Concert Boiler Control

Concert Boiler Control
Concert Boiler Control
Consulting Engineer
Suggested Specification
A.
Boiler Control System
1.
Scope of Supply
Boiler Control System shall provide safety interlocks and water
temperature control. The control system shall be fully integrated into the
boiler control cabinet and incorporate single and multiple boiler control
logic, inputs, outputs and communication interfaces. The control system
shall coordinate the operation of up to eight (8) fully modulating hot water
boilers and circulation pumps. The control system shall simply control
boiler modulation and on/off outputs based on the boiler water supply
temperature and an operator-adjusted setpoint. However, using
parameter menu selections, the control system shall allow the boiler to
respond to remote system water temperature and outside air
temperatures with domestic hot water priority (DHWP) and warm weather
shut down (WWSD) or energy management system (EMS) firing rate
demand, remote setpoint or remote start/stop commands. In order to
support large domestic demands it shall be parameter selectable to start
two boilers simultaneously in response to a DHWP demand.
2.
Boiler Control
Using PID (proportional-integral-derivative) based control, the remote
system water temperature shall be compared with a setpoint to establish
a target boiler firing rate. If the secondary loop flow speed is greater than
the primary loop flow speed, firing rate is increased in response to the
decrease in secondary loop temperature. When the remote system
temperature is near the boiler high limit temperature, the boiler supply
sensor shall limit the maximum boiler supply temperature to prevent boiler
high limit events. Alternately, using parameter menu selections, the
control system shall allow the boiler to respond directly to boiler supply
temperature and setpoint to establish a target boiler firing rate while
remote system water temperature is used for display purposes only. Each
boiler’s fuel flow control valve shall be mechanically linked to the air flow
control device to assure an air rich fuel/air ratio. All the automated logic
required to ensure that pre-purge, post-purge, light-off, and burner
modulation shall be provided.
3.
Hot Water Temperature Setpoint
When the controller is in the local control mode, the control system shall
establish the setpoint based on outside air temperature and a reset
function curve, or be manually adjusted by the operator. When enabled,
the setpoint shall be adjusted above a preset minimum setpoint upon
sensing a domestic hot water demand contact input. When in remote
mode, the control system shall accept a 4-20ma or Modbus [*OPTION:
0-10Vdc] remote setpoint or firing rate demand signal from an external
EMS.
4.
Multiple Boiler Sequence
The controller shall incorporate its peer-to-peer communications on each
connected boiler (up to eight [8] units) by using standard RJ45 ethernet
cables. The control system shall allow the connected boilers to exchange
signals as required to provide coordinated fully modulating lead/lag
functions. It shall not be required to wire individual control signals
between boilers. Multiple boilers shall be modulated in “Unison” (all at the
same firing rate). To increase operational efficiency, the control system
shall utilize both water temperature and firing rate based boiler
sequencing algorithms to start and stop the boilers and shall minimize the
total number of boilers in operation. The control system shall start and
stop boilers when the water temperature is outside the adjustable
temperature limit for longer than the adjustable time delay. In order to
minimize temperature deviations, the control system shall start and stop
the next boiler when the “lead” boiler is at an adjustable firing rate limit for
longer than the adjustable time delay. The control system shall monitor
both boiler lockout and limit circuits to automatically skip over those
boilers that are powered down for maintenance, tripped or otherwise will
not start. The boiler shall be run at low fire for warm-up for a preset low
fire hold time. When enabled, warm weather shut down control logic shall
prevent boiler operation. The controller shall also be capable of autorotation of the boilers based on user-selected run time hours.
5.
User Interface
A touch screen message display shall be provided to display real time
BTU/hr, numeric data, startup and shutdown sequence status, alarm,
system diagnostic, first-out messages and boiler historical information. In
the event of a fault condition, the display shall provide help screens to
determine the cause of the problem and corrective actions. Historical
information shall include graphical trends, lockout history, boiler &
circulator cycle counts and run time hours.
6.
Circulator Control
The controller shall be capable of sequencing the boiler, domestic hot
water or system circulators. Simple parameter selections shall allow all
three pumps to respond properly to various hydronic piping arrangements
including either a boiler or primary piped indirect water heater. The
controller shall perform circulator exercise to help prevent pump rotor
seizing. [OPTIONAL: The boiler circulator shall be variable speed and
supplied by the boiler manufacturer to work integrally with the boiler’s
control system to optimize energy savings.]
7.
EMS Communication
Control and monitor the boiler via communication RS485 Modbus or
direct wiring. The control shall allow for simultaneous communication for
boiler peer-to-peer communication and EMS communication interfaces.
Loss of EMS communication shall automatically transfer the boiler control
to local operation. Boiler operation shall not be lost due to corrupt or loss
of EMS communication. The boiler control system shall allow individual
boiler limits, lockout, boiler and system temperatures and firing rate status
to be readable and water setpoint, boiler firing rate, and start/stop
command to be readable and writable. The control shall provide easy
parameter selection and options for the following: Modulation Source (420ma or Modbus [*OPTION: 0-10Vdc]); Setpoint Source (4-20ma or
Modbus [*OPTION: 0-10Vdc]); and Enable/Disable (contact wired or
Modbus). The control shall allow a real time, live & convenient list of all
interface signals to allow for quick interface verification. [OPTION: The
boiler control system shall network with a communication gateway to
connect with BACnet [LonWorks] [Johnson Controls Metasys N2]
communication protocol.]
*Note to Spec Writer: 0-10Vdc option available with EMS Signal
Converter
8.
External Data Transfer
The control system shall include the ability to transfer parameters from
boiler to boiler. Upon completion of commissioning the first boiler, a USB
flash drive shall allow settings to be “downloaded” from one boiler and
“uploaded” into the next. Additionally, these files shall be able to be sent
via email and “uploaded” to a remote technical support system.
Additionally, it shall be possible to restore parameters to the “as shipped
state” by selecting a “Factory Default” Button.
9.
Archive History
All hard lockouts, soft lockouts (holds), sensor faults, Energy
Management System (EMS) signal faults, sequencer faults and limit
string faults shall be recorded with a time and date stamp. The time and
date log shall stores up to 3000 alarm & events even after power cycle.”
The alarm & event log must be downloadable to a USB thumb drive. The
control shall include collect and store supply & return temperature, flame
intensity and firing rate for at least 4 months. It shall be a simple matter
to page through the boiler’s operation using the boiler mounted display or
download the historical data to a USB thumb drive for off-site analysis.
All data must be stored in standardly compatible CRV files.
10.
Quality Assurance
The boiler control system shall be supplied as part of a factory-assembled
and tested burner control cabinet
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