

Operating states and the transitions between them help to

describe the unit sequences of operation. Figure 7 shows all

of the operating state transitions that can occur as a result of normal control. Depending on the unit options, some operating states may not apply.

Startup Control

A rooftop unit can startup and run for a variety of reasons.

Examples are the internal time schedule function, an external time clock signal, a tenant override signal or the unoccupied heating (night setback) and cooling (night setup and purge) functions. Regardless of the reason it is started, the unit always transitions through a “controlled” startup sequence before allowing temperature control to begin.

Before Startup

Table 29: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

-

Timer Settings Start Init = 3 min

Minimum Inlet Vane Position

Limit

Startup Initialization Timer

When the controller receives a startup command, its operating state changes from the Off to Startup operating state.

During the Startup operating state, the Fan Operation Output

(MCB-BO3) is closed to indicate that the fans are about to start. On units with return fan inlet vanes, the vanes are driven open to the non-adjustable Minimum Inlet Vane Position Limit. This limit is 17% and is not adjustable. The Minimum Inlet Vane Position Limit assures that the return fan does not start with a completely blocked airflow path. On units with a return fan VFD, the VFD remains at 0% speed.

The unit remains in the Startup operating state until the Startup Initialization Timer expires.

Note: On 100% OA units equipped with gas heat, the

Startup period may last longer than the period defined by the Startup Initialization Timer if heat is required at unit startup. For a description of this special 100% OA gas heat startup sequence, refer to

Figure on page 82.

Caution: The Startup Initialization Timer should be set so that the Startup operating state lasts long enough to allow any field-supplied equipment (such as isolation damper sets) controlled by the Fan

Operation Output (MCB-BO3) to prepare for fan operation.

64 OM 138

Fan Startup

Table 30: Programmable Parameters

Keypad/Display ID

Menu Name

-

-

Timer Settings

Item Name

-

-

Recirculate= 3 min

Parameter Name

Fan Delay Timer

Airflow Check Timer

Recirculate State Timer

Return Air Units

The unit enters the Recirc operating state after leaving the

Startup operating state. During the Recirc operating state, the fans are stated and operated with the outdoor air dampers closed to allow temperature conditions throughout the unit and space to equalize before temperature control begins.

Cooling and heating remain disabled.

As soon as the unit leaves the Startup operating state, the discharge fan starts and the following three timers are reset and start timing down: (1) the Fan Delay Timer, (2) the Airflow

Check Timer, and (3) the Recirculate State Timer.

When the Fan Delay Timer expires, the return fan is started

(if present). The Fan Delay Timer value is a fixed four seconds. Once both fans start, the return fan capacity (if variable) is modulated to maintain the building static pressure or position set point as applicable. For detailed information

regarding return fan capacity control, refer to “Return Fan

Capacity Control” on page 88.

The Fan Fail fault which indicates loss of airflow is prevented from occurring after leaving the Startup operating state until the Airflow Check Timer expires. The Airflow

Check Timer value is a fixed two minutes.

Once in the Recirc operating state, the unit remains there until the Recirculate State Timer and Airflow Check Timerexpire. After the unit leaves the Recirc operating state, the operating state entered is a function of the current occupied/unoccupied as well as the current temperature conditions. The Heat/Cool Changeover section describes the heating/cooling changeover function, which dictates whether the unit enters a heating, cooling or the Fan Only operating state.

100% Outdoor Air Units

If the unit is equipped with a 100% outdoor air hood, the

Recirc operating state is bypassed and the fans are started as the unit directly enters either a heating or the Fan Only operating state after leaving the Startup operating state.

As soon as the unit leaves the Startup operating state, the discharge fan starts and the Airflow Check Timer is reset and starts timing down. This timer value is a fixed two minutes.

The Fan Fail fault which indicates loss of airflow is prevented from occurring after leaving the Startup operating state until the Airflow Check Timer expires.

After the unit leaves the Startup operating state, the operating state entered is a function of the current occupied/unoccupied as well as the current temperature conditions. The following section describes the heating/cooling changeover function, which dictates whether the unit enters a heating, cooling or fan only operating state.

Note: While the Airflow Check Timer is timing down and, therefore, while the Fan Fail fault alarm is being ignored, the unit will not be allowed to enter a cooling operating state.

Heat/Cool Changeover

In general, a unit configured for zone (or space comfort) control either operates to maintain the Effective Cooling

Enable Set Point using economizer and/or mechanical cooling or the Effective Heating Enable Set Point using the heating equipment.

The Effective Cooling Enable Set Point and Effective Heating Enable Set Point are not adjustable from the keypad.

They are set equal to the Cooling Enable Set Point and Heating Enable Set Point respectively or based on a signal from an optional space temperature sensor with set point adjustment capability. For details regarding the use of thermostat

supplied set points, refer to “Tstat Source Set Points” on page 66.

Note: Except when the dehumidification function is active, cooling and heating do not operate simultaneously. The controller prevents the set points and dead bands from being set so that the Cooling

Enable Dead Band and Heating Enable Dead Band overlap. In doing this, the controller always gives the Effective Cooling Enable Set Point the highest priority. Regardless of whether the cooling set point is lowered, the heating set point is raised or either of the dead bands are raised, the controller automatically lowers the Effective Heating Set Point enough to prevent the dead bands from overlapping.

The following sections describe the unit heat/cool changeover function.

OM 138 65

Temperature Control

Table 31: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Zone Cooling

Zone Heating

Zone Temp

Setup

Parameter Name

CntlTemp Src=

Eff Clg Spt=

Occ Clg Spt=

Clg Deadband= 1.0 ºF

CntlTemp Src=

Eff Htg Spt=

Occ Htg Spt=

Htg Deadband= 1.0 ºF

Spt Source=

Return

____ °F

75.0 ºF

Return

____ °F

70.0 ºF

Keypad

Control Temperature

Source

Effective Cooling

Enable Set Point

Cooling Enable Set

Point

Cooling Enable Dead

Band

Control Temperature

Source

Effective Heating

Enable Set Point

Heating Enable Set

Point

Heating Enable Dead

Band

Zone Set Point Source

Flag

Control Temperature

The “Control Temperature” is defined as the unit temperature input used to make the heat/cool changeover decision which determines whether the unit is controlling to the

Effective Cooling Enable Set Point or the Effective Heating

Enable Set Point. Also, when cooling is active, the “Control

Temperature” is maintained at the Effective Cooling Enable

Set Point and when heating is active the “Control Temperature” is maintained at the Effective Heating Enable Set Point.

Either the return air or space temperature sensor can be selected as the “Control Temperature.”

When the Control Temperature Source is set to “Return”, the unit return air temperature sensor acts as the “Control Temperature.”

When the Control Temperature Source is set to “Space”, the unit space air temperature sensor acts as the “Control Temperature.”

Note: The Control Temperature Source can not be set to

“Return” on a 100% OA unit and it can only be set to “Space” when the unit is equipped with an optional space sensor. This means that an optional space sensor is required on a 100% OA unit.

The current value of the “Control Temperature” can be displayed be viewing the Ctrl Temp= parameter in the Temperatures menu.

Once enabled by the “Control Temperature” cooling or heat-

ing capacity control operates as described in “Economizer”

on page 68, “Cooling: Multistage” on page 72, “Cooling:

Modulating” on page 77, “Heating: Multistage” on page 78,

or “Heating: Modulating” on page 80 as applicable. The fol-

lowing sections describe in detail how the “Control Temperature” enables cooling and heating operation.

Note: Although enabled based on the “Control Temperature”, cooling or heating operation can be disabled

for other reasons. Refer to “Clg Status” on

page 43and “Htg Status” on page 44.

Set Points and Dead Bands

In determining whether heating or cooling operation is enabled, the controller compares the “Control Temperature” input with the Effective Cooling Enable Set Point and the

Effective Heating Enable Set Point.

Keypad/Network Source Set Points. When the Zone

Set Point Source Flag is set to “Keypad”, the Effective Cooling Enable Set Point and the Effective Heating Enable Set

Point are set to the Cooling Enable Set Point and the Heating

Enable Set Point. The Cooling Enable Set Point and the

Heating Enable Set Point can then be set as required via a network signal.

Tstat Source Set Points. When the Zone Set Point

Source Flag is set to “Tstat”, the Effective Cooling Enable

Set Point and the Effective Heating Enable Set Point are set based on an analog signal from an optional space temperature sensor with set point adjustment capability.

To set the Effective Cooling Enable Set Point and the Effective Heating Enable Set Points based on the remote set point input, the controller first determines the difference between the Cooling Enable Set Point to the Heating Enable Set

Point. The controller then sets the Effective Cooling Enable

Set Point to the current setting on the space sensor plus half this difference. The controller then sets the Effective Heating

Enable Set Point to the current setting on the space sensor minus half this difference.

For example, if the Cooling Enable Set Point is set to 75°F, the Heating Enable Set Point is set to 70°F and the set point adjustment on the space temperature sensor is set to70°F, the

Effective Cooling Set Point would be set to 72.5°F and the

Heating Enable Set Point would be set to 67.5°F.

Cooling. When the “Control Temperature” rises above the

Effective Cooling Enable Set Point by more than half the

Cooling Enable Dead Band, cooling operation is enabled and the controller starts to increase the cooling capacity. This is

shown as Point A in Figure 8.

66 OM 138

OM 138

Figure 8: Illustrative Heat/Cool Changeover Operating Sequence

Cooling Enabled

A

Effective Cooling

Enable Set Point

B

D

}

}

}

Cooling Enable Dead Band

Fan Only

Heating Enable Dead Band

C

Effective Heating

Enable Set Point

Heating Enabled

Time

Cooling to Fan Only. When cooling is active and the

“Control Temperature” then drops below the Effective Cooling Enable Set Point by more than half the Cooling Enable

Dead Band, the controller starts to decrease the cooling capacity. As soon as the cooling is staged or modulate off completely the unit enters and runs in the Fan Only operating

state. This shown as Point B in Figure 8.

1

While in the Fan Only operating state and if the unit is equipped with modulating or multistage heat, the unit can operate the heat in this case based on a discharge tempera-

1. While in the Fan Only operating state and if the unit is equipped with modulating or multistage heat, the unit can operate the heat in this case based on a discharge temperature low limit function if the discharge air temperature gets

too cold. Refer to “Discharge Air Low Limit Control” on

page 80 (multistage heat) or “Discharge Air Low Limit Control” on page 84 (modulating heat) as applicable.

ture low limit function if the discharge air temperature gets

too cold. Refer to “Discharge Air Low Limit Control” on

page 80 (multistage heat) or “Discharge Air Low Limit Control” on page 84 (modulating heat) as applicable.

Heating. When the “Control Temperature” drops below the

Effective Heating Enable Set Point by more than half the

Heating Enable Dead Band, heating operation is enabled and the controller starts to increase the heating capacity. This is

shown as Point C in Figure 8.

Heating to Fan Only. When heating is active and the

“Control Temperature” then rises above the Effective Heating Enable Set Point by more than half the Heating Enable

Dead Band, the controller starts to decrease the heating capacity. As soon as the heating is staged or modulate off completely the unit enters and runs in the Fan Only operating

state. This shown as Point D in Figure 8.

1

67

0-30% Outdoor Air Damper Control

Minimum Ventilation Control

Table 32: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

OA Damper

MinOA Type= None

MinOA Pos= 10%

Minimum Outdoor

Damper Position

Reset Flag

Minimum Outdoor

Damper Position Set

Point

Whenever the unit is in the Fan Only, Cooling, Heating or

Min DAT operating state, the outdoor air dampers are prevented from closing below the Minimum Outdoor Damper

Position Set Point.

During the Off, Startup, Recirc, and MWU operating states, the outdoor air dampers are driven continuously to 0%.

Unoccupied Operation

Whenever the unit is operating in the unoccupied operating states UnocEcon, UnocClg, or UnocHtg, the outdoor air dampers are driven continuously to 0%.

No Minimum OA Reset

With the 0-30% OA Damper arrangement, the Minimum

Outdoor Damper Position Reset Flag can only be set to

“None”. The dampers are always control to the Minimum

Outdoor Damper Position Set Point except as noted in the previous section when they are continuously driven to 0%.

Network OA Reset

When the Minimum Outdoor Damper Position Reset Flag is set to “None”, the Minimum Outdoor Damper Position Set

Point can be reset between 0-30% via a network signal.

100% Outdoor Air Damper Control

When a unit is equipped with a 100% outdoor air hood, the outdoor air dampers are driven open continuously whenever the unit enters the Startup operating state. If they are not open (above 50%) at the end of the Startup operating state or any time afterward while the fans are running, the unit is shutdown on the OA Dmpr Stuck fault.

When the unit is shut down, the dampers remain open for 30 seconds after the unit airflow switch opens up indicating loss of airflow.

Note: The dampers remain open in the event that the airflow switch does not open after the fans are shut down.

Economizer

Temperature Control

Table 33: Programmable Parameters

Keypad/Display ID

Parameter Name

Menu Name Item Name

Zone Cooling

Discharge Cooling

Zone Temp Setup

Compressor Setup

Economizer Setup

Eff Clg Spt=

Occ Clg Spt=

Clg Deadband= 1.0 ºF

Eff Clg Spt=

Clg Db=

Period=

Clg IntTime=

___ ºF

1.0 ºF

Min Clg Spt=

Max Clg Spt=

Clg Propbd=

Clg IntTime=

8.0ºF

60 sec

Stage Timer=

Clg Propbd=

Clg Period=

____ °F

75.0 ºF

55.0 ºF

65.0 ºF

700 sec

5 min

30.0 ºF

100 sec

30 sec

Effective Cooling

Enable Set Point

Cooling Enable Set

Point

Cooling Enable Dead

Band

Effective Discharge

Cooling Set Point

Discharge Cooling

Dead Band

Minimum Discharge

Cooling Set Point

Maximum Discharge

Cooling Set Point

Zone Cooling Proportional Band

Zone Cooling Integral

Time

Zone Control Period

Cooling Interstage

Timer

Economizer Cooling

Proportional Band

Economizer Cooling

Integral Time

Economizer Cooling

Period

Entering Econo Operating State

If a unit is equipped with a 0-100% modulating economizer,

and economizer operation is available (refer to “Economizer

Changeover Method” on page 69) the unit attempts to satisfy

the cooling load by using outdoor air before using mechanical cooling. When this is the case, the unit enters the Econo operating state when the Ctrl Temp= value rises above the

Effective Cooling Enable Set Point by more than half the

Cooling Enable Dead Band.

Note: Unless it is set by a signal from an optional space temperature sensor, the Effective Cooling Enable

Set Point is set by the controller equal to the Cooling Enable Set Point.

There are two processes involved in the Economizer control function. The first is the process of modulating the outdoor air dampers to maintain the Effective Discharge Cooling Set

Point. The second is the process of adjusting the Effective

Discharge Cooling Set Point up and down between the Mini-

68 OM 138

mum Discharge Cooling Set Point and the Maximum Discharge Cooling Set Point as the Ctrl Temp= value varies above and below the Effective Cooling Enable Set Point.

The following sections describe these two processes.

Economizer Damper Modulation. When the Disch

Air= value rises above the Effective Discharge Cooling Set

Point by more than half the Discharge Cooling Dead Band, the outdoor damper position is increased. When the Disch

Air= value falls below the Effective Discharge Cooling Set

Point by more than half the Discharge Cooling Dead Band, the outdoor damper position is decreased.

The controller uses three PID control loop parameters to modulate the economizer dampers as the discharge air temperature changes. Theses are the Economizer Cooling Proportional Band, Economizer Cooling Integral Time and

Economizer Cooling Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters,

refer to “MicroTech II DDC Features” on page 99.

Effective Discharge Cooling Set Point Adjustment.

When the Ctrl Temp= value rises above the Effective Cooling Enable Set Point by more than half the Cooling Enable

Dead Band, the Effective Discharge Cooling Set Point is decreased. When the Ctrl Temp= value falls below the Effective Cooling Enable Set Point by more than half the Cooling

Enable Dead Band, the Effective Discharge Cooling Set

Point is increased.

Note: When the unit first enters the Econo operating state, the Effective Discharge Cooling Set Point is set to the current Disch Temp= value.

The controller uses three PID control loop parameters to raise and lower the Effective Discharge Cooling Set Point as the Ctrl Temp= value changes. These are the Zone Cooling

Proportional Band, Zone Cooling Integral Time and Zone

Control Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters, refer to

“MicroTech II DDC Features” on page 99.

Economizer to Cooling Operating State

The transition from the Econo to Cooling operating state occurs when the economizer is unable to satisfy the cooling load and mechanical cooling is available. Normally, this occurs when the OA Damper Pos= parameter indicates more than 95% open and the discharge air temperature is above the Effective Discharge Cooling Set Point by more than half the Discharge Cooling Dead Band for longer than the Cooling Interstage Timer.

To allow for the transition from the Econo to Cooling operating state in the event the outdoor air dampers get stuck or there is a problem with the damper actuator feedback circuit and the OA Damper Pos= parameter does not reach 95%, the controller continually estimates the position of the dampers.

This estimate is based on the accumulative damper drive open versus drive close time compared to the nominal stroke of the actuator. If the controller position estimate reaches

100% open and the discharge air temperature is above the

Effective Discharge Cooling Set Point by more than half the

Discharge Cooling Dead Band for longer than the Cooling

Interstage Timer, the unit makes the transition from the

Econo to Cooling operating state regardless of the current

OA Damper Pos= parameter indication.

If economizer operation becomes disabled while the unit is in the Econo operating state, the transition from the Econo to

Cooling operating state occurs. The outdoor air dampers are driven to the Effective Minimum Outdoor Damper Position

Set Point (refer to “Minimum Ventilation Control” on page 70).

