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IP TRONIKEICHSTÄTT GMBH

Project Scope:

“Simulation of car refrigerant circuit with the software GT–SUITEand its comparison with real test bench measurements“

Christian Schwegler 17. October 2016

October 2016 © IPETRONIK Eichstätt GmbH

Table of Contents

1. Project Description

2. Life Cycle Climate Performance-Evaluation

‣ Presentation of assessment criteria

‣ Test Matrix - Society of Automotive Engineers

3. Structure of the Simulation Model

‣ Compressor

‣ Condenser

‣ Heat Exchanger

‣ Thermostatic Expansion Valve

‣ Evaporator

‣ Final Model

4. Performance of Simulation

‣ Overall Result LCCP-Evaluation

‣ Deviation from Reality

5. Conclusion


Project Description

The basic idea:

• Bench tests and vehicle tests are very time-consuming and costly.

• Through the use of simulation software, results can be forecasted anddevelopment time can be reduced.

• The basic approach of the simulation is performed using aLCCP(Life Cycle Climate Performance)-Evaluation.

• The simulation of a refrigerant circuit has several steps.

• Using GT-SUITE v7.5, the individual components of the refrigerant circuit are first modeled and then the entire model is simulated.

• Finally, the results are compared with the real measurement data.

• Evaluation parameter is the COP (Coefficient of Performance).


• Simulation of the refrigerant circuit of the Audi A4, the current fifth generation

• Modeling of all components:Compressor, Condenser, Heat Exchanger, Thermostatic Expansion Valve, Evaporator

• Assembly of the complete model

• Comparison with real test bench measurements using a LCCP-Evaluation

Project Description


Life Cycle Climate Performance-Evaluation

LCCP

DirectEmissions

RefrigerantLeakage

AtmosphericDegredation by

Refrigerants

IndirectEmissions

EnergyConsumption

Material Manufacturing

RefrigerantManufacturing

Material andRefrigerantRecycling

• LCCP stands for Life Cycle Climate Performance.

• The fundamental target is to evaluate a refrigeration system’s equivalent mass of carbon dioxide released into the atmosphere from its manufacturing over its operation until its recycling.

• Thereby, indirect und direct emissions are classified.


Life Cycle Climate Performance-Evaluation

Test matrix with 45 different measuring points

• Introduced by the Society of Automotive Engineers

• Representation of the range of operating conditions of an AC-system

• Each measuring point is defined by

- Compressor speed

- Air temperature at inlet (condenser and evaporator)

- Humidity at inlet (condenser and evaporator)

- Cooling capacity

Measuring point Condenser [Temp. / Humidity] Evaporator [Temp. / Humidity]

1 bis 5 45°C / 25% r.F. 45°C / 25% r.F.

6 bis 10 45°C / 25% r.F. 35°C / 25% r.F.

11 bis 15 35°C / 40% r.F. 35°C / 40% r.F.

16 bis 25 25°C / 80% r.F. 25°C / 80% r.F.

26 bis 35 25°C / 50% r.F. 25°C / 50% r.F.

36 bis 45 15°C / 80% r.F. 15°C / 80% r.F.


Structure of the Simulation Model

Compressor Model

• Externally regulated compressor from Denso

• Stroke control is based on mass flow

• The pipe´s current mass flow is sent to the controller of the compressor via Wi-Fi.

• The system is controlled by a PID controller.

• To operate a speed setting is necessary.



Compressor Model Parameterization

Data for diferent displacement setpoints (10%-100%) can be entered in each Rack Position



Condenser Model

• Condenser from Denso

• Flow Splits to create volumes which connect pipes with condenser

• Calibration of the pressure drop in the condenser with the help of a discharge coefficient



Condenser Geometry

Global Data

• Height

• Width

• Depth

• Tubes

• Passes

• Weight

Tube data



Condenser Parameterization

• Parameterization data should map the widest possible operating range of the condenser, from two-phase currently only be realized with power ,until subcooled outlet states.

