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I am modelling a simple HVAC system in OpenStudio 2.5.0. I have a zone exhaust fan that is to operate when the zone temperature exceeds the cooling setpoint temperature. I defined the outdoor ventilation design specification which is constant throughout the year in the Space Type Tab grid. I then added the zone exhaust fan in the Thermal Zones tab in the grid. I defined the availability schedule as always on and the minimum zone temperature limit schedule as the zone cooling setpoint temperature. Initially I did not have a schedule for balanced exhaust fraction. I ran the simulation and noted in the error report that the exhaust flow was not balanced. I then added a simple empty air loop in the HVAC systems tab. In this loop I added an AirLoopHVAC:OutdoorAirSystem, an uncontrolled diffuser and assigned the zone. I then went back to the Thermal Zone Tab and I set the System availability manager as coupled. Looking into DView, the yearly hourly zone temperature goes from near the outdoor ambient temperature to well over the design cooling setpoint as would be expected with an outdoor only cooling system. I then reran the simulation with the exhaust fan flow set below the outdoor ventilation design spec and the minimum zone temperature in the winter was tempered. I seems like the exhaust fan is not being controlled by the zone temperature limit schedule. Any suggestions are welcome.

I am modelling a simple HVAC system in OpenStudio 2.5.0. I have a zone exhaust fan that is to operate when the zone temperature exceeds the cooling setpoint temperature. I defined the outdoor ventilation design specification which is constant throughout the year in the Space Type Tab grid. I then added the zone exhaust fan in the Thermal Zones tab in the grid. I defined the availability schedule as always on and the minimum zone temperature limit schedule as the zone cooling setpoint temperature. Initially I did not have a schedule for balanced exhaust fraction. I ran the simulation and noted in the error report that the exhaust flow was not balanced. I then added a simple empty air loop in the HVAC systems tab. In this loop I added an AirLoopHVAC:OutdoorAirSystem, an uncontrolled diffuser and assigned the zone. I then went back to the Thermal Zone Tab and I set the System availability manager as coupled. Looking into DView, the yearly hourly zone temperature goes from near the outdoor ambient temperature to well over the design cooling setpoint as would be expected with an outdoor only cooling system. I then reran the simulation with the exhaust fan flow set below the outdoor ventilation design spec and the minimum zone temperature in the winter was tempered. I seems like the exhaust fan is not being controlled by the zone temperature limit schedule. Any suggestions are welcome.