Econo to Fan Only Operating State

The unit will leave the Econo operating state and enter the

Fan Only operating state when the Ctrl Temp= value falls below the Effective Cooling Enable Set Point by more than half the Cooling Enable Dead Band and either of the following are true:

1. The economizer damper position, as indicated by the

OA Damper Pos= parameter in the OA Damper menu, indicates that the dampers have been at the Effective

Minimum Outdoor Damper Position Set Point for one

Cooling Interstage Timer period.

2. The Effective Discharge Cooling Set Point has been at the Maximum Discharge Cooling Set Point for one

Cooling Interstage Timer period.

The unit will also leave the Econo operating state and enter the Fan Only operating state if all cooling is disabled for any

reason. Refer to “Clg Status” on page 43.

Economizer Changeover Method

Table 34: Programmable Parameters

Keypad/Display ID

Menu

Name

Item Name

OA Damper

Parameter Name

EconChgovr= Enthalpy

EconChgovrT= 60 ºF

EconChgovrDiff= 1ºF

Economizer Changeover

Flag

Economizer Changeover

Set Point

Economizer Changeover

Differential

There are three methods of determining whether or not the outdoor air is suitable for free cooling. Two of them sense enthalpy (dry bulb temperature and humidity) and one senses outdoor air dry bulb temperature only.

Enthalpy Changeover

The two optional enthalpy changeover methods use external control devices. One device compares the outdoor enthalpy with a set point; the other compares the outdoor air enthalpy

OM 138 69

with the return air enthalpy. All units with economizers are at least equipped with the outdoor air enthalpy version. The comparative version is optional. In either case a binary input

(MCB-BI11) is delivered to the controller indicating whether or not outdoor air is suitable for free cooling. When the outdoor air is suitable for free cooling (MCB-BI11 on), the OA

Ambient= parameter indicates “Low” and the economizer

operates as described above in the Figure on page 68. When

the outdoor air is not suitable for free cooling (MCB-BI11 off), the OA Ambient= parameter indicates “High” and economizer operation is disabled.

To use either of these enthalpy methods, the Economizer

Changeover Flag must be set to “Enthalpy.” In this case, the

Economizer Changeover Set Point is ignored.

For detailed information regarding the external enthalpy controls, refer to the “Unit Options” section of the model-

specific installation manual (refer to Table 1 on page 4).

Dry Bulb Temperature Changeover

When a unit is equipped with and economizer, an internal dry-bulb temperature changeover strategy can be selected.

When this method is selected, the controller compares the

OA Temp= value to the Economizer Changeover Set Point.

The enthalpy control input is ignored in this case.

To use the dry bulb method, the Economizer Changeover

Flag must be set to “Dry Bulb.” The controller then uses the

Economizer Changeover Set Point to determine whether or not outdoor air may be used for cooling. If the OA Temp= value is less than or equal to this set point, economizer cooling is enabled ( OA Ambient= parameter indicates “Low”). If the OA Temp= value rises above this set point by more than the Economizer Changeover Differential, economizer cooling is disabled ( OA Ambient= parameter indicates “High”) and the outdoor air dampers are driven to the Effective Mini-

mum Outdoor Damper Position Set Point (refer to “Minimum Ventilation Control” on page 70).

Minimum Ventilation Control

Table 35: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

OA Damper

DesignFlow

Setup

Eff Min OA Pos= ___%

MinOA Type= None

DesingFlow= No

MinOA Pos= 10%

MinOA Flow= 2000 CFM

MinOA @Max Sig= 100%

Min Signal= 0%

Max Signal= 100%

MinOA ResetMax= 100%

Max Fan Diff= 50%

Min Fan Diff= 20%

Reset T Limit= 0°F

Wait Time= 30 sec

Modband= 50%

Max Step= 5%

Deadband= 6%

Effective Minimum

Outdoor Damper

Position Set Point

Minimum Outdoor

Damper Position

Reset Flag

DesignFlow Flag

Minimum Outdoor

Damper Position Set

Point

Minimum Outdoor

Airflow Set Point

Outdoor Damper

Position Set Point at

Maximum External

Signal

Minimum External

OA Reset Signal

Maximum External

OA Reset Signal

Effective Minimum

Outdoor Damper

Position Set Point

Maximum Limit

Maximum Fan

Capacity Differential

Minimum Fan

Capacity Differential

OA Reset Temperature Limit

DesignFlow Wait

Time

DesignFlow Modulation Band

DesignFlow Maximum Step

DesignFlow Deadband

Whenever power is applied to the controller, the outdoor air dampers are prevented from closing below the Effective

Minimum Outdoor Damper Position Set Point. This is to ensure that a minimum amount of ventilation air is always supplied to the space.

Note: During the Off, Startup, Recirc, and MWU operating states, the Effective Minimum Outdoor Damper

Position Set Point is set to 0%.

The Effective Minimum Outdoor Damper Position Set Point can be reset between the Minimum Outdoor Damper Posi-

70 OM 138

tion Set Point and the Effective Minimum Outdoor Damper

Position Set Point Maximum Limit in a number of ways.

These are described as follows:

Unoccupied Operation

Whenever the unit is operating in the unoccupied operating states UnocEcon, UnocClg, or UnocHtg, the Effective Minimum Outdoor Damper Position Set Point is set to 0%.

No Minimum OA Reset

When the Minimum Outdoor Damper Position Reset Flag is set to “None” and the DesignFlow Flag is set to “No”, the

Effective Minimum Outdoor Damper Position Set Point is set equal to the Minimum Outdoor Damper Position Set

Point.

External OA Reset

The Effective Minimum Outdoor Damper Position Set Point can be reset via a field supplied analog voltage or current signal. This signal can be in the range of 0-10 VDC or 0-

20 mA. When the Minimum Outdoor Damper Position Reset

Flag is set to “Ext V” or “Ext mA”, the Effective Minimum

Outdoor Damper Position Set Point varies linearly between the Minimum Outdoor Damper Position Set Point and the

Outdoor Damper Position Set Point at Maximum External

Signal as the field voltage or current signal varies between a minimum and maximum (or maximum and minimum) value.

The range and type of field reset signal is configured using the Minimum External OA Reset Signal and the Maximum

External OA Reset Signal and setting a jumper on the main control board associated with analog input MCB-AI07. The analog input jumper is placed in either the “voltage” or “current” position. When the jumper is in the “voltage” position, the range of the input signal can be from 0-10 VDC and when in the “current” position, 0-20 mA. The input range is scaled using the Minimum External OA Reset Signal and the

Maximum External OA Reset Signal parameters. If for example, the field signal is to be 1-5 VDC, the Minimum

External OA Reset Signal must be set to 10% since 1 VDC is

10% of the 0-10 VDC range. The Maximum External OA

Reset Signal must be set to 50% since 5 VDC is 50% of the

0-10 VDC range.

Note: The previous example demonstrated “direct acting” reset where the Effective Minimum Outdoor

Damper Position Set Point increases as the voltage or current signal increases. “Reverse acting” reset can be accomplished as well. In the previous example, if instead the Minimum External OA Reset Signal were set to 50% and the Maximum External OA

Reset Signal where set to 10%, then the Effective

Minimum Outdoor Damper Position Set Point would decrease as the voltage or current signal increases.

Refer to “External Outdoor Air Damper Reset Signal” in the

“Field Wiring” section of IM 696, MicroTech Applied Rooftop Unit Controller .

Note: The Minimum Outdoor Damper Position Reset

Flag automatically reverts to “None” if the Design-

Flow= parameter is set to “Yes”

Network OA Reset

When the Minimum Outdoor Damper Position Reset Flag is set to “None” and the DesignFlow Flag is set to “No”, the

Effective Minimum Outdoor Damper Position Set Point is set equal to the Minimum Outdoor Damper Position Set

Point. The Minimum Outdoor Damper Position Set Point can then be set via a network signal to meet the outdoor air requirements.

DesignFlow OA Airflow Measurement Reset

When a unit is equipped with the optional DesignFlow outdoor air measuring system and the DesignFlow Flag is set to

“Yes”, the Effective Minimum Outdoor Damper Position Set

Point is adjusted based on the measured amount of outdoor air being brought into the unit. If that airflow is below the desired value, the Effective Minimum Outdoor Damper

Position Set Point is increased and if that airflow is above the desired value, Effective Minimum Outdoor Damper Position

Set Point is decreased. The Effective Minimum Outdoor

Damper Position Set Point is limited between the Minimum

Outdoor Damper Position Set Point and the Effective Minimum Outdoor Damper Position Set Point Maximum Limit.

Note: The DesignFlow Flag can be set to “Yes” only when the unit is configured with the optional

DesignFlow outdoor air measurement feature.

Note: The Minimum Outdoor Damper Position Reset

Flag automatically reverts to “None” if the Design-

Flow= parameter is set to “Yes”

The current outdoor air for each of the two OA inlets is determined by comparing the resistance of the left and right airflow monitoring devices (input to MCB-AO7 and MCB-

AO8 respectively). These resistances are compared to tabulated airflow data. The two CFM values are added together to determine the Current Flow ( OA Flow= ) value.

At increments equal to the DesignFlow Wait Time, a Step

Value is calculated. If the Flow Ratio (the ratio of the Current Flow to the Minimum Outdoor Airflow Set Point multiplied by 100%) is greater than 100% by more than half of the

DesignFlow Deadband, the Effective Minimum Outdoor

Damper Position Set Point is decreased by the Step Value. If the Flow Ratio is less than 100% by more than half of the

DesignFlow Deadband, the Effective Minimum Outdoor

Damper Position Set Point is increased by the Step Value.

The Step Value is determined using the smaller of the following two calculations:

Step Value = DesignFlow Maximum Step

Or

Step Value = (Error)

DesignFlow Modulation Band

OM 138 71

Where:

Error = Absolute Value of 100% Flow Ratio

Discharge/Return Fan Differential OA Reset

When a unit is equipped with return air fan inlet vanes or a return fan VFD, it may be necessary to increase the amount of outdoor air if the difference between the discharge and return fan capacity gets to large. If this is not done the discharge air fan can potentially be “starved” for air. A discharge fan operating in a “starved” condition not only has difficulty meeting the system airflow requirements but may cause damage to damper sets and/or the return fan motor or

VFD. To overcome this type of problem, the MicroTech II unit controller provides a discharge/return fan differential

OA reset strategy, which automatically resets the Effective

Minimum Outdoor Damper Position Set Point as the difference between the discharge and return air fan capacity varies.

Note: The discharge fan capacity is always assumed to be

100% on a zone (or space comfort) control unit.

The discharge/return fan OA reset strategy is automatically used when the difference between the discharge and return fan capacity exceeds the Minimum Fan Capacity Differential. When the difference is less than or equal to the Minimum Fan Capacity Differential, the Effective Minimum

Outdoor Damper Position Set Point is set to the Minimum

Outdoor Damper Position Set Point (unless it is reset higher by another one of the reset methods). As the fan differential varies between the Minimum Fan Capacity Differential and the Maximum Fan Capacity Differential, the Effective Minimum Outdoor Damper Position Set Point is reset between the Minimum Outdoor Damper Position Set Point and the

Effective Minimum Outdoor Damper Position Set Point

Maximum Limit.

OA Reset Override

Under some conditions the discharge air can contain a high percentage of outdoor air when any of the available OA reset features are active. If the outdoor air is very cold, the discharge air could also become very cold, particularly if the unit is equipped with no heat. Therefore, very cold discharge temperatures could result unless some other provision is made for tempering the air. If no other provisions are available for tempering the air it may be necessary to override the outdoor air reset strategy if the discharge air becomes to cold.

To allow for such a contingency, the MicroTech II controller is equipped with an OA Reset Temperature Limit. If the discharge air temperature drops below this adjustable limit by more than half the Clg Db= parameter in the Discharge

Cooling menu, any of the OA reset functions (with the exception of the discharge/return fan differential OA reset function) are overridden and the Effective Minimum Outdoor Damper Position Set Point is reset to maintain the discharge air temperature at this limit.

Note: This temperature override function is disabled when the OA Reset Temperature Limit is set to 0°F and when the unit is in the Cooling operating state.

Once the OA reset override function is active, normal control resume as follows:

1. If the Minimum Outdoor Damper Position Reset Flag is set to “Ext mA” or “Ext V”, normal control resumes if the Effective Minimum Outdoor Damper Position Set

Point is more than 2% above the calculated position based on the external OA reset function for more than

two minutes. Refer to “External OA Reset” on page 71.

2. If the DesignFlow Flag is set to “Yes”, normal control resumes if the Flow Ratio exceeds 100% by more than half the DesignFlow Deadband for more than two min-

utes. Refer to “DesignFlow OA Airflow Measurement

Reset” on page 71.

Cooling: Multistage

Temperature Control

Table 36: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Zone Cooling

Discharge Cooling

Compressor Setup

Eff Clg Spt= ____ °F

Occ Clg Spt= 75.0 ºF

Clg Deadband= 1.0 ºF

Min Clg Spt= 55.0 ºF

Max Clg Spt= 65.0 ºF

Clg Method= Average

Stage Time= 5 min

Effective Cooling

Enable Set Point

Cooling Enable Set

Point

Cooling Enable

Dead Band

Minimum Discharge Cooling Set

Point

Maximum Discharge Cooling Set

Point

Discharge Cooling

Method Flag

Cooling Interstage

Timer

Entering Cooling Operating State

The unit enters the Cooling operating state from the Recirc or Fan Only operating state when the Ctrl Temp= value rises above the Effective Cooling Enable Set Point by more than half the Cooling Enable Dead Band and economizer operation is not available. The unit enters the Cooling operating

state from the Econo operating state as describe in “Economizer to Cooling Operating State” on page 69

When the unit is in the Cooling operating state, cooling stages are turned on and off to maintain the Ctrl Temp= value at the Effective Cooling Enable Set Point.

72 OM 138

Note: Unless it is set by a signal from an optional space temperature sensor, the Effective Cooling Enable

Set Point is set by the controller equal to the Cooling Enable Set Point.

The controller activates the first stage of mechanical cooling as it enters the Cooling operating state. When the Ctrl

Temp= value is above the Effective Cooling Enable Set Point by more than half the Cooling Enable Dead Band and the

Cooling Interstage Timer has expired since the last stage change, cooling capacity is increased by one stage. When the

Ctrl Temp= value is below the Effective Cooling Enable Set

Point by more than half the Cooling Enable Dead Band and the Cooling Interstage Timer has expired since the last stage change, cooling capacity is decreased by one stage.

Discharge Temperature Override. While controlling the Ctrl Temp= value to the Effective Cooling Enable Set

Point, the controller places limits on the discharge air temperature. The controller does not allow the Disch Temp= value to exceed the Maximum Discharge Cooling Set Point or fall below the Minimum Discharge Cooling Set Point without taking action. If the Disch Temp= value exceeds the

Maximum Discharge Cooling Set Point, cooling capacity is increased by one stage (subject to the Cooling Interstage

Timer). If the Disch Temp= value falls below the Minimum

Discharge Cooling Set Point, cooling capacity is decreased by one stage (subject to the Cooling Interstage Timer).

Cooling to Econo Operating State

The unit will transition from the Cooling to Econo operating state when either of the following are true:

1. Economizer operation is available and compressor oper-

ation be comes disabled as describe in “Low Ambient

Cooling Lockout“ below.

2. The Ctrl Temp= value is below the Effective Cooling

Enable Set Point by more than half the Cooling Enable

Dead Band, economizer operation is available and the cooling capacity is at 0% for more than the Cooling

Interstage Timer period.

Cooling to Fan Only Operating State

The unit will transition from the Cooling to Fan Only operating state when any of the following are true:

1. Compressor operation is disabled as described below in

“Low Ambient Cooling Lockout“ and economizer oper-

ation is not available.

2. The Ctrl Temp= value is below the Effective Cooling

Enable Set Point by more than half the Cooling Enable

Dead Band, economizer operation is not available and the cooling capacity is at 0% for more than the Cooling

Interstage Timer period.

3. All cooling is disabled for any reason. Refer to “Clg Status” on page 43.

Low Ambient Cooling Lockout

Table 37: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Zone Cooling

Parameter Name

OATComp Lock= 55.0 ºF

OATLock Diff= 3.0 °F

Low Ambient Cooling

Lockout Set Point

Low Ambient Cooling

Lockout Set Point Differential

Compressorized cooling is disabled when the outdoor air temperature is below the Low Ambient Cooling Lockout Set

Point. When this occurs, the Clg Status= parameter indicates either “Econo” or “Off Amb” if all cooling is not disabled for some other reason. When the outdoor air temperature rises above the Low Ambient Cooling Lockout Set Point by more than the Low Ambient Cooling Lockout Differential, compressorized cooling is re-enabled. The Clg Status= parameter indicates either “All Clg” or “Mech Clg” if all cooling is not disabled for some other reason.

Caution: Unless the unit is equipped with the SpeedTrol low ambient condenser fan control option, the

Low Ambient Cooling Lockout Set Point should never be set below 45°F.

Compressor Staging

Table 38: Programmable Parameters

Keypad/Display ID

Parameter Name

Menu Name Item Name

Lead Circuit= # 1

Compressor Setup

CompCtrl= Cross Circ

Circuit Lead/Lag Flag

Circuit Staging

Method Flag

On units equipped with compressorized cooling, there are many different compressor staging configurations available, depending upon unit size. For specific output staging information for the possible configurations, refer to the “Cooling

Control Boards (CCB1 & CCB2)” section of IM 696, Micro-

Tech Applied Rooftop Unit Controller .

