.Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.ASHRAE62_1.AHU

Information

This sequence outputs AHU level uncorrected minimum outdoor airflow rate VUncOutAir_flow and effective minimum outdoor airflow rate VEffOutAir_flow when complying with ASHRAE Standard 62.1 ventilation requirements. It is implemented according to Section 5.16.3.1 of ASHRAE Guideline G36, May 2020.

It requires following inputs which are sum or maximum of the outputs from the zone level calculation. See Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.ASHRAE62_1.SumZone for these inputs.

1. Sum of the adjusted population component breathing zone flow rate for all zones that are in all zone groups in occupied mode, VSumAdjPopBreZon_flow.
2. Sum of the adjusted area component breathing zone flow rate for all zones that are in all zone groups in occupied mode, VSumAdjAreBreZon_flow.
3. Sum of the zone primary airflow rates for all zones in all zone groups that are in occupied mode,VSumZonPri_flow.
4. Maximum zone outdoor air fraction for all zones in all zone groups that are in occupied mode, uOutAirFra_max.

The calculation is done using the steps below.

1. See Section 3.1.4.2.a of Guideline 36 for setpoints VUncDesOutAir_flow and VDesTotOutAir_flow.
2. The uncorrected outdoor airflow rate setpoint VUncOutAir_flow is recalculated continuously based on the adjusted population and area component breathing zone flow rate of the zones being served determined in accordance with Section 5.2.1.3. See Buildings.Controls.OBC.ASHRAE.G36.VentilationZones.ASHRAE62_1.Setpoints.

       VUncOutAir_flow = min(VUncDesOutAir_flow, (VSumAdjPopBreZon_flow + VSumAdjAreBreZon_flow))
   

3. Calculate the current system ventilation efficiency as

       sysVenEff = 1 + (VUncOutAir_flow/VSumZonPri_flow) - uOutAirFra_max
   

4. Calculate the effective minimum outdoor air setpoint VEffOutAir_flow as the uncorrected outdoor air intake divided by the system ventilation efficiency, but no larger than the design total outdoor airflow rate VDesTotOutAir_flow:

       VEffOutAir_flow = min(VUncOutAir_flow/sysVenEff, VDesTotOutAir_flow)
   

Revisions

• April 6, 2024, by Michael Wetter:
  Corrected wrong annotation.
• March 12, 2022, by Jianjun Hu:
  First implementation.