112039.00 – CORE & SHELL
SECTION 230993
SEQUENCE OF OPERATIONS FOR HVAC CONTROLS
SECTION 230993 - SEQUENCE OF OPERATIONS FOR HVAC CONTROLS
PART 1 - GENERAL
1.1
RELATED DOCUMENTS
A.
1.2
Drawings and general provisions of the Contract, including General and Supplementary
Conditions and Division 01 Specification Sections, apply to this Section.
SUMMARY
A.
This Section includes control sequences for HVAC systems, subsystems, and equipment.
B.
Related Sections include the following:
1.
1.3
Section 230900 "Instrumentation and Control for HVAC" for control equipment and
devices and for submittal requirements.
DEFINITIONS
A.
DDC: Direct digital control.
B.
VAV: Variable air volume.
1.4
RTU SEQUENCE OF OPERATIONS:
A.
General: Provide factory mounted and wired microprocessor based controls, interfaced with the
Building Automation System (BAS). Provide any field supplied devices to complete this
sequence of operation. Install any RTU manufacture supplied devices to complete this
sequence of operation. Coordinate with Section 15782 for RTU manufacturer supplied devices.
The BAS will determine Occupied/Unoccupied mode for the rooftop unit from Owner defined
schedule.
B.
Unoccupied Mode: Unit fans, heat, and refrigeration will be de-energized, and the outside air
damper will be closed. When at least 3 zones associated with a particular unit fall outside of the
unoccupied mode temperature range (60°F to 85°F-adjustable), the unit fan will be energized
and controlled as described below. The unit outside air damper shall remain closed and
exhaust fan shall remain de-energized, unless cooling is called for and economizer operation is
available. The unit shall be de-energized once all zones are within the unoccupied mode
temperature range.
1.
Unoccupied Heating Mode: If the zone temperatures are below the unoccupied mode
range, all zone air terminals’ control sequence shall be changed to reverse acting (see
below), and the unit discharge air temperature will be controlled to 95°F (adjustable) by
modulating the gas furnace.
2.
Unoccupied Cooling Mode: If the zone temperatures are above the range, the unit
discharge air temperature will be controlled to 55°F (adjustable) by staging on DX cooling
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and economizer. Unit packaged controls shall use economizer mode for first stage of
cooling if conditions are appropriate.
C.
RTU Morning Start-up: BAS shall use an optimized morning start-up routine, incorporating
outside air temperature, zone temperatures, and past history of building response to determine
the optimum time to start the rooftop unit. BAS shall stagger the start of the Rooftop Units to
avoid a sudden electrical current inrush. Upon initiating morning start-up, either by the
optimized start-up routine, or from a request for unoccupied mode override at a room sensor,
the zone temperature setpoint range shall be reset to occupied mode, and the unit fan shall be
energized and control as described for Occupied Mode. The unit outside air dampers shall
remain closed and relief fans are de-energized, unless cooling is called for and economizer
operation is available. Once scheduled building occupancy time is reached, outside air
dampers and relief fans are enabled. If Start-up was initiated by an unoccupied mode override
button, initiate occupied mode as soon as neither Morning Warm-up nor Morning Cool-down
conditions apply. Unit discharge air temperature shall be controlled as described below:
1.
2.
3.
4.
Morning Warm-Up: If more than 25% of the zones are below occupied mode setpoint, all
zone air terminals’ control sequence shall be changed to reverse acting (see Air Terminal
sequence), and the unit discharge air temperature will be controlled to 95°F (adjustable)
by modulating the gas furnace. Morning warm-up is terminated when no more than 15%
of zones are below setpoint. Upon termination, unit operates to maintain discharge air
temperature as described for Occupied Mode.
Morning Cool-Down: If more than 40% of the zones are above setpoint, DX cooling or
economizer will operate to maintain discharge air temperature setpoint as described for
Occupied Mode.
Morning Recirculation: If neither of the above two conditions apply, unit fans simply
recirculate building air until occupied time is reached or one of the above two conditions
apply.
Conflict Resolution: If conditions for both Morning Warm-up and Cool-down apply, initiate
Warm-up mode.
D.
Supply Fan Speed Control: Modulate the supply fan variable frequency drive, to maintain
discharge air static pressure set point of 1.25” WG (adjustable) at a sensor located
approximately 2/3 of the way downstream of the fan.
E.
