Heat Pump System Modeling GT Conference 2012
matthiase_the_dread/photocase.de
Oleg Kaplan, Frankfurt am Main, Oktober 2012
Maximaler Raum für Titelbild (wenn kleiner dann linksbündig an Rand angesetzt)
Power [kW] / Waste heat flow [kW]
Motivation
Required waste heat fow
Insufficient waste heat flow to accomplish the customer’s demand for comfort especially for HEVs and BEVs Temperature level of coolant too low to fulfill the customer’s demand for comfort High demand for additional heat sources especially for BEVs
ICE Internal Combustion Engine HEV Hybrid Electric Vehicle BEV Battery Electric Vehicle
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Impact of Conventional Auxiliary Heaters • Electric heaters significantly decrease the pure electric driving range
Power [kW]
• Strong conflict between acceptable driving range and high comfort level • Fuel heaters do not fulfill zero emission requirement. • Refueling an additional fuel decreases the driver’s comfort New system approaches must be investigated to fulfill the customer’s demand
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Motivation for Heat Pump Investigation • Use of the environment as a heat source at low temperature levels
saturated vapor saturated liquid
• Use of further waste heat producers like EM, PE, as a heat source
Pressure [bar]
Spec. heater power
The use of a heat pump makes a COP of 3 or higher possible .
Heat pump system is superior to conventional electric heaters.
Q
Spec. compressor power
.
Q Pfluid Enthalpy [kJ/kg]
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EM Electric Motor PE Power Electronic COP Coefficient Of Performance
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Concept for a New Heat Pump Design
PE
EM
BPHE1
BPHE2
P2
P1 DC
TH
EXV2
Radiator
EXV1
Power electronics
CU
Charging unit
D/C
DC/DC-converter
EM
Electric motor
HC
CV1 CV2
HC HVH
CU
PE
HVC
Heater core High voltage heater Electrically driven pump
Electric expansion valve
Receiver Check valve
SOV4
Electrically driven refrigerant compressor
SOV3 Brazed plate heat exchanger
SOV1 EDRC
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SOV2
Shut-off valve Thermostat
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Concept for a New Heat Pump Design Heating Mode PE
EM
BPHE1
BPHE2
P2
P1 DC
TH
EXV2
Radiator
EXV1
Power electronics
CU
Charging unit
D/C
DC/DC-converter
EM
Electric motor
HC
CV1 CV2
HC HVH
CU
PE
HVC
Heater core High voltage heater Electrically driven pump
Electric expansion valve
Receiver Check valve
SOV4
Electrically driven refrigerant compressor
SOV3 Brazed plate heat exchanger
SOV1 EDRC
SOV2
Shut-off valve Thermostat
High temperature coolant loop Low temperature coolant loop closed
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Refrigerant loop
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From Concept to Model Core components of the heat pump system to be modeled • Refrigerant compressor mechanically driven with and without displacement or electrically driven • Brazed plate heat exchanger. One used as an evaporator and one as a condenser • Expansion valve thermostatic and electrically driven
Further components • Water pumps • Heat exchangers such as Radiator and Heater core • Auxiliary heaters Boundary conditions • Airflow through the heater core heat • Ambient temperature • Driving cycle waste heat from power train
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Refrigerant Compressor Input from Test Bench Input variables
Output variables
• Compressor charge volume
• Refrigerant mass flow
• Compressor speed
• Refrigerant discharge temperature
• Displacement of swash plate (if available) • Inlet pressure • Inlet superheat • Desired pressure ratio Compressor
Compressor map with isentropic efficiency and a friction map with mechanical efficiency Easy implementation if reliable and accurate test results are available © IAV · 10/2012 · oka · VI-E22
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Refrigerant Compressor Simulation vs. Test n [RPM] pi = 2.6 test pi = 4.3 test
pi = 4.3 simulation pi = 7.8 simulation
Compressor power [kW]
pi = 7.8 test
pi = 2.6 simulation
pi [-]
Tin [°C] pin [bar]
.
