SECTION 23 09 93 SEQUENCE OF OPERATIONS FOR HVAC CONTROLS PART 1 - GENERAL 1.1 SUMMARY A. This Section includes control sequences for HVAC systems, subsystems, and equipment. B. See Division 23 Section "230900 Instrumentation and Control" for control equipment and devices and for submittal requirements. 1.2 GENERAL A. The DDC system shall utilize a single main computer (connected to the Westlake School System Wide Area Network (WAN)) located at the High School, where all software, graphics, alarms, and trends shall reside, and shall communicate to the Middle School DDC System and Elementary School DDC System via the Westlake School System Wide Area Network (WAN). The DDC System communication protocol shall be BacNet where indicated on the drawings, and can be the DDC system communication standard protocol between controllers and devices as long as the communication speed is sufficient to perform all functions described in the Sequence of Operation in a stable manner and must be demonstrated to the satisfaction of the Architect/Engineer. B. The DDC system shall be capable of accepting any device that communicates via Bac Net TC/IP. The DDC system shall be capable of communicating to the Lighting Controls System via BacNet TC/IP, see Electrical Specifications for additional information. The DDC system shall be capable of communicating to the Fire Alarm System via BacNet TC/IP, see Electrical Specifications for additional information. C. The DDC system software shall have a Microsoft Windows base, and any personal computer, smart phone or tablet with Wi-Fi capability can monitor and control any part of the system via the Internet using Microsoft Windows Internet Explorer and without any proprietary software on the computer or any licensing requirements, and, there shall be a minimum of 5 access levels from view only to full access. See Specification 230990 Instrumentation and Control for additional requirements and information. D. Controls Contractor shall provide temperature differentials and time delays as required to maintain systems stability. E. Controls Contractor shall furnish and install all communication cabling between all DDC system controllers and device. The Controls Contactor shall coordinate with the Division 27 Technology Contractor all required connections to the Westlake School System Wide Area Network (WAN). F. DDC system shall be capable of providing alarms of any point within the system. The DDC system shall be capable of trending any point within the system. G. All Air Handling Unit outdoor air airflow monitors and exhaust air airflow monitors are not temperature compensating type. DDC System shall compute temperature compensation based on temperature data from the global outdoor air temperature sensor and shall control outdoor 09-ED1-045C 23 09 93-1
air cfm based on temperature compensation. Each graphic display that contains an outdoor air airflow rate shall show the following; outdoor air airflow control point, temperature compensated outdoor air airflow rate and non-temperature compensated outdoor air airflow rate, and shall include on the graphic display; design non-temperature compensated outdoor air airflow setpoint summer and design non-temperature compensated outdoor air airflow setpoint winter. Design outdoor air airflow setpoint is defined as the values shown on Drawing M902 within the Air Handling Unit Equipment Schedule. H. DDC System Graphics shall consist as a minimum of : 1. Cover Graphic Display showing entire floor plan, with hot spot to move to individual floor plans. 2. 7 Floor Plans that match the drawing floor plans shown on drawings M101 through M107, and each floor plan shall display the room temperature and CO2 level, and has a hot spot at the room temperature or CO2 level such that the cursor can be brought to this hot spot and then the graphic display of the FPVAV or VAV box is then displayed. 3. Display of the heating hot water plant 4. Display of the chilled water plant 5. Display of the heat pump chiller 6. Display of each Air Handling Unit, 6 graphic displays 7. Display of each Fan Powered VAV Box 8. Display of each single duct shutoff type VAV box 9. Display of cabinet unit heaters, one display for all cabinet unit heaters. 10. Display of status of all exhaust fans (one display for all fans) controlled and/or monitored by the DDC system 11. Display of Mechanical Room unit heaters, one display for unit heaters. 12. Display of Cross-Connect Room Temperature and Kitchen Freezer and Kitchen Cooler temperature 13. Display of Electricity Meter data 14. Display of Water Meter data 15. Display of Natural Gas Meter data 1.3 HEATING HOT WATER BOILERS AND PUMPS SEQUENCE OF OPERATION A. The heating hot water boiler system consists of two heating hot water boilers, two circulating pumps (lead/standby) and a heat pump chiller. The boilers provide heating hot water during Fall, Winter and Spring. The heat pump chiller provides heating hot water during Summer. B. One heating hot water pump shall be designated as the lead pump (adj) and other shall be the lag pump. The lag pump shall automatically start on a lead pump failure. The DDC system shall rotate the lead pump and lag pump on a weekly (adj.) basis. C. One heating hot boiler shall be designated as the lead boiler (adj) and other shall then be the lag boiler. The lag boiler shall automatically start on a lead boiler failure, and the lag boiler shall also operate when the DDC system requires two boilers to operate. The DDC system shall rotate the lead boiler and lag boiler on a weekly (adj.) basis. 23 93 93-2 09-ED1-045C