Relief Fan Speed Control: Modulate the exhaust fan variable frequency drive to maintain
building static pressure within a range of 0.05 to 0.1 inches water column (adjustable). Locate
the building static pressure sensor above the ceiling of the ground floor, or in the lobby. Locate
as determined by field conditions, being careful to find a representative condition.
F.
Minimum Outside Air Damper Control: Once the fans are proven on, the minimum outdoor air
damper will modulate to maintain a constant outside air quantity as measured by unit’s outside
air sensor.
G.
Supply Air Temperature Setpoint - Optimized: The controller shall monitor the supply air
temperature and shall modulate the gas fired furnace, or stage on DX cooling to maintain a
supply air temperature setpoint reset based on zone cooling requirements, and to minimize
terminal unit electric heat operation. Cooling demand may be measured by a combination of air
terminal damper position and variance from space setpoint, or other method as proposed by the
Contractor and approved by the Engineer.
1.
The supply air temperature setpoint shall be reset based on zone cooling requirements
as follows:
a.
The initial supply air temperature setpoint shall be 56°F (adj.).
b.
As cooling demand increases, the setpoint shall incrementally reset down to a
minimum of 52°F (adj.).
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c.
2.
As cooling demand decreases, the setpoint shall incrementally reset up to a
maximum of 62°F (adj.).
Supply Air Temp alarms: If the supply air temperature is greater than 110°F (adj.) or less
than 45°F (adj.) send an alarm to the OWS.
H.
Economizer Control: If the outdoor air temperature is 5 Deg F (adjustable) or more, below return
air temperature, the mixed air dampers will modulate to maintain discharge air temperature set
point. DX cooing shall be allowed to operate during economizer operation, once the outside air
dampers have opened fully.
I.
Low Temperature Protection Control: When air temperature downstream of the heating coil
drops below 40 Deg F (adjustable, as sensed by low limit thermostat), the following will occur:
1.
The supply and exhaust fans will shut down
2.
The outdoor air damper will close
3.
The return air damper will open
4.
An alarm will be sent to the BAS.
The low limit thermostat will need to be manually reset for normal operation to resume.
J.
Smoke Detection Control: Upon detection of smoke from the return or supply duct smoke
detector, the fans will cycle off, the outdoor air dampers close, and an alarm will be sent to the
BAS. Once the detectors are reset, the unit will return to normal control.
K.
High Static Pressure Detection Control: Upon detection of high static pressure from either the
supply static pressure switch or the return static pressure switch, the fans will cycle off, the
outdoor air and exhaust dampers will close, and an alarm will be sent to the BAS. Once the
static pressure switches are reset, the unit will return to normal control.
L.
Filter Status: Monitor pressure switch at filter bank, and alarm when ∆p increases above .80” wg
(adjustable).
M.
Early Occupancy Operation: If the HVAC system is required to operate with less than 40% of
the floor area occupied, only one Rooftop Unit shall be energized at a time. The operating and
standby Rooftop Units shall be alternated every week.
1.5
AHU SEQUENCE OF OPERATIONS:
A.
General: The unit will be controlled to operate continuously by a local DDC control panel,
interfaced with the Building Automation System (BAS). The system will be complete with
access through local or remote terminals. Whenever the fans are off, the outdoor air and
exhaust air dampers, the chilled water and hot water coil valves will all be closed, the return air
dampers will be open, and heating and refrigeration will be locked out.
B.
Fan Start-up: The BAS will open minimum outdoor air dampers and supply fan shall be allowed
to start. Once the supply fan is proven on (through current switch), the BAS will start the return
fan). Once the return fan is proven on (through current switch), the unit will be allowed to go
under control. If either fan fails to prove flow, an alarm will be sent to the BAS.
C.
Fan Speed Control: The BAS will modulate the supply fan variable frequency drive, to maintain
discharge air static pressure set point of 1.25” WG (adjustable) at a sensor located
approximately 2/3 of the way downstream of the fan. The BAS will modulate the return fan VFD
to maintain a fixed air flow differential between the supply fan air flow monitoring station and the
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return fan air flow monitoring station. This differential will be coordinated with the air balance
contractor for proper building pressurization.
D.
