Cooling performance and evaluation of automotive

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A new design of automotive refrigeration system for a passenger car was proposed. ... 1400, and 2100 rpm at a set temperature of 22°C. A set of thermocouples that combined by data logger .... ᒡ௥௘௙ = mass flow rate of the refrigerant [kg/s] b.

Cooling performance and evaluation of automotive refrigeration system for a passenger car Prajitno, Deendarlianto, Akmal Irfan Majid, Mahardeka Dhias Mardani, Wendi Wicaksono, Samsul Kamal, Teguh Pudji Purwanto, and Fauzun Citation: AIP Conference Proceedings 1737, 030005 (2016); doi: 10.1063/1.4949285 View online: http://dx.doi.org/10.1063/1.4949285 View Table of Contents: http://scitation.aip.org/content/aip/proceeding/aipcp/1737?ver=pdfcov Published by the AIP Publishing Articles you may be interested in The effect of buffeting noise in passenger cars Proc. Mtgs. Acoust. 23, 040002 (2015); 10.1121/2.0000097 The effect of buffering noise in passenger car J. Acoust. Soc. Am. 137, 2256 (2015); 10.1121/1.4920231 Cooling performance of a room-temperature magnetic refrigerator prototype J. Appl. Phys. 107, 09A937 (2010); 10.1063/1.3358616 Psychoacoustic evaluation of music reproduction in passenger cars J. Acoust. Soc. Am. 122, 2943 (2007); 10.1121/1.2942479 The fifty years with passenger rail cars J. Acoust. Soc. Am. 67, S61 (1980); 10.1121/1.2018319

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Cooling Performance and Evaluation of Automotive Refrigeration System for a Passenger Car Prajitno1,2,a), Deendarlianto1,2, Akmal Irfan Majid1,2, Mahardeka Dhias Mardani1, Wendi Wicaksono1, Samsul Kamal1,2, Teguh Pudji Purwanto1, Fauzun1 1

Dept. of Mechanical and Industrial Engineering, Gadjah Mada University, Jl. Grafika No. 2, Yogyakarta 2 Center for Energy Studies, Gadjah Mada University, Sekip K-1A, Bulaksumur, Yoyakarta Corresponding author: a) [email protected]

Abstract. A new design of automotive refrigeration system for a passenger car was proposed. To ensure less energy consumption and optimal thermal comfort, the performance of the system were evaluated. This current research was aimed to evaluate the refrigeration characteristics of the system for several types of cooling load. In this present study, a four-passenger wagon car with 1500 cc gasoline engine that equipped by a belt driven compressor (BDC) was used as the tested vehicle. To represent the tropical condition, a set of lamps and wind sources are installed around the vehicle. The blower capacity inside a car is varied from 0.015 m/s to 0.027 m/s and the compressor speed is varied at variable 820, 1400, and 2100 rpm at a set temperature of 22qC. A set of thermocouples that combined by data logger were used to measure the temperature distribution. The system uses R-134a as the refrigerant. In order to determine the cooling capacity of the vehicle, two conditions were presented: without passengers and full load conditions. As the results, cooling capacity from any possible heating sources and transient characteristics of temperature in both systems for the cabin, engine, compressor, and condenser are presented in this work. As the load increases, the outlet temperature of evaporator also increases due to the increase of condensed air. This phenomenon also causes the increase of compressor work and compression ratio which associated to the addition of specific volume in compressor inlet. Keywords: Cooling load, Tropical region, Automotive refrigeration, Belt Driven Compressor, Refrigeration performance