D. Once the boiler is energized, the DDC system shall reset the boiler discharge temperature to maintain its heating hot water temperature setpoint, and shall be reset based on outdoor air temperature according to the following schedule: Outdoor Air Temp Above 55 F (adj.) Below 35 F (adj.) Hot Water Supply Temp 110 F (adj.) 140 F (adj.) E. When the outdoor temperature is below 35F (adj), the DDC system shall energize the lead hot water pump and enable lead boiler to run continuously. When the outdoor temperature is below 55F (adj) the DDC system shall energize the lead hot water pump and enable lead boiler to run continuously during occupied periods and during the optimal start period (see AHU sequence of operation). During unoccupied periods when the outdoor air temperature is above 35F the DDC system shall energize the lead hot water pump and enable lead boiler to run continuously when there is a demand for heat from any heating coil (AHU, VAV Box, Unit Heater, Etc) on the DDC system, and the pump and boiler shall be energized/enabled for a minimum 30 minute period. During occupied periods when the outdoor air temperature is above 55F the DDC system shall energize the lead hot water pump and enable lead boiler to run continuously when there is a demand for heat from any heating coil (AHU, VAV Box, Unit Heater, etc) on the DDC system, and the pump and boiler shall be energized/enabled for a minimum 30 minute period. When there is a call for chilled water the DDC system shall energize the heat pump chiller and heat rejected from the heat pump chiller shall be utilized as heating hot water, see Heat Pump Chiller Sequence of Operation for additional information. F. When the lead boiler is energized by the DDC system, its water isolation valve shall open and the boiler shall not be allowed to be enabled until the DDC system verifies proof of water flow through the boiler by the flow switch located in the boiler water discharge pipe. When the lag boiler is enabled by the DDC system, its water isolation valve shall open and the boiler shall not be allowed to be enabled until the DDC system verifies proof of water flow through the boiler by the flow switch located in the boiler water discharge pipe. G. The DDC system shall monitor the firing rate of each boiler. When the lead boiler firing rate exceeds 50%, the DDC system shall enable the lag boiler. When both boiler firing rates fall below 20% for 10 minutes, the DDC system shall disable the lag boiler. H. When a boiler is disabled, the water isolation valve shall remain open for 5 minutes (adj) to allow the exchanger to cool down, and then this isolation valve shall close. When the lead boiler is disabled and the pump is going to be de-energized, the pump shall operate a minimum of 5 minutes (adj) to allow the boiler heat exchanger to cool down. I. Each heating hot water pump is variable speed and the DDC system shall vary the speed of the pump motor as required to maintain differential pressure at both differential pressure sensors. The pump variable speed drive shall be set such that minimum speed is 15 Hz (25%) and maximum speed is 60 Hz (100%). J. Heating hot water flow is monitored through a flow meter located upstream of the pumps intake. Each boiler requires 20 gpm minimum water flow, therefore when one boiler is operating the minimum water flow is 20 gpm and when two boilers are operating the minimum water flow is 40 gpm. 40 gpm minimum water flow shall be maintained by modulating the bypass valve. If water flow falls below 40 gpm for more than 2 minutes, the DDC system shall initiate an alarm. K. Each boiler can be operated in manual mode. Whenever a boiler is to be operated in manual mode, its associated water flow valve must be manually opened. 09-ED1-045C 23 09 93-3
L. Each heating hot water pump can be operated in manual mode, and the operator must select the pump speed at which the pump is to operate. M. The boilers individual operating and safety controls shall be in place for proper boiler firing. The DDC system shall monitor boiler and pump failures. Should a boiler or pump failure occur, the DDC system shall provide an alarm. N. If the fire alarm system is activated for any reason, such as; smoke detector, pull station, flow switch, etc., the DDC system shall disable the heating hot water boilers, de-energize the heating hot water pump and de-energize the heat pump chiller, with the time delays described above to remove heat from the boiler heat exchanger. When the fire alarm system is reset, the DDC system shall automatically restart the heating hot water system. O. When depressed, the boilers Emergency Shutdown switch located within Mechanical Room E18 by mandoor E18b, shall immediately shutdown boiler B-1 and boiler B-2 burners, and the DDC system shall indicate an alarm that this switch has been depressed. Boiler burner shutdown shall occur when the boiler is in either automatic or manual mode. The mushroom switch shall be reset by pulling on the switch. The mushroom switch shall be mounted under a Plexiglas cover to prevent inadvertently pushing on the switch. A red sign with white lettering shall be placed above the switch and state Boiler Emergency Shutdown Switch. 1.4 AIR COOLED CHILLER AND CHILLED WATER PUMPS SEQUENCE OF OPERATION A. The chilled water system consists of one air cooled chiller, two circulating pumps (lead/standby) and a heat pump chiller. The air cooled chiller and heat pump chiller provide chilled water when the outdoor temperature is above 55F. The stand-alone microprocessor based air cooled chiller control panel shall monitor and control the air cooled chiller as directed by its chiller control software. The air cooled chiller control software shall perform control strategies described herein. B. The Controls Contractor shall be responsible to provide any and all BacNet interface equipment in order to achieve the degree of interface and control as required by these sequences of operation. These interfaces shall include the hardware and software of the temperature control system and the chiller manufacturer as well. C. One chilled water pump shall be designated as the lead pump (adj) and other shall be the lag pump. The lag pump shall automatically start on a lead pump failure. The DDC system shall rotate the lead pump and lag pump on a weekly (adj.) basis. D. The DDC system shall energize the lead chilled water pump and enable the chiller whenever the outdoor air temperature is above 55F and the time schedule indicates occupied period. The DDC system shall enable the chiller whenever there is a call for cooling from any Air Handling Unit and the outdoor air temperature is above 55F during unoccupied periods and during the optimal start period. When the chiller is disabled by the DDC system, the chilled water pump shall operate for 5 minutes before shutting down to remove energy from the evaporator and sufficient chilled water valves shall remain open to aid in removing energy from the evaporator. E. The chiller shall be enabled after chilled water pump flow has been proven. When the chiller is enabled, the DDC system shall reset the chiller discharge temperature based on outdoor air temperature according to the following schedule: Outdoor Air Temp Chilled Water Supply Temp 23 93 93-4 09-ED1-045C
