blockController

Multizone VAV air handling unit controller
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Information

Block that is applied for multizone VAV AHU control. It outputs the supply fan status and the operation speed, outdoor and return air damper position, supply air temperature setpoint and the valve position of the cooling and heating coils. It is implemented according to the Section 5.16 of ASHRAE Guideline 36, May 2020.

The sequence consists of eight types of subsequences.

Supply fan speed control

The fan speed control is implemented according to Section 5.16.1. It outputs the boolean signal y1SupFan to turn on or off the supply fan. In addition, based on the pressure reset request uZonPreResReq from the VAV zones controller, the sequence resets the duct pressure setpoint, and uses this setpoint to modulate the fan speed ySupFanSpe using a PI controller. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.SupplyFan for more detailed description.

Minimum outdoor airflow setting

According to current occupany, supply operation status ySupFan, zone temperatures and the discharge air temperature, the sequence computes the minimum outdoor airflow rate setpoint, which is used as input for the economizer control. More detailed information can be found in Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.

Economizer control

The block outputs outdoor and return air damper position, yOutDamPos and yRetDamPos. First, it computes the position limits to satisfy the minimum outdoor airflow requirement. Second, it determines the availability of the economizer based on the outdoor condition. The dampers are modulated to track the supply air temperature loop signal, which is calculated from the sequence below, subject to the minimum outdoor airflow requirement and economizer availability. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.Economizers.Controller for more detailed description.

Supply air temperature setpoint

Based on the Section 5.16.2, the sequence first sets the maximum supply air temperature based on reset requests collected from each zone uZonTemResReq. The outdoor temperature TOut and operation mode uOpeMod are used along with the maximum supply air temperature, for computing the supply air temperature setpoint. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.SupplyTemperature for more detailed description.

Coil valve control

The subsequence retrieves supply air temperature setpoint from previous sequence. Along with the measured supply air temperature and the supply fan status, it generates coil valve positions. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.SupplySignals for more detailed description.

Freeze protection

Based on the Section 5.16.12, the sequence enables freeze protection if the measured supply air temperature belows certain thresholds. There are three protection stages. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.FreezeProtection for more detailed description.

Building pressure control

By selecting different building pressure control designs, which includes using actuated relief damper without fan, using actuated relief dampers with relief fan, using return fan with direct building pressure control, or using return fan with airflow tracking control, the sequences controls relief fans, relief dampers and return fans. See belows sequences for more detailed description:

Plant request

According to the Section 5.16.16, the sequence send out heating or cooling plant requests if the supply air temperature is below or above threshold value, or the heating or cooling valves have been widely open for certain times. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.PlantRequests for more detailed description.

