54
Master of Science Thesis KTH School of Industrial Engineering and Management Energy Technology EGI- 2018-619 Division of Applied Thermodynamics and Refrigeration SE-100 44 STOCKHOLM Air Conditioning System Modeling for Car Fuel Economy Simulation Arturo Alejandro Torres Arevalo Changhao Han

Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

  • Upload
    others

  • View
    2

  • Download
    0

Embed Size (px)

Citation preview

Page 1: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Master of Science Thesis

KTH School of Industrial Engineering and Management

Energy Technology EGI- 2018-619

Division of Applied Thermodynamics and Refrigeration

SE-100 44 STOCKHOLM

Air Conditioning System Modeling for

Car Fuel Economy Simulation

Arturo Alejandro Torres Arevalo

Changhao Han

Page 2: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Master of Science Thesis EGI 2018:619

Air Conditioning System Modeling for Car

Fuel Economy Simulation

Arturo Alejandro Torres Arevalo

Changhao Han

Approved

Examiner

Samer Sawalha

Supervisor

Samer Sawalha

Commissioner

Contact person

Page 3: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

iii

Abstract

The automotive air conditioning system is the greatest auxiliary loadof a vehicle, having a considerable impact on its fuel consumption andCO2 emissions. For this reason, forecasting the influence that this sys-tem has on the fuel economy of a car is desired. The present work isdedicated to model the air conditioning system of a plug-in hybrid ve-hicle in order to predict its energy consumption.

GT-SUITE was chosen as the simulation tool, where the air condi-tioner, which is a vapor-compression refrigeration system, was mod-eled by specifying its components: compressor, evaporator, thermalexpansion valve and condenser. Moreover, additional sub-systemswhich influence the energy consumption were also considered, theseare the vehicle’s cabin and the battery cooling loop.

The simulated model shows good agreement with test data for impor-tant parameters such as the compressor power consumption and theair temperature after the evaporator. The percent difference betweenthe test data and the simulation for the auxiliary power consumption(energy consumed by the A/C compressor and the charging load ofthe low voltage battery) is 6.25%.

Page 4: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

iv

Sammanfattning

På ett fordon utgör luftkonditioneringssystem den främsta extraordi-nära energibelastningen, vilket har stor påverkan på bränsleförbruk-ning och koldioxidutsläpp. Av detta skäl är det önskvärt att förutse detinflytande som detta system har på fordonets bränsleekonomi. Dettaarbete är har för avsikt att simulera luftkonditioneringssystemet för ettplug-in hybridfordon för att förutsäga energiförbrukningen.

GT-SUITE valdes som simuleringsverktyg, där klimatanläggningen,som är ett ångkomprimerat kylsystem, modellerades genom att speci-ficera komponenterna: kompressor, förångare, värmeutvidgningsven-til och kondensor. Dessutom beaktades ytterligare delsystem som på-verkar energiåtgången, nämligen fordonets hytt och batterikylnings-loop.

Den simulerade modellen visar en god korrelation med testdata för be-tydelsefulla parametrar såsom kompressorns energiförbrukning ochlufttemperaturen efter förångarsteget. Den procentuella skillnaden mel-lan testdata och simuleringen för den extra energiförbrukningen (ener-gi som förbrukas av A/C-kompressorn och laddningen av lågspän-ningsbatteriet) är 6,25%.

Page 5: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

v

Acknowledgements

We would like to express our gratitude to our KTH professor and su-pervisor Samer Sawalha, who gave us the technical background thatmade possible for us to obtain this thesis.

Furthermore, we express our gratitude to our CEVT supervisors: LeiXu and Anna Rimark, who provided us with the necessary guidanceand tools that helped us accomplish this work. Additionally, we wouldlike to thank our manager at CEVT: Sofia Ore, whose optimism andsympathy helped us communicate with our colleagues and create apositive work environment.

Finally, Arturo would like to thank the Mexican National Council forScience and Technology (CONACYT) together with the Mexican En-ergy Ministry (SENER) for providing the financial resources neededto obtain his master’s degree through the scholarship: "CONACYT-SECRETARIA DE ENERGIA- SUSTENTABILIDAD ENERGETICA ref.:601279 / 439254”

Page 6: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

vi

Abbreviations and Acronyms

AAC Automotive Air Conditioning

A/C Air Conditioning

EPA Environmental Protection Agency (United States)

EV Electric Vehicle

GHG Greenhouse Gas

HEV Hybrid Electric Vehicle

HVAC Heating, Ventilation, and Air Conditioning

IEA International Energy Agency

PHEV Plug-in Hybrid Electric Vehicle

PID Proportional-Integral-Derivative

UDDS Urban Dynamometer Driving Schedule

Page 7: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Contents

1 Introduction 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.3 Methodology . . . . . . . . . . . . . . . . . . . . . . . . . 21.4 Limitations . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Literature Review 42.1 Automotive HVAC models . . . . . . . . . . . . . . . . . 42.2 A/C Compressor Control . . . . . . . . . . . . . . . . . . 62.3 Driving Cycles . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3.1 SC03 Driving Cycle . . . . . . . . . . . . . . . . . . 7

3 Current A/C system 93.1 Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . 103.2 Condenser, Battery Radiator, and Evaporator . . . . . . . 113.3 Chiller and Battery Cooling Circuit . . . . . . . . . . . . . 113.4 A/C Blower and Condenser Fan . . . . . . . . . . . . . . 123.5 High and Low Voltage Battery . . . . . . . . . . . . . . . . 123.6 Thermal Expansion Valve . . . . . . . . . . . . . . . . . . 12

4 System Modeling 144.1 Solver . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144.2 Compressor . . . . . . . . . . . . . . . . . . . . . . . . . . 154.3 Heat Exchangers . . . . . . . . . . . . . . . . . . . . . . . 174.4 Cabin and Air Loop . . . . . . . . . . . . . . . . . . . . . . 194.5 HV Battery . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

4.5.1 Battery Cooling Circuit . . . . . . . . . . . . . . . 214.5.2 Battery Current Coupling . . . . . . . . . . . . . . 22

4.6 Fans and pumps . . . . . . . . . . . . . . . . . . . . . . . . 234.7 Thermal Expansion Valves . . . . . . . . . . . . . . . . . . 24

vii

Page 8: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

viii CONTENTS

4.8 Pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

5 Validation 265.1 Battery Model Validation . . . . . . . . . . . . . . . . . . . 265.2 A/C System Validation . . . . . . . . . . . . . . . . . . . . 29