At 55 F (adj.) Above 75 F (adj.) 50 F (adj.) 44 F (adj.) F. Chiller Soft Start and Demand Limit. The chiller control software shall provide a user-adjustable loading time or a chilled water pull down delay program at system start-up. This prevents the unnecessary full load operation of chiller and limits system electrical demand during chilled water loop pulldown. The DDC system shall also demand limit the chiller according to the following schedule; Outdoor Air Temp Chiller Demand Limit At 55 F (adj.) 60% (adj.) Above 75 F (adj.) 100% (adj.) G. Each chilled water pump is variable speed and the DDC system shall vary the speed of the pump motor as required to maintain differential pressure at both differential pressure sensors. The pump variable speed drive shall be set such that minimum speed is 15 Hz (25%) and maximum speed is 60 Hz (100%). H. Chilled water flow is monitored through a flow meter located upstream of the pumps intakes. Chiller requires 211 gpm minimum waterflow, and shall be accomplished by utilizing 3-way chilled water control valves on AHU-4 and AHU-6. If water flow falls below 211 gpm for more than 2 minutes, the DDC system shall initiate an alarm. During morning cool-down, the DDC system shall limit the pump speed so that chilled water flow does not exceed 460 GPM, I. The chiller can be operated in manual mode, and each chilled water pump can be operated in manual mode, and the operator must select the pump speed at which the pump is to operate. The pump must be operating before manually starting the chiller and must operate for at least five minutes after the chiller is manually disabled. However, the DDC system must still control the chilled water bypass, or sufficient chilled water valves must be manually opened to ensure chiller minimum water flow. J. The chiller has an integral outdoor thermostat that senses outdoor air temperature, and when it is below 50F (adj) outdoors, this outdoor thermostat shall prevent the chiller from operating. This is to prevent chiller operation if the DDC system global outdoor temperature sensor has failed. K. Chiller Status Report. Provide an operating status report for the chiller. The report shall provide the present status of all binary information and for analog information present value, today s average, and the month-to-date average for the following information to provide the operator with critical chiller operating data: 1. Compressor On/Off Status. 2. Compressor Starts/Run hours Compressor A, B. 3. Phase 1/2/3 percent RLA Compressor A, B. 4. Active chiller diagnostics or alarms. 5. Leaving chilled water temperature. 6. Entering chilled water temperature. 7. Chilled water supply temperature setpoint. 8. Percent RLA/Percent current limit. 9. Outdoor air temperature. 09-ED1-045C 23 09 93-5
L. Diagnostic/Protection. The DDC system shall be able to alarm from all sensed points and diagnostic alarms sensed by the chiller controller. M. All points and diagnostics shall be made available throughout the building control system. The Controls Contractor shall coordinate with the chiller manufacturer to furnish and install the required hardware and software for the information to be relayed through the building control system. The system shall utilize the industry standard BacNet protocol for all information exchange. N. If the fire alarm system is activated for any reason, such as; smoke detector, pull station, flow switch, etc., the DDC system shall disable the air cooled chiller, de-energize the chilled water pump and de-energize the heat pump chiller, with the time delays described above to remove energy from the chiller exchanger. When the fire alarm system is reset, the DDC system shall automatically restart the chilled water system. 1.5 HEAT PUMP CHILLER AND ASSOCIATED PUMPS SEQUENCE OF OPERATION A. The heat pump chiller consists of a water-to-water heat pump, and shall operate in heating mode. The load side (acting as condenser) of the heat pump is utilized to produce heating hot water, the source side (acting as evaporator) is utilized to produce chilled water. B. The Controls Contractor shall be responsible to provide any and all BacNet interface equipment in order to achieve the degree of interface and control as required by these sequences of operation. These interfaces shall include the hardware and software of the temperature control system and the heat pump chiller manufacturer as well. The heat pump chiller shall be enabled whenever the air cooled chiller is enabled, the lead chilled water pump is energized and the lead heating hot water pump is energized. Whenever the heat pump chiller is enabled, its load side pump and source side pump are energized (through an across-the-line motor starter, and these pumps each are a constant speed pumps. When the DDC system disables the heat pump chiller, the load side pump and source side pump shall operate for 5 minutes (adj) to remove energy from the evaporator and condenser. The DDC system shall energize the refrigerant compressors within the heat pump chiller. The DDC system shall monitor the air cooled chiller return water temperature and shall operate the heat pump chiller refrigerant compressors to maintain the following return water temperature; Outdoor Air Temp Chiller Return Water Temp At 55 F (adj.) 50F (adj.) Above 75 F (adj.) 44F (adj.) C. The DDC system shall energize both refrigerant compressors whenever there is a call for cooling. The DDC system shall provide a 30 second (adj) time delay between starting the lead and lag compressors. Both compressors are to operate simultaneously so as to provide the warmest condenser water to the heating hot water system. D. Whenever the heat pump chiller is enabled, the lead boiler shall also be enabled so as to provide additional heat if the heat pump chiller cannot provide sufficient heat to the heating hot water system. E. The heat pump chiller safety controls shall protect the heat pump and shall provide an alarm to the DDC system if any safety is activated. The DDC system shall monitor the status of the load side pump and source side pump (through current sensors) and shall not allow the heat pump chiller compressors to operate if status is not proven, and shall provide an alarm if status is not proven. 23 93 93-6 09-ED1-045C