Mixed Air Damper Control: Once the fans are proven on, the minimum outdoor air damper will
modulate to maintain the minimum outside air quantity as measured by the minimum outside air
low monitor. If the outdoor air temperature is 5 Deg F (adjustable) or more, below return air
temperature, the mixed air dampers will modulate to maintain discharge air temperature set
point. Return, Relief, Minimum Outside air, and Outside Air dampers shall each be controlled
individually. Hardware or software linking is not allowed.
E.
Discharge Air Temperature Control: The BAS shall sequence the modulating gas furnace and
stages of DX cooling as required to maintain a discharge air temperature of 50°F (adjustable).
F.
Low Temperature Protection Control: When the discharge air temperature drops below 45 Deg
F (adjustable), the mixed air dampers will go to their normal positions. And, an alarm will be
sent to the BAS.
When air temperature downstream of the heating coil drops below 40 Deg F (adjustable, as
sensed by low limit thermostat), the following will occur:
1.
The supply and return fans will shut down he outdoor air and exhaust air dampers will
close 100%
2.
The return air damper will open 100%
3.
The hot water coil pump will continue to run
4.
The control valves will open to full flow to the coil
5.
An alarm will be sent to the BAS.
The low limit thermostat will need to be manually reset for normal operation to resume.
G.
Smoke Detection Control: Upon detection of smoke from either the supply smoke detector or
the return smoke detector, the fans will cycle off, the outdoor air, exhaust dampers, all associate
fire/smoke dampers will close, and an alarm will be sent to the BAS. Once the detectors are
reset, the unit will return to normal control.
H.
High Static Pressure Detection Control: Upon detection of high static pressure from either the
supply static pressure switch or the return static pressure switch, the fans will cycle off, the
outdoor air and exhaust dampers will close, and an alarm will be sent to the BAS. Once the
static pressure switches are reset, the unit will return to normal control.
1.6
TERMINAL UNIT OPERATING SEQUENCE
A.
VAV, Terminal Air Units
1.
General: Provide BAS VAV terminal controller and room sensor with warmer/cooler
setpoint adjustment. Each zone shall be allowed a fixed range of setpoint adjustment
(72°F to 77 °F adjustable). BAS shall adjust the range; user may adjust within this range
via the "Warmer/Cooler" selector on the thermostat. Each tenant suite shall have the
capability of an individual occupied/unoccupied schedule, which may be different from the
RTU schedule, except that when RTU is in unoccupied mode, all zones must also be in
unoccupied mode. At least one sensor in each tenant suite shall have an override button.
BAS shall enable override buttons on an Owner defined basis, so that only Ownerapproved tenants can override unoccupied mode. Log all override requests, totalizing
each suite’s requested override hours on a monthly basis for Owner billing purposes.
Group suites’ schedules together as required to assure that when a rooftop unit is
energized, enough terminal boxes are in occupied mode to meet the rooftop unit
manufacturer’s minimum airflow requirements. \
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2.
3.
4.
B.
SECTION 230993
SEQUENCE OF OPERATIONS FOR HVAC CONTROLS
Occupied Mode: The controller shall measure room temperature and inlet duct velocity
and modulate the primary air volume damper through PI control logic to close the damper
on decreasing room temperature and open the damper on increasing room temperature,
to maintain room temperature setpoint while providing pressure independent operation.
For terminals with heating coils, upon reaching the minimum primary air volume and
room temperature continues to fall below the setpoint, increase the air volume to the
scheduled heating value and stage on/modulate the electric heaters.
Unoccupied Mode: Revise setpoint to a dead band range of 60°F to 85°F. (adjustable).
Within this range, air terminal dampers shall be closed. If Unoccupied Heating Mode is
initiated (see RTU sequence), lock out the electric heaters, and the air terminal controller
shall be set for reverse acting control, i.e. measure room temperature and inlet duct
velocity and modulate the primary air volume damper through PI control logic to open the
damper on decreasing room temperature and close the damper on increasing room
temperature. Otherwise, air terminal shall operate similar to occupied mode. Where
enabled by the BAS, pushing the override button on a room sensor causes all associated
air terminals within a tenant suite and the associated rooftop unit to go through Morning
Start-up and return to Occupied Mode for two hours (adjustable). Group additional
terminal boxes together as required to assure that the rooftop unit manufacturer’s
minimum airflow is maintained.