In most cases the unit can be configured to either cross-load the two cooling circuits or to stage up one circuit before the other. In either case, when possible, compressors are staged up and down to equalize run hours. Also, in most of the available unit staging configurations, circuit # 1 or circuit #2 can be designated as the “lead” circuit or the unit can be set for automatic “lead/lag” of the circuits. The circuit lead/lag, cross-circuit loading and lead-circuit loading functions are described in the following sections.

OM 138 73

Circuit Lead/Lag

2 Compressors/2 Stages or 4 Compressors/4

Stages. The “lead” refrigeration circuit can be selected by setting the Circuit Lead/Lag Flag. When the Circuit

Lead/Lag Flag is set to “Auto”, the “lead” refrigeration circuit alternates each time cooling is staged down until all the compressors are off. The refrigeration circuit with the compressor with the fewest run hours becomes the “lead.”

When the Circuit Lead/Lag Flag is set to “#1”, circuit #1 always acts as the “lead.” When the Circuit Lead/Lag Flag is set to “#2”, circuit #2 always acts as the “lead.”

Caution: Automatic lead/lag or circuit #2 lead operation should not be used if the unit is equipped with the hot gas bypass option on circuit #1 only.

2 Compressors/3 Stages or 3 Compressors/4

Stages. Both of these staging configurations have unequally sized compressors in the two cooling circuits and the staging sequence is fixed. Therefore, circuit lead/lag operation does not apply to these staging configurations and the Circuit Lead/Lag Flag has no affect on the unit operation.

2 Compressors/4 Stages, 2 Compressors/6 Stages,

4 Compressors/8 Stages. The “lead” refrigeration circuit can be selected by setting the Circuit Lead/Lag Flag.

When the Circuit Lead/Lag Flag is set to “Auto”, the “lead” refrigeration circuit alternates each time cooling is staged down until all compressors are off. The refrigeration circuit with the lower run hours then becomes the “lead.” When the

Circuit Lead/Lag Flag is set to “#1” circuit #1 always acts as the “lead.” When the Circuit Lead/Lag Flag is set to “#2” circuit #2 always acts as the “lead.”

Note: In these cooling staging configurations, circuit #1 run hours are considered equal to the run hours of compressor #1 and circuit #2 run hours are considered equal to the run hours of compressor #2.

Caution: Automatic lead/lag or circuit #2 lead operation should not be used if the unit is equipped with the hot gas bypass option on circuit #1 only.

Cross Circuit Loading

When the Circuit Staging Method Flag is set to “Cross Circ”, the two circuits are loaded and unloaded as evenly as possible. This is the more efficient method. There are differences in “Cross Circuit” staging method depending on the unit compressor stage configuration.

2 Compressors/2 Stages or 4 Compressors/4

Stages. When a capacity increase is required and the number of operating compressors in both circuits is the same, the compressor in the “lead” circuit with the fewest run hours that is not operating is turned on. When a capacity increase is required and the number of compressors in the two circuits is not the same, the compressor with the fewest run hours in the circuit with the fewest operating compressors is turned on.

When a capacity decrease is required and the number of operating compressors in both circuits is the same, the operating compressor with the highest run hour total in the “lag” circuit is turned off. When a capacity decrease is required and the number of operating compressors in the two circuits is not the same, the operating compressor with the most run hours in the circuit with most operating compressors is turned off.

Note: A disabled circuit remains at zero capacity. If the other circuit is enabled, the circuit capacity is controlled similar to the Lead-Loading method. If a previously disabled circuit becomes enabled, the cooling capacity remains where it is until there is a call for a capacity change at which time normal

“Cross Circuit” operation resumes.

2 Compressors/4 Stages, 2 Compressors/6 Stages or 4 Compressors/8 Stages. When a capacity increase is required, the circuit operating at the lower capacity is staged up. If both circuits are operating at the same capacity, the “lead” circuit is staged up if not already at its maximum.

When a capacity decrease is required, the circuit operating at the higher capacity is staged down. If both circuits are operating at the same capacity, the “lag” circuit is staged down.

Note: A disabled circuit remains at zero capacity. If the other circuit is enabled, it acts as the “lead” and the circuit capacity is controlled similar to the Lead-

Loading method. If a previously disabled circuit becomes enabled, the cooling capacity remains where it is until there is a call for a capacity change at which time normal “Cross Circuit” operation resumes.

2 Compressors/3 Stages. With this staging configuration, the compressors are always controlled in the same way.

There are no circuit “lead/lag”, “compressor run hour” or

“Cross Circuit” variations to the staging sequence. Starting with 0% capacity, when a capacity increase is required, the

“small” compressor on circuit #1 is turned on. When a further increase is required, the “large” compressor on circuit #

2 is turned on and the “small” compressor on circuit #1 is turned off. For the final capacity increase, the “small” compressor on circuit #1 is turned on while the “large” compressor on circuit #2 remains on.

Note: If the “small” compressor on circuit #1 is disabled, the “large” compressor on circuit # 2 operates when cooling is required and the cooling capacity is set to

66%. If the “large” compressor on circuit # 2 is disabled, the “small” compressor on circuit # 1 operates when cooling is required and the cooling capacity is set to 33%.

3 Compressors/4 Stages. With this staging configuration, there are no circuit “lead/lag” or “Cross Circuit” variations to the staging sequence. Starting with 0% capacity, when a capacity increase is required, the “small” compressor

74 OM 138

on circuit #1 with the fewest run hours is turned on. When a further increase is required, the other “small” compressor on circuit #1 is turned on. When a further increase is required, the “large” compressor on circuit # 2 is turned on and the

“small” compressor on circuit #1 with the most run hours is turned off. For the final capacity increase, the “small” compressor on circuit #1 that is off is turned on.

Note: If one of the “small” compressor on circuit #1 is disabled, the staging sequence would remain the same except that the last stage increase would be unavailable and the capacity would be limited to

75%. If both of the “small” compressors on circuit

#1 are disabled, the “large” compressor on circuit

#2 (50% capacity) would cycle on and off to maintain the load. If the “large” compressor on circuit #2 is disabled, the two “small” compressors on circuit

#1 would cycle on and off (based on run hours) to maintain the load.

Lead Circuit Loading

When the Circuit Staging Method Flag is set to “Lead

Load”, one circuit is loaded completely before the first compressor in the second circuit is turned on, and one circuit is unloaded completely before the other circuit begins to be unloaded. This method provides better dehumidification but is less efficient. There are differences in “Lead Load” staging method depending on the unit compressor stage configuration.

2 Compressors/2 Stages or 4 Compressors/4Stages. When a capacity increase is required and the number of operating compressors is 0, the compressor in the “lead” circuit with the fewest run hours is turned on.

When a capacity increase is required, “lead” circuit is staged up if not already fully loaded. If the “lead” circuit is fully loaded, the compressor in the “lag” circuit with the fewest run hours is turned on. When a further capacity increase is required, the “lag” circuit is staged up. When a capacity decrease is required, the operating compressor in the “lag” circuit with the most run hours is turned off. When a further capacity decrease is required and the “lag” circuit is not already fully unloaded, the remaining compressor in the

“lag” circuit is turned off. When a further capacity decrease is required, the operating compressor in the “lead” circuit with the most run hours is turned off. Finally, when a further capacity decrease is required and the “lead” circuit is not already fully unloaded, the remaining compressor in the

“lead” circuit is turned off.

Note: A disabled circuit remains at zero capacity. If the other circuit is enabled, it acts as the “lead” and the circuit capacity is controlled using the Lead-Loading method. If a previously disabled circuit is enabled, the cooling capacity remains where it is until there is a call for a capacity change when normal “Lead Load” operation resumes.

2 Compressors/4 Stages, 2 Compressors/6 Stages or 4 Compressors/8 Stages. When a capacity increase is required and the “lead” circuit is not at maximum, the

“lead” circuit is staged up. When a capacity increase is required and the “lead” circuit is already at its maximum, the

“lag” circuit is staged up. When a capacity decrease is required and the “lag” circuit is not at zero capacity, the

“lag” circuit is staged down. When a capacity decrease is required and the “lag” circuit is at zero capacity, the “lead” circuit is staged down.

Note: A disabled circuit remains at zero capacity. If the other circuit is enabled, it acts as the “lead” and the circuit capacity is controlled using the Lead-Loading method. If a previously disabled circuit is enabled, the cooling capacity remains where it is until there is a call for a capacity change when normal “Lead Load” operation resumes.

2 Compressors/3 Stages . With this staging configuration, the compressors are always controlled in the same way.

There are no circuit “lead/lag”, “compressor run hour” or

“Lead Load” variations to the staging sequence. Starting with 0% capacity, when a capacity increase is required, the

“small” compressor on circuit #1 is turned on. When a further increase is required, the “large” compressor on circuit

#2 is turned on and the “small” compressor on circuit #1 is turned off. For the final capacity increase, the “small” compressor on circuit #1 is turned on while the “large” compressor on circuit #2 remains on.

Note: If the “small” compressor on circuit #1 is disabled, the “large” compressor on circuit #2 operates when cooling is required and the cooling capacity is set to

66%. If the “large” compressor on circuit #2 is disabled, the “small” compressor on circuit #1 operates when cooling is required and the cooling capacity is set to 33%.

3 Compressors/4 Stages. With this staging configuration, there are no circuit “lead/lag” or “Lead Load” variations to the staging sequence. Starting with 0% capacity, when a capacity increase is required, the “small” compressor on circuit #1 with the fewest run hours is turned on. When a further increase is required, the other “small” compressor on circuit #1 is turned on. When a further increase is required, the “large” compressor on circuit #2 is turned on and the

“small” compressor on circuit #1 with the most run hours is turned off. For the final capacity increase, the “small” compressor on circuit #1 that is off is turned on.

Note: If one of the “small” compressors on circuit #1 is disabled, the staging sequence would remain the same except that the last stage increase is unavailable and the capacity is limited to 75%. If both of the “small” compressors on circuit #1 are disabled, the “large” compressor on circuit #2 (50% capacity) cycle on and off to maintain the load. If the “large” compressor on circuit #2 is disabled, the two

OM 138 75

“small” compressors on circuit #1 would cycle on and off (based on run hours) to maintain the load.

Generic Condensing Unit Staging

When a unit is equipped with a DX cooling coil and is interfaced with a field supplied condensing unit, it is equipped with a generic condenser control board (CCB1) for controlling the cooling stages on the condensing unit. In this case, circuit lead/lag, cross-circuit loading and lead-circuit loading are not applicable. The outputs on the condenser control board (CCB1) are simply staged up and down sequentially as the cooling capacity changes.

Condenser Fan Control

Table 39: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Compressor Setup

Cond Fan1 Spt=

Cond Fan2 Spt= 55°F

Cond Fan3 Spt= 65°F

Cond Fan4 Spt= 75°F

Cond Fan Diff=

0°F

10°F

First Condenser Fan

Set Point

Second Condenser

Fan Set Point

Third Condenser

Fan Set Point

Fourth Condenser

Fan Set Point

Condenser Fan Differential

On units equipped with compressorized cooling, there are up to four condenser fans per cooling circuit depending on the size of the unit. The fans in each circuit are started and stopped based on outdoor air temperature when circuit is operating. The first condenser fan in each operating circuit is turned on when the OA Temp= value rises above the First

Condenser Fan Set Point and is turned off when the OA

Temp= value falls below the First Condenser Fan Set Point by more than the Condenser Fan Differential. The second condenser fan in each operating circuit is turned on when the

OA Temp= value rises above the Second Condenser Fan Set

Point and is turned off when the OA Temp= value falls below the Second Condenser Fan Set Point by more than the Condenser Fan Differential. The third condenser fan in each operating circuit is turned on when the OA Temp= value rises above the Third Condenser Fan Set Point and is turned off when the OA Temp= value falls below the Third Condenser Fan Set Point by more than the Condenser Fan Differential. The fourth condenser fan in each operating circuit is turned on when the OA Temp= value rises above the Fourth

Condenser Fan Set Point and is turned off when the OA

Temp= value falls below the Fourth Condenser Fan Set Point by more than the Condenser Fan Differential.

Circuit Pumpdown

Normal Circuit Pumpdown

During normal cooling circuit operation, the circuit is pumped down when the last compressor in the circuit is shut down due to normal staging. It is also pumped down if the entire circuit is shut down due to any alarms other than Hi

Pres-Ckt1, Hi Pres-Ckt2, Comp #1 Alm, Comp #2 Alm,

Comp #3 Alm, and Comp #4 Alm.

When pumdown is required for a circuit, the Liquid Line

Solenoid Valve for that circuit is closed (output turned off) and a compressor on that circuit operates until the circuit low pressure switch opens at which time the compressor is turned off. If the low pressure switch does not open within 180 seconds, pumpdown is terminated by turning off the compressor and the PumpDown-Ckt1 (or PumpDown-Ckt2) problem is generated.

Manual Circuit Pumpdown

Compressors in a Circuit are Operating: Circuit pumpdown is manually initiated if either the master pumpdown switch (PS3) in the main control panel or the circuit pumpdown switch (PS1-Circuit #1 or PS2-Circuit #2) in the condenser control panel is placed in the Pumpdown (Off) position.

Compressors in a Circuit are not Operating: Circuit pumpdown is manually initiated if either the master pumpdown switch (PS3) or the circuit pumpdown switch (PS1-

Circuit #1 or PS2-Circuit #2) is cycled from the Auto (On) to the Pumpdown (Off) position twice in less than 20 seconds and the low pressure switch is closed.

When pumdown is initiated for a circuit, the liquid line solenoid valve for that circuit is closed (output turned off) and a compressor on that circuit operates until the circuit low pressure switch opens at which time the compressor is turned off.

If the low pressure switch does not open within 180 seconds, pumpdown is terminated by turning off the compressor and the PumpDown-Ckt1 (or PumpDown-Ckt2) problem is generated.

76 OM 138

Cooling: Modulating

Temperature Control

Table 40: Programmable Parameters

Keypad/Display ID

Parameter Name

Menu Name Item Name

Zone Cooling

Discharge Cooling

Zone Temp Setup

Chilled Water Setup

Eff Clg Spt= ____ °F

Occ Clg Spt=

Clg Deadband= 1.0 ºF

Eff Clg Spt=

75.0 ºF

___ ºF

Effective Cooling

Enable Set Point

Cooling Enable Set

Point

Cooling Enable Dead

Band

Effective Discharge

Cooling Set Point

Clg Db= 1.0 ºF

Min Clg Spt=

Max Clg Spt=

Clg Propbd=

55.0 ºF

65.0 ºF

8.0ºF

Discharge Cooling

Dead Band

Minimum Discharge

Cooling Set Point

Maximum Discharge

Cooling Set Point

Zone Cooling Proportional Band

Clg IntTime= 700 sec

Period= 60 sec

Clg Propbd= 30.0 ºF

Cooling Proportional

Band

Clg IntTime= 100 sec Cooling Integral Time

Clg Period= 30 sec

Zone Cooling Integral

Time

Zone Control Period

Stage Timer= 5 min

Cooling Period

Cooling Interstage

Timer

Entering Cooling Operating State

The unit enters the Cooling operating state from the Recirc or Fan Only operating state when the Ctrl Temp= value rises above the Effective Cooling Enable Set Point by more than half the Cooling Enable Dead Band and economizer operation is not available. The unit enters the Cooling operating

state from the Econo operating state as describe in “Economizer to Cooling Operating State” on page 69.

Note: Unless it is set by a signal from an option space temperature sensor, the Effective Cooling Enable

Set Point is set by the controller equal to the Cooling Enable Set Point.

Chilled Water: Valve Control

When the unit is in the Cooling operating state, the chilled water valve is modulated to satisfy the cooling load. There are two processes involved in the chilled water valve control function. The first is the process of modulating the valve to maintain the Effective Discharge Cooling Set Point. The second is the process of adjusting the Effective Discharge Cooling Set Point up and down between the Minimum Discharge

Cooling Set Point and the Maximum Discharge Cooling Set

Point as the Ctrl Temp= value varies above and below the

Effective Cooling Enable Set Point. The following sections describe these two processes.

Valve Modulation. When the Disch Air= value rises above the Effective Discharge Cooling Set Point by more than half the Discharge Cooling Dead Band, the chilled water valve position is increased. When the Disch Air= value falls below the Effective Discharge Cooling Set Point by more than half the Discharge Cooling Dead Band, the chilled water valve position is decreased.

The controller uses three PID control loop parameters to modulate the chilled water valve as the discharge air temperature changes. Theses are the Cooling Proportional Band,

Cooling Integral Time and Cooling Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control

loop parameters, refer to “MicroTech II DDC Features” on page 99.

Effective Discharge Cooling Set Point Adjustment.

When the Ctrl Temp= value rises above the Effective Cooling Enable Set Point by more than half the Cooling Enable

Dead Band, the Effective Discharge Cooling Set Point is decreased. When the Ctrl Temp= value falls below the Effective Cooling Enable Set Point by more than half the Cooling

Enable Dead Band, the Effective Discharge Cooling Set

Point is increased.

Note: When the unit first enters the Cooling operating state, the Effective Discharge Cooling Set Point is set to the current Disch Temp= value.

The controller uses three PID control loop parameters to raise and lower the Effective Discharge Cooling Set Point as the Ctrl Temp= value changes. These are the Zone Cooling

Proportional Band, Zone Cooling Integral Time and Zone

Control Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters, refer to

“MicroTech II DDC Features” on page 99.

Chilled Water: Face and Bypass Damper Control

When the unit is in the Cooling operating state, the chilled water valve is driven fully open and the face and bypass dampers are modulated to satisfy the cooling load. There are two processes involved in the face and bypass damper control function. The first is the process of modulating the dampers to maintain the Effective Discharge Cooling Set

Point. The second is the process of adjusting the Effective

Discharge Cooling Set Point up and down between the Minimum Discharge Cooling Set Point and the Maximum Discharge Cooling Set Point as the Ctrl Temp= value varies above and below the Effective Cooling Enable Set Point.