1.6 AIR HANDLING UNIT AHU-1 SEQUENCE OF OPERATION SERVES ADMINISTRATION AREA A. General Operation 1. The AHU operates as a variable air volume system and consists of; a supply fan with variable frequency drive, return fan with variable frequency drive, relief air section, outdoor air section, air filters, heating hot water coil, chilled water cooling coil, and UVc lights downstream of the cooling coil. Note, the variable frequency drives do not have a bypass contactor, that is, the variable frequency drives only contain an inverter section which will control the speed of the motor. 2. The AHU is scheduled for automatic operation through the DDC system on a time of day basis for occupied and unoccupied modes. 3. Heating coil operation note The heating coil has a temperature sensor on the downstream side, and its purpose is to prevent the heating coil discharge temperature from falling below 50F (adj). B. Occupied Mode 1. The supply and return fans run continuously, the outdoor air dampers and relief air dampers modulate as required to maintain minimum outdoor air setpoint, The unit is controlled as follows 2. The DDC system shall determine the discharge air temperature control point. When the outdoor air temperature is above 55F (adj), the supply air temperature will be maintained at 55F (adj). When the outdoor air temperature is below 55F (adj), the supply air temperature shall be linearly reset between 55F (adj) and 60F (adj) as follows; when the outside air temperature is above 55F (adj) AHU supply air temperature is 55F and when the outside air temperature is below 10F (adj) the supply air temperature is 60F (adj). 3. The DDC system shall determine the supply air duct static pressure control point and shall operate the supply fan variable frequency drive. The DDC system shall monitor the damper position of each terminal unit associated with the AHU and shall reset the supply air duct static pressure control point based on the zone requiring the most pressure, that is, the static pressure control point shall be reset lower until one zone damper is nearly wide open, and the duct static pressure shall be limited to operate between 1.5 WC (adj) and 3.0 WC (adj) measured 2/3 downstream of the supply fan discharge. Supply fan motor speed shall not fall below 25% rated speed, and shall not exceed 100% rated speed. 4. Return fan operation The DDC system shall operate the return fan variable frequency drive. The return fan is interlocked with the supply fan. The return fan speed shall track the supply fan speed. When the AHU is operating in occupied mode, the return fan shall track the supply fan at a rate 10% less (adj) than the supply fan, that is, when the supply fan is at 100% speed the return fan is at 90% speed. When the AHU is operating in unoccupied mode, the return fan shall track the supply fan, that is, when the supply fan is at 100% speed the return fan is at 100% speed. Return fan motor speed shall not fall below 25% rated speed, and shall not exceed 100% rated speed. 5. Economizer operation When the outdoor air temperature is below 60 degree F (adj) economizer operation free cooling shall be allowed. The DDC system shall operate the outdoor air and relief air dampers, heating hot water coil control valve and cooling coil control valve in sequence and without overlap to maintain discharge air temperature. The unit shall maximize economizer operation by allowing the cooling coil to operate during economizer. When the outdoor air temperature is above 60F (adj), economizer is 09-ED1-045C 23 09 93-7
disabled. During economizer operation, outdoor air airflow rate shall not fall below minimum outdoor air airflow setpoint. 6. Minimum outdoor air airflow (as scheduled on drawings). Outdoor air airflow is measured and controlled by the DDC system. Minimum outdoor airflow setpoint adjustment is through the DDC System. There are two minimum outdoor airflow setpoints. When the outdoor temperature is above 75F, the design cooling minimum outdoor air airflow setpoint is used (ASHRAE 62 Ventilation Effectiveness of 1.0). When the outdoor temperature is below 75F, the design heating minimum outdoor air airflow setpoint is used (ASHRAE 62 Ventilation Effectiveness of 0.8). C. Unoccupied Mode 1. When the AHU is off, the supply fan is off, the return fan is off, the cooling coil control valve if closed, the heating coil control modulates to maintain 70F interior temperature as sensed by the discharge air temperature sensor, the outdoor air dampers are closed, the exhaust air dampers are closed, and, all terminal units associated with the AHU enter unoccupied mode. 2. Unoccupied heating The DDC system shall monitor each space temperature associated with each terminal unit associated with the AHU. When a space temperature falls below 60F (adj), fan powered terminal units shall activate their fan and heat the space, and, terminal units without fans shall activate the air handling unit and heat the space, and the terminal unit heating coil shall be utilized to provide heat to the space. When the AHU is activated, the AHU shall maintain 75F (adj) discharge air temperature and the DDC system shall open the primary air damper in sufficient terminal units to allow the AHU to exceed minimum supply CFM operation. 3. Unoccupied cooling - The DDC system shall monitor each space temperature associated with each terminal unit associated with the AHU. When a space temperature rises above 85F (adj), the AHU shall start and discharge 55F supply air, the outdoor air dampers remain closed, the exhaust air dampers remain closed, and the terminal unit serving that space shall go to full cooling mode, and, the DDC system shall open the primary air damper in sufficient terminal units to allow the AHU to exceed minimum supply CFM operation. When the critical zone space temperature falls below 80F, the AHU shall stop. Note; Economizer operation shall be utilized if the outdoor air temperature is less than the economizer changeover setpoint, see Economizer Operation in Occupied Mode above. 4. Unoccupied override - Each terminal unit room temperature sensor has an override pushbutton which when depressed during unoccupied periods causes the associated AHU to enter occupied mode for 2 hours to allow the space to be ventilated, cooled or heated. Other terminal units shall go to occupied mode as required to allow the AHU to exceed minimum supply CFM operation. 5. Morning warm-up The DDC system shall monitor each zone temperature and outdoor air temperature and automatically start the AHU prior to the occupancy schedule start time based on optimal start time to get all the spaces up to occupied setpoint temperature by occupied start time, and during this period of operation the outdoor air dampers remain closed and the exhaust dampers are closed. During morning warm-up, the AHU shall discharge 75F (adj) supply air, all terminal units shall operate at maximum cooling cfm setpoint, and all terminal units heating hot water control valve shall modulate as required to maintain room temperature setpoint. When a room temperature rises above the occupied heating setpoint, the terminal unit shall enter occupied mode, and all terminal units shall enter occupied mode at occupied period start time. 23 93 93-8 09-ED1-045C
