4-1287
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AE4-1287
AE4-1287-R2
COPELAND DISCUS DEMAND COOLING
Introduction
September 2003
reached, the module energizes a long life injection
valve which meters a controlled amount of saturated
refrigerant into the compressor suction cavity to cool
the suction gas. This process controls the discharge
temperature to a safe level. If, for some reason, the
discharge temperature rises above a preset maximum
level. the Demand Cooling module will turn the compressor off (requiring a manual reset) and actuate its
alarm contact. To minimize the amount of refrigerant
which must be injected, the suction gas cooling process is performed after the gas has passed around
and through the motor.
HCFC-22, when used in a properly designed and
controlled refrigeration system, is a realistic low temperature refrigerant alternative to CFC-502, which
must be phased out due to its high ozone depletion
potential. However, experience has shown that
HCFC-22 can present problems as a low temperature
refrigerant because under some conditions the internal compressor discharge temperature exceeds the
safe temperature limit for long term stability of refrigeration oil.
The Copeland Demand Cooling System (see Figure 1) uses modern electronics to provide a reliable cost
effective solution to this problem. It is required for all
single stage HCFC-22 applications with saturated
suction temperatures below -10°F.
Injection valve orifices have been carefully chosen
for each body style to be large enough to provide the
necessary cooling when required but not so large that
dangerous amounts of liquid are injected, or that
excessive system pressure fluctuation occurs during
injection valve cycling. Normally, pressure fluctuations are no greater than 1 to 2 psi. It is important to
use the correct valve for each compressor body style.
Demand Cooling is compatible with single (conventional) units as well as parallel racks.
The Demand Cooling module uses the signal of a
discharge head temperature sensor to monitor discharge gas temperature. If a critical temperature is
Performance data for Demand Cooling compressors includes the effects of injection when it is
DEMAND COOLING SYSTEM
Figure 1
1
© 2002-2003 Copeland Corporation.
Printed in the U.S.A.
AE4-1287
Figure 2
required. The approximate conditions where injection
occurs are shown in Figure 2. At the conditions
where Demand Cooling is operating, the performance
values are time averages of the instantaneous values,
since small fluctuations in suction and discharge
conditions occur as the Demand Cooling injection
valve cycles.
pressor protection control much as the oil failure control protects the compressor during periods of low oil
pressure. Demand Cooling will be called to operate
only during those periods when condensing temperatures and return gas temperatures are high or in periods where a system failure (such as an iced
evaporator, an expansion valve which does not control superheat, blocked condenser, or a failed condenser fan) raises condensing temperatures or return
gas temperatures to abnormally high levels or lowers
suction pressure to abnormally low levels.
While the refrigerant injection concept has been
widely recognized for some time, its application has
not been widely used since the early 1960’s because
of the widespread availability of CFC-502, reduction
of capacity and efficiency, and poor reliability of injection
systems.
Operating Range
Demand Cooling is designed to protect the compressor from high discharge temperatures over the
evaporating and condensing temperature ranges
shown in Figure 2 at a maximum return gas temperature of 65ºF.
The Copeland Demand Cooling system addresses
the capacity and efficiency issues by limiting injection
to those times when it is required to control discharge
temperatures to safe levels. For most applications this
will only be during periods of high condensing temperatures, high return gas temperatures, or abnormally
low suction pressure. The Demand Cooling system
has been designed to meet the same high reliability
standards as Discus compressors.
Demand Cooling System Design
When Demand Cooling operates, it “diverts” refrigeration capacity in the form of injected saturated
refrigerant from the evaporator to the compressor
(See Figure 3 for a typical single system schematic).
The effect of this diversion on evaporator capacity is
minimal because the diverted capacity is used to cool
In most cases, with floating head systems where
condensing temperatures are low during most of the
year. Demand Cooling will operate primarily as a com-
© 2002-2003 Copeland Corporation.
Printed in the U.S.A.
2
AE4-1287
the gas entering the compressor. As the gas is
cooled, it naturally becomes more dense, increasing
the mass flow through the compressor, which partly
compensates for the capacity diverted from the
evaporator.
