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400 Commonwealth Drive Warrendale PA 15096 0001 U S A Tel 724 776 4841 Fax 724 776 5760 Web www sae org SAE TECHNICAL PAPER SERIES 2003 01 0731 R 152a Refrigeration System for Mobile Air Conditioning James A Baker Mahmoud Ghodbane Lawrence P Scherer and Prasad S Kadle Delphi William R Hill General Motors Corporation Stephen O Andersen U S Environmental Protection Agency Reprinted From Advances in Automotive Climate Control SP 1733 2003 SAE World Congress Detroit Michigan March 3 6 2003 All rights reserved No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photocopying recording or otherwise without the prior written permission of SAE For permission and licensing requests contact SAE Permissions 400 Commonwealth Drive Warrendale PA 15096 0001 USA Email permissions sae org Fax 724 772 4028 Tel 724 772 4891 For multiple print copies contact SAE Customer Service Tel 877 606 7323 inside USA and Canada Tel 724 776 4970 outside USA Fax 724 776 1615 Email CustomerService sae org ISSN 0148 7191 Copyright 2003 SAE International Positions and opinions advanced in this paper are those of the author s and not necessarily those of SAE The author is solely responsible for the content of the paper A process is available by which discussions will be printed with the paper if it is published in SAE Transactions Persons wishing to submit papers to be considered for presentation or publication by SAE should send the manuscript or a 300 word abstract of a proposed manuscript to Secretary Engineering Meetings Board SAE Printed in USA 2003 01 0731 R 152a Refrigeration System for Mobile Air Conditioning James A Baker Mahmoud Ghodbane Lawrence P Scherer and Prasad S Kadle Delphi William R Hill General Motors Corporation Stephen O Andersen U S Environmental Protection Agency ABSTRACT In recent years climate protection has become as important as ozone layer protection was in the late 1980 s and early 1990s Concerns about global warming and climate change have culminated in the Kyoto Protocol a treaty requiring its signatories to limit their total emission of greenhouse gases to pre 1990 levels by 2008 The inclusion of hydrofluorocarbons HFCs as one of the controlled substances in the Kyoto Protocol has increased global scrutiny of the global warming impact of HFC 134a called R 134a when used as a refrigerant the current mobile air conditioning refrigerant Industry s first response was to begin improving current R 134a systems to reduce leakage reduce charge and increase system energy efficiency which in turn reduces tailpipe CO2 emissions An additional option would be to replace the current R 134a with a refrigerant of lower global warming impact This paper documents the use of another HFC R 152a in a mobile A C system It compares its cooling and energy performance with that of a comparable R 134a system This paper also highlights the environmental benefit of R 152a and pinpoints safety issues that need to be addressed in the future INTRODUCTION This work is the product of a cooperative effort sponsored by General Motors Delphi and the U S EPA The intent was to demonstrate the potential use of R 152a in a mobile air conditioning system The work included the building and testing of a prototype system wind tunnel testing on a production vehicle for performance and ride testing the vehicle at the 2002 SAE Alternate Refrigerants Symposium 1 This paper is complemented by a prior SAE publication 2 in 1999 by one of the authors wherein the potential of R 152a was assessed via system simulation techniques That paper provides valuable supporting information on many of the properties and characteristics of R 152a that make it suitable for use in mobile A C systems WARNING HFC 152a is a flammable refrigerant and should not be used in systems unless specifically designed for its use FF HCC F HF Molecular Weight 102 1 1 1 2 Tetrafluoroethane Molecular Weight 66 1 1 Difluoroethane Similar Materials Compatibility Chemically Similar Environmentally VeryDifferent GWP 1300 GWP 120 94 Reduction in Climate Impact from Refrigerant Change not including energy savings HH HCC F HF Why R 152a R 134a R 152a Table 1 R 134a and R152a Chemical Environmental Comparison The use of R 152a was discussed in a cursory manner during the search for an alternative to CFC 12 for mobile A C in the 1980 s in response to concerns about protection of the Earth s ozone layer Such discussions however quickly moved to selecting and developing systems suitable for R 134a Recent concerns about R 134a emissions in Europe have led to unsuccessful attempts to ban all HFCs in several European countries Some have pending regulations aimed at reducing both Copyright 2003 SAE International HFC refrigerant emissions and tailpipe emissions from the fuel burned to power the air conditioning The potential use of R 152a as a replacement for R 134a presumes that nations will ultimately differentiate greenhouse gases on the basis of their environmental performance not simply by their chemical class as they seek to reduce emissions R 152a offers chemical properties and refrigerating characteristics very similar to those of R 134a but with dramatically lower climate impact While Table 1 provides a brief introductory comparison of R 152a and R 134a reference 2 offers more in depth analysis of both