Scholarly article on topic 'Comparative Evaluation of an Automobile Air - Conditioning System Using R134a and Its Alternative Refrigerants'

Comparative Evaluation of an Automobile Air - Conditioning System Using R134a and Its Alternative Refrigerants Academic research paper on "Materials engineering"

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Abstract of research paper on Materials engineering, author of scientific article — Jignesh K. Vaghela

Abstract This research involves the theoretical aspects of R134a automobile air conditioning system. The main aim of the research is to evaluate the different alternative refrigerants as a drop in substitute of R134a theoretically. For this purpose, thermodynamic properties of different alternative refrigerants i.e. R290, R600a, R407C, R410A, R404A, R152a and R1234yf are compared to R134a. Thermodynamic evaluation of standard rating cycle of vapour compression refrigeration system is carried out. Engineering equation solver and refprop soft wares have been used for the thermodynamic analysis purpose. From thermodynamic analysis, it is derived that R1234yf is best suitable alternative refrigerants as a drop in substitute of R134a. R1234yf has lower coefficient of performance as compared to R134a; however it is best suitable alternative refrigerants as a drop in substitute because it has very low global warming potential and can be substituted in the existing automobile air conditioning system with minimum modification.

Academic research paper on topic "Comparative Evaluation of an Automobile Air - Conditioning System Using R134a and Its Alternative Refrigerants"

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Energy Procedia 109 (2017) 153 - 160

International Conference on Recent Advancement in Air Conditioning and Refrigeration, RAAR 2016, 10-12 November 2016, Bhubaneswar, India

Comparative evaluation of an automobile air - conditioning system using R134a and its alternative refrigerants

Prof. Jignesh K. Vaghelaa*

aAssistant Professor, ITM Universe, Vadodara-391510, India

Abstract

This research involves the theoretical aspects of R134a automobile air conditioning system. The main aim of the research is to evaluate the different alternative refrigerants as a drop in substitute of R134a theoretically. For this purpose, thermodynamic properties of different alternative refrigerants i.e. R290, R600a, R407C, R410A, R404A, R152a and R1234yf are compared to R134a. Thermodynamic evaluation of standard rating cycle of vapour compression refrigeration system is carried out. Engineering equation solver and refprop soft wares have been used for the thermodynamic analysis purpose. From thermodynamic analysis, it is derived that R1234yf is best suitable alternative refrigerants as a drop in substitute of R134a. R1234yf has lower coefficient of performance as compared to R134a; however it is best suitable alternative refrigerants as a drop in substitute because it has very low global warming potential and can be substituted in the existing automobile air conditioning system with minimum modification.

©2017 The Authors.PublishedbyElsevierLtd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.Org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of RAAR 2016.

Keywords: Automobile Air Conditioning System, R134a, alternative refrigerants, low GWP, R1234yf.

1. Introduction:

Since 1995, the standard refrigerant in the automobile industry has changed from R12 to R134a due to ozone layer protection measures given by the montreal protocol (1989). However, concerns about global warming have since led to the creation of the global environment change report (1997). In this report, the goal was set to reduce the emissions of greenhouse gas up to 2008.

R134a refrigerant, which is widely used in current automobile air conditioning systems, is one of the controlled substances in the kyoto protocol (1997). In United Nations, the current air conditioning system was banned for refrigerants that have a Global Warming Potential (GWP) of over 150 by 2011. In India, Higher GWP refrigerants are also going to be banned in near future. The first response to the kyoto protocol by the automobile manufacturers was thus to improve R134a systems by reducing leakage. However, efforts are being made to find an

1876-6102 © 2017 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Peer-review under responsibility of the organizing committee of RAAR 2016. doi:10.1016/j.egypro.2017.03.083

-alternative refrigerants to replace R134a due to its high GWP of 1430 [1]. Hence this study involves finding of suitable alternative refrigerants of R134a AAC system so that kyoto protocol requirements are fulfilled.

