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ZoneHVAC:OutdoorAirUnit cooling temperaturecontrol unmet setpoint #10136

Closed ccruveiller closed 1 year ago

ccruveiller commented 1 year ago

Issue overview

Hello, I am used to work with ZoneHVAC:OutdoorAirUnit objects, and I needed for a project to convert it into a AirLoopHVAC in order to handle dehumidification. I tried the simple conversion with supply temperature control (before trying dehumidification). That's when I realised that ZoneHVAC:OAU was not always meeting the cooling supply temperature setpoint, whereas the AirLoopHVAC was (26°C) There are no issues with the heating supply temperature (19°C)

image image The system is providing ventilation only between 8am and 5pm. In the original (ZoneHVAC) during night hours the node gets outdoor air temperature while the feature (Airloop) gets return air temperature. I am using the following ZoneHVAC:OAU:

ZoneHVAC:OutdoorAirUnit, z-7ik1vgwyt|air_loop, ! Name , ! Availability Schedule Name z-7ik1vgwyt, ! Zone Name autosize, ! Outdoor Air Flow Rate schedule|vent_bureau|outdoor_air|shadow, ! Outdoor Air Schedule Name z-7ik1vgwyt|air_loop|fan_supply, ! Supply Fan Name blowthrough, ! Supply Fan Placement z-7ik1vgwyt|air_loop|fan_exhaust, ! Exhaust Fan Name autosize, ! Exhaust Air Flow Rate schedule|vent_bureau|outdoor_air|shadow, ! Exhaust Air Schedule Name temperaturecontrol, ! Unit Control Type non_ideal_default_supply_upper_setpoint|fixed_supply_temperature_ahu, ! High Air Control Temperature Schedule Name non_ideal_default_supply_lower_setpoint|fixed_supply_temperature_ahu, ! Low Air Control Temperature Schedule Name z-7ik1vgwyt|mechanical_ventilation|supply|0, ! Outdoor Air Node Name z-7ik1vgwyt|mechanical_ventilation|supply|4, ! AirOutlet Node Name z-7ik1vgwyt|mechanical_ventilation|return|0, ! AirInlet Node Name z-7ik1vgwyt|mechanical_ventilation|supply|1, ! Supply FanOutlet Node Name z-7ik1vgwyt|air_loop|equipment_list; ! Outdoor Air Unit List Name

And the following AirLoopHVAC branch: Branch, AHU 1 Main Branch, !- Name , !- Pressure Drop Curve Name AirLoopHVAC:OutdoorAirSystem, !- Component 1 Object Type DOAS OA System, !- Component 1 Name DOAS Air Loop Inlet, !- Component 1 Inlet Node Name DOAS Mixed Air Outlet, !- Component 1 Outlet Node Name CoilSystem:Cooling:DX, !- Component 2 Object Type z-7ik1vgwyt|air_loop|cta|cooling_coil, !- Component 2 Name DOAS Mixed Air Outlet, !- Component 2 Inlet Node Name cooling_outlet, !- Component 2 Outlet Node Name Coil:Heating:Electric, !- Component 3 Object Type z-7ik1vgwyt|air_loop|cta|heating_coil, !- Component 3 Name cooling_outlet, !- Component 3 Inlet Node Name heating_outlet, !- Component 3 Outlet Node Name Fan:SystemModel, !- Component 4 Object Type DOAS Supply Fan, !- Component 4 Name heating_outlet, !- Component 4 Inlet Node Name DOAS Supply Fan Outlet; !- Component 4 Outlet Node Name

When I look into the .eio I get same cooling coil sizing. Are these results pertinent with the way temperaturecontrol of ZoneHVAC:OutdoorAirUnit was implemented?

It finally results into relative difference of 20% on the cooling coil consumption: image

Thanks in advance for your help, and a big thanks for all your work!

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ccruveiller commented 1 year ago

I understood where the difference comes from. The ZoneHVAC:OutdoorAirUnit control depends only on outdoor air temperature, the coil cools only if the oudoor air temperature is above 26 independently from the cooling coil air inlet temperature. Whereas in the airloophvac the control is really on the outletof the coil, it won't supply air above 26.