5.2.1 Air Temperature after the Evaporator . . . . . . . 295.2.2 Compressor Speed . . . . . . . . . . . . . . . . . . 325.2.3 Compressor Power Consumption . . . . . . . . . 325.2.4 Cabin Temperature . . . . . . . . . . . . . . . . . . 35

6 Results 366.1 SC03 Test Conditions . . . . . . . . . . . . . . . . . . . . . 366.2 Simulation Results . . . . . . . . . . . . . . . . . . . . . . 37

7 Conclusions 39

Bibliography 41

Page 9: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

List of Figures

2.1 SC03 Driving Cycle [28] . . . . . . . . . . . . . . . . . . . 8

3.1 A/C system with battery cooling loop . . . . . . . . . . . 103.2 Simplified compressor control strategy . . . . . . . . . . . 11

4.1 Compressor map (example) [30] . . . . . . . . . . . . . . . 164.2 Modeled compressor in GT-SUITE . . . . . . . . . . . . . 174.3 Discretization of both “master” and “slave” objects for

both crossflow (right) and counterflow (left) heat exchang-ers [31] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4.4 Sources of heat from the ambient, and heat transferredfrom the mass to the cabin . . . . . . . . . . . . . . . . . . 19

4.5 Cabin Air Loop . . . . . . . . . . . . . . . . . . . . . . . . 204.6 Thermal and electrical parts of the HV battery (exam-

ple) [32] . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 214.7 Battery Cooling Circuit . . . . . . . . . . . . . . . . . . . . 224.8 High Voltage Battery in GT-SUITE . . . . . . . . . . . . . 234.9 Low Voltage Battery in GT-SUITE . . . . . . . . . . . . . . 234.10 ‘TXVDetail4Quadrant’ template[34] . . . . . . . . . . . . 25

5.1 Actual and Simulated Battery Temperature . . . . . . . . 275.2 Different Natural Convection Heat Transfer Coefficients

for Battery Cooling . . . . . . . . . . . . . . . . . . . . . . 285.3 Battery Temperature Validation . . . . . . . . . . . . . . . 295.4 P-h Diagram at 1162.3s (Before Modification) . . . . . . . 305.5 P-h Diagram at 1159.5s (After Modification) . . . . . . . . 315.6 Air Temperature After the Evaporator Validation . . . . . 315.7 Compressor Speed Validation . . . . . . . . . . . . . . . . 325.8 Compressor Power Validation . . . . . . . . . . . . . . . . 335.9 Refrigerant Mass Flow Rate through the evaporator . . . 34

ix

Page 10: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

x LIST OF FIGURES

5.10 Cabin Temperature Validation . . . . . . . . . . . . . . . . 35

6.1 Laboratory Ambient Air Temperature for the Cold-Startand Warm-Start Cases . . . . . . . . . . . . . . . . . . . . 37

6.2 Auxiliary Power Consumption Comparison . . . . . . . . 38

Page 11: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Chapter 1

Introduction

1.1 Background

Between 1971 and 2015 the world’s energy consumption more thandoubled. In this time the transport sector share in the total final energyconsumption increased from 23% to 29% [1]. This sector, which ac-counts for 23% of the current global GHG emissions related to energy,will need to deliver considerable emission reductions if the countrieswish to meet their GHG goal [2]. To provide a solution for this prob-lem, a roadmap was outlined by the European Commission to reduce50% of the GHG emissions of the transport sector by 2050 with respectto 1990 [3].

To solve current problems regarding emissions and energy security,electrification of transport becomes an important pathway [4]. In re-cent years, various countries have launched initiatives to promote thedevelopment and deployment of electric and hybrid vehicles. [5][6][7][8]EVs and PHEVs have gained popularity in the world’s automotivemarket. The Global EV Outlook shows that the global electric car stock(EVs, PHEVS, HEVs and fuel cell vehicles) surpassed 2 million vehi-cles in 2016 after crossing the 1 million threshold in 2015. Additionally,the period from 2010 to 2016 was the fastest growing time in historyfor the stock of PHEVs and EVs [2].

One of the prevailing issues regarding fuel economy in vehicles arethe current A/C systems. It has been said that the A/C is the great-est auxiliary load of a vehicle’s engine [9]. In 2004, the total vehicle

1

Page 12: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

2 CHAPTER 1. INTRODUCTION

fleet’s A/C systems consumed at least 7.0 billion gallons of fuel in theUnited States, which was equivalent to 9.5% of the imported oil of thiscountry [10]. Depending on the the size of the system and the drivingcycle, the A/C loads can reduce the driving range and fuel economy ofEVs and HEVs nearly 40%. For these reasons, the Supplemental Fed-eral Test Procedure (U.S.), which is an emissions procedure, providesmotivation for reducing the size of automotive A/C systems [11].

1.2 Objectives

China Euro Vehicle Technology AB (CEVT), is an automotive develop-ment center who wants to introduce new vehicles to the U.S. market inthe near future. Currently, CEVT’s Energy CAE department is lookingto develop a model to predict how the A/C system of a PHEV affectsthe fuel economy when the car is performing the U.S. driving cycles.

There are four tasks that need to be completed in this thesis:

• Adjust and improve an existing A/C model and make it validfor simulating the SC03 driving cycle

• Couple the A/C model with a vehicle driveline in GT-SUITE(software)

• Carry out the validation of the A/C system with test data fromthe climate department

• Carry out the simulation of the SC03 driving cycle, including val-idation with test data

1.3 Methodology

The A/C system was modeled with the help of GT-SUITE. This modelwas based on components previously developed by other membersof CEVT’S Energy CAE department. The compressor, which was notpreviously defined by the CAE department, was modeled using mapsthat correlate different physical parameters, which were provided byCEVT’s climate department and its suppliers. The connection of thecomponents and the airflow system was described with the help of

Page 13: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 1. INTRODUCTION 3

system diagrams provided by other departments within the company.Once the basic model was finished, it was coupled with other sub-models like the drivetrain and the battery-cooling circuit.

The complete model was validated with a “Cool-Down” test from theclimate department. This test was used because it provided the nec-essary measurements to validate the whole system like compressorpower consumption, cabin temperature and battery temperature. Af-ter simulating the driving cycle, the model’s results were comparedto the ones obtained in an SCO3 test performed in a target vehicle inaccordance to the descriptions provided by EPA [12][13].

1.4 Limitations

While performing this work, one strong limitation was the lack of datato compare the simulation results with the SC03 driving cycle test. Forthis reason, it is assumed that the initial temperature of several compo-nents did not match the actual temperature, which caused a deviationin the result of the final energy consumption.

