Buildings.Fluid.HeatPumps.Compressors

Package with compressor models

Information

This package contains components models for compressors.

Extends from Modelica.Icons.VariantsPackage (Icon for package containing variants).

Package Content

Name	Description
ReciprocatingCompressor	Model for a reciprocating compressor, based on Jin (2002)
ScrollCompressor	Model for a scroll compressor, based on Jin (2002)
Validation	Collection of models that validate the compressor models
BaseClasses	Package with base classes for compressors

Buildings.Fluid.HeatPumps.Compressors.ReciprocatingCompressor

Model for a reciprocating compressor, based on Jin (2002)

Buildings.Fluid.HeatPumps.Compressors.ReciprocatingCompressor

Information

Model for a reciprocating processor, as detailed in Jin (2002). 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}.

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.

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. 2012.

Extends from Buildings.Fluid.HeatPumps.Compressors.BaseClasses.PartialCompressor (Partial compressor model).

Parameters

Type	Name	Default	Description
replaceable package ref		R410A	Refrigerant in the component
VolumeFlowRate	pisDis		Piston displacement [m3/s]
Real	cleFac	cleFac( min = 0, final...	Clearance factor [1]
Efficiency	etaEle		Electro-mechanical efficiency of the compressor [1]
Power	PLos	PLos( ...	Constant part of the compressor power losses [W]
AbsolutePressure	pDro		Pressure drop at suction and discharge of the compressor [Pa]
TemperatureDifference	dTSup	dTSup( ...	Superheating at compressor suction [K]
Initialization
AbsolutePressure	pEva.start	100e3	Pressure of saturated vapor at evaporator temperature [Pa]
AbsolutePressure	pCon.start	1000e3	Pressure of saturated liquid at condenser temperature [Pa]
AbsolutePressure	pDis.start	1000e3	Discharge pressure of the compressor [Pa]
AbsolutePressure	pSuc.start	100e3	Suction pressure of the compressor [Pa]
SpecificVolume	vSuc.start	1e-4	Specific volume of the refrigerant at suction of the compressor [m3/kg]

Connectors

Type	Name	Description
HeatPort_a	port_a	Refrigerant connector a (corresponding to the evaporator)
HeatPort_b	port_b	Refrigerant connector b (corresponding to the condenser)
input RealInput	y	Modulating signal for compressor frequency, equal to 1 at full load conditions [1]
output RealOutput	P	Electric power consumed by compressor [W]

Modelica definition

model ReciprocatingCompressor "Model for a reciprocating compressor, based on Jin (2002)" extends Buildings.Fluid.HeatPumps.Compressors.BaseClasses.PartialCompressor; parameter Modelica.SIunits.VolumeFlowRate pisDis "Piston displacement"; parameter Real cleFac( min = 0, final unit = "1") "Clearance factor"; parameter Modelica.SIunits.Efficiency etaEle "Electro-mechanical efficiency of the compressor"; parameter Modelica.SIunits.Power PLos(min = 0) "Constant part of the compressor power losses"; parameter Modelica.SIunits.AbsolutePressure pDro "Pressure drop at suction and discharge of the compressor"; parameter Modelica.SIunits.TemperatureDifference dTSup(min = 0) "Superheating at compressor suction"; Modelica.SIunits.MassFlowRate m_flow "Refrigerant mass flow rate"; Modelica.SIunits.Power PThe "Theoretical power consumed by the compressor"; Modelica.SIunits.Efficiency COP(start=5) "Heating COP of the compressor"; protected Modelica.SIunits.IsentropicExponent k(start = 1.2) "Isentropic exponent of the refrigerant"; Real pisDis_norm "Normalized piston displacement at part load conditions"; equation // Limit compressor speed to the full load speed pisDis_norm = Buildings.Utilities.Math.Functions.smoothLimit(y, 0.0, 1.0, 0.001); if isOn then // Suction pressure pSuc = Buildings.Utilities.Math.Functions.smoothMin(pEva - pDro, pCon - pDro, 0.01*ref.pCri); // Discharge pressure pDis = pCon + pDro; // Refrigerant mass flow rate k = ref.isentropicExponentVap_Tv(TSuc, vSuc); m_flow = pisDis_norm*pisDis/vSuc*(1 + cleFac - cleFac*(PR)^(1/k)); // Theoretical power of the compressor PThe = k/(k-1) * m_flow*pSuc*vSuc*((PR)^((k-1)/k)-1); // Power consumed by the compressor P = PThe/etaEle + PLos; // Temperature at suction of the compressor TSuc = port_a.T + dTSup; // Energy balance of the compressor port_a.Q_flow = m_flow * (hEva - hCon); port_b.Q_flow = - (port_a.Q_flow + P); -port_b.Q_flow = P * COP; else // Heat pump is turned off k = 1.0; pSuc = pEva; pDis = pCon; m_flow = 0; PThe = 0; P = 0; TSuc = port_a.T; port_a.Q_flow = 0; port_b.Q_flow = 0; COP = 1.0; end if; end ReciprocatingCompressor;

Buildings.Fluid.HeatPumps.Compressors.ScrollCompressor

Model for a scroll compressor, based on Jin (2002)

Buildings.Fluid.HeatPumps.Compressors.ScrollCompressor

Information

Model for a scroll processor, as detailed in Jin (2002). 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}.