Nomenclature

AAC Automobile Air Conditioning

CFC ChloroFluoroCarbon

COP Coefficient of Performance

GWP Global Warming Potential

h specific enthalpy (kJ /kg)

HCFC HydroChloroFluoroCarbon

HFC HydroFluoroCarbon

HFO HydroFlouroOlefin

m mass flow rate (kg/s)

N Speed (rpm)

NIST National Institute of Standard and Technology

ODP Ozone Depletion Potential

P Pressure (MPa)

PR Pressure Ratio

q Heat transfer (kJ/kg)

RE Refrigerating Effect (kJ/kg)

SCD Specific Compressor Displacement (m3/kJ)

T Temperature (°c)

v Specific volume (m3/kg)

VCR Vapour Compression Refrigeration

w Work (kJ/ kg)

W Work (kW)

Subscripts

1 refrigerant inlet condition to compressor

c compressor

ca compressor actual

ci compressor isentropic

co condenser

D or 2n discharge

E evaporator

r refrigerant

sat saturation

AAC is a competitive and technology-oriented industry; so the open literature on the experimental performance of AAC systems is very limited. Because of the Montreal Protocol, some investigators determined the performance of AAC systems using refrigerants alternative to R12, which was the refrigerant widely used in AAC systems until 1994. Although the automobile industry has been using R134a as a standard replacement for CFC12 since 1994, refrigerant R134a has a very high global warming potential. Therefore, some recent studies have aimed to lower the global warming caused by the AAC systems by designing systems requiring less amounts of R134a or using CO2 or hydrocarbons or HFO as an alternative to R134a [2].

J. Steven Brown, Samuel F. Yana-Motta, Piotr A. Domanski [3] had carried out comparative analysis of an automotive air conditioning systems operating with CO2 and R134a. The analysis showed R134a having a better COP than CO2 with the COP disparity being dependent on compressor speed and ambient temperature.

S. Devotta et. al [4] has searched alternatives to HCFC-22 for air conditioners. NIST CYCLE_D has been used for the comparative thermodynamic analysis. Among the refrigerants studied (HFC134a, HC290, R407C, R410A, and three blends of HFC32, HFC134a and HFC125), HFC134a offers the highest COP, but its capacity is the lowest and requires much larger compressors.

Mahmoud Ghodbane [5] had done an investigation of R152a and hydrocarbon refrigerants in mobile air conditioning. He concluded that R152a and cyclopropane (RC270) exhibit superiority as refrigerants when compared to R134a. Pamela Reasor et al. [6] carried out a refrigerant R1234yf performance comparison investigation. Comparisons are made between R1234yf, R134a, and R410A, and simulations are conducted to determine the feasibility of using R1234yf as a replacement for R134a or R410A.

B. Takabi et al. [7] had carried out an effects of Al2O3-Cu/water hybrid nanofluid on heat transfer and flow characteristics in turbulent regime. The results indicate that employing hybrid nanofuid improves the heat transfer rate with respect to pure water and nanofuid, yet it reveals an adverse effect on friction factor and appears severely outweighed by pressure drop penalty. B. Takabi et al. [8] had also done an augmentation of the heat transfer performance of a sinusoidal corrugated enclosure by employing hybrid nanofluid. To predict the average number of nanofluid and hybrid nanofluid, two correlations have been developed. These equations are based on the modeling results and calculated by employing the classical least square method.

Kakag et al. [9] had done an analysis of convective heat transfer enhancement by nanofluids: single-phase and two-phase treatments. Despite the advantages of the mixture model, such as implementation of physical properties and less computational power requirements, some studies showed that the results of the single-phase and two-phase models are very similar. Only the main difference consists in the effect of the drift velocities of the phases relative to each other.

1.1. Objectives:

• The main aim of the project is to evaluate the different alternative refrigerants as a drop in substitute of R134a.

• To evaluate thermodynamic properties of R134a and its alternative refrigerants.

• To carry out thermodynamic evaluation of standard Rating cycle of VCR system.

2. Thermodynamic Property Analysis:

Table 1. Thermodynamic properties comparison of different refrigerants [4] [5] [6]

Refrigerants Chemical composition Molecular weight [kg/kmol] Normal boiling Point[°C] Critical Temp[°C] Critical Pressure [MPa] Safety class ODP GWP