Parameters

TypeNameDefaultDescription
Buildings.Controls.OBC.ASHRAE.G36.Types.EnergyStandardeneStdEnergy standard, ASHRAE 90.1 or Title 24
Types.VentilationStandardvenStdVentilation standard, ASHRAE 62.1 or Title 24
Buildings.Controls.OBC.ASHRAE.G36.Types.ASHRAEClimateZoneashCliZonBuildings.Controls.OBC.ASHRAE.G36.Types.ASHRAEClimateZone.Not_SpecifiedASHRAE climate zone
Buildings.Controls.OBC.ASHRAE.G36.Types.Title24ClimateZonetit24CliZonBuildings.Controls.OBC.ASHRAE.G36.Types.Title24ClimateZone.Not_SpecifiedCalifornia Title 24 climate zone
Booleanhave_freProtrueTrue: enable freeze protection
Buildings.Controls.OBC.ASHRAE.G36.Types.FreezeStatfreStaBuildings.Controls.OBC.ASHRAE.G36.Types.FreezeStat.Hardwired_to_equipmentType of freeze stat
Economizer design
Buildings.Controls.OBC.ASHRAE.G36.Types.OutdoorAirSectionminOADesBuildings.Controls.OBC.ASHRAE.G36.Types.OutdoorAirSection.DedicatedDampersAirflowType of outdoor air section
Buildings.Controls.OBC.ASHRAE.G36.Types.PressureControlbuiPreConBuildings.Controls.OBC.ASHRAE.G36.Types.PressureControl.ReliefFanType of building pressure control system
Booleanhave_ahuRelFantrueTrue: relief fan is part of AHU; False: the relief fans group that may associate multiple AHUs
Buildings.Controls.OBC.ASHRAE.G36.Types.ControlEconomizerecoHigLimConBuildings.Controls.OBC.ASHRAE.G36.Types.ControlEconomizer.FixedDryBulbEconomizer high limit control device
System and building parameters
Buildings.Controls.OBC.ASHRAE.G36.Types.CoolingCoilcooCoiBuildings.Controls.OBC.ASHRAE.G36.Types.CoolingCoil.WaterBasedCooling coil type
Buildings.Controls.OBC.ASHRAE.G36.Types.HeatingCoilheaCoiBuildings.Controls.OBC.ASHRAE.G36.Types.HeatingCoil.WaterBasedHeating coil type
Booleanhave_perZonRehBoxfalseCheck if there is any VAV-reheat boxes on perimeter zones
Minimum outdoor air setpoint
RealVUncDesOutAir_flow0Uncorrected design outdoor airflow rate, including diversity where applicable. It can be determined using the 62MZCalc spreadsheet from ASHRAE 62.1 User's Manual
RealVDesTotOutAir_flow0Design total outdoor airflow rate. It can be determined using the 62MZCalc spreadsheet from ASHRAE 62.1 User's Manual
RealVAbsOutAir_flow0Design outdoor airflow rate when all zones with CO2 sensors or occupancy sensors are unpopulated. Needed when complying with Title 24 requirements
RealVDesOutAir_flow0Design minimum outdoor airflow rate with the areas served by the system are occupied at their design population, including diversity where applicable. Needed when complying with Title 24 requirements
Fan speed › Trim and respond for reseting duct static pressure setpoint
RealpIniSet120Initial pressure setpoint for fan speed control
RealpMinSet25Minimum pressure setpoint for fan speed control
RealpMaxSet1000Duct design maximum static pressure. It is the Max_DSP shown in Section 3.2.1.1 of Guideline 36
RealpDelTim600Delay time after which trim and respond is activated
RealpSamplePeriod120Sample period
IntegerpNumIgnReq2Number of ignored requests
RealpTriAmo-12.0Trim amount
RealpResAmo15Respond amount (must be opposite in to trim amount)
RealpMaxRes32Maximum response per time interval (same sign as respond amount)
Fan speed › PID controller
Buildings.Controls.OBC.CDL.Types.SimpleControllerfanSpeConBuildings.Controls.OBC.CDL.Types.SimpleController.PISupply fan speed PID controller
RealkFanSpe0.1Gain of supply fan speed PID controller
RealTiFanSpe60Time constant of integrator block for supply fan speed PID controller
RealTdFanSpe0.1Time constant of derivative block for supply fan speed PID controller
RealsupFanSpe_max1Maximum allowed supply fan speed
RealsupFanSpe_min0.1Lowest allowed supply fan speed if fan is on
RealiniFanSpesupFanSpe_minInitial speed when fan is enabled. It has to be greater than the lowest allowed speed
Supply air temperature › Temperature limits
RealTSupCoo_min285.15Lowest cooling supply air temperature setpoint when the outdoor air temperature is at the higher value of the reset range and above
RealTSupCoo_max291.15Highest cooling supply air temperature setpoint. It is typically 18 degC (65 degF) in mild and dry climates, 16 degC (60 degF) or lower in humid climates
RealTOut_min289.15Lower value of the outdoor air temperature reset range. Typically value is 16 degC (60 degF)
RealTOut_max294.15Higher value of the outdoor air temperature reset range. Typically value is 21 degC (70 degF)
RealTSupWarUpSetBac308.15Supply temperature in warm up and set back mode
Supply air temperature › Trim and respond for reseting supply air temperature setpoint
RealdelTimSupTem600Delay timer
RealsamPerSupTem120Sample period of component
IntegerignReqSupTem2Number of ignorable requests for TrimResponse logic
RealtriAmoSupTem0.1Trim amount
RealresAmoSupTem-0.2Response amount
