blockDamperValves

Output signals for controlling constant-volume parallel fan-powered terminal unit
Diagram of DamperValvesOpen the diagram
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Information

This sequence sets the fan status, damper and valve position for constant-volume parallel fan-powered terminal unit. The implementation is according to Section 5.7.5 of ASHRAE Guideline 36, May 2020. The calculation is done following the steps below.

  1. When the zone state is cooling (uCoo > 0), then the cooling loop output uCoo shall be mapped to the airflow setpoint from the minimum VActMin_flow to the cooling maximum VActCooMax_flow airflow setpoints. The heating coil is disabled (yVal=0).
    • If supply air temperature TSup from the AHU is greater than room temperature TZon, cooling supply airflow setpoint shall be no higher than the minimum.
  2. When the zone state is deadband (uCoo=0 and uHea=0), then the active airflow setpoint shall be the minimum airflow setpoint VActMin_flow. The heating coil is disabled (yVal=0).
  3. When the zone state is heating (uHea > 0),
    • As the heating-loop output uHea increases from 0% to 100%, it shall reset the discharge temperature THeaDisSet from the current AHU setpoint temperature TSupSet to a maximum of dTDisZonSetMax above space temperature setpoint.
    • The airflow setpoint shall be the minimum flow VActMin_flow.
    • The heating coil shall be modulated to maintain the discharge temperature at setpoint.
  4. The VAV damper shall be modulated by a control loop to maintain the measured airflow at the active setpoint.
  5. Fan control
    • Fan shall run whenever zone state is heating.
    • The fan shall run in deadband and cooling zone state when the primary airflow rate VPri_flow is less than the minimum outdoor airflow setpoint VOAMin_flow (if using California Title 24, it should be the zone absolute minimum outdoor airflow rate) for 1 minute, and shall shut off when the VPri_flow is above VOAMin_flow (or the zone absolute minimum outdoor airflow rate) by 10% for 3 minutes.

The sequences of controlling fan, damper position for constant-volume parallel fan-powered terminal unit are described in the following figure below.

Image of damper control for constant-volume parallel fan-powered terminal unit

As specified in Section 5.7.7 of ASHRAE Guideline 36, the airflow setpoint could be override by providing software switches that interlock to a system-level point to:

  1. when oveFloSet equals to 1, force the zone airflow setpoint VPri_flow_Set to zero,
  2. when oveFloSet equals to 2, force the zone airflow setpoint VPri_flow_Set to zone cooling maximum airflow rate VCooMax_flow,
  3. when oveFloSet equals to 3, force the zone airflow setpoint VPri_flow_Set to zone minimum airflow setpoint VMin_flow.

Parameters

TypeNameDefaultDescription
RealdTDisZonSetMax11Zone maximum discharge air temperature above heating setpoint
RealVMin_flowDesign zone minimum airflow setpoint
RealVCooMax_flowDesign zone cooling maximum airflow rate
Valve
Buildings.Controls.OBC.CDL.Types.SimpleControllercontrollerTypeValBuildings.Controls.OBC.CDL.Types.SimpleController.PIType of controller
RealkVal0.5Gain of controller for valve control
RealTiVal300Time constant of integrator block for valve control
RealTdVal0.1Time constant of derivative block for valve control
Damper
Buildings.Controls.OBC.CDL.Types.SimpleControllercontrollerTypeDamBuildings.Controls.OBC.CDL.Types.SimpleController.PIType of controller
RealkDam0.5Gain of controller for damper control
RealTiDam300Time constant of integrator block for damper control
RealTdDam0.1Time constant of derivative block for damper control
Advanced
RealdTHys0.25Temperature difference hysteresis below which the temperature difference will be seen as zero
ReallooHys0.05Loop output hysteresis below which the output will be seen as zero
RealfloHys0.01Hysteresis for checking airflow rate
RealiniDam0.01Initial damper position when the damper control is enabled

Connectors

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputoveFloSetIndex of overriding flow setpoint, 1: set to zero; 2: set to cooling maximum; 3: set to minimum flow; 4: set to heating maximum
Buildings.Controls.OBC.CDL.Interfaces.RealInputVPri_flowMeasured primary airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInputuCooCooling control signal
Buildings.Controls.OBC.CDL.Interfaces.RealInputVActCooMax_flowActive primary cooling maximum airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInputTSupTemperature of the air supplied from central air handler
Buildings.Controls.OBC.CDL.Interfaces.RealInputTZonMeasured zone temperature
Buildings.Controls.OBC.CDL.Interfaces.RealInputVActMin_flowActive primary minimum airflow rate
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputu1FanAHU supply fan status
Buildings.Controls.OBC.CDL.Interfaces.RealInputTSupSetSupply air temperature setpoint from central air handler
Buildings.Controls.OBC.CDL.Interfaces.RealInputTHeaSetZone heating setpoint temperature
Buildings.Controls.OBC.CDL.Interfaces.RealInputuHeaHeating control signal
Buildings.Controls.OBC.CDL.Interfaces.RealInputTDisMeasured discharge air temperature
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputuOpeModZone operation mode
Buildings.Controls.OBC.CDL.Interfaces.RealInputVOAMin_flowMinimum outdoor airflow setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealOutputVPri_flow_SetPrimary airflow setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyDamVAV damper commanded position
Buildings.Controls.OBC.CDL.Interfaces.RealOutputTHeaDisSetDischarge airflow setpoint temperature for heating
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyValHot water valve commanded position
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutputy1FanTerminal fan command on

Revisions

  • August 24, 2023, by Jianjun Hu:
    Added AHU supply fan status for damper position reset.
    This is for issue 3257.
  • January 12, 2023, by Jianjun Hu:
    Removed the parameter have_preIndDam to exclude the option of using pressure independant damper.
    This is for issue 3139.
  • August 1, 2020, by Jianjun Hu:
    First implementation.