6. Morning cool-down - The DDC system shall monitor each zone temperature and outdoor air temperature and automatically start the AHU prior to the occupancy schedule start time based on optimal start time to get all the spaces down to occupied setpoint temperature by occupied start time, and during this period of operation the outdoor air dampers remain closed and the exhaust dampers are closed. During morning cooldown, the AHU shall discharge 55F (adj) supply air and each terminal unit shall operate in occupied mode. Note; Economizer operation shall be utilized if the outside air temperature is less than the economizer changeover setpoint, see Economizer Operation in Occupied Mode above. 7. Area relative humidity check. When the outdoor air temperature is above 70F, the AHU shall start once each night and run for 20 minutes to check return air relative humidity, and the outdoor air damper is closed, the exhaust air dampers are closed, and all associated terminal units are at maximum cooling cfm. If relative humidity sensed is above 65%RH, then AHU shall supply 55F supply air until return air relative humidity falls below 60%. D. External Safeties 1. The UVc lights downstream of the cooling coil remain energized during occupied and unoccupied periods. There is an On-Off switch on the AHU, and if the access door is opened, the door switch shall de-energize the UVc lights. 2. Duct smoke detector, supplied by others, installed in the return air duct shall automatically shut-down the AHU when activated. The AHU shall automatically restart after the fire alarm system has been reset. 3. Activation of any fire alarm pull station or fire sprinkler system water flow switch shall automatically shut-down the AHU when activated. The AHU shall automatically restart after the fire alarm system has been reset. 4. The low temperature cutout stat shall activate if a temperature of less than 38F is sensed at any one foot of the sensing element. When the low temperature cutout stat actives, the AHU immediately shuts down, the heating coil control valve fully opens, and the DDC system provides an alarm that the low temperature cutout stat has activated. The low temperature cutout stat requires a manual reset. 5. A high static pressure cutout switch measures supply air duct static pressure and shall automatically shut-down the AHU when activated and the DDC system shall provide an alarm that the unit has shut-down. The high static cutout switch shall require a manual reset and the AHU shall require a manual restart after the high static pressure cutout switch has reset. The high static cutout switch static pressure setpoint shall be 4.0 WC (adj). 6. Supply fan and return fan status shall be monitored through the BacNet communication link from each VFD. If supply fan state changes to off when it should be operating, the return fan shall be stopped and the AHU shall go to an off state and the DDC system shall generate an alarm. If the return fan state changes to off when it should be operating, the DDC system generates an alarm and the AHU continues to operate. 7. The DDC system shall monitor the AHU discharge temperature. If the supply air temperature falls below 50F (adj) the DDC system shall generate an alarm, and if the supply air temperature falls below 45F (adj) the DDC system shall stop the AHU, generate an alarm and not allow the AHU to restart until the alarm is acknowledged and the unit is manually restarted. If during occupied mode, the supply air temperature rises above 75F (adj) the DDC system shall generate an alarm, and if during any mode of 09-ED1-045C 23 09 93-9
operation the supply air temperature rises above 100F (adj) for 5 minutes the DDC system shall stop the AHU, generate an alarm and not allow the AHU to restart until the alarm is acknowledged and the unit is manually restarted. E. Other 1. The DDC system shall directly monitor; mixed air temperature, return air temperature, and return air relative humidity. 2. The DDC system shall directly monitor outside air temperature and relative humidity globally. 3. All points on the DDC system shall be capable of providing a user adjustable alarm and being trended. 1.7 AIR HANDLING UNIT AHU-2 and AHU-6 SEQUENCE OF OPERATION, SERVES CLASSROOM AREAS A. General Operation 1. The AHU operates as a variable air volume system and consists of; a supply fan with variable frequency drive, exhaust fan with variable frequency drive, enthalpy energy recovery wheel with outdoor air and exhaust air bypasses, air filters, heating hot water coil, chilled water cooling coil, and UVc lights downstream of the cooling coil. Note, the variable frequency drives do not have a bypass contactor, that is, the variable frequency drives only contain an inverter section which will control the speed of the motor. 2. The AHU is scheduled for automatic operation through the DDC system on a time of day basis for occupied and unoccupied modes. B. Occupied Mode 1. The supply fan and exhaust fan run continuously, the outdoor air dampers and return air bypass dampers modulate as required to maintain minimum outdoor air setpoint, the return air dampers and toilet exhaust damper upstream of the energy recovery wheel open to allow return air and toilet exhaust air through the energy recovery wheel, and the return air damper upstream of the AHU modulates as require to maintain sufficient static pressure in the exhaust air duct to maintain design exhaust airflow. The unit is controlled as follows 2. The DDC system shall determine the discharge air temperature control point. When the outdoor air temperature is above 55F (adj), the supply air temperature shall be maintained at 55F (adj). When the outdoor air temperature is below 55F (adj), the supply air temperature shall be linearly reset between 55F (adj) and 60F (adj) as follows; when the outside air temperature is above 55F (adj) AHU supply air temperature is 55F and when the outside air temperature is below 10F (adj) the supply air temperature is 60F (adj). 3. The DDC system shall determine the supply air duct static pressure control point and shall operate the supply fan variable frequency drive. The DDC system shall monitor the damper position of each terminal unit associated with the AHU and shall reset the supply air duct static pressure control point based on the zone requiring the most pressure, that is, the static pressure control point shall be reset lower until one zone damper is nearly wide open, and the duct static pressure shall be limited to operate between 1.5 WC (adj) and 3.0 WC (adj) measured 2/3 downstream of the supply fan discharge. Supply fan 23 93 93-10 09-ED1-045C