One more limitation was that the developed model did not includesome of the controllers implemented in the actual car because the con-trol strategy is kept in secret by the manufacturers, these are: the cool-ing fan speed controller and the cabin blower controller. Another con-troller that was not added was the one that sends a requested air tem-perature after the evaporator to the system, this controller was notadded because it is calculated by the cooling manager, which is a com-plex control unit. Consequently, the energy consumed by these fansand the one consumed by the compressor due to a higher or lowerrequested air temperature varies with respect to test data.

Page 14: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Chapter 2

Literature Review

2.1 Automotive HVAC models

Complete vehicle test is a common approach used in the automotiveindustry. In 2010, Rugh [14] performed several complete vehicle teststo investigate the fuel consumption of automotive A/C systems. Heobserved that climate control had a significant influence on reducingthe A/C fuel consumption for PHEVs and EVs. One of his conclu-sions was that although the method of complete vehicle test leads toreasonable results, it is time and resource consuming, especially con-sidering the large amount of the cases that have to be evaluated duringthe research and development period. For this reason, more industrialengineers and researchers support CAE simulation in recent years.

As previously mentioned, GT-SUITE software (developed by GammaTechnologies) is employed to create the vehicle model in this thesis.Nielsen [15] developed a 1D model to obtain the energy used by anAAC system in GT-SUITE, which included an air-handling unit (AHU),A/C system, engine cooling system and cabin. This model was suc-cessfully verified with several vehicle tests, and can be used to pre-dict the energy usage at different ambient and driving conditions. InNielsen’s Ph.D dissertation [15], an on-site experimental test of a VolvoS60 is conducted and its results well match with the predictions fromhis model. Moreover, several energy saving measures are proposedand investigated in his thesis, like utilizing the A/C just when needed.

There are several vehicle simulation tools available in the market apart

4

Page 15: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 2. LITERATURE REVIEW 5

from GT-SUITE that can be used to develop robust models for com-plete vehicle simulation such as CarSim, MATLAB/Simulink, and IPGCarMaker. For instance, in Kiss’ study [16], an AAC system was mod-eled in MATLAB/Simulink. In this approach, both the cabin and theA/C system were accounted in order to perform a transient evalua-tion of the system’s load on the engine. The SC03 driving cycle wassimulated and validated with test data, leading to and average errorfor the cooling load of less than 2%, and also having a good agreementwith the cabin air temperature in the test.

The cooling load of the cabin is one of the key parameters of an AACsystem. In Fayazbakhsh’s study [17], a comprehensive cabin model isdeveloped using the Heat Balance Method (HBM). Furthermore, Ka-mar et al. [18] created a semi-empirical model to evaluate the energyperformance of the A/C system and cabin, employing empirical evap-orator correlations and running dynamic load simulation, which ledto a good agreement with test data, having errors of about 3%. InBoettcher’s master thesis [19], a vehicle cabin model is simulated withTAITherm and GT-SUITE for a pull-down case. The co-simulation re-sult is evaluated and compared with the results from a previous modeldeveloped in STAR-CCM+ aiming to propose a new cabin-model method,however, due to the differences in the boundary conditions of the cabin’swalls, the TAITherm/GT-SUITE model could not be successfully cali-brated with the STAR-CCM+ model.

The cooling load of the battery has a crucial impact on A/C systemsfor EVs. When the battery temperature is high, a separate coolant loopneeds to work to provide additional cooling. In Valentina’s et al. re-search [20], a detailed EV-based HVAC system is modeled, where thebattery cooling system is also considered. The model dynamically re-sponds to external changes, which consequently predicts the HVACpower consumption with a higher accuracy. In Abdullah’s and Vatan-parvar’s paper [21], the HVAC system of an EV was modeled in AD-VISOR (software). It was able to match the thermodynamic behaviorof the actual system accurately. The paper concludes that the HVACsystem have a considerable impact on energy consumption, which cancause problems with the lifetime of the battery.

A frequent problem with HVAC models is the verification/validation

Page 16: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

6 CHAPTER 2. LITERATURE REVIEW

with test data because simulation results are rarely validated with morethan one case [22].

2.2 A/C Compressor Control

Using smart controls, the compressors can not only meet peak de-mand, but also run efficiently at part-load. A well-designed compres-sor control strategy can lead to a good reduction of energy consump-tion. For fluctuating cooling loads, more sophisticated control strate-gies are needed [23].

In AAC systems there exist two types of compressors: electrically-driven and mechanically-driven. The difference between these twotypes of compressors is illustrated in Dahlana et al.’s paper [24]; thespeed of the electric compressor is independent of the shaft speed ofthe engine, and the speed of the mechanical compressor is synchro-nized with the engine. The paper concludes that the performance ofthe electric compressor is better than the conventional mechanical onebecause there are more opportunities to improve the control strategyusing an the electric compressor.

Several strategies of compressor control have been proposed for auto-motive purposes, for instance, in Quansheng’s study [25], a continuous-time optimal control of a mechanical compressor is applied, showingenhanced energy performance by finding the optimal amount of com-pressor cycling. In recent studies, a common way to improve compres-sor control is to implement a PID control to modify the compressorspeed and increase the energy efficiency. In Chiang’s Boon Chiang’sstudy [26], a PID and an “Adaptive Neural Network Based Model Pre-dictive Controller” are applied to an AAC compressor, achieving 47%of energy savings when compared to a traditional cycling method. InNan’s research [27], a Fuzzy-PID control method is applied to an AACelectric compressor using MATLAB/Simulink. The designed controlmethod displays energy savings of around 6% when compared to thetraditional ON/OFF method.

Page 17: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 2. LITERATURE REVIEW 7

2.3 Driving Cycles

Vehicle manufacturers must pursue certificates of conformity issuedby EPA in order for them to be able to sell vehicles in the United Statesmarket, these certificates ensure compliance with GHG and fuel econ-omy standards [12].To evaluate the vehicles in these two aspects, theEPA has created five driving cycles which are a function of “vehiclespeed” vs “test time” [13]:

• UDDS: Used to represent a vehicle driving in the city

• Highway Fuel Economy Driving Cycle: Used to represent a ve-hicle driving in the highway

• US06 Driving Cycle: Used to represent a vehicle driving at highspeeds with heavy accelerations

• SC03 Driving Cycle: Used to represent a vehicle operation whenusing air conditioner

• “Cold” UDDS: Used to represent a vehicle driving in cold ambi-ent conditions

Since the emissions and fuel economy of the SC03 depend heavily onthe A/C system of the vehicle, this driving cycle will be further dis-cussed in section 2.3.1.