Propane (R290) CH3-CH2-CH3 44.096 -42.09 134.6 4.23 A3 0 11

Isobutane (R600a) CH3-CH-CH3 CH3 58.12 -11.67 134.6 3.65 A3 0 3

R407C R32+R125+R134(23/25/ 52) 86.2 -43.6 86.1 4.62 A1/A1 0 1530

R410A R32+R125(50/50) 72.56 -50.5 72.5 4.96 A1/A1 0 1730

R404A R125+R134+R143(44/4/ 52) 97.60 -46.5 72.04 3.72 A1/A1 0 3300

R134a CH2FCF3 102 -26 101.1 4.059 A1 0 1430

R152a CH3-CH-F2 66.05 -25.0 113.5 45.8 A2 0 140

R1234yf CF3CF=CH2 114 -29 95 3.382 A2L 0 4

The thermodynamic properties of different refrigerants as well as safety and flammability data are described in Table 1. The saturation pressure of the different refrigerants for wide range of temperatures (between -30 and 70 °C) is compared in fig. 1. This is done by using Refprop and Engineering Equation Solver (EES) softwares. Fig. 1 depicts the variation of saturation pressure of R134a, R290, R600a, R407C, R410A, R404A, R152a and R1234yf against temperature. It is observed that R152a and R1234yf have approximately the same saturation vapour pressure as R134a. Hence system can operate with minimum modification in the existing system in case of R152a and R1234yf.

-R134a ---R407C -R152a

---R290 --- R600a ---R410A --- R404A -R1234yf

/ '' f

»Hiss 1 ''' '

-10 10 30 50

TEMPERATURE [°C]

Fig. 1. Saturation pressure Vs Temperature

3. Thermodynamic Cycle Analysis Procedure:

Fig. 2. Schematic Diagram of VCR [10]

Fig. 3. Pressure-Enthalpy Chart of VCR [10]

AAC system works on Vapour Compression Refrigeration (VCR) cycle. The representation of cycle on schematic and the p-h diagram are shown in fig. 2 and 3, respectively; when the vapour at the end of compression is assumed to -be superheated. Assuming that 1 kg of refrigerant flows in the system, we can analyse the system as follows with help of steady flow energy equation. Thermodynamic analysis is as follows [10]:

(a) Isentropic Compressor work, Wci:

Wci = h2s - h1 , kJ/kg Actual Compressor work, Wca: Wca = h2n - h1 , kJ/kg

(b) Heat rejected at the condenser, qco:

(i) (2)

qCo = h3 - h4 , kJ/kg (3)

Condenser pressure,

Pco Psat (Tco) (4)

(c) Expansion device:

h5 = h6 , kJ/kg (5)

(d) Refrigerating effect, RE:

RE = h7 - h , kJ/kg (6)

Evaporator pressure,

PE = Psat (TE) (7)

(e) COP:

COP = RE/Wca

COP = (h7-h6)/(h2n-h0 (8)

(f) Compressor Power, Wc:

Wc = mr (h2n- hi) , kW (9)

(g) Mass of refrigerant to be circulated, mr per sec:

mr =Q/qe , kJ/s (10)

(h) Specific Compressor Displacement, m3/kJ:

SCD = vi/qo (11)

• Assumptions :

Pressure drops in suction and discharge lines are neglected. Cooling capacity of evaporator is assumed to be 4 kW. Analysis is based on steady-state condition.

The size of tiny air bubbles and solid particles in refrigerant are assumed so small that they do not have a significant effect on the thermo-mechanical properties of the basic refrigerant.

4. Results and Discussion:

Table 2. Calculated thermodynamic data of R134a and its alternatives for Evaporating temperature=7.2°c, Condenser temperature= 55°c, _compressor inlet temperature=35°c_

Refrigerant Discharge Temp. T2n (°C) Pressure Ratio COP Refrigerating Effect RE (kJ/kg) Compressor Work W (kW)

R290 103.4 3.245 2.499 266.8 1.601

R600a 92.96 3.787 2.64 251.4 1.515

R407C 119.8 3.844 2.36 152.6 1.695

R410A 122.8 3.44 2.256 152.9 1.773

R404A 100.7 3.411 2.185 104.2 1.831

R134a 105.7 3.954 2.562 141.8 1.561

R152a 119.7 3.923 2.668 233.8 1.499

R1234yf 88.7 3.658 2.4 61.64 1.667

By using data of standard rating cycle and by making simulation program in EES soft-ware, the thermodynamic analysis of R134a and its alternative refrigerants is performed. This is done by varying its evaporator temperature for the given cooling capacity. Condenser temperature is 55°c and Evaporator temperature varies from 0°c to 12°c. For different evaporator temperature, the different parameters are measured. There is noticeable change in performance of different refrigerants for the same condition due to their characteristics. Table 2 presents the calculated theoretical (thermodynamic) data of R134a and its alternative refrigerants.

Fig. 4 shows the pressure ratio of R134a and its alternative refrigerants for various evaporating temperatures for TC=55°c. As shown in fig. 4, with decrease in evaporating temperature, pressure ratio increases. If the pressure ratio is higher, then the compressor efficiency is lower.

