Savings-by-Design
EnergyDesignResources.Com
Cx AssistantTM
Sequences of Operation
Developed by
CTG Energetics, Inc.
Under contract to
Pacific Gas and Electric Company
April 2004
Cx Assistant’s Sequence of Operation
April 2004
IMPORTANT NOTICE: This sample document is provided for instructional
purposes only. CCC is not rendering advice concerning any commission
project or practices. This document is neither approved nor intended to
serve as a standard form. The user of these documents should confer with
qualified advisors with respect to its commissioning and other
documentation.
Cx Assistant’s Sequence of Operation
April 2004
About Cx Assistant
Energy Design Resources' Commissioning Assistant is a web-based
tool designed to provide project-specific building commissioning
information to design teams. The tool currently enables the users to
accomplish the following six functions:
1. Evaluate probable commissioning cost.
2. Identify the appropriate commissioning scope for each project,
and develop sample scope documents.
3. Develop a sample design intent document with specific inputs
from their projects.
4. Develop a sample basis of design document with specific inputs
from their projects.
5. Access sample commissioning specifications related to specific
inputs for his/her construction project.
6. View sample sequence of operations for their HVAC equipment
based upon the requirements in California Title 24- 2005.
Modules are planned to be added in 2005 that will generate a
Commissioning Plan, a Training Plan and a Systems Manual.
Cx Assistant’s Sequence of Operation
April 2004
About EDR
Energy Design Resources offers a valuable palette of energy design
tools and resources that help make it easier to design and build
energy-efficient commercial and industrial buildings in California. The
goal of this effort is to educate architects, engineers, lighting
designers, and developers about techniques and technologies that
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Utilities Commission.
Cx Assistant’s Sequence of Operation
April 2004
Table of Contents
1.
2.
3.
4.
Split System Units with DX Cooling
Economy Heat Pump Packaged Units
Evaporative Cooler Units
Packaged VVT Units
5. Standard Packaged Units
6. Four Pipe Fan Coil Units
7. Constant Air Volume (CAV) Units with Central Plant
8. Variable Air Volume (VAV Units with Air-Cooled Chiller
9. Variable Air Volume (VAV Units with Water-Cooled Chiller
10. Water Source Heat Pump System
Cx Assistant’s Sequence of Operation
April 2004
Cx Assistant’s Sequence of Operation
April 2004
Notes: [SPLIT SYSTEM WITH DX COOLING]. The system consists of an indoor fan coil unit and an outdoor condensing
unit that are connected by a direct expansion (DX) refrigerant loop. The fan coil unit has a supply fan and a cooling coil.
The outdoor unit has a compressor, a heat rejection fan, and a condensing coil. This system is designed to provide
cooling for machinery such as electrical transformers and computer equipment. The system does not include ventilation
air. Vendor-provided packaged controls operate the equipment.
Appropriate reference in the specifications should be made for products that are integrated with these sequences
including packaged units, economizers, and the like.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
SEQUENCE OF OPERATION: SPLIT SYSTEM WITH DX COOLING
SEQUENCES OF OPERATION
1. Occupied Periods (Normal occupied operation): The zone is typically unoccupied, but the unit is enabled to run, as needed, 24 hours per day, 7 days per
week.
2. Fan Operation: Run the indoor unit fan when the unit is in cooling mode.
Split System with DX Cooling
1
Cx Assistant’s Sequence of Operation
April 2004
3. Temperature Control: A thermostat is used to determine when the space requires
cooling. Set the thermostat for the following ranges:
a. Cooling: 60° F to 85° F. The default is 75° F.
Maintain a dead band of 1°F to cycle the system on and off.
4. Fire Alarm: Interface system with the fire alarm controls. When the fire alarm
control initiates a fire alarm, shut down the supply fan by a hardwired contact.
Once reset, the unit will resume the current mode of operation.
5. Shutdown: The fan and compressor will stop when the system goes to unoccupied
mode or when there is no call for cooling. The fan runs for 1 minute after a
shutdown has been initiated.
6. Fire Alarm: For fire alarm mode operation, the unit will be shut down by
hardwired contact. Once reset, the affected unit will resume the current mode of
operation.
7. Cooling Mode Enable: When the thermostat generates a call for cooling, enable
the unit’s compressor. The supply air setpoint in cooling mode is 55° F. Allow the
unit’s controls to cycle the compressor to supply the needed air temperature. The
package unit’s internal controls protect the equipment from excessive operating
conditions including low oil pressure, high discharge pressure, low suction
pressure, excessive cycling (more than one every 5 minutes or 6 cycles/hour), low
refrigerant charge, high and low refrigerant temperatures, etc. If excessive
operating conditions occur, shut down the unit to protect it.
8. Cooling Mode Shutdown: If a call for cooling has been satisfied, a system failure
has occurred, or the supply air temperature has fallen below 50° F for more than
one minute, cycle the compressor off. After the compressor has shut down,
continue running the supply fan for 5 minutes before shutting it down.
9. Space Temperature Alarm: An independent thermostat will sound an alarm if the
room temperature rises above 78° F for more than 5 minutes.
POINTS TABLE
Key: X Indicates type of point (only 1 point is needed)
CU Outdoor condensing unit with indoor fan coil (i.e. split system)
Note that these points are typically hard wired and not readily accessible
Point Name
AI AO DI DO Analog
Software
Value
Split System with DX Cooling
Digital
Software
Value
Other Software
Value
2
Cx Assistant’s Sequence of Operation
April 2004
CU Space Temperature X
Alarm Setpoint-Cooling
CU Cooling Alarm
X
CU Cooling Enable
X
CU Mode
CU Fire Alarm
X
X
CU Space Temperature
Setpoint-Cooling
X
CU Space Temperature
Setpoint-Deadband
X
Split System with DX Cooling
3
Cx Assistant’s Sequence of Operation
April 2004
Notes: The system consists of multiple packaged HVAC units each serving one or more zones in the building. The
packaged units each have a supply fan, direct expansion (DX) cooling and heating (i.e. a heat pump), and an electric
resistance back-up heater. The unit provides 100% outdoor air (i.e. “once-through” system). The system is controlled
with vendor-provided packaged controls.
Appropriate reference in the specifications should be made for products that are integrated with these sequences
including packaged units, economizers, and the like.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
ECONOMY HEAT PUMP PACKAGED UNIT
SEQUENCES OF OPERATION
1. Occupied Periods (Normal occupied operation): Operate the system on a
programmed occupancy schedule from 7:00 AM to 6:00 PM, M-F. These periods
are considered “occupied periods”. During occupied periods, run the system in
Occupied Mode, including enabling the packaged unit fans.
NOTE: Schedule occupied start time 1 hour before the building is expected to be occupied (for Title 24 required purge).
2. Unoccupied Periods: All hours not included in an occupied period are part of an
“unoccupied period”. During these periods, the system is available for tenant calls
as needed but is not running unless commanded.
3. Fan Operation (Ventilation Mode): Run the unit fans in all modes except
unoccupied mode.
Economy Heat Pump Packaged Unit
4
Cx Assistant’s Sequence of Operation
April 2004
4. Temperature Control: A thermostat is used to determine each space’s required
mode. Set each thermostat for the following ranges:
a. Occupied Heating: 55° F to 73° F during occupied hours. The default is
73° F.
b. Occupied Cooling: 73° F to 85° F during occupied hours. The default is
78° F.
Maintain a deadband of at least 5° F between heating and cooling setpoints. When
the system is operating, the thermostat is either in heating, cooling, or ventilation
mode. If a space’s temperature is more than 1.5° F higher than its temperature
setpoint, the thermostat generates a call for cooling. Likewise, if a space’s
temperature is more than 1.5° F lower than its temperature setpoint, the
thermostat generates a call for heating. Otherwise, the thermostat generates a call
for ventilation mode. During unoccupied hours, set the heating setpoint default to
55° F (adjustable) and the cooling setpoint default to 85° F (adjustable).
5. Fire Alarm: Interface system with the fire alarm controls. When the fire alarm
control initiates a fire alarm, shut down the supply fan by a hardwired contact.
Once reset, the affected unit(s) will resume the current mode of operation.
6. Cooling Mode Enable: When the zone thermostat generates a call for cooling,
enable the unit’s compressor. The cooling mode supply air setpoint is 55° F.
Allow the package unit’s controls to cycle the compressor to supply the needed
air temperature. The package unit’s internal controls protect the equipment from
excessive operating conditions including low oil pressure, high discharge
pressure, low suction pressure, excessive cycling (more than one every 5 minutes
or 6 cycles/hour), low refrigerant charge, high and low refrigerant temperatures,
etc. If excessive operating conditions occur, shut down the unit to protect it.
7. Heating Mode Enable: When the zone thermostat generates a call for heating and
outdoor temperature is above 42° F, switch the packaged unit heat pump to switch
to heating mode. If the outdoor temperature is less than 42° F, lock out the heat
pump t and enable the back-up resistance heater to supply heat to the zone. The
package unit’s internal controls protect the equipment from excessive operating
conditions including low oil pressure, high discharge pressure, low suction
pressure, excessive cycling (more than one every 5 minutes or 6 cycles/hour), low
refrigerant charge, high and low refrigerant temperatures, etc. If excessive
operating conditions occur, shut down the unit to protect it.
8. Compressor Shutdown: If a call for cooling or heating has ended, a system failure
has occurred, or the supply air temperature has fallen below 40° F (or risen above
120° F) for more than one minute, cycle the compressor off. After the compressor
has shut down, continue running the supply fan for 5 minutes before shutting it
down (even if an unoccupied period begins).
9. Unoccupied Mode: Unoccupied mode occurs during unoccupied periods. In
unoccupied mode, disable the packaged unit. When a thermostat’s override button
is depressed during an unoccupied period, operate the system in the occupied
mode for one hour. At the end of the hour, return the system to unoccupied mode.
Economy Heat Pump Packaged Unit
5
Cx Assistant’s Sequence of Operation
April 2004
10. Warm-up Mode: Identify Warm-up start time using an optimal start strategy
based on average zone temperature. If the average zone temperature is less than
69°F (adjustable) at the projected start of the warm-up period, enable the package
unit in occupied mode. Terminate the warm-up mode after the average zone
temperature has risen above 70°F (adjustable) and transition the system to
occupied mode (if scheduled) or to unoccupied mode.
11. Cool-down Mode: Identify cool-down start time using an optimal start strategy
based on average zone temperature. If the average zone temperature is greater
than 79°F (adjustable) at the projected start of the cool-down period, enable the
packaged unit in occupied mode. Terminate the cool-down mode after the average
zone temperature has fallen below 78°F (adjustable) and transition the system to
occupied mode (if scheduled) or to unoccupied mode.
12. Night Setback/Setup: Enable system operation during unoccupied periods in the
warm-up or cool-down mode if the space temperature falls below 55°F (adj.) or
rises above 85°F (adj.). Stop the system when the thermostat reaches either its
unoccupied cooling or unoccupied heating setpoints.
Points Table
Key: X Indicates type of point (only 1 point is needed)
n Indicates type of point (1 point is needed for each unit – a total of “n” points are needed
for this line item)
OA outside air (OAT = outside air temperature)
PKG packaged unit
Note that these points are typically hard-wired and not readily accessible
Point Name
AI AO DI DO Analog
Software
Value
OA DB Temp
n
PKG-n Cooling Alarm
Other Software
Value
n
PKG-n Fan Enable
n
PKG-n Heating Alarm
n
PKG-n Mode
PKG Fire Alarm
Digital
Software
Value
n
X
PKG Warm-up Mode
Low Temp Setpoint
Economy Heat Pump Packaged Unit
n
6
Cx Assistant’s Sequence of Operation
PKG Cool -down
Mode High Temp
Setpoint
April 2004
n
PKG-n Override
n
PKG-n Space
Temperature SetpointCooling
n
PKG-n Space
Temperature SetpointHeating
n
PKG-n Space
Temperature
Unoccupied SetpointCooling
n
PKG-n Space
Temperature
Unoccupied SetpointHeating
n
PKG-n Space
Temperature SetpointDeadband
n
Economy Heat Pump Packaged Unit
7
Cx Assistant’s Sequence of Operation
April 2004
Notes: The system consists of multiple packaged HVAC units each serving one or more zones in the building. The
packaged units each have a supply fan, direct evaporative cooling and natural gas heating. The unit provides 100%
outdoor air (i.e. “once-through” system). The system is controlled with vendor-provided packaged controls.
Appropriate reference in the specifications should be made for products that are integrated with these sequences
including packaged units, economizers, and the like.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
EVAPORATIVE COOLING PACKAGED UNIT
SEQUENCES OF OPERATION
1. Occupied Periods (Normal occupied operation): Operate the system on a
programmed occupancy schedule from 7:00 AM to 6:00 PM, M-F. These periods
are considered “occupied periods”. During occupied periods, run the system in
Occupied Mode, including enabling the packaged unit fans.
NOTE: Schedule occupied start time 1 hour before the building is expected to be occupied (for Title 24 required purge).
2. Unoccupied Periods: All hours not included in an occupied period are part of an
“unoccupied period”. During these periods, the system is available for tenant calls
as needed but is not running unless commanded.
3. Fan Operation (Ventilation Mode): Run the unit fans in all modes except
unoccupied mode.
Evaporative Cooler Units
8
Cx Assistant’s Sequence of Operation
April 2004
4. Temperature Control: A thermostat is used to determine each space’s required
mode. Set each thermostat for the following ranges:
a. Occupied Heating: 55° F to 73° F during occupied hours. The default is
73° F.
b. Occupied Cooling: 73° F to 85° F during occupied hours. The default is
78° F.
Maintain a deadband of at least 5° F between heating and cooling setpoints. When
the system is operating, the thermostat is either in heating, cooling, or ventilation
mode. If a space’s temperature is more than 1.5° F higher than its temperature
setpoint, the thermostat generates a call for cooling. Likewise, if a space’s
temperature is more than 1.5° F lower than its temperature setpoint, the
thermostat generates a call for heating. Otherwise, the thermostat generates a call
for ventilation mode. During unoccupied hours, set the heating setpoint default to
55° F (adjustable) and the cooling setpoint default to 85° F (adjustable).
5. Fire Alarm: Interface system with the fire alarm controls. When the fire alarm
control initiates a fire alarm, shut down the supply fan by a hardwired contact.
Once reset, the affected unit(s) resume the current mode of operation.
6. Cooling Mode: When the zone thermostat generates a call for cooling, enable the
evaporative cooler. Allow the packaged unit controls to operate the internal
circulating pump that carries water to the cooling surface. Provide makeup water
to the circulating pump basin as needed. The packaged unit’s internal controls
protect the equipment from excessive operating conditions including low water
level. If excessive operating conditions occur, shut off the circulating pump to
protect it. When the call for cooling has ended, shut off the circulating pump.
7. Heating Mode Enable: When the zone thermostat generates a call for heating, the
packaged unit will cycle on the gas heater to supply heat to the zone. The package
unit’s internal controls protect the equipment from excessive operating conditions
including high temperature, flame failure, excessive cycling (more than one every
5 minutes or 6 cycles/hour), low gas pressure, etc. If excessive operating
conditions occur, shut down the unit to protect it.
8. Heating Mode Shutdown: If a call for heating has ended, a system failure has
occurred, or the supply air temperature has risen above 120° F for more than one
minute, cycle the heater off. After the heater has shut down, continue running the
supply fan for 5 minutes before shutting it down (even if the unoccupied period
begins)
9. Unoccupied Mode: Unoccupied mode occurs during unoccupied periods. In
unoccupied mode, disable the packaged unit. When a thermostat’s override button
is depressed during an unoccupied period, operate the system in the occupied
mode for one hour. At the end of the hour, return the system to unoccupied mode.
10. Warm-up Mode: Identify Warm-up start time using an optimal start strategy
based on average zone temperature. If the average zone temperature is less than
69°F (adjustable) at the projected start of the warm-up period, enable the
packaged unit in heating mode. Terminate the warm-up mode after the average
Evaporative Cooler Units
9
Cx Assistant’s Sequence of Operation
April 2004
zone temperature has risen above 70°F (adjustable) and transition the system to
occupied mode (if scheduled) or to unoccupied mode.
11. Cool-down Mode: Identify cool-down start time using an optimal start strategy
based on average zone temperature. If the average zone temperature is greater
than 79°F (adjustable) at the projected start of the cool-down period, enable the
unit in cooling mode. Terminate the cool-down mode after the average zone
temperature has fallen below 78°F (adjustable) and transition the system to
occupied mode (if scheduled) or to unoccupied mode.
12. Night Setback/Setup: Enable system operation during unoccupied periods in the
warm-up or cool-down mode if the space temperature falls below 55°F (adj.) or
rises above 85°F (adj.). Stop the system when the thermostat reaches either its
unoccupied cooling or unoccupied heating setpoints.
Points Table
Key:
X Indicates type of point (only 1 point is needed)
n Indicates type of point (1 point is needed for each zone – a total of “n” points are
needed for this line item)
PKG packaged unit
Note that these points are typically hard wired and not user accessible
Point Name
AI
AO DI
PKG-n Fan Enable
DO Analog Digital
Other
Software Software Software
Value
Value
Value
n
PKG-n Heating Alarm
n
PKG-n Mode
PKG Fire Alarm
n
n
PKG Warm-up Mode Low
Temp Setpoint
n
PKG Cool -down Mode High
Temp Setpoint
n
PKG-n Override
PKG-n Space Temperature
Setpoint-Cooling
Evaporative Cooler Units
n
n
10
Cx Assistant’s Sequence of Operation
April 2004
PKG-n Space Temperature
Setpoint-Heating
n
PKG-n Space Temperature
Unoccupied Setpoint-Cooling
n
PKG-n Space Temperature
Unoccupied Setpoint-Heating
n
PKG-n Space Temperature
Setpoint-Deadband
n
Evaporative Cooler Units
11
Cx Assistant’s Sequence of Operation
April 2004
Notes: The system consists of multiple packaged roof top HVAC units each serving variable volume / variable
temperature (VVT) zone equipment. The packaged units each have a supply fan, direct expansion (DX) cooling, natural
gas heating, outside air temperature cooling/heating lockout, and an integrated differential temperature economizer. The
unit’s economizer uses return and exhaust dampers to regulate “free” cooling. Supply duct bypass dampers and
variable volume terminal units control the supply air delivered to each zone. The system is controlled with vendorprovided packaged controls that operate in a master and slave fashion.
Appropriate reference in the specifications should be made for products that are integrated with these sequences
including packaged units, VVT equipment, and the like.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
PACKAGED GAS HEAT AND DX COOLING HVAC UNITS WITH ECONOMIZERS
AND VARIABLE VOLUME, VARIABLE TEMPERATURE (VVT) ZONES
SEQUENCES OF OPERATION
System Modes
1. Occupied Periods (Normal occupied operation): Operate the system on a
programmed occupancy schedule from 7:00 AM to 6:00 PM, M-F. These periods
are considered “occupied periods”. During occupied periods, run the system in
Occupied Mode, including enabling the packaged unit fans, opening the outside
Packaged VVT Units
12
Cx Assistant’s Sequence of Operation
April 2004
air dampers to minimum position, and operating the zone dampers to maintain at
least minimum ventilation rates.
NOTE: Schedule occupied start time 1 hour before the building is expected to be occupied (for Title 24 required purge).
2. Unoccupied Periods: All hours not included in an occupied period are part of an
“unoccupied period”. During these periods, the system is available for tenant calls
as needed but is not running unless commanded. The following holidays are
considered to be unoccupied periods: New Years Day, Memorial Day, Fourth of
July, Labor Day, Thanksgiving and the following day, Christmas. These should
be set up as re-occurring holidays for each zone.
3. Start-up & System “changeover”: “Changeover” occurs at the beginning of every
occupied period and whenever the VVT master controller switches between
cooling and heating modes (use a hard-wired stop to signal changeover). During
changeover, open the bypass damper fully and allow the air contained in the
supply duct to circulate directly to the return air stream. When the supply air
temperature reaches an acceptable temperature (80°F if the system is beginning a
heating mode or 65° F if the system is beginning a cooling mode), modulate the
damper closed. Stop modulating the bypass damper closed when the supply air
duct static pressure transmitter, referenced to space pressure, registers the
operating pressure of 1.0” WC. During operation, modulate the bypass damper to
maintain the SA static pressure at a setpoint of 1.0” WC.
4. Occupied Modes: During occupied periods, the VVT master controller polls the
slave controllers at least every 30 seconds to confirm their operating status. A call
for a particular mode (heating, cooling, or ventilation) is based upon the number
of requests for that mode from the slave controllers. Once the number of callers
for a particular mode exceeds that of the other modes, the mode is changed. At the
beginning of each new mode, the VVT master controller selects the reference
zone (see Determination of Reference Zone). Do not change the mode more
frequently than every 5 minutes. NOTE: To initiate a mode change, at least 2
(adjustable) slave controllers must request it.
5. Determination of the Reference Zone: When the system mode is changed, the
master controller selects the zone with the greatest difference between room
temperature and room setpoint. This becomes the reference zone.
6. Unoccupied Mode: Unoccupied mode occurs during unoccupied periods. In
unoccupied mode, disable the packaged unit, close the outside air damper, and
position the return/exhaust air dampers for full return air (no exhaust). When a
zone sensor’s override button is depressed during unoccupied period, operate the
system in the occupied mode for one hour.