refrigerants WARNING HFC 152a is a flammable refrigerant and should not be used in systems unless specifically designed for its use Compressor Condenser Evaporator Liquid Line Solenoid Shut off Valve normally closed Suction Line Solenoid Shut off Valve normally closed Expansion Device Accumulator Shut off valves Figure 1 System Description COOLING PERFORMANCE COMPARISON A full size sedan production vehicle served as the base vehicle for this testing The vehicle was first tested with the original equipment OE R 134a system then equipped and tested with an R 152a system Components used to convert from R 134a to R 152a were all current production R 134a components chosen to represent more up to date technology and to reduce the total system refrigerant charge The expansion device was modified to account for the different thermal physical properties of R 152a In addition solenoid operated normally closed shut off valves were placed on the inlet and outlet to the evaporator and electrically connected to the air bag system and compressor circuit Figure 1 is a pictorial representation of the prototype R 152a system Heat exchanger face areas and airflows for all testing were identical for both systems and all testing was performed in the same wind tunnel The system refrigerant charges including reserve charge were 0 908kg 2 lbs for the R 134a system and 0 454 kg 1 lb for the R 152a system WARNING HFC 152a is a flammable refrigerant and should not be used in systems unless specifically designed for its use Discharge A C Temperature Comparison 100 0F x 40 R H Ambient 38 0C x 40 R H Full Size Sedan 30 50 70 90 110 130 150 0102030405060 Time min Temperature 0F Average Breath Average Discharge R 152aR 134a Soak Temperature 1 66 54 43 32 21 10 0C 40 kph Recir Air City Traffic Recir Air 40 kph Recir Air 50 kph Recir Air 100 kph Outside Air Idle Recir Air Idle Outside Air Figure 2 Performance Comparison Figure 2 represents a typical wind tunnel test data that simulates the cooling down of a parked hot vehicle soaking in the sun The soak temperature is the interior breath temperature reached after parking the vehicle for more than one hour in the hot sun Average breath temperature is the average temperature at the driver and passenger head levels The average discharge temperature is the average temperature of the air coming out of the A C vents The data shows that the R 152a system has equal or better cooling performance than the R 134a system WARNING HFC 152a is a flammable refrigerant and should not be used in systems unless specifically designed for its use Compressor Pressure and Discharge Temperature Comparison 100 0F x 40 R H Ambient 38 0C x 40 R H Full Size Sedan 10 60 110 160 210 260 0102030405060 Time min Pressure psig 50 100 150 200 250 300 350 400 40 kph Recir Air City Traffic Recir Air 40 kph Recir Air 50 kph Recir Air 100 kph Outside Air Idle Recir Air Idle Outside Air Discharge Pressure Suction Pressure Discharge Temperture 0F 69 149 414 758 1103 1448 1793 0C 121 66 93 38 10 kPa R 152aR 134a Figure 3 Compressor Thermal Characteristics Figure 3 depicts the thermal characteristic behavior of the two refrigerants during the tests As expected from its saturation properties an R 152a system shows lower suction and discharge pressures than R 134a system while it exhibits higher compressor discharge temperatures than the R 134a baseline system Lower discharge pressures would allow longer idles without A C cut offs due to high discharge pressures However it may be necessary to assess the effect of higher operating temperatures on current discharge hose materials joint seals and compressor durability In summary R 152a systems can provide the same or better comfort cooling as current OE R 134a systems ENERGY COMPARISON A full size sedan production vehicle equipped with an original equipment OE R 134a system served as the base vehicle for this testing a b Table 2 High Load Tests All Testing in Ouside Air Mode The vehicle was first tested with the OE R 134a system then evacuated recharged and tested with R 152a in the same wind tunnel In this test the components were kept the same for both systems except for the desiccant and the expansion device As previously stated the heat exchangers and their respective airflows remained identical throughout both series of testing These tests were primarily intended to directly compare the energy usage of the two refrigerants when tested using identical components and subjected to the same conditions and constraints As expected the critical charges for these systems were proportional to their molecular weights Figures 4 5 compare the energy use of R 134a versus R 152a expressed as their respective mechanical coefficients of performance COP versus ambient temperature and road speed Note that in all cases the COP of R 152a exceeded that of R 134a indicating that less energy was required for operation It should also be noted that the COP computation is based on the measured compressor torque instead of the change in refrigerant thermal properties across the compressor The measured torque is a more accurate means of determining the compressor energy requirements Table 2 a and b show the cooling performance of the R 152a system to be superior to that of the R 134a system at road speeds and equal at idle The R 152a system outperformed the R 134a