INTRODUCTION Although many campaigns on the shifting program of using the public transport instead the private transport, reduction of the traffic jam, air pollution, and car population are still being difficult especially in some developed countries, including Indonesia. The Indonesian energy consumption by transportation sector grew annually at a rate of 6.5% from 2000-2011 but the oil production decreased annually at a rate of 4% [1]. This fact shows a lameness due to the presence of many vehicles. Moreover, the transportation sector consumes over 60% of Indonesian oil and the number of passenger vehicles will increase from 3.4 million units (2002) to 13.9 million units by 2030, as it was predicted by The Asia Pacific Energy Research Centre [2]. Consequently, the oil demand will increase. According to the report of The Association of Indonesian Automotive Industries, from 2005 to 2012 the compound annual growth rate of the passenger car was 11.5% for vehicle sales and 12.2% for vehicle production. The data shows that the population of passenger cars in Indonesia is still in high number which may cause pollution-related problems. Therefore, it induces the global warming phenomena if they use impolite refrigerant or has bad refrigeration system. The design process of the automotive air conditioning system requires more intricate analysis due to some requirements related to the optimum passenger comfort (thermal, humidity, and air availability) and less energy consumption by the system. Some parameters in AC outlet such as flow rates, air volume, effective direction, and temperature should be adjusted over a wide range of driving and climatic conditions [3]. The technical aspects examples which influence the effective automotive refrigeration system are observed in this study. It consists of the compressor rotating speed which has a correlation with vehicle speed, the heating source from sunlight through vehicle windows which has a different calculation to common buildings, and the automotive AC system. These examples are expected to cool down the vehicle effectively (in a good flow distribution), quickly, and minimize the vibration (quietly) [3,4,5]. Particularly, two main parameters are usually considered in the evaluation of refrigeration characteristics, such as cooling capacity and each system’s device performance. Generally, research on automotive refrigeration systems has been conducted by many scholars in the widely area. In the discussion of refrigerant, Brown et al. compared

Proceedings of the 3rd AUN/SEED-NET Regional Conference on Energy Engineering and the 7th International Conference on Thermofluids (RCEnE/THERMOFLUID 2015) AIP Conf. Proc. 1737, 030005-1–030005-11; doi: 10.1063/1.4949285 Published by AIP Publishing. 978-0-7354-1391-7/$30.00

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performance merits between R134a and CO2 by using semi-theoretical cycle mode. Better performance was showed by R134a-based system, performed by the better COP values than CO2-based system [6]. Meanwhile, the performance of the automotive refrigeration system is also affected by the compressor performance. In general, the belt driven compressor (BDC) is still used for the refrigeration system of the internal combustion engine cars. On the other hand, it is predicted for the future that the electric vehicle will play an important role in the future. Hence, the existing automotive refrigeration system needs to be evaluated. However, there is still a lack of studies that concern on the vehicle cooling load calculation for a tropical area, especially Indonesia. The tropical areas have the specific sun positioning, high relative humidity, particular clothing type, and different human activities to adapt to the tropical condition. All these aspects make the cooling capacity analysis more complicated than that of common calculation. On the other hand, the time-based temperature profiles are still rarely to be discussed. The present study is purposed to determine the cooling capacity of the vehicle in a tropical region. Performance analysis of automotive refrigeration systems, such as transient temperature characteristics and evaluation of each refrigeration parameters are also carried out.

EXPERIMENTAL SETUP The experiments are conducted in Heat and Mass Transfer Laboratory of Gadjah Mada University. In this present work, evaluation of refrigeration performance was conducted in a wagon car of Toyota Vios 2013. List of general specifications of the vehicle is mentioned in Table 1. The automotive air-conditioner is designed based on the vapor-compression cycle of the refrigeration cycle, as performed in Fig. 1. This system has main components such as: compressor, condenser, expansion valve, and evaporator. This car uses R-134a as the refrigerant. The rate of refrigerant flowing into evaporator is regulated by Thermal Expansion Valve (TXV). The working temperature of the evaporator is designed at 0qC and 50qC for the condenser. Table 1. Car’s specifications [7]

Type

Specifications

Dimension Overall length (mm) Overall width (mm) Overall height (mm) Wheelbase (mm) Curb height (kg)

4410 1700 1475 2550 1035-1095

Engine Engine type Displacement (cc) Bore x stroke (mm) Max. power (ps/rpm) Max. torque (kgm/rpm) Tank Capacity (liter) Fuel

4 cylinders in line, 16 valve, DOHC, VVT-i 1,497 75 x 84,7 109 / 6000 14.4/4200 42 Unleaded gasoline, regulated by EFI

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FIGURE 1. Vapor-compression cycle of refrigeration cycle

Details of the measurement procedure are clearly depicted in Fig. 2. In the experiments, each refrigeration component was measured by the measuring devices. The refrigerant was evaporated and a phase change occurs. After leaving the evaporator, the refrigerant, which was formed as the gas-phase afterward, was compressed inside a belt-driven compressor (BDC). In order to measure the pressure (PS) and temperature (T4 ) of the compressor suction, a pressure gauge and the thermocouples (K-type) were installed, respectively. The pressure and temperature were increased due to the compression effect. Before entering the condenser, the discharge pressure (P D) and temperature (T2) were also monitored. There are two three-way valves to control the refrigerant after leaving the condenser and entering the expansion valve (tap valve). The refrigerant’s flow rate was measured by a flowmeter and the temperature before entering the tap valve was well monitored by the thermocouples. All measurement data were acquitted inside a data logger. The air conditioning system was tested in various cooling load and the speed of evaporator blowers. To represent the presence of the passengers, the cooling load from human body was simulated by 36qC water that circulated inside 2 bodies of a human mannequin. The mannequins were placed in the front row of the passenger seat. The series of halogen lamps were installed above the vehicle roof to represent the solar radiation. To simulate outer-air velocity, 3 air fans were placed in front of the vehicle. A hotwire anemometer was also used to measure the air-flow rate, generated by the wind sources. The evaporator blowers were controlled with a level switch.