7. Warm-up Mode: Identify Warm-up start time using an optimal start strategy
based on outdoor air temperature and average zone temperature. If the average
zone temperature is less than 69°F (adjustable) at the projected start of the warmup period, initiate the warm-up mode. If building warm-up is required, command
the return/exhaust air dampers to the return position (no exhaust) and enable the
Packaged VVT Units
13
Cx Assistant’s Sequence of Operation
April 2004
package unit. Terminate the warm-up mode after the average zone temperature
has risen above 70°F (adjustable) and transition the system to occupied mode (if
scheduled) or to unoccupied mode.
8. Cool-down Mode: Identify cool-down start time using an optimal start strategy
based on outdoor air temperature and average zone temperature. If the average
zone temperature is greater than 79°F (adjustable) at the projected start of the
cool-down period, initiate the cool-down mode. If building cool-down is required,
command the return/exhaust air damper to the return position (no exhaust) and
enable the packaged unit. Terminate the cool-down mode after the average zone
temperature has fallen below 78°F (adjustable) and transition the system to
occupied mode (if scheduled) or to unoccupied mode.
9. Supply Temperature Limits: During any mode, when the supply air temperature
exceeds 140° F, or falls below 50° F, disable the cooling or heating in the
packaged unit and initiate an alarm in the VVT control system.
VVT Zone Control
1. Temperature Control: A slave controller is used to determine each space’s
required mode. Set each controller for the following ranges:
1. Occupied Heating: 55° F to 73° F during occupied hours. The default is
73° F.
2. Occupied Cooling: 73° F to 85° F during occupied hours. The default is
78° F.
Maintain a deadband of at least 5° F between heating and cooling setpoints. When
the system is operating, the slave controller is either in heating, cooling, or
ventilation mode. If a space’s temperature is more than 1.5° F higher than its
temperature setpoint, the zone controller generates a call for cooling. Likewise, if
a space’s temperature is more than 1.5° F lower than its temperature setpoint, the
zone controller generates a call for heating. Otherwise, the controller generates a
call for ventilation mode. During unoccupied hours, set the heating setpoint
default to 55° F (adjustable) and the cooling setpoint default to 85° F (adjustable).
Provide each zone with its own adjustable unoccupied heating and cooling
setpoints.
2. Cooling Mode: When a zone controller calls for cooling and the supply air
temperature is less than the space temperature, enable the zone controller to open
the zone damper to provide cooling to the space. If the zone is calling for cooling
and the supply air temperature is higher than the space temperature, the controller
closes the damper to minimum position (minimum position is determined by air
balance).
3. Heating Mode: When a zone controller calls for heating and the supply air
temperature is greater than the space temperature, enable the zone controller to
open the zone damper to provide heating to the space. If the zone is calling for
heating and the supply air temperature is lower than the space temperature, the
controller closes the damper to minimum position (minimum position is
determined by air balance).
Packaged VVT Units
14
Cx Assistant’s Sequence of Operation
April 2004
4. Ventilation Mode: When in ventilation mode, enable the zone controller to open
and close the zone damper to satisfy heating or cooling needs.
5. Night Setback/Setup: Enable system operation during unoccupied periods in the
warm-up or cool-down mode if the lowest space temperature from a slave
controller falls below 55°F (adj.) or rises above 85°F (adj.). Stop the system when
the reference zone reaches either its unoccupied cooling or unoccupied heating
setpoints.
6. Zone Grouping: Provide zone groups to establish enough heating or cooling load
for the package system to work against when answering off-hours calls or setback
calls. When one zone calls for system operation after hours, (either in the night
setback mode or by authorized tenant request), command all zones in the
associated group to come out of setback into normal operating temperature
settings used for Occupied Modes.
7. Unoccupied Operation: When a zone override button is depressed during
unoccupied period, operate the system in occupied mode for one hour. At the end
of the hour, return the system to unoccupied mode.
Packaged Unit
1. Fan Operation: Run the unit fans in all modes except unoccupied mode. Any time
the supply fan is running, open the outside air damper to provide minimum
outdoor air.
2. Shutdown: When shutdown is initiated, place the packaged unit in unoccupied
mode.
3. Fire Alarm: For fire alarm mode operation, the supply fan will be shut down by
hardwired contact. Once reset, the affected unit(s) will resume the current mode
of operation.
4. Cooling Mode Enable: When the VVT master controller generates a call for
cooling, enable the economizer mode in order to satisfy the cooling requirement.
If the economizer mode cannot provide the required supply air temperature (55°
F) for at least 2 minutes, disable economizer mode and enable the unit’s
compressor. Reset the supply air temperature upward from 55°F to 65°F as the
outdoor temperature falls from 90° F or greater to 65° F or lower. Allow the
package unit’s controls to cycle the compressor to supply the needed air
temperature. The package unit’s internal controls protect the equipment from
excessive operating conditions including low oil pressure, high discharge
pressure, low suction pressure, excessive cycling (more than one every 5 minutes
or 6 cycles/hour), low refrigerant charge, high and low refrigerant temperatures,
etc. If excessive operating conditions occur, generate an alarm on the VVT master
controller and shut down the package unit to protect it.
5. Cooling Mode Shutdown: If a call for cooling has been satisfied, a system failure
has occurred, or the supply air temperature has fallen below 50° F for more than
one minute, cycle the compressor off. After the compressor has shut down,
Packaged VVT Units
15
Cx Assistant’s Sequence of Operation
April 2004
continue running the supply fan for 5 minutes before shutting it down (even if the
unoccupied mode is issued by the VVT).
6. Enthalpy Economizer Mode: Enable enthalpy economizer mode when the VVT
master controller issues a call for cooling or ventilation, and outdoor air
temperature is 2° F less than return air temperature. Open outside air damper to
100%. Modulate the return air and exhaust air dampers in unison to maintain
supply air temperature setpoint. When the return air enthalpy is 2 BTU/lb dry air
(adjustable deadband) above the outdoor air enthalpy, the dampers are to be in the
full exhaust position (exhaust damper fully open and return damper fully closed).
As the return enthalpy decreases below this point, the dampers transition to a full
return position (exhaust damper is closed to allow only minimum outdoor air and
the return damper is fully open).
7. Heating Mode Enable: When the VVT master controller generates a call for
heating, transition the return & exhaust dampers to full return position (exhaust
damper is closed to allow only minimum outdoor air and the return damper is
fully open), and the packaged unit will cycle on the gas heater to supply heat to
the zone. Reset the supply air temperature upward from 90°F to 110°F as the
outdoor temperature falls from 65° F or greater to 40° F or lower. The package
unit’s internal controls protect the equipment from excessive operating conditions
including high temperature, flame failure, excessive cycling (more than one every
5 minutes or 6 cycles/hour), low gas pressure, etc. If excessive operating
conditions occur, generate an alarm on the VVT master controller and shut down
the package unit to protect it.
8. Heating Mode Shutdown: If a call for heating has ended, a system failure has
occurred, or the supply air temperature has risen above 120° F for more than one
minute, cycle the heater off. After the heater has shut down, continue running the
supply fan for 5 minutes before shutting it down (even if the unoccupied mode is
issued by the VVT master controller).
9. Heating System Outdoor Air Temperature Lockout: If the outdoor air temperature
rises above 68 ° F (adjustable), the heating system shall be locked out. If the
outdoor air temperature falls below 65° F (adjustable), the heater will be allowed
to function as required to maintain load.
10. Mechanical Cooling System Outdoor Air Temperature Lockout: If the outdoor air
temperature is below 63° F (adjustable), the mechanical cooling system shall be
locked out. If the outdoor air temperature rises above 65° F (adjustable), the
compressors will be allowed to function as required to maintain load.
Points Table
Key:
X Indicates type of point (only 1 point is needed)
n Indicates type of point (1 point is needed for each zone - a total of "n" points are needed
for this line item)
Packaged VVT Units
16
Cx Assistant’s Sequence of Operation
April 2004
OA outside air (OAT = outside air temperature)
RTU rooftop unit (i.e. packaged unit)
VVT variable volume and temperature terminal
Point Name
AI AO DI DO Analog
Software
Value
OA DB Temp
X
OA RH
X
OA Enthalpy
X
Cooling Lockout
Temp
X
Heating Lockout
Temp
X
RTU- Low Limit
Setpoint Temp
n
RTU- High Limit
Setpoint Temp
n
RTU-n Economizer
Staging Setpoint
Temp
n
AHU-n RAT
n
AHU-n RA RH
n
AHU-n RA
Enthalpy
n
RTU-n Staging
Deadband Temp
n
RTU-n Cooling
Alarm
Packaged VVT Units
Alarm Logic
n
RTU-n Cooling
Status
RTU-n Heating
Alarm
Other
Software
Value
n
RTU-n Fan Enable
RTU-n Heating
Status
Digital
Software
Value
n
n
Proof after 1
minute
Proof after 1
minute
n
17
Cx Assistant’s Sequence of Operation
April 2004
RTU-n VVT Mode
n
RTU-n Economizer
Mode
n
VVT Fire Alarm
X
VVT Mode
Override
X
VVT Supply
Pressure Setpoint
VVT Supply
Pressure
X
X
VVT Warm-up
Mode Low Temp
Setpoint
X
VVT Cool -down
Mode High Temp
Setpoint
X
VVT Mode
X
VVT Low Limit
Setpoint Temp
X
VVT High Limit
Setpoint Temp
X
VVT Reference
Zone
X
VVT Override
X
VVT Operating
Mode
VVT Supply Air
Temperature
X
X
VAV-n Supply Air
Temp Reset
VVT OAT
X
X
VVT Bypass Mode
VVT Bypass Status
X
X
Zone-n Space
Temperature
Setpoint-Cooling
n
Zone-n Space
n
Packaged VVT Units
18
Cx Assistant’s Sequence of Operation
April 2004
Temperature
Setpoint-Heating
Zone-n Space
Temperature
Unoccupied
Setpoint-Cooling
n
Zone-n Space
Temperature
Unoccupied
Setpoint-Heating
n
Zone-n Space
Temperature
Setpoint-Deadband
n
Zone-n Damper
Command
Zone-n Override
Zone-n Operating
Mode
Packaged VVT Units
n
n
n
19
Cx Assistant’s Sequence of Operation
April 2004
Notes: The system consists of multiple packaged roof top HVAC units each serving one or more zones in the building.
The packaged units each have a supply fan, direct expansion (DX) cooling, natural gas heating, outside air temperature
cooling/heating lockout, and an integrated differential enthalpy economizer. The unit’s economizer uses return and
exhaust dampers to regulate “free” cooling. The system is controlled with vendor-provided packaged controls.
Appropriate reference in the specifications should be made for products that are integrated with these sequences
including packaged units, economizers, and the like.
The system(s) in your building that are most similar to the system described above include:
•
Packaged VAV System
•
Typical AHU Controls
•
proto 1
•
Packaged VaV
•
classroom hvac
•
Underfloor
•
Roof-top packaged AC-4
•
AH-1
•
test ahu
•
AHU-1
•
Central System
•
asdf
•
VAV
•
VAVS
Please note that this sample sequence will have to be modified to meet the exact systems defined in your building.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
PACKAGED UNIT WITH ECONOMIZER, DX COOLING AND GAS HEAT
Standard Packaged Units
20
Cx Assistant’s Sequence of Operation
April 2004
SEQUENCES OF OPERATION
1. Occupied Periods (Normal occupied operation): Operate the system on a
programmed occupancy schedule from 7:00 AM to 6:00 PM, M-F. These periods
are considered “occupied periods”. During occupied periods, run the system in
Occupied Mode, including enabling the packaged unit fans and opening the
outside air dampers to minimum position.
NOTE: Schedule occupied start time 1 hour before the building is expected to be occupied (for Title 24 required purge).
2. Unoccupied Periods: All hours not included in an occupied period are part of an
“unoccupied period”. During these periods, the system is available for tenant calls
as needed but is not running unless commanded. The following holidays are
considered to be unoccupied periods: New Years Day, Memorial Day, Fourth of
July, Labor Day, Thanksgiving and the following day, Christmas. These should
be set up as re-occurring holidays for each zone.
3. Fan Operation (Ventilation Mode): Run the unit fans in all modes except
unoccupied mode. Any time the supply fan is running, open the outside air
damper to provide minimum outdoor air.
4. Temperature Control: A thermostat is used to determine each space’s required
mode. Set each thermostat for the following ranges:
a. Occupied Heating: 55° F to 73° F during occupied hours. The default is
73° F.
Standard Packaged Units
21
Cx Assistant’s Sequence of Operation
5.
6.
7.
8.
9.
April 2004
b. Occupied Cooling: 73° F to 85° F during occupied hours. The default is
78° F.
Maintain a deadband of at least 5° F between heating and cooling setpoints. When
the system is operating, the thermostat is either in heating, cooling, or ventilation
mode. If a space’s temperature is more than 1.5° F higher than its temperature
setpoint, the thermostat generates a call for cooling. Likewise, if a space’s
temperature is more than 1.5° F lower than its temperature setpoint, the
thermostat generates a call for heating. Otherwise, the thermostat generates a call
for ventilation mode. During unoccupied hours, set the heating setpoint default to
55° F (adjustable) and the cooling setpoint default to 85° F (adjustable). Provide
each zone with its own adjustable unoccupied heating and cooling setpoints.
Fire Alarm: Interface system with the fire alarm controls. When the fire alarm
control initiates a fire alarm, shut down the supply fan by a hardwired contact.
Once reset, the affected unit(s) will resume the current mode of operation.
Cooling Mode Enable: When the zone thermostat generates a call for cooling,
enable the economizer mode in order to satisfy the cooling requirement. If the
economizer mode cannot provide the required supply air temperature (55° F,
adjustable) for at least 2 minutes, disable economizer mode and enable the unit’s
compressor. Allow the package unit’s controls to cycle the compressor to supply
the needed air temperature. The package unit’s internal controls protect the
equipment from excessive operating conditions including low oil pressure, high
discharge pressure, low suction pressure, excessive cycling (more than one every
5 minutes or 6 cycles/hour), low refrigerant charge, high and low refrigerant
temperatures, etc. If excessive operating conditions occur, shut down the unit to
protect it.
Cooling Mode Shutdown: If a call for cooling has been satisfied, a system failure
has occurred, or the supply air temperature has fallen below 50° F for more than
one minute, cycle the compressor off. After the compressor has shut down,
continue running the supply fan for 5 minutes before shutting it down (even if an
unoccupied period begins).
Enthalpy Economizer Mode: Enable enthalpy economizer mode when the zone
thermostat issues a call for cooling or ventilation, and outdoor air temperature is
2° F less than return air temperature. Open outside air damper to 100%. Modulate
the return air and exhaust air dampers in unison to maintain supply air
temperature setpoint. When the return air enthalpy is 2 BTU/lb dry air (adjustable
deadband) above the outdoor air enthalpy, the dampers are to be in the full
exhaust position (exhaust damper fully open and return damper fully closed). As
the return enthalpy decreases below this point, the dampers transition to a full
return position (exhaust damper is closed to allow only minimum outdoor air and
the return damper is fully open).
Heating Mode Enable: When the zone thermostat generates a call for heating,
transition the return & exhaust dampers to full return position (exhaust damper is
closed to allow only minimum outdoor air and the return damper is fully open),
and the packaged unit will cycle on the gas heater to supply heat to the zone. The
package unit’s internal controls protect the equipment from excessive operating
Standard Packaged Units
22
Cx Assistant’s Sequence of Operation
April 2004
conditions including high temperature, flame failure, excessive cycling (more
than one every 5 minutes or 6 cycles/hour), low gas pressure, etc. If excessive
operating conditions occur, shut down the unit to protect it.
10. Heating Mode Shutdown: If a call for heating has ended, a system failure has
occurred, or the supply air temperature has risen above 120° F for more than one
minute, cycle the heater off. After the heater has shut down, continue running the
supply fan for 5 minutes before shutting it down (even if the unoccupied period
begins).
11. Unoccupied Mode: Unoccupied mode occurs during unoccupied periods. In
unoccupied mode, disable the packaged unit, close the outside air damper, and
position the return/exhaust air dampers for full return air (no exhaust). When a
thermostat’s override button is depressed during an unoccupied period, operate
the system in the occupied mode for one hour. At the end of the hour, return the
system to unoccupied mode.
12. Warm-up Mode: Identify Warm-up start time using an optimal start strategy
based on outdoor air temperature and average zone temperature. If the average
zone temperature is less than 69°F (adjustable) at the projected start of the warmup period, initiate the warm-up mode. If building warm-up is required, command
the return/exhaust air dampers to the return position (no exhaust) and enable the
package unit. Terminate the warm-up mode after the average zone temperature
has risen above 70°F (adjustable) and transition the system to occupied mode (if
scheduled) or to unoccupied mode.
13. Cool-down Mode: Identify cool-down start time using an optimal start strategy
based on outdoor air temperature and average zone temperature. If the average
zone temperature is greater than 79°F (adjustable) at the projected start of the
cool-down period, initiate the cool-down mode. If building cool-down is required,
command the return/exhaust air dampers to the return position (no exhaust) and
enable the packaged unit. Terminate the cool-down mode after the average zone
temperature has fallen below 78°F (adjustable) and transition the system to
occupied mode (if scheduled) or to unoccupied mode.
14. Night Setback/Setup: Enable system operation during unoccupied periods in the
warm-up or cool-down mode if the space temperature falls below 55°F (adj.) or
rises above 85°F (adj.). Stop the system when the thermostat reaches either its
unoccupied cooling or unoccupied heating setpoints.
15. Heating System Outdoor Air Temperature Lockout: If the outdoor air temperature
rises above 68 ° F (adjustable), the heating system shall be locked out. If the
outdoor air temperature falls below 65° F (adjustable), the heater will be allowed
to function as required to maintain load.
16. Mechanical Cooling System Outdoor Air Temperature Lockout: If the outdoor air
temperature is below 63° F (adjustable), the mechanical cooling system shall be
locked out. If the outdoor air temperature rises above 65° F (adjustable), the
compressors will be allowed to function as required to maintain load.
Standard Packaged Units
23
Cx Assistant’s Sequence of Operation
April 2004
Points Table
Key:
X Indicates type of point (only 1 point is needed)
n Indicates type of point (1 point is needed for each zone – a total of “n” points are
needed for this line item)
OA outside air (OAT = outside air temperature)
RTU rooftop unit (i.e. packaged unit)
Note that these points are typically hard wired and not user accessible
Point Name
AI AO DI DO Analog
Software
Value
OA DB Temp
X
OA RH
X
OA Enthalpy
X
Cooling Lockout Temp
X
Heating Lockout Temp
X
RTU-n Low Limit
Setpoint Temp
n
RTU-n High Limit
Setpoint Temp
n
RTU-n Economizer
Staging Setpoint Temp
n
RTU-n RAT
n
RTU-n RA RH
n
RTU-n RA Enthalpy
n
RTU-n Staging
Deadband Temp
n
RTU-n Cooling Alarm
n
RTU-n Cooling Status
Standard Packaged Units
Other Software
Value
n
RTU-n Fan Enable
RTU-n Heating Status
Digital
Software
Value
n
n
24
Cx Assistant’s Sequence of Operation
April 2004
RTU-n Heating Alarm
n
RTU-n Mode
n
RTU-n Economizer
Mode
n
RTU Fire Alarm
X
RTU-n Minimum Air
Damper Command
n
RTU-n
Economizer/Return air
damper Command
n
RTU-n Warm-up Mode
Low Temp Setpoint
n
RTU-n Cool -down
Mode High Temp
Setpoint
n
RTU-n Override
n
RTU-n Space
Temperature SetpointCooling
n
RTU-n Space
Temperature SetpointHeating
n
RTU-n Space
Temperature
Unoccupied SetpointCooling
n
RTU-n Space
Temperature
Unoccupied SetpointHeating
n
RTU-n Space
Temperature SetpointDeadband
n
Standard Packaged Units
25
Cx Assistant’s Sequence of Operation
April 2004
Notes:
The system consists of Primary/Secondary chilled and hot water loops that serve multiple four-pipe fan coil units (FCUs)
for each zone in the building. Each FCU has a constant volume supply fan, a chilled water cooling coil, a hot water
heating coil, and a ducted air intake for ventilation air (outdoor air). Barometric relief dampers maintain building
pressurization and allow building air to be exhausted outside. The chilled water loop includes water-cooled chillers and
variable speed secondary chilled water pumps. The hot water loop includes two-stage boilers and variable speed
secondary hot water pumps. A building automation system (BAS) controls the HVAC equipment.
Appropriate reference in the specifications should be made for products that are integrated with these sequences
including chillers, boilers, variable frequency drives (VFDs), and the like.
Controls: Furnish control device with an interface for monitoring and control of points specified in the points table. The
points table includes the minimum acceptable list of interface points. The selected component controls shall easily
integrate into the BAS and allow for the collection, control, trending, and archiving of the specified points with a minimal
need for intermediary gateways or hardwired connections to link control systems together. Interoperable control
systems are preferred.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
FOUR PIPE FAN COIL UNITS WITH A CENTRAL PLANT, WATER COOLED
CHILLERS AND COOLING TOWERS
Four Pipe Fan Coil Units
26
Cx Assistant’s Sequence of Operation
April 2004
SEQUENCES OF OPERATION
Fan Coil Units (FCUs)
1. Occupied Periods (Normal operation): When an isolation area is scheduled to be
occupied, operate the fan coil units that serve it. These scheduled periods are
considered “occupied periods”.