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.

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. 2012.

Extends from Buildings.Fluid.HeatPumps.Compressors.BaseClasses.PartialCompressor (Partial compressor model).

Parameters

Type	Name	Default	Description
replaceable package ref		R410A	Refrigerant in the component
Real	volRat	volRat( min = 1.0, fin...	Built-in volume ratio [1]
VolumeFlowRate	V_flow_nominal	V_flow_nominal( ...	Refrigerant volume flow rate at suction at full load conditions [m3/s]
MassFlowRate	leaCoe	leaCoe( min = 0)	Leakage mass flow rate at a pressure ratio of 1 [kg/s]
Efficiency	etaEle		Electro-mechanical efficiency of the compressor [1]
Power	PLos	PLos( ...	Constant part of the compressor power losses [W]
TemperatureDifference	dTSup	dTSup( ...	Superheating at compressor suction [K]
Initialization
AbsolutePressure	pEva.start	100e3	Pressure of saturated vapor at evaporator temperature [Pa]
AbsolutePressure	pCon.start	1000e3	Pressure of saturated liquid at condenser temperature [Pa]
AbsolutePressure	pDis.start	1000e3	Discharge pressure of the compressor [Pa]
AbsolutePressure	pSuc.start	100e3	Suction pressure of the compressor [Pa]
SpecificVolume	vSuc.start	1e-4	Specific volume of the refrigerant at suction of the compressor [m3/kg]

Connectors

Type	Name	Description
HeatPort_a	port_a	Refrigerant connector a (corresponding to the evaporator)
HeatPort_b	port_b	Refrigerant connector b (corresponding to the condenser)
input RealInput	y	Modulating signal for compressor frequency, equal to 1 at full load conditions [1]
output RealOutput	P	Electric power consumed by compressor [W]

Modelica definition

model ScrollCompressor "Model for a scroll compressor, based on Jin (2002)" extends Buildings.Fluid.HeatPumps.Compressors.BaseClasses.PartialCompressor; parameter Real volRat( min = 1.0, final unit = "1") "Built-in volume ratio"; parameter Modelica.SIunits.VolumeFlowRate V_flow_nominal(min=0) "Refrigerant volume flow rate at suction at full load conditions"; parameter Modelica.SIunits.MassFlowRate leaCoe( min = 0) "Leakage mass flow rate at a pressure ratio of 1"; parameter Modelica.SIunits.Efficiency etaEle "Electro-mechanical efficiency of the compressor"; parameter Modelica.SIunits.Power PLos(min = 0) "Constant part of the compressor power losses"; parameter Modelica.SIunits.TemperatureDifference dTSup(min = 0) "Superheating at compressor suction"; Modelica.SIunits.MassFlowRate m_flow "Refrigerant mass flow rate"; Modelica.SIunits.MassFlowRate mLea_flow "Refrigerant leakage mass flow rate"; Modelica.SIunits.Power PThe "Theoretical power consumed by the compressor"; Modelica.SIunits.Efficiency COP(start=5) "Heating COP of the compressor"; protected Modelica.SIunits.IsentropicExponent k(start = 1.2) "Isentropic exponent of the refrigerant"; Real v_norm "Normalized refrigerant volume flow rate at suction at part load conditions"; Real PRInt(start = 2.0) "Built-in pressure ratio"; equation PRInt = volRat^k; // Limit compressor speed to the full load speed v_norm = Buildings.Utilities.Math.Functions.smoothLimit(y, 0.0, 1.0, 0.001); if isOn then // Suction pressure pSuc = pEva; // Discharge pressure pDis = pCon; // Refrigerant mass flow rate mLea_flow = leaCoe*PR; m_flow = v_norm* Buildings.Utilities.Math.Functions.smoothMax( V_flow_nominal/vSuc - mLea_flow, 1e-5*V_flow_nominal/vSuc, 1e-6*V_flow_nominal/vSuc); // Theoretical power of the compressor k = ref.isentropicExponentVap_Tv(TSuc, vSuc); // If the external pressure ratio does not match the built-in pressure ratio PThe = v_norm * k/(k - 1.0) * pSuc * V_flow_nominal * (((k - 1.0)/k) * PR/volRat + 1.0/k * PRInt^((k - 1.0)/k) - 1.0); // This equation reduces to the equation for the built-in pressure ratio // if the external pressure ratio matches the built-in pressure ratio: // PThe = v_norm * k/(k - 1.0) * pSuc*v_flow * ((PRInt)^((k - 1.0)/k) - 1.0) // Temperature at suction of the compressor TSuc = port_a.T + dTSup; // Power consumed by the compressor P = (PThe/etaEle + PLos); // Energy balance of the compressor port_a.Q_flow = m_flow * (hEva - hCon); port_b.Q_flow = - (port_a.Q_flow + P); -port_b.Q_flow = P * COP; else // Heat pump is turned off k = 1.0; pSuc = pEva; pDis = pCon; mLea_flow = 0.0; m_flow = 0.0; PThe = 0.0; P = 0.0; TSuc = port_a.T; port_a.Q_flow = 0.0; port_b.Q_flow = 0.0; COP = 1.0; end if; end ScrollCompressor;