2.3.1 SC03 Driving Cycle

PHEVs are required to perform the SC03 driving cycle (Figure 2.1) in“charge sustaining” mode, where the vehicle’s fuel is consumed whilethe energy from the battery is sustained [12].

The purpose of the SC03 Driving Cycle is to test the energy usage andemissions of the vehicle on a warm day, when the A/C is heavily used.The following are some important characteristics of the test that arespecific to this driving cycle [13]:

• Ambient air: 35 ◦C

• Solar heat load intensity: full load (850 W/m2)

• Closed windows

Page 18: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

8 CHAPTER 2. LITERATURE REVIEW

• Air conditioner system controls [12]:

1. A/C mode at maximum settings

2. Recirculating airflow

3. Fan at highest setting

4. Temperature control set at 22 ◦C

Figure 2.1: SC03 Driving Cycle [28]

Page 19: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Chapter 3

Current A/C system

The actual A/C system in the investigated vehicle works under thevapor compression cycle, just like any conventional refrigeration sys-tem. It uses a thermal expansion valve, a compressor, an air-cooledcondenser and an evaporator as it is shown in Figure 3.1. The refriger-ant used during the previous years by the company is R134a, but forthe new tests, for example the SC03 driving cycle, the refrigerant ofchoice is the R1234yf. In the ventilation system, outside air is blownthrough the evaporator into the cabin in order to be cooled down, andair is recirculated back to the cabin using an HVAC door (or flap).

The chiller is the component that couples the battery cooling loop withthe refrigeration system; if the ambient temperature is high and thesystem cannot use ambient air to cool down the battery, the chillervalve opens and provides active cooling to the battery with the help ofthe refrigeration cycle. If the ambient temperature is more than 10 ◦C

below the battery temperature, the battery cooling loop uses an aircooled radiator and a pump to provide passive cooling to the battery.

9

Page 20: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

10 CHAPTER 3. CURRENT A/C SYSTEM

Figure 3.1: A/C system with battery cooling loop

3.1 Compressor

The actual system uses an electric reciprocating compressor with aFeedforward-Proportional Integral control strategy, which is summa-rized in Figure 3.2. With this strategy, the compressor controller de-termines the control error by comparing the current air temperatureafter the evaporator with the target air temperature after the evapora-tor. It then uses this error to obtain a Proportional Integral speed. Forthe Feedforward speed the controller uses the target air temperatureafter the evaporator. The two speeds are added and a final compressorspeed is requested to the system. The compressor further increases thespeed if battery cooling is needed.

Page 21: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 3. CURRENT A/C SYSTEM 11

Figure 3.2: Simplified compressor control strategy

3.2 Condenser, Battery Radiator, and Evap-orator

The condenser and the battery radiator are located at the front of thevehicle in order to be exposed to the convection of air imposed by thespeed of the vehicle. Both of them are fin-and-tube heat exchangers.The battery radiator is located in front of the condenser, which meansthat the air is heated up by the battery radiator before passing throughthe condenser. The evaporator, which is also an aluminum fin-and-tube heat exchanger, is exposed to a flow of air imposed by the A/Cblower.

3.3 Chiller and Battery Cooling Circuit

The chiller is a plate heat exchanger that transfers heat from the batterycooling fluid (mixture of 50% glysantin and 50% water) to the refrig-erant. A shutoff valve is positioned before the chiller in the refrigerantside and implements the active cooling by enabling the chiller whenthe battery temperature reaches 37 ◦C. When the ambient tempera-ture is low, a 3-way valve in the battery cooling loop let the coolingfluid flow through the battery radiator, however, if there is not enoughtemperature difference between the battery and the ambient air, thebattery radiator is disabled.

Page 22: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

12 CHAPTER 3. CURRENT A/C SYSTEM

3.4 A/C Blower and Condenser Fan

The A/C blower is a key component of the automotive air condition-ing system, it is used to circulate the air between the evaporator andcabin, and it is also used for the recirculation. The A/C blower canwork at various angular speeds dependending on the requirement.

The condenser fan is used to impose flow of outside air to severalheat exchangers: battery air radiator, electric drive radiator, A/C con-denser and engine cooling radiator successively. In this study, only thebattery air radiator and the A/C condenser are taken into considera-tion. The battery air radiator transfers the heat between the ram airand the coolant of the battery cooling circuit, and the A/C condenserexchanges heat between the ram air and the refrigerant in the A/C sys-tem. The cooling fan is driven by an electrovent with conveyor, and itcan work at different levels of power load depending on the vehicle’sspeed and battery temperature.

3.5 High and Low Voltage Battery

There are two types of battery used in this vehicle, one is 12V lowvoltage (LV) battery and the other is the high voltage (HV) battery.Regarding the A/C system, its auxiliary power load is added to theLV battery, including the cooling fan, the A/C blower and the batterycoolant pump. Three different power loads are added to the HV bat-tery, which are the electric motor of the propulsion system, the A/Ccompressor, and the charging load of the LV battery (when the State ofCharge (SOC) of the LV battery is below 90%, it starts to take currentfrom the HV battery).

3.6 Thermal Expansion Valve

The thermal expansion valve is an important component of a refrig-eration system because it helps to control the amount mass flow rateof refrigerant in the system. There are two thermal expansion valvesin the model, one is the valve of the front evaporator, and the other isthe valve of the chiller. Both of them are externally equalized, whichmeans the pressure at the outlet of the evaporator and chiller affects

Page 23: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 3. CURRENT A/C SYSTEM 13

the valve lift, which eventually changes the refrigerant mass flow rateof the system.

Page 24: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Chapter 4

System Modeling

The A/C system was modeled using GT-SUITEmp (version 2017), whichis GT-SUITE’s multi-physics platform dedicated to model Cooling Sys-tems and A/C. This chapter provides a description of how the systemcomponents were modeled in GT-SUITE and how this software solvesthe governing equations.

4.1 Solver

The solution provided by GT-SUITE [29] is given by an implicit flowsolver, which takes longer time steps than the available explicit flowsolver. However, the software recommends to use the first one forthermal management simulations, such as the A/C system, since theexplicit solver is only useful when wave dynamics are being simu-lated.