RealmaxResSupTem-0.6Maximum response per time interval
Coils › Valves PID controller
Buildings.Controls.OBC.CDL.Types.SimpleControllervalConBuildings.Controls.OBC.CDL.Types.SimpleController.PIType of controller for coil valves control
RealkVal0.05Gain of controller for valve control
RealTiVal600Time constant of integrator block for valve control
RealTdVal0.1Time constant of derivative block for valve control
Coils › Limits
RealuHeaCoi_max-0.25Upper limit of controller signal when heating coil is off. Require -1 < uHea_max < uCoo_min < 1.
RealuCooCoi_min0.25Lower limit of controller signal when cooling coil is off. Require -1 < uHea_max < uCoo_min < 1.
Economizer › Limits, separated with AFMS
Buildings.Controls.OBC.CDL.Types.SimpleControllerminOAConTypBuildings.Controls.OBC.CDL.Types.SimpleController.PIType of minimum outdoor air controller
RealkMinOA0.03Gain of controller
RealTiMinOA120Time constant of integrator block
RealTdMinOA0.1Time constant of derivative block
Economizer › Limits, separated with DP
Booleanhave_CO2SenfalseTrue: some zones have CO2 sensor
RealdpAbsMinOutDam5Absolute minimum pressure difference across the minimum outdoor air damper. It provides the absolute minimum outdoor airflow
RealdpDesMinOutDam20Design minimum pressure difference across the minimum outdoor air damper. It provides the design minimum outdoor airflow
Buildings.Controls.OBC.CDL.Types.SimpleControllerdpConTypBuildings.Controls.OBC.CDL.Types.SimpleController.PIType of differential pressure setpoint controller
RealkDp1Gain of controller
RealTiDp0.5Time constant of integrator block
RealTdDp0.1Time constant of derivative block
Economizer › Limits, Common
RealuRetDam_min0.5Loop signal value to start decreasing the maximum return air damper position
Economizer › Enable
RealdelTOutHis1Delta between the temperature hysteresis high and low limit
RealdelEntHis1000Delta between the enthalpy hysteresis high and low limits
RealretDamFulOpeTim180Time period to keep return air damper fully open before releasing it for minimum outdoor airflow control at disable to avoid pressure fluctuations
RealdisDel15Short time delay before closing the outdoor air damper at disable to avoid pressure fluctuations
Economizer › Commissioning, limits
RealretDamPhy_max1.0Physically fixed maximum position of the return air damper
RealretDamPhy_min0.0Physically fixed minimum position of the return air damper
RealoutDamPhy_max1.0Physically fixed maximum position of the outdoor air damper
RealoutDamPhy_min0.0Physically fixed minimum position of the outdoor air damper
RealminOutDamPhy_max1.0Physically fixed maximum position of the minimum outdoor air damper
RealminOutDamPhy_min0.0Physically fixed minimum position of the minimum outdoor air damper
Economizer › Commissioning, modulation
RealuHeaMax-0.25Lower limit of controller input when outdoor damper opens (see diagram)
RealuCooMin+0.25Upper limit of controller input when return damper is closed (see diagram)
Freeze protection
IntegerminHotWatReq2Minimum heating hot-water plant request to active the heating plant
Freeze protection › Heating coil PID Controller
Buildings.Controls.OBC.CDL.Types.SimpleControllerfreProHeaCoiConBuildings.Controls.OBC.CDL.Types.SimpleController.PIFreeze protection heating coil controller
RealkFrePro0.05Gain of coil controller
RealTiFrePro120Time constant of integrator block
RealTdFrePro0.1Time constant of derivative block
RealyMaxFrePro1Upper limit of output
RealyMinFrePro0Lower limit of output
Pressure control
RealdpBuiSet12Building static pressure difference relative to ambient (positive to pressurize the building)
Pressure control › Relief damper
RealkRelDam0.5Gain, applied to building pressure control error normalized with dpBuiSet
Pressure control › Return fan
RealdifFloSet0.1Airflow differential between supply air and return air fans required to maintain building pressure at desired pressure
Buildings.Controls.OBC.CDL.Types.SimpleControllerretFanConBuildings.Controls.OBC.CDL.Types.SimpleController.PIType of controller for return fan
RealkRetFan1Gain, normalized using dpBuiSet
RealTiRetFan0.5Time constant of integrator block
RealTdRetFan0.1Time constant of derivative block
RealretFanSpe_max1Maximum return fan speed
RealretFanSpe_min0.1Minimum return fan speed
Realp_rel_RetFan_min2.4Minimum return fan discharge static pressure difference setpoint
Realp_rel_RetFan_max40Maximum return fan discharge static pressure difference setpoint
Pressure control › Relief fan
RealrelFanSpe_min0.1Relief fan minimum speed
RealkRelFan1Gain of relief fan controller, normalized using dpBuiSet
Advanced
RealTHys0.25Hysteresis for checking temperature difference
RealposHys0.01Hysteresis for checking valve position difference
Realhys0.005Hysteresis for checking the relief fan controller output value

