Which values should I set in the design cooling/heating supply air temperatures so I get less than 300 unmet hours for heating?
I am trying to set a baseline model according to ASHRAE 90.1.2010 in OpenStudio using system7 VAV with reheat. In the HVAC tab, I chose the ''supply air to room air temperature'' method. Running the model using the default values (14oC for cooling and 40oC for heating, zone supply air temperature difference=11.1oC) the unmet hours for heating exceed the value of 300.
The thermostat schedules in the thermal zones are 25oC (cooling) and 21oC (heating) during occupation. I can think of the following possible solutions: - zone cooling/heating design supply air temperatures 25oC and 21oC respectively with delta T=11.1 - zone cooling/heating design supply air temperatures 25-11.1=13.9oC and 21+11.1=32.1oC respectively with delta T=11.1.
Did you run the unmet hours load troubleshooting measure? That may help determine the cause of your unmet hours. Check individual zone VAV terminals and the main air handler supply air temperature - are the heating coils operating at full capacity?