2. Unoccupied Periods: All hours not included in an occupied period are part of an
“unoccupied period”. During these periods, the system is available for tenant calls
as needed but is not running unless commanded. The following holidays are
considered to be unoccupied periods: New Years Day, Memorial Day, Fourth of
July, Labor Day, Thanksgiving and the following day, Christmas. These should
be set up as re-occurring holidays for each zone.
3. Fan Operation: Run the unit fans in all modes except unoccupied mode.
4. Fire Alarm: Interface system with the fire alarm controls. When the fire alarm
control initiates a fire alarm, shut down the supply fan by a hardwired contact
interface. Simultaneously, the fire alarm control must notify the BAS of the fire
event to enable the BAS to disable the affected units. Once the fire alarm is reset,
enable the affected unit(s) to resume normal operation.
5. Duct Pressure Safety: If negative static pressure over 2” WC is measured in the
mixed air plenum or positive supply duct static pressure over 3” WC is measured
in the supply duct, disable the fan via a hard wired interlock and initiate an
equipment specific alarm (i.e. “FC-3 High Static Pressure” or “FC-2 Low Static
Pressure”) at the operator workstation. An operator must reset each fan’s
differential pressure switch before the fan may be re-enabled. Provide a local or
BAS reset for this purpose.
6. Temperature Control: Use a solid state, electronic wall temperature sensor to
switch the fan coil unit between “fan operation”, “cooling mode”, and “heating
mode”. Each mode will vary the FCUs supply air temperature in order to satisfy
the zone’s temperature setpoint. Set each temperature sensor for the following
ranges:
1. Occupied Heating: 55° F to 73° F during occupied hours. The default is
73° F.
2. Occupied Cooling: 73° F to 85° F during occupied hours. The default is
78° F.
Maintain a deadband of at least 5° F between the heating and cooling setpoints.
When the zone is in this deadband, set the fan coil unit to operate in “fan
operation” mode only. During unoccupied hours, set the heating setpoint default
to 55° F (adjustable) and the cooling setpoint default to 85° F (adjustable).
Provide each zone its own adjustable unoccupied heating and cooling setpoints.
7. Cooling Mode: When the zone temperature rises to the cooling setpoint, begin
modulating the chilled water valve with a control loop. When the cooling valve
opens more than 30% (adj.), send a call for cooling to the central plant to maintain
Four Pipe Fan Coil Units
27
Cx Assistant’s Sequence of Operation
April 2004
a cooling mode supply air temperature setpoint of 55° F (adjustable). When the
cooling valve closes to 5% (adj.), cancel the call for cooling .
8. Heating Mode: When the zone temperature falls to the heating setpoint, begin
modulating the hot water valve. When the heating valve opens more than 10%
(adj.), send a call for heating to the central plant to maintain a heating mode
supply air temperature setpoint of 110° F (adjustable). When the heating valve
closes to 5% (adj.), cancel the call for heating.
9. Filter Status: A differential pressure indicator is used to manually determine if the
filter is dirty. The filter status indicator is not connected to the BAS.
Isolation Areas
1. Isolation Areas: There are XX isolation areas as indicated on the plans. Each area
is composed of 1 or more spaces served by 1 or more fan coil units that are
operated together. Configure each isolation area separately from other isolation
areas. Configuration includes scheduling and operational modes. The default
occupancy schedule is 7:00 AM to 6:00 PM, M-F.
NOTE: Schedule occupied start time 1 hour before the building is expected to be occupied (for Title 24 required purge).
2. Occupied Mode: Prior to an occupied period, initiate a Warm-up mode or Cooldown mode if necessary. During Occupied Mode, enable operation of the system,
including enabling the fan coil units that serve this area. At the end of an occupied
period, initiate unoccupied mode.
3. Warm-up Mode: Use an optimal start strategy to initiate the warm-up start time.
Base optimal start strategy upon outdoor air temperature and average zone
temperature within the isolation area. If the average zone temperature is less than
69°F (adjustable) at the projected start of the warm-up period, initiate the warmup mode. The optimal start period should pre-heat the building so that the average
zone temperature is 70°F (adjustable) by the occupied period. If building warmup is required, enable the fan coil units. Leave the chilled water valve closed (or
in bypass), and leave the general exhaust fans off. Enable the central heating plant
but leave the central cooling disabled. After the average zone temperature has
risen above 70°F (adjustable), terminate the warm-up cycle, and initiate occupied
mode.
4. Cool-down Mode: Use an optimal start strategy to initiate the cool-down start
time. Base the optimal start strategy upon outdoor air temperature and average
zone temperature within the isolation area. If the average zone temperature is
greater than 79°F (adjustable) at the projected start of the cool-down period,
initiate the cool-down mode. The optimal start period should pre-cool the building
so that the average zone temperature is 78°F (adjustable) by the occupied period.
If a cool-down cycle is required, enable the fan coil units and leave the general
exhaust fans off. Enable the chilled water system but leave the central heating
disabled. After the average zone temperature has dropped below 78°F
(adjustable), terminate the cool-down cycle and initiate occupied mode.
Four Pipe Fan Coil Units
28
Cx Assistant’s Sequence of Operation
April 2004
5. Night Setback/Setup Mode: During an unoccupied period, start the fan coil units
in the warm-up or cool-down mode if a zone temperature falls below the
unoccupied heating setpoint or rises above the unoccupied cooling setpoint. End
the setback/setup mode when the zones are below/above their unoccupied
setpoints.
6. Unoccupied Mode: During unoccupied periods, disable the fan coil units, close
their chilled water valves (or put them in bypass), and close their hot water valves
(or put them in bypass). Cancel calls for central plant cooling and heating. When a
thermostat override button is depressed during unoccupied period, operate the
isolation area in occupied mode for one hour as follows:
Operate the fan coil units in the isolation area in occupied mode except for the
general exhaust fans (leave them off). Enable the central plant.
Chilled Water System
1. Cooling Mode Enable/Disable: When building comfort cannot be maintained, the
fan coil units call for supplementary cooling by sending a cooling request to the
central plant. When all of the FCU chilled water valve positions fall below 5%
full open, cancel the call for cooling and initiate chiller shutdown.
2. Secondary Chilled Water Pump Enable: When the BAS registers a call for central
plant cooling, enable both the secondary chilled water pumps by a start-stop
command from the BAS. Initially, start the pumps at 10% speed. Proof the start of
both of the pumps after 5 seconds. Modulate the speed of the pumps in order to
maintain a differential pressure setpoint of 15 PSID (adj.) at the central plant.
Inhibit starting of the primary pumps and chiller if both pumps fail to prove
running status or fail while running. When the commanded speed falls below
40%, disable the lag pump. When the commanded speed rises above 60%, enable
the lag pump. When they are both enabled, lead and lag pumps should run at the
same speed.
3. Primary Chilled Water Pump Enable (Chiller Initiation): When the BAS registers
a call for central plant cooling, determine the lead chiller as indicated below.
Open the chilled water isolation valve to the lead chiller. If the valve has not
proofed open after 30 seconds, close the valve and enable and start the lag chiller.
Repeat valve operation with lag chiller. If both valves fail to open, initiate chiller
shutdown operation and send equipment specific critical alarm (“CH-1 CHW
Isolation Valve Failed to Open”) to operator workstation. If valve proofs open,
enable the primary chilled water pump dedicated to the lead chiller. After 30
seconds, proof flow. If the flow is not proved by a differential pressure switch,
disable the pump, close the valve and set the lag chiller as the lead chiller. If both
pumps fail to provide flow, initiate the chiller shutdown operation. If either pump
fails, send equipment specific critical alarms to the operator workstation.
4. Chiller Enable: Upon proof of primary chilled water and condenser water flow,
enable the selected chiller. A hard-wired flow switch will act as a back up to
ensure that chiller only starts with chilled water flow. Set the chilled water
Four Pipe Fan Coil Units
29
Cx Assistant’s Sequence of Operation
5.
6.
7.
8.
April 2004
temperature supply temperature to 45° F (adjustable). After 30 seconds, prove
chiller operation by means of a hard-wired current switch. If the chiller fails to
prove operation, initiate its shutdown sequence. Then, enable the lag chiller and
it’s primary pump. If both chillers fail to proof, send an equipment specific alarm
(“Chillers Failed”) to the operator workstation. During operation, use the chillers
internal safeties to cause an alarm and shut down the machine. If the chiller does
not develop at least a 3°F temperature difference after 15 minutes of being proved
on, initiate an alarm on the operator work station. Operate the chillers and their
associated primary pumps lead/lag. Swap the lead and lag chillers (as well as their
primary pumps) on Sunday at 3:00 AM as long as the lead chiller has operated at
least 40 hours and all equipment are disabled.
Chiller Staging: If the chilled water return temperature rises to 12°F (adjustable)
above the chilled water setpoint, enable lag chiller operation and start the chiller.
Run both chillers until the chilled return temperature falls to 5°F above the chilled
water setpoint. At this point, initiate the lag chiller shutdown sequence. Continue
running the lead chiller until the chilled water return temperature falls to the
setpoint minus the deadband.
Chiller Shutdown: Upon a call from the BAS or an internal chiller alarm, initiate
chiller shutdown. Disable the chiller but continue to run the primary pump and the
condenser water pump serving the chiller for 5 minutes. After 5 minutes, disable
the pumps and close the chiller’s isolation valves. If no other chiller is enabled,
initiate the condenser water system shutdown and shutoff the secondary water
pumps. Use a timer in the BAS to keep the chiller from cycling on and off more
often than every 5 minutes [this may be redundant to the chiller’s internal
safeties].
Chiller Safeties: Initiate chiller shutdown if the BAS senses low chilled water
flow, low condenser water flow, low chilled water temperature (less than 38° F),
or high condenser water temperature (over 90° F). Initiate an equipment specific
alarm at the operator workstation.
Chilled Water System Outdoor Air Temperature Lockout: If the outdoor air
temperature falls below 63° F (adjustable), lock out the chilled water system such
that the chillers and chilled water pumps do not run. If the outdoor air temperature
rises above 65° F (adjustable) for 20 minutes (adjustable), enable the chilled water
system.
Condenser Water System
1. Chemical Treatment: Provide chemical treatment for the cooling towers via an
automatic chemical feed and bleed system. Run the water treatment system
independently of the BAS.
2. Safeties: Disable the condenser water pump and the chiller operation if the water
level in the cooling tower basin falls below the minimum. Initiate an equipment
specific alarm (“Low Water Level in CT-1”) at the operator workstation.
3. Condenser Water Pump Enable: When the BAS registers a call for cooling from
the central plant, enable the lead condenser water pump. Prove condenser water
Four Pipe Fan Coil Units
30
Cx Assistant’s Sequence of Operation
April 2004
flow within 30-seconds (adjustable) using a differential pressure switch. If the
flow is not proved, disable the pump, and enable and start the lag pump. Send
equipment specific critical alarm (“CWP-1 Failed”) to the operator workstation.
The lag pump is also enabled by the start-up of the lag chiller. If both pumps fail
to provide flow, initiate chiller shutdown operation and initiate a critical alarm
(“Condenser Water Pumps failed”) to the operator workstation. Swap the lead and
lag pumps on Sunday at 3:00 AM as long as the lead pump has operated at least
40 hours and both pumps are shut down.
4. Condenser Water Temperature Control: Prior to operation of the condenser water
pump, the cooling tower bypass valve should be in the bypass position (bypassing
the cooling towers) and the cooling tower fans shut off. Once condenser water
flow is proved, operate the cooling tower fan and bypass valve in order to
maintain a condenser water supply setpoint between 75° F and 85° F. Modulate
the condenser water bypass valve so that at 80° F condenser water supply
temperature, the water is not bypassing the cooling tower. Start both cooling
tower fans at minimum speed when the water temperature increases to 82°F.
Modulate the tower fans speed as necessary to maintain the setpoint temperature.
If the temperature exceeds the high limit of 90° F, initiate the chiller shutdown
sequence and send an equipment specific alarm (“Condenser Water High Limit
Temperature”) to the operator workstation. As the temperature falls below 82 ° F,
disable the fans and modulate the bypass valve to maintain setpoint temperature.
If the condenser supply temperature falls below the low limit of 70° F after
running for 5 minutes, initiate the chiller shutdown sequence and send an
equipment specific alarm (“Condenser Water Low Limit Temperature”) to the
operator workstation.
5. Condenser Water System Shutdown: When the lag chiller is shutdown, disable the
lag chilled water pump after a 5 minute run time. Adjust the condenser water fan
speed and bypass valve positions to maintain temperature as indicated elsewhere.
When the lead chiller is shutdown, run the lead condenser water pump for 5
minute. Then disable the cooling tower fans, disable the lead pump, and modulate
the bypass valve to full bypass.
Heating Hot Water System
1. Heating Mode Enable: Generate a call for heating from zone controllers if any of
the zone valve positions is greater than 10% (adjustable) of full open until all are
below 5% (adjustable).
2. Secondary Hot Water Pump Enable: When the BAS registers a call for central
plant heating, enable both the secondary hot water pumps by a start-stop
command from the BAS. Initially, start the pumps at 10% speed. Proof the start of
both of the pumps after 15 seconds using a differential pressure switch. Modulate
the speed of the pumps in order to maintain a pressure drop of 10 PSID at the hot
water using a differential pressure transmitter. Inhibit starting of the primary
pumps and boiler if both pumps fail to prove running status or fail while running.
When the commanded speed falls below 40%, disable the lag pump. When the
commanded speed rises above 60%, enable the lag pump. If either pump fails to
Four Pipe Fan Coil Units
31
Cx Assistant’s Sequence of Operation
3.
4.
5.
6.
7.
April 2004
start, initiate an equipment specific critical alarm at the operator workstation.
When they are both enabled, lead and lag pumps should run at the same speed.
Primary Hot Water Pump Enable (Boiler Initiation): Open the lead boiler’s
isolation valves. If the valve opening fails to proof within 30-seconds, close the
valve, enable the lag boiler, and send an equipment specific alarm (“B-1 Isolation
Valve Failed to Open”) to the operator workstation. If valve opening is successful,
enable the primary hot water pump dedicated to the lead boiler. If the flow is not
proved within 30 seconds, disable the pump, close the valve and set the lag boiler
as the lead boiler. If both valves fail to open, initiate boiler shutdown operation
and send equipment specific alarms to the operator workstation. If both pumps
fail to provide flow, initiate boiler shutdown operation and send equipment
specific alarms to the operator workstation. After 40 hours of operation, on
Sunday at 3:00 AM when both boilers and pumps are shut down, swap the lead
and lag pumps.
Boiler Enable: Upon proof of primary hot water flow, enable the selected boiler.
Use a hard-wired flow switch as a back up to ensure that boiler only starts with
hot water flow. Send an initial hot water temperature of 180° F to the boiler
controller. After 60 seconds, prove boiler operation by means of a hard-wired
current switch. Operate the boilers lead/lag. After 40 hours of operation, on
Sunday at 3:00 AM when both boilers and pumps are shut down, swap the lead
position. Enable the lag boiler to start. If either or both boilers fail to prove or fail
to proof when required to operate, initiate boiler shutdown and send equipment
specific alarms to the operator workstation. During operation, use the boiler’s
internal safeties to initiate an equipment alarm at the operator workstation and
disable the machine. If the boiler does not develop at least a 3°F temperature
difference after 15 minutes of being enabled initiate a equipment specific alarm at
the operator workstation.
Boiler Staging: Modulate internal boilers controls between the boiler’s two stages
to meet the BAS water loop setpoint. If during boiler operation, the hot water
temperature differential falls to 5°F (adjustable), initiate the lag boiler operation.
Continue to run both boilers until the hot water temperature differential rises to
12° F. At this point, initiate the lag boiler shutdown sequence.
Boiler Shutdown: When all calls for central plant heating are cancelled or an
internal alarm occurs, initiate boiler shutdown. Provide the BAS with redundant
sensors for hot water flow, hot water temperature Hi Limit (more than 200° F).
Disable operation of the affected boiler(s) if the limits are exceeded. If both
boilers trip or fail to proof, initiate an equipment specific alarm at the operator
workstation. Prevent the boiler from cycling on and off more often than once
every 5 minutes (this may be redundant to the boiler’s internal safeties). For each
boiler, disable the boiler before shutting down its pump. After disabling the
boiler, run the primary boiler pump serving the boiler for 5 minutes. After 5
minutes, shut down the primary boiler pump and close the hot water isolation
valves. If no other boiler is enabled, shut off the secondary water pumps.
Hot Water System Outdoor Air Temperature Lockout: If the outdoor air
temperature rises above 75° F (adjustable), lock out the hot water system so the
Four Pipe Fan Coil Units
32
Cx Assistant’s Sequence of Operation
April 2004
boilers and hot water pumps do not run. If the outdoor air temperature falls below
70° F (adjustable) for 20 minutes (adjustable), enable the hot water system.
Points Table
Key:
X Indicates type of point (only 1 point is needed)
n Indicates type of point (1 point is needed for each zone – a total of “n” points are
needed for this line item)
B boiler
DB dry-bulb
CH chiller or chilled (i.e. CHW = chilled water)
Cmd command
COV change of value
CT cooling tower
FCU Fan coil unit
OA outside air (OAT = outside air temperature)
P pump (PP = primary pump, SP = secondary pump)
R return (RAT = return air temperature)
S supply (SAT = supply air temperature)
SL secondary loop
W water (CW = condenser water, HW = hot water)
Resolution of analog inputs:
°F 0.1
psid 0.005 ” water
cfm 1
Four Pipe Fan Coil Units
33
Cx Assistant’s Sequence of Operation
April 2004
rpm 1
kW 0.1
% 0.1
Point Name
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
Interval Show
on
or
Graphic
COV
OA DB
Temp
X
15
X
CHW
Lockout
Temp
X
COV
0.5,15
X
HHW
Lockout
Temp
X
COV
0.5,15
X
X1
15
X
CHWS Temp X1
>60
when
CH
15
flow
after 1
minute,
<38
X
CHWR
Temp
CHW SL
Pressure
Drop
Setpoint
CHW SL
Pressure
Drop
=Cmd
COVX
after 1
10%,15
minute
X
CHWSP-n
Enable
n1
CHWSP-n
Override
CHWSP-n
Status
COVX
10%,15
X
COV
X
COV
X
Proof
after 1 COV
minute
X
n
n1
CHWSP-n
Four Pipe Fan Coil Units
n
>1000
COV 1
34
Cx Assistant’s Sequence of Operation
Point Name
April 2004
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
Interval Show
on
or
Graphic
COV
Runtime
CHWSP-n
Cycle
Counter
n
CHWSP-n
Cmd Speed
CHWSP-n
Run Speed
>6
hour
COV
n
=Cmd
COVX
after 1
10%,15
minute
n
CHWSP-n
Alarm
n
CHWSP-n
Power
n
CHWSP
Lead/Lag
X
X
COV
X
n1
15
X
CH-n Outlet
Temp
n1
>60
when
call for 15
cooling,
<38
X
CH Setpoint
Temp
X
COV
CH Staging
Setpoint
Temp
X
COV
CH Staging
Deadband
Temp
X
COV
CH-n Inlet
Temp
CH-n CHW
Isolation
Valve Cmd
CH-n CHW
Isolation
Valve
Feedback
n1
n1
Four Pipe Fan Coil Units
COV
COV
X
35
Cx Assistant’s Sequence of Operation
Point Name
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
CH-n CW
Isolation
Valve Cmd
CH-n CW
Isolation
Valve
Feedback
April 2004
n1
COV
n1
CH-n Alarm
n
n1
CH-n Enable
Interval Show
on
or
Graphic
COV
CH-n
Override
n
COV
X
COV
X
COV
X
COV
X
CH-n CHW
flow status
n1
COV
X
CH-n CW
flow status
n1
COV
X
Proof
after 1 COV
minute
X
1
CH-n Status
n
CH-n Chiller
Runtime
CH-n ReStart Timer
n
>1000
n
5
Minutes
to restart
CH-n Cycle
Counter
n
CH Lead/Lag
X
CHWPP-n
Enable
X
COV
X
COV
X
Proof
after 1 COV
minute
X
n
n1
CHWPP-n
Runtime
Four Pipe Fan Coil Units
n
COV
COV
n1
CHWPP-n
Override
CHWPP-n
Status
>6
hour
COV 1
>1000
COV 1
36
Cx Assistant’s Sequence of Operation
Point Name
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
CHWPP
Lead/Lag
CWR Temp
CWS Temp
X
Interval Show
on
or
Graphic
COV
COV
X
X1
15
X
X1
>87 , <
72
when
15
flowing
for 5
minutes
X
CWP-n
Enable
n1
CW-n
Override
COV
X
COV
X
Proof
after 1 COV
minute
X
n
CWP-n
Status
n
1
CWP-n
Runtime
n
CWP
Lead/Lag
>1000
X
CW Bypass
Cmd
CW Bypass
Feedback
April 2004
COV 1
COV
COVX
10%,15
X
=Cmd
COVX
after 1
10%,15
minute
X
CW Temp
Set point
X
COV0.5,15
CW
Minimum
Temp
X
COV
CW
Maximum
Temp
X
COV
CW Temp
Set point
deadband
X
COV
Four Pipe Fan Coil Units
X
X
37
Cx Assistant’s Sequence of Operation
Point Name
April 2004
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
CW Valve
Set point
Temp
X
CT-n Alarm
COV
n
CT-n Enable
n
1
n
CT-n Power
n
CT-n
Runtime
n
COV
X
COV
X
Proof
after 1 COV
minute
X
15
CT-n Cycle
Counter
n
CT Lead/Lag
X
CT-n Low
Water Alarm
n
X1
Four Pipe Fan Coil Units
>6
hour
COV
COV
X
COV
X
X
=Cmd
COVX
after 1
10%,15
minute
X
HWSP-n
override
COV 1
X
COVX
10%,15
X
HWSP-n
Enable
>1000
>180 or
<110
when
15
CH
flow
after 1
minute
HW SL
Pressure
Drop
Setpoint
HW SL
Pressure
Drop
X
n
CT-n Status
HWS Temp
COV
1
CT-n
Override
Interval Show
on
or
Graphic
COV
n1
n
COV
X
COV
X
38
Cx Assistant’s Sequence of Operation
Point Name
April 2004
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
HWSP-n
Status
Proof
after 1 COV
minute
n1
HWSP-n
Runtime
n
HWSP-n
Cycle
Counter
HWSP-n
Cmd Speed
Interval Show
on
or
Graphic
COV
n
>1000
COV 1
>6
hour
COV
X
n1
=Cmd
COVX
after 1
10%,15
minute
HWSP-n Run
n
Speed
HWSP
Lead/Lag
X
B-n Inlet
Temp
n
COV
X
15
X
>190 or
<110
when
15
CH
flow
after 1
minute
X
B-n Outlet
Temp
n1
B Setpoint
Temp
X
COV
B Staging
Setpoint
Temp
X
COV
B Staging
Deadband
Temp
X
COV
B-n Isolation
Valves
n1
B-n Alarm
B-n Enable
Four Pipe Fan Coil Units
COV
n
n1
COV
X
COV
X
39
Cx Assistant’s Sequence of Operation
Point Name
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
B-n HW
Isolation
Valve Cmd
B-n HW
Isolation
Valve
Feedback
n1
n1
n
B-n Re-Start
Timer
COV
X
COV
X
Proof
after 1 COV
minute
X
n
>1000
n
5
Minutes
to restart
B-n Cycle
Counter
n
B Lead/Lag
X
HWPP-n
Enable
>6
hour
HWPP-n
Runtime
n
HWPP
Lead/Lag
COV
X
COV
X
Proof
after 1 COV
minute
X
>1000
X
n1
FCU-n
Operating
Four Pipe Fan Coil Units
n
COV
X
n
n1
COV 1
COV
n1
HWPP-n
Override
FCU-n Fire
Alarm
X
n
B-n Status
HWPP-n
Status
COV
n
B-n Runtime
Interval Show
on
or
Graphic
COV
COV
B-n Override
B-n HW flow
status
April 2004
COV 1
COV
X
COV
X
COV
X
40
Cx Assistant’s Sequence of Operation
Point Name
April 2004
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
Interval Show
on
or
Graphic
COV
Mode
FCU-n Mode
Override
FCU-n SAT
n
15
X
COV
X
Proof
after 1 COV
minute
X
n1
FCU-n
Supply Fan
Status
n
1
FCU-n
Supply Fan
Runtime
n
FCU-n
CHWV
Bypass Cmd
>1000
COV 1
COVX
10%,15
n
=Cmd
COVX
after 1
10%,15
minute
n
FCU-n
HHWV
Bypass Cmd
FCU-n
HHWV
Bypass
Feedback
X
n
FCU-n
Supply Fan
Enable
FCU-n
CHWV
Bypass
Feedback
COV
COVX
10%,15
n
=Cmd
COVX
after 1
10%,15
minute
n
FCU-n
Warm-up
Mode Low
Temp
Setpoint
n
COV
X
FCU-n CoolDown Mode
High Temp
Setpoint
n
COV
X
FCU-n Call
Four Pipe Fan Coil Units
n
COV
41
Cx Assistant’s Sequence of Operation
Point Name
April 2004
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
Interval Show
on
or
Graphic
COV
for Heating
FCU-n Call
for Cooling
n
FCU-n Space
Temperature n
Sensor
COV
COV0.5,15
X
FCU-n Space
Temperature
SetpointCooling
n
COV
X
FCU-n Space
Temperature
SetpointHeating
n
COV
X
FCU-n Space
Temperature
Unoccupied
SetpointCooling
n
COV
X
FCU-n Space
Temperature
Unoccupied
SetpointHeating
n
COV
X
FCU-n Space
Temperature
SetpointDeadband
n
COV
X
1 When a gateway is used to integrate controls, these points shall be hardwired to the
DDC system.