motor speed shall not fall below 25% rated speed, and shall not exceed 100% rated speed. 4. Economizer operation When the outdoor air temperature is below 60F (adj) economizer operation free cooling shall be allowed. The DDC system shall operate the outdoor air and return air dampers, energy recovery section, heating hot water coil control valve and cooling coil control valve in sequence and without overlap to maintain discharge air temperature, that is, if the energy recovery section cannot provide sufficient energy transfer then heating hot water coil control valve shall modulate as required to provide additional heat to maintain discharge air control point, and if the energy recovery wheel is providing too much heat then the exhaust air bypass damper shall modulate and when this damper is fully open and if the energy recovery wheel still provides too much heat then the outside air bypass dampers shall modulate open as required to maintain discharge air temperature. When the outdoor air temperature is above 60F (adj), economizer is disabled. During economizer operation, outdoor air airflow rate shall not fall below minimum outdoor air airflow control point. 5. Energy Recovery Section operation The DDC system shall operate the energy recovery section as required to maximize energy recovery, including modulating each of the two bypass dampers to control AHU discharge air temperature. The energy recovery section shall maximize energy recovery prior to allowing the heating coil to operate. The energy recovery section shall maximize energy recovery during mechanical cooling by allowing the cooling coil to operate during economizer, and, during cooling energy recovery each bypass damper shall remain fully closed. The energy recovery wheel shall also operate whenever the outdoor air temperature exceeds the return air temperature, incorporating a 2F (adj) differential to prevent the wheel from excessive starting and stopping. The energy recovery section shall incorporate a frost control mode when the outdoor temperature is below 30F (adj), to prevent the energy recovery wheel from accumulating too much frost, and, the DDC system shall determine when frost is occurring by measuring the pressure differential across the energy recovery wheel and shall modulate the bypass dampers as required to reduce energy recovery to remove frost from the wheel. During frost control the mixed air temperature sensor shall control the outdoor air and return air bypass dampers to maintain 45F mixed air temperature. If the DDC system detects the energy recovery wheel is not operating when it should be operating when the outdoor air temperature is below 40F, then the mixed air temperature sensor shall control the outdoor air and return air bypass dampers to maintain 45F mixed air temperature. If the DDC system detects the energy recovery wheel is not operating when it should be operating, the DDC system shall indicate an alarm. 6. Exhaust fan operation The DDC system shall operate the exhaust fan variable frequency drive. The exhaust fan is interlocked with the supply fan and exhaust damper end switch and shall not operate until supply fan status is proven and the exhaust damper is fully open. Exhaust air airflow is measured and controlled by the DDC system. The exhaust fan speed shall be based on maintaining a 2000 cfm positive differential between outdoor air airflow and exhaust airflow, and the exhaust fan operates anytime the supply fan operates to maintain minimum 1000 cfm exhaust for the toilet room exhaust. Exhaust fan motor speed shall not fall below 25% rated speed, and shall not exceed 100% rated speed. 7. Minimum outdoor air airflow (as scheduled on drawings). Outdoor air airflow is measured and controlled by the DDC system. Minimum outdoor airflow setpoint adjustment is through the DDC System. There are three minimum outdoor airflow setpoints. When the outdoor temperature is above 75F, the design cooling minimum outdoor air airflow setpoint is used (ASHRAE 62 Ventilation Effectiveness of 1.0). When the outdoor temperature is below 75F, the design heating minimum outdoor air airflow setpoint is used (ASHRAE 62 Ventilation Effectiveness of 0.8). When the unit enters occupied 09-ED1-045C 23 09 93-11
mode, the outdoor air airflow shall be maintained at the design minimum amount for 3 hours, after which CO2 demand ventilation shall occur. If all associated space CO2 sensors are reading CO2 below setpoint, then the outdoor air airflow shall be 3000 cfm. If any space CO2 sensor is reading above setpoint and the associated VAV box primary air damper has operated at VAV box maximum cooling cfm setpoint for 5 minutes, then the Air Handling Unit controller shall modulate the outdoor air airflow to the design value scheduled on the drawings. See FPVAV and Single Duct Shutoff VAV Box Sequence of Operation for additional information. C. Unoccupied Mode 1. When the AHU is off, the supply fan is off, the exhaust fan is off, the cooling coil control valve if closed, the heating coil control modulates to maintain 70F interior temperature as sensed by the discharge air stat, the outdoor air dampers are closed, the return air bypass dampers are open, the return air dampers upstream of the energy recovery wheel are closed, the toilet exhaust dampers upstream of the energy recovery wheel are closed, the exhaust dampers are closed, the energy recovery wheel bypass dampers are closed, and, all terminal units associated with the AHU enter unoccupied mode. 2. Unoccupied heating The DDC system shall monitor each space temperature associated with each terminal unit associated with the AHU. When a space temperature falls below 60F (adj), fan powered terminal units shall activate their fan and heat the space, and, terminal units without fans shall activate the air handling unit and heat the space, and the terminal unit heating coil shall be utilized to provide heat to the space. When the AHU is activated, the AHU shall maintain 75F (adj) discharge air temperature and the DDC system shall open the primary air damper in sufficient terminal units to allow the AHU to exceed minimum supply CFM operation. 