Tout [°C] m [kg/h] P [kW]
• Mean deviation in power calculation: 0.1 kW • Mean deviation in discharge temperature calculation: 2 K
• Mean deviation in mass flow calculation: 6 kg/h Accurate results at all relevant operation points Compressor speed [rpm]
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Accurate results for the modeled refrigerant compressors 9
BPHE as a Condenser Input from Test Bench Input variables water
Input variables refrigerant
• Inlet temperature
• Inlet temperature
• Inlet pressure
• Inlet pressure
• Inlet volume flow
• Mass flow
Output variables water
Output variables refrigerant
• Outlet temperature
• Outlet temperature
• Outlet pressure
• Outlet pressure
• Heat flow BPHE
• Heat flow
Additional information • Detailed geometry data © IAV · 10/2012 · oka · VI-E22
BPHE Brazed Plate Heat Exchanger
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Modeling a BPHE as a Condenser Nusselt – Reynolds map for the water side Refrigerant single – phase flow calculation by Dittus – Boelter correlation for cooling
Refrigerant two – phase flow calculation by Shah correlation
h: Heat transfer coefficient
k: Thermal conductivity
x: Refrigerant quality
Re: Reynolds number
D: Characteristic length
NuL: Liquid phase Nusselt number
Pr: Prandtl number
Pre: Reduced pressure
ReL: Liquid phase Reynolds number
P: Actual pressure
PrL: Liquid phase Prandtl number
Pcr: Critical pressure
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BPHE as a Condenser Simulation vs. Test 100
Simulation [%]
Heat flow condenser + 10 %
80
60
- 10 %
40
20 20
30
40
50
60 Test [%]
70
80
90
100
• Mean deviation in power calculation: 0.1 kW Accurate results at all performance map points © IAV · 10/2012 · oka · VI-E22
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BPHE as an Evaporator Input from Test Bench Input variables water
Input variables refrigerant
• Inlet temperature
• Inlet temperature
• Inlet pressure
• Inlet pressure
• Inlet volume flow
• Superheat at outlet
Output variables water
Output variables refrigerant
• Outlet temperature
• Outlet temperature
• Outlet pressure
• Outlet pressure
• Heat flow BPHE
• Mass flow • Heat flow
Additional information • Detailed geometry data © IAV · 10/2012 · oka · VI-E22
BPHE Brazed Plate Heat Exchanger
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Modeling a BPHE as a Evaporator Nusselt – Reynolds map for the water side Refrigerant single – phase flow calculation by Dittus – Boelter correlation for heating
Refrigerant two – phase flow calculation by Klimenko correlation
h: Heat transfer coefficient
k: Thermal conductivity
kl: Liquid thermal conductivity
Re: Reynolds number
D: Characteristic length
kw: Wall material thermal conductivity
Pr: Prandtl number
ρL: Liquid density
PrL: Liquid phase Prandtl number
ρV: Vapor density
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BPHE as an Evaporator Simulation vs. Test 100 Heat flow evaporator Simulation [%]
80
+ 10 %
60 - 10 %
40 20 0 0
20
40
60
80
100
Test [%] • Mean deviation in power calculation: 0.1 kW Accurate results at all performance map points © IAV · 10/2012 · oka · VI-E22
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Heat Pump System in GT – Suite
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Determination of Refrigerant Charge Boundary conditions
20 Test
• Ambient temperature: 40 °C
Simulation
• Ambient humidity: 40 %
Conventional system
• Air flow heater core: 480 kg/h
Subcooling [K]
15
• Air flow radiator: 1600 kg/h
• Compressor speed: 4000 U/min • EXV target SH: 5 K
10
No subcooling track in the system 5
No subcooling plateau The optimal refrigerant charge is at the kink at 700 g
0 500 550 600 650 700 750 800 850 Refrigerant charge [g]
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SC Subcooling SH Superheat
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Validation of the Heat Pump Model Compressor Power Boundary conditions
2.2
Power [kW]
2.0
With 0.7 kW waste heat flow
• Air flow heater core: 300 kg/h
1.8
• Air flow radiator: 1600 kg/h
1.6
• EXV target SH: 5 K
1.4 1.2 1.0
Without waste heat flow
0.8
• Mean deviation in power calculation: < 0.2 kW Accurate results at all test points
0.6 0.4
Test
Simulation
0.2
Test
Simulation
0.0 @ -10 °C 2000 U/min
@ 0°C @ 5°C 5000 U/min 5000 U/min Operating point
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Heat flow [kW]
Validation of the Heat Pump Model Heater Core Heat Flow 3.6 3.4 3.2 3.0 2.8 2.6 2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8
Boundary conditions With 0.7 kW waste heat flow
• Air flow heater core: 300 kg/h • Air flow radiator: 1600 kg/h • EXV target SH: 5 K
Without waste heat flow
@ -10 °C 2000 U/min
Test
Simulation
Test
Simulation
• Maximum deviation in heat flow calculation: < 0.4 kW • Mean deviation in heat flow calculation: < 0.3 kW Accurate results at all test points
@ 0°C @ 5°C 5000 U/min 5000 U/min Operating point
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Validation of the Heat Pump Model Radiator Heat Flow 2.2
Heat flow [kW]
2.0
Boundary conditions Without waste heat flow
• Air flow heater core: 300 kg/h
1.8
• Air flow radiator: 1600 kg/h
1.6
• EXV target SH: 5 K
1.4 1.2 1.0
With 0.7 kW waste heat flow
0.8 0.6 0.4
Test
Simulation
0.2
Test
Simulation
0.0 @ -10 °C 2000 U/min
• Maximum deviation in heat flow calculation: < 0.4 kW • Mean deviation in heat flow calculation: < 0.3 kW Accurate results at all test points
@ 0°C @ 5°C 5000 U/min 5000 U/min Operating point
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Conclusion Presented concept • Promising system approach • New components were introduced
Heat pump modeling and simulation: • Modeling of components and of system was achieved • Accurate results both on component and system level • Advantages compared to conventional heater were shown by test data and simulation
Outlook • Further know-how development and investigation on transient behavior • Comparison to air / refrigerant heat pumps
• Cabin modeling and integration into thermal vehicle simulation © IAV · 10/2012 · oka · VI-E22
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Thank you Oleg Kaplan IAV GmbH Domagkstr. 11b, 80807 München Telefon +49 89 23542 6631
[email protected] www.iav.com
