Model for a water to water heat pump with a scroll compressor, as described in Jin (2002). The thermodynamic heat pump cycle is represented below.
The rate of heat transferred to the evaporator is given by:
Q̇_{Eva} = ṁ_{ref} ( h_{Vap}(T_{Eva}) - h_{Liq}(T_{Con}) ).
The power consumed by the compressor is given by a linear efficiency relation:
P = P_{Theoretical} / η + P_{Loss,constant}.
Heat transfer in the evaporator and condenser is calculated using an ε-NTU method, assuming constant refrigerant temperature and constant heat transfer coefficient between fluid and refrigerant.
Variable speed is achieved by multiplying the full load suction volume flow rate by the normalized compressor speed. The power and heat transfer rates are forced to zero if the resulting heat pump state has higher evaporating pressure than condensing pressure.
The model parameters are obtained by calibration of the heat pump model to manufacturer performance data. Calibrated model parameters for various heat pumps from different manufacturers are found in Buildings.Fluid.HeatPumps.Data.ScrollWaterToWater. The calibrated model is located in Buildings.Fluid.HeatPumps.Calibration.ScrollWaterToWater.
Parameters TConMax
and TEvaMin
may be used to set an upper or lower bound for the
condenser and evaporator.
The compressor is disabled when these conditions
are not satisfied, or when the
evaporator temperature is larger
than the condenser temperature.
This mimics the temperature protection
of heat pumps and moreover it avoids
non-converging algebraic loops of equations,
or freezing of evaporator medium.
This option can be disabled by setting
enable_temperature_protection = false
.
The compression process is assumed isentropic. The thermal energy of superheating is ignored in the evaluation of the heat transferred to the refrigerant in the evaporator. There is no supercooling.
H. Jin. Parameter estimation based models of water source heat pumps. PhD Thesis. Oklahoma State University. Stillwater, Oklahoma, USA. 2002.