Closed Nigusse closed 11 months ago
See current and expected supply air flow rates based on a defect file for an AirLoop serving a single zone.
Current code:
MassFlowRateUpStreamLeakMax = max(state.dataDefineEquipment->AirDistUnit(AirDistUnitNum).UpStreamLeakFrac * state.dataLoopNodes->Node(InNodeNum).MassFlowRateMax * DesFlowRatio, 0.0);
This code should have been:
MassFlowRateUpStreamLeakMax = max(state.dataDefineEquipment->AirDistUnit(AirDistUnitNum).UpStreamLeakFrac * state.dataLoopNodes->Node(InNodeNum).MassFlowRateMaxAvail * DesFlowRatio, 0.0);
Air Distribution Unit inlet node's maximum mass flow rate can differ from the maximum available. The maximum available flow rate is set based on the Minimum Turndown Ratio
specified at SetpointManager:WarmestTemperatureFlow
object but the current code calculates upstream leakage rate based on the Maximum Flow, which is often different from the maximum available flow.
It looks to me like you can remove all references to DesFlowRatio elsewhere in code and simply use:
state.dataDefineEquipment->AirDistUnit(AirDistUnitNum).UpStreamLeakFrac * state.dataLoopNodes->Node(InNodeNum).MassFlowRateMaxAvail
Issue overview
Air Distribution Unit (ADU) simple air leakage model uses a constant leakage flow rate regardless of the air terminal type. The upstream air-leakage mass flow rate calculation should be proportional to the maximum available flow for CV air terminal types. The current code results in a higher leakage rate than the user-specified fraction for a CV system.
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