Incorrect Autosizing of AirLoopHVAC:DedicatedOutdoorAirSystem

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Another bug report for AirLoopHVAC:DedicatedOutdoorAirSystem. Autosized maximum air flow rate of AirLoopHVAC:DedicatedOutdoorAirSystem does not make sense. Let me explain with the ExampleFile SmallOffice_CentralDOAS.idf.

I expected that the autosized supply air flow rate of AirLoopHVAC:DedicatedOutdoorAirSystem to be the sum of the minimum outdoor air flow rate of the connected AirLoops i.e. 0.275112m3/s in the ExampleFile. However, the simulation result shows that the autosized supply air flow rate is 1.61692m3/s. I don't know where this value comes from. This value is also different from the sum of the maximum outdoor air flow rate of the connected AirLoops i.e. 1.903809m3/s.

Some settings in the ExampleFile that might be relevant are as follows.Cooling Sizing Factor is 1.2, but that seems irrelevant. 1.903809 / 1.61692 = 1.17742931 ≠ 1.2. System sizing method is NonCoincident. The AirLoops connected to the AirLoopHVAC:DedicatedOutdoorAirSystem do not have Economizer. There is no input for AirLoopHVAC:DedicatedOutdoorAirSystem in Sizing:System.

Autosizing is shown above. On the other hand, what about the hourly air flow rate of AirLoopHVAC:DedicatedOutdoorAirSystem during the annual run? It is the sum of the minimum outdoor air flow rate of the connected AirLoops. Then, you might think that there is no problem, but there is. The problem is that the Coil:Cooling:Water in AirLoopHVAC:DedicatedOutdoorAirSystem is oversized, which also oversizes Chiller:Electric and Pump:VariableSpeed in the PlantLoop. As a result, the annual end use increases.

The following may be a new feature request rather than a bug report.

The maximum air flow rate of AirLoopHVAC:DedicatedOutdoorAirSystem should depend on whether the connected AirLoops have Economizer or not. If Economizer Control Type in Controller:OutdoorAir of the connected AirLoops is NoEconomizer, EnergyPlus should refer to the minimum OA flow rates of the AirLoops to autosize the maximum air flow rate of AirLoopHVAC:DedicatedOutdoorAirSystem. If Economizer Control Type of the connected AirLoops is anything other than NoEconomizer, EnergyPlus should refer to the maximum OA flow rate (= the maximum supply air flow rate) of the AirLoops to autosize the maximum air flow rate of AirLoopHVAC:DedicatedOutdoorAirSystem. Or users should be able to choose autosizing option with or without an economiser in AirLoopHVAC:DedicatedOutdoorAirSystem.