blockCommon

Outdoor air and return air damper position limits for units with common damper
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Information

This block models the multi zone VAV AHU minimum outdoor air control with a single common damper for minimum outdoor air and economizer functions based on outdoor airflow measurement, designed in line with the Section 5.16.6 of the ASHRAE Guideline 36, May 2020.

The controller is enabled when the supply fan is proven on (u1SupFan=true) and the AHU operation mode Buildings.Controls.OBC.ASHRAE.G36.Types.OperationModes equals occupied. Otherwise the damper position limits are set to their corresponding maximum and minimum physical or at commissioning fixed limits. The state machine chart below illustrates listed conditions:

Image of damper position limits state machine chart

The controller sets the outdoor and return damper position limits so that the outdoor airflow rate VOut_flow stays equal or above the minimum outdoor air setpoint VOutMinSet_flow. The fraction of the controller output signal between yMin and uRetDam_min is linearly mapped to the outdoor air damper minimal position yOutDam_min while the fraction of the controller output between uRetDam_min and yMax is linearly mapped to the return air damper maximum position yRetDam_max. Thus the dampers are not interlocked.

The following control charts show the input/output structure and an expected damper position limits for a well configured controller.

Image of damper position limits control diagram

The expected damper position limits vs. the control loop signal are as follows:

Image of damper position limits control chart

Parameters

TypeNameDefaultDescription
Controller
Buildings.Controls.OBC.CDL.Types.SimpleControllercontrollerTypeBuildings.Controls.OBC.CDL.Types.SimpleController.PIType of controller
Realk0.05Gain of damper limit controller
RealTi120Time constant of damper limit controller integrator block
RealTd0.1Time constant of damper limit controller derivative block
Commissioning › Controller
RealuRetDam_min0.5Loop signal value to start decreasing the maximum return air damper position
Commissioning › Physical damper position 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

Connectors

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Interfaces.RealInputVOut_flow_normalizedMeasured outdoor volumetric airflow rate, normalized by design minimum outdoor airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInputVOutMinSet_flow_normalizedEffective minimum outdoor airflow setpoint, normalized by design minimum outdoor airflow rate
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputuOpeModAHU operation mode status signal
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputu1SupFanSupply fan proven on
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyOutDam_minMinimum outdoor air damper position limit
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyOutDam_maxMaximum outdoor air damper position limit
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyRetDam_minMinimum return air damper position limit
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyRetDam_maxMaximum return air damper position limit
Buildings.Controls.OBC.CDL.Interfaces.RealOutputyRetDamPhy_maxPhysical maximum return air damper position limit. Required as an input for the economizer enable disable sequence
Buildings.Controls.OBC.CDL.Interfaces.BooleanOutputyEnaMinOutTrue: enable minimum outdoor air control loop

Components

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Reals.PIDWithResetdamLimConDamper position limit controller

Revisions

  • March 1, 2023, by Michael Wetter:
    Changed constants from 0 to 0.0 and 1 to 1.0.
    This is for #3267.
  • July 10, 2020, by Antoine Gautier:
    Changed default value of integral time for minimum outdoor air control. Set yMin to 0.
    This is for #2019.
  • March 14, 2020, by Jianjun Hu:
    Replaced mulAnd by logic and block to avoid vector-valued calculation.
    This is for #1829.
  • July 17, 2017, by Michael Wetter:
    Replaced block that checks for equality of real values within a tolerance by two inequality checks.
  • June 06, 2017, by Milica Grahovac:
    First implementation.