Morning Start-up: Upon initiation of Morning Start-up (see RTU sequence), zone setpoint
is returned to Occupied Mode. If the BAS determines the need for morning warm-up (see
RTU sequence), all air terminal controllers shall be set for reverse acting control similar to
Unoccupied Heating mode, and electric heaters shall be locked out until unit is returned
to occupied mode. If the BAS determines the need for morning cool-down or
recirculation (see RTU sequence), the air terminal controller shall operate similar to
Occupied mode.
Fan Powered VAV, Terminal Air Units:
1.
General: Provide BAS VAV terminal controller and room sensor with NO setpoint
adjustment. The setpoint for each fan powered terminal box zone shall set at the BAS.
Occupied/Unoccupied mode shall follow the associated rooftop unit’s schedule. Fan
powered terminal boxes shall not be included in determining initiation of unoccupied
heating or cooling mode, or in determining morning start up mode at the rooftop unit
level.
2.
Occupied Mode: The fan shall operate continuously. The controller shall measure room
temperature and inlet duct velocity and modulate the primary air volume damper through
PI control logic to close the damper on decreasing room temperature and open the
damper on increasing room temperature, to maintain room temperature setpoint while
providing pressure independent operation. Upon reaching the minimum primary air
volume and room temperature continues to fall below the setpoint, stage on/modulate the
electric heaters.
3.
Unoccupied Mode: Fan shall be de-energized. Revise setpoint to a dead band range of
60°F to 85°F. (adjustable). Within this range, air terminal primary dampers shall be
closed. If space temperature falls below this range, energize fan and stage on electric
heaters. If Unoccupied Heating Mode is initiated at the rooftop unit (see RTU sequence),
energize the terminal box fan, lock out the electric heaters and set the air terminal
controller for reverse acting control, i.e. measure room temperature and inlet duct velocity
and modulate the primary air volume damper through PI control logic to open the damper
on decreasing room temperature and close the damper on increasing room temperature.
If Unoccupied Cooling Mode is initiated at the rooftop unit, the terminal box fan shall be
energized and the air terminal shall operate similar to occupied.
4.
Morning Start-up: Upon initiation of Morning Start-up (see RTU sequence), energize
terminal unit fan, and zone setpoint shall be returned to Occupied Mode. If the BAS
determines the need for morning warm-up (see RTU sequence), fan powered air terminal
controllers shall be set for reverse acting control similar to Unoccupied Heating mode,
and electric heaters shall be locked out until unit is returned to occupied mode. If the
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BAS determines the need for morning cooldown or recirculation (see RTU sequence), the
air terminal controller shall operate similar to Occupied mode
1.7
EXHAUST FAN SEQUENCES
A.
The BAS shall have start/stop control, status indication, runtime, and alarm notification for all
fans.
B.
General exhaust fans shall operate on an adjustable 7-day Time-of-Day schedule. Fans shall be
scheduled to operate with building occupancy.
C.
Mechanical/Electrical Room Exhaust Fans shall operate on a space thermostat to maintain
room temperature at 75°F (adj.)
1.8
SPLIT SYSTEM COOLING UNIT SEQUENCE
A.
Occupied/unoccupied :
1.
Evaporator fan shall activate.
2.
Upon call for cooling via wall-mounted thermostat, the associated air-cooled condenser
shall activate and stage compressors as required to maintain temperature.
B.
Alarms:
1.
Upon detection of high condensate level via high condensate sensor, the ac system shall
shutdown and send alarm signal to bas.
1.9
UNIT HEATER AND CABINET UNIT HEATER SEQUENCE
A.
The BAS shall have start/stop control, status indication
B.
Unit heaters shall each be provided with a low voltage electric wall-mounted room thermostat,
which shall cause the fan to be cycled "on" or "off" as required to satisfy the thermostat setting.
Control circuit voltage shall not exceed 120 volts to ground. A relay shall activate the electric
heating coil when the fan is on, and shall deactivate when the fan is off
C.
All unit heaters located in public areas, stairs and shell spaces shall be accessible thru the bas
system.
1.10
ELEVATOR SUMP PUMP SEQUENCE
A.
The BAS shall have start/stop control, status indication, runtime, and alarm notification.
B.
The Sump alarm shall alarm BAS for:
1.
Hydraulic oil spill alert.
2.
High liquid connection.
3.
High amperage.
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PART 2 - PRODUCTS (Not Applicable)
PART 3 - EXECUTION (Not Applicable)
END OF SECTION 230993
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