Four Pipe Fan Coil Units
42
Cx Assistant’s Sequence of Operation
April 2004
Notes:
The system consists of Primary/Secondary chilled and hot water loops, multiple air handling units (AHUs), and 1 single
duct constant air volume (CAV) terminal unit for each zone in the building. The CAV units provide conditioned air to the
occupied space and, at the perimeter of the building, they include a hot water coil and automatic two-way valve to reheat the main supply air. Each AHU has a constant volume supply fan, a chilled water cooling coil, and an outdoor air
damper with a 2-position actuator. Barometric relief dampers maintain building pressurization and allow building air to
be exhausted outside. The chilled water loop includes air-cooled chillers and variable speed secondary chilled water
pumps. The hot water loop includes two-stage boilers and variable speed secondary hot water pumps. A building
automation system (BAS) controls the HVAC equipment.
Appropriate reference in the specifications should be made for products that are integrated with these sequences
including chillers, boilers, and the like.
Controls: Furnish control device with an interface for monitoring and control of points specified in the points table. The
points table includes the minimum acceptable list of interface points. The selected component controls shall easily
integrate into the BAS and allow for the collection, control, trending, and archiving of the specified points with a minimal
need for intermediary gateways or hardwired connections to link control systems together. Interoperable control
systems are preferred.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
CONSTANT-AIR VOLUME (CAV) UNITS WITH A CENTRAL PLANT, AIR
COOLED CHILLERS
Constant Air Volume Units with Central Plant
43
Cx Assistant’s Sequence of Operation
April 2004
SEQUENCES OF OPERATION
Air Handling Units (AHUs)
1. Occupied Periods (Normal operation): When an isolation area is scheduled to be
occupied, operate the air handling unit that serves it. These scheduled periods are
considered “occupied periods”.
2. Unoccupied Periods: All hours not included in an occupied period are part of an
“unoccupied period”. During these periods, the system is available for tenant calls
as needed but is not running unless commanded. The following holidays are
considered to be unoccupied periods: New Years Day, Memorial Day, Fourth of
July, Labor Day, Thanksgiving and the following day, Christmas. These should
be set up as re-occurring holidays for each zone.
3. Fan Operation: Run the unit fans in all modes except unoccupied mode. Open the
minimum outside air dampers when the supply fan is running. Proof the supply
fan using an external current switch (CS).
4. Fire Alarm: Interface system with the fire alarm controls. When the fire alarm
control initiates a fire alarm, shut down the supply fan by a hardwired contact
interface. Simultaneously, the fire alarm control must notify the BAS of the fire
event to enable the BAS to disable the affected units. Once the fire alarm is reset,
enable the affected unit(s) to resume normal operation.
5. Duct Pressure Safety: If negative static pressure over 2” WC is measured in the
mixed air plenum or positive supply duct static pressure over 3” WC is measured
in the supply duct, disable the fan via a hard wired interlock and initiate an
equipment specific alarm (i.e. “AH-3 High Static Pressure” or “AH-2 Low Static
Pressure”) at the operator workstation. An operator must reset each fan’s
differential pressure switch before the fans may be re-enabled. Provide a local or
BAS reset for this purpose.
6. Supply Air Temperature Control: The chilled water valve modulates to maintain
the supply air temperature when at least one zone serves by the unit is calling for
cooling. The supply air temperature setpoint is 55° F (adjustable). When the valve
opens more than 30% (adj.), send a call for cooling to the central plant. When the
valve closes to 5% (adj.), cancel the call for cooling. If no zones are calling for
cooling, close the chilled water valve.
7. Filter Status: Whenever the supply fan is running, send an equipment specific
alarm (“AH-1 Dirty Filter”) to the operator workstation if the differential pressure
over the filter exceeds 150% (adjustable) of the its design value.
Isolation Areas
1. Isolation Areas: There are XX isolation areas as indicated on the plans. Each area
is composed of 1 or more spaces served by 1 or more CAV terminal units that are
operated together. Configure each isolation area separately from other isolation
areas. Configuration includes scheduling and operational modes. The default
occupancy schedule is 7:00 AM to 6:00 PM, M-F.
Constant Air Volume Units with Central Plant
44
Cx Assistant’s Sequence of Operation
April 2004
NOTE: Schedule occupied start time 1 hour before the building is expected to be occupied (for Title 24 required purge).
2. Occupied Mode: Prior to an occupied period, initiate a Warm-up mode or Cooldown mode if necessary. During Occupied Mode, enable operation of the system,
including enabling the air handling unit fans that serve this area and opening the
outdoor air dampers to100% open. At the end of an occupied period, initiate
unoccupied mode.
3. Warm-up Mode: Use an optimal start strategy to initiate the warm-up start time.
Base optimal start strategy upon outdoor air temperature and average zone
temperature within the isolation area. If the average zone temperature is less than
69°F (adjustable) at the projected start of the warm-up period, initiate the warmup mode. The optimal start period should pre-heat the building so that the average
zone temperature is 70°F (adjustable) by the occupied period. If building warmup is required, enable the air handling units. Leave the chilled water valve closed
(or in bypass), and leave the general exhaust fans off. Enable the CAV unit hot
water valves to normal occupied operation. Enable the central heating plant but
leave the central cooling disabled. After the average zone temperature has risen
above 70°F (adjustable), terminate the warm-up cycle, and initiate occupied
mode.
4. Cool-down Mode: Use an optimal start strategy to initiate the cool-down start
time. Base the optimal start strategy upon outdoor air temperature and average
zone temperature within the isolation area. If the average zone temperature is
greater than 79°F (adjustable) at the projected start of the cool-down period,
initiate the cool-down mode. The optimal start period should pre-cool the building
so that the average zone temperature is 78°F (adjustable) by the occupied period.
If a cool-down cycle is required, enable the air handling units and leave the
general exhaust fans off. Enable the chilled water system but leave the central
heating and CAV hot water valves disabled. After the average zone temperature
has dropped below 78°F (adjustable), terminate the cool-down cycle and initiate
occupied mode.
5. Night Setback/Setup Mode: During an unoccupied period, start the air-handling
unit in the warm-up or cool-down mode if a zone temperature falls below the
unoccupied heating setpoint or rises above the unoccupied cooling setpoint. End
the setback/setup mode when the zones are below/above their unoccupied
setpoints.
6. Unoccupied Mode: During unoccupied periods, close CAV unit hot water valves
(or put them in bypass), disable the air handling units, close their chilled water
valves (or put them in bypass), and close their outside air damper(s). Cancel calls
for central plant cooling and heating. When a thermostat override button is
depressed during unoccupied period, operate the isolation area in occupied mode
for one hour as follows:
Operate the air handling unit in occupied mode except for the general exhaust
fans (leave them off). Enable the central plant.
CAV Zone Control
Constant Air Volume Units with Central Plant
45
Cx Assistant’s Sequence of Operation
April 2004
1. Temperature Control: Use a solid state, electronic wall temperature sensor to
adjust the zone setpoint. Set each temperature sensor for the following ranges:
a. Occupied Heating: 55° F to 73° F during occupied hours. The default is
73° F.
b. Occupied Cooling: 73° F to 85° F during occupied hours. The default is
78° F.
Maintain a deadband of at least 5° F between the heating and cooling setpoints.
During unoccupied hours, set the heating setpoint default to 55° F (adjustable)
and the cooling setpoint default to 85° F (adjustable). Provide each zone its own
adjustable unoccupied heating and cooling setpoints.
2. Zone Cooling Mode: When the zone’s temperature rises to 1°F (adjustable) above
its setpoint, send a call for cooling to the air handling unit.
3. Zone Heating Mode (Perimeter Zones Only): When the zone’s temperature falls
to 1 ° F (adjustable) below its setpoint, the zone is in heating mode. Modulate the
reheat coil control valve to satisfy the space temperature. Once the valve opens to
more than 10% (adj.), send a call for heating to the central plant. When the valve
closes to 5% (adj.), cancel the call for heating.
Chilled Water System
1. Cooling Mode Enable/Disable: When building comfort cannot be maintained, the
air handlers call for cooling by sending a cooling request to the central plant.
When all of the AHU chilled water valve positions fall below 5% full open,
cancel the call for cooling and initiate chiller shutdown.
2. Secondary Chilled Water Pump Enable: When the BAS registers a call for central
plant cooling, enable both the secondary chilled water pumps by a start-stop
command from the BAS. Initially, start the pumps at 10% speed. Proof the start of
both of the pumps after 5 seconds. Modulate the speed of the pumps in order to
maintain a differential pressure setpoint of 15 PSID (adj.) at the central plant.
Inhibit starting of the primary pumps and chiller if both pumps fail to prove
running status or fail while running. When the commanded speed falls below
40%, disable the lag pump. When the commanded speed rises above 60%, enable
the lag pump. When they are both enabled, lead and lag pumps should run at the
same speed.
3. Primary Chilled Water Pump Enable (Chiller Initiation): When the BAS registers
a call for central plant cooling, determine the lead chiller as indicated below.
Open the chilled water isolation valve to the lead chiller. If the valve has not
proofed open after 30 seconds, close the valve and enable and start the lag chiller.
Repeat valve operation with lag chiller. If both valves fail to open, initiate chiller
shutdown operation and send equipment specific critical alarm (“CH-1 CHW
Isolation Valve Failed to Open”) to operator workstation. If valve proofs open,
enable the primary chilled water pump dedicated to the lead chiller. After 30
seconds, proof flow. If the flow is not proved by a differential pressure switch,
disable the pump, close the valve and set the lag chiller as the lead chiller. If both
Constant Air Volume Units with Central Plant
46
Cx Assistant’s Sequence of Operation
4.
5.
6.
7.
8.
April 2004
pumps fail to provide flow, initiate the chiller shutdown operation. If either pump
fails, send equipment specific critical alarms to the operator workstation.
Chiller Enable: Upon proof of primary chilled water, enable the selected chiller. A
hard-wired flow switch will act as a back up to ensure that chiller only starts with
chilled water flow. Set the chilled water temperature supply temperature to 45° F
(adjustable). After 30 seconds, prove chiller operation by means of a hard-wired
current switch. If the chiller fails to prove operation, initiate its shutdown
sequence. Then, enable the lag chiller and it’s primary pump. If both chillers fail
to proof, send an equipment specific alarm (“Chillers Failed”) to the operator
workstation. During operation, use the chillers internal safeties to cause an alarm
and shut down the machine. If the chiller does not develop at least a 3°F
temperature difference after 15 minutes of being proved on, initiate an alarm on
the operator work station. Operate the chillers and their associated primary pumps
lead/lag. Swap the lead and lag chillers (as well as their primary pumps) on
Sunday at 3:00 AM as long as the lead chiller has operated at least 40 hours and
all equipment are disabled.
Chiller Staging: If the chilled water return temperature rises to 12°F (adjustable)
above the chilled water setpoint, enable lag chiller operation and start the chiller.
Run both chillers until the chilled return temperature falls to 5°F above the chilled
water setpoint. At this point, initiate the lag chiller shutdown sequence. Continue
running the lead chiller until the chilled water return temperature falls to the
setpoint minus the deadband.
Chiller Shutdown: Upon a call from the BAS or an internal chiller alarm, initiate
chiller shutdown. Disable the chiller but continue to run the primary pump serving
the chiller for 5 minutes. After 5 minutes, disable the pump and close the chiller’s
isolation valves. If no other chiller is enabled, shutoff the secondary water pumps.
Use a timer in the BAS to keep the chiller from cycling on and off more often
than every 5 minutes [this may be redundant to the chiller’s internal safeties].
Chiller Safeties: Initiate chiller shutdown if the BAS senses low chilled water
flow or low chilled water temperature (less than 38° F). Initiate an equipment
specific alarm at the operator workstation.
Chilled Water System Outdoor Air Temperature Lockout: If the outdoor air
temperature falls below 63° F (adjustable), lock out the chilled water system such
that the chillers and chilled water pumps do not run. If the outdoor air temperature
rises above 65° F (adjustable) for 20 minutes (adjustable), enable the chilled water
system.
Heating Hot Water System
1. Heating Mode Enable: Generate a call for heating from zone controllers if
any of the zone valve positions is greater than 10% (adjustable) of full
open until all are below 5% (adjustable).
2. Secondary Hot Water Pump Enable: When the BAS registers a call for
central plant heating, enable both the secondary hot water pumps by a
start-stop command from the BAS. Initially, start the pumps at 10% speed.
Constant Air Volume Units with Central Plant
47
Cx Assistant’s Sequence of Operation
3.
4.
5.
6.
April 2004
Proof the start of both of the pumps after 15 seconds using a differential
pressure switch. Modulate the speed of the pumps in order to maintain a
pressure drop of 10 PSID at the hot water using a differential pressure
transmitter. Inhibit starting of the primary pumps and boiler if both pumps
fail to prove running status or fail while running. When the commanded
speed falls below 40%, disable the lag pump. When the commanded speed
rises above 60%, enable the lag pump. If either pump fails to start, initiate
an equipment specific critical alarm at the operator workstation. When
they are both enabled, lead and lag pumps should run at the same speed.
Primary Hot Water Pump Enable (Boiler Initiation): Open the lead boiler’s
isolation valves. If the valve opening fails to proof within 30-seconds,
close the valve, enable the lag boiler, and send an equipment specific
alarm (“B-1 Isolation Valve Failed to Open”) to the operator workstation.
If valve opening is successful, enable the primary hot water pump
dedicated to the lead boiler. If the flow is not proved within 30 seconds,
disable the pump, close the valve and set the lag boiler as the lead boiler.
If both valves fail to open, initiate boiler shutdown operation and send
equipment specific alarms to the operator workstation. If both pumps fail
to provide flow, initiate boiler shutdown operation and send equipment
specific alarms to the operator workstation. After 40 hours of operation,
on Sunday at 3:00 AM when both boilers and pumps are shut down, swap
the lead and lag pumps.
Boiler Enable: Upon proof of primary hot water flow, enable the selected
boiler. Use a hard-wired flow switch as a back up to ensure that boiler
only starts with hot water flow. Send an initial hot water temperature of
180° F to the boiler controller. After 60 seconds, prove boiler operation by
means of a hard-wired current switch. Operate the boilers lead/lag. After
40 hours of operation, on Sunday at 3:00 AM when both boilers and
pumps are shut down, swap the lead position. Enable the lag boiler to start.
If either or both boilers fail to prove or fail to proof when required to
operate, initiate boiler shutdown and send equipment specific alarms to the
operator workstation. During operation, use the boiler’s internal safeties to
initiate an equipment alarm at the operator workstation and disable the
machine. If the boiler does not develop at least a 3°F temperature
difference after 15 minutes of being enabled initiate a equipment specific
alarm at the operator workstation.
Boiler Staging: Modulate internal boilers controls between the boiler’s
two stages to meet the BAS water loop setpoint. If during boiler operation,
the hot water temperature differential falls to 5°F (adjustable), initiate the
lag boiler operation. Continue to run both boilers until the hot water
temperature differential rises to 12° F. At this point, initiate the lag boiler
shutdown sequence.
Boiler Shutdown: When all calls for central plant heating are cancelled or
an internal alarm occurs, initiate boiler shutdown. Provide the BAS with
redundant sensors for hot water flow, hot water temperature Hi Limit
Constant Air Volume Units with Central Plant
48
Cx Assistant’s Sequence of Operation
April 2004
(more than 200° F). Disable operation of the affected boiler(s) if the limits
are exceeded. If both boilers trip or fail to proof, initiate an equipment
specific alarm at the operator workstation. Prevent the boiler from cycling
on and off more often than once every 5 minutes (this may be redundant to
the boiler’s internal safeties). For each boiler, disable the boiler before
shutting down its pump. After disabling the boiler, run the primary boiler
pump serving the boiler for 5 minutes. After 5 minutes, shut down the
primary boiler pump and close the hot water isolation valves. If no other
boiler is enabled, shut off the secondary water pumps.
7. Hot Water System Outdoor Air Temperature Lockout: If the outdoor air
temperature rises above 75° F (adjustable), lock out the hot water system
so the boilers and hot water pumps do not run. If the outdoor air
temperature falls below 70° F (adjustable) for 20 minutes (adjustable),
enable the hot water system.