The following sections describe these two processes.

OM 138 77

Face and Bypass Damper Modulation. When the

Disch Air= value rises above the Effective Discharge Cooling Set Point by more than half the Discharge Cooling Dead

Band, the face and bypass dampers position is increased to the face. When the Disch Air= value falls below the Effective Discharge Cooling Set Point by more than half the Discharge Cooling Dead Band, the face and bypass damper position is decreased to the face.

The controller uses three PID control loop parameters to modulate the face and bypass dampers as the discharge air temperature changes. Theses are the Cooling Proportional

Band, Cooling Integral Time and Cooling Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID con-

trol loop parameters, refer to “MicroTech II DDC Features” on page 99.

Effective Discharge Cooling Set Point Adjustment.

When the Ctrl Temp= value rises above the Effective Cooling Enable Set Point by more than half the Cooling Enable

Dead Band, the Effective Discharge Cooling Set Point is decreased. When the Ctrl Temp= value falls below the Effective Cooling Enable Set Point by more than half the Cooling

Enable Dead Band, the Effective Discharge Cooling Set

Point is increased.

Note: When the unit first enters the Cooling operating state, the Effective Discharge Cooling Set Point is set to the current Disch Temp= value.

The controller uses three PID control loop parameters to raise and lower the Effective Discharge Cooling Set Point as the Ctrl Temp= value changes. These are the Zone Cooling

Proportional Band, Zone Cooling Integral Time and Zone

Control Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters, refer to

“MicroTech II DDC Features” on page 99.

Cooling to Econo Operating State

When economizer operation is available, the unit will leave the Cooling operating state and enter the Econo operating state when the Ctrl Temp= value falls below the Effective

Cooling Enable Set Point by more than half the Cooling

Enable Dead Band and either of the following are true:

1. The chilled water valve is closed for more than one

Cooling Interstage Timer period.

2. The Effective Discharge Cooling Set Point has been at the Maximum Discharge Cooling Set Point for one

Cooling Interstage Timer period.

Cooling to Fan Only Operating State

When economizer operation is not available, the unit will leave the Cooling operating state and enter the Fan Only operating state when the Ctrl Temp= value falls below the

Effective Cooling Enable Set Point by more than half the

Cooling Enable Dead Band and any of the following are true:

1. The chilled water valve is closed for more than one

Cooling Interstage Timer period.

2. The Effective Discharge Cooling Set Point has been at the Maximum Discharge Cooling Set Point for one

Cooling Interstage Timer period.

3. All cooling is disabled for any reason. Refer to “Clg Status” on page 43.

Heating: Multistage

Temperature Control

Table 41: Programmable Parameters

Keypad/Display ID

Parameter Name

Menu Name Item Name

Zone Heating

Discharge Heating

Heating Setup

Eff Htg Spt= ____ °F

Occ Htg Spt=

Min Htg Spt=

Max Htg Spt=

75.0 ºF

Htg Deadband= 1.0 ºF

55.0 ºF

65.0 ºF

Stage Time= 5 Min

Effective Heating

Enable Set Point

Heating Enable Set

Point

Heating Enable Dead

Band

Minimum Discharge

Heating Set Point

Maximum Discharge

Heating Set Point

Heating Interstage

Timer

Entering Heating Operating State

The unit enters the Heating operating state from the Recirc or Fan Only operating state when the Ctrl Temp= value falls below the Effective Heating Enable Set Point by more than half the Heating Enable Dead Band.

When the unit is in the Heating operating state, heating stages are turned on and off to maintain the Ctrl Temp= value at the Effective Heating Enable Set Point.

Note: Unless it is set by a signal from an option space temperature sensor or by the dehumidification function, the Effective Heating Enable Set Point is set by the controller equal to the Heating Enable Set

Point.

The controller activates the first stage of electric heat as it enters the Heating operating state. When the Ctrl Temp= value is below the Effective Heating Enable Set Point by more than half the Heating Enable Dead Band and the Heating Interstage Timer has expired since the last stage change, heating capacity is increased by one stage. When the Ctrl

Temp= value is above the Effective Heating Enable Set Point by more than half the Heating Enable Dead Band and the

Heating Interstage Timer has expired since the last stage change, heating capacity is decreased by one stage.

78 OM 138

Discharge Temperature Override

While controlling the Ctrl Temp= value to the Effective

Heating Enable Set Point, the controller places limits on the discharge air temperature. The controller does not allow the

Disch Temp= value to exceed the Maximum Discharge Heating Set Point or fall below the Minimum Discharge Heating

Set Point without taking action. If the Disch Temp= value exceeds the Maximum Discharge Heating Set Point, heating capacity is decreased by one stage (subject to the Heating

Interstage Timer). If the Disch Temp= value falls below the

Minimum Discharge Heating Set Point, heating capacity is increased by one stage (subject to the Heating Interstage

Timer).

Effective Discharge Heating Set Point Limiting

On units equipped with multistage electric heat, the Effective

Discharge Heating Set Point is limited by a factory set 60°F maximum heater temperature rise limit. The controller does not allow the Effective Discharge Heating Set Point to be set higher than 60°F above the current temperature entering the discharge fan as indicated by the Ent Fan= parameter in the

Temperatures menu.

Heating to Fan Only Operating State

The unit will transition from the Heating to Fan Only operating state when either of the following are true

1. The Ctrl Temp= value is above the Effective Heating

Enable Set Point by more than half the Heating Enable

Dead Band and the heating capacity is a 0% for longer than the Heating Interstage Timer period.

2. Heating is disabled for any reason. Refer to “Htg Status” on page 44.

Morning Warm-up Control

Table 42: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Zone Heating

Timer Settings

Eff Htg Spt= ____ °F

Occ Htg Spt= 70.0 ºF

Htg Deadband= 1.0 ºF

Max MWU= 90 min

Effective Heating

Enable Set Point

Heating Enable Set

Point

Heating Enable Dead

Band

Maximum Morning

Warm-up Timer

On return air units, morning warm up operation occurs after the transition from unoccupied to occupied mode when the

Ctrl Temp= value is below the Effective Heating Enable Set

Point by more than half the Heating Enable Dead Band.

Under these conditions, the controller enters the MWU operating state after the normal startup sequence.

Note: Unless it is set by a signal from an option space temperature sensor or by the dehumidification function, the Effective Heating Enable Set Point is set by the controller equal to the Heating Enable Set

Point.

The MWU operating state is similar to the Heating operating state; the only difference is that the Eff Min OA Pos= parameter is set to 0% during MWU. The unit remains in the

MWU operating state until either the Ctrl Temp= value is equal to or greater than the Effective Heating Enable Set

Point or the duration of the MWU operating state exceeds the Maximum Morning Warm-up Timer setting. In either case, since the Ctrl Temp= value has not risen above the

Effective Heating Enable Set Point by more than half the

Heating Enable Dead Band when this occurs, the controller enters the Heating operating state.

The Maximum Morning Warm-up Timer parameter is provided to ensure that the required minimum ventilation air is being supplied after a known time regardless of the space temperature condition. For example, if actual occupancy is at

8:00 a.m. and unit startup is scheduled for 6:30 a.m., a Maximum Morning Warm-up Timer setting of 90 minutes would ensure that the outdoor air dampers open to minimum position when building occupancy occurs.

Note: The morning warm-up function does not occur on units equipped with 100% OA hoods.

High Ambient Heating Lockout

Table 43: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Zone Heating

OATHtg Lock= 55.0 ºF

OATLock Diff= 1.0 °F

High Ambient Heating

Lockout Set Point

High Ambient Heating

Lockout Differential

Heating is disabled when the outdoor air temperature is greater than the High Ambient Heating Lockout Set Point.

When this occurs, the Htg Status= parameter in the System and Zone Heating menu indicates “Off Amb” if heating is not disabled for some other reason. When the outdoor air temperature drops below the High Ambient Heating Lockout

Set Point by more than the High Ambient Heating Lockout

Differential, heating operation is re-enabled.

OM 138 79

Discharge Air Low Limit Control

Table 44: Programmable Parameters

Keypad/Display ID

Menu Name

Discharge Heating

Parameter Name

Item Name

Min DAT Ctrl= Yes Min DAT Control Flag

MinDAT Limit= 55.0

ºF

Minimum Discharge

Temperature Limit

Htg Db= 1.0 ºF

Discharge Heating

Dead Band

If heating is enabled and there is no heating load (normally

Fan Only operating state), the controller can activate the unit staged electric heating equipment as required to prevent the discharge air temperature from becoming too cool. It accomplishes this by entering the Min DAT operating state when necessary.

Entering Min DAT Operating State

When the Min DAT Control Flag is set to “Yes” and if the

Disch Temp= parameter falls below the Minimum Discharge

Temperature Limit by more than half the Discharge Heating

Dead Band, the unit operating state changes from Fan Only to Min DAT. When in the Min DAT operating state, heating capacity is increased by one stage if the Disch Temp= parameter is below the Minimum Discharge Temperature

Limit by more than half the Discharge Heating Dead Band

(subject to the Heating Interstage Timer). Heating capacity is decreased by one stage if the Disch Temp= parameter rises above the Minimum Discharge Temperature Limit by more than half the Discharge Heating Dead Band (subject to the

Heating Interstage Timer).

Leaving Min DAT Operating State

When the heating capacity has be 0% for one Heat Interstage

Time period and the Disch Temp= parameter is above the

Minimum Discharge Temperature Limit by more than half the Discharge Heating Dead Band, the unit leaves the Min

DAT operating state and re-enters the Fan Only operating state.

Heating: Modulating

Temperature Control

Table 45: Programmable Parameters

Keypad/Display ID

Parameter Name

Menu Name Item Name

Zone Heating

Discharge Heating

Eff Htg Spt=

Htg Db=

____ °F

Occ Htg Spt= 70.0 ºF

Htg Deadband=

Eff Htg Spt=

1.0 ºF

___ ºF

1.0 ºF

Min Htg Spt=

Max Htg Spt=

55.0 ºF

65.0 ºF

Effective Heating

Enable Set Point

Heating Enable Set

Point

Heating Enable Dead

Band

Effective Discharge

Heating Set Point

Discharge Heating

Dead Band

Minimum Discharge

Heating Set Point

Maximum Discharge

Heating Set Point

Min DAT Control Flag Min DAT Ctrl= Yes

Min DAT Limit= 55.0 ºF

Htg Propbd= 8.0ºF

Minimum Discharge

Temperature Limit

Zone Heating Proportional Band

Zone Temp Setup

Heating Setup

Htg IntTime=

Period=

Stage Timer=

F&BP Ctrl=

700 sec

60 sec

5 min

OpenValve

Zone Heating Integral Time

Zone Control Period

Heating Interstage

Timer

Face and Bypass

Method Flag

F&BP Chgovr=

Htg Propbd=

37 °F

30.0 ºF

Face and Bypass

Changeover Temperature

Heating Proportional

Band

Htg IntTime= 100 sec Heating Integral Time

Htg Period= 30 sec Heating Period

Entering Heating Operating State

The unit enters the Heating operating state from the Recirc or Fan Only operating state when the Ctrl Temp= value falls below the Effective Heating Enable Set Point by more than half the Heating Enable Dead Band.

Note: Unless it is set by a signal from an option space temperature sensor or by the dehumidification function, the Effective Heating Enable Set Point is set by the controller equal to the Heating Enable Set

Point.

80 OM 138

There are several different modulating heating types available with this equipment. There are some differences in the control sequence depending on the heat type installed. The different types are described in the following sections.

Steam or Hot Water: Valve Control

When the unit is in the Heating operating state, the hot water or steam valve is modulated to satisfy the heating load.

There are two processes involved in the heating valve control function. The first is the process of modulating the heating valve to maintain the Effective Discharge Heating Set

Point. The second is the process of adjusting the Effective

Discharge Heating Set Point up and down between the Minimum Discharge Heating Set Point and the Maximum Discharge Heating Set Point as the Ctrl Temp= value varies above and below the Effective Heating Enable Set Point. The following sections describe these two processes.

Valve Modulation. When the Disch Air= value falls below the Effective Discharge Heating Set Point by more than half the Discharge Heating Dead Band, the heating valve position is increased. When the Disch Air= value rises above the

Effective Discharge Heating Set Point by more than half the

Discharge Heating Dead Band, the heating valve position is decreased.

The controller uses three PID control loop parameters to modulate the heating valve as the discharge air temperature changes. Theses are the Heating Proportional Band, Heating

Integral Time and Heating Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control.

For detailed information regarding tuning PID control loop

parameters, refer to “MicroTech II DDC Features” on page 99.

Effective Discharge Heating Set Point Adjustment.

When the Ctrl Temp= value rises above the Effective Heating Enable Set Point by more than half the Heating Enable

Dead Band, the Effective Discharge Heating Set Point is decreased. When the Ctrl Temp= value falls below the Effective Heating Enable Set Point by more than half the Heating

Enable Dead Band, the Effective Discharge Heating Set

Point is increased.

Note: When the unit first enters the Heating operating state, the Effective Discharge Heating Set Point is set to the current Disch Temp= value.

The controller uses three PID control loop parameters to raise and lower the Effective Discharge Heating Set Point as the Ctrl Temp= value changes. These are the Zone Heating

Proportional Band, Zone Heating Integral Time and Zone

Control Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters, refer to

“MicroTech II DDC Features” on page 99.

Steam or Hot Water Heat: Face and Bypass Damper

Control-Open Valve Method

When a unit is equipped with steam or hot water with face and bypass damper heating there are two different methods available for controlling the heating arrangement - the “Open

Valve” and “Modulating Valve” methods. This section describes the “Open Valve” method.

When the Face and Bypass Method Flag is set to “Open-

Valve”, the steam or hot water valve is driven fully open when the unit enters the Heating operating state. The face and bypass dampers are then modulated to satisfy the heating load. There are two processes involved in the face and bypass damper control function. The first is the process of modulating the dampers to maintain the Effective Discharge

Heating Set Point. The second is the process of adjusting the

Effective Discharge Heating Set Point up and down between the Minimum Discharge Heating Set Point and the Maximum Discharge Heating Set Point as the Ctrl Temp= value varies above and below the Effective Heating Enable Set

Point. The following sections describe these two processes.

Face and Bypass Damper Modulation. When the

Disch Air= value falls below the Effective Discharge Heating Set Point by more than half the Discharge Heating Dead

Band, the face and bypass damper position is increased to the face. When the Disch Air= value rises above the Effective Discharge Heating Set Point by more than half the Discharge Heating Dead Band, the face and bypass damper position is decreased to the face.

The controller uses three PID control loop parameters to modulate the face and bypass dampers as the discharge air temperature changes - the Heating Proportional Band, Heating Integral Time and Heating Period. Although these parameters can be adjusted, the factory default values for these parameters provide the best control for most applications. For detailed information regarding tuning PID control

loop parameters, refer to “MicroTech II DDC Features” on page 99.

Effective Discharge Heating Set Point Adjustment.

When the Ctrl Temp= value rises above the Effective Heating Enable Set Point by more than half the Heating Enable

Dead Band, the Effective Discharge Heating Set Point is decreased. When the Ctrl Temp= value falls below the Effective Heating Enable Set Point by more than half the Heating

Enable Dead Band, the Effective Discharge Heating Set

Point is increased.

Note: When the unit first enters the Heating operating state, the Effective Discharge Heating Set Point is set to the current Disch Temp= value.

The controller uses three PID control loop parameters to raise and lower the Effective Discharge Heating Set Point as the Ctrl Temp= value changes. These are the Zone Heating

Proportional Band, Zone Heating Integral Time and Zone

Control Period. Although these parameters can be adjusted, for most applications, the factory default values for these

OM 138 81

parameters provide the best control. For detailed information regarding tuning PID control loop parameters, refer to

“MicroTech II DDC Features” on page 99.When the unit is

in the Heating operating state, the hot water or steam valve is modulated to satisfy the heating load. There are two processes involved in the heating valve control function. The first is the process of modulating the heating valve to maintain the Effective Discharge Heating Set Point. The second is the process of adjusting the Effective Discharge Heating Set

Point up and down between the Minimum Discharge Heating Set Point and the Maximum Discharge Heating Set Point as the Ctrl Temp= value varies above and below the Effective Heating Enable Set Point. The following sections describe these two processes.

Steam or Hot Water Heat: Face and Bypass Damper

Control-Modulating Valve Method

When a unit is equipped with steam or hot water with face and bypass damper heating there are two different methods available for controlling the heating arrangement. These are the “Open Valve” and “Modulating Valve” methods. This section describes the “Modulating Valve” method.

When the Face and Bypass Method Flag is set to “Mod

Valve”, action of the steam or hot water valve versus the face and bypass dampers changes depending on the OA Temp= value.

If the OA Temp= value is below the Face and Bypass

Changeover Temperature setting, the steam or hot water valve is driven fully open when the unit enters the Heating operating state. The face and bypass dampers are then modu-

lated to satisfy the heating load as described in the “Steam or

Hot Water Heat: Face and Bypass Damper Control-Open

Valve Method“ section above.

If the OA Temp= value is above the Face and Bypass

Changeover Temperature setting, the face and bypass dampers are driven fully open to the face when the unit enters the

Heating operating state. The hot water or steam valve is then modulated to satisfy the heating load as described in the

“Steam or Hot Water: Valve Control“ section above.