3. Unoccupied cooling - The DDC system shall monitor each space temperature associated with each terminal unit associated with the AHU. When a space temperature rises above 85F (adj), the AHU shall start and discharge 55F supply air, the outdoor air dampers remain closed, the return air bypass dampers remain open, the return air dampers upstream of the energy recovery wheel are closed, the toilet exhaust dampers upstream of the energy recovery wheel are closed, the exhaust dampers are closed, the energy recovery wheel bypass dampers are closed, and the terminal unit serving that space shall go to full cooling mode, and, other terminal units shall go to occupied mode as required to allow the AHU to exceed minimum supply CFM operation. When the critical zone space temperature falls below 80F, the AHU shall stop. Note; Economizer operation shall be utilized if the outside air temperature is less than the economizer changeover setpoint, see Economizer Operation in Occupied Mode above. 4. Unoccupied override - Each terminal unit room temperature sensor has an override pushbutton which when depressed during unoccupied periods causes the associated AHU to enter occupied mode for 2 hours to allow the space to be ventilated, cooled or heated. Other terminal units shall go to occupied mode as required to allow the AHU to exceed minimum supply CFM operation. 5. Morning warm-up The DDC system shall monitor each zone temperature and outdoor air temperature and automatically start the AHU prior to the occupancy schedule start time based on optimal start time to get all the spaces up to occupied setpoint temperature by occupied start time, and during this period of operation the outdoor air dampers remain closed, the return air bypass dampers are open, the return air dampers upstream of the energy recovery wheel are closed, the toilet exhaust dampers upstream of the energy recovery wheel are closed, the exhaust dampers are closed, and the energy recovery wheel bypass dampers are closed. During morning warm-up, the AHU shall discharge 75F (adj) supply air, all terminal units shall operate at maximum cooling CFM setpoint, and all terminal units heating hot water control valve shall modulate as 23 93 93-12 09-ED1-045C
required to maintain room temperature setpoint. This is to allow the AHU to provide additional heat for morning warm-up. When a room temperature rises above the occupied heating setpoint, the FPVAV shall enter occupied mode, and all FPVAV s shall enter occupied mode at occupied period start time. 6. Morning cool-down - The DDC system shall monitor each zone temperature and outdoor air temperature and automatically start the AHU prior to the occupancy schedule start time based on optimal start time to get all the spaces down to occupied setpoint temperature by occupied start time, and during this period of operation the outdoor air dampers remain closed, the return air bypass dampers are open, the return air dampers upstream of the energy recovery wheel are closed, the toilet exhaust dampers (AHU-2 and AHU-6 only) upstream of the energy recovery wheel are closed, the exhaust dampers are closed, and the energy recovery wheel bypass dampers are closed. During morning cool-down, the AHU shall discharge 55F (adj) supply air and each terminal unit shall operate in occupied mode. Note; Economizer operation shall be utilized if the outside air temperature is less than the economizer changeover setpoint, see Economizer Operation in Occupied Mode above. 7. Area relative humidity check. When the outdoor air temperature is above 70F, the AHU shall start once each night and run for 20 minutes to check return air relative humidity, while the outdoor air damper is closed, return air bypass dampers are open, the return air dampers upstream of the energy recovery wheel are closed, return air dampers in the return air duct are open, the toilet exhaust dampers upstream of the energy recovery wheel are closed, the exhaust dampers are closed, and the energy recovery wheel bypass dampers are closed, exhaust fan is off and all associated terminal units are at maximum cooling cfm. If relative humidity sensed is above 65%RH, then AHU shall supply 55F supply air until return air relative humidity falls below 60%. D. External Safeties 1. The UVc lights downstream of the cooling coil remain energized during occupied and unoccupied periods. There is an On-Off switch on the AHU, and if the access door is opened, the door switch shall de-energize the UVc lights. 2. Duct smoke detector, supplied by others, installed in the return air duct shall automatically shut-down the AHU when activated. The AHU shall automatically restart after the fire alarm system has been reset. 3. Activation of any fire alarm pull station or fire sprinkler system water flow switch shall automatically shut-down the AHU when activated. The AHU shall automatically restart after the fire alarm system has been reset. 4. The low temperature cutout stat shall activate if a temperature of less than 38F is sensed at any one foot of the sensing element. When the low temperature cutout stat actives, the AHU immediately shuts down, the heating coil control valve fully opens, and the DDC system provides an alarm that the low temperature cutout stat has activated. The low temperature cutout stat requires a manual reset. 5. A high static pressure cutout switch measures supply air duct static pressure and shall automatically shut-down the AHU when activated and the DDC system shall provide an alarm that the unit has shut-down. The high static cutout switch shall require a manual reset and the AHU shall require a manual restart after the high static pressure cutout switch has reset. The high static cutout switch static pressure setpoint shall be 4.0 WC (adj). 6. Supply fan and exhaust fan status shall be monitored through the BacNet communication link from each VFD. If supply fan state changes to off when it should be operating, the 09-ED1-045C 23 09 93-13