If there is substantial heat gain along the suction
line, injection may result in a substantial loss in
evaporator capacity during Demand Cooling operation. In order to minimize this loss, good practice indicates Demand Cooling operation be kept to a minimum through proper system design and installation
practices. There are three areas which can be addressed to minimize the impact of Demand Cooling
operation on performance.
1) Compressor Return Gas Temperature: Suction
lines should be well insulated to reduce suction
line heat gain. Return gas superheat should be
as low as possible consistent with safe compressor operation.
2) Condensing Temperatures: It is important when
using HCFC-22 as a low temperature
refrigerant that condensing temperatures be
minimized to reduce compression ratios and
compressor discharge temperature.
3) Suction pressure: Evaporator design and system control settings should provide the maximum suction pressure consistent with the application in order to have as low a compression
ratio as possible.
Demand Cooling Compressors
No new compressor models have been introduced
for Demand Cooling. Instead, existing low temperature Discus CFC-502 compressors have been
modified and rerated for use with HCFC-22 and
Demand Cooling. The modifications are the addition
of an injection port on the compressor body and a
temperature sensor port in the head of the compressor. The locations of these ports are critical and were
determined through an extensive development program.
The HCFC-22 rating data includes the effects of
Demand Cooling injection when operating conditions
require it.
Condenser Sizing
Condensers should be sized using conventional
methods. Demand Cooling has virtually no effect on
system heat of rejection.
Figure 3
3
© 2002-2003 Copeland Corporation.
Printed in the U.S.A.
AE4-1287
Demand Cooling System Components
The Demand Cooling System (see Figure 1) consists of: The Demand Cooling Temperature Sensor
(TS), The Demand Cooling Module (CM), and the
Injection Valve (lV).
The TS uses a precision Negative Temperature
Coefficient (NTC) Thermistor (thermistor resistance
drops on temperature rise) to provide temperature
signals to the CM.
The IV meters refrigerant flow from the liquid line
to the compressor. The IV solenoid receives on-off
signals from the CM. When compressor cooling is
required the solenoid is energized and opens the IV
orifice to deliver saturated refrigerant to the compressor for cooling. The valve orifice is carefully sized to
meet the requirements of each body style of Discus
compressors.
The CM has three functional groups:
A) The Input signal and calculator circuits
compare the temperature sensor input signal to
an internal set-point and decide whether to
energize the IV solenoid or, in the case of a
problem. The CM alarm relay.
B) The output signal to the IV is controlled by
an electronic switch connected to the IV solenoid so that, when required, refrigerant vapor
can be metered to the compressor to prevent
compressor overheating. One side of the electronic switch is connected internally to “L1” and
the other side to output terminal “S” (see
Figure 4)
C) The alarm signal for local or remote control.
The alarm relay is energized, after a one minute
delay, by a continuous, low or high TS temperature signal. An alarm signal can indicate the
following:
1) Compressor discharge temperature has
risen above the level designed to be
controlled by Demand Cooling.
The alarm relay uses a single-pole-double-throw
contact. The contact terminals are “L”, “M”, and
“A”:
“L” - Common (to “A” and “M”)
“L - M” - Normally Closed (compressor run. open on
alarm)
“L - A” - Normally Open (alarm signal, close on
alarm)
The Normally Closed (NC) contact of the alarm
relay (“L” to “M”) should be wired in the compressor contactor control circuit so that opening this
contact removes the compressor from the line and
removes power to the CM. See Figure 4A, B, C, & D.
Figures 4A & B also shows a current sensing relay
(which must be used with compressors employing internal overcurrent protection) and Sentronic
oil pressure switch. The control circuit is purposely
arranged so that an internal overload protector trip
removes power to both the Sentronic and the Demand
Cooling module. This precaution prevents the oil
pressure switch from timing out and the Demand
Cooling solenoid from injecting when the compressor
is not operating.
The alarm relay requires a manual reset in order to
call attention to a system problem.
System Information
1) Demand Cooling is designed to work on all
Copeland Discus compressors equipped with
injection ports. A different kit is required for
each compressor body style and control voltage. See Table 2 for a listing of Demand Cooling Kit part numbers.