Gas Heat

When the unit enters the Heating operating state, the controller first holds the gas valve and the minimum fire position

(either 5% or 33% depending on the burner model installed) until the Heating Interstage Timer expires. When the Heating

Interstage Timer expires, the controller modulates the gas valve to maintain satisfy the heating load. There are two processes involved in the heating valve control function. The first is the process of modulating the gas valve to maintain the Effective Discharge Heating Set Point. The second is the process of adjusting the Effective Discharge Heating Set

Point up and down between the Minimum Discharge Heating Set Point and the Maximum Discharge Heating Set Point as the Ctrl Temp= value varies above and below the Effective Heating Enable Set Point. The following sections describe these two processes.

Gas Valve Modulation. When the Disch Air= value falls below the Effective Discharge Heating Set Point by more than half the Discharge Heating Dead Band, the gas valve position is increased. When the Disch Air= value rises above the Effective Discharge Heating Set Point by more than half the Discharge Heating Dead Band, the gas valve position is decreased.

The controller uses three PID control loop parameters to modulate the gas valve as the discharge air temperature changes -the Heating Proportional Band, Heating Integral

Time and Heating Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters, refer

to “MicroTech II DDC Features” on page 99.

Effective Discharge Heating Set Point Adjustment.

When the Ctrl Temp= value rises above the Effective Heating Enable Set Point by more than half the Heating Enable

Dead Band, the Effective Discharge Heating Set Point is decreased. When the Ctrl Temp= value falls below the Effective Heating Enable Set Point by more than half the Heating

Enable Dead Band, the Effective Discharge Heating Set

Point is increased.

Note: When the unit first enters the Heating operating state, the Effective Discharge Heating Set Point is set to the current Disch Temp= value.

The controller uses three PID control loop parameters to raise and lower the Effective Discharge Heating Set Point as the Ctrl Temp= value changes. These are the Zone Heating

Proportional Band, Zone Heating Integral Time and Zone

Control Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters, refer to

“MicroTech II DDC Features” on page 99.

Effective Discharge Heating Set Point Limiting. On units equipped with modulating gas heat, the Effective Discharge Heating Set Point is limited according to a maximum heat exchanger temperature rise limit. This factory set limit varies depending on the unit burner model and can be found on the gas heat data plate attached to the unit. The controller does not allow the Effective Discharge Heating Set Point to be set above the current temperature entering the discharge fan, as indicated by the Ent Fan= parameter in the Temperatures menu, by more than this maximum heat exchanger temperature rise limit.

100% OA Units-Special Startup Sequence. If a unit is equipped with a 100% OA hood and high-turndown (5%) modulating gas heat, and heat is required at unit startup, the furnace enters a special burner startup sequence when the unit enters the Startup operating state. Pre-firing the burner allows the gas heat pre-purge sequence to occur and the burner to fire and warm up so that tempered air is available immediately when the fans start. The special sequence

82 OM 138

occurs if the Heat Status= parameter in the System or Zone

Heating menu indicates “Htg Ena” and either of the following conditions are true:

1. The Ctrl Temp= value is below Effective Heating

Enable Set Point by more than half the Heating Enable

Dead Band.

2. The Min DAT Control Flag is set to “Yes” and the outdoor air temperature is below the Minimum Discharge

Temperature Limit by more than half the Discharge

Heating Dead Band.

When the special gas heat startup sequence is activated upon entering the Startup operating state, the burner 90 pre-purge cycle is started at the same time as a four-minute timer. The burner starts and operates at the minimum fire position (5%) during this four-minute time period after the completion of the pre-purge cycle. When the four-minute timer expires, the burner variable orifice is modulated to a “preheat firing rate” according to the formula below, and where:

Preheat Firing Time: The time increment that the variable orifice “increase” output relay (MCB-BO10) is energized to achieve the “preheat firing rate.” Thirty seconds is the maximum.

Variable Orifice Travel Time: The amount of time it takes the burner variable orifice to drive from the fully closed to fully open position (30 seconds-fixed).

Applicable Discharge Air Temperature Set Point: Either the Effective Discharge Heating Set Point or the Minimum

Discharge Temperature Limit. It is the Effective Discharge

Heating Set Point if the Ctrl Temp= value is below Effective

Heating Enable Set Point by more than half the Heating

Enable Dead Band. It is the Minimum Discharge Temperature Limit if the Ctrl Temp= value is above the Effective

Heating Enable Set Point by more than half the Heating

Enable Dead Band, the Min DAT Control Flag is set to “Yes” and the outdoor air temperature is below the Minimum Discharge Temperature Limit by more than half the Discharge

Heating Dead Band.

Preheat Firing Time = Variable Orifice Travel Time ×

Maximum Heat Exchanger Temperature Rise

Maximum Heat Exchanger Temperature Rise: The maximum temperature rise across the heat exchanger for safe operation. This number varies with burner model and the baffle position and is programmed into the controller at the factory. This value can be found on the gas heat data plate

attached to the unit. Refer also to “Software Identification and Configuration” on page 102.

Outdoor Air Temperature: The current outdoor air temperature input to the controller.

Once modulated to the “preheat firing rate”, the burner remains at this rate for a fixed thirty second time period to allow the heat exchanger to warm-up before the unit leaves the Startup and enters the Heating operating state at which time the fans are started. After entering the Heating operating state, the burner remains at the “preheat firing rate” for a fixed four minute time period to allow the temperature to stabilize at this rate before “normal” gas heat control begins.

When the unit enters the Heating operating state and “normal” gas heat control begins, the controller then modulates the gas valve to maintain the Ctrl Temp= value at Effective

Heating Enable Set Point as described above.

Heating to Fan Only Operating State

The unit will transition from the Heating to Fan Only operating state when the Ctrl Temp= value is above the Effective

Heating Enable Set Point by more than half the Heating

Enable Dead Band and the heating capacity has been at 0% for longer than the Heating Interstage Timer period. The unit will be at 0% capacity after the heating value reaches and has been at the low fire position (either 5% or 33% depending on the burner model installed) for longer than the Heating Interstage Timer period.

Note: The unit will also transition from the Heating to Fan

Only operating state if Heating is disabled for any

reason. Refer to “Htg Status” on page 44.

Morning Warm-up Control

Table 46: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Zone Heating

Timer Settings

Eff Htg Spt= ____ °F

Occ Htg Spt= 70.0 ºF

Htg Deadband= 1.0 ºF

Max MWU= 90 min

Effective Heating

Enable Set Point

Heating Enable Set

Point

Heating Enable Dead

Band

Maximum Morning

Warm-up Timer

On return air units, morning warm up operation occurs after the transition from unoccupied to occupied mode when the

Ctrl Temp= value is below the Effective Heating Enable Set

Point by more than half the Heating Enable Dead Band.

Under these conditions, the controller enters the MWU operating state after the normal startup sequence.

Note: Unless it is set by a signal from an option space temperature sensor or by the dehumidification func-

OM 138 83

tion, the Effective Heating Enable Set Point is set by the controller equal to the Heating Enable Set

Point.

The MWU operating state is similar to the Heating operating state; the only difference is that the Eff Min OA Pos= parameter is set to 0% during MWU. The unit remains in the

MWU operating state until either the Ctrl Temp= value is equal to or greater than the Effective Heating Enable Set

Point or the duration of the MWU operating state exceeds the Maximum Morning Warm-up Timer setting. In either case, since the Ctrl Temp= value has not risen above the

Effective Heating Enable Set Point by more than half the

Heating Enable Dead Band when this occurs, the controller enters the Heating operating state.

The Maximum Morning Warm-up Timer parameter is provided to ensure that the required minimum ventilation air is being supplied after a known time regardless of the space temperature condition. For example, if actual occupancy is at

8:00 a.m. and unit startup is scheduled for 6:30 a.m., a Maximum Morning Warm-up Timer setting of 90 minutes would ensure that the outdoor air dampers open to minimum position when building occupancy occurs.

Note: The morning warm-up function does not occur on units equipped with 100% OA hoods.

High Ambient Heating Lockout

Table 47: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Zone Heating

OATHtg Lock= 55.0 ºF

OATLock Diff= 1.0 °F

High Ambient Heating

Lockout Set Point

High Ambient Heating

Lockout Differential

Heating is disabled whenever the outdoor air temperature is greater than the High Ambient Heating Lockout Set Point.

When this occurs, the Htg Status= parameter in the System and Zone Heating menu indicates “Off Amb” if heating is not disabled for some other reason. When the outdoor air temperature drops below the High Ambient Heating Lockout

Set Point by more than the High Ambient Heating Lockout

Differential, heating operation is re-enabled.

Discharge Air Low Limit Control

Table 48: Programmable Parameters

Keypad/Display ID

Parameter Name

Menu Name Item Name

Eff Clg Spt= 55.0 ºF

Effective Discharge

Cooling Set Point

Discharge Cooling

Clg Db= 1.0 ºF

Discharge Cooling

Dead Band

Discharge Heating Min DAT Ctrl= Yes Min DAT Control Flag

If heating is enabled and there is no heating load (normally

Fan Only operating state), the controller can activate the unit heating equipment as required to prevent the discharge air temperature from becoming too cool. It accomplishes this by entering the Min DAT operating state when necessary.

Entering Min DAT Operating State

When the Min DAT Control Flag is set to “Yes” and if the

Disch Temp= parameter falls below the Minimum Discharge

Temperature Limit by more than half the Discharge Heating

Dead Band, the unit operating state changes from Fan Only to Min DAT. When in the Min DAT operating state, heating capacity is increased if the Disch Temp= parameter is below the Minimum Discharge Temperature Limit by more than half the Discharge Heating Dead Band. Heating capacity is decreased if the Disch Temp= parameter rises above the

Minimum Discharge Temperature Limit by more than half the Discharge Heating Dead Band.

Leaving Min DAT Operating State

When the heating capacity has be 0% for one Heat Interstage

Time period and the Disch Temp= parameter is above the

Minimum Discharge Temperature Limit by more than half the Discharge Heating Dead Band, the unit leaves the Min

DAT operating state and re-enters the Fan Only operating state.

84 OM 138

Dehumidification

Table 49: Programmable Parameters

Keypad/Display ID

Menu Name

Dehumidification

Dehum Setup

Zone Cooling

Zone Heating

Parameter Name

Item Name

Dehum Method=

RH Setpoint=

DewPoint Spt=

RH Db= 2%

None

50%

50 ºF

Dehumidification

Method Flag

Relative Humidity Set

Point

Dew Point Set Point

Relative Humidity

Dead Band

DewPnt Db= 2 ºF

Dehum Ctrl= Occupied

Dew Point Dead Band

Occupied/Unoccupied Dehumidification Flag

Minimum Stages=

Maximum Stages=

DH Stage Timer= min

Sensor Loc=

Occ Clg Spt=

Eff Htg Spt=

10

____ ºF

Occ Htg Spt=

2

4

Return

75.0ºF

70.0ºF

Minimum Dehumidification Cooling Stages

Maximum Dehumidification Stages

Dehumidification

Interstage Timer

Humidity Sensor

Location Flag

Cooling Enable Set

Point

Effective Heating

Enable Set Point

Heating Enable Set

Point

When the dehumidification function is active, the unit cooling coil is controlled to cool the air low enough to wring out moisture. Reheat is then supplied as necessary to provide properly conditioned air to the space. This is the only case in which the unit cooling and heating can be active simultaneously.

Enabling Dehumidification

The dehumidification function should only be enabled when the unit heating coil is located in a position down stream of the unit cooling coil. Also, before the dehumidification function can be utilized, an optional humidity sensor must be field installed and wired to the unit. For details regarding humidity sensor installation, refer to IM696, MicroTech II

Applied Rooftop Unit Controller .

With the conditions mentioned above met, the dehumidification function is enabled by setting the Dehumidification

Method Flag to either “RH” or “DewPnt”. When this parameter is set to “RH”, dehumidification operation is controlled to maintain the Rel Humidity= value at the Relative Humidity Set Point. When this parameter is set to “DewPnt”, dehumidification operation is controlled to maintain the Dew

Point= value at the Dew Point Set Point.

Note: The Dew Point= value is calculated by the controller using the Rel Humidity= value and either the

Space Temp= or Return Air= value, depending on the setting of the Humidity Sensor Location Flag.

This parameter can either be set to “Space” or

“Return”.

When the Dehumidification Method Flag is set to “None”, the dehumidification function is disabled.

The dehumidification function is also disabled if mechanical cooling is disabled for any reason or if heating is disabled for any reason other than due to outdoor air temperature lockout.

Occupied/Unoccupied Dehumidification

When the Occupied/Unoccupied Dehumidification Flag is set to “Occupied” then the dehumidification function will be enabled during occupied and disabled during unoccupied unit operation. If unoccupied dehumidification operation is required, the Occupied/Unoccupied Dehumidification Flag must be set to “Always”. In this case the dehumidification function is enabled both during occupied and unoccupied operation. During unoccupied periods the unit will start up an operate the dehumidification function until the relative humidity (or dew point) set point is satisfied and then shut back off.

Dehumidification Cooling Operation

When the dehumidification function is enabled and the Rel

Humidity= ( or Dew Point= ) value rises above the Relative

Humidity Set Point (or Dew Point Set Point) by more than half the Relative Humidity Dead Band, the dehumidification function is turned on. When the dehumidification function is turned on, the unit enters the Heating operating state. When the dehumidification function is turned on, the unit is prevented from entering the Econo or Cooling operating state.

The cooling equipment functions as described in the following sections.

Compressorized Cooling

When the dehumidification function is turned on, the cooling is staged up to the Minimum Stages and the Dehumidification Interstage Timer begins timing down.

When the Dehumidification Interstage Timer expires, if the

Rel Humidity= ( or Dew Point= ) value is still above the Relative Humidity Set Point (or Dew Point Set Point) by more than half the Relative Humidity Dead Band, cooling is staged up to the Maximum Stages. The Dehumidification

Interstage Timer again is reset and begins timing down.

If at the Maximum Stages and the Rel Humidity= ( or Dew

Point= ) value is below the Relative Humidity Set Point (or

Dew Point Set Point) by more than half the Relative Humidity Dead Band when the Dehumidification Interstage Timer expires, cooling is staged down to the Minimum Stages. The

Dehumidification Interstage Timer again is reset and begins timing down.

If at the Minimum Stages and the Rel Humidity= ( or Dew

Point= ) value is below the Relative Humidity Set Point (or

OM 138 85

Dew Point Set Point) by more than half the Relative Humidity Dead Band when the Dehumidification Interstage Timer expires, cooling is staged off and the dehumidification function is turned off.

Chilled Water Cooling

When the dehumidification function is turned on, the chilled water valve is driven to 100% capacity and the Relative

Humidity Interstage Timer begins timing down.

If the Rel Humidity= ( or Dew Point= ) value is below the

Relative Humidity Set Point (or Dew Point Set Point) by more than half the Relative Humidity Dead Band when the

Dehumidification Interstage Timer expires, the chilled water valve is driven closed and the dehumidification function is turned off.

Dehumidification Heating Operation

When the dehumidification function is turned on, the unit enters the Heating operating state and then is allow to transition between the Heating, Min DAT and Fan Only operating states as required to maintain the zone temperature conditions. The unit is prevented from entering the Econo or Cooling operating states.

The one difference between dehumidification heating and normal heating operation. The Eff Heating Enable Set Point is set equal to the current Space Temp= value when the dehumidification function is turned on. The Eff Heating Enable

Set Point then remains at this value while the dehumidification function is on. When the dehumidification function is turned off, the Eff Heating Enable Set Point returns to its normal value.

Note: The value the Eff Heating Enable Set Point is set to when the dehumidification function is turned on is limited between the Cooling Enable Set Point and the Heating Enable Set Point.

Energy Recovery

When a unit is equipped with an optional energy recovery wheel, energy recovery is provided by drawing outside air across half of an enthalpy wheel and drawing exhaust air across the other half. Latent and sensible heat is transferred from the hotter moist exhaust air to the colder dry outside air in winter. Latent and sensible heat is transferred from the hotter moist outside air to the cooler dry exhaust air in summer. Energy recovery control consists of starting and stopping an exhaust fan, modulating the speed of the exhaust fan, starting and stopping an enthalpy wheel, optionally controlling the speed of the enthalpy wheel and opening and closing a set of bypass dampers. The outdoor dampers are controlled

in the normal manner. Refer to “100% Outdoor Air Damper

Control” on page 68 or “Economizer” on page 68 as applica-

ble. The following sections describe the control of the enthalpy wheel, exhaust fan and bypass dampers.

Enthalpy Wheel Control

Table 50: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

OA Damper

Energy Recovery

Energy Rec

Setup

Parameter Name

Eff Min OA Pos= ___%

Energy Rec=

EWhl Propbd=

EWhl IntTime= 100 sec

EWhl Period=

No

30.0 ºF

30 se c

Effective Minimum Outdoor Damper Position

Set Point

Energy Recovery Control Flag

Energy Recovery Wheel

Proportional Band

Energy Recovery Wheel

Integral Time

Heat Recovery Wheel

Period

When the Energy Recovery Control Flag is set to “Yes”, the enthalpy wheel is turned on whenever the unit exhaust fan is on and the current OA Damper Pos= parameter in the OA

Damper menu indicates a value equal to the Effective Minimum Outdoor Damper Position Set Point. It is turned off when the exhaust fan is turned off or the OA Damper Pos= value is greater than the Effective Minimum Outdoor

Damper Position Set Point.

Constant Speed Enthalpy Wheel

When the unit is equipped with a constant speed enthalpy wheel, the wheel is driven to maximum speed whenever the enthalpy wheel is on.

Variable Speed Enthalpy Wheel

When the unit is equipped with a variable speed enthalpy wheel, the wheel is driven to maximum speed whenever the enthalpy wheel is on. The speed of the wheel may be modulated as described below to prevent wheel frosting.

