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)
Information
Model for a reciprocating processor, as detailed in Jin (2002). The rate of heat transfered to the evaporator is given by:
Q̇Eva = ṁref ( hVap(TEva) - hLiq(TCon) ).
The power consumed by the compressor is given by a linear efficiency relation:
P = PTheoretical / η + PLoss,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 transfered 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 | Clearance factor [1] | |
| Efficiency | etaEle | Electro-mechanical efficiency of the compressor [1] | |
| Power | PLos | Constant part of the compressor power losses [W] | |
| AbsolutePressure | pDro | Pressure drop at suction and discharge of the compressor [Pa] | |
| TemperatureDifference | 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] |
| Boolean | isOn.start | false | State of the compressor, true if turned on |
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.AbsolutePressure pDis(start = 1000e3)
"Discharge pressure of the compressor";
Modelica.SIunits.AbsolutePressure pSuc(start = 100e3)
"Suction pressure of the compressor";
Modelica.SIunits.SpecificVolume vSuc(start = 1e-4, min = 0)
"Specific volume of the refrigerant at suction of the compressor";
Modelica.SIunits.Power PThe
"Theoretical power consumed by the compressor";
Modelica.SIunits.Temperature TSuc
"Temperature at suction of the compressor";
Modelica.SIunits.Efficiency COP
"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";
Real PR(min = 1.0, final unit = "1", start = 2.0)
"Pressure ratio";
Boolean shut_off(fixed=true, start=false)
"Shutdown signal for invalid pressure ratios";
equation
PR = max(pDis/pSuc, 0);
// The compressor is turned off if the resulting condensing pressure is lower
// than the evaporating pressure
when PR <= 1.0 then
shut_off = true;
elsewhen PR > 1.01 then
shut_off = false;
end when;
// The specific volume at suction of the compressor is calculated
// from the Martin-Hou equation of state
vSuc = ref.specificVolumeVap_pT(pSuc, TSuc);
// 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 = if shut_off then 0 else
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 = if shut_off then 0 else 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)
Information
Model for a scroll processor, as detailed in Jin (2002). The rate of heat transfered to the evaporator is given by:
Q̇Eva = ṁref ( hVap(TEva) - hLiq(TCon) ).
The power consumed by the compressor is given by a linear efficiency relation:
P = PTheoretical / η + PLoss,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 transfered 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 | Built-in volume ratio [1] | |
| VolumeFlowRate | V_flow_nominal | Refrigerant volume flow rate at suction at full load conditions [m3/s] | |
| MassFlowRate | leaCoe | Leakage mass flow rate at a pressure ratio of 1 [kg/s] | |
| Efficiency | etaEle | Electro-mechanical efficiency of the compressor [1] | |
| Power | PLos | Constant part of the compressor power losses [W] | |
| TemperatureDifference | 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] |
| Boolean | isOn.start | false | State of the compressor, true if turned on |
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.AbsolutePressure pDis(start = 1000e3)
"Discharge pressure of the compressor";
Modelica.SIunits.AbsolutePressure pSuc(start = 100e3)
"Suction pressure of the compressor";
Modelica.SIunits.SpecificVolume vSuc(start = 1e-4, min = 0)
"Specific volume of the refrigerant at suction of the compressor";
Modelica.SIunits.Power PThe
"Theoretical power consumed by the compressor";
Modelica.SIunits.Temperature TSuc
"Temperature at suction of the compressor";
Modelica.SIunits.Efficiency COP
"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 PR(min = 0.0, unit = "1", start = 2.0)
"Pressure ratio";
Real PRInt(start = 2.0)
"Built-in pressure ratio";
Boolean shut_off(fixed=true, start=false)
"Shutdown signal for invalid pressure ratios";
equation
PR = max(pDis/pSuc, 0);
PRInt = volRat^k;
// The compressor is turned off if the resulting condensing pressure is lower
// than the evaporating pressure
when PR <= 1.0 then
shut_off = true;
elsewhen PR > 1.01 then
shut_off = false;
end when;
// The specific volume at suction of the compressor is calculated
// from the Martin-Hou equation of state
vSuc = ref.specificVolumeVap_pT(pSuc, TSuc);
// 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 = if shut_off then 0 else 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 = if shut_off then 0 else (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;