-D-R134a -H-R407C -»-R152a -6-R290 -V-R410A -1-R1234yl

2 4 6 8 10

EVAPORATING TEMPERATURE TE [°c]

Fig. 4. PR Vs Te for Tc=55°c

HI H HI

o (0 Q

-OR134a -M-R407C R152a

-ft-R290 -«-R600a -V-R410A -B-R404A -■-R1234yf

2 4 6 8

EVAPORATING TEMPERATURE TE [°c]

Fig. 5. Td Vs Te for Tc=55°c

The pressure ratio is highest for R134a and lowest for R290 for the entire range of TE in this study. This is because of higher molecular weight and normal boiling pressure of R134a compared to R290. R152a and R1234yf have lower pressure ratio compared to R134a and hence volumetric efficiencies of R152a and R1234yf are higher. Fig. 5 shows the discharge temperature of R134a and its alternative refrigerants for various evaporating temperatures for TC=55°c. As shown in fig. 5, with decrease in evaporating temperature, discharge temperature increases. For better lubricant and refrigerant stability, lower discharge temperature is beneficial. At lower discharge temperature, compressor is expected to be running at slow speed. Compressor life is higher in case of slow speed. R152a has slightly higher discharge temperature while R1234yf has lowest discharge temperature compared to R134a. Compressor life in case of R1234yf is higher.

£C O W 0) LU £C Q.

2 4 6 8 10

EVAPORATING TEMPERATURE Te [°c]

Fig. 6. W Vs Te for Tc=55°c

0 2 4 6 8 10

EVAPORATING TEMPERATURE Te [°c]

Fig. 7. COP Vs Te for Tc=55°c

Fig. 6 shows the compressor work of R134a and its alternative refrigerants for various evaporating temperatures for TC=55°c. As shown in fig. 6, with decrease in evaporating temperature, compressor work increases. Lower compressor work is desirable for better overall system efficiency. The compressor work is highest for R404A

and the lowest for R152a for the entire range of TE in this study. Compared to R134a, R1234yf has higher while R152a has lower compressor work respectively. Fig. 7 shows the COP of R134a and its alternative refrigerants for various evaporating temperatures for TC=55°c. As shown in fig. 7, with decrease in evaporating temperature, COP decreases. Higher COP is always desirable parameter for refrigerants. The COP is highest for R152a and the lowest for R404A for the entire range of TE in this study. Compared to R134a, R152a has higher while R1234yf has lower COP respectively.

4.1. Thermodynamic cycle analysis Results relative to R134a:

The summary of the derived thermodynamic data for all mentioned alternative refrigerants is presented in Table 3. The data have been derived by taking R134a as a basic refrigerant.

Table. 3. Summary of Thermodynamic cycle analysis Evaporating temperature=7.2°c, Condenser temperature= 55°c, compressor inlet

temperature=35°c

REFRIGERANT %COP RELATIVE TO R134a

COP Refrigerating effect, RE (kJ/kg) Pressure ratio Compressor Work, W (kW) Discharge temp. T2n (°c)

R290 -2.459 88.152 -17.931 2.562 -2.176

R600a 3.044 77.292 -4.224 -2.947 -12.053

R407C -7.884 7.616 -2.782 8.584 13.340

R410A -11.944 7.828 -12.999 13.581 16.178

R404A -14.715 -26.516 -13.733 17.297 -4.730

R134a 0.000 0.000 0.000 0.000 0.000

R152a 4.137 64.880 -0.784 -3.972 13.245

R1234yf -6.323 -56.530 -7.486 6.791 -16.083

• R290 and R600a (Hydrocarbons):

R290 has about 2.4% lower COP but has 17.9% lower pressure ratio compared to R134a. Hence compressor efficiency is higher. Discharge temperature is about 2.1% lower. Main advantage of R290 is having low GWP i.e. 11.Main disadvantage is that it falls in A3 safety class. Flammability of R290 is very high but it can be used if safety aspects are addressed and diminished.

R600a has about 3% higher COP and has 4.2% lower pressure ratio compared to R134a. Hence compressor efficiency is higher. Discharge temperature is about 12% lower. Main advantage of R600a is having low GWP i.e. 3 only. Main disadvantages are that it falls in A3 safety class and requires higher SCD hence larger capacity of compressor is required. It is also highly flammable but can be used if safety aspects of using R600a are addressed and diminished.

