I am modeling a 90.1 appendix G baseline. My baseline system is a VAV terminal reheat system. I am auto-sizing the baseline system and specifying the OA requirement per code.
The applicable ventilation code requires very high ventilation rates based on the room area. When trying to run the simulation I get the following error:
*** Beginning Plant Sizing Calculations
* Severe * For Controller:OutdoorAir: CONTROLLER OUTDOOR AIR 1
* ~~~ * maximum outdoor air flow rate (6.6752) < minimum outdoor air flow rate (7.2538)
* ~~~ * To set the minimum outside air flow rate use the "Design (minimum) outdoor air flow rate" field in the Sizing:System object
* Warning * InitOAController: Minimum Outdoor Air Flow Rate for Controller:OutdoorAir=CONTROLLER OUTDOOR AIR 1 is greater than Design Supply Air Flow Rate for AirLoopHVAC=PACKAGED ROOFTOP VAV WITH REHEAT.
* ~~~ * ...Minimum Outdoor Air Flow Rate=7.253832 will be reset to loop Design Supply Air Flow Rate=6.675242
* Fatal * Error in Controller:OutdoorAir; program terminated
The way I understand it is that the designed supply air flow rate is smaller than the minimum OA requirement, therefore the "maximum designed OA" is when the system is working at 100% OA. Because it still cannot provide the minimum OA requirement, it stops.
To fix it I tried hard-sizing the design minimum OA to my required OA in the OS:Sizing:System (as the error states). This did not work.
I tried hard-sizing the design supply air flow rate to my required OA. This did not work.
I fixed it by hard-sizing the Maximum Outside Air Flow Rate to my required OA in the Controller:OutdoorAir. However, this does not make sense to me (maybe it does make sense). I would expect the Minimum OA flow rate to override the design air flow rate if MIN OA < Designed OA. Or when I hard-size the supply flow rate for it to be able to serve as 100% OA (it looks like the maximum OA calculation still uses the auto-sized supply air value).