The Navier-Stokes equations (mass, continuity, momentum and en-ergy) are calculated in one dimension by an iterative method whenusing the implicit flow solver. The whole system is discretized us-ing the staggered grid method. With this method, the flow is dis-cretized in many volumes, each one connected by boundaries, hav-ing the scalar quantities uniform across the volume and the vectorquantities calculated at the boundary. To ensure that numerical con-vergence is reached, the solver calculates residual quantities for eachiteration. These residuals are computed for pressure, continuity, en-ergy and mass flow. A time step of 0.1 seconds and a number of 400iterations provide convergence for the majority of the time steps and

14

Page 25: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 4. SYSTEM MODELING 15

for this reason they are used for the simulations presented in this work.

4.2 Compressor

The compressor’s performance is described using a compressor mapwhich is a table provided by the manufacturer that describes the be-havior of the compressor at different operating conditions. The pa-rameters used to describe the compressor were:

• Compressor speed

• Mass Flow rate

• Suction pressure

• Suction temperature

• Discharge pressure

• Discharge temperature

• Total shaft power input (electric)

After specifying several points, the software interpolates the data toobtain the rest of the points that were not provided. In Figure 4.1,an example shows how the pressure ratio and mass flow for the non-specified compressor speeds are obtained by interpolation, applyingalso extrapolation to find the lower speeds.

Page 26: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

16 CHAPTER 4. SYSTEM MODELING

Figure 4.1: Compressor map (example) [30]

The compressor control strategy is implemented in Simulink and isexported to GT-SUITE as a black-box FMU (Functional MockUp Unit),which is a file that contains the code in C programming language thatdescribes all the equations and parameters used in the controller. Thecontents of the controller cannot be seen in GT-SUITE because it is ablack box, therefore, only the inputs and the outputs of the controllercan be visualized and specified in the FMU.

Figure 4.2 shows the imported compressor control (FMU) which sendsa requested speed to the compressor as it’s only output. Additionally,the displayed shaft was implemented to account for the compressor’smechanical efficiency.

Page 27: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 4. SYSTEM MODELING 17

Figure 4.2: Modeled compressor in GT-SUITE

4.3 Heat Exchangers

The heat exchangers in GT-SUITE are defined using two objects called“master” and “slave” heat exchangers. These objects are used to modelthe heat transfer between the fluid on one side of the heat exchangerand the wall of the heat exchanger. The general convention is that theside of the heat exchanger where the fluid is being cooled is the “mas-ter”, and the side where the cooling fluid is flowing is the “slave”.

GT-SUITE discretizes both “master” and “slave” objects as it shownin Figure 4.3 to provide a more precise wall temperature distribution .For this model, a discretization of 3 subvolumes per pass was applied.

Page 28: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

18 CHAPTER 4. SYSTEM MODELING

Figure 4.3: Discretization of both “master” and “slave” objects for bothcrossflow (right) and counterflow (left) heat exchangers [31]

The temperature of the wall is calculated with a balance of heat trans-fer rates between the wall and the two fluids using the following equa-tion [31]:

dTwall

dt=Qm +Qs

ρV Cp

=(hA∆T − 2kA∆Tw

t)m + (hA∆T − 2kA∆Tw

t)s

ρV Cp

h Heat transfer coefficientA Heat transfer area∆T Temperature difference between the fluid and the wallk Thermal conductivity∆ Tw Temperature difference between the surface and wall (average)t Tube thicknessρ Density of the wall materialV Volume of the wall materialCp Heat capacity of the wall material

The heat transfer coefficients are calculated with the Nusslet number[31]:

Nu = CRemPr1/3

Nu = (hL

k) Re = (

ρUL

µ) Pr = (

µCp

k)

L Reference lengthh Convective heat transfer coefficient

Page 29: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 4. SYSTEM MODELING 19

U Fluid velocityk Thermal conductivity of the fluidρ Fluid densityCp Heat capacity of the fluidµ Dynamic viscosity of the fluid

4.4 Cabin and Air Loop

There are five different cabin templates in GT-SUITE, including smallcar, medium car, large car, semi trailer truck and tractor. In this study,the cabin is modeled based on a small car template. This template usesthe approach of the lumped volume model, where the cabin is repre-sented as a single volume of air and the energy balance is calculated todetermine several heat rates and temperatures.

The cabin exchanges heat with the ambient in the form of convec-tion with the outside air, radiation between cabin and outside air, andsolar radiation. This sources of heat increase the temperature of thecabin’s thermal mass, which releases the heat to the air volume insidethe cabin as demonstrated in Figure 4.4. Additionally, solar radiationwas considered to be transmitted through the windshields and the sidewindows. However, one potential source of heat was not consideredin the model: the high voltage battery, whose mass is also part of theactual cabin.

Figure 4.4: Sources of heat from the ambient, and heat transferred fromthe mass to the cabin

Page 30: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

20 CHAPTER 4. SYSTEM MODELING

The cabin’s thermal masses considered in the model are:

• Side windows

• Doors

• Front windshield

• Rear windshield

• Roof

• Floor

The cabin model was previously calibrated with experimental data fora non-hybrid vehicle. The calibration parameters include the materi-als, physical properties and masses of the interior components.

Figure 4.5 shows the air loop between the evaporator and the cabin.Pipes in purple are used to model the recirculation, where the recircu-lation degree is defined by the Recirculation Door (or Flap). The A/Cblower circulates the air in the loop and outputs the power consump-tion calculated with the angular speed and the embedded fan map.

Figure 4.5: Cabin Air Loop

4.5 HV Battery

The battery was modeled as two separate parts: thermal and electri-cal. In the electrical part, heat is generated from the cell when the HV

Page 31: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 4. SYSTEM MODELING 21

battery works. The heat generation is governed by the Joule–Lenz law:

P = I2R

where:

P Released heatI Delivered currentR HV battery internal resistance

The heat generated by the battery is sensed and feedbacked to thethermal mass of the battery (Figure 4.6), which will in turn increaseits temperature. Then, the temperature will work as an input to theelectric part modifying it’s internal resistance.

Figure 4.6: Thermal and electrical parts of the HV battery (example)[32]

4.5.1 Battery Cooling Circuit

Natural convection between the battery and the surrounding air is theprevailing heat transfer mechanism when there is no active cooling.However, when either the radiator or the chiller are being used, theheat transfer is dominated by forced convection between the HV bat-tery and the coolant.

Figure 4.7 shows how the system components are coupled in GT Suite;the battery is connected with the coolant circuit, where the coolant iscirculated with a pump. Additionally, a subassembly containing theair-cooled radiator was coupled to the cooling circuit.

