.BuildingSystems.Fluid.HeatPumps.ReciprocatingWaterToWater

Information

Model for a water to water heat pump with a reciprocating 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 acheived by multiplying the full load piston displacement 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.

Options

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.

Assumptions and limitations

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.

References

H. Jin. Parameter estimation based models of water source heat pumps. PhD Thesis. Oklahoma State University. Stillwater, Oklahoma, USA. 2002.

Revisions

• May 30, 2017, by Filip Jorissen:
  Revised documentation for temperature protection. See #769.
• November 14, 2016, by Massimo Cimmino:
  First implementation.