Connectors

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputuAhuOpeModOperation mode for AHU operation
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputuZonPreResReqZone static pressure reset requests
Buildings.Controls.OBC.CDL.Interfaces.RealInputdpDucMeasured duct static pressure
Buildings.Controls.OBC.CDL.Interfaces.RealInputTOutOutdoor air temperature
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputuZonTemResReqZone cooling supply air temperature reset request
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputu1SupFanSupply fan status
Buildings.Controls.OBC.CDL.Interfaces.RealInputTAirSupMeasured supply air temperature
Buildings.Controls.OBC.CDL.Interfaces.RealInputVSumAdjPopBreZon_flowSum of the adjusted population component breathing zone flow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInputVSumAdjAreBreZon_flowSum of the adjusted area component breathing zone flow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInputVSumZonPri_flowSum of the zone primary airflow rates for all zones in all zone groups that are in occupied mode
Buildings.Controls.OBC.CDL.Interfaces.RealInputuOutAirFra_maxMaximum zone outdoor air fraction, equals to the maximum of primary outdoor air fraction of all zones
Buildings.Controls.OBC.CDL.Interfaces.RealInputVSumZonAbsMin_flowSum of the zone absolute minimum outdoor airflow setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealInputVSumZonDesMin_flowSum of the zone design minimum outdoor airflow setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealInputVAirOut_flowMeasured outdoor air volumetric flow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInputuCO2Loo_maxMaximum zone CO2 control loop output
Buildings.Controls.OBC.CDL.Interfaces.RealInputdpMinOutDamMeasured pressure difference across the minimum outdoor air damper
Buildings.Controls.OBC.CDL.Interfaces.RealInputTAirRetUsed only for fixed plus differential dry bulb temperature high limit cutoff
Buildings.Controls.OBC.CDL.Interfaces.RealInputhAirOutOutdoor air enthalpy
Buildings.Controls.OBC.CDL.Interfaces.RealInputhAirRetOA enthalpy high limit cutoff. For differential enthalpy use return air enthalpy measurement
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputu1FreStaFreeze protection stat signal. The stat is normally close (the input is normally true), when enabling freeze protection, the input becomes false
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputu1SofSwiResFreeze protection reset signal from software switch
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputu1RelFanRelief fan status
Buildings.Controls.OBC.CDL.Interfaces.RealInputTAirMixMeasured mixed air temperature
Buildings.Controls.OBC.CDL.Interfaces.RealInputdpBuiMeasured building static pressure difference, relative to ambient (positive if pressurized)
Buildings.Controls.OBC.CDL.Interfaces.RealInputVAirSup_flowMeasured AHU supply airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInputVAirRet_flowMeasured AHU return airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealOutputTAirSupSetAHU supply air temperature setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealOutputVEffAirOut_flow_minEffective minimum outdoor airflow setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyMinOutDamMinimum outdoor air damper commanded position
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutputy1MinOutDamMinimum outdoor air damper command on
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyRetDamReturn air damper commanded position
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyRelDamRelief air damper commanded position
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyOutDamEconomizer outdoor air damper commanded position
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutputy1EneCHWPumCommanded on to energize chilled water pump
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutputy1SupFanSupply fan command on
Buildings.Controls.OBC.CDL.Interfaces.RealOutputySupFanAir handler supply fan commanded speed
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutputy1RetFanReturn fan commanded on
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyRetFanReturn fan commanded speed
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutputy1RelFanRelief fan commanded on
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyRelFanRelief fan commanded speed
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutputy1RelDamTrue: 2-position relief damper is commanded open
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyCooCoiCooling coil valve commanded position
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyHeaCoiHeating coil valve commanded position
Buildings.Controls.OBC.CDL.Interfaces.IntegerOutputyAlaAlarm level
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyDpBuiBuilding static pressure difference, relative to ambient (positive if pressurized)
Buildings.Controls.OBC.CDL.Interfaces.RealOutputdpDisSetReturn fan discharge static pressure setpoint
Buildings.Controls.OBC.CDL.Interfaces.IntegerOutputyChiWatResReqChilled water reset request
Buildings.Controls.OBC.CDL.Interfaces.IntegerOutputyChiPlaReqChiller plant request
Buildings.Controls.OBC.CDL.Interfaces.IntegerOutputyHotWatResReqHot water reset request
Buildings.Controls.OBC.CDL.Interfaces.IntegerOutputyHotWatPlaReqHot water plant request