• R407C, R410A and R404A (Zeotropic mixtures):

R407C, R410A and R404A have about 7.8%, 11.9% and 14.7% lower COP compared to R134a respectively. They have about 2.7%, 12.9% and 13.7% lower pressure ratio compared to R134a respectively. Hence compressor efficiency is higher. Discharge temperature is about 13.3% and 16.1% higher in case of R407C and R410A while it is 4% lower in case of R404A. Main advantage of zeotropic mixtures are that they falls in A1 safety class. It is nonflammable refrigerants. Main disadvantages are that they are high discharge pressure refrigerants and hence pipelines connecting main components of AAC must be very reliable that can sustain high pressure. They have high GWP also.

• R152a (Hydro Fluorocarbon):

R152a (1, 1-difluoroethane) can be possible substitute of R134a if safety measures are provided. Refrigerating effect is 64.8% higher while compressor work is 3.9% lower compared to R134a. Discharge temperature is 13.2% is

-higher but COP is 4.1% higher compared to R134a. Pressure ratio is almost similar to that of R134a. Main advantages of R152a refrigerant are that it has low GWP and higher COP compared to R134a. Main disadvantage are that it is flammable refrigerant and discharge temperature is higher than R134a.

• R1234yf (HydroFlouroOlefin): R1234yf (2, 3, 3, 3-Tetrafluoropropene) is new categorical HFO refrigerant. Discharge temperature is lowest among the above all refrigerants that is 16% lower compared R134a. R1234yf has lower COP of about 6.3% compared to R134a. Pressure ratio is 7.4% lower compared to R134a. Main advantages of 1234yf refrigerant are that it has very low GWP (i.e. 4) compared to R134a (i.e. 1430 GWP) and has lowest discharge temperature. Also it can be substitute in the existing AAC system without any modification since SCD is close to R134a. Main disadvantage is that; Since R1234yf is just newly launched; its price is high in commercial market.

5. Conclusions

Thermodynamic properties of different alternative refrigerants i.e. R290, R600a, R407C, R410A, R404A, R152a and R1234yf are compared to R134a which is used in AAC system. R290 and R600a cannot be substituted in AAC system due to high flammability issue. From thermodynamic property analysis it is clear that R407C, R410A and R404A having very high saturation pressure so it cannot be used in current AAC system. R152a can be substituted of R134a if and only if safety mitigations are provided. From thermodynamic cycle analysis, it is derived that R1234yf has 6.3% lower COP compared to R134a; however it is best suitable alternative refrigerants as a drop in substitute of R134a AAC system because it has very low GWP and can be substituted in the existing AAC system with minimum modification. This study is useful to design engineers of AAC system for future aspect.

Acknowledgments

The author would like to thank Dr. Ragesh G. Kapadia, Principal, SVMIT, Bharuch, Gujarat, India for their valuable input during the course of this investigation. The author would also like to thank Mr. Chintan Lad, AP, S.S. Agrawal College, Navsari; Mr. Harshit Trivedi, AP, ITM Universe, Vadodara; Mr. Ravi Parekh, Lecturer, KJP, Bharuch and Mr. Dhaval Prajapati, Engineer, IPR, Ahmedabad for their help in this study.

References

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[2] Alpaslan Alkan, Murat Hosoz, 2010. Comparative performance of an automotive air conditioning system using fixed and variable capacity compressors , International Journal of Refrigeration 33, p. 487-495.

[3] J. Steven Brown ,Samuel F. Yana-Motta , Piotr A. Domanski, 2002. Comparative analysis of an automotive air conditioning systems operating with CO2 and R134a, International Journal of Refrigeration 25, p. 19-32.

[4] S. Devotta, A.V. Waghmare, N.N. Sawant, B.M. Domkundwar, 2001. Alternatives to HCFC-22 for air conditioners, Applied Thermal Engineering 21, p. 703-715.

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[6] Pamela Reasor,Vikrant Aute ,Reinhard Radermacher, 2010. Refrigerant R1234yf Performance Comparison Investigation, International Refrigeration and Air Conditioning Conference, School of Mechanical Engineering, Purdue University, Purdue e-Pubs.

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[8] B. Takabi, S. Salehi, 2014. Augmentation of the Heat Transfer Performance of a Sinusoidal Corrugated Enclosure by Employing Hybrid Nanofluid, Advances in Mechanical Engineering, Vol. 6, 147059.

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[10] http://nptel.iitk.ac.in/courses/Webcoursecontents/IIT%20Kharagpur/Ref%20and%20Air%20Cond/pd^RAC%20Lecture%2 10.pdf