exhaust fan shall be stopped and the AHU shall go to an off state and the DDC system shall generate an alarm. If the exhaust fan state changes to off when it should be operating the DDC system generate an alarm, the exhaust damper shall close and the AHU continues to operate. 7. The DDC system shall monitor the AHU discharge temperature. If the supply air temperature falls below 50F (adj) the DDC system shall generate an alarm, and if the supply air temperature falls below 45F (adj) the DDC system shall stop the AHU, generate an alarm and not allow the AHU to restart until the alarm is acknowledged and the unit is manually restarted. If during occupied mode, the supply air temperature rises above 75F (adj) the DDC system shall generate an alarm, and if during any mode of operation the supply air temperature rises above 100F (adj) for 5 minutes the DDC system shall stop the AHU, generate an alarm and not allow the AHU to restart until the alarm is acknowledged and the unit is manually restarted. 8. Exhaust air volume The DDC system shall monitor exhaust air airflow rate and not allow the exhaust air airflow rate to exceed the quantity indicated on the drawings in the equipment schedule. E. Other 1. The DDC system shall directly monitor; mixed air temperature, exhaust air temperature, return air temperature, and return air relative humidity. 2. The DDC system shall directly monitor outside air temperature and relative humidity globally. 3. All points on the DDC system shall be capable of providing a user adjustable alarm and being trended. 1.8 AIR HANDLING UNIT AHU-3 AND KITCHEN HOODS EXHAUST FAN EF-25 SEQUENCE OF OPERATION, SERVES KITCHEN AND STUDENT DINING A. General Operation 1. The AHU operates as a variable air volume system and consists of; a supply fan with variable frequency drive, exhaust fan with variable frequency drive, enthalpy energy recovery wheel with outdoor air and exhaust air bypasses, air filters, heating hot water coil, chilled water cooling coil, and UVc lights downstream of the cooling coil. Note, the variable frequency drives do not have a bypass contactor, that is, the variable frequency drives only contain an inverter section which will control the speed of the motor. 2. The AHU is scheduled for automatic operation through the DDC system on a time of day basis for occupied and unoccupied modes. 3. The heating coil shall have a run-a round pump that operates whenever the outdoor temperature is below 38F or the freeze stat activates. And the heating coil has a temperature sensor on the downstream side, its purpose is to prevent the heating coil discharge temperature from falling below 50F (adj). B. Occupied Mode 1. The supply and exhaust fans run continuously, the outdoor air dampers and return air bypass dampers modulate as required to maintain minimum outdoor air setpoint. The unit is controlled as follows 23 93 93-14 09-ED1-045C
2. The DDC system shall determine the discharge air temperature control point. When the outdoor air temperature is above 55F (adj), the supply air temperature will be maintained at 55F (adj). When the outdoor air temperature is below 55F (adj), the supply air temperature shall be linearly reset between 55F (adj) and 60F (adj) as follows; when the outside air temperature is above 55F (adj) AHU supply air temperature is 55F and when the outside air temperature is below 10F (adj) the supply air temperature is 60F (adj). 3. The DDC system shall determine the supply air duct static pressure control point and shall operate the supply fan variable frequency drive. The DDC system shall monitor the damper position of each terminal unit associated with the AHU and shall reset the supply air duct static pressure control point based on the zone requiring the most pressure, that is, the static pressure control point shall be reset lower until one zone damper is nearly wide open, and the duct static pressure shall be limited to operate between 1.5 WC (adj) and 3.0 WC (adj) measured 2/3 downstream of the supply fan discharge. Supply fan motor speed shall not fall below 25% rated speed, and shall not exceed 100% rated speed. 4. Economizer operation When the outdoor air temperature is below 60F (adj) economizer operation free cooling shall be allowed. The DDC system shall operate the outdoor air and return air dampers, energy recovery section, heating hot water coil control valve and cooling coil control valve in sequence and without overlap to maintain discharge air temperature, that is, if the energy recovery section cannot provide sufficient energy transfer then heating hot water coil control valve shall modulate as required to provide additional heat to maintain discharge air control point, and if the energy recovery wheel is providing too much heat then the exhaust air bypass damper shall modulate and when this damper is fully open and if the energy recovery wheel still provides too much heat then the outside air bypass dampers shall modulate open as required to maintain discharge air temperature. When the outdoor air temperature is above 60F (adj), economizer is disabled. During economizer operation, outdoor air airflow rate shall not fall below minimum outdoor air airflow control point. 5. Energy Recovery Section operation The DDC system shall operate the energy recovery section as required to maximize energy recovery, including modulating each of the two bypass dampers to control AHU discharge air temperature. The energy recovery section shall maximize energy recovery prior to allowing the heating coil to operate. The energy recovery section shall maximize energy recovery during mechanical cooling by allowing the cooling coil to operate during economizer, and, during cooling energy recovery each bypass damper shall remain fully closed. The energy recovery wheel shall also operate whenever the outdoor air temperature exceeds the return air temperature, incorporating a 2F (adj) differential to prevent the wheel from excessive starting and stopping. The energy recovery section shall incorporate a frost control mode when the outdoor temperature is below 30F (adj), to prevent the energy recovery wheel from accumulating too much frost, and, the DDC system shall determine when frost is occurring by measuring the pressure differential across the energy recovery wheel and shall modulate the bypass dampers as required to reduce energy recovery to remove frost from the wheel. During frost control the mixed air temperature sensor shall control the outdoor air and return air bypass dampers to maintain 45F mixed air temperature. If the DDC system detects the energy recovery wheel is not operating when it should be operating when the outdoor air temperature is below 40F, then the mixed air temperature sensor shall control the outdoor air and return air bypass dampers to maintain 45F mixed air temperature. If the DDC system detects the energy recovery wheel is not operating when it should be operating, the DDC system shall indicate an alarm. 6. Exhaust fan operation The DDC system shall operate the exhaust fan variable frequency drive. The exhaust fan is interlocked with the supply fan and exhaust damper end switch and shall not operate until supply fan status is proven and the exhaust 09-ED1-045C 23 09 93-15