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Fix FanPerformance:NightVentilation across fan types - #11883
Removes “Maximum Flow Rate” from FanPerformance:NightVentilation. The field was enforced only by Fan:VariableVolume; other fan types ignored it. For VAV fans, the local cap could reduce fan outlet flow without reducing the upstream flow request, leaving inlet and outlet flows inconsistent. Applying the cap consistently would require coordinating flow limits across fan models and their connected systems, so this change removes the VAV-only cap. The transition warns when it discards a nonblank value.
Fan:ConstantVolume: Air loop behavior is unchanged; zone equipment uses the scoped night ventilation state.
Fan:VariableVolume: Uses alternate night pressure and efficiency, bypasses the normal part load curve, and calculates power from actual airflow, including at low flow.
Fan:OnOff: Applies alternate night settings without the normal speed ratio curves.
Fan:SystemModel: Uses its night pressure when specified, otherwise falls back to design pressure. In continuous mode, night power scales with actual flow. Its built-in “Night Ventilation Mode Flow Fraction” input remains unused.
Scopes night ventilation state to the relevant equipment: zone equipment follows its component’s AvailabilityManager:NightVentilation status; air distribution units follow their connected air loop; coupled Fan:ZoneExhaust fans follow a serving air loop, while decoupled exhaust fans do not enter night mode.
For primary air loops, the night venting flow fraction requests a fraction of design flow. For zone equipment, the manager controls availability and does not scale component flow.
Fouled-filter airflow reduction is calculated against rated fan pressure while the selected night pressure is retained for operating calculations.
Updates the IDD, transition rules, documentation, examples, and regression tests to cover these changes and resolving an air distribution unit’s serving loop before its first simulation.
The figure below shows before (blue, orange) and after (red, black) for 5ZoneNightVent3.idf (Fan:SystemModel) and 5ZoneNightVent4.idf (FanPerformance:NightVentilation) simulation results for the run period:
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Label the PR with at least one of: Defect, Refactoring, NewFeature, Performance, and/or DoNoPublish
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Addresses #11808 by making night-ventilation fan performance consistent across supported fan types and scoping night-mode state to the relevant equipment.
Changes:
Removes the night-ventilation maximum-flow field and adds input transition support.
Updates fan calculations and equipment-specific night-mode handling.
Adds regression coverage and updates documentation and example inputs.
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🔵 Needs a closer look
Cross-equipment state handling and input migration need verified simulation and transition results, with unresolved low-flow power and regression-coverage concerns.
Add end-to-end regression for zone fan night performance selection
src/EnergyPlus/SystemAvailabilityManager.cc:283
The zone-fan regressions assign availManagers(1).availStatus manually, so they would still pass if this production assignment were removed and zone equipment stopped selecting night performance. Add a regression that runs ManageSystemAvailability through actual manager evaluation, changes night ventilation from CycleOn to NoAction, and checks the stored component-specific status and resulting fan performance.
Use the fixed-speed night power multiplier in both low-flow heat-safeguard branches instead of reapplying the normal fan power curve. Add a cubic-curve regression that verifies expected night power at very low flow.
Evaluate zone NightVentilation managers through ManageSystemAvailability instead of manually assigning CycleOn and NoAction statuses. Verify component-specific manager and aggregate statuses transition from CycleOn to NoAction and that fan power returns to its design value, while retaining stale-global-state coverage.
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🔵 Needs a closer look
Cross-system control changes, revised fan-energy calculations, and input migration warrant human confirmation of simulation and transition regression results.
- Add ZoneAirLoopEquipmentManager::getAirDistUnitIndex and use it in
both ManageZoneAirLoopEquipment and SimZoneEquipment instead of
duplicating the lazy input load and name lookup
- Delete any stale Transition.audit before each transition test run and
return the audit text from the fixture
- Assert that a blank FanPerformance:NightVentilation Maximum Flow Rate
does not produce a discard warning
- Document that continuous-speed Fan:SystemModel night-ventilation power
uses actual airflow, pressure rise, and total efficiency, without the
power curve or low-flow fan heat adjustment
It limited night-ventilation flow for Fan:VariableVolume, but other fan types ignored it.
When the VAV limit reduced fan flow, the connected inlet-side flow was not necessarily reduced with it, which could cause a mass-balance issue across the fan.
The transition discards the field's value and preserves the following Motor Efficiency and Motor in Airstream Fraction values.
If the field is nonblank, the transition writes a warning to Transition.audit identifying the discarded value.
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DefectIncludes code to repair a defect in EnergyPlusIDDChangeCode changes impact the IDD file (cannot be merged after IO freeze)StagedBy adding the "Staged" label, some expensive checks needed before merge are run.
4 participants
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Pull request overview
FanPerformance:NightVentilationhandling across fan types #11808FanPerformance:NightVentilation. The field was enforced only byFan:VariableVolume; other fan types ignored it. For VAV fans, the local cap could reduce fan outlet flow without reducing the upstream flow request, leaving inlet and outlet flows inconsistent. Applying the cap consistently would require coordinating flow limits across fan models and their connected systems, so this change removes the VAV-only cap. The transition warns when it discards a nonblank value.Fan:ConstantVolume: Air loop behavior is unchanged; zone equipment uses the scoped night ventilation state.Fan:VariableVolume: Uses alternate night pressure and efficiency, bypasses the normal part load curve, and calculates power from actual airflow, including at low flow.Fan:OnOff: Applies alternate night settings without the normal speed ratio curves.Fan:SystemModel: Uses its night pressure when specified, otherwise falls back to design pressure. In continuous mode, night power scales with actual flow. Its built-in “Night Ventilation Mode Flow Fraction” input remains unused.AvailabilityManager:NightVentilationstatus; air distribution units follow their connected air loop; coupledFan:ZoneExhaustfans follow a serving air loop, while decoupled exhaust fans do not enter night mode.The figure below shows before (blue, orange) and after (red, black) for 5ZoneNightVent3.idf (Fan:SystemModel) and 5ZoneNightVent4.idf (FanPerformance:NightVentilation) simulation results for the run period:
Description of the purpose of this PR
Pull Request Author
Reviewer