FIGURE 2. Schematic diagram of the experimental apparatus.

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In the performance test, the refrigeration characteristics are evaluated based on the three conditions, stated in Table 2. First, the performance test is only focused on investigating the solely vehicle load. Hence, the cabin temperature is remained in 22oC without any passengers. The external loads such as sunlight (modeled by lighting sources) and the wind (modeled by a fan) are not evaluated. For the “B-case”, the external heating source from the sunlight is considered. Since the present of the external heating source (a series of lamps, as the representation of Indonesian and tropical area’s sunlight), the external temperature is increased and then measured to be 34 oC. Moreover, the third scenario (“C-case”) represents the actual model by considering the presence of 2 passengers and all external loads. The previews of the actual experimental conditions were illustrated in Fig. 3.

Scenario Case A Case B Case C

Table 2. Data matrix of experimental conditions Cabin temperature External loads Passengers 22 NO NO 22 YES (sun) NO 22 YES (sun & wind) YES (2 persons)

Purposes Load due to vehicle Effect of external loads Effect of passengers

Table 3. Blower capacity Blower Capacity (m3/s) Level 1 0,0196 Level 2 0,0271 Level 3 0,0356

(a) (b) FIGURE 3. (a) Actual experimental condition; (b) Measurement of human cooling load

FIGURE 4. Standard vapor compression cycle

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To analyze the system performance, the thermodynamics’ first law was used to determine the important variables of the automotive refrigeration process. The refrigeration process follows the standard vapor compression cycle that depicted in Fig. 4. Detail of each stage calculation is presented as follows: a.

Compression process The compression system by a compressor is assumed as the adiabatic process. The kinetic and potential energies are also neglected. Therefore, the compressor work (W C) and compressor power (PC) can be formulated in Equation (1) and (2), respectively. (1) ܹ௖ ൌ  ݄ଶ െ ݄ଵ ܲ௖ ൌ  ᒡ௥௘௙ሺ݄ଶ െ ݄ଵ )

(2)

where ܹ௖ ܲ௖ ݄ଵ ݄ଶ ᒡ௥௘௙ b.

= compressor work [kJ/kg] = compressor power [kW] = refrigerant enthalpy at point 1 [kJ/kg] = refrigerant enthalpy at point 2 [kJ/kg] = mass flow rate of the refrigerant [kg/s]

Condensation process To measure the heat transfer at the condenser, the following equation is used: ܳ௞ ൌ  ᒡ௥௘௙ሺ݄ଶ െ ݄ଷ)

(3)

Where: ܳ௞ ݄ଶ ݄ଷ ᒡ௥௘௙ c.

= condensation capacity [kW] = refrigerant enthalpy at point 2 [kJ/kg] = refrigerant enthalpy at point 3 [kJ/kg] = mass flow rate of the refrigerant [kg/s]

Throttling process This process occurs in the expansion valve. In this process, there is no assumed work therefore ‫ = ݓ‬0. The conversion of kinetic energy to potential energy was also neglected and system is an adiabatic. Thus, the variables follow the following relationship, stated in Equation (4). (4) ݄ଷ ൌ  ݄ସ Where: ݄ଷ ݄ସ

d.

= refrigerant enthalpy at point 3 [kJ/kg] = refrigerant enthalpy at point 4 [kJ/kg]

Evaporation process The heat transfer during the evaporation process can be formulated as follows: ‫ݍ‬௥ ൌ  ሺ݄ଵ െ ݄ସሻ ܳ௥ ൌ  ᒡ௥௘௙ሺ݄ଵ െ ݄ସሻ

(5) (6)

Where : ܹ௖ ܲ௖ ݄ଵ ݄ଶ ᒡ௥௘௙

= compressor work [kJ/kg] = compressor power [kW] = refrigerant enthalpy at point 1 [kJ/kg] = refrigerant enthalpy at point 2 [kJ/kg] = mass flow rate of the refrigerant [kg/s]

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e.

