Appendix B:
Building Systems Sequence of Operations - Sample
The Building Systems Sequence of Operations outlines the as-operating sequence of operations for all HVAC and lighting control systems, as well as integration of the fire/life safety and HVAC systems. This document was developed in order to satisfy LEED-EB Energy & Atmosphere prerequisite and credit requirements.
BestBuilding
Sequence of Operation
Index
Air Handling System Description and Control
Cold-deck Air Handlers: AHU1 through AHU4
Fan OFF condition
Fan Start-up or Shut-down
Return Fan Volume Control
Discharge Air Temperature Controls
Static Pressure Controls
Warm-up Control
Night Low Limit
Night purge
Alarms and Safeties
Manual smoke pressurization system
Dedicated Ventilation Air Fans: AHU7 through AHU10
Hot deck air handlers: AHU 5 and AHU 6
Fan OFF condition:
Fan Start-up or Shut-down:
Discharge Air Temperature Controls
Static Pressure Controls
Warm-up Control
Night Low Limit
Alarms and Safeties
VAV Box Description and Control
Conference Room VAV Boxes
Conference Room is Occupied (during normal building operating hours)
Conference Room is Unoccupied (during normal building operating hours)
Building is Unoccupied
Dual Duct VAV Boxes
Occupied Condition
Unoccupied Conditions
Cooling-only VAV Boxes
Occupied Condition
Unoccupied Conditions
Chilled Water System Description and Control
Chillers and Primary / Secondary Pump Control
The EMCS control points for Chillers 1, 2, and 3
Chilled water supply (CHWS) temperature reset
Chilled Water System Enable
Chiller Staging
Primary Chilled Water Pumps
Secondary Chilled Water Pumps
Condensing Water and Cooling Tower Control
Cooling Tower Operation
Condenser Water Pumps for Chillers
Condenser Water Pumps for the Heat Exchanger (cooling tower side)
Distribution Water Pumps for the Heat Exchanger (Liebert side)
Heating Water System Description and Control
General System Control
System start-up
System Shutdown
Condensing Boiler Control
Non-condensing Boiler Control
Distribution Water Loop Control
General Control Features
Garage Exhaust Fan (EF-1) Control
General Exhaust Fan Control
Lighting Control
Parking Area
General Public and Jury Assembly Areas
Office Spaces
Mechanical Rooms
Conference Rooms
Fire/Life Safety System Control
Ongoing Commissioning Plan Appendix B – Sequence of Operation Sample1
Air Handling System Description and Control
Heating and cooling for the building is provided by dual duct variable air volume (VAV) air handling systems, consisting of the following equipment:
AHU1 and AHU2:Cold-deck air handling units serving the B2 through 8th floors
AHU3 and AHU4:Cold-deck air handling units serving the 9th through 16th floors
AHU5 and AHU6:Hot-deck air handling units serving the B2 through 16th floors
AHU7 and AHU8:Ventilation air handling units serving AHU1 and AHU2, respectively
AHU9 and AHU10:Ventilation air handling units serving AHU3 and AHU4, respectively
Central exhaust for the building includes EF5 through EF9 and EF12, and operation of these exhaust fans is interlocked with central air handling unit operation. Detailed sequence of operations for each air handling system,and the central exhaust fans, is provided below.
Cold-deck Air Handlers: AHU1 through AHU4
Each cold-deck air handling unit consists of two supply and return fans, each with separate VFD’s and motors, economizer dampers, and chilled water cooling coils. Operation of each air handling unit is based on the general schedule of 5:30AM to 5:30PM, Tuesday through Friday, with Monday (or the first day after a holiday shutdown) start-up at 3:30AM.
Fan OFF condition
Normally open return air damper is open
Normally closed economizer and relief dampers are closed
Normally closed cooling coil valves are closed
Isolation dampers on each supply fan are closed
Fan Start-up or Shut-down
Fans start or shutdown upon signal from the EMCS. Basic system operating schedule is from 5:30AM to 5:30PM, Tuesday through Friday, with Monday (or the first day after a holiday shutdown) start-up at 3:30AM. The system is shut down on weekends and holidays.
Upon an enable command from the EMCS, the supply fan isolation dampers are commanded open. The supply fan VFD starts, along with the central exhaust fans (EF-5, EF-6, EF-7, EF-8, EF-9, EF-12).
Both supply fans ramp up and down at the same speed based on maintaining duct static pressure setpoint.
The operator can shut down any one of the fan motors from the EMCS. When a fan shuts down, the respective isolation damper is closed as well to prevent recirculation of air through the fan that is not operating.
Return Fan Volume Control
Due to envelope leakage, stack effect created a negative pressure in the lobby and lower floors, allowing unconditioned air to infiltrate into the building. To alleviate building pressurization issues, all return fans associated with AHU1, AHU2, AHU3, and AHU4 and have been commanded OFF at the operator work station via a software override. If the lobby experiences excessive positive pressure during warmer outdoor air conditions (i.e. negative stack effect), facility operators should release the software override on the return fans associated with AHU1 and AHU2 only, allowing these fans to operate. The return fans associated with AHU3 and AHU4, should remain OFF. Command AHU1 and AHU2 return fans back OFF at the end of the day or when the lobby doesn’t experience excess positive pressure (typically when outdoor air temperature is below 75F).