Page 32: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

22 CHAPTER 4. SYSTEM MODELING

Figure 4.7: Battery Cooling Circuit

4.5.2 Battery Current Coupling

As discussed in Chapter 3, there are two types of batteries in the car.One is the LV battery, where the auxiliary load of the A/C system isconnected, and the other is the high voltage (HV) battery, which pro-vides current to the electric motor, the A/C compressor and the thelow voltage (LV) battery. The LV battery will only be charged by theHV battery when its State of Charge (SOC) is below certain level. Fig-ure 4.8 shows how the three mentioned loads are added to the HV bat-tery in GT SUITE. For the LV battery (Figure 4.9), a similar logic wasimplemented, including also a feedback of the SOC to the drivetrainin order to tell the HV battery when to start charging the LV battery.

Page 33: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 4. SYSTEM MODELING 23

Figure 4.8: High Voltage Battery in GT-SUITE

Figure 4.9: Low Voltage Battery in GT-SUITE

4.6 Fans and pumps

To define the behavior and performance of the fans and pumps, mea-sured data from the suppliers is used as an input to the model. InGT-SUITE [33], the solver can create a densely populated map basedon limited measured data using a standard interpolation approach.

The parameters used to describe the fans/pump were:

Page 34: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

24 CHAPTER 4. SYSTEM MODELING

• Fan angular speed

• Mass flow rate

• Pressure rise (or ratio)

• Isentropic efficiency

By using the isentropic efficiency, the fluid enthalpy at the outlet of thefan can be calculated with the following equation:

hout = hin +∆hsηs

hout Enthalpy at fan outlethin Enthalpy at fan inlet∆ hs Ideal enthalpy differenceηs Isentropic efficiency

Additionally, tabular data of the fan/pump mechanical efficiency isalso used as an input in order to get a more accurate simulation resultof the power consumption.

4.7 Thermal Expansion Valves

To model the thermal expansion valves, a template called ‘TXVDe-tail4Quadrant’ was used. In Figure 4.10, the quadrants 1,2, and 3are used to model how the thermal expansion valves work, and thequadrant 4 is used to verify the model. The thermal expansion valvesare externally equalized, which means that the outlet temperature andpressure will affect the opening of the valves, changing the mass flowrate of refrigerant.

Page 35: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 4. SYSTEM MODELING 25

Figure 4.10: ‘TXVDetail4Quadrant’ template[34]

4.8 Pipes

The pipes were modeled providing it’s geometry in GT-SUITE. Nei-ther the friction losses in the pipes nor the pressure losses due to bendswere considered.

Page 36: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Chapter 5

Validation

To ensure that the model is a reasonable representation of the actualsystem, validation is essential. Since the target of this study is to pre-dict an accurate power consumption of the A/C system while con-ducting the SC03 driving cycle, a similar test performed under hot cli-mate with constant air conditioner operation was chosen.

The selected validation test has the following features:

• Long test period (4348 seconds)

• Hot climate (ambient temperatures around 32 ◦C - 34 ◦C)

• Air conditioner and battery cooling enabled

• Sufficient amount of test data

• Usage of R134a

5.1 Battery Model Validation

Figure 5.1 shows the first simulated result and test data for the bat-tery temperature. According to the test, the battery temperature grad-ually increases until reaching 37 ◦C, afterwards it is cooled down bythe battery cooling circuit. There was no active cooling applied in thesimulation since the heating process of the battery was first being ob-served. The figure shows how the battery in the simulation heats upfaster than the battery in the test, this is because there was no heatlosses to the air applied to the model, therefore, different convection

26

Page 37: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 5. VALIDATION 27

coefficients were investigated (Figure 5.2). Finally, a convective heattransfer coefficient of 8 W/m2K was chosen.

Figure 5.1: Actual and Simulated Battery Temperature

Page 38: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

28 CHAPTER 5. VALIDATION

Figure 5.2: Different Natural Convection Heat Transfer Coefficients forBattery Cooling

After modifying the convection heat transfer coefficient and addingthe active cooling from the battery cooling system, the simulation re-sult properly matches the test data as shown in Figure 5.3.

Page 39: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 5. VALIDATION 29

Figure 5.3: Battery Temperature Validation

5.2 A/C System Validation

Several variables were used to ensure that the A/C system model wasworking properly, such as: the air temperature after the evaporator,the compressor speed, the compressor power consumption and thecabin temperature.

5.2.1 Air Temperature after the Evaporator

The temperature of the air after the evaporator is an important param-eter which affects the compressor speed. Previously, the air temper-ature after the evaporator didn’t match the test data, for this reason,a further investigation on the refrigeration cycle was carried out. Asdisplayed in Figure 5.4, the simulated refrigeration system worked in-correctly; the refrigerant in the system was overloaded which meansthat it could not evaporate completely in the evaporator, this is be-cause a wrong mass flow rate was set in the compressor map. Afterscaling the map, the model demonstrates a more reasonable refriger-ation cycle (Figure 5.5), which led to an acceptable match of the air

Page 40: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

30 CHAPTER 5. VALIDATION

temperature after the evaporator between the simulation and the testdata Figure 5.6.

Figure 5.4: P-h Diagram at 1162.3s (Before Modification)

Page 41: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 5. VALIDATION 31

Figure 5.5: P-h Diagram at 1159.5s (After Modification)

Figure 5.6: Air Temperature After the Evaporator Validation

Page 42: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

32 CHAPTER 5. VALIDATION

5.2.2 Compressor Speed

Since the compressor control imported from Simulink contained mul-tiple inputs, it was crucial to verify if the control was delivering theproper compressor speed. Figure 5.7, shows a good match betweentest and simulation, however it can be seen that when the active cool-ing is enabled, almost at the end of the test, the compressor speed ishigher in the simulation. The reasons that cause this increased speedare discussed in the following section.

Figure 5.7: Compressor Speed Validation

5.2.3 Compressor Power Consumption

The final goal of this study is to obtain a reasonable result of powerconsumption. According to Figure 5.8, the simulation result matcheswell with the test data, except for the following times: 0 seconds, 1219seconds and 3848 seconds.

Page 43: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 5. VALIDATION 33

Figure 5.8: Compressor Power Validation

The initial temperatures of the heat exchangers, pipes, refrigerant, andcar components were not measured in the test, so they were estimated.As a result, a deviation occurs at the beginning of the test. At 1219seconds, another deviation where the air temperature after the evapo-rator rose around 20 ◦C is caused possibly by a recording error in theair temperature sensor, which results in a higher compressor speedand power consumption. Regarding the deviation at the end of thetest, the battery temperature reached 37 ◦C, which enabled the activecooling with the chiller. Part of the refrigerant which was supposedto go through the evaporator, eventually splitted to the chiller circuit.Figure 5.9 shows that suddenly, the refrigerant mass flow through theevaporator in the simulation drastically dropped during this time pe-riod, causing a higher air temperature at the outlet of the evaporator,resulting in a higher compressor speed and power consumption.