Coefficient of performance (COP) This parameter is defined as the comparison of heat that is released from room (refrigeration effect) to the compressor work, formulated as follow: ‫ ܱܲܥ‬ൌ 

(7)

‫ݍ‬௥  ݄ଵ െ ݄ସ ൌ ܹ௖ ݄ଶ െ݄ଵ

RESULTS AND DISCUSSION 1.

Performance of refrigeration system

In order to analyze vehicle cooling performance, first, the effect of compressor rotating speed to the important refrigeration parameters such as the refrigeration capacity (QR), the coefficient of performance (COP), the compressor work (WK), and the condenser heat (QC) are evaluated. Next, the transient data of time-based temperature profile for each scenario condition are also presented. The first data express the refrigeration performance, evaluated by its important parameters whereas the second data shows the cooling performance for each refrigerating component. In this measurement, the two scenarios were first compared (case-A and case-B). The main reason for comparing the two conditions is to investigate the increase of cooling capacity by the load addition from the sunlight. Basically, case-A was used as the control variable which showed a condition without passenger and external load. In those experiments, the cabin temperature is remained at similar condition of 22qC but the sunlight was considered in case B. Fig. 5 (a) shows the effect of compressor speed to the refrigeration capacity (Q R). Generally, as the compressor speed increases, QR also increases for each level of blower air flow rate. The presence of light sources, represents the sunlight, becomes one heat sources which add the cooling load of the vehicle. The refrigeration unit has to make more effort to cool the cabin air. Consequently, the general trend of the refrigeration effect on the case B is always higher than case A. The similar trend is presented in Fig. 5 (b) which explain the effects of compressor speed to the compressor work. The data describe that the increase of compressor speed leads the compressor work increases therefore theoretically consumed energy also increases.

1.5

2.5

Compressor work (kW)

Refrigeration effect (kW)

3.0

1.0

2.0 Level 1 (case A)

1.5

Level 2 (case A)

1.0

500

1000

1500

2000

2500

Level 1 (case A)

0.5

Level 2 (case A)

0.0 500

1000

1500

2000

2500

Compressor speed (rpm)

Compressor speed (rpm)

(a)

(b)

FIGURE 5. (a) Effects of compressor speed to the refrigeration effect for case A and case B (b) Effects of compressor speed to the compressor work for case A and case B The effects of compressor speed to the cooling capacity and coefficient of performance (COP) are shown in Fig. 6 (a) and (b), respectively. The cooling capacity increases as the increase of compressor speed. On the other hand, the COP has a decreasing trend as the increase of the compressor speed. As the cooling capacity of the system

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increases, shown by the increase of refrigeration effect, the increase of Q condenser, and the lower COP, the refrigerant mass flow rate also increases. Hence, the compressor work becomes higher. The presence of lighting source shows a representation of radiation load. It has been validated by the measurement of environmental temperature as in 34qC.

5.0

5.0 Level 1 (case A) Level 2 (case A) Level 3 (case A)

4.0 3.0 2.0

Level 1 (case A) Level 2 (case A) Level 3 (case A)

1.0 0.0 500

1000

(a)

1500

2000

COP [-]

Q condenser [kW]

4.0

3.0

2.0

2500

Compressor speed (rpm)

500

1000

1500

(b) 2000

2500

Compressor speed (rpm)

FIGURE 6. (a) Effects of compressor speed to the condenser heat (case A and case B) (b) Effects of compressor speed to the COP (case A and case B) 2.

