blockSystemRequests

Output system requests for VAV cooling only terminal unit
Diagram of SystemRequestsOpen the diagram
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Information

This sequence outputs the system reset requests for cooling only terminal unit. The implementation is according to the Section 5.5.8 of ASHRAE Guideline 36, May 2020.

Cooling SAT reset requests yZonTemResReq

  1. If the zone temperature TZon exceeds the zone cooling setpoint TZonCooSet by 3 °C (5 °F)) for 2 minutes and after suppression period (uAftSup=true) due to setpoint change per G36 Part 5.1.20, send 3 requests (yZonTemResReq=3).
  2. Else if the zone temperature TZon exceeds the zone cooling setpoint TZonCooSet by 2 °C (3 °F) for 2 minutes and after suppression period (uAftSup=true) due to setpoint change per G36 Part 5.1.20, send 2 requests (yZonTemResReq=2).
  3. Else if the cooling loop uCoo is greater than 95%, send 1 request (yZonTemResReq=1) until uCoo is less than 85%.
  4. Else if uCoo is less than 95%, send 0 request (yZonTemResReq=0).

Static pressure reset requests yZonPreResReq

  1. If the measured airflow VDis_flow is less than 50% of setpoint VSet_flow while the setpoint is greater than zero and the damper position uDam is greater than 95% for 1 minute, send 3 requests (yZonPreResReq=3).
  2. Else if the measured airflow VDis_flow is less than 70% of setpoint VSet_flow while the setpoint is greater than zero and the damper position uDam is greater than 95% for 1 minute, send 2 requests (yZonPreResReq=2).
  3. Else if the damper position uDam is greater than 95%, send 1 request (yZonPreResReq=1) until uDam is less than 85%.
  4. Else if the damper position uDam is less than 95%, send 0 request (yZonPreResReq=0).

Parameters

TypeNameDefaultDescription
RealthrTemDif3Threshold difference between zone temperature and cooling setpoint for generating 3 cooling SAT reset requests
RealtwoTemDif2Threshold difference between zone temperature and cooling setpoint for generating 2 cooling SAT reset requests
Duration times
RealdurTimTem120Duration time of zone temperature exceeds setpoint
RealdurTimFlo60Duration time of airflow rate less than setpoint
Advanced
RealdTHys0.25Near zero temperature difference, below which the difference will be seen as zero
RealfloHysNear zero flow rate, below which the flow rate or difference will be seen as zero
ReallooHysLoop output hysteresis below which the output will be seen as zero
RealdamPosHysNear zero damper position, below which the damper will be seen as closed
RealsamplePeriod120Sample period of component, set to the same value as the trim and respond that process yPreSetReq

Connectors

TypeNameDefaultDescription
Buildings.Controls.OBC.CDL.Interfaces.BooleanInputuAftSupAfter suppression period due to the setpoint change
Buildings.Controls.OBC.CDL.Interfaces.RealInputTCooSetZone cooling setpoint temperature
Buildings.Controls.OBC.CDL.Interfaces.RealInputTZonZone temperature
Buildings.Controls.OBC.CDL.Interfaces.RealInputuCooCooling loop signal
Buildings.Controls.OBC.CDL.Interfaces.RealInputVSet_flowDischarge airflow rate setpoint
Buildings.Controls.OBC.CDL.Interfaces.RealInputVDis_flowMeasured discharge airflow rate
Buildings.Controls.OBC.CDL.Interfaces.RealInputuDamDamper position setpoint
Buildings.Controls.OBC.CDL.Interfaces.IntegerOutputyZonTemResReqZone cooling supply air temperature reset request
Buildings.Controls.OBC.CDL.Interfaces.IntegerOutputyZonPreResReqZone static pressure reset requests

Revisions

  • August 1, 2020, by Jianjun Hu:
    First implementation.