A future recommendation is to automatically control only the return fans associated with AHU1 and AHU2 based on outdoor air temperature. For example all return fans are OFF when outdoor air temperature is less than 75F and AHU1/AHU2 return fans are commanded ON when outdoor air temperature exceeds 75F (user adjustable value). This would eliminate the need for manual control.
Discharge Air Temperature Controls
For AHU1 through AHU4, the economizer, relief air, and return air dampers are modulated in sequence with the normally closed cooling coil valve to maintain discharge air temperature setpoint. When the outdoor air dry-bulb temperature is less than return air dry-bulb temperature, the economizer is enabled and the outdoor air dampers are modulated as necessary in conjunction with the cooling coil valve to meet discharge air temperature setpoint. The economizer is disabled and goes to 100% return air when the outdoor air dry-bulb temperature is greater than return air dry-bulb temperature. In this condition, the cooling coil valve is modulated as necessary to meet discharge air temperature setpoint.
Discharge air temperature (DAT) setpoint is reset based on loads within the building as determined by the deviation of zone temperature from the active cooling setpoint for selected zones. If the zone temperature of four (4) or more selected zones is warmer than the active cooling setpoint by 2F, then discharge air temperature setpoint is lowered by 2F. If four (4) or more selected zones remain warmer than the active cooling setpoint by 2F the next time the control loop is executed (every 5minutes), then the discharge air temperature setpoint is lowered again by 2F. This process continues until either there are less than four (4) zones warmer than the active cooling setpoint by 2F (at which point the discharge air temperature setpoint is held steady at the current value) OR until a minimum setpoint value of 55F is reached.
The discharge air temperature setpoint is raised by 2F when two (2) or less selected zones are warmer than the active cooling setpoint by 2F. If two (2) or less selected zones remain warmer than the active cooling setpoint by 2F the next time the control loop is executed (every 5minutes), then the discharge air temperature setpoint is raised again by 2F. This process continues until either there are greater than two (2) zones warmer than the active cooling setpoint by 2F (at which point the discharge air temperature setpoint is held steady at the current value) OR until a maximum setpoint value of 70F is reached.
Note that the Excel spreadsheets AHU1&2.xls and AHU3&4.xls(located on the operator work station under file folder C:\Project\BestBuilding) can be used to help troubleshoot discharge air temperature reset controls. The spreadsheet documents all of the polled zones and their respective deviation from setpoint. This can assist facility staff in identifying which zones are driving the control strategy (either legitimately due to zone loads or as a “rogue” box that may warrant further investigation or maintenance).
Static Pressure Controls
Variable frequency drives are used to control supply fan speed based on maintaining duct static pressure setpoint. Static pressure setpoint is reset based on loads within the building as determined by VAV box cold-deck damper position for selected zones. If the cold-deck damper for four (4) or more selected zones is 100% open, then static pressure setpoint is raised by 0.2in.wc. If the cold-deck damper for four (4) or more selected zones remain 100% open the next time the control loop is executed (every 5minutes), then duct static pressure setpoint is raised again by 0.2in.wc. This process continues until either there are less than four (4) zones with cold-deck dampers 100% open (at which point duct static pressure setpoint is held steady at the current value) OR until a maximum setpoint value of 2.5in.wc.is reached. An alarm is sent when duct static pressure is greater than 3.5in.wc. and the system shuts down when the pressure exceeds 4.0in.wc. through a hard-wired safety.
The duct static pressure setpoint is lowered by 0.2in.wc. when the cold-deck damper for two (2) or less selected zones are 100% open. If the cold-deck damper for two (2) or less selected zones remain 100% open the next time the control loop is executed (every 5minutes), then duct static pressure setpoint is loweredagain by 0.2in.wc. This process continues until either there are greater than two (2) zones with cold-deck dampers 100% open (at which point duct static pressure setpoint is held steady at the current value) OR until a minimum setpoint value of 1.5in.wc. is reached.
Note that the Excel spreadsheets AHU1&2.xls and AHU3&4.xls(located on the operator work station under file folder C:\Project\BestBuilding) can be used to help troubleshoot static pressure reset controls. The spreadsheet documents all of the polled zones and their respective cold-deck damper position. This can assist facility staff in identifying which zones are driving the control strategy (either legitimately due to zone loads or as a “rogue” box that may warrant further investigation or maintenance).
Warm-up Control
The warm-up control sequence is enabled when the discharge air temperature setpoint is greater than or equal to 70F between 4AM and 7AM. During warm-up, the air handling units operate in 100% return air mode with cooling locked out. Central exhaust fans (EF-5, EF-6, EF-7, EF-8, EF-9, and EF-12) are commanded OFF during warm-up operating mode.