Points Table:
Key:
X Indicates type of point (only 1 point is needed)
n Indicates type of point (1 point is needed for each zone – a total of “n” points
are needed for this line item)
AHU air handling unit
B boiler
CH chiller or chilled (i.e. CHW = chilled water)
Cmd command
COV change of value
DB dry-bulb
CAV constant air volume terminal unit
OA outside air (OAT = outside air temperature)
P pump (PP = primary pump, SP = secondary pump)
R return (RAT = return air temperature)
S supply (SAT = supply air temperature)
Constant Air Volume Units with Central Plant
49
Cx Assistant’s Sequence of Operation
April 2004
SL secondary loop
Temp temperature
W water (CHW = chilled water, HW = hot water)
Resolution of analog inputs:
°F 0.1
psid 0.005 ” water
cfm 1
rpm 1
kW 0.1
% 0.1
Analog Digital
Other
Alarm
Point Name AI AO DI DO Software Software
Software Logic
Value
Value
OA DB
Temp
X
Interval Show
on
or
Graphic
COV
15 X
CHW
Lockout
Temp
X
COV
0.5,15
X
HHW
Lockout
Temp
X
COV
0.5,15
X
CHWR
Temp
CHWS
Temp
CHW SL
Pressure
Drop
Setpoint
X1
15 X
>60
when
CH
flow
after 1
minute,
<38
X1
X
Constant Air Volume Units with Central Plant
15 X
COVX
10%,15
50
Cx Assistant’s Sequence of Operation
CHW SL
Pressure
Drop
April 2004
=Cmd
after 1
minute
X
CHWSP-n
Enable
n1
CHWSP-n
Override
n1
CHWSP-n
Runtime
n
CHWSP-n
Cycle
Counter
CHWSP-n
Cmd Speed
COV
X
COV
X
Proof
after 1
minute
COV
X
>1000
COV 1
>6
hour
COV
n
CHWSP-n
Status
n
COVX
10%,15
n
CHWSP-n
Alarm
n
CHWSP
Lead/Lag
X
CH-n Inlet
Temp
COV
n1
15 X
>60
when
call for
cooling,
<38
CH-n
Outlet
Temp
n1
CH
Setpoint
Temp
X
COV
CH Staging
Setpoint
Temp
X
COV
CH Staging
Deadband
Temp
X
COV
CH-n CHW
Isolation
Valve Cmd
n1
Constant Air Volume Units with Central Plant
X
15 X
COV
51
Cx Assistant’s Sequence of Operation
CH-n CHW
Isolation
Valve
Feedback
April 2004
n1
COV
X
COV
X
COV
X
COV
X
COV
X
Proof
after 1
minute
COV
X
n
>1000
COV 1
n
5
Minutes
to restart
CH-n
Alarm
n
CH-n
Alarm Text
n
CH-n
Enable
n1
CH-n
Override
n
CH-n
Status
n1
CH-n
Chiller
Runtime
CH-n ReStart Timer
CH-n Cycle
Counter
n
CH
Lead/Lag
X
CHWPP-n
Enable
CHWPP-n
Runtime
X
COV
X
COV
X
Proof
after 1
minute
COV
X
>1000
COV 1
n
n1
n
CHWPP
Lead/Lag
HWS Temp X1
Constant Air Volume Units with Central Plant
COV
COV
n1
CHWPP-n
Override
CHWPP-n
Status
>6
hour
X
COV
>180 or
<110
X
15 X
52
Cx Assistant’s Sequence of Operation
April 2004
when B
flow
after 1
minute
HW SL
Pressure
Drop
Setpoint
HW SL
Pressure
Drop
=Cmd
after 1
minute
X
HWSP-n
Enable
n1
HWSP-n
override
n1
HWSP-n
Runtime
n
HWSP-n
Cycle
Counter
n
X
COV
X
Proof
after 1
minute
COV
X
>1000
COV 1
>6
hour
COV
n1
HWSP-n
Alarm
n
HWSP
Lead/Lag
X
B-n Inlet
Temp
COVX
10%,15
COV
n
HWSP-n
Status
HWSP-n
Cmd Speed
COVX
10%,15
X
COV
n
15 X
>190 or
<110
when B
flow
after 1
minute
B-n Outlet
Temp
n1
B Setpoint
Temp
X
COV
B Staging
X
COV
Constant Air Volume Units with Central Plant
X
15 X
53
Cx Assistant’s Sequence of Operation
April 2004
Setpoint
Temp
B Staging
Deadband
Temp
X
B-n Alarm
COV
n
B-n Alarm
Text
n
COV
X
COV
X
X
B-n Enable
n1
COV
B-n HW
Isolation
Valve Cmd
n1
COV
B-n HW
Isolation
Valve
Feedback
n1
COV
X
COV
X
Proof
after 1
minute
COV
X
n
>1000
COV 1
n
5
Minutes
to restart
B-n
Override
n
B-n Status
n
B-n
Runtime
B-n ReStart Timer
B-n Cycle
Counter
n
B Lead/Lag
X
HWPP-n
Enable
HWPP-n
Runtime
X
COV
X
COV
X
Proof
after 1
minute
COV
X
>1000
COV 1
n
n1
n
Constant Air Volume Units with Central Plant
COV
COV
n1
HWPP-n
Override
HWPP-n
Status
>6
hour
54
Cx Assistant’s Sequence of Operation
April 2004
HWPP
Lead/Lag
X
AHU-n
Fire Alarm
n1
AHU-n
Operating
Mode
n
AHU-n
Mode
Override
n
COV
X
COV
X
COV
X
COV
X
AHU-n
SAT
n
15 X
AHU-n
OAT
n
15 X
AHU-n OA
Damper
Cmd
n
COVX
10%,15
AHU-n
Supply Fan
Enable
n1
COV
X
COV
X
AHU-n
Supply Fan
Status
AHU-n
CHWV
Bypass
Cmd
Proof
after 1
minute
n1
COVX
10%,15
n
AHU-n
Warm-up
Mode Low
Temp
Setpoint
n
COV
X
AHU-n
Cool-Down
Mode High
Temp
Setpoint
n
COV
X
COV
X
AHU-n
Filter
Alarm
n
Constant Air Volume Units with Central Plant
55
Cx Assistant’s Sequence of Operation
April 2004
AHU-n
Call for
Cooling
n
COV
CAV-n
n
Zone Temp
COV0.5,15
X
CAV-n
Zone Temp
SetpointCooling
n
COV
X
CAV-n
Zone Temp
SetpointHeating
n
COV
X
CAV-n
Zone Temp
Unoccupied
SetpointCooling
n
COV
X
CAV-n
Zone Temp
Unoccupied
SetpointHeating
n
COV
X
CAV-n
Zone Temp
SetpointDeadband
n
COV
X
COV
X
CAV-n
Override
n
CAV-n
Operating
Mode
CAV-n
HW Valve
Cmd
n
n
Constant Air Volume Units with Central Plant
COV
COVX
10%,15
56
Cx Assistant’s Sequence of Operation
April 2004
Notes:
The system consists of Primary/Secondary chilled and hot water loops, multiple air handling units (AHUs), and 1 single
duct variable air volume (VAV) terminal unit for each zone in the building. The VAV units (VAV boxes) adjust the air
volume delivered to the occupied space and, at the perimeter of the building, VAV boxes include a hot water coil and
automatic two-way valve to re-heat the main supply air. Each AHU has a variable volume supply fan, a variable volume
return fan, a chilled water cooling coil, and a set of dampers that act as an airside economizer. The economizer has a 2position outdoor air damper and the return and exhaust air dampers are modulated to regulate “free” cooling. The
chilled water loop includes air-cooled chillers and variable speed secondary chilled water pumps. The hot water loop
includes two-stage boilers and variable speed secondary hot water pumps. A building automation system (BAS) controls
the HVAC equipment.
Appropriate reference in the specifications should be made for products that are integrated with these sequences
including chillers, boilers, variable frequency drives (VFDs), and the like.
Controls: Furnish control device with an interface for monitoring and control of points specified in the points table. The
points table includes the minimum acceptable list of interface points. The selected component controls shall easily
integrate into the BAS and allow for the collection, control, trending, and archiving of the specified points with a minimal
need for intermediary gateways or hardwired connections to link control systems together. Interoperable control
systems are preferred.
The system(s) in your building that are most similar to the system described above include:
•
Central VAV Air Handling Units
•
Built-Up VAV Air Handlers
•
1
•
Jail
•
123
•
vav
•
j
•
VAV system
•
System
•
System 1
•
AH-1
•
Central
•
Air Handling Unit AH-3
•
VAV retrofit
•
Jail
•
HVAC test
•
East MOB
•
AHU with air-cooled chiller
•
AHU 1
•
AC-1
•
AHU-1
•
roof
•
The Plant
•
HVAC - Enthalpy Economizer
•
HVAC - Minimum OA
Variable Air Volume Units with Air-Cooled Chiller
57
Cx Assistant’s Sequence of Operation
April 2004
Please note that this sample sequence will have to be modified to meet the exact systems defined in your building.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
VARIABLE-AIR VOLUME (VAV) UNITS WITH A CENTRAL PLANT, AIR
COOLED CHILLERS
SEQUENCES OF OPERATION
Air Handling Units (AHUs)
1. Occupied Periods (Normal operation): When an isolation area is scheduled to be
occupied, operate the air handling unit that serves it. These scheduled periods are
considered “occupied periods”
2. Unoccupied Periods: All hours not included in an occupied period are part of an
“unoccupied period”. During these periods, the system is available for tenant calls
as needed but is not running unless commanded. The following holidays are
considered to be unoccupied periods: New Years Day, Memorial Day, Fourth of
July, Labor Day, Thanksgiving and the following day, Christmas. These should
be set up as re-occurring holidays for each zone.
Variable Air Volume Units with Air-Cooled Chiller
58
Cx Assistant’s Sequence of Operation
April 2004
3. Fan Operation: Run the unit fans in all modes except unoccupied mode. Open the
minimum outside air dampers when the supply fan is running. Proof the supply
fan using an external current switch (CS). Interlock each return fan to its
respective supply fan.
4. Supply and Return Fan Capacity Control: When the fans are running, vary the
supply fan (SF) speed to maintain the supply duct static pressure setpoint. Reset
the duct pressure setpoint from 1.5” to 0.2” (adjustable) based on the damper
position of the most open VAV damper as long as that damper is at least 90%
open (In other words the static setpoint will be reset to maintain the VAV box
requiring the most static pressure at 90% open.). Vary the return fan (RF) speed to
allow the return fan to volumetrically track the supply fan by maintaining the
scheduled fixed flow offset equal to XXX CFM (adjustable) between the SF and
RF.
5. Fire Alarm: Interface system with the fire alarm controls. When the fire alarm
control initiates a fire alarm, shut down the supply and return fans by a hardwired
contact interface at each fan’s variable frequency drive (VFD) E-stop contact.
Simultaneously, the fire alarm control must notify the BAS of the fire event to
enable the BAS to disable the affected units. Once the fire alarm is reset, enable
the affected unit(s) to resume normal operation.
6. Differential Enthalpy Economizer Mode: Enable differential enthalpy economizer
mode when there is a call for cooling or ventilation, and outdoor air temperature
is 2° F less than return air temperature. Open outside air damper to 100%.
Modulate the return air and exhaust air dampers in unison and modulate the
chilled water valve, as required, to maintain supply air temperature setpoint.
Maintain the chilled water valve in the closed position when outdoor air enthalpy
is below 21 BTU/lb dry air (adjustable). When the return air enthalpy is 2 BTU/lb
dry air (adjustable deadband) above the outdoor air enthalpy, the dampers are to
be in the full exhaust position (exhaust damper fully open and return damper fully
closed). As the return enthalpy decreases below this point, the dampers transition
to a full return position (exhaust damper is closed to allow only minimum outdoor
air and the return damper is fully open).
7. Supply Air Temperature Control: Operate economizer mode dampers and chilled
water valve in conjunction to maintain the supply air temperature. When the
outside air temperature is not sufficient to provide “free” cooling, open the chilled
water valve to maintain the supply air temperature setpoint. When the valve opens
more than 30% (adj.), send a call for cooling to the central plant. When the valve
closes to 5% (adj.), cancel the call for cooling. Reset the supply air temperature
upward from 55°F to 65°F as the outdoor temperature falls from above 90° F to
below 65° F.
8. Filter Status: Establish the filter pressure drop alarm with the system in operation
at actual flow rate as follows:
Where DP 100 is the high limit pressure drop at design cfm (determine limit from
filter manufacturer) and DP x is the high limit at speed signal x (expressed as a
fraction of full supply fan signal). For instance, the setpoint at 50% of speed
Variable Air Volume Units with Air-Cooled Chiller
59
Cx Assistant’s Sequence of Operation
April 2004
would be (0.5) 1.4 or 38% of the design high limit pressure drop.
Send an equipment specific alarm (“AH-1 Dirty Filter”) to the operator
workstation at 150% (adjustable) of the value calculated during system operation.
Isolation Areas
1. Isolation Areas: There are XX isolation areas as indicated on the plans. Each area
is composed of 1 or more spaces served by 1 or more VAV terminal units that are
operated together. Configure each isolation area separately from other isolation
areas. Configuration includes scheduling and operational modes. The default
occupancy schedule is 7:00 AM to 6:00 PM, M-F.
NOTE: Schedule occupied start time 1 hour before the building is expected to be occupied (for Title 24 required purge).
2. Occupied Mode: Prior to an occupied period, initiate a Warm-up mode or Cooldown mode if necessary. During Occupied Mode, enable operation of the system,
including enabling the air handling unit fans that serve this area and opening the
outdoor air dampers to100% open. At the end of an occupied period, initiate
unoccupied mode.
3. Warm-up Mode: Use an optimal start strategy to initiate the warm-up start time.
Base optimal start strategy upon outdoor air temperature and average zone
temperature within the isolation area. If the average zone temperature is less than
69°F (adjustable) at the projected start of the warm-up period, initiate the warmup mode. The optimal start period should pre-heat the building so that the average
zone temperature is 70°F (adjustable) by the occupied period. If building warmup is required, enable the air handling units and set the return fan tracking offset
to 0. Set the economizer mode to the return position, leave the chilled water valve
closed (or in bypass), and leave the general exhaust fans off. Enable the VAV
units to normal occupied operation. Enable the central heating plant but leave the
central cooling disabled. After the average zone temperature has risen above 70°F
(adjustable), terminate the warm-up cycle, and initiate occupied mode.
4. Cool-down Mode: Use an optimal start strategy to initiate the cool-down start
time. Base the optimal start strategy upon outdoor air temperature and average
zone temperature within the isolation area. If the average zone temperature is
greater than 79°F (adjustable) at the projected start of the cool-down period,
initiate the cool-down mode. The optimal start period should pre-cool the building
so that the average zone temperature is 78°F (adjustable) by the occupied period.
If a cool-down cycle is required, enable the air handling units, command the
return fan tracking offset to 0, and leave the general exhaust fans off. Enable the
VAV units to normal occupied operation. Enable the chilled water system but
leave the central heating disabled. After the average zone temperature has
dropped below 78°F (adjustable), terminate the cool-down cycle and initiate
occupied mode.
5. Night Setback/Setup Mode: During an unoccupied period, start the air-handling
unit in the warm-up or cool-down mode if a zone temperature falls below the
unoccupied heating setpoint or rises above the unoccupied cooling setpoint. End
Variable Air Volume Units with Air-Cooled Chiller
60
Cx Assistant’s Sequence of Operation
April 2004
the setback/setup mode when the zones are below/above their unoccupied
setpoints.
6. Unoccupied Mode: During unoccupied periods, disable VAV units, disable the air
handling units, close their chilled water valves (or put them in bypass), close their
outside air damper(s) and position their return/exhaust air dampers for full return
air (no exhaust). Cancel calls for central plant cooling and heating. When a
thermostat override button is depressed during unoccupied period, operate the
isolation area in occupied mode for one hour as follows:
Operate the air handling unit in occupied mode except for the return-fan
volumetric tracking offset (set it to 0) and the general exhaust fans (leave them
off). Enable the central plant.
VAV Zone Control
1. Temperature Control: Use a solid state, electronic wall temperature sensor to
adjust the zone velocity controller setpoint. Airflow to the zone will fluctuate
between its minimum and the maximum and supply air temperature will vary in
order to maintain a constant room temperature based on this setpoint. Set each
temperature sensor for the following ranges:
a. Occupied Heating: 55° F to 73° F during occupied hours. The default is
73° F.
b. Occupied Cooling: 73° F to 85° F during occupied hours. The default is
78° F.
Maintain a deadband of at least 5° F between the heating and cooling setpoints.
During unoccupied hours, set the heating setpoint default to 55° F (adjustable)
and the cooling setpoint default to 85° F (adjustable). Provide each zone its own
adjustable unoccupied heating and cooling setpoints.
2. Zone Cooling Mode: When the zone’s temperature rises to 1°F (adjustable) above
its setpoint, the zone is in cooling mode and the VAV damper begins to modulate
open. As the temperature rises 2° F hotter than its setpoint, the VAV damper is
fully open and the zone’s airflow is increased to maximum. As the zone’s
temperature approaches the cooling setpoint, modulate the air volume toward
minimum.
3. Zone Heating Mode (Perimeter Zones Only): When the zone’s temperature falls
to 1 ° F (adjustable) below its setpoint, the zone is in heating mode and the VAV
damper modulates to minimum airflow. Once the valve opens to more than 10%
(adj.), send a call for heating to the central plant. Modulate the reheat coil control
valve to satisfy the space temperature within the reset bounds. Reset the supply air
temperature upward from 90°F to 110°F as the outdoor temperature falls from 65°
F or greater to 40° F or lower. When the valve closes to 5% (adj.), cancel the call
for heating.
Variable Air Volume Units with Air-Cooled Chiller
61
Cx Assistant’s Sequence of Operation
April 2004
Chilled Water System
1. Cooling Mode Enable/Disable: When building comfort cannot be maintained by
economizer mode outdoor air temperature, the air handlers call for supplementary
cooling by sending a cooling request to the central plant. When all of the AHU
chilled water valve positions fall below 5% full open, cancel the call for cooling
and initiate chiller shutdown.
2. Secondary Chilled Water Pump Enable: When the BAS registers a call for central
plant cooling, enable both the secondary chilled water pumps by a start-stop
command from the BAS. Initially, start the pumps at 10% speed. Proof the start of
both of the pumps after 5 seconds. Modulate the speed of the pumps in order to
maintain a differential pressure setpoint of 15 PSID (adj.) at the central plant.
Inhibit starting of the primary pumps and chiller if both pumps fail to prove
running status or fail while running. When the commanded speed falls below
40%, disable the lag pump. When the commanded speed rises above 60%, enable
the lag pump. When they are both enabled, lead and lag pumps should run at the
same speed.
3. Primary Chilled Water Pump Enable (Chiller Initiation): When the BAS registers
a call for central plant cooling, determine the lead chiller as indicated below.
Open the chilled water isolation valve to the lead chiller. If the valve has not
proofed open after 30 seconds, close the valve and enable and start the lag chiller.
Repeat valve operation with lag chiller. If both valves fail to open, initiate chiller
shutdown operation and send equipment specific critical alarm (“CH-1 CHW
Isolation Valve Failed to Open”) to operator workstation. If valve proofs open,
enable the primary chilled water pump dedicated to the lead chiller. After 30
seconds, proof flow. If the flow is not proved by a differential pressure switch,
disable the pump, close the valve and set the lag chiller as the lead chiller. If both
pumps fail to provide flow, initiate the chiller shutdown operation. If either pump
fails, send equipment specific critical alarms to the operator workstation.
4. Chiller Enable: Upon proof of primary chilled water, enable the selected chiller. A
hard-wired flow switch will act as a back up to ensure that chiller only starts with
chilled water flow. Set the chilled water temperature supply temperature to 45° F
(adjustable). After 30 seconds, prove chiller operation by means of a hard-wired
current switch. If the chiller fails to prove operation, initiate its shutdown
sequence. Then, enable the lag chiller and it’s primary pump. If both chillers fail
to proof, send an equipment specific alarm (“Chillers Failed”) to the operator
workstation. During operation, use the chillers internal safeties to cause an alarm
and shut down the machine. If the chiller does not develop at least a 3°F
temperature difference after 15 minutes of being proved on, initiate an alarm on
the operator work station. Operate the chillers and their associated primary pumps
lead/lag. Swap the lead and lag chillers (as well as their primary pumps) on
Sunday at 3:00 AM as long as the lead chiller has operated at least 40 hours and
all equipment are disabled.
5. Chiller Staging: If the chilled water return temperature rises to 12°F (adjustable)
above the chilled water setpoint, enable lag chiller operation and start the chiller.
Variable Air Volume Units with Air-Cooled Chiller
62
Cx Assistant’s Sequence of Operation
April 2004
Run both chillers until the chilled return temperature falls to 5°F above the chilled
water setpoint. At this point, initiate the lag chiller shutdown sequence. Continue
running the lead chiller until the chilled water return temperature falls to the
setpoint minus the deadband.
6. Chiller Shutdown: Upon a call from the BAS or an internal chiller alarm, initiate
chiller shutdown. Disable the chiller but continue to run the primary pump serving
the chiller for 5 minutes. After 5 minutes, disable the pump and close the chiller’s
isolation valves. If no other chiller is enabled, shutoff the secondary water pumps.
Use a timer in the BAS to keep the chiller from cycling on and off more often
than every 5 minutes [this may be redundant to the chiller’s internal safeties].
7. Chiller Safeties: Initiate chiller shutdown if the BAS senses low chilled water
flow or low chilled water temperature (less than 38° F). Initiate an equipment
specific alarm at the operator workstation.
8. Chilled Water System Outdoor Air Temperature Lockout: If the outdoor air
temperature falls below 63° F (adjustable), lock out the chilled water system such
that the chillers and chilled water pumps do not run. If the outdoor air temperature
rises above 65° F (adjustable) for 20 minutes (adjustable), enable the chilled water
system.
Heating Hot Water System
1. Heating Mode Enable: Generate a call for heating from zone controllers if any of
the zone valve positions is greater than 10% (adjustable) of full open until all are
below 5% (adjustable).
