There has been apparently an autosizing problem with Air-to-Water HeatPumps in EnergyPlus, which may or may not have been resolved in latest edition.
As a user I succeeded in getting around the autosizing problems by
- setting the
Rated Evaporator Air Flow Rate {m3/s} to an appropriate fixed numerical value - making sure that the associated HeatPump Fan is assigned the same
Maximum Flow Rate {m3/s}, (avoiding the autosizing option, if necessary).
I also adjusted
Rated Sensible Heat Ratio .
In order to avoid troubles, make also sure the entries for
* `Rated Evaporator Inlet Air Dry-Bulb Temperature {C}`
* `Rated Evaporator Inlet Air Wet-Bulb Temperature {C}`
* `Rated Condenser Inlet Water Temperature {C}`
are correct, and the COP- and Capacity curves are normalized at the rated temperatures.
An Example of how a solution may look like is as follows:
Coil:WaterHeating:AirToWaterHeatPump,
AWHP_Coil_DHW, !- Name
700, !- Rated Heating Capacity {W}
3.7, !- Rated COP {W/W}
0.75, !- Rated Sensible Heat Ratio
7, !- Rated Evaporator Inlet Air Dry-Bulb Temperature {C}
6, !- Rated Evaporator Inlet Air Wet-Bulb Temperature {C}
35, !- Rated Condenser Inlet Water Temperature {C}
0.1, !- Rated Evaporator Air Flow Rate {m3/s}
autocalculate, !- Rated Condenser Water Flow Rate {m3/s}
No, !- Evaporator Fan Power Included in Rated COP
No, !- Condenser Pump Power Included in Rated COP
No, !- Condenser Pump Heat Included in Rated Heating Capacity and Rated COP
12, !- Condenser Water Pump Power {W}
0.1, !- Fraction of Condenser Pump Heat to Water
Fan_AWHP_DHW_OUT, !- Evaporator Air Inlet Node Name
ExhaustAirDHW_OUT, !- Evaporator Air Outlet Node Name
DHWTankSourceOUT, !- Condenser Water Inlet Node Name
DHWTankSourceIN, !- Condenser Water Outlet Node Name
0, !- Crankcase Heater Capacity {W}
5, !- Maximum Ambient Temperature for Crankcase Heater Operation {C}
WetBulbTemperature, !- Evaporator Air Temperature Type for Curve Objects
AWHP_DHW_rCAP, !- Heating Capacity Function of Temperature Curve Name
, !- Heating Capacity Function of Air Flow Fraction Curve Name
, !- Heating Capacity Function of Water Flow Fraction Curve Name
AWHP_DHW_rCOP, !- Heating COP Function of Temperature Curve Name
, !- Heating COP Function of Air Flow Fraction Curve Name
, !- Heating COP Function of Water Flow Fraction Curve Name
HPWHPLFFPLR_DHW; !- Part Load Fraction Correlation Curve Name
and finally:
Fan:OnOff,
Fan_AWHP_DHW, !- Name
Always On Discrete, !- Availability Schedule Name
0.6, !- Fan Total Efficiency
250, !- Pressure Rise {Pa}
0.1, !- Maximum Flow Rate {m3/s}
0.8, !- Motor Efficiency
1, !- Motor In Airstream Fraction
OutdoorAirIN_DHW, !- Air Inlet Node Name
Fan_AWHP_DHW_OUT, !- Air Outlet Node Name
, !- Fan Power Ratio Function of Speed Ratio Curve Name
, !- Fan Efficiency Ratio Function of Speed Ratio Curve Name
DHW; !- End-Use Subcategory