When there is a threat of frost on the enthalpy wheel, a variable speed wheel is slowed down so that less enthalpy transfer occurs and frosting of the wheel is avoided. Frosting can occur on the enthalpy wheel when the exhaust air leaving the wheel is saturated. This condition occurs when two lines intersect on a psychometric chart, and it does not occur when these two lines do not intersect. One of these lines is the

Humidity Ratio versus the dry bulb temperature for saturated air. The other line is the Humidity Ratio versus the dry bulb temperature of the exhaust air leaving the enthalpy wheel.

The two ends of this second straight line on a psychometric chart are the outdoor air temperature at 95% relative humid-

ity (point 1 in Figure 9) and the return air temperature at the return air relative humidity (point 2 in Figure 9). One

exhaust air line showing frosting conditions and another showing no frost conditions are shown. The controller makes a continuous calculation to determine if and at what temperatures the saturated air and exhaust air lines intersect. When they do not intersect, the enthalpy wheel runs at full speed.

When they do intersect, the enthalpy wheel is controlled to a slower speed to maintain the dry bulb temperature of the

86 OM 138

exhaust air leaving the enthalpy wheel 3°F above the higher of the two intersecting dry bulb temperatures (point ST

2

Figure 9). This prevents the wheel from operating under

in frosting conditions.

When enthalpy wheel frost protection is active, the controller modulates the speed of the enthalpy wheel using three

PID control loop parameters. These are the Energy Recovery

Proportional Band, Energy Recovery Integral Time and

Energy Recovery Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters, refer

to “MicroTech II DDC Features” on page 99.

Figure 9: Variable Speed Enthalpy Wheel Frost

Protection - Psychometric Chart

Saturation

Temperature

ST

2

Saturated Air

Enthalpy Wheel

Exhaust Air (Frost

Conditions)

2

Enthalpy Wheel

Exhaust Air (No

Frost Conditions)

2

Saturated Air

1

ST

1

Dry Bulb Temperature

Exhaust Fan Control

Table 51: Programmable Parameters

Keypad/Display ID

Parameter Name

Menu Name Item Name

Bldg Pressure

Building Static P

Setup

Energy Recovery

Timer Settings

Unit Configuration

BldgSP Spt=

BSP Db=

1.00 “WC

0.080 “WC

BSP Propbd= 0.400 “WC

BSP IntTime=

BSP Period=

2.0 sec

2.0 sec

EF Min Cap=

Energy Rec=

Min Exh On=

Min Exh Off=

120 sec

120 sec

2nd P Sensor=

RF/EF Ctrl=

5%

No

None

Tracking

Rem RF/EF Cap= 25%

Building Static Pressure Set Point

Building Static Pressure Dead Band

Building Static Pressure Proportional

Band

Building Static Pressure Integral Time

Building Static Pressure Period

Exhaust Fan Minimum Capacity Value

Energy Recovery

Control Flag

Minimum Exhaust

Fan On Timer

Minimum Exhaust

Fan Off Timer

Second Pressure

Sensor Present Flag

Return/Exhaust Fan

Capacity Control Flag

Remote

Return/Exhaust Fan

Capacity Set Point

Building Pressure Control

The energy recovery option includes a variable capacity exhaust fan equipped with either a VFD or variable inlet vanes. When the Energy Recovery Control Flag is set to

“Yes”, the Return/Exhaust Fan Capacity Control Flag is set to “BldgPres” and the Second Pressure Sensor Present Flag is set to “Bldg”, the exhaust fan is controlled based on the building static pressure. The exhaust fan is turned on when the outdoor air dampers are opened and the Bldg Press= parameter value is above the Building Static Pressure Set

Point high by more than half the Building Static Pressure

Dead Band for longer than the Minimum Exhaust Fan Off

Timer.

Note: The exhaust fan is not turned on when the outdoor air dampers are closed (as in the Recirc or MWU operating states).

The exhaust fan remains on until any of the following occur:

1. The Bldg Press= parameter value drops below the

Building Static Pressure Set Point by more than half the

Building Static Pressure Deadband and the RF/EF Fan

Cap= value has been at the Exhaust Fan Minimum

Capacity Value for longer than the Minimum Exhaust

Fan On Timer.

2. The discharge fan is turned off.

3. The outdoor dampers are completely closed.

OM 138 87

When the exhaust fan is on, its capacity is modulated to maintain the Bldg Press= parameter value at the Building

Static Pressure Set Point using three PID control loop parameters. These are the Building Static Pressure Proportional

Band, Building Static Pressure Integral Time and Building

Static Pressure Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters, refer

to “MicroTech II DDC Features” on page 99.

Direct Position Control

The energy recovery option includes a variable capacity exhaust fan equipped with either a VFD or variable inlet vanes. When the Energy Recovery Control Flag is set to

“Yes” and the Return/Exhaust Fan Capacity Control Flag is set to “Position”, the exhaust fan is controlled based on

Remote Return/Exhaust Fan Capacity Set Point. This set point can be adjusted via network signal. The exhaust fan is turned on when the outdoor air dampers are opened and the exhaust fan capacity is commanded above the Exhaust Fan

Minimum Capacity Value for longer than the Minimum

Exhaust Fan Off Timer.

Note: The exhaust fan is not turned on when the outdoor air dampers are closed (as in the Recirc or MWU operating states).

The exhaust fan remains on until any of the following occur:

1. The Remote Return/Exhaust Fan Capacity Set Point is commanded to the Exhaust Fan Minimum Capacity

Value for longer than the Minimum Exhaust Fan On

Timer.

2. The discharge fan is turned off

3. The outdoor dampers are completely closed.

Energy Recovery Bypass Damper Control

Table 52: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

OA Damper Eff MinOA Pos= ___%

Effective Minimum

Outdoor Damper

Position Set Point

The energy recovery option includes a set of bypass dampers when the unit is equipped with a 0-100% modulating economizer. The bypass dampers are closed whenever the OA

Damper Pos= parameter in the OA Damper menu is equal to the Effective Minimum Outdoor Damper Position Set Point.

The bypass dampers are driven fully open when the OA

Damper Pos= parameter is driven above the Effective Minimum Outdoor Damper Position Set Point while the unit is in the Econo or Cooling operating state.

Return Fan Capacity Control

When a unit is equipped with return fan inlet guide vanes or a return fan VFD, there are two optional methods for controlling the return fan capacity. These are “direct building static pressure” control and “position” control. The following sections describe the two methods.

Direct Building Static Pressure Control

Table 53: Programmable Parameters

Keypad/Display ID

Parameter Name

Menu Name Item Name

Bldg Pressure

Building Static P

Setup

Unit Configuration

BldgSP Spt=

BSP Db= 0.080 “WC

BSP Propbd= 0.400 “WC

BSP IntTime=

BSP Period=

2nd P Sensor=

RF/EFCtrl=

1.00 “WC

2.0 sec

2.0 sec

Bldg

BldgPres

Building Static Pressure Set Point

Building Static Pressure Dead Band

Building Static Pressure Proportional

Band

Building Static Pressure Integral Time

Building Static Pressure Period

Second Pressure

Sensor Present Flag

Return/Exhaust Fan

Capacity Control Flag

When the Return/Exhaust Fan Capacity Control Flag is set to

“BldgPres” and the Second Pressure Sensor Present Flag is set to “Bldg”, the controller modulates the return fan capacity to maintain the Bldg Static Pressure Set Point.

Note: Note that this feature requires an optional building static pressure sensor.

To do this it uses three PID control loop parameters to modulate the return capacity as the building static pressure changes. Theses are Building Static Pressure Proportional

Band, Building Static Pressure Integral Time and Building

Static Pressure Period. Although these parameters can be adjusted, for most applications, the factory default values for these parameters provide the best control. For detailed information regarding tuning PID control loop parameters; refer

to “MicroTech II DDC Features” on page 99.

Building static pressure control of the return air fan airflow is overridden under two conditions.

1. The first condition is when the return fan capacity modulates down to 17% or the VFD speed is reduced to

25%. The controller does not allow the return fan capacity to modulate below these fixed values.

2. The second condition is when the outdoor air dampers are completely closed. In this case the return fan capacity tracks the discharge fan capacity one-to-one. In the case of a constant volume discharge fan the return fan airflow is driven to 100%.

88 OM 138

Return Fan Direct Position Control

Table 54: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Unit Configuration

RF/EF Ctrl= BldgPres

Rem RF/EF Cap=

25%

Return/Exhaust Fan

Capacity Control

Flag

Remote

Return/Exhaust Fan

Capacity Set Point

When the Return/Exhaust Fan Capacity Control Flag is set to

“Position”, the controller positions the return or exhaust fan inlet vanes or VFD speed to the Remote Return/Exhaust Fan

Capacity Set Point. Normal building static pressure control is overridden in this case. The Remote Return/Exhaust Fan

Capacity Set Point is then set via a network signal. If network communications is interrupted or is not present, the

Remote Return/Exhaust Fan Capacity Set Point remains at the last commanded setting and then can be adjusted via the unit keypad/display. The Remote Return/Exhaust Fan

Capacity Set Point can be adjusted from the fixed minimum

(17% for vanes or 25% for VFD applications) to 100%.

When the Return/Exhaust Fan Capacity Control Flag is set to

“BldgPres”, the Remote Return/Exhaust Fan Capacity Set

Point has no effect on the unit operation.

SAF/RAF Differential OA Reset

When a unit is equipped with return air fan inlets vanes or

VFD it may be necessary to increase the amount of outdoor air if the difference between the discharge and return fan capacity gets to large. If this is not done the discharge air fan can potentially become “starved” for air. A discharge fan operating in a “starved” condition not only has difficulty meeting the system airflow requirements but may cause damage to damper sets and/or return fan motors or VFD. To overcome this type of problem, the MicroTech II unit controller provides a discharge/return fan differential OA reset strategy, which automatically resets outdoor air dampers as the difference between the discharge and return air fan

capacity varies. Refer to “Discharge/Return Fan Differential

OA Reset” on page 72.

Note: On a zone (or space comfort) control unit, the discharge fan capacity is always assumed to be 100%.

Unoccupied Control

Unoccupied Heating (Night Setback)

Table 55: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Zone Heating

Unit Configuration

UnoccHtg Spt= 55.0 ºF

UnoccHtgDiff= 3°F

Space Sensor= Yes

Unoccupied Heating Set Point

Unoccupied Heating Differential

Space Sensor

Present Flag

If an optional space (or zone) temperature sensor (ZNT1) is connected to the controller, the Space Sensor Present Flag is set to “Yes” and the Unoccupied Heating Set Point is set higher than 0°F, unoccupied heating (night setback) operation is available. Unoccupied heating operation is disabled if either the Space Sensor Present Flag is set to “No” or the

Unoccupied Heating Set Point is set to 0°F. The following is a description of unoccupied heating operation:

If the space temperature falls to the Unoccupied Heating Set

Point while the unit is in the Off Unoc operating state, the unit starts and runs.

1 The controller enters the UnocHtg operating state after the normal startup sequence. Refer to

“Startup Control” on page 64. The UnocHtg operating state

is similar to the Heating operating state except that the outdoor air dampers remain closed in the UnocHtg operating state.

When the space temperature rises above the Unoccupied

Heating Set Point by more than the Unoccupied Heating Differential, heating operation ends and the controller shuts down the fans and returns to the Off Unoc state.

Note: The Unoccupied Heating Set Point cannot be set higher than the Occ Htg Spt= parameter.

Emergency Space Sensor Failure Operation

A unit starts and runs in an emergency mode of operation if all of the following are true:

1. The Space Sensor Present Flag is set to “Yes”

2. The Unoccupied Heating Set Point is set higher than 0°F

3. The current value of the OA Temp= parameter is below

40°F.

4. The Space Temp problem alarm occurs.

5. Unit is equipped with a functioning return temperature sensor.

In this mode of operation the unit starts and runs continuously using the return air temperature sensor as the “Control

Temperature.” Refer to “Control Temperature” on page 66.

1. The unit does not activate unoccupied heating or cooling operation if the UnitStatus= parameter in the System menu indicates “Off Man”, “Off Sw”, “Off Net” or “Off Alm.”

OM 138 89

Unoccupied Cooling (Night Setup)

Table 56: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Zone Cooling

Unit Configuration

UnoccClg Spt= 85.0 ºF

UnoccClgDiff= 3°F

Space Sensor= Yes

Unoccupied Cooling Set Point

Unoccupied Cooling Differential

Space Sensor

Present Flag

If an optional space (or zone) temperature sensor (ZNT1) is connected to the controller, the Space Sensor Present Flag is set to “Yes” and the Unoccupied Cooling Set Point is set lower than 99°F, unoccupied cooling (night setup) operation is available. Unoccupied cooling operation is disabled if either the Space Sensor Present Flag is set to “No” or the

Unoccupied Cooling Set Point is set to 99°F. The following is a description of unoccupied cooling operation:

If the space temperature rises to the Unoccupied Cooling Set

Point while the unit is in the Off Unoc state, the unit starts and runs.

1 If the unit has an economizer and the

OA Ambient= parameter indicates “Low”, the controller enters the

UnocEcon operating state after the normal startup sequence.

If OA Ambient= parameter indicates “High” or the outdoor air is not cool enough to maintain the Eff Clg Spt= setting in the Discharge Cooling menu (or the unit has no economizer), the controller enters the UnocClg operating state and activates mechanical cooling after the normal startup sequence.

The UnocEcon and UnocClg operating states are similar to the Econo and Cooling operating states except that the Eff

MinOA Pos= parameter is set to 0%. If the OA Ambient= parameter indicates “Low”, the outdoor air dampers are wide open during UnocClg. If the OA Ambient= parameter indicates “High” (or there is no economizer), the outdoor air dampers are fully closed during UnocClg.

When the space temperature drops below the Unoccupied

Cooling Set Point by more than the Unoccupied Cooling

Differential, cooling operation ends and the controller shuts down the fans and returns to the Off Unoc state.

Note: The Unoccupied Cooling Set Point cannot be set lower than the Occ Clg Spt= parameter.

Purge

Table 57: Programmable Parameters

Keypad/Display ID

Menu Name Item Name

Parameter Name

Zone Cooling

OA Damper

Eff Clg Spt= 75.0 ºF

Clg Deadband= 1.0 ºF

Max Purge= 60 min

Effective Cooling

Enable Set Point

Cooling Enable Deadband

Maximum Purge Time

If a unit is equipped with an economizer and an optional space (or zone) temperature sensor (ZNT1) is connected to the controller, pre-occupancy purge control is available.

Designed to take advantage of cool pre-dawn outdoor air, purge control starts the fans and modulates the economizer dampers to maintain occupied cooling requirements during unoccupied periods. The purge function can only be used in conjunction with the unit internal time schedule or with a network supplied time schedule.

Purge operation is possible only during a time window prior to occupancy that is defined by the Maximum Purge Time parameter (0 to 240 minutes). For example, if the unit is scheduled to start at 6:30 a.m., a Maximum Purge Time of 60 minutes (default) allows purge operation to occur between

5:30 a.m. and 6:30 a.m.

During the purge time window, the unit starts and runs when the following three requirements are all met: l l l

The Space Temp= parameter value is greater than the

Effective Cooling Enable Set Point by more than half the Cooling Enable Deadband.

The OA Ambient= parameter in the OA Damper menu indicates “Low.”

The OA Temp= parameter value is below the Space

Temp= parameter value by more than 4°F.

During purge operation, the controller enters and remains in the UnocEcon operating state after the normal startup sequence. Mechanical cooling is disabled. Economizer control during purge operation is similar to that during occupied operation.

The unit returns to the Off Unoc state when any of the following three conditions occur: l l l

The Space Temp= parameter value is less than the

Effective Cooling Enable Set Point by more than half the Cooling Enable Deadband.

The OA Ambient= parameter in the OA Damper menu indicates “High.”

The outdoor air temperature rises above the space temperature by more than 2°F.

As conditions allow, purge control cycles the unit in this manner until normal occupied operation begins. If the scheduled occupied startup time occurs during purge operation, the unit continues running without interruption.

90 OM 138

Alarm Control

The following are descriptions of the various alarms that can occur in zone (or space comfort) control rooftop units.

Note: The cause of a manual reset alarm should be investigated and eliminated before the unit or any disabled equipment in it is placed back into service.

Faults

Freeze

When a unit is equipped with a chilled water, hot water, or steam coil, the Freeze fault occurs when the optional freezestat (FS1) contacts open (binary input MCB-BI7 off) as a result of detecting an abnormally low water or steam coil temperature while the fans are running.

When the Freeze fault occurs, the controller shuts down the fans, closes the outdoor air dampers, opens the chilled water and heating valves and set a 10-minute timer.

When the 10-minute timer expires, the controller checks the freezestat input again. If the freezestat contacts are closed

(binary input MCB-BI7 on), the valves close. If the freezestat contacts are still open (binary input MCB-BI7 off), the valves remain open, and the 10-minute timer resets. This continues until the fault is manually cleared through the unit keypad or via a network signal.

Smoke

The Smoke fault occurs when the contacts of either optional discharge or return air smoke detector (SD1 or SD2) open

(binary input MCB-BI8 off).

When the Smoke fault occurs, the unit is immediately shut down. The unit remains shut down until the smoke detector is manually reset and the Smoke fault is manually cleared through the unit keypad or via a network signal.

Note: The smoke detector can be reset by momentarily removing power form the device. This can be accomplishes by cycling control power (S1 switch).

Space Sensor

If the optional space temperature sensor (ZNT1) fails (analog input MCB-AI1 open or short-circuited) while it is acting as the “Control Temperature” ( CtrlTemp Src= parameter is set to “Space”) and the unit has no return air sensor, the

Space Sensor fault occurs.

