zWSHP object input rated (reference) conditions?

asked 2024-09-26 11:44:51 -0600

Greg Estep
719 ●22 ●6

updated 2024-09-26 12:04:31 -0600

Hello all, this question is regarding the rated inputs for object Coil:Cooling:WaterToAirHeatPump:EquationFit

I have a project (hotel) where I want to hard size the heat pumps to match what is shown on the mechanical drawings schedule. OK, this is annoying, but I have model data grid view, and I start bulk editing the inputs. A typical guest room is using the water source HP BOSCH CL 07 unit and has a rated cooling capacity of about 7000 Btu/h and rated airflow of 300 CFM. Great. I run the simulation for the summer design week and get more unmet hours than expected. I look at the cooling coil total cooling rate and find that unit is peaking out at about 3000 Btu/h. This is less than half the output. I try to convince myself this is due to warmer water temperature (75F) and cooler entering air temperature, but I can’t justify a 50% capacity reduction.

The engineering reference says, For cooling mode, the reference conditions; reference load side air volumetric flow rate (˙Vair,ref), reference source side water volumetric flow rate(˙Vw,ref), reference sensible capacity (Qsens,ref) and reference power input (Powerc,ref) are the conditions when the heat pump is operating at the highest cooling capacity or reference cooling capacity (Qtotal,ref) indicated in the manufacturer’s catalog

Question: Are the reference conditions different from AHRI (13256-1)?

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My understanding is that this is a generic object where the coefficients are representative of several zone water to air heat pumps manufacturers and covers a wide range of operating conditions. Do you agree? Or are you suggesting that the default coefficients in DesignBuilder are random? The reference conditions need to be specified by the user.

this is the correct link to the Eng Ref: Single Speed Equation-Fit Model

Greg Estep ( 2024-09-27 10:30:03 -0600 )edit

I didn't create the DesignBuilder curves, so I can't tell you to what conditions they are normalized. For the Engineering reference, the coils referenced in both links are the same. In the underlying EnergyPlus engine, Coil:Cooling:WaterToAirHeatPump:EquationFit and Coil:Heating:WaterToAirHeatPump:EquationFit can be used in both ZoneHVAC:WaterToAir:HeatPump and some AirLoopHVAC:Unitary equipment.