blockDampers

Output signals for controlling VAV cooling only box damper position
Diagram of DampersOpen the diagram
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Information

This sequence sets the damper position for VAV cooling only terminal unit. The implementation is according to Section 5.5.5 and 5.5.7 of ASHRAE Guideline 36 (G36), May 2020.

  1. When the zone state (uZonSta) is cooling, the cooling-loop output (uCoo) shall be mapped to the active airflow setpoint from the minimum (VActMin_flow) to the cooling maximum airflow setpoints (VActCooMax_flow).
    • If supply air temperature TSup from the air handler is greater than room temperature TZon, cooling supply airflow setpoint shall be no higher than the minimum.
  2. When the zone state is deadband or heating, the active airflow setpoint shall be the minimum airflow setpoint.
  3. The VAV damper yDam shall be modulated by a control loop to maintain the measured airflow VDis_flow at the active setpoint.

The sequences of controlling damper position for the cooling only terminal unit are described in the following figure below.

Image of damper control for VAV cooling only unit

Override the airflow setpoint and the damper position setpoint by providing software switches that interlock to a system-level point to:

  1. when oveFloSet equals to 1, force the zone airflow setpoint VSet_flow to zero,
  2. when oveFloSet equals to 2, force the zone airflow setpoint VSet_flow to zone cooling maximum airflow rate VCooMax_flow,
  3. when oveFloSet equals to 3, force the zone airflow setpoint VSet_flow to zone minimum airflow setpoint VMin_flow.
  4. when oveDamPos equals to 1, force the damper to full closed by setting yDam to 0,
  5. when oveDamPos equals to 2, force the damper to full open by setting yDam to 1.

Parameters

TypeNameDefaultDescription
RealVMin_flowDesign zone minimum airflow setpoint
RealVCooMax_flowDesign zone cooling maximum airflow rate
Buildings.Controls.OBC.CDL.Types.SimpleControllerdamConBuildings.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
RealdTHys0.25Delta between the temperature hysteresis high and low limit
RealiniDam0.01Initial damper position when the damper control is enabled

Connectors

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Interfaces.RealInputVActMin_flowActive minimum 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.RealInputuCooCooling loop signal
Buildings.Controls.OBC.CDL.Interfaces.RealInputVActCooMax_flowActive cooling maximum airflow rate
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputuZonStaCurrent zone state
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputoveFloSetIndex of overriding flow setpoint, 1: set to zero; 2: set to cooling maximum; 3: set to minimum flow
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputu1FanAHU supply fan status
Buildings.Controls.OBC.CDL.Interfaces.RealInputVDis_flowMeasured primary discharge airflow rate
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputoveDamPosIndex of overriding damper position, 1: set to close; 2: set to open
Buildings.Controls.OBC.CDL.Interfaces.RealOutputVSet_flowAirflow setpoint after considering override
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyDamCommanded damper position after considering override

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.