2. Secondary Hot Water Pump Enable: When the BAS registers a call for central
plant heating, enable both the secondary hot water pumps by a start-stop
command from the BAS. Initially, start the pumps at 10% speed. Proof the start of
both of the pumps after 15 seconds using a differential pressure switch. Modulate
the speed of the pumps in order to maintain a pressure drop of 10 PSID at the hot
water using a differential pressure transmitter. Inhibit starting of the primary
pumps and boiler if both pumps fail to prove running status or fail while running.
When the commanded speed falls below 40%, disable the lag pump. When the
commanded speed rises above 60%, enable the lag pump. If either pump fails to
start, initiate an equipment specific critical alarm at the operator workstation.
When they are both enabled, lead and lag pumps should run at the same speed.
3. Primary Hot Water Pump Enable (Boiler Initiation): Open the lead boiler’s
isolation valves. If the valve opening fails to proof within 30-seconds, close the
valve, enable the lag boiler, and send an equipment specific alarm (“B-1 Isolation
Valve Failed to Open”) to the operator workstation. If valve opening is successful,
enable the primary hot water pump dedicated to the lead boiler. If the flow is not
proved within 30 seconds, disable the pump, close the valve and set the lag boiler
as the lead boiler. If both valves fail to open, initiate boiler shutdown operation
and send equipment specific alarms to the operator workstation. If both pumps
fail to provide flow, initiate boiler shutdown operation and send equipment
specific alarms to the operator workstation. After 40 hours of operation, on
Variable Air Volume Units with Air-Cooled Chiller
63
Cx Assistant’s Sequence of Operation
4.
5.
6.
7.
April 2004
Sunday at 3:00 AM when both boilers and pumps are shut down, swap the lead
and lag pumps.
Boiler Enable: Upon proof of primary hot water flow, enable the selected boiler.
Use a hard-wired flow switch as a back up to ensure that boiler only starts with
hot water flow. Send an initial hot water temperature of 180° F to the boiler
controller. After 60 seconds, prove boiler operation by means of a hard-wired
current switch. Operate the boilers lead/lag. After 40 hours of operation, on
Sunday at 3:00 AM when both boilers and pumps are shut down, swap the lead
position. Enable the lag boiler to start. If either or both boilers fail to prove or fail
to proof when required to operate, initiate boiler shutdown and send equipment
specific alarms to the operator workstation. During operation, use the boiler’s
internal safeties to initiate an equipment alarm at the operator workstation and
disable the machine. If the boiler does not develop at least a 3°F temperature
difference after 15 minutes of being enabled initiate a equipment specific alarm at
the operator workstation.
Boiler Staging: Modulate internal boilers controls between the boiler’s two stages
to meet the BAS water loop setpoint. If during boiler operation, the hot water
temperature differential falls to 5°F (adjustable), initiate the lag boiler operation.
Continue to run both boilers until the hot water temperature differential rises to
12° F. At this point, initiate the lag boiler shutdown sequence.
Boiler Shutdown: When all calls for central plant heating are cancelled or an
internal alarm occurs, initiate boiler shutdown. Provide the BAS with redundant
sensors for hot water flow, hot water temperature Hi Limit (more than 200° F).
Disable operation of the affected boiler(s) if the limits are exceeded. If both
boilers trip or fail to proof, initiate an equipment specific alarm at the operator
workstation. Prevent the boiler from cycling on and off more often than once
every 5 minutes (this may be redundant to the boiler’s internal safeties). For each
boiler, disable the boiler before shutting down its pump. After disabling the
boiler, run the primary boiler pump serving the boiler for 5 minutes. After 5
minutes, shut down the primary boiler pump and close the hot water isolation
valves. If no other boiler is enabled, shut off the secondary water pumps.
Hot Water System Outdoor Air Temperature Lockout: If the outdoor air
temperature rises above 75° F (adjustable), lock out the hot water system so the
boilers and hot water pumps do not run. If the outdoor air temperature falls below
70° F (adjustable) for 20 minutes (adjustable), enable the hot water system.
Points Table
Key:
X Indicates type of point (only 1 point is needed)
n Indicates type of point (1 point is needed for each zone – a total of “n” points are
needed for this line item)
Variable Air Volume Units with Air-Cooled Chiller
64
Cx Assistant’s Sequence of Operation
April 2004
AHU air handling unit
B boiler
CH chiller or chilled (i.e. CHW = chilled water)
Cmd command
COV change of value
DB dry-bulb
M “mixed” such as the air in the mixed air plenum (MAT = mixed air temperature)
OA outside air (OAT = outside air temperature)
P pump (PP = primary pump, SP = secondary pump)
R return (RAT = return air temperature)
S supply (SAT = supply air temperature)
SL secondary loop
Temp temperature
W water (CHW = chilled water, HW = hot water)
Resolution of analog inputs:
°F 0.1
psid 0.005 ” water
cfm 1
rpm 1
kW 0.1
% 0.1
Point Name
Analog Digital Other
Alarm
AI AO DI DO Software Software Software
Logic
Value
Value
Value
Variable Air Volume Units with Air-Cooled Chiller
Interval Show
on
or
Graphic
COV
65
Cx Assistant’s Sequence of Operation
April 2004
OA DB
Temp
X
15 X
OA RH
X
15 X
OA Enthalpy
X
CHW
Lockout
Temp
X
COV
0.5,15
X
HHW
Lockout
Temp
X
COV
0.5,15
X
CHWR
Temp
CHWS Temp
X
1
15 X
>60
when
CH
flow
after 1
minute,
<38
X
1
CHW SL
Pressure
Drop
Setpoint
CHW SL
Pressure
Drop
15 X
COVX
10%,15
X
=Cmd
COVX
after 1
10%,15
minute
X
CHWSP-n
Enable
n1
CHWSP-n
Override
COV
X
COV
X
Proof
after 1 COV
minute
X
n
CHWSP-n
Status
n
1
CHWSP-n
Runtime
n
CHWSP-n
Cycle
Counter
CHWSP-n
Cmd Speed
15 X
n
>1000
COV 1
>6
hour
COV
n
Variable Air Volume Units with Air-Cooled Chiller
66
Cx Assistant’s Sequence of Operation
CHWSP-n
Run Speed
April 2004
=Cmd
COVX
after 1
10%,15
minute
n
CHWSP-n
Alarm
n
CHWSP-n
Power
n
CHWSP
Lead/Lag
X
X
CH-n Inlet
Temp
COV
n1
15 X
>60
when
call for
cooling,
<38
CH-n Outlet
Temp
n1
CH Setpoint
Temp
X
COV
CH Staging
Setpoint
Temp
X
COV
CH Staging
Deadband
Temp
X
COV
CH-n CHW
Isolation
Valve Cmd
CH-n CHW
Isolation
Valve
Feedback
n1
n
CH-n Alarm
Text
n
CH-n Enable
n1
CH-n
Override
CH-n CHW
flow status
15 X
COV
n
1
CH-n Alarm
X
n
n
1
Variable Air Volume Units with Air-Cooled Chiller
COV
X
COV
X
COV
X
COV
X
COV
X
COV
X
67
Cx Assistant’s Sequence of Operation
CH-n Status
April 2004
n1
Proof
after 1 COV
minute
10%
high or
low
X
CH-n
Voltage
3n
CH-n
Amperage
3n
60
CH-n Power
n
15 X
CH-n Phase
monitor
alarm
n
COV
CH-n Chiller
Runtime
CH-n ReStart Timer
n
>1000
n
5
Minutes
to restart
CH-n Cycle
Counter
n
CH Lead/Lag
X
CHWPP-n
Enable
>6
hour
CHWPP-n
Override
CHWPP-n
Runtime
n
CHWPP-n
Power
n
CHWPP
Lead/Lag
X
1
HWS Temp
X
1
COV
COV
X
COV
X
Proof
after 1 COV
minute
X
>1000
COV 1
X
X
HWR Temp
COV 1
X
n
n
1
X
COV
n1
CHWPP-n
Status
60
Variable Air Volume Units with Air-Cooled Chiller
COV
X
15 X
>180 or
<110
when B
15 X
68
Cx Assistant’s Sequence of Operation
April 2004
flow
after 1
minute
HW SL
Pressure
Drop
Setpoint
HW SL
Pressure
Drop
COVX
10%,15
X
=Cmd
COVX
after 1
10%,15
minute
X
HWSP-n
Enable
n1
HWSP-n
override
n
1
HWSP-n
Runtime
n
HWSP-n
Cycle
Counter
n
Proof
after 1 COV
minute
X
>1000
COV 1
>6
hour
COV
n
n
HWSP
Lead/Lag
B-n Outlet
Temp
X
=Cmd
COVX
after 1
10%,15
minute
HWSP-n
Alarm
B-n Inlet
Temp
COV
n1
HWSP-n Run
n
Speed
HWSP-n
Power
X
n
HWSP-n
Status
HWSP-n
Cmd Speed
COV
X
X
COV
n
n1
Variable Air Volume Units with Air-Cooled Chiller
X
15 X
>190 or
<110
when B
flow
after 1
15 X
69
Cx Assistant’s Sequence of Operation
April 2004
minute
B Setpoint
Temp
X
COV
B Staging
Setpoint
Temp
X
COV
B Staging
Deadband
Temp
X
COV
B-n Alarm
n
B-n Alarm
Text
n
COV
X
COV
X
X
B-n Enable
n1
COV
B-n HW
Isolation
Valve Cmd
n1
COV
B-n HW
Isolation
Valve
Feedback
n
1
B-n Override
B-n HW flow
status
COV
X
COV
X
Proof
after 1 COV
minute
X
n
n
B-n Runtime
B-n Re-Start
Timer
n
>1000
n
5
Minutes
to restart
B-n Cycle
Counter
n
B Lead/Lag
X
HWPP-n
Override
X
n
B-n Status
HWPP-n
Enable
COV
n1
n
Variable Air Volume Units with Air-Cooled Chiller
>6
hour
COV 1
COV
COV
X
COV
X
COV
X
70
Cx Assistant’s Sequence of Operation
HWPP-n
Status
April 2004
Proof
after 1 COV
minute
n
1
HWPP-n
Runtime
n
HWPP-n
Power
n
HWPP
Lead/Lag
>1000
n
1
AHU-n
Operating
Mode
n
AHU-n
Mode
Override
COV 1
X
X
AHU-n Fire
Alarm
X
n
COV
X
COV
X
COV
X
COV
X
AHU-n SAT n
15 X
AHU-n OAT n
15 X
AHU-n RAT n
15 X
AHU-n RA
RH
15 X
n
AHU-n RA
Enthalpy
n
15 X
AHU-n MAT n
15 X
AHU-n
n
Supply Flow
Proof
after 1
minute
15 X
AHU-n
Return Flow
n
Proof
after 1
minute
15 X
n
<5000
CFM
for 5
minutes
15 X
AHU-n
Outdoor Air
Flow
AHU-n Flow
Offset
AHU-n OA
Damper Cmd
n
n
Variable Air Volume Units with Air-Cooled Chiller
COV
COVX
10%,15
71
Cx Assistant’s Sequence of Operation
April 2004
AHU-n RA
Damper Cmd
n
COVX
10%,15
AHU-n MA
Damper Cmd
n
COVX
10%,15
AHU-n
Economizer
High
Ambient
Lockout
Temp
n
COV0.5,15
X
AHU-n
Economizer
CHW
Minimum
Temp
n
COV0.5,15
X
AHU-n
Supply Reset
Temp
n
COV0.5,15
X
AHU-n
Supply
Pressure
Setpoint
n
COVX
10%,15
AHU-n
Supply
Pressure
n
>3”
AHU-n
Supply Fan
Enable
n1
AHU-n
Supply Fan
Status
n
1
AHU-n
Supply Fan
Runtime
n
AHU-n
Supply Fan
Cmd Speed
AHU-nSupply Fan
Run Speed
AHU-n
COV
X
Proof
after 1 COV
minute
X
>1000
n1
15 X
COV 1
15 X
=Cmd
COVX
after 1
10%,15
minute
n
n
Variable Air Volume Units with Air-Cooled Chiller
72
Cx Assistant’s Sequence of Operation
April 2004
Supply Fan
Alarm
AHU-n
Supply Fan
Power
n
AHU-n
Return Fan
Enable
n1
AHU-n
Return Fan
Status
n
1
AHU-n
Return Fan
Runtime
n
AHU-n
Return Fan
Cmd Speed
AHU-nReturn Fan
Run Speed
COV
X
Proof
after 1 COV
minute
X
>1000
COV 1
n1
15 X
=Cmd
COVX
after 1
10%,15
minute
n
AHU-n
Return Fan
Alarm
n
AHU-n
Return Fan
Power
n
AHU-n
CHWV
Bypass Cmd
AHU-n
CHWV
Bypass
Feedback
X
X
COVX
10%,15
n
=Cmd
COVX
after 1
10%,15
minute
n
AHU-n
Warm-up
Mode Low
Temp
Setpoint
n
COV
X
AHU-n CoolDown Mode
High Temp
n
COV
X
Variable Air Volume Units with Air-Cooled Chiller
73
Cx Assistant’s Sequence of Operation
April 2004
Setpoint
AHU-n Filter
Alarm
n
COV
AHU-n Call
for Cooling
n
X
COV
VAV-n Zone
n
Temp
COV0.5,15
X
VAV-n Zone
Temp
SetpointCooling
n
COV
X
VAV-n Zone
Temp
SetpointHeating
n
COV
X
VAV-n Zone
Temp
Unoccupied
SetpointCooling
n
COV
X
VAV-n Zone
Temp
Unoccupied
SetpointHeating
n
COV
X
VAV-n Zone
Temp
SetpointDeadband
n
COV
X
COV
X
VAV-n
Override
n
VAV-n
Operating
Mode
n
VAV-n
Supply Air
n
Temperature
VAV-n
Supply Air
Temp Reset
COV
COV0.5,15
n
Variable Air Volume Units with Air-Cooled Chiller
X
X
74
Cx Assistant’s Sequence of Operation
VAV-n HW
Valve Cmd
n
VAV-n
n
Damper Cmd
Variable Air Volume Units with Air-Cooled Chiller
April 2004
COVX
10%,15
COV
X
75
Cx Assistant’s Sequence of Operation
April 2004
Notes: The system consists of Primary/Secondary chilled and hot water loops, multiple air handling units (AHUs), and 1
single duct variable air volume (VAV) terminal unit for each zone in the building. The VAV units (VAV boxes) adjust the
air volume delivered to the occupied space and, at the perimeter of the building, VAV boxes include a hot water coil and
automatic two-way valve to re-heat the main supply air. Each AHU has a variable volume supply fan, a variable volume
return fan, a chilled water cooling coil, and a set of dampers that act as an airside economizer. The economizer has a 2position outdoor air damper and the return and exhaust air dampers are modulated to regulate “free” cooling. The
chilled water loop includes water-cooled chillers and variable speed secondary chilled water pumps. The hot water loop
includes two-stage boilers and variable speed secondary hot water pumps. A building automation system (BAS) controls
the HVAC equipment.
Appropriate reference in the specifications should be made for products that are integrated with these sequences
including chillers, boilers, variable frequency drives (VFDs), and the like.
Controls: Furnish control device with an interface for monitoring and control of points specified in the points table. The
points table includes the minimum acceptable list of interface points. The selected component controls shall easily
integrate into the BAS and allow for the collection, control, trending, and archiving of the specified points with a minimal
need for intermediary gateways or hardwired connections to link control systems together. Interoperable control
systems are preferred.
The system(s) in your building that are most similar to the system described above include:
•
AH-1
Please note that this sample sequence will have to be modified to meet the exact systems defined in your building.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
Variable Air Volume Units with Water-Cooled Chiller
76
Cx Assistant’s Sequence of Operation
April 2004
VARIABLE-AIR VOLUME (VAV) UNITS WITH A CENTRAL PLANT, WATER
COOLED CHILLERS AND COOLING TOWERS
SEQUENCES OF OPERATION
Air Handling Units (AHUs)
1. Occupied Periods (Normal operation): When an isolation area is scheduled to be
occupied, operate the air handling unit that serves it. These scheduled periods are
considered “occupied periods”.
2. Unoccupied Periods: All hours not included in an occupied period are part of an
“unoccupied period”. During these periods, the system is available for tenant calls
as needed but is not running unless commanded. The following holidays are
considered to be unoccupied periods: New Years Day, Memorial Day, Fourth of
July, Labor Day, Thanksgiving and the following day, Christmas. These should
be set up as re-occurring holidays for each zone.
3. Fan Operation: Run the unit fans in all modes except unoccupied mode. Open the
minimum outside air dampers when the supply fan is running. Proof the supply
fan using an external current switch (CS). Interlock each return fan to its
respective supply fan.
4. Supply and Return Fan Capacity Control: When the fans are running, vary the
supply fan (SF) speed to maintain the supply duct static pressure setpoint. Reset
the duct pressure setpoint from 1.5” to 0.2” (adjustable) based on the damper
Variable Air Volume Units with Water-Cooled Chiller
77
Cx Assistant’s Sequence of Operation
5.
6.
7.
8.
9.
April 2004
position of the most open VAV damper as long as that damper is at least 90%
open (In other words the static setpoint will be reset to maintain the VAV box
requiring the most static pressure at 90% open.). Vary the return fan (RF) speed to
allow the return fan to volumetrically track the supply fan by maintaining the
scheduled fixed flow offset equal to XXX CFM (adjustable) between the SF and
RF.
Fire Alarm: Interface system with the fire alarm controls. When the fire alarm
control initiates a fire alarm, shut down the supply and return fans by a hardwired
contact interface at each fan’s variable frequency drive (VFD) E-stop contact.
Simultaneously, the fire alarm control must notify the BAS of the fire event to
enable the BAS to disable the affected units. Once the fire alarm is reset, enable
the affected unit(s) to resume normal operation.
Duct Pressure Safety: If negative static pressure over 2” WC is measured in the
mixed air plenum or positive supply duct static pressure over 3” WC is measured
in the supply duct, disable the fan VFDs via hard wired interlocks to their E-stop
contacts and initiate an equipment specific alarm (i.e. “AH-3 High Static
Pressure” or “AH-2 Low Static Pressure”) at the operator workstation. An
operator must reset each fan’s differential pressure switch before the VFDs may
be re-enabled. Provide a local or BAS reset for this purpose.
Differential Dry-Bulb Economizer Mode: Enable differential economizer mode
when there is a call for cooling or ventilation, and outdoor air temperature is 2° F
less than return air temperature. Open outside air damper to 100%. Modulate the
return air and exhaust air dampers in unison and modulate the chilled water valve,
as required, to maintain supply air temperature setpoint. Maintain the chilled
water valve in the closed position when outdoor air temperature is below 52° F
(adjustable). When the return air temperature is 2° F (adjustable deadband) or
more above the outdoor air temperature, exhaust and return dampers are to be in
the full exhaust position (exhaust damper fully open and return damper fully
closed). As the return air temperature decreases below this point, the dampers
transition to a full return position (exhaust damper is closed to allow only
minimum outdoor air and the return damper is fully open).
Supply Air Temperature Control: Operate economizer mode dampers and chilled
water valve in conjunction to maintain the supply air temperature. When the
outside air temperature is not sufficient to provide “free” cooling, open the chilled
water valve to maintain the supply air temperature setpoint. When the valve opens
more than 30% (adj.), send a call for cooling to the central plant. When the valve
closes to 5% (adj.), cancel the call for cooling. The supply air temperature is reset
upwards from 90°F to 110°F as the outdoor temperature falls from 65° F or
greater to 40° F or lower.
Filter Status: Establish the filter pressure drop alarm with the system in operation
at actual flow rate as follows:
Where DP 100 is the high limit pressure drop at design cfm (determine limit from
filter manufacturer) and DP x is the high limit at speed signal x (expressed as a
fraction of full supply fan signal). For instance, the setpoint at 50% of speed
Variable Air Volume Units with Water-Cooled Chiller
78
Cx Assistant’s Sequence of Operation
April 2004
would be (0.5) 1.4 or 38% of the design high limit pressure drop.
Send an equipment specific alarm (“AH-1 Dirty Filter”) to the operator
workstation at 150% (adjustable) of the value calculated during system operation.
Isolation Areas
1. Isolation Areas: There are XX isolation areas as indicated on the plans. Each area
is composed of 1 or more spaces served by 1 or more VAV terminal units that are
operated together. Configure each isolation area separately from other isolation
areas. Configuration includes scheduling and operational modes. The default
occupancy schedule is 7:00 AM to 6:00 PM, M-F.
NOTE: Schedule occupied start time 1 hour before the building is expected to be occupied (for Title 24 required purge).
2. Occupied Mode: Prior to an occupied period, initiate a Warm-up mode or Cooldown mode if necessary. During Occupied Mode, enable operation of the system,
including enabling the air handling unit fans that serve this area and opening the
outdoor air dampers to100% open. At the end of an occupied period, initiate
unoccupied mode.
3. Warm-up Mode: Use an optimal start strategy to initiate the warm-up start time.
Base optimal start strategy upon outdoor air temperature and average zone
temperature within the isolation area. If the average zone temperature is less than
69°F (adjustable) at the projected start of the warm-up period, initiate the warmup mode. The optimal start period should pre-heat the building so that the average
zone temperature is 70°F (adjustable) by the occupied period. If building warmup is required, enable the air handling units and set the return fan tracking offset
to 0. Set the economizer mode to the return position, leave the chilled water valve
closed (or in bypass), and leave the general exhaust fans off. Enable the VAV
units to normal occupied operation. Enable the central heating plant but leave the
central cooling disabled. After the average zone temperature has risen above 70°F
(adjustable), terminate the warm-up cycle, and initiate occupied mode.
