PackagedTerminalAirConditioner prevent Outdoor air during night cycle

I am setting up a PackagedTerminalAirConditioner to run on constant fan during the day and cycle the fan at night. The system also provides outside air and looking to close the outside air dampers when the fan cycles at night. How could I achieve this?

The setup I have below does cycle the fan at night but also brings in outside air during night fan cycling.

ZoneHVAC:PackagedTerminalAirConditioner,
   zone1 PTAC,                  ! Component name
   On 24/7,                     ! Availability schedule
   zone1 PTAC Return,           ! Air inlet node to heat pump; also a zone exhaust node
   zone1 PTAC Supply Inlet,     ! Air outlet node to heat pump; also a zone inlet node
   OutdoorAir:Mixer,            ! Outdoor air mixer object type
   zone1 PTAC Outdoor Air Mixer,! Outdoor air mixer name
   autosize,                ! Supply air flow rate during cooling operation (m3/s)
   autosize,                    ! Supply air flow rate during heating operation (m3/s)
   autosize,           ! Supply air flow rate when no heating or cooling is needed (m3/s)
   autosize,                    ! Outdoor air flow rate during cooling operation (m3/s)
   autosize,             ! Outdoor air flow rate during heating operation (m3/s)
   autosize,          ! Outdoor air flow rate when no heating or cooling is needed (m3/s)
   Fan:OnOff,                   ! Type of supply fan
   zone1 PTAC Supply Fan,       ! Name of supply fan
   Coil:Heating:Gas,            ! Type of heating coil
   zone1 PTAC Heating Coil,     ! Name of heating coil
   Coil:Cooling:DX:SingleSpeed, ! Type of cooling coil
   zone1 PTAC DX Cooling Coil,  ! Name of cooling coil
   DrawThrough,                 ! Fan placement
   Fan cycle mode sch;          ! Supply air fan operating mode schedule

Schedule:Compact,Fan cycle mode sch,
   on/off,
   Through: 12/31,
   For: Weekdays SummerDesignDay,
   Until: 06:00,0.0,
   Until: 20:00,1.0,
   Until: 24:00,0.0,
   For: Saturday WinterDesignDay,
   Until: 06:00,0.0,
   Until: 18:00,1.0,
   Until: 24:00,0.0,
   For: Sunday Holidays AllOtherDays,
   Until: 24:00,0.0;

601

kbk78

asked 2017-07-07 16:28:33 -0500, updated 2017-07-07 16:30:25 -0500

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3 Answers

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In some instances, ZoneHVAC:UnitVentilator can do what you need in one ZoneHVAC unit. It allows more control of outdoor air, but has limited heating and cooling coil options.

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kwalkerman

answered 2017-07-10 10:57:07 -0500

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As a workaround, instead of the ZoneHVAC object you could use the scheduling flexibility of an AirLoopHVAC with:

AirLoopHVACOutdoorAirSystem
ControllerOutdoorAir
CoilHeatingGas
CoilCoolingDXSingleSpeed
FanOnOff (might not be allowed on an AirLoopHVAC)
AirTerminalSingleDuctUncontrolled

To schedule the fan to run during the day create a schedule for the AirLoopHVAC object's Availability Schedule field.

To schedule the fan to cycle on during the night use an AvailabilityManagerNightCycle object with the Control Type set to CycleOnAny.

To schedule the OA damper to be closed at night create a schedule for the ControllerOutdoorAir object's Minimum Outdoor Air Schedule or Maximum Fraction of Outdoor Air Schedule fields, which could be the same as the AirLoopHVAC Availability Schedule (e.g. fractional 0 to 1). Note that an economizer may interact with this.

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MatthewSteen

answered 2017-07-08 14:14:40 -0500, updated 2017-07-08 14:16:11 -0500

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Good suggestion, using an air loop for each zone will give the flexibility in controlling outdoor air and will replicate use of the PTAC per zone.

rraustad (2017-07-08 18:13:43 -0500) edit

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Unfortunately, the PTHP and PTAC models do not have an outdoor air fraction schedule (e.g., 1 during the day and 0 during unoccupied hours). I can't think of a way to do this without modifying the existing models.