Page 44: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

34 CHAPTER 5. VALIDATION

Figure 5.9: Refrigerant Mass Flow Rate through the evaporator

To obtain the electric energy consumed by the compressor throughoutthe test, a numerical integration was performed. The trapezoidal in-tegration method was executed in MATLAB using the function “cum-trapz”. This function applies eq. 1 [35] to compute the area covered bythe function, which is equivalent to the electric energy (in kWh).

Equation 1:∫ b

a

f(x)dx ≈ b− a

2N(f(xn) + f(xn+1)) =

b− a

2N[f(x1) + 2f(x2) + ...+ 2f(xN) + f(xN+1)]

After comparing the compressor power consumption results of thesimulation with the test, the percentage difference calculated with eq.2 is around 9%.

Equation 2:

Percenterror =Energytest − Energysimulation

Energytest∗ 100

Page 45: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 5. VALIDATION 35

5.2.4 Cabin Temperature

The cabin temperature from the simulation was compared to the tem-perature of the cabin above the driver’s head in the test. This mea-surement was taken as a reference since from test data it is possible tosee that the temperature inside the cabin is evenly distributed. Figure5.10 demonstrates how there is a deviation from the test data, wherethe temperature of the simulated cabin is about 3 ◦C below the actualcabin. The reason for this is that neither the thermal mass of the HVbattery, nor the heat rejected from the battery to the cabin were ac-counted in the model. This lower amount of heat generation led to alower cabin temperature in the simulation.

Figure 5.10: Cabin Temperature Validation

Page 46: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Chapter 6

Results

6.1 SC03 Test Conditions

As described in section 2.3.1, the SC03 driving cycle operates under ahot and sunny weather. To investigate both cold start and warm startcases, the test consisted of two SC03 driving cycle with a 10 minutesparking period, which was carried out in a test rig, where the lab tem-perature varied as shown in Figure 6.1 (it was not kept constant 35 ◦C

like in the official test).

36

Page 47: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

CHAPTER 6. RESULTS 37

Figure 6.1: Laboratory Ambient Air Temperature for the Cold-Startand Warm-Start Cases

The conditions present in the test were:

• Solar flux on the vehicle: (850 W/m2)

• Refrigerant: R1234yf (because of U.S. regulation)

• Recirculation Degree: 92%

• Air conditioner: On (at maximum level)

• Ambient temperature: from 31 ◦C to 36 ◦C

6.2 Simulation Results

Due to the limited test data, the only parameter which was comparedin this study is the auxiliary load of the HV battery. As discussed insection 4.5.2 (Battery Current Coupling), three different power loadswere added to the HV battery, including propulsion system, A/C com-pressor and LV battery charging.

Page 48: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

38 CHAPTER 6. RESULTS

The simulation result matches well with the test data, except for thebeginning of the two SC03 driving cycles. The reason for the devia-tion at the first 100 seconds is the assumption of the initial conditionparameters. There is not enough test data for the SC03 test, all the con-ditions apart from ambient temperature and power consumption wereconjectured in this study. Regarding the start of the second SC03 driv-ing cycle, it was found that a significant amount of current leaked fromthe LV battery in the test during the parking period. As discussed insection 3.5, when the SOC of the LV battery is lower than 90%, it startsto be charged by the HV battery, which eventually increases the aux-iliary load of the HV battery. For this reason, at the beginning of thesecond driving cycle, the auxiliary load of the HV battery was not onlythe A/C compressor power, but also the charging load to the LV bat-tery.

Figure 6.2: Auxiliary Power Consumption Comparison

The percent difference of the auxiliary power consumption of the HVbattery between the test and the simulation calculated with eq. 1 andeq. 2 is about 6.25%.

Page 49: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Chapter 7

Conclusions

In this study, a PHEV’s A/C system was modeled and coupled with avehicle driveline and a battery cooling circuit using GT-SUITE. Diffi-culties like compressor control design, battery thermal performanceadjustment, and complete system validation were solved to ensurethat the model could represent the actual system and output a reli-able power consumption.

The results of the validation process show a good agreement with testdata between most of the relevant parameters of the A/C system: com-pressor speed, compressor power, battery temperature, and air tem-perature after the evaporator. When accounting for the energy con-sumed for the whole test by the compressor (electricity), there is a 9%difference between the actual and the simulated consumption. How-ever, a more refined model of the cabin is required, since in this modelno heat exchange between the high voltage battery and the cabin wasconsidered, resulting in a lower temperature of the cabin (approxi-mately 3 ◦C) when the A/C system reaches steady state.

The simulations of the SC03 driving cycle display a good agreementwith the test, with a difference of auxiliary power of only 6.25%. Thebiggest drawback when performing the simulation was the lack of testdata since most of the initial conditions had to be assumed. Also, theelectric current leaked through the low voltage battery by accidentduring the parking time caused a mismatch of the trend line whenstarting the second SC03 driving cycle (warm-start).

39

Page 50: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

40 CHAPTER 7. CONCLUSIONS

There is still future work to be performed. First, the cabin modelshould include the thermal mass of the battery and the amount of heatrejected from the battery model. Also, the compressor map needs to befurther validated with robust test data, since erroneous data can leadto an incorrect mass flow rate, causing in this case an increased energyconsumption. Furthermore, a fan control model and evaporator airtemperature control model shall be designed to make the results morereliable, since this parameters could greatly influence the power con-sumption, specially the requested air temperature after the evaporator.

In the future, this model can be used to predict the power consump-tion of the A/C system and active battery cooling to conduct a morerobust fuel economy analysis for the new generation of PHEVs.

Page 51: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

Bibliography

[1] IEA(2017a). “World Energy Balances 2017”. In: International En-ergy Agency (2017).

[2] IEA(2017b). “Global EV Outlook 2017: Two million and count-ing”. In: International Energy Agency (2017).

[3] European Commision (2011). “Roadmap to a Single EuropeanTransport Area – Towards a competitive and resource efficienttransport system”. In: COM 0144 (2011).

[4] U.S. Department of Energy (2017). “Benefits and Considerationsof Electricity as a Vehicle Fuel”. In: https : / / www . afdc .energy.gov/fuels/electricity_benefits.html Ac-cessed: March (2018).

[5] European Green Vehicles Initiative Association(2013). “EuropeanGreen Vehicles Initiative”. In: https://egvi.eu/about-the-egvi-ppp/objectives-and-scope Accessed: March(2018).