Evaluation of the time-series temperature characteristics The data address that the transient characteristics of temperature which were measured in some points, i.e. engine, compressor, condenser, cabin, and blowers. In this work, the dry-bulb temperature (Tdb ) and wet-bub temperature (Twb). The temperature profiles for case A are expressed by Fig. 7. When the car was tested with no passengers and external loads the minimum cooling load is presented, as stated before in Fig. 4 and 5 above. As the result, the system could maintain the ambient temperature along approximately 150 seconds. Fig. 7 (a) shows the temperature profile of the refrigeration components, such as the discharge and suction of compressor, engine temperature, and condenser discharge. The engine temperature gradually increases as the time goes by. Also, the similar trend happens at the discharge point of compressor and condenser, but the opposite trend exists for the data of compressor suction. The temperature profile of the air blown by the AC blower is illustrated by Fig. 7 (b). Although the mass flow rate is similar for any blower level, the measurement shows that rough temperature distribution is still presented from the first 200th to around 1050 seconds. Ideally, the car’s cooling system is able to generate a uniform cool temperature for all passengers’ area (indicated by a uniform temperature of left-middle-right blowers). This obtained data are also in agreement with the measurement of temperature point for all passengers’ area, pointed out in Fig. 7 (c). In this figure, there are some fluctuate trends which may cause by a disturbance of data acquisition. However, the general trend shows that an undistributed temperature in vehicle cabin is still occurred although there is no passenger and external load. Furthermore, a new design improvement of air cooling system inside the cabin is maybe suggested. The similar works were also conducted for the second case (case B). The main purpose of this case was to investigate the effect of the external load by the presence of radiation load. Fig. 8(a) points out a similar graphic trend to the case A trend, but the temperature range during the first 1000 seconds is wider. By the presence of the external load, the temperature profile for each blower shows a more uniform trend due to the system ability to adapt from the presence of load source. A good point that can be noted is the less time required to maintain the ambient temperature. As the radiation load exists, the ambient temperature is only existed during first 100 seconds, which less than in case A. The almost similar phenomenon of the more uniform temperature distribution is also existed in

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the passenger’s area. Nevertheless, some fluctuate conditions are still found in those two last diagrams with a small fluctuating magnitude, compared to the previous case.

40

Temperature (qC)

35 30 25 20 15 10 5 0 0

150

300

(a)

450

600

Time (s)

750

900

1050

(b) 30 25 Temperature (qC)

20

15

10 5 0 0

150

300

450

600 750 Time (s)

900

1050

(c) FIGURE 7. Transient characteristics of temperature: (a) inside the machine room: engine, compressor, and condenser; (b) Tdb and Twb for AC blower inside the vehicle cabin; (c) Temperature distribution for each passenger’s zone inside the vehicle cabin (for case A)

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(a)

(b) 40 35

Temperature (qC)

30 25 20

15 10 5 0 0

100

200

300

400

500

600

700

800

900 1000 1100

Time (s)

(c) FIGURE 8. Transient characteristics of temperature: (a) inside the machine room: engine, compressor, and condenser; (b) Tdb and Twb for AC blower inside the vehicle cabin; (c) Temperature distribution for each passenger’s zone inside the vehicle cabin (for case B) The temperature profiles for case C are represented in Fig. 9. In this case, the vehicle was tested in full load, which means the presence of radiation load and wind were considered. The system was only able to keep the ambient temperature in about 100 seconds. Compared to the previous two cases, the higher of cooling load for the vehicle affects the smaller duration of ambient temperature. In the Fig. 9 (a), the temperature profile of the refrigeration components, such as the discharge and suction of compressor, engine temperature, and condenser discharge is presented. During the measurement time, engine temperature gradually increases. Additionally, the similar trend occurs for the discharge point of compressor and condenser but the opposite trend exists for the data of compressor suction.

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(a)

(b) 40 35 30

Temperature (qC)

25 20

15 10 5 0

Time (s)

(c) FIGURE 9. Transient characteristics of temperature: (a) inside the machine room: engine, compressor, and condenser; (b) Tdb and Twb for AC blower inside the vehicle cabin; (c) Temperature distribution for each passenger’s zone inside the vehicle cabin (for case C)

CONCLUSION REMARK Performance test of the automotive refrigeration system has been conducted. The study revealed the cooling performance of the refrigeration system for automobile in tropical region. Some important notes that can be addressed from the study: for all cases, as the compressor speed increases, the refrigeration effect (Q R), compressor work, and condenser heat (Qcond ) also increases. However, due to that phenomenon, the COP decreases. The transient characteristics of temperature show that there was a stable point to reach the steady temperature. The external loads affected the automotive refrigeration characteristics, especially for the transient temperature profiles on both of refrigeration components and cabin temperature profiles. The compressor required energy also increased as the external loads were added. In all, the cooling capacity adjustment of automotive refrigeration system affects the overall cooling performances, especially for the belt driven a compressor to be not consuming a lot of energy.

ACKNOWLEDGEMENT This research is supported by Indonesia Endowment Fund for Education in the scheme of Innovative-Productive Research (RISPRO) scheme. The authors also thank to Mr. Sasmono and Mr. Arief Widiarto, the technicians from Dept. of Mechanical and Industrial Engineering UGM for the technical support. Also, Mr. Akhsanto Anandito who contributed in the graphic design of this paper.

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