When the Space Sensor fault occurs, the unit is shut down. It remains shut down until the Space Sensor fault is manually cleared through the unit keypad or via a network signal.

Return Sensor

If the unit is equipped with a return air temperature sensor

(RAT) and it fails (analog input MCB-AI4 open or short-circuited) while it is acting as the “Control Temperature” ( CtrlTemp Src= parameter is set to “Return”), the Return Sensor fault occurs.

When the Return Sensor fault occurs, the unit is shut down.

It remains shut down until the Return Sensor fault is manually cleared through the unit keypad or via a network signal.

Disch Sensor

If the discharge air temperature sensor (DAT) fails (analog input MCB-AI3 open or short-circuited), the Disch Sensor fault occurs.

When the Disch Sensor fault occurs, the unit is shut down. It remains shut down until the Disch Sensor fault is manually cleared through the unit keypad or via a network signal.

Hi Return Tmp

If the unit is equipped with a return air temperature sensor and the Return Air= parameter value exceeds the Hi Return

Alm= value in the Alarm Limits menu, while the unit is operational, the Hi Return Tmp fault occurs.

When the Hi Return Tmp fault occurs, the unit is shut down.

It remains shut down until the Hi Return Tmp fault is manually cleared through the unit keypad or via a network signal.

Hi Disch Tmp

If the Disch Air= parameter value exceeds the Hi Disch

Alm= setting in the Alarm Limits menu, while the unit is operational, the Hi Disch Tmp fault occurs.

When the Hi Disch Tmp fault occurs, the unit is shut down.

It remains shut down until the Hi Disch Tmp fault is manually cleared through the unit keypad or via a network signal.

Lo Disch Tmp

If the Disch Air= parameter value drops below the Lo Disch

Alm= setting in the Alarm Limits menu while the unit is operational, the Lo Disch Tmp fault occurs.

When the Lo Disch Tmp fault occurs, the unit is shut down.

It remains shut down until the Lo Disch Tmp fault is manually cleared through the unit keypad or via a network signal.

Note: The Lo Disch Tmp fault is ignored when the unit leaves the Startup operating state for a time period defined by the Low DAT= parameter in the Timer

Settings menu and when the unit is in the Cooling operating state.

Fan Fail

If differential pressure switch PC7 fails to detect airflow

(binary input MCB-BI6 off) within two minutes after the unit leaves the Startup operating state or any time afterward, while the unit is running, the Fan Fail fault occurs.

When the Fan Fail fault occurs, the unit is shut down. It remains shut down until the Fan Fail fault is manually cleared through the unit keypad or via a network signal.

OA Dmpr Stuck

On units equipped with a 100% outdoor air hood, the outdoor air dampers are driven fully open during the Startup operating state before the discharge fan is started. If the OA

Damper Pos= parameter in the OA Damper menu does not

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indicate 50% or greater when the unit leaves the Startup operating state, the OA Dmpr Stuck fault occurs.

When the OA Dmpr Stuck fault occurs, the unit is shut down. The unit remains shut down until the OA Dmpr Stuck fault is manually cleared through the unit keypad or via a network signal.

Problems

Freeze

When a unit is equipped with a chilled water, hot water, or steam coil, the Freeze problem occurs when the optional freezestat (FSl) contacts open (binary input MCB-B7 off) as a result of detecting an abnormally low water or steam coil temperature while the fans are off.

When the Freeze problem occurs, the controller opens the chilled water and heating valves and set a 10-minute timer.

When the 10-minute timer expires, the controller checks the freezestat input again. If the freezestat contacts are closed

(binary input MCB-BI7 on), the valves close. If the freezestat contacts are still open (binary input MCB-BI7 off), the valves remain open, and the 10-minute timer resets. This continues while the unit remains off.

Whenever the freezestat closes (binary input MCB-BI7 on), the Freeze problem automatically clears. This feature protects the coil(s) and allows the system to start normally when an occupied command is received.

OAT Sensor

If the outdoor air temperature sensor (OAT) fails (analog input MCB-AI5 open or short-circuited) and it is not acting as the “Control Temperature” ( CtrlTemp Src= parameter is not set to “OAT”), the OAT Sensor problem occurs.

When the OAT Sensor problem occurs, the unit continues to operate with the following modifications:

1. Discharge temperature set point reset based on outdoor air is unavailable.

2. Compressor low ambient lockout is disabled.

3. High ambient heating lockout is disabled.

4. Purge operation is disabled. Space Sensor

When the alarm condition is no longer present, the OAT Sensor problem automatically clears.

Space Sensor

If the optional space temperature sensor ZNT1 fails (analog input MCB-AI1 open or short-circuited) on a unit equipped with a return air temperature sensor, the Space Sensor problem occurs as long as the Space Sensor= parameter in the

Unit Configuration menu is set to “Yes.” If this parameter is set to “No” the Space Sensor problem indication is disabled.

When the Space Sensor problem occurs, the unit continues to operate with the following modifications:

1. Discharge temperature set point reset based on space temperature is unavailable.

2. Purge operation is disabled.

3. If the space temperature input is acting as the “Control

Temperature” ( CtrlTemp Src= parameter is set to

“Space”), the controller automatically changes the CtrlTemp Src= parameter to “Return”.

When the Space Sensor problem occurs during an unoccupied time period, the unit starts and runs continuously in the

UnocHtg operating state, using the return air temperature sensor as the “Control Temperature” if all of the following conditions are true:

1. The unit is equipped with a return air temperature sensor.

2. The OA Temp= parameter value is below 40 °F.

3. The UnoccHtg Spt= parameter in the Zone Heating menu is set higher than 0°F.

When the alarm condition is no longer present, the Space

Sensor problem automatically clears and normal unit operation resumes.

Return Sensor

If the return air temperature sensor (RAT) fails (analog input

MCB-AI4 open or short-circuited) while it is not acting as the “Control Temperature” ( CtrlTemp Src= parameter is not set to “Return”), the Return Sensor problem occurs.

When the Return Sensor problem occurs, the unit continues to operate with the following modifications:

1. Discharge temperature set point reset based on return temperature is unavailable.

2. The Hi Return Tmp fault is disabled.

When the alarm condition is no longer present, the Return

Sensor problem automatically clears.

Ent Fan Sensor

If the unit is equipped with an entering fan air temperature sensor (EFT) and it fails (analog input MCB-AI6 open or short-circuited), the Ent Fan Sensor problem occurs as long as the EFT Sensor= parameter in the Unit Configuration menu is set to “Yes.” If this parameter is set to “No” the Ent

Fan Sensor problem indication is disabled.

When the Ent Fan Sensor problem occurs, the unit continues to operate with the following modifications.

1. The Low Airflow problem is disabled.

2. The function on gas or electric heat units that limits the

Eff Htg Spt= parameter in the Discharge Heating menu based the maximum heat rise for the heat exchanger on units equipped with gas or electric heat is disabled.

Refer to “Heating: Multistage” on page 78 (electric heat

units) or “Gas Heat” on page 82 (gas heat units).

When the alarm condition is no longer present, the Ent Fan

Sensor problem automatically clears.

Note: Note that the EFT sensor is only provided with units that have gas or electric heat.

Heat Fail

If a unit is equipped with a gas furnace (one-stage or modulating) and the burner flame safeguard (FSG) control enters

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the “safety lockout” state after a call for heat, relay R24 energizes and closes a set of contacts and delivers a binary input (binary input MCB-BI5 on) to the controller. When this binary input is present the Heat Fail problem occurs.

When the Heat Fail problem occurs, the unit continues to operate with the heating system disabled by the FSG. Heating remains disabled until the flame safeguard control is manually reset. When the FSG is reset, relay R24 de-energizes, removing the binary input (binary input MCB-BI5 off) from the controller, causing the Heat Fail problem to automatically clear.

For detailed information regarding the FSG control, refer to the separate installation manual supplied with the gas furnace and the “Sequences of Operation” section of the model-

specific installation manual (refer to Table 1 on page 4).

Hi Pres-Ckt1

This alarm occurs on units equipped with compressorized cooling only. If either of the cooling circuit #1 high pressure switches (HP1 or HP3) opens (binary input CCB1-BI7 off), indicating a high refrigerant pressure situation, the Hi Pres-

Ckt1 problem occurs.

When the Hi Pres-Ckt1 problem occurs, the unit continues to operate but cooling circuit #1 is disabled. Circuit #1 remains disabled until both high pressure switches are closed and the

Hi Pres-Ckt1 problem is manually cleared through the unit keypad or via a network signal.

Hi Pres-Ckt2

This alarm occurs on units equipped with compressorized cooling only. If either of the cooling circuit #2 high pressure switches (HP2 or HP4) opens (binary input CCB2-BI7 off) indicating a high refrigerant pressure situation, the Hi Pres-

Ckt2 problem occurs.

When the Hi Pres-Ckt2 problem occurs, the unit continues to operate but cooling circuit #2 is disabled. Circuit #2 remains disabled until both high pressure switches are closed and the

Hi Pres-Ckt2 problem is manually cleared through the unit keypad or via a network signal.

Lo Pres-Ckt1

This alarm occurs on units equipped with compressorized cooling only. When a call is made for circuit #1 operation, if the cooling circuit #1 low pressure switch (LP1) remains open (input removed from CCB1-BI6) beyond a “low pressure time period” after the circuit #1 liquid line solenoid is opened, the Lo Pres-Ckt1 problem occurs. The alarm also occurs any time after the “low pressure time period” expires while the circuit is operating if LP1 opens. If the unit is equipped with low ambient condenser operation capability and the OA Temp= parameter value is below 45°F, the “low pressure time period” is 165 seconds. Otherwise the “low pressure time period” is 45 seconds.

When the Lo Pres-Ckt1 problem occurs, the unit continues to operate but cooling circuit #1 is disabled. Circuit #1 remains disabled for at least one cooling stage time period.

After the cooling stage time period expires, the alarm automatically clears and the circuit is re-enabled. If the Lo Pres-

Ckt1 problem occurs three times between 2:00 a.m. of one day and 2:00 a.m. of the next, the alarm does not automatically clear the third time but must be manually cleared through the unit keypad or via a network signal.

Lo Pres-Ckt2

This alarm occurs on units equipped with compressorized cooling only. When a call is made for circuit #2 operation, if the cooling circuit #2 low pressure switch (LP2) remains open (binary input CCB2-BI6 off) beyond a “low pressure time period” after the circuit #2 liquid line solenoid is opened, the Lo Pres-Ckt2 problem occurs. The alarm also occurs any time after the “low pressure time period” expires while the circuit is operating if LP2 opens. If the unit is equipped with low ambient condenser operation capability and the OA Temp= parameter value is below 45°F, the “low pressure time period” is 165 seconds. Otherwise the “low pressure time period” is 45 seconds.

When the Lo Pres-Ckt2 problem occurs, the unit continues to operate but cooling circuit #2 is disabled. Circuit #2 remains disabled for at least one cooling stage time period.

After the cooling stage time period expires, the alarm automatically clears and the circuit is re-enabled. If the Lo Pres-

Ckt2 problem occurs three times between 2:00 a.m. of one day and 2:00 a.m. of the next, the alarm does not automatically clear the third time but must be manually cleared through the unit keypad or via a network signal.

Frost-Ckt1

This alarm occurs on units equipped with compressorized cooling without hot gas bypass operation only. If the circuit

#1 frost protection switch (FP1) opens (binary input CCB1-

BI8 off) while a compressor on cooling circuit #1 has been on for at least two minutes and the circuit #1 liquid line solenoid valve (SV1) is open, the Frost-Ckt1 problem occurs.

This indicates a cold refrigerant temperature exists at the unit evaporator coil on circuit #1, creating the possibility of frost build-up on the coil.

When the Frost-Ckt1 problem occurs, the unit continues to operate but cooling circuit #1 is disabled. Circuit #1 remains disabled for at least one cooling stage time period. After the cooling stage time period expires, the alarm automatically clears and the circuit is re-enabled. If the Frost-Ckt1 problem occurs three times between 2:00 a.m. of one day and 2:00 a.m. of the next, the alarm does not automatically clear the third time but must be manually cleared through the unit keypad or via a network signal.

Frost-Ckt2

This alarm occurs on units equipped with compressorized cooling without hot gas bypass operation only. If the circuit

#2 frost protection switch (FP2) opens (binary input CCB2-

BI8 off) while a compressor on cooling circuit #2 has been on for at least two minutes and the circuit #2 liquid line solenoid valve (SV2) is open, the Frost-Ckt2 problem occurs.

This indicates a cold refrigerant temperature exists at the unit

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evaporator coil on circuit #2, creating the possibility of frost build-up on the coil.

When the Frost-Ckt2 problem occurs, the unit continues to operate but cooling circuit #2 is disabled. Circuit #2 remains disabled for at least one cooling stage time period. After the cooling stage time period expires, the alarm automatically clears and the circuit is re-enabled. If the Frost-Ckt2 problem occurs three times between 2:00 a.m. of one day and 2:00 a.m. of the next, the alarm does not automatically clear the third time but must be manually cleared through the unit keypad or via a network signal.

Comp #1 Alm

This alarm occurs only on units equipped with compressorized cooling. If compressor #1 has been commanded on for longer than ten seconds and the compressor #1 input to the compressor control board is off (binary input CCB1-BI9 off), the Comp #1 Alm problem occurs as long as the circuit is not off on a high pressure alarm. The compressor #1 input is delivered to the compressor control board through an auxiliary switch on the compressor #1 contactor. Therefore, precisely speaking, the alarm indicates that the controller commanded the compressor to start but the contactor did not pull in. When the unit is equipped with a compressor #1 oil pressure switch (OP1) and/or a compressor #1 external motor protector (MP1), this condition normally occurs when either MP1or OP1 trip. If the unit is equipped with neither

MP1 nor OP1, this alarm simply indicates the contactor did not pull in for electrical or mechanical reasons.

1

When the Comp 1 Alm problem occurs, the unit continues to operate but compressor #1 is disabled. Compressor #1 remains disabled for one cooling stage time period after which the alarm automatically clears and the compressor is re-enabled. The controller can then attempt to start compressor #1 again when required. If the Comp 1 Alm problem occurs three times between 2:00 a.m. of one day and 2:00 a.m. of the next, the alarm does not automatically clear the third time but must be manually cleared through the unit keypad or via a network signal.

Note: The OP1 device itself requires a manual reset once it trips. The MP1 device automatically resets when the compressor motor windings cool.

Comp #2 Alm

This alarm occurs only on units equipped with compressorized cooling. If compressor #2 has been commanded on for longer than ten seconds and the compressor #2 input to the compressor control board is off (binary input CCB2-BI9 off), the Comp #2 Alm problem occurs as long as the circuit

1. Unit models 018 through 060 are equipped with scroll compressors. Oil pressure switches are not used on these units.

Also, some scroll compressor sizes are equipped with internal motor protection. In these cases, external motor protectors are not used. These include Comp #1 on unit models

018 through 036, Comp #3 on unit models 025 through 036 and Comp2 on unit model 018.

is not off on a high pressure alarm. The compressor #2 input is delivered to the compressor control board through an auxiliary switch on the compressor #2 contactor. Therefore, precisely speaking, the alarm indicates that the controller commanded the compressor to start but the contactor did not pull in. When the unit is equipped with a compressor #2 oil pressure switch (OP2) and/or a compressor #2 external motor protector (MP2), this condition normally occurs when either MP2or OP2 trip. If the unit is equipped with neither

MP2 nor OP2, this alarm simply indicates the contactor did not pull in for electrical or mechanical reasons.

2

When the Comp #2 Alm problem occurs, the unit continues to operate but compressor #2 is disabled. Compressor #2 remains disabled for one cooling stage time period after which the alarm automatically clears and the compressor is re-enabled. The controller can then attempt to start compressor #2 again when required. If the Comp #2 Alm problem occurs three times between 2:00 a.m. of one day and 2:00 a.m. of the next, the alarm does not automatically clear the third time but must be manually cleared through the unit keypad or via a network signal.

Note: The OP2 device itself requires a manual reset once it trips. The MP2 device automatically resets when the compressor motor windings cool.

Comp #3 Alm

This alarm occurs only on units equipped with compressorized cooling. If compressor #3 has been commanded on for longer than ten seconds and the compressor #3 input to the compressor control board is off (binary input CCB1-

BI10 off), Comp #3 Alm problem occurs as long as the circuit is not off on a high pressure alarm. The compressor #3 input is delivered to the compressor control board through an auxiliary switch on the compressor #3 contactor. Therefore, precisely speaking, the alarm indicates that the controller commanded the compressor to start but the contactor did not pull in. When the unit is equipped with a compressor #3 oil pressure switch (OP3) and/or a compressor #3 external motor protector (MP3), this condition normally occurs when either MP3 or OP3 trip. If the unit is equipped with neither

MP3 nor OP3, this alarm simply indicates the contactor did not pull in for electrical or mechanical reasons

2 .

When the Comp #3 Alm problem occurs, the unit continues to operate but compressor #3 is disabled. Compressor #3 remains disabled for one cooling stage time period after which the alarm automatically clears and the compressor is re-enabled. The controller can then attempt to start compressor #3 again when required. If the Comp #3 Alm problem occurs three times between 2:00 a.m. of one day and 2:00

2. Unit models 018 through 060 are equipped with scroll compressors. Oil pressure switches are not used on these units.

Also, some scroll compressor sizes are equipped with internal motor protection. In these cases, external motor protectors are not used. These include Comp #1 on unit models

018 through 036, Comp #3 on unit models 025 through 036 and Comp2 on unit model 018.

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a.m. of the next, the alarm does not automatically clear the third time but must be manually cleared through the unit keypad or via a network signal.