2) The system must be clean. A dirty system may
have foreign material that can lodge in the
solenoid orifice. Always install a liquid line filter
dryer in the injection valve inlet line capable of
removing particles as small as 25 microns.
2) A shorted sensor.
3) An open sensor.
© 2002-2003 Copeland Corporation.
Printed in the U.S.A.
In order to avoid nuisance trips, a one minute
time delay is provided before alarm after a continuous high or low resistance reading or over temperature condition.
4
Figure 4A
Figure 4C
Figure 4D
Figure 4B
Demand Cooling™ Wiring Schematic
AE4-1287
5
© 2002-2003 Copeland Corporation.
Printed in the U.S.A.
AE4-1287
Capacity Modulation
3) Do not use any filters containing materials that
con leave the filter and possibly clog the IV
orifice.
Demand Cooling is not approved as yet for compressors with capacity modulation.
4) The liquid refrigerant supply line must be a
minimum of 3/8" and routed so it will not interfere with compressor maintenance. Liquid refrigerant must have sufficient subcooling at the
injection valve to prevent flashing upstream of
the valve.
Performance Adjustment Factors
Since compressor discharge temperature depends
strongly on the return gas temperature. the amount of
injection and its effect on evaporator capacity and
mass flow will vary somewhat with return gas temperature. The approximate effects of return gas
temperature on evaporator capacity and mass flow are
tabulated in Table 3A and B. These factors should be
applied to the 65ºF return gas capacity and mass
flow values in the published performance data sheets.
5) The liquid refrigerant supply line to the IV must
be supported so that it does not place stress on
the IV and IV tubing or permit excess vibration.
Failure to make this provision may result in
damage to the IV and its tubing and/or refrigerant loss.
Demand Cooling Specifications
6) A head fan must be used to help lower compressor discharge temperatures.
Demand Cooling is designed to operate and protect
the compressor within the evaporating and condensing envelope identified in Figure 2. Operating
setpoints and control actions are listed in Table 1.
7) Return gas temperatures must NOT exceed
65°F.
8) System designers are advised to review their
defrost schemes to avoid floodback to the compressor which may occur at defrost termination
with HCFC-22. HCFC-22 has a significantly
higher heat of vaporization than does CFC502, and, if the same design parameters used
with CFC-502 are used with HCFC-22.
floodback could occur.
Table 1
© 2002-2003 Copeland Corporation.
Printed in the U.S.A.
6
AE4-1287
Attached is the Demand Cooling Diagnostic Troubleshooting Guide (form number 92-91).
Table 2
7
© 2002-2003 Copeland Corporation.
Printed in the U.S.A.
AE4-1287
Table 3A
DEMAND COOLING EVAPORATOR CAPACITY ADJUSTMENT FACTORS
Table 3B
DEMAND COOLING EVAPORATOR MASS FLOW ADJUSTMENT FACTORS
© 2002-2003 Copeland Corporation.
Printed in the U.S.A.
8
Copeland Demand Cooling Diagnostics
Demand Cooling
Operating Characteristics
The Copeland Demand Cooling control uses a Negative
Temperature Coefficient Thermistor (NTC). Incorporated in
the Demand Cooling Temperature Sensor (hereafter called
“sensor”), is a compressor discharge temperature monitor.
When the temperature sensed by the NTC Thermistor rises,
its resistance falls, and when temperature sensed by the
thermistor drops, its resistance increases.
The sensor resistance signal is coupled to the Demand
Cooling Module (hereafter called “module”). The module uses
the signal to determine when the compressor discharge
temperature has risen to a point where Demand Cooling is
required. When Demand Cooling is required the module
energizes the Demand Cooling Injection Valve (hereafter
called “injection valve”) and the injection valve inject s
saturated refrigerant into the compressor suction cavity until
the discharge temperature drops to an acceptable level.
Whenever the compressor starts and the module first
receives power, there is a one minute delay during which
the Demand Cooling system injects saturated refrigerant if it
is required, but waits for compressor discharge temperature
to stabilize before checking for alarm conditions. After one
minute, if the resistance of the probe is too low (the resistance
equivalent of 310°F), or too high (the resistance equivalent
of 4°F) the module will trip and deenergize the compressor.
wire or tiewraps if necessary. There should be no free air
movement over the metal part of the taped-sensor.