0.5

1

1.5

2

2.5

0 50 100 150 200

Pre

ssure

Dro

p [b

ar]

Mass Flow Rate [kg/s]

Peer Pressure loss for different mass flow• An evaluation criterion is the refrigerant´s

pressure drop.

- The pressure drop is not constant, but depending on the mass flow.

- Automatic calibration of the pressuredrop caused significant deviations.

- A manual calibration with a multiplier was necessary.



Internal Heat Exchanger Model

• The heat exchanger´s main task is the heat transfer from the slave to the master side.

• Master = Low pressure side

• Slave = High pressure side

• On the slave side, the refrigerant flows from the condenser into the heat exchanger where it is cooled by the colder incoming flow from the evaporator (Master).

• On the master side, the refrigerant flows from the evaporator to the compressor.

Heat Exchanger Parameterization

Due to two-phase operation points in the heat exchangerpredictive correlations were used for calibration.



TXV Model

In the A4(B9) refrigerant circuit the standard expansion valve has a 1.5ton capacity andand a 1.05 slope.

TXV Parameterization

The pressure and temperature at the evaporator outlet is required.

The TXV´s specific 4-quadrant-

diagram is also required. It describes the correlations of pressure, temperature, stroke and mass flow.



Evaporator Model

• Evaporator from Mahle

• Air is cooled and as the case my be dehumidified while flowing through the evaporator.Condensate is considered in the simulation.

• The two flow splits are used for uniform air distribution up and downstream.



Evaporator Model

• Similarity to the condenser model

• The component is divided in two cores with three areas each (12, 9 and 12 tubes).

• The refrigerant´s flow pattern is of particular importance and must be specified.

Evaporator Parameterization

• Similarity to the condenser model

• Widest possible data range

• Bench data were used



Final Model

• Compressor

• Condenser

• Heat Exchanger

• Thermostatic Expansion Valve

• Evaporator

After completion of modeling and simulation, all system components will be analyzed with GT-POST and the results can be plotted.


Performance of Simulation

Overall result LCCP

• Target is the COP value.

• Its values can be compared with the real measurement values deviations analyzed.



Deviation from Reality



Deviation from Reality

• Sorting of cases by the refrigeration capacity

• With increasing refrigeration capacity at the evaporator,the relative deviation of the simulated COP values decrease exponentially



Analysis of case 45 (relative deviation 45,3%)

• In the real measurement the states at condenser outlet, through the heat exchanger and TXV inlet is two-phase wet steam.

• Different pressure ratio between measurement and simulation.

• Simulated refrigeration capacity is higher than the measurement.

Messung Simulation40bar

20bar

30bar

1bar

10bar

?

Position of thecondenser outletunknown (onlyTemperaturemeasured)



Analysis of case 5 (relative deviation 10,8%)

• Deviating heat transmission resistances of the components may be on reason the system´s COP deviation.

• Better pressure accordance in this case.

Messung Simulation40bar

20bar

30bar

1bar

10bar


Conclusion

General Variance of Deviation

• The relative deviation increases with decreasing refrigeration capacity.

• Different heat transmission resistances of the condenser, evaporator andrefrigerant pipes

• In the simulation the condenser outlet state is always subcooled.

• In the simulation the evaporator outlet state is always superheated.

• Different states at compressor inlet at low load

• Characteristic diagram of the compressor has a single entry state.Its pressure is 3,0bar and its superheat is 10K.

• The simulation quality depends on the input data of the single components.They are essential for a successful simulation and thus the quality of the results.

Note also therefrigerantcharge ofthe system


Conclusion

Own experiences

• Working with GT-SUITE is very easy and comfortable.

• GT-SUITE´s user interface has a clear layout.

• GT-SUITE offers a wide range of options.

• Complex refrigerant circuits can be modeled within short time.

• Difficulty of finding appropriate validation sizes for the individual components

• Dependency of availability of suitable parameterization data

IP TRONIKEICHSTÄTT GMBH

Industriestrasse 10 ◦ 85072 Eichstätt ◦ Tel. +49 8421 9374-0 ◦ www.ipetronik.com

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