Note: The OP3 device itself requires a manual reset once it trips. The MP3 device automatically resets when the compressor motor windings cool.

Comp #4 Alm

This alarm occurs only on units equipped with compressorized cooling. If compressor #4 has been commanded on for longer than ten seconds and the compressor #4 input to the compressor control board is off (binary input CCB2-

BI10 is off), the Comp #4 Alm problem occurs as long as the circuit is not off on a high pressure alarm. The compressor

#4 input is delivered to the compressor control board through an auxiliary switch on the compressor #4 contactor. Therefore, precisely speaking, the alarm indicates that the controller commanded the compressor to start but the contactor did not pull in. When the unit is equipped with a compressor #4 oil pressure switch (OP4) and/or a compressor #4 external motor protector (MP4), this condition normally occurs when either MP4or OP4 trip. If the unit is equipped with neither

MP4 nor OP4, this alarm simply indicates the contactor did not pull in for electrical or mechanical reasons

2 .

When the Comp #4 Alm problem occurs, the unit continues to operate but compressor #4 is disabled. Compressor #4 remains disabled for one cooling stage time period after which the alarm automatically clears and the compressor is re-enabled. The controller can then attempt to start compressor #4 again when required. If the Comp #4 Alm problem occurs three times between 2:00 a.m. of one day and 2:00 a.m. of the next, the alarm does not automatically clear the third time but must be manually cleared through the unit keypad or via a network signal.

Note: The OP4 device itself requires a manual reset once it trips. The MP4 device automatically resets when the compressor motor windings cool.

PumpDown-Ckt1

This alarm occurs on units equipped with compressorized cooling only. If the cooling circuit #1 low pressure switch

(LP1) fails to open (binary input CCB1-BI6 off) within 180 seconds of the initiation of a cooling circuit #1 pumpdown cycle, the PumpDown-Ckt1 problem occurs.

When the PumpDown-Ckt1 problem occurs, the unit continues to operate but pump down operation is terminated and cooling circuit #1 is disabled. Circuit #1 remains disabled until the PumpDown-Ckt1 problem is manually cleared through the unit keypad or via a network signal

PumpDown-Ckt2

This alarm occurs on units equipped with compressorized cooling only. If the cooling circuit #2 low pressure switch

(LP2) fails to open (binary input CCB2-BI6 off) within 180 seconds of the initiation of a cooling circuit #2 pumpdown cycle, the PumpDown-Ckt2 problem occurs.

When the PumpDown-Ckt2 problem occurs, the unit continues to operate but pump down operation is terminated and cooling circuit #2 is disabled. Circuit #2 remains disabled until the PumpDown-Ckt2 problem is manually cleared through the unit keypad or via a network signal.

Ckt1 Clg Ena

When a unit is equipped with compressorized cooling, the main control board (MCB) controls the cooling outputs on and receives cooling circuit input information from the circuit #1 compressor control board (CCB1) via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication between the two boards there must be an external method for the MCB to command the CCB1 board to shut off the cooling on that circuit. This is accomplished with a “cooling enable” output from MCB (MCB-

BO7) hard wired to a “cooling enable” input to the CCB1 board (binary input CCB1-BI12).

If the MCB is communicating with the CCB1 board and the

“cooling enable” output from MCB is on but the “cooling enable” input to CCB1 remains off, indicating a wiring problem between the boards, the Ckt1 Clg Ena problem occurs.

When the Ckt1 Clg Ena problem occurs, cooling circuit #1 is disabled. Cooling circuit #1 remains disabled until the problem is corrected and the Ckt1 Clg Ena problem is manually cleared through the unit keypad or via a network signal.

Ckt2 Clg Ena

When a unit is equipped with compressorized cooling, the main control board (MCB) controls the cooling outputs on and receives cooling circuit input information from the circuit #2 compressor control board (CCB2) via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication between the two boards there must be an external method for the MCB to command the CCB2 board to shut off the cooling on that circuit. This is accomplished with a “cooling enable” output from MCB (MCB-

BO7) hard wired to a “cooling enable” input to the CCB2 board (binary input CCB2-BI12).

If the MCB is communicating with the CCB2 board and the

“cooling enable” output from MCB is on but the “cooling enable” input to CCB2 remains off, indicating a wiring problem between the boards, the Ckt2 Clg Ena problem occurs.

When the Ckt2 Clg Ena problem occurs, cooling circuit #2 is disabled. Cooling circuit #2 remains disabled until the problem is corrected and the Ckt2 Clg Ena problem is manually cleared through the unit keypad or via a network signal.

GenC Clg Ena

When a unit is equipped with a DX cooling coil and is interfaced with a field supplied condensing unit; it is equipped with a generic condenser control board for controlling the field supplied condensing unit (CCB1). The main control board (MCB) controls the cooling outputs on the generic condenser control board via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication there must be an external method for the MCB to command

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the CCB1 board to shut off the cooling. This is accomplished with a “cooling enable” output from MCB (MCB-BO7) hard wired to a “cooling enable” input to the CCB1 board (binary input CCB1-BI12).

If the MCB is communicating with the CCB1 board and the

“cooling enable” output from MCB is on but the “cooling enable” input to CCB1 remains off, indicating a wiring problem between the boards, the GenC Clg Ena problem occurs.

When the GenC Clg Ena problem occurs, cooling is disabled. Cooling remains disabled until the problem is corrected and the GenC Clg Ena problem is manually cleared through the unit keypad or via a network signal.

HtgB Htg Ena

When a unit is equipped with multi-stage electric heat, it is equipped with an electric heat control board for controlling the heat (EHB1). The main control board (MCB) controls the heating outputs on the electric heat control board via an

N2 bus interface between the two boards. If the MCB detects a loss of N2 communication there must be an external method for the MCB to command the EHB1 board to shut off the heating. This is accomplished with a “heating enable” output from MCB (MCB-BO9) hard wired to a “heating enable” input to the EHB1 board (EHB1-BI1).

If the MCB is communicating with the EHB1 board and the

“heating enable” output from MCB is on but the “heating enable” input to EHB1 remains off, indicating a wiring problem between the boards, the HtgB Htg Ena problem occurs.

When the HtgB Htg Ena problem occurs, heating is disabled.

Heating remains disabled until the problem is corrected and the HtgB Htg Ena problem is manually cleared through the unit keypad or via a network signal.

Ckt1 Comm Fail

When a unit is equipped with compressorized cooling, the main control board (MCB) controls the cooling outputs on and receives cooling circuit input information from the circuit #1 compressor control board (CCB1) via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication between the two boards, the Ckt1

Comm Fail problem occurs.

When the Ckt1 Comm Fail problem occurs while the unit is not in the Cooling operating state, the unit is allowed to enter the Cooling operating state as long as the MCB is communicating with the circuit #2 cooling control board (CCB2). In this case the cooling capacity is limited to that available from circuit #2. If the MCB is not communicating with either cooling control board (CCB1 or CCB2), the unit is not allowed to enter the Cooling operating state.

When the Ckt1 Comm Fail problem occurs while the unit is in the Cooling operating state, the unit remains in the Cooling operating state. However, the maximum cooling capacity is limited to that of circuit #2 if the MCB is communicating with the circuit #2 cooling control board (CCB2). If the

MCB is not communicating with either cooling control board (CCB1 or CCB2), the current cooling capacity in the

MCB is set to 0%. Any cooling that may be operating at the time of the communication failure remains on (on either circuit) until the MCB leaves the Cooling operating state due to normal operation. When the MCB leaves the Cooling operating state the “cooling enable” output (MCB-BO7) is turned off and, therefore, the “cooling enable” input to the CCB1 and CCB2 boards is removed (binary inputs CCB1-BI12 and

CCB2-BI12 off) and this causes the CCB1 and CCB2 to completely stage off all cooling. The MCB then does not reenter the Cooling operating state until communication is reestablished with at lease one cooling control board. When communications between the MCB and CCB1 is re-established, the Ckt1 Comm Fail problem automatically clears.

Ckt2 Comm Fail

When a unit is equipped with compressorized cooling, the main control board (MCB) controls the cooling outputs on and receives cooling circuit input information from the circuit #2 compressor control board (CCB2) via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication between the two boards, the Ckt2

Comm Fail problem occurs.

When the Ckt2 Comm Fail problem occurs while the unit is not in the Cooling operating state, the unit is allowed to enter the Cooling operating state as long as the MCB is communicating with the circuit #1 cooling control board (CCB1). In this case the cooling capacity is limited to that available from circuit #1. If the MCB is not communicating with either cooling control board (CCB1 or CCB2), the unit is not allowed to enter the Cooling operating state.

When the Ckt2 Comm Fail problem occurs while the unit is in the Cooling operating state, the unit remains in the Cooling operating state. However, the maximum cooling capacity is limited to that of circuit #1 if the MCB is communicating with the circuit #1 cooling control board (CCB1). If the

MCB is not communicating with either cooling control board (CCB1 or CCB2), the current cooling capacity in the

MCB is set to 0%. Any cooling that may be operating at the time of the communication failure remains on (on either circuit) until the MCB leaves the Cooling operating state due to normal operation. When the MCB leaves the Cooling operating state the “cooling enable” output (MCB-BO7) is turned off and, therefore, the “cooling enable” input to the CCB1 and CCB2 boards is removed (binary inputs CCB1-BI12 and

CCB2-BI12 off) and this causes the CCB1 and CCB2 to completely stage off all cooling. The MCB then does not reenter the Cooling operating state until communication is reestablished with at lease one cooling control board. When communications between the MCB and CCB2 is re-established, the Ckt2 Comm Fail problem automatically clears.

GenC Comm Fail

When a unit is equipped with a DX cooling coil and is interfaced with a field supplied condensing unit; it is equipped with a generic condenser control board (CCB1) for controlling the field supplied condensing unit. The main control board (MCB) controls the cooling outputs on the generic

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condenser control board via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication between the two boards, the GenC Comm Fail problem occurs.

When the GenC Comm Fail problem occurs while the unit is not in the Cooling operating state, the unit is not allowed to enter the Cooling operating state.

When the GenC Comm Fail problem occurs while the unit is in the Cooling operating state, the unit remains in the Cooling operating state. However, the current cooling capacity in the MCB is set to 0%. Any cooling that may be operating at the time of the communication failure remains on until the

MCB leaves the Cooling operating state due to normal operation. When the MCB leaves the Cooling operating state the

“cooling enable” output (MCB-BO7) is turned off and, therefore, the “cooling enable” input to the CCB1 board is removed (binary input CCB1-BI12 off) and this causes the

CCB1 to completely stage off all cooling. The MCB then does not re-enter the Cooling operating state until communication is re-established with the cooling control board

(CCB1). When communications between the MCB and

CCB1 is re-established, the GenC Comm Fail problem automatically clears.

HtgB Comm Fail

When a unit is equipped with multi-stage electric heat, it is equipped with an electric heat control board for controlling electric heat (EHB1). The main control board (MCB) controls the heating outputs on the electric heat control board via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication between the two boards, the HtgB Comm Fail problem occurs.

When the HtgB Comm Fail problem occurs while the unit is not in a heating operating state, the unit is not allowed to enter the a heating operating state.

When the HtgB Comm Fail problem occurs while the unit is in a heating operating state, the unit remains in the heating operating state. However, the current heating capacity in the

MCB is set to 0%. Any heating that may be operating at the time of the communication failure remains on until the MCB leaves the Heating operating state due to normal operation.

When the MCB leaves the heating operating state the “heating enable” output (MCB-BO9) is turned off and, therefore, the “heating enable” input to the EHB1 board is removed

(binary input EHB1-BI1 off) and this causes the EHB1 to completely stage off all heating. The MCB then does not reenter any heating operating state until communication is reestablished with the cooling control board (EHB1). When communications between the MCB and EHB1 is re-established, the HtgB Comm Fail problem automatically clears.

ERecB Comm Fail

When a unit is equipped with an energy recovery wheel, it is equipped with an energy recovery control board for controlling the energy recovery wheel (ERB1). The main control board (MCB) controls the energy recovery outputs on the energy recovery control board via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication between the two boards, the ERecB Comm

Fail problem occurs.

When the ERecB Comm Fail problem occurs, the energy recovery system is disabled. When communications between the MCB and EHB1 is re-established, the ERecB Comm Fail problem automatically clears.

Warnings

OA Dmpr Stuck

The OA Dmpr Stuck warning occurs if either of the following conditions exist:

1. The OA Damper Pos= parameter in the OA Damper menu indicates more than 5% open three minutes after the controller enters the Off operating state.

2. The unit is equipped with and economizer and the OA

Damper Pos= parameter in the OA Damper menu is less than 95% open when the OA Ambient= parameter in the OA Damper menu indicates “low” and the controller is in either the Cooling or UnocClg operating state. Note that the outdoor air dampers should be at

100% under these conditions.

When the OA Dmpr Stuck warning occurs unit operation is not affected. When the alarm condition is corrected, the OA

Dmpr Stuck warning must be manually cleared through the unit keypad or via a network signal.

Airflow Switch

If the unit has been in the Off operating state for at least thirty minutes and the PC7 airflow switch input to the main controller indicates airflow (binary input MCB-BI6 on), the

Airflow Switch warning occurs. This normally indicates a problem with the PC7 airflow switch.

When the Airflow Switch warning occurs, unit operation is not affected. When the alarm condition is corrected, the Airflow Switch warning must be manually cleared through the unit keypad or via a network signal.

Dirty Filter

If the pressure drop across the first filter section in the unit exceeds the setting of the PC5 differential pressure switch while the unit is operational, the dirty first filter input is removed from MCB (binary input MCB-BI9 off) and the

Dirty Filter warning occurs.

When the Dirty Filter warning occurs, unit operation is not affected. The Dirty Filter warning must be manually cleared through the unit keypad or via a network signal.

Dirty FnlFltr

If the pressure drop across the final filter section in the unit exceeds the setting of the PC6 differential pressure switch while the unit is operational, the dirty final filter input is removed from MCB (binary input MCB-BI10 off) and the

Dirty FnlFltr warning occurs.

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When the Dirty FnlFltr warning occurs, unit operation is not affected. The Dirty FnlFltr warning must be manually cleared through the unit keypad or via a network signal.

Ckt1 H/W

When a unit is equipped with compressorized cooling, the main control board (MCB) controls the cooling outputs on and receives cooling circuit input information from the circuit #1 compressor control board (CCB1) via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication between the two boards there must be an external method for the MCB to command the CCB1 board to shut off the cooling on that circuit. This is accomplished with a “cooling enable” output from MCB (MCB-

BO7) hard wired to a “cooling enable” input to the CCB1 board (binary input CCB1-BI12).

If the MCB is communicating with the CCB1 board and the

“cooling enable” output from MCB is off but the “cooling enable” input to CCB1 remains on, indicating that the “cooling enable” input to the CCB1 board is “stuck” on, the Ckt1

H/W warning occurs.

When the Ckt1 H/W warning occurs, unit operation is not affected. The Ckt1 H/W warning must be manually cleared through the unit keypad or via a network signal.

Ckt2 H/W

When a unit is equipped with compressorized cooling, the main control board (MCB) controls the cooling outputs on and receives cooling circuit input information from the circuit #2 compressor control board (CCB2) via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication between the two boards there must be an external method for the MCB to command the CCB2 board to shut off the cooling on that circuit. This is accomplished with a “cooling enable” output from MCB (MCB-

BO7) hard wired to a “cooling enable” input to the CCB2 board (binary input CCB2-BI12).

If the MCB is communicating with the CCB2 board and the

“cooling enable” output from MCB is off but the “cooling enable” input to CCB2 remains on, indicating that the “cooling enable” input to the CCB2 board is “stuck” on, the Ckt2

H/W warning occurs.

When the Ckt2 H/W warning occurs, unit operation is not affected. The Ckt2 H/W warning must be manually cleared through the unit keypad or via a network signal.

GenC H/W

When a unit is equipped with a DX cooling coil and is interfaced with a field supplied condensing unit; it is equipped with a generic condenser control board for controlling the field supplied condensing unit (CCB1). The main control board (MCB) controls the cooling outputs on the generic condenser control board via an N2 bus interface between the two boards. If the MCB detects a loss of N2 communication there must be an external method for the MCB to command the CCB1 board to shut off the cooling. This is accomplished with a “cooling enable” output from MCB (MCB-BO7) hard wired to a “cooling enable” input to the CCB1 board (binary input CCB1-BI12).

If the MCB is communicating with the CCB1 board and the

“cooling enable” output from MCB is off but the “cooling enable” input to CCB1 remains on, indicating that the “cooling enable” input to the CCB1 board is “stuck” on, the GenC

H/W warning occurs.

When the GenC H/W warning occurs, unit operation is not affected. The GenC H/W warning must be manually cleared through the unit keypad or via a network signal.

HtgB H/W

When a unit is equipped with multi-stage electric heat, it is equipped with an electric heat control board for controlling the heat (EHB1). The main control board (MCB) controls the heating outputs on the electric heat control board via an

N2 bus interface between the two boards. If the MCB detects a loss of N2 communication there must be an external method for the MCB to command the EHB1 board to shut off the heating. This is accomplished with a “heating enable” output from MCB (MCB-BO9) hard wired to a “heating enable” input to the EHB1 board (EHB1-BI1).

If the MCB is communicating with the EHB1 board and the

“heating enable” output from MCB is off but the “heating enable” input to EHB1 remains on, indicating that the “heating enable” input to the EHB1 board is “stuck” on, the HtgB

H/W warning occurs.

When the HtgB H/W warning occurs, unit operation is not affected. The HtgB H/W warning must be manually cleared through the unit keypad or via a network signal.

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