3) Connect the digital ohmmeter to the two pins on the plug
of the sensor. Make sure there is a good connection. Do
not take a sensor resistance measurement until there is
no change in the ohmmeter display.
4) Measure the temperature of the thermometer sensor and
find the corresponding calculated sensor resistance value
from Table 1. Since the values of Table 1 are not
continuous, you may have to interpolate.
5) The sensor resistance reading should be within +/- 5% of
the calculated resistance value of Step 4.
End of Test
TABLE 1
Thermomter
Temp. (F°)
Calculated Sensor
Resistance (Ohms)
59
60.8
62.6
64.4
66.2
141426
135000
128907
123129
117639
68
69.8
71.6
73.4
75.2
112437
107478
102762
98289
94041
77
78.8
80.6
82.4
84.2
90000
86139
82476
78984
75663
86
87.8
89.6
91.4
93.2
72504
69480
66609
63864
61254
Room temperature should be stable and between 60°F and
110°F.
95
96.8
98.6
100.4
102.2
58770
56394
54126
51966
49914
1) Wrap the end of the digital thermometer probe and the
metal end of the Demand Cooling sensor probe together
with electrical tape or “Velcro”. The end of the probe and
the end of the thermometer must touch.
104
105.8
107.6
109.4
47943
46053
44262
42543
Bench Testing Demand Cooling Components
Bench Check of the Sensor
Required Equipment:
• A digital thermometer of +/- 1 % full scale accuracy. The
thermometer probe should be checked for calibration in
an ice water bath or compared with another accurately
known temperature source.
• A digital ohmmeter capable of +/- 1 % accuracy. The
ohmmeter should be checked for accuracy with a known
resistance value such as a +1 % resistor.
2) Place the wrapped probe-sensor inside an insulation
shield to protect it from air currents. Use a material such
as “Permagum” or piping insulation such as “ArmafleX”.
The insulating material should be tightly wrapped around
the taped-sensor and the wrap should be secured with
Bench Check of the Module and Injection Valve
Required equipment:
• A controlled voltage source the same as the rating of the
module and the injection valve.
6) After one minute, the module should trip. The run cont act
“L” to “M” should open, and the alam contact “L” to “A”
should close. Deenergize the module, disconnect the
injection valve, read zero ohms between “L” and “A” and
an open circuit between “L” and “M”
• A multimeter.
7) Reset the module. Remove the jumper from the module
probe plug so there is an open circuit at the plug input.
• If the jumper supplied on the sensor plug of the module is
not available you may use a small paper clip for the test.
8) Energize the module.
Before starting the test, make sure you have the correct
module and injection valve.
1) With the module control voltage disconnected, short the
module sensor plug female terminals with the jumper or
the paperclip. Press the module reset button.
2) Attach the injection valve leads to terminals “L2” and “S”
of the module. The injection valve should be propped in
an upright position.
3) You should read zero ohms between the “L” and “M”
terminals of the module. This is the Normally Closed (NC)
contact of the Single Pole Double Throw (SPDT) module
alarm relay. You should read an open circuit between “L”
and “A”. This is Normally Open (NO) contact of the alarm
relay.
4) Energize the module by bringing module rated voltage
to terminals “Ll” and “L2”.
*When the sensor connection at the module is shorted,
a very low resistance is seen by the module as a very
high temperature, and an injection signal is sent to the
injection valve.
5) The injection valve will be energized by the closing of an
electronic switch in the module. The control voltage to
energize the injection valve may be measured across
module terminals “S” and “L2”.
*Because this measurement is made across an electronic
switch some “leakage” voltage may be measured when
the switch is deenergized. This voltage is much less than
the control voltage which is measured when the electronic
switch is closed.
5a) The injection valve operation may also be checked by
listening to the “click” heard each time the coil of the
injection valve is energized and the injection valve
solenoid plunger seats itself.
5b)If background noise prevents an audible check of the
injection valve coil and magnant operation, grip the
injection valve magnet housing and loosen its housing
cover screw until magnant vibration is felt. This proves
solenoid operation. Retighten the magnet housing cover
screw after this check.