4. Cool-down Mode: Use an optimal start strategy to initiate the cool-down start
time. Base the optimal start strategy upon outdoor air temperature and average
zone temperature within the isolation area. If the average zone temperature is
greater than 79°F (adjustable) at the projected start of the cool-down period,
initiate the cool-down mode. The optimal start period should pre-cool the building
so that the average zone temperature is 78°F (adjustable) by the occupied period.
If a cool-down cycle is required, enable the air handling units, command the
return fan tracking offset to 0, and leave the general exhaust fans off. Enable the
VAV units to normal occupied operation. Enable the chilled water system but
leave the central heating disabled. After the average zone temperature has
dropped below 78°F (adjustable), terminate the cool-down cycle and initiate
occupied mode.
5. Night Setback/Setup Mode: During an unoccupied period, start the air-handling
unit in the warm-up or cool-down mode if a zone temperature falls below the
unoccupied heating setpoint or rises above the unoccupied cooling setpoint. End
Variable Air Volume Units with Water-Cooled Chiller
79
Cx Assistant’s Sequence of Operation
April 2004
the setback/setup mode when the zones are below/above their unoccupied
setpoints.
6. Unoccupied Mode: During unoccupied periods, disable VAV units, disable the air
handling units, close their chilled water valves (or put them in bypass), close their
outside air damper(s) and position their return/exhaust air dampers for full return
air (no exhaust). Cancel calls for central plant cooling and heating. When a
thermostat override button is depressed during unoccupied period, operate the
isolation area in occupied mode for one hour as follows:
Operate the air handling unit in occupied mode except for the return-fan
volumetric tracking offset (set it to 0) and the general exhaust fans (leave them
off). Enable the central plant.
VAV Zone Control
1. Temperature Control: Use a solid state, electronic wall temperature sensor to
adjust the zone velocity controller setpoint. Airflow to the zone will fluctuate
between its minimum and the maximum and supply air temperature will vary in
order to maintain a constant room temperature based on this setpoint. Set each
temperature sensor for the following ranges:
a. Occupied Heating: 55° F to 73° F during occupied hours. The default is
73° F.
b. Occupied Cooling: 73° F to 85° F during occupied hours. The default is
78° F.
Maintain a deadband of at least 5° F between the heating and cooling setpoints.
During unoccupied hours, set the heating setpoint default to 55° F (adjustable)
and the cooling setpoint default to 85° F (adjustable). Provide each zone its own
adjustable unoccupied heating and cooling setpoints.
2. Zone Cooling Mode: When the zone’s temperature rises to 1°F (adjustable) above
its setpoint, the zone is in cooling mode and the VAV damper begins to modulate
open. As the temperature rises 2° F hotter than its setpoint, the VAV damper is
fully open and the zone’s airflow is increased to maximum. As the zone’s
temperature approaches the cooling setpoint, modulate the air volume toward
minimum.
3. Zone Heating Mode (Perimeter Zones Only): When the zone’s temperature falls
to 1 ° F (adjustable) below its setpoint, the zone is in heating mode and the VAV
damper modulates to minimum airflow. Modulate the reheat coil control valve to
satisfy the space temperature within the reset bounds. Reset the supply air
temperature upward from 90°F to 110°F as the outdoor temperature falls from 65°
F or greater to 40° F or lower. Once the valve opens to more than 10% (adj.), send
a call for heating to the central plant. When the valve closes to 5% (adj.), cancel
the call for heating.
Variable Air Volume Units with Water-Cooled Chiller
80
Cx Assistant’s Sequence of Operation
April 2004
Chilled Water System
1. Cooling Mode Enable/Disable: When building comfort cannot be maintained by
economizer mode outdoor air temperature, the air handlers call for supplementary
cooling by sending a cooling request to the central plant. When all of the AHU
chilled water valve positions fall below 5% full open, cancel the call for cooling
and initiate chiller shutdown.
2. Secondary Chilled Water Pump Enable: When the BAS registers a call for central
plant cooling, enable both the secondary chilled water pumps by a start-stop
command from the BAS. Initially, start the pumps at 10% speed. Proof the start of
both of the pumps after 5 seconds. Modulate the speed of the pumps in order to
maintain a differential pressure setpoint of 15 PSID (adj.) at the central plant.
Inhibit starting of the primary pumps and chiller if both pumps fail to prove
running status or fail while running. When the commanded speed falls below
40%, disable the lag pump. When the commanded speed rises above 60%, enable
the lag pump. When they are both enabled, lead and lag pumps should run at the
same speed.
3. Primary Chilled Water Pump Enable (Chiller Initiation): When the BAS registers
a call for central plant cooling, determine the lead chiller as indicated below.
Open the chilled water isolation valve to the lead chiller. If the valve has not
proofed open after 30 seconds, close the valve and enable and start the lag chiller.
Repeat valve operation with lag chiller. If both valves fail to open, initiate chiller
shutdown operation and send equipment specific critical alarm (“CH-1 CHW
Isolation Valve Failed to Open”) to operator workstation. If valve proofs open,
enable the primary chilled water pump dedicated to the lead chiller. After 30
seconds, proof flow. If the flow is not proved by a differential pressure switch,
disable the pump, close the valve and set the lag chiller as the lead chiller. If both
pumps fail to provide flow, initiate the chiller shutdown operation. If either pump
fails, send equipment specific critical alarms to the operator workstation.
4. Chiller Enable: Upon proof of primary chilled water and condenser water flow,
enable the selected chiller. A hard-wired flow switch will act as a back up to
ensure that chiller only starts with chilled water flow. Set the chilled water
temperature supply temperature to 45° F (adjustable). After 30 seconds, prove
chiller operation by means of a hard-wired current switch. If the chiller fails to
prove operation, initiate its shutdown sequence. Then, enable the lag chiller and
it’s primary pump. If both chillers fail to proof, send an equipment specific alarm
(“Chillers Failed”) to the operator workstation. During operation, use the chillers
internal safeties to cause an alarm and shut down the machine. If the chiller does
not develop at least a 3°F temperature difference after 15 minutes of being proved
on, initiate an alarm on the operator work station. Operate the chillers and their
associated primary pumps lead/lag. Swap the lead and lag chillers (as well as their
primary pumps) on Sunday at 3:00 AM as long as the lead chiller has operated at
least 40 hours and all equipment are disabled.
5. Chiller Staging: If the chilled water return temperature rises to 12°F (adjustable)
above the chilled water setpoint, enable lag chiller operation and start the chiller.
Variable Air Volume Units with Water-Cooled Chiller
81
Cx Assistant’s Sequence of Operation
April 2004
Run both chillers until the chilled return temperature falls to 5°F above the chilled
water setpoint. At this point, initiate the lag chiller shutdown sequence. Continue
running the lead chiller until the chilled water return temperature falls to the
setpoint minus the deadband.
Condenser Water System
1. Chemical Treatment: Provide chemical treatment for the cooling towers via an
automatic chemical feed and bleed system. Run the water treatment system
independently of the BAS.
2. Safeties: Disable the condenser water pump and the chiller operation if the water
level in the cooling tower basin falls below the minimum. Initiate an equipment
specific alarm (“Low Water Level in CT-1”) at the operator workstation.
3. Condenser Water Pump Enable: When the BAS registers a call for cooling from
the central plant, enable the lead condenser water pump. Prove condenser water
flow within 30-seconds (adjustable) using a differential pressure switch. If the
flow is not proved, disable the pump, and enable and start the lag pump. Send
equipment specific critical alarm (“CWP-1 Failed”) to the operator workstation.
The lag pump is also enabled by the start-up of the lag chiller. If both pumps fail
to provide flow, initiate chiller shutdown operation and initiate a critical alarm
(“Condenser Water Pumps failed”) to the operator workstation. Swap the lead and
lag pumps on Sunday at 3:00 AM as long as the lead pump has operated at least
40 hours and both pumps are shut down.
4. Condenser Water Temperature Control: Prior to operation of the condenser water
pump, the cooling tower bypass valve should be in the bypass position (bypassing
the cooling towers) and the cooling tower fans shut off. Once condenser water
flow is proved, operate the cooling tower fan and bypass valve in order to
maintain a condenser water supply setpoint between 75° F and 85° F. Modulate
the condenser water bypass valve so that at 80° F condenser water supply
temperature, the water is not bypassing the cooling tower. Start both cooling
tower fans at minimum speed when the water temperature increases to 82°F.
Modulate the tower fans speed as necessary to maintain the setpoint temperature.
If the temperature exceeds the high limit of 90° F, initiate the chiller shutdown
sequence and send an equipment specific alarm (“Condenser Water High Limit
Temperature”) to the operator workstation. As the temperature falls below 82 ° F,
disable the fans and modulate the bypass valve to maintain setpoint temperature.
If the condenser supply temperature falls below the low limit of 70° F after
running for 5 minutes, initiate the chiller shutdown sequence and send an
equipment specific alarm (“Condenser Water Low Limit Temperature”) to the
operator workstation.
5. Condenser Water System Shutdown: When the lag chiller is shutdown, disable the
lag chilled water pump after a 5 minute run time. Adjust the condenser water fan
speed and bypass valve positions to maintain temperature as indicated elsewhere.
When the lead chiller is shutdown, run the lead condenser water pump for 5
Variable Air Volume Units with Water-Cooled Chiller
82
Cx Assistant’s Sequence of Operation
April 2004
minute. Then disable the cooling tower fans, disable the lead pump, and modulate
the bypass valve to full bypass.
Heating Hot Water System
1. Heating Mode Enable: Generate a call for heating from zone controllers if any of
the zone valve positions is greater than 10% (adjustable) of full open until all are
below 5% (adjustable)
2. Secondary Hot Water Pump Enable: When the BAS registers a call for central
plant heating, enable both the secondary hot water pumps by a start-stop
command from the BAS. Initially, start the pumps at 10% speed. Proof the start of
both of the pumps after 15 seconds using a differential pressure switch. Modulate
the speed of the pumps in order to maintain a pressure drop of 10 PSID at the hot
water using a differential pressure transmitter. Inhibit starting of the primary
pumps and boiler if both pumps fail to prove running status or fail while running.
When the commanded speed falls below 40%, disable the lag pump. When the
commanded speed rises above 60%, enable the lag pump. If either pump fails to
start, initiate an equipment specific critical alarm at the operator workstation.
When they are both enabled, lead and lag pumps should run at the same speed.
3. Primary Hot Water Pump Enable (Boiler Initiation): Open the lead boiler’s
isolation valves. If the valve opening fails to proof within 30-seconds, close the
valve, enable the lag boiler, and send an equipment specific alarm (“B-1 Isolation
Valve Failed to Open”) to the operator workstation. If valve opening is successful,
enable the primary hot water pump dedicated to the lead boiler. If the flow is not
proved within 30 seconds, disable the pump, close the valve and set the lag boiler
as the lead boiler. If both valves fail to open, initiate boiler shutdown operation
and send equipment specific alarms to the operator workstation. If both pumps
fail to provide flow, initiate boiler shutdown operation and send equipment
specific alarms to the operator workstation. After 40 hours of operation, on
Sunday at 3:00 AM when both boilers and pumps are shut down, swap the lead
and lag pumps.
4. Boiler Enable: Upon proof of primary hot water flow, enable the selected boiler.
Use a hard-wired flow switch as a back up to ensure that boiler only starts with
hot water flow. Send an initial hot water temperature of 180° F to the boiler
controller. After 60 seconds, prove boiler operation by means of a hard-wired
current switch. Operate the boilers lead/lag. After 40 hours of operation, on
Sunday at 3:00 AM when both boilers and pumps are shut down, swap the lead
position. Enable the lag boiler to start. If either or both boilers fail to prove or fail
to proof when required to operate, initiate boiler shutdown and send equipment
specific alarms to the operator workstation. During operation, use the boiler’s
internal safeties to initiate an equipment alarm at the operator workstation and
disable the machine. If the boiler does not develop at least a 3°F temperature
difference after 15 minutes of being enabled initiate a equipment specific alarm at
the operator workstation.
Variable Air Volume Units with Water-Cooled Chiller
83
Cx Assistant’s Sequence of Operation
April 2004
5. Boiler Staging: Modulate internal boilers controls between the boiler’s two stages
to meet the BAS water loop setpoint. If during boiler operation, the hot water
temperature differential falls to 5°F (adjustable), initiate the lag boiler operation.
Continue to run both boilers until the hot water temperature differential rises to
12° F. At this point, initiate the lag boiler shutdown sequence.
6. Boiler Shutdown: When all calls for central plant heating are cancelled or an
internal alarm occurs, initiate boiler shutdown. Provide the BAS with redundant
sensors for hot water flow, hot water temperature Hi Limit (more than 200° F).
Disable operation of the affected boiler(s) if the limits are exceeded. If both
boilers trip or fail to proof, initiate an equipment specific alarm at the operator
workstation. Prevent the boiler from cycling on and off more often than once
every 5 minutes (this may be redundant to the boiler’s internal safeties). For each
boiler, disable the boiler before shutting down its pump. After disabling the
boiler, run the primary boiler pump serving the boiler for 5 minutes. After 5
minutes, shut down the primary boiler pump and close the hot water isolation
valves. If no other boiler is enabled, shut off the secondary water pumps.
Points Table
Key:
X Indicates type of point (only 1 point is needed)
n Indicates type of point (1 point is needed for each zone – a total of “n” points are
needed for this line item)
AHU air handling unit
B boiler
CH chiller or chilled (i.e. CHW = chilled water)
Cmd command
COV change of value
CT cooling tower
DB dry-bulb
M “mixed” such as the air in the mixed air plenum (MAT = mixed air temperature)
OA outside air (OAT = outside air temperature)
P pump (PP = primary pump, SP = secondary pump)
Variable Air Volume Units with Water-Cooled Chiller
84
Cx Assistant’s Sequence of Operation
April 2004
R return (RAT = return air temperature)
S supply (SAT = supply air temperature)
SL secondary loop
Temp temperature
W water (CW = condenser water, HW = hot water)
Resolution of analog inputs:
°F 0.1
psid 0.005 ” water
cfm 1
rpm 1
kW 0.1
% 0.1
Interval Show
on
or
Graphic
COV
Point Name
Analog Digital
Other
Alarm
AI AO DI DO Software Software
Software Logic
Value
Value
OA DB
Temp
X
15 X
OA RH
X
15 X
OA Enthalpy
CHWR
Temp
CHWS Temp
CHW SL
Pressure
Drop
Setpoint
X
15 X
X
1
15 X
>60
when
CH
flow
after 1
minute,
<38
X
1
X
Variable Air Volume Units with Water-Cooled Chiller
15 X
COVX
10%,15
85
Cx Assistant’s Sequence of Operation
CHW SL
Pressure
Drop
=Cmd
COVX
after 1
10%,15
minute
X
CHWSP-n
Enable
n1
CHWSP-n
Override
n
1
CHWSP-n
Runtime
n
CHWSP-n
Cycle
Counter
n
CHWSP-n
Cmd Speed
COV
X
Proof
after 1 COV
minute
X
>1000
COV 1
>6
hour
COV
=Cmd
COVX
after 1
10%,15
minute
n
n
n
CHWSP
Lead/Lag
CH-n Inlet
Temp
X
n
CHWSP-n
Alarm
CHWSP-n
Power
COV
n
CHWSP-n
Status
CHWSP-n
Run Speed
April 2004
X
X
COV
n1
15 X
>60
when
call for
cooling,
<38
CH-n Outlet
Temp
n1
CH Setpoint
Temp
X
COV
CH Staging
Setpoint
Temp
X
COV
CH Staging
X
COV
Variable Air Volume Units with Water-Cooled Chiller
X
15 X
86
Cx Assistant’s Sequence of Operation
April 2004
Deadband
Temp
CH-n CHW
Isolation
Valve Cmd
CH-n CHW
Isolation
Valve
Feedback
n1
n
1
CH-n CW
Isolation
Valve Cmd
CH-n CW
Isolation
Valve
Feedback
COV
COV
n1
COV
n
1
CH-n Alarm
n
CH-n Alarm
Text
n
CH-n Enable
X
n1
CH-n
Override
n
COV
X
COV
X
COV
X
COV
X
COV
X
CH-n CHW
flow status
n
1
COV
X
CH-n CW
flow status
n
1
COV
X
Proof
after 1 COV
minute
X
CH-n Status
n1
10%
high or
low
CH-n
Voltage
3n
CH-n
Amperage
3n
60
CH-n Power
n
15 X
CH-n Phase
monitor
alarm
CH-n Chiller
n
60
COV
n
Variable Air Volume Units with Water-Cooled Chiller
>1000
X
COV 1
87
Cx Assistant’s Sequence of Operation
April 2004
Runtime
CH-n ReStart Timer
5
Minutes
to restart
n
CH-n Cycle
Counter
n
CH Lead/Lag
X
CHWPP-n
Enable
n
1
CHWPP-n
Runtime
n
CHWPP-n
Power
n
CHWPP
Lead/Lag
CWS Temp
COV
X
COV
X
Proof
after 1 COV
minute
X
>1000
COV 1
X
X
COV
X
1
X
15 X
>87 , <
72
when
flowing
for 5
minutes
X
1
CWP-n
Enable
n1
CW-n
Override
CWP-n
Status
X
n
CHWPP-n
Status
COV
COV
n1
CHWPP-n
Override
CWR Temp
>6
hour
COV
X
COV
X
Proof
after 1 COV
minute
X
n
n
1
CWP-n
Runtime
n
CWP-n
n
Variable Air Volume Units with Water-Cooled Chiller
15 X
>1000
COV 1
X
88
Cx Assistant’s Sequence of Operation
April 2004
Power
CWP
Lead/Lag
X
CW Bypass
Cmd
CW Bypass
Feedback
COV
X
COVX
10%,15
X
=Cmd
COVX
after 1
10%,15
minute
X
CW Temp
Set point
X
COV0.5,15
CW
Minimum
Temp
X
COV
CW
Maximum
Temp
X
COV
CW Temp
Set point
deadband
X
COV
CW Valve
Set point
Temp
X
COV
CT-n Alarm
n
CT-n Enable
n
CT-n Status
n1
CT-n Power
n
CT-n
Runtime
n
X
COV
X
COV
X
Proof
after 1 COV
minute
X
15 X
CT-n Cycle
Counter
n
CT Lead/Lag
X
CT-n Low
Water Alarm
HWR Temp
COV
n1
CT-n
Override
X
n
X
Variable Air Volume Units with Water-Cooled Chiller
>1000
COV 1
>6
hour
COV
COV
X
COV
X
15 X
89
Cx Assistant’s Sequence of Operation
April 2004
1
HWS Temp
>180 or
<110
when B
flow
after 1
minute
X
1
HW SL
Pressure
Drop
Setpoint
HW SL
Pressure
Drop
COVX
10%,15
X
=Cmd
COVX
after 1
10%,15
minute
X
HWSP-n
Enable
n1
HWSP-n
override
n
1
HWSP-n
Runtime
n
HWSP-n
Cycle
Counter
n
COV
X
Proof
after 1 COV
minute
X
>1000
COV 1
>6
hour
COV
=Cmd
COVX
after 1
10%,15
minute
HWSP-n
Alarm
n
n
HWSP
Lead/Lag
B-n Inlet
Temp
X
n1
HWSP-n Run
n
Speed
HWSP-n
Power
COV
n
HWSP-n
Status
HWSP-n
Cmd Speed
15 X
X
X
n
Variable Air Volume Units with Water-Cooled Chiller
COV
X
15 X
90
Cx Assistant’s Sequence of Operation
April 2004
>190 or
<110
when B
flow
after 1
minute
B-n Outlet
Temp
n1
B Setpoint
Temp
X
COV
B Staging
Setpoint
Temp
X
COV
B Staging
Deadband
Temp
X
COV
B-n Alarm
n
B-n Alarm
Text
n
15 X
COV
X
COV
X
X
B-n Enable
n1
COV
B-n HW
Isolation
Valve Cmd
n1
COV
B-n HW
Isolation
Valve
Feedback
n
1
B-n Override
B-n HW flow
status
B-n Re-Start
Timer
X
COV
X
COV
X
Proof
after 1 COV
minute
X
n
n
B-n Status
B-n Runtime
COV
n
n
>1000
n
5
Minutes
to restart
B-n Cycle
Counter
n
B Lead/Lag
X
Variable Air Volume Units with Water-Cooled Chiller
>6
hour
COV 1
COV
COV
X
91
Cx Assistant’s Sequence of Operation
HWPP-n
Enable
April 2004
n1
HWPP-n
Override
COV
X
COV
X
Proof
after 1 COV
minute
X
n
HWPP-n
Status
n
1
HWPP-n
Runtime
n
HWPP-n
Power
n
HWPP
Lead/Lag
>1000
X
X
AHU-n Fire
Alarm
n
1
AHU-n
Operating
Mode
n
AHU-n
Mode
Override
COV 1
n
COV
X
COV
X
COV
X
COV
X
AHU-n SAT n
15 X
AHU-n OAT n
15 X
AHU-n RAT n
15 X
AHU-n RA
RH
15 X
n
AHU-n RA
Enthalpy
n
15 X
AHU-n MAT n
15 X
AHU-n
n
Supply Flow
Proof
after 1
minute
15 X
AHU-n
Return Flow
n
Proof
after 1
minute
15 X
n
<5000
CFM
for 5
minutes
15 X
AHU-n
Outdoor Air
Flow
Variable Air Volume Units with Water-Cooled Chiller
92
Cx Assistant’s Sequence of Operation
AHU-n Flow
Offset
April 2004
n
COV
AHU-n OA
Damper Cmd
n
COVX
10%,15
AHU-n RA
Damper Cmd
n
COVX
10%,15
AHU-n MA
Damper Cmd
n
COVX
10%,15
AHU-n
Economizer
High
Ambient
Lockout
Temp
n
COV0.5,15
X
AHU-n
Economizer
CHW
Minimum
Temp
n
COV0.5,15
X
AHU-n
Supply Reset
Temp
n
COV0.5,15
X
AHU-n
Supply
Pressure
Setpoint
n
COVX
10%,15
AHU-n
Supply
Pressure
n
>3”
AHU-n
Supply Fan
Enable
n1
AHU-n
Supply Fan
Status
n
1
AHU-n
Supply Fan
Runtime
AHU-n
Supply Fan
Cmd Speed
n
n1
Variable Air Volume Units with Water-Cooled Chiller
15 X
COV
X
Proof
after 1 COV
minute
X
>1000
COV 1
15 X
93
Cx Assistant’s Sequence of Operation
AHU-nSupply Fan
Run Speed
=Cmd
COVX
after 1
10%,15
minute
n
AHU-n
Supply Fan
Alarm
n
AHU-n
Supply Fan
Power
n
AHU-n
Return Fan
Enable
n
1
AHU-n
Return Fan
Runtime
n
AHU-n
Return Fan
Cmd Speed
X
Proof
after 1 COV
minute
X
>1000
COV 1
15 X
=Cmd
COVX
after 1
10%,15
minute
n
n
AHU-n
Return Fan
Power
n
AHU-n
CHWV
Bypass Cmd
AHU-n
Warm-up
Mode Low
Temp
COV
n1
AHU-n
Return Fan
Alarm
AHU-n
CHWV
Bypass
Feedback
X
n1
AHU-n
Return Fan
Status
AHU-nReturn Fan
Run Speed
April 2004
X
COVX
10%,15
n
=Cmd
COVX
after 1
10%,15
minute
n
n
Variable Air Volume Units with Water-Cooled Chiller
COV
X
94
Cx Assistant’s Sequence of Operation
April 2004
Setpoint
AHU-n CoolDown Mode
High Temp
Setpoint
AHU-n Filter
Alarm
n
n
AHU-n Call
for Cooling
n
COV
X
COV
X
COV
VAV-n Zone
n
Temp
COV0.5,15
X
VAV-n Zone
Temp
SetpointCooling
n
COV
X
VAV-n Zone
Temp
SetpointHeating
n
COV
X
VAV-n Zone
Temp
Unoccupied
SetpointCooling
n
COV
X
VAV-n Zone
Temp
Unoccupied
SetpointHeating
n
COV
X
VAV-n Zone
Temp
SetpointDeadband
n
COV
X
COV
X
VAV-n
Override
VAV-n
Operating
Mode
n
n
VAV-n
Supply Air
n
Temperature
Variable Air Volume Units with Water-Cooled Chiller
COV
COV0.5,15
X
95
Cx Assistant’s Sequence of Operation
VAV-n
Supply Air
Temp Reset
VAV-n HW
Valve Cmd
April 2004
n
n
VAV-n
n
Damper Cmd
Variable Air Volume Units with Water-Cooled Chiller
X
COVX
10%,15
COV
X
96
Cx Assistant’s Sequence of Operation
April 2004
Notes: The system consists of multiple water source heat pump units, 2 boilers with primary pumps and 2 fluid coolers
with integral pumps (not shown) all connected to a condenser water loop. The water source heat pump units (WSHP)
have integral variable flow supply fans, internally controlled by the unit, that provide conditioned air to the occupied
spaces. Outside air is provided through ducted air intakes. Barometric relief dampers maintain building pressurization
and allow building air to be exhausted outside. The fluid coolers and boilers provide temperature control for the
condenser water loop (or water loop) and two variable-speed water loop pumps circulate the water to each component of
the system. Together the water loop, its pumps, the fluid coolers, and the boilers are described as the “water loop
central plant”. A building automation system (BAS) controls the equipment.
