Question-and-Answer Resource for the Building Energy Modeling Community
 | 1 | initial version |
COP will not be used until AFTER the sizing run is complete. The "sizing run" is ideal in that only a zone supply air temperature is required to complete sizing. No COP is needed in this step. The program uses a heat balance to determine a load using occupants, lights, equipment, infiltration, etc. to determine the zone load. Then the program uses the user entered supply air temperature to calculate a zone air mass flow rate as Mdot,zone = Qzone / (Cp,supply air * (Tsupply air - Tzone)).
At the end of the sizing run the zone load (Q) and air mass flow rate (Mdot) are known quantities. Qload is net.
From this point forward the components can be autosized and will use the zone air mass flow rate for sizing the fan and coils. The zone load, Q, from the sizing run is not used to size the components. It's more of a check to compare with other metrics (e.g., if there is no outdoor air mixer blending air at the coil inlet then the coil capacity should roughly size equal to the zone load, cooling capacity will include fan heat, heating capacity will not include fan heat. The fan will simply size to meet the maximum zone cooling and heating air mass flow rate. The coils will be sized using the zone air mass flow rate and the coil entering/mixed and exiting air temperatures and humidity ratios that are used to calculate coil entering/exiting enthalpy (e.g., Qcoil = Mdot,zone * (Hcoil,in - Hcoil,out)). This calculation will provide the coil capacity. Qcoil is gross capacity. Now that a coil capacity is known the power of the system can be determined using EER/COP.
COP is not required for a sizing run. COP is used to set the properties (power) of the HVAC system once the coil capacity is known, which happens after a sizing run.
