blockAHU

AHU level setpoint calculation
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Information

This sequence outputs AHU level effective outdoor air absolute minimum and design minimum setpoints VEffAbsOutAir_flow, VEffDesOutAir_flow and the nomalized minimum setpoint effOutAir_normalized when complying with California Title 24 ventilation requirements. It is implemented according to Section 5.16.3.2 of ASHRAE Guideline G36, May 2020.

It calculates as below:

  1. See the sum of zone absolute and design minimum outdoor airflow setpoint VSumZonAbsMin_flow and VSumZonDesMin_flow from Buildings.Controls.OBC.ASHRAE.G36.AHUs.MultiZone.VAV.SetPoints.OutdoorAirFlow.Title24.SumZone for the detailed description.
  2. Effective outdoor air absolute minimum and design minimum setpoints (VEffAbsOutAir_flow and VEffDesOutAir_flow) are recalculated continuously based on the mode of the zones being served.
    • Effective outdoor air absolute minimum setpoint VEffAbsOutAir_flow is the sum of VZonAbsMin_flow for all zones in all zone groups that are in occupied mode but shall be no larger than the absolute minimum outdoor airflow VAbsOutAir_flow.
    • Effective outdoor air design minimum setpoint VEffDesOutAir_flow is the sum of VZonDesMin_flow for all zones in all zone groups that are in occupied mode but shall be no larger than the absolute minimum outdoor airflow VDesOutAir_flow.
  3. According to section 5.16.4, 5.16.5 and 5.16.6, the effective minimum outdoor airflow setpoint should be reset based on the highest zone CO2 control- loop signal from VEffAbsOutAir_flow at 50% signal to VEffDesOutAir_flow at 100% signal. When there is no CO2 sensor in any zone, the effective minimum outdoor airflow setpoint should be equal to the VEffDesOutAir_flow.

Parameters

TypeNameDefaultDescription
Booleanhave_CO2SenTrue: there are zones have CO2 sensor
Economizer design
Buildings.Controls.OBC.ASHRAE.G36.Types.OutdoorAirSectionminOADesType of outdoor air section
Nominal condition
RealVAbsOutAir_flowDesign outdoor airflow rate when all zones with CO2 sensors or occupancy sensors are unpopulated
RealVDesOutAir_flowDesign minimum outdoor airflow rate with the areas served by the system are occupied at their design population, including diversity where applicable

Connectors

TypeNameDefaultDescription
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.RealInputuCO2Loo_maxMaximum Zone CO2 control loop
Buildings.Controls.OBC.CDL.Interfaces.RealInputVAirOut_flowMeasured outdoor air volumetric flow rate
Buildings.Controls.OBC.CDL.Interfaces.RealOutputVEffAbsOutAir_flowEffective outdoor air absolute minimum setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealOutputeffAbsOutAir_normalizedEffective minimum outdoor airflow setpoint, normalized by the absolute outdoor airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealOutputVEffDesOutAir_flowEffective outdoor air design minimum setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealOutputeffDesOutAir_normalizedEffective minimum outdoor airflow setpoint, normalized by the design outdoor airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealOutputeffOutAir_normalizedEffective minimum outdoor airflow setpoint, normalized by the design total outdoor airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealOutputoutAir_normalizedNormalized outdoor airflow rate

Components

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantabsOutAirDesign outdoor airflow rate when all zones with CO2 sensors or occupancy sensors are unpopulated
Buildings.Controls.OBC.CDL.Reals.Minmin1Effective outdoor air absolute minimum setpoint
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantdesOutAirDesign minimum outdoor airflow with areas served by the system are occupied at their design population, including diversity where applicable
Buildings.Controls.OBC.CDL.Reals.Minmin2Effective outdoor air design minimum setpoint
Buildings.Controls.OBC.CDL.Reals.DividenorVOutMinNormalization for minimum outdoor air flow rate
Buildings.Controls.OBC.CDL.Reals.DividenorVOutMin1Normalization for minimum outdoor air flow rate
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantconConstant value
Buildings.Controls.OBC.CDL.Reals.Sources.Constantcon1Constant value
Buildings.Controls.OBC.CDL.Reals.LineeffOutAirNormalized effective outdoor air setpoint
Buildings.Controls.OBC.CDL.Reals.MultiplyByParametergaiWhen there is no zone has CO2 sensor, design setpoint will be applied
Buildings.Controls.OBC.CDL.Reals.DividenorVOutMin2Normalization for minimum outdoor air flow rate
Buildings.Controls.OBC.CDL.Reals.DividenorVOutNormalization for outdoor air flow rate
Buildings.Controls.OBC.CDL.Reals.Sources.ConstantneaZerNear zero value
Buildings.Controls.OBC.CDL.Reals.Maxmax2Avoid devide by zero
Buildings.Controls.OBC.CDL.Reals.Maxmax1Avoid devide by zero

Revisions

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