When the sensor connection to the Demand Cooling
Module (module) is opened the very high resistance is
interpreted by the module as a very low temperature.
Consequently no injection signal is sent to the injection
valve.
9) The injection valve should be energized. A recheck of
Step 5 will confirm this.
10)Refer to the test of Step 6 to check the alarm circuit.
Reset the module after the test. If the module or injection
valve fails any of the checks it should be replaced.
End of Test
Installed System Checks of
Demand Cooling Components
When the Demand Cooling control injects saturated
refrigerant into the suction cavity of the compressor, the
outlet tube of the injection valve frosts. If the module
sensor connection is opened or shorted while the module
is energized, the module will trip after one minute of
operation and must be reset to continue.
Before starting the test, make sure you have the correct
module and injection valve.
If the Injection Valve is not Injecting
1) With the system deenergized, disconnect the sensor from
the module and jumper the terminals of the module
connector. Energize the system so the compressor is
running and the module energized. The injection valve
should begin injecting, and frost should form on the outlet
tube of the injection valve. If frost forms, go to Step 4
otherwise go to Step 2.
2) If frost does not form in Step 1, check to see if there is
control voltage on the coil of the injection valve (terminals
“L2” and “S” of the module).
*Because this measurement is made across an electronic
switch in the module some “leakage” voltage may be
measured when the switch is deenergized. This voltage
is much less than the control voltage which is measured
when the switch is closed. If correct control voltage is
not present, replace the module.
3) If correct control voltage is present, make sure there is a
full sight glass of liquid from the receiver at the injection
valve. If there is not a full sight glass of liquid, the piping
from the receiver should be checked before proceeding.
Piping connections and sizes must be chosen to assure
a full sight glass of liquid for the injection valve during
any phase of the refrigeration system operation. Piping
that is too small, or connections taken from the tops of
manifolds rather from the bottom may result in a lack of
refrigerant available for the injection valve just when it
needs it most, such as after a defrost.
If a full sight glass is present and frost still does not form,
replace the injection valve.
4) With the module sensor connector shorted or open and
the module and compressor running, the module should
trip in one minute and stop the compressor.
If the compressor does not stop, check the control circuit
wiring to be sure the module is wired to stop the
compressor when the module trips. If the wiring is correct,
replace the module.
5) Check the discharge temperature by performing Steps
1-6 of the Injection Valve is Cycling On and Off test.
If the discharge temperature is higher than the allowable
Table 2 selection, remove the sensor from the compressor
and use the Bench Check of the Sensor Test to check
the probe. Replace the sensor if necessary.
End of Test
If the Injection Valve is Continually Injecting
1) Make sure there is a full sight glass of liquid from the
receiver. If there is not a full sight glass of liquid, there
may not be enough liquid to allow Demand Cooling to
cycle because it uses all available liquid to keep the
discharge temperature below a dangerous level. The
piping from the receiver to the injection valve should be
checked before proceeding.
Piping connections and sizes must be chosen to assure
a full sight glass of liquid for the injection valve during
any phase of the refrigeration system operation. If the
suction pressure rises then go to Step 6.
2) Deenergize the system and disconnect the sensor from
the module. Energize the system so the compressor is
running. The frosting should stop.
If Step 2 is successful, go to Step 4 otherwise go to Step 3.
3) If frosting does not stop, with the sensor disconnected,
deenergize the system. Disconnect the voltage supply
to the injection valve and restart the compressor. If frosting
does not stop, replace the injection valve. If frosting stops,
replace the module.
4) If frosting stops when the sensor is disconnected, check
the system for high suction and/or condensing
temperatures before proceeding. As suction and/or
discharge temperatures rise toward the Demand Cooling
limits (40° F evaporator temperature, 130°F condensing
temperature), Demand Cooling will call for injection for
longer periods of time and may appear to be continuously
injecting. Use Figure 1 to check Demand Cooling
operating areas. Figure 1 shows where injection begins
for two return gas temperatures (65°F and 20°F). The
arrows marked (A) and (B) on the graph show the lowest
allowable evaporating temperatures using a given
condensing temperature.
Point (A) shows that with 65°F return gas and 110° F
condensing temperature, the lowest evaporating
temperature without Demand Cooling injection is -5°F.
