blockOutsideAirFlow

Output the minimum outdoor airflow rate setpoint for systems with a single zone
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Information

This atomic sequence sets the minimum outdoor airflow setpoint for compliance with the ventilation rate procedure of ASHRAE 62.1-2013. The implementation is according to ASHRAE Guidline 36 (G36), PART 5.P.4.b, PART 5.B.2.b, PART3.1-D.2.a.

Step 1: Minimum breathing zone outdoor airflow required breZon

  • The area component of the breathing zone outdoor airflow: breZonAre = AFlo*VOutPerAre_flow.
  • The population component of the breathing zone outdoor airflow: breZonPop = occCou*VOutPerPer_flow.

The number of occupant occCou could be retrieved directly from occupancy sensor nOcc if the sensor exists (have_occSen=true), or using the default occupant density occDen to find it AFlo*occDen. The occupant density can be found from Table 6.2.2.1 in ASHRAE Standard 62.1-2013.

Step 2: Zone air-distribution effectiveness zonDisEff

Table 6.2.2.2 in ASHRAE 62.1-2013 lists some typical values for setting the effectiveness. Depending on difference between zone space temperature TZon and supply air temperature TDis, Warm-air effectiveness zonDisEffHea or Cool-air effectiveness zonDisEffCoo should be applied.

Step 3: Minimum required zone outdoor airflow zonOutAirRate

For each zone in any mode other than occupied mode and for zones that have window switches and the window is open, zonOutAirRate shall be zero. Otherwise, the required zone outdoor airflow zonOutAirRate shall be calculated as follows:

If the zone is populated, or if there is no occupancy sensor:
  • If discharge air temperature at the terminal unit is less than or equal to zone space temperature: zonOutAirRate = (breZonAre+breZonPop)/disEffCoo.
  • If discharge air temperature at the terminal unit is greater than zone space temperature: zonOutAirRate = (breZonAre+breZonPop)/disEffHea
If the zone has an occupancy sensor and is unpopulated:
  • If discharge air temperature at the terminal unit is less than or equal to zone space temperature: zonOutAirRate = breZonAre/disEffCoo
  • If discharge air temperature at the terminal unit is greater than zone space temperature: zonOutAirRate = breZonAre/disEffHea

For the single zone system, the required minimum outdoor airflow setpoint VOutMinSet_flow equals to the zonOutAirRate.

Parameters

TypeNameDefaultDescription
Booleanhave_occSenSet to true if zones have occupancy sensor
RealoccDen0.05Default number of person in unit area
RealzonDisEffHea0.8Zone air distribution effectiveness during heating
RealzonDisEffCoo1.0Zone air distribution effectiveness during cooling
Nominal condition
RealVOutPerAre_flow3e-4Outdoor air rate per unit area
RealVOutPerPer_flow2.5e-3Outdoor air rate per person
RealAFloFloor area
Advanced
RealuLow-0.5If zone space temperature minus supply air temperature is less than uLow, then it should use heating supply air distribution effectiveness
RealuHigh0.5If zone space temperature minus supply air temperature is more than uHig, then it should use cooling supply air distribution effectiveness

Connectors

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Interfaces.RealInputnOccNumber of occupants
Buildings.Controls.OBC.CDL.Interfaces.RealInputTZonMeasured zone air temperature
Buildings.Controls.OBC.CDL.Interfaces.RealInputTDisMeasured discharge air temperature
Buildings.Controls.OBC.CDL.Interfaces.IntegerInputuOpeModAHU operation mode status signal
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputuSupFanSupply fan status, true if on, false if off
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputuWinWindow status, true if open, false if closed
Buildings.Controls.OBC.CDL.Interfaces.RealOutputVOutMinSet_flowEffective minimum outdoor airflow setpoint

Revisions

  • November 2, 2018, by Michael Wetter:
    Made the input connector nOcc conditionally removable, as it is for the multizone implementation. This is for issue 1270.
  • July 6, 2017, by Jianjun Hu:
    Replaced cooCtrlSig input with TZon and TDis inputs to check if cool or warm air distribution effectiveness should be applied. Applied hysteresis to avoid rapid change.
  • May 12, 2017, by Jianjun Hu:
    First implementation.