Appropriate reference(s) in the specifications should be made for products that are integrated with these sequences
including fluid coolers, boilers, variable frequency drives (VFDs), and the like.
Controls: Furnish control device with an interface for monitoring and control of points specified in the points table. The
points table includes the minimum acceptable list of interface points. The selected component controls shall easily
integrate into the BAS and allow for the collection, control, trending, and archiving of the specified points with a minimal
need for intermediary gateways or hardwired connections to link control systems together. Interoperable control
systems are preferred.
The system(s) in your building that are most similar to the system described above include:
Please note that this sample sequence will have to be modified to meet the exact systems defined in your building.
Disclaimer: The files produced by Cx Assistant are not suitable for bidding without prior review by the project's architect
or engineer of record. The information is provided to the user as a sample document that is based upon a hypothetical
system design. It may need to be modified in order to suit specific project requirements prior to inclusion in contract
documents.
CONDENSER WATER LOOP HEAT PUMP SYSTEM
Water Source Heat Pump System
97
Cx Assistant’s Sequence of Operation
April 2004
SEQUENCES OF OPERATION
Water Source Heat Pump Units
1. Occupied Periods (normal operation): Operate the system on a programmed
occupancy schedule from 7:00 AM to 6:00 PM, M-F. These periods are
considered “occupied periods”. During occupied periods, run the system in
Occupied Mode.
NOTE: Schedule occupied start time 1 hour before the building is expected to be occupied
(for Title 24 required purge).
2. Unoccupied Periods: All hours not included in an occupied period are part of an
“unoccupied period”. During these periods, the system is available for tenant calls
as needed but is not running unless commanded. The following holidays are
considered to be unoccupied periods: New Years Day, Memorial Day, Fourth of
July, Labor Day, Thanksgiving and the following day, Christmas. These should
be set up as re-occurring holidays for each zone.
3. Fan Operation: Run the unit fans in all modes except unoccupied mode. Minimum
outside air will enter the unit when the supply fan is running based on the
building’s pressurization.
4. Fire Alarm: Interface system with the fire alarm controls. When the fire alarm
control initiates a fire alarm, shut down the affected supply fan(s) by hardwired
contact interface at the contactor. Simultaneously, fire alarm control must notify
the BAS of a fire event to enable the BAS to disable the affected units. Once the
fire alarm is reset, enable the affected unit(s) to resume normal operation.
5. Occupied Mode: Prior to an occupied period, use an optimal start strategy to
initiate a Warm-up mode or Cool-down mode. During Occupied Mode, enable
operation of heat pump units and the water loop central plant. At the end of an
occupied period, initiate water loop shutdown, disable the heat pump units, and
close their condenser water valves.
6. Unoccupied Mode: During unoccupied periods, the heat pump unit’s supply fans
are off and the heat pump unit’s condenser water (CW) valve is closed. Each heat
pump unit, supported by the central plant, can be started by the BAS to respond to
after-hours calls from the zone thermostats. When a thermostat override button is
depressed during unoccupied period (i.e. after-hours call), operate the system in
occupied mode for one hour.
7. Warm-up Mode: Base the Warm-up start time on an optimal start strategy
calculated using outdoor air temperature and average zone temperature. If the
average zone temperature is less than 69°F (adjustable), initiate the warm-up
mode and set the Warm-up Mode Low Temperature Setpoint to 70°F (adjustable).
Enable the water loop pumps, the boilers, and the boiler pumps. Once water loop
is proved, enable the heat pump unit(s), as required, to operate in heating mode.
Disable fluid coolers during warm-up mode. Terminate warm-up mode when the
average zone temperature rises above the Warm-up Mode Low Temperature
Water Source Heat Pump System
98
Cx Assistant’s Sequence of Operation
April 2004
Setpoint and transition the system to occupied mode (if scheduled) or to
unoccupied mode.
8. Cool-down Mode: Base the cool-down start time on an optimal start strategy
calculated using outdoor air temperature and average zone temperature. If the
average zone temperature is greater than 79°F (adjustable), initiate the cool-down
mode and set the Cool-down Mode High Temperature Setpoint to 78°F
(adjustable). To initiate a cool-down mode, enable the water loop pumps, and the
fluid coolers. Once water loop flow is proved, enable each heat pump unit to
operate in cooling mode. Disable the boilers during cool-down mode. Terminate
Cool-down mode when the average zone temperature falls below the Cool-down
Mode High Temperature Setpoint and transition the system to occupied mode (if
scheduled) or to unoccupied mode.
9. Supply Air Temperature Control: When a call for heating or cooling is made from
a zone thermostat, open the condenser water valve and prove flow with a flow
switch. If flow is proved within 60 seconds of valve opening, the enable the heat
pump unit. If the flow is not proved, generate an equipment specific alarm at the
operator workstation. Prevent the heat pump compressor from cycling between
cooling and heating more often than once every 3 minutes. Also, prevent the heat
pump compressor from cycling on and off more often than once every 3 minutes.
10. Filter Status: Monitor the air filter condition with a differential pressure
transducer to determine if the filter is dirty.
11. Zone Temperature Control: Use a programmable, solid state, electronic
thermostat to adjust the zone velocity controller setpoint integral to each heat
pump unit’s supply fan. Airflow to the zone will fluctuate between its minimum
and the maximum to maintain a constant room temperature based on this setpoint.
Set each thermostat for the following ranges:
a. Occupied Heating: 55° F to 73° F during occupied hours. The default is
73° F.
b. Occupied Cooling: 73° F to 85° F during occupied hours. The default is
78° F.
Maintain a deadband of at least 5° F between heating and cooling setpoints.
During unoccupied hours, set the heating setpoint default to 55° F (adjustable)
and the cooling setpoint default to 85° F (adjustable). Allow each zone to have its
own adjustable unoccupied heating and cooling setpoints.
12. Cooling Mode: When the thermostat indicates a call for cooling, set the heat
pump to cooling mode.
13. Heating Mode: When the thermostat indicates a call for heating, set the heat pump
to heating mode.
14. Night Setback/Setup: During an unoccupied period, enable the warm-up mode if
any zone thermostat falls below the unoccupied heating setpoint and set the
Warm-up Mode Low Temperature Setpoint equal to the unoccupied heating
setpoint. Also, enable the cool-down mode if any zone thermostat rises above the
unoccupied cooling setpoint and set the Cool-Down Mode High Temperature
Water Source Heat Pump System
99
Cx Assistant’s Sequence of Operation
April 2004
Setpoint equal to the unoccupied cooling setpoint. Allow each unit to have its own
adjustable night setback and night setup setpoints.
15. Heat Pump Compressor Shutdown: If the unit stops generating a call for heating
or cooling, the condenser water system shuts down, or a refrigeration fault occurs,
disable the compressor operation. After the compressor is disabled, leave the flow
control valve open for two minutes and then close it.
Water Loop Central Plant
1. Chemical Treatment: Chemically treat the fluid cooler via an automatic chemical
feed and bleed system. The fluid cooler water treatment system runs
independently of the BAS.
2. Safeties: Disable the fluid cooler’s pump if the water level in the fluid cooler’s
basin falls below its minimum allowable level. Initiate a Low Water Basin Alarm
at the BAS operator workstation.
3. Water Loop Pump Enable: Start the pumps at 10% speed. If the flow is not proved
within 60 seconds (adjustable) as indicated by a differential pressure switch,
disable the pump(s), and initiate an equipment specific critical alarm (“CP-1
Failed”) at the operator workstation. Modulate the speed of the pumps in order to
maintain a differential pressure setpoint of 15 PSID at the central plant. When the
commanded speed falls below 40%, shut down the lag pump. When the
commanded speed rises above 60%, start the lag pump. After 40 hours of
operation, on Sunday at 3:00 AM when the system is in unoccupied mode, swap
the lead and lag pumps.
4. Water Loop Cooling Temperature Control: When the water loop pumps are
enabled, the fluid cooler bypass valve is in the bypass position (bypassing the
fluid coolers) and the fluid cooler fans are off. As the water loop supply
temperature increases to above 86° F, begin opening valve (to no bypass) and
start the fluid cooler pump. As the water loop temperature increases to 87°F, start
both fluid cooler fans at minimum speed. Modulate the fan speed to maintain
85°F. Below 84° F, cycle the fans off. If the water loop temperature exceeds the
high limit of 90° F, generate an alarm at the operator workstation. As the water
loop supply temperature falls below 83° F, begin modulating the bypass valve to
full bypass and turn off the fluid cooler pump.
5. Water Loop Heating Temperature Control: When the water loop pumps are
enabled, the boiler bypass valve is in the bypass position (bypassing the boilers)
and the boilers are off. If the water loop supply temperature falls below 71° F for
3 minutes, begin opening the bypass valve (to no bypass) and enable the boiler
pumps. As the condenser supply water temperature falls to 69° F, modulate the
bypass valve to no bypass in order to maintain temperature. Enable the boilers
when the bypass valve is all the way open (no bypass). If the water loop supply
temperature falls below the low limit of 68° F, generate an alarm at the operator
workstation. As the water loop supply temperature rises above 72° F for 3
minutes, initiate boiler shutdown and begin modulating the bypass valve to full
bypass.
Water Source Heat Pump System
100
Cx Assistant’s Sequence of Operation
April 2004
6. Boiler Pump Enable (Boiler Initiation): When the boiler bypass valve begins to
modulate open, open the isolation valves to the lead boiler. If the valve opening
fails to prove within 60 seconds, close the valve, set the lag boiler as lead and
send an equipment specific alarm (“B-1 Isolation Valve Failed to Open”) to the
operator workstation. Repeat valve operation with lag boiler. If both valves fail to
open, initiate boiler shutdown operation and send equipment specific alarms to the
operator workstation. If valve opening is successful, enable the lead primary
boiler pump. If the flow is not proofed within 60 seconds, disable the pump, and
set the lag pump as lead. If both pumps fail to provide flow, initiate the boiler
shutdown operation. Initiate equipment specific alarms at the operator workstation
for the failure of either pump. The primary pumps are operated lead/lag. After 40
hours of operation, on Sunday at 3:00 AM when both boilers and pumps are shut
down, swap the lead and lag pumps.
7. Boiler Enable: Upon proof of primary hot water flow, enable the selected boiler.
Provide a hard-wired flow switch to act as a back up to ensure that boiler only
starts with hot water flow. Send an initial hot water temperature of 140° F to the
boiler controller. Prove the boiler operation after 60 seconds in the following
manner: if the boiler has not developed at least 3° F of differential temperature
between its supply and return temperatures, disable the boiler and initiate its
shutdown sequence. Operate the boilers lead/lag. After 40 hours of operation, on
Sunday at 3:00 AM when both boilers and pumps are shut down, swap the lead
position. Enable the lag boiler to start. If either or both boilers fail to prove or fail
to proof when required to operate, initiate boiler shutdown and send equipment
specific alarms to the operator workstation. During operation, use the boiler’s
internal safeties to initiate an equipment alarm at the operator workstation and
disable the machine. If the boiler does not develop at least a 3°F temperature
difference after 15 minutes of being enabled initiate a equipment specific alarm at
the operator workstation.
8. Boiler Staging: Modulate the internal boilers controls between the boiler’s two
stages to meet the BAS water loop setpoint. If during boiler operation, the hot
water temperature differential falls to 5°F (adjustable), initiate the lag boiler
operation. Maintain operation of both boilers until the hot water temperature
differential rises to 12° F. At this point, initiate the lag boiler shutdown sequence.
9. Boiler Shutdown: Upon a call from the BAS or an internal alarm, initiate the
boiler shutdown. Provide the BAS with redundant sensors for hot water flow, hot
water temperature Hi Limit (more than 200° F). Disable operation of the affected
boiler(s) if the limits are exceeded. If both boilers trip or fail to proof, initiate an
equipment specific alarm at the operator workstation. Prevent the boiler from
cycling on and off more often than once every 5 minutes (this may be redundant
to the boiler’s internal safeties). For each boiler, disable the boiler first before
shutting down its pump. After disabling the boiler, run the primary boiler pump
serving the boiler for 5 minutes. After 5 minutes, shut down the primary boiler
pump and close the hot water isolation valves.
Water Source Heat Pump System
101
Cx Assistant’s Sequence of Operation
April 2004
10. Water Loop Shutdown: When water loop shutdown is initiated, run the pumps for
5 minutes and then shut them off. When the water loop is shut down due to being
disabled or due to a fault, lockout operation of the heat pump compressors.
Points Table
Key:
X Indicates type of point (only 1 point is needed)
n Indicates type of point (1 point is needed for each zone – a total of “n” points are
needed for this line item)
B boiler
FLC fluid cooler
Cmd command
COV change of value
DB dry-bulb
WSHP water-source heat pump unit
HW Hot water
M “mixed” such as the air in the mixed air plenum (MAT = mixed air temperature)
OA outside air (OAT = outside air temperature)
P pump (FLCP = fluid cooler pump, PP = primary pump)
R return (FLCR = fluid cooler return water temperature)
S supply (SAT = supply air temperature)
SL secondary loop
CW condenser water (i.e. water loop)
Resolution of analog inputs:
°F 0.1
Water Source Heat Pump System
102
Cx Assistant’s Sequence of Operation
April 2004
psid 0.005 ” water
cfm 1
rpm 1
kW 0.1
% 0.1
Point Name
Analog Digital Other
AI AO DI DO Software Software Software
Value
Value
Value
OA DB Temp
X
Alarm Logic
CWS Temperature X
CWR
Temperature
X
CW Temp Set
point
X
CW Minimum
Temp
X
Water loop
min. temp
CW Maximum
Temp
X
Water loop
max. temp
CW Pressure Drop
Setpoint
X
=Cmd after 1
minute
CW Pressure Drop X
CWP-n Enable
n1
CWP-n override
n
CWP-n Status
CWP-n Runtime
n
CWP-n Cycle
Counter
>1000
n
CWP-n Cmd
Speed
CWP-n Run
Speed
Proof after 1
minute
n1
> 6 hour
n1
=Cmd after 1
minute
n
CWP Lead/Lag
Water Source Heat Pump System
X
103
Cx Assistant’s Sequence of Operation
April 2004
FLC Temp Set
point deadband
X
FLC Bypass
Valve Set point
Temp
X
FLC Bypass
Valve Cmd
Position
FLC Bypass
Valve Feedback
X
=Cmd after 1
minute
X
FLC-n Inlet Temp X 1
FLC-n Outlet
Temp
>87 , < 72
when flowing
for 5 minutes
X1
FLC-n Enable
n1
FLC-n Override
n
FLC-n Status
n1
FLC-n Runtime
n
>1000
FLC-n Cycle
Counter
n
FLC Lead/Lag
X
FLC-n Low Water
Alarm
> 6 hour
n
FLCP-n Enable
n1
FLCP-n Override
n
FLCP-n Status
Proof after 1
minute
n1
HW Temp Set
point deadband
X
HW Bypass Valve
Set point Temp
X
HW Bypass Valve
Cmd Position
X
HW Bypass Valve
X
Feedback
HWR Temp
Proof after 1
minute
=Cmd after 1
minute
X1
Water Source Heat Pump System
104
Cx Assistant’s Sequence of Operation
HWS Temp
April 2004
>180 or <110
when HW
flow after 1
minute
X1
B-n Inlet Temp
n
B-n Outlet Temp
n1
B Setpoint Temp
X
B Staging Setpoint
Temp
X
B Staging
Deadband Temp
X
B-n Alarm
n
B-n Enable
n1
B-n HW Isolation
Valve Cmd
n1
B-n HW Isolation
Valve Feedback
n1
B-n Override
B-n HW flow
status
>190 or <110
when HW
flow after 1
minute
n
n
B-n Status
n
Proof after 1
minute
B-n Runtime
n
>1000
B-n Re-Start
Timer
n
5 Minutes to
re-start
B-n Cycle Counter
n
B Lead/Lag
X
HWPP-n Enable
n1
HWPP-n Override
HWPP-n Status
> 6 per hour
n
Proof after 1
minute
n1
HWPP-n Runtime
HWPP Lead/Lag
Water Source Heat Pump System
n
>1000
X
105
Cx Assistant’s Sequence of Operation
WSHP-n Fire
Alarm
April 2004
n1
WSHP-n Enable
Cooling
n1
WSHP-n Enable
Heating
n1
WSHP-n Supply
Fan Enable
n1
WSHP-n CWV
Bypass Cmd
n
WSHP- Flow
Status
=Cmd after 1
minute
n
WSHP-n Warmup Mode Low
Temp Setpoint
n
WSHP-n CoolDown Mode High
Temp Setpoint
n
WSHP-n Zone
Temperature
Sensor
n
WSHP-n Zone
Temperature
Setpoint-Cooling
n
WSHP-n Zone
Temperature
Setpoint-Heating
n
WSHP-n Zone
Temperature
Unoccupied
Setpoint-Cooling
n
WSHP-n Zone
Temperature
Unoccupied
Setpoint-Heating
n
WSHP-n Zone
Temperature
SetpointDeadband
n
WSHP-n Override
Water Source Heat Pump System
n
106
Cx Assistant’s Sequence of Operation
Water Source Heat Pump System
April 2004
107