[6] U.S National Conference of State Legislatures (2017). “State Ef-forts to Promote Hybrid and Electric Vehicles”. In: http://www.ncsl.org/research/energy/state-electric-vehicle-incentives-state-chart.aspx Accessed: March(2018).

[7] Japanese Ministry of Economy. “Enhancement of the InitiativesConcerning the Promotion of Electric Vehicles”. In: http://www.meti.go.jp/english/press/2015/0312_02.html(2015).

[8] Natural Resources Canada. “Electric Vehicle Technology RoadmapExecutive Summary”. In: https:// www.nrcan.gc.ca/energy/alternative-fuels/fuel-facts/ecoenergy/18352 Accessed: March (2018).

41

Page 52: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

42 BIBLIOGRAPHY

[9] Rugh J. et al. “Reduction in Vehicle Temperatures and Fuel Usefrom Cabin Ventilation, Solar-Reflective Paint, and a New Solar-Reflective Glazing”. In: SAE Technical Paper 01 (2007), p. 1194.

[10] J. Rugh, V. Hovland, and S. Anderson. “Significant Fuel Savingsand Emission Reductions by Improving Vehicle Air Condition-ing”. In: Mobile Air Conditioning Summit. Washington DC. (2004).

[11] R. Farrington, M. Keyser M. Cuddy, and J. Rugh. “Opportuni-ties to reduce air-conditioning loads through lower cabin soaktemperatures”. In: 16th Electric Vehicle Symposium Beijing Beijing,China (1999).

[12] National Highway Traffic Safety Administration and Environ-mental Protection Agency. “Rules and Regulations”. In: FederalRegister. 40 CFR (2012), pp. 62623–63200.

[13] Society of Automotive Engineers(SAE). “Recommended Prac-tice for Measuring the Exhaust Emissions and Fuel Economy ofHybrid-Electric Vehicles, Including Plug-in Hybrid Vehicles”. In:SAE Standard J1711 (2010).

[14] John Rugh. “Proposal for a Vehicle Level Test Procedure to Mea-sure Air Conditioning Fuel Use”. In: SAE World Congress 01 (2010),p. 0799.

[15] Filip Nielsen. “Automotive Climate System Investigation of In-vestigation of Current Energy Use and Future Energy SavingMeasures”. In: Building Services Engineering Department of Civiland Environmental Engineering. Chalmers University of Technology(2016).

[16] Tibor Kiss, Lawrence Chaney, and John Meyer. “A new automo-tive air conditioning system simulation tool developed in MAT-LAB/Simulink”. In: SAE World Congress and Exhibition (2013).

[17] Mohammed Ali Fayazbakhsh and Majid Bahrami. “Comprehen-sive Modeling of Vehicle Air Conditioning Loads Using HeatBalance Method”. In: SAE International 01 (2013), p. 1507.

[18] Haslinda Mohamed Kamar, Mohd Yusoff Senawi, and Nazri Kam-sah. “Computerized simulation of automotive air-conditioningsystem: development of mathematical model and its validation”.In: CSI International Journal of Computer Science Issues 19 (2012),pp. 23–34.

Page 53: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

BIBLIOGRAPHY 43

[19] Christoph Boettcher. “Simulation of a passenger car cabin usinga coupled GT-SUITE-TAITherm simulation model”. In: Univer-sity of Stuttgart (2016).

[20] Rehea Valentina et al. “HVAC System Modeling for Range Pre-diction of Electric Vehicles”. In: 2014 IEEE Intelligent Vehicles Sym-posium (IV) (2014).

[21] Mohammad Abdullah, Al Faruque, and Korosh Vatanparvar. “Mod-eling, Analysis, and Optimization of Electric Vehicle HVAC Sys-tems”. In: Department of Electrical Engineering and Computer Sci-ence, University of California, Irvine 17 (2016), pp. 4711–4721.

[22] Filip Nielsen et al. “Simulation of Energy Used for Vehicle Inte-rior Climate”. In: SAE International 01 (2015), p. 911.

[23] U.S. Department of Energy. “Energy Tips – Compressed Air”. In:https://www.energy.gov/sites/prod/files/2014/05/f16/compressed_air7.pdf Accessed: March (2018).

[24] Afiq Aiman Dahlana, Amirah Haziqah Zulkiflia, and Henry Na-sution. “Efficient and ‘Green’ Vehicle Air Conditioning Systemusing Electric Compressor”. In: The 6th International Conferenceon Applied Energy – ICAE (2014).

[25] Quansheng Zhang, Stephanie Stockar, and Marcello Canova. “Energy-Optimal Control of an Automotive Air Conditioning System forAncillary Load Reduction”. In: IEEE Transactions on Control Sys-tems Technology 24 (2016), pp. 67–80.

[26] Boon Chiang. “Soft Computing Based Controllers for Automo-tive Air Conditioning System with Variable Speed Compressor.Dissertation”. In: Faculty of Mechanical Engineering, University ofTechnology Malaysia (2015).

[27] Jinrui Nan and Zhichao Zhou. “Control Algorithm Optimizationof Electric Air Conditioning Based on ADVISOR”. In: Interna-tional Conference on Computer and Information Application (2012).

[28] U.S. Environmental Protection Agency. “Detailed Test Informa-tion”. In: https://www.fueleconomy.gov/feg/fe_test_schedules.shtml Accessed: March (2018).

[29] Gamma Technologies. “Flow Theory Manual”. In: Modeling The-ory Manual (2017).

Page 54: Air Conditioning System Modeling for Car Fuel Economy ...1295967/FULLTEXT01.pdf · The automotive air conditioning system is the greatest auxiliary load of a vehicle, having a considerable

44 BIBLIOGRAPHY

[30] Gamma Technologies. “CompressorMap-Corrected Data”. In: GT-ISE v2017 Help Navigator (2017).

[31] Gamma Technologies. “Cooling Systems and Thermal Manage-ment Application Manual and Tutorial”. In: Modeling Applica-tions Manual (2017).

[32] Gamma Technologies. “CellLithiumIon-Li-Ion Cell Model”. In:GT-ISE v2017 Help Navigator (2017).

[33] Gamma Technologies. “FanMap-Fan Performance with ImposedSpeed”. In: GT-ISE Help Navigator (2017).

[34] Gamma Technologies. “TXVDetail4Quadrant - Detailed ThermalExpansion Valve”. In: GT-ISE Help Navigator (2017).

[35] MATLAB R2016b. “Trapz”. In: MATLAB Help Navigator (2016).