Point (B) shows that if the return gas temperature can be
lowered to -20°F, while still at a condensing temperature
of 110°F, the evaporating temperature may be lowered
to 20°F without Demand Cooling operation.
Your injection point can be approximated by drawing a
line representing your return gas temperature in between
and parallel to the two return gas temperatures on the
Figure 1 (Area 2). The higher your return gas temperature
is, the closer it will be to the “65°F line”. The lower it is,
the closer it will be to the “20°F line”. You can then draw
your own dotted lines representing your condensing and
evaporating temperatures to see if you are in the in a
Demand Cooling injection zone.
The higher your condensing and suction temperatures
are for a given evaporating temperature, the more
injection is required until finally Demand Cooling may be
energized constantly.
If the suction and condensing temperatures are lower
than, or borderline to the injection areas of Figure 1 then
go to Step 5.
If they are much higher the system should be corrected
to lower the temperatures or there may be occasional
Demand Cooling trips. If lowering system temperatures
corrects the continuous problem, the test is ended, if not
go to Step 5.
5) Deenergize the refrigeration system. Close the suction
service valve. Turn the system on and pump down the
compressor to 2-3 PSIG. Turn the system off. Wait one
minute. The pumpdown should hold and the pressure
should not rise.
If the suction pressure rises then go to Step 6. If the
suction pressure does not rise the sensor is calling for
injection when it is not required and should be replaced.
6) If the suction pressure rises, the suction service valve
may not be entirely closed, the valve plate or valve plate
gasket may have been damaged. Damage to the valve
plate or its gasket can cause discharge gas to be
introduced to the suction cavity, resulting in an artificially
high suction temperature. The artificial suction
temperature, in turn, causes an earlier than required
Demand Cooling injection.
Replace the compressor valve plate and gaskets if
required.
If the measured discharge temperature is more than
280°F, replace the sensor.
End of Test
TABLE 2
Compressor
Room
Condensing Discharge
Model
Temperature Temperature Temperature
(°F)
(°F)
(°F)
End of Test
2D
80
110
80
110
250-270
270-280
If the Injection Valve is Cycling On and Off
3D
80
110
80
110
240-256
265-280
4D
80
110
80
110
230-260
260-280
6D
80
110
80
110
250-270
250-270
When the saturated refrigerant is injected into the compressor
suction cavity it lowers the temperature sensed by the sensor.
The lower temperature in turn causes the injection valve to
shutoff. After shutoff the temperature in the suction cavity
rises again until it is high enough for injection to start. The
result of this cycling is that frost on the injection valve outlet
tubing alternately appears during injection, and then
disappears after injection stops.
FIGURE 1
1) Measure the room temperature.
2) Connect the temperature sensor probe to the compressor
discharge line 6" from the discharge valve. The probe
must be tightly secured to the discharge line, and must
be well insulated so that moving air will not produce a
false reading (a poorly insulated probe may cause errors
of more than 30°F!).
Discus, R-22 Demand Cooling
Areas of Expected Injection
(See page 3 for chart usage)
3) Use Table 2 to select the family of the test compressor:
2D, 3D, 4D or 6D.
4) Use Table 2 to select the room temperature and
condensing temperature closest to yours. (The
evaporator temperature chosen for the data of Table 2
was 25°F).
5) Because of system variations, there will be deviations
from Table 2. A measurement of +5% or 10% of the
selected Table 2 discharge pressure may be considered
satisfactory.
6) When operating under published conditions, the
discharge temperature should never be more than 280°F
or less than 200°F. If successful, the test is ended.
Otherwise go to the next step.
7) If the measured discharge temperature is lower by more
than 10% of the discharge temperature of Table 2,
perform Steps 5-8 of the “If The Injection Valve Is
Continually Injecting” test.
Form No. 92-91 R1 (7/03)
Emerson Climate Technolgies is a service mark and a trademark of Emerson Electric Co.
Copeland is a registered trademark of Copeland Corporation. © 1992, 2003 Copeland Corporation. Printed in the USA.
Copeland Corporation
1675 W. Campbell Rd.
Sidney, OH 45365-0669
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