I am trying to use a VRF system to condition my residential zones in a multifamily apartment building. However, the model has a high number of unmet hours for heating only (approx 500). The only way that I have been able to eliminate these high unmet hours is to zero out the ventilation and infiltration, which is of course not a realistic solution. I have put each individual zone on its own system, so it is not a simultaneous heating and cooling problem.
I have dug into the outputs and concluded the following based on the attached graphs.
1) The autosizing method is not properly maintaining the thermostat heating setpoint during the design days. As you can see there is mechanical ventilation during the design day and the zone temp trend follows the ventilation ACH trend. However, it is not in the way you would expect, as more ventilation results in a higher temperature in the zone.
2) During the annual run, the VRF system is not maxing out on capacity in an attempt to meet the heating demand.
It is as if somewhere in the back end there is a disconnect between the ventilation/infiltration load and the VRF system. Has anyone else experienced this or has an idea what might be causing this?
Thanks in advance for any advice!