Components

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Integers.GreaterThresholdfreProModCheck if it is in freeze protection mode
Buildings.Controls.OBC.CDL.Integers.SwitchintSwiHot water plant request
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.FreezeProtectionfreProFreeze protection
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.PlantRequestsplaReqPlant requests
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.Economizers.ControllerecoConEconomizer controller
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.SupplyFanconSupFanSupply fan speed setpoint
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.SupplySignalssupSigHeating and cooling valve position
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.SupplyTemperatureconTSupSetSupply temperature setpoint
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.ASHRAE62_1.AHUashOutAirSetMinimum outdoor airflow setpoint, when complying with ASHRAE 62.1 requirements
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.ReliefDamperrelDamRelief damper control for AHUs using actuated dampers without fan
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.ReturnFanDirectPressureretFanDpConReturn fan control with direct building pressure control, using the minimum outdoor air damper
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.ReturnFanAirflowTrackingretFanAirTraReturn fan control for AHUs using return fan with airflow tracking
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.Title24.AHUtit24OutAirSetMinimum outdoor airflow setpoint, when complying with Title 24 requirements
Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.ReliefFanrelFanConControl of relief fan when it is part of AHU

Revisions

  • September 26, 2025, by Jianjun Hu:
    Renamed the parameter Thys to THys.
    This is for issue 4374.
  • September 18, 2023, by Jianjun Hu:
    Removed the connectors uCooCoi_actual and uHeaCoi_actual, added 2-position relief damper position output y1RelDam, added coil type enumeration so to avoid using flag parameters.
    This is for issue 3526.
  • March 1, 2023, by Michael Wetter:
    Changed constants from 0 to 0.0 and 1 to 1.0.
    This is for #3267.
  • December 15, 2022, by Jianjun Hu:
    Removed input connectors uRelFan and uSupFanSpe_actual.
    This is for issue 3139.
  • December 20, 2021, by Jianjun Hu:
    First implementation.