Heat Pump System Modeling

Heat Pump System Modeling GT Conference 2012 matthiase_the_dread/photocase.de Oleg Kaplan, Frankfurt am Main, Oktober 2012 Maximaler Raum für Titel...
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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

© IAV · 10/2012 · oka · VI-E22

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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

© IAV · 10/2012 · oka · VI-E22

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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]

© IAV · 10/2012 · oka · VI-E22

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

© IAV · 10/2012 · oka · VI-E22

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

© IAV · 10/2012 · oka · VI-E22

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

© IAV · 10/2012 · oka · VI-E22

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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]

© IAV · 10/2012 · oka · VI-E22

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

© IAV · 10/2012 · oka · VI-E22

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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

© IAV · 10/2012 · oka · VI-E22

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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

© IAV · 10/2012 · oka · VI-E22

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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]

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• 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]

© IAV · 10/2012 · oka · VI-E22

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

© IAV · 10/2012 · oka · VI-E22

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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

© IAV · 10/2012 · oka · VI-E22

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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

© IAV · 10/2012 · oka · VI-E22

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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