Night Low Limit
AHU1 through AHU4 stay OFF when night low limit control sequence is enabled.
Night purge
The building is flushed with outside air if the space temperature rises above 80F in any zone and the outside air is below65F. All supply fans are commanded ON and economizer dampers 100% open. Night purge is disabled when return air temperature drops to 75F.
Alarms and Safeties
The following alarms and safeties are programmed as part of the operating sequences.
- Dirty Filter. A differential switch across the filter banks generates alarm at the operator work station when the pressure drop exceeds the manual setpoint. This indicates the filters need to be replaced.
- Freeze Stat. A low limit thermostat is used to stop the fan, return all dampers to their normal positions, and alarm the EMCS upon detection of 40F at the mixed air low limit thermostat.
- Supply Fan Failure. A fan failure alarm is sent to the operator work station if a supply fan is commanded ON but a positive status signal is not received to verity fan operation. Fan failure is detected via a current switch mounted on the electrical power leads to the motor. Both supply fans within the respective air handling unit receive the same enable and speed signal from the EMCS based on the static pressure control discussed above.
- Smoke Alarm. On a fire signal, as determined by smoke detectors or through the building fire system alarm, all air handling units and exhaust fans are shut down and all dampers return to “normal” positions (normally open return damper, normally closed economizer and relief dampers, normally closed fan isolation dampers).
Manual smoke pressurization system
Each air handling unit can be controlled manually through the Fireman’s CommandCenter. Supply and return fans, as well as outdoor, return, and relief dampers, can be commanded independently in order to achieve the desired smoke control strategy.
Dedicated VentilationAir Fans: AHU7 through AHU10
Each cold-deck air handling unit has a dedicated ventilation fan unit which consists of a constant volume supply fan, fan isolation damper, pre-heat coil, and a face-and-bypass damper. The original intent of the system was to provide minimum ventilation to each central air handling unit whenever itis enabled. However, it was noted during the retrocommissioning process that the amount of ventilation air introduced by the dedicated fan systems far exceeded the ventilation need for the building based on actual occupancy. Tests verified that adequate ventilation was drawn in through the ventilation fan air handling units even if the ventilation fans were turned OFF. Hence, these fans are commanded OFF, but the isolation dampers are commanded open to allow ventilation air to be drawn into the central air handling unit by the supply fan.
The pre-heat coil valve is modulated as necessary to meet discharge air temperature setpoint. The valve is commanded closed when there is a call for cooling (economizer and/or cooling coil valve is modulating) and allowed to pre-heat ventilation air when the economizer is commanded closed. The pre-heat coil tempers the ventilation air before it is mixed with return air to meet discharge air temperature setpoint. The pre-heat valve is also commanded open whenever the outdoor air temperature is below 35F.
Hot deck air handlers: AHU 5 and AHU 6
Each hot-deck air handling unit consists of two supply fans, each with separate VFD’s and motors, and hot water heating coils. Operation of each air handling unit is based on the general schedule of 5:30AM to 5:30PM, Tuesday through Friday, with Monday (or the first day after a holiday shutdown) start-up at 3:30AM.
Fan OFF condition:
Normally openheating coil valves are closed
Isolation dampers on each supply fan are closed
Fan Start-up or Shut-down:
Fans start or shutdown upon signal from the EMCS. Basic system operating schedule is from 5:30AM to 5:30PM, Tuesday through Friday, with Monday (or the first day after a holiday shutdown) start-up at 3:30AM. The system is shut down on weekends and holidays.
Upon an enable command from the EMCS, the supply fan isolation dampers are commanded open and the supply fan starts.
Both supply fan VFDs ramp up and down at the same speed based on maintaining duct static pressure setpoint.
The operator can shut down any one of the fan motors from the EMCS. When a fan shuts down, the respective isolation damper is closed as well to prevent recirculation of air through the fan that is not operating.
Discharge Air Temperature Controls
Discharge air temperature setpoint is reset based on outdoor air temperature per the following schedule:
- 70F DAT setpoint when outdoor air temperature is greater than 60F (basically use return air to meet the load)
- 110F DAT setpoint when outdoor air temperature is less than 48F.
Static Pressure Controls
Variable frequency drives are used to control supply fan speed based on maintaining duct static pressure setpoint. Static pressure setpoint is reset based on loads within the building as determined by VAV box hot-deck damper position for selected zones. If the hot-deck damper for four (4) or more selected zones is 100% open, then static pressure setpoint is raised by 0.2in.wc. If the hot-deck damper for four (4) or more selected zones remain 100% open the next time the control loop is executed (every 5minutes), then duct static pressure setpoint is raised again by 0.2in.wc. This process continues until either there are less than four (4) zones with hot-deck dampers 100% open (at which point duct static pressure setpoint is held steady at the current value) OR until a maximum setpoint value of 2.5in.wc. is reached. An alarm is sent when duct static pressure is greater than 3.5in.wc. and the system shuts down when the pressure exceeds 4.0in.wc. through a hard-wired safety.