on cooling performance and did while using less energy The environmental importance of this energy saving is discussed in the next section WARNING HFC 152a is a flammable refrigerant and should not be used in systems unless specifically designed for its use Ambient Sweep of Mechanical COP at Different Vehicle Speeds in Outside Air Mode 115 0F x 25 R H 46 0C x 25 0 000 0 200 0 400 0 600 0 800 1 000 1 200 1 400 1 600 1 800 30 mph 48 kph 50 mph 80 kph 70 mph 113 kph Vehicle Speed COP R134aR152a 11 1 11 4 9 100 0F x 40 R H 38 0C x 40 0 000 0 500 1 000 1 500 2 000 2 500 30 mph 48 kph 50 mph 80 kph 70 mph 113 kph Idle Vehicle Speed COP R134aR152a 9 7 9 7 12 1 17 3 Mechanical COP System Air Cooling Capacity Measured Compressor Shaft Power 81 0F x 55 R H 27 0C x 55 0 000 0 500 1 000 1 500 2 000 2 500 30 mph 48 kph 50 mph 80 kph 70 mph 113 kph Idle Vehicle Speed COP R134aR152a 3 5 2 6 8 4 1 8 Figure 4 Energy Comparison at Various Ambients ENVIRONMENTAL CONSIDERATIONS The substitution of R 152a for R 134a would result in a dramatic improvement in the climate impact of mobile A C systems The much lower greenhouse gas global warming impact of R 152a GWP 120 for R 152a versus GWP 1300 for R 134a combined with its lower system charge 35 to 40 less than R 134a system would reduce the system s climate impact by almost 94 According to the Mobile Air Conditioning Society MACS 3 R 134a emissions are estimated to be approximately 96 grams per year with refrigerant recycling during service and recovery during scrap Assuming R 152a emissions would be the same 96 R 152aR 134aR 152aR 134a 37 99 37 99 38 100 37 99 1323 192 1452 210 6 1361 197 1456 2 211 88 190 76 169 97 207 79 174 41 106 41 106 40 104 40 104 13 56 15 59 12 54 14 58 233 33 8 289 6 42 214 31 274 4 39 8 Evap Out kPag psig 48 kph 30 mph 80 kph 50 mph Comp Out kPag psig Comp Out 0C 0F Blower Air Out 0C 0F Average A C Front 0C 0F Ambient 38 0C x 40 R H 100 0C x 40 R H Grille Air 0C 0F R 152aR 134aR 152aR 134a 37 99 37 99 50 121 54 129 1331 4 193 1541 224 1655 240 2176 7 315 7 112 233 98 208 89 193 89 193 39 103 39 103 58 137 61 142 12 54 13 56 23 73 26 79 204 29 6 233 33 8 391 6 56 8 502 6 73 Evap Out kPag psig 113 kph 70 mph Idle Comp Out kPag psig Comp Out 0C 0F Blower Air Out 0C 0F Average A C Front 0C 0F Ambient 38 0C x 40 R H 100 0C x 40 R H Grille Air 0C 0F grams of R 152a would be equivalent in global warming impact to 1 3 gallons of fuel use Compared to R 134a systems of equal weight the fuel savings due to lower energy requirements of R 152a systems would completely counterbalance the climate impact of R 152a emissions Thus climate impact of today s R 134a refrigerant emissions in mobile A C systems would be completely offset by substituting R 152a for R 134a WARNING HFC 152a is a flammable refrigerant and should not be used in systems unless specifically designed for its use Mechanical COP Variation with Ambient in Outside Air Mode Vehicle Speed 30 mph 48 kph 0 000 0 500 1 000 1 500 2 000 2 500 Ambient COP R134aR152a 81 0F x 55 R H 27 0C 100 0F x 40 R H 38 0C 115 0F x 26 R H 46 0C 3 5 9 7 11 1 Vehicle Speed 50 mph 48 kph 0 000 0 500 1 000 1 500 2 000 2 500 Ambient COP R134aR152a 81 0F x 55 R H 27 0C 100 0F x 40 R H 38 0C 115 0F x 26 R H 46 0C 2 6 9 7 11 5 Vehicle Speed 70 mph 113 kph 0 000 0 200 0 400 0 600 0 800 1 000 1 200 1 400 1 600 1 800 Ambient COP R134aR152a 81 0F x 55 R H 27 0C 100 0F x 40 R H 38 0C 115 0F x 26 R H 46 0C 1 8 17 3 9 Vehicle Idle 0 000 0 500 1 000 1 500 2 000 2 500 Ambient COP R134aR152a 81 0F x 55 R H 27 100 0F x 40 R H 38 8 4 12 1 Figure 5 Energy Comparison at Various Road Load Conditions Figure 6 shows a Life Cycle Climate Performance LCCP analysis of some of the proposed alternatives to the current R 134a system This is an update of the presentation made in 1999 at the Earth Technologies Forum 4 that incorporates R 152a in this analysis LCCP takes into account the energy and refrigerant emissions from all phases of manufacturing use servicing recycling and scrap throughout the life cycle of the A C system The figure compares the baseline R 134a system to an enhanced R 134a system and to systems using R 152a and R 744 carbon dioxide in different climates operated under simulated drive cycle conditions for those locations The drive cycles and ambient profiles are specific for these locales and the same as those used in reference 4 The enhanced R 134a system assumes a 50 reduction in the leakage rates from the baseline R 134a system used in 4 and a 30 improvement in efficiency Recently published results of the SAE Alternative Refrigerant Cooperative Research Program 6 indicate a 10 to 47 improvement in COP between an R 134a production system and an enhanced R 134a system The R 152a system is shown as having the lowest climate impact of any alternative refrigerant system under consideration to date This system was by no means optimized The same improvements that were applied to the enhanced R 134a system could be applied here as well These systems are expected to improve for better environmental and cooling performance A C SYSTEM CONSIDERATIONS The similarity in chemical properties and vapor pressures between R 152a and R 134a allows the use of the current system components This can be a significant advantage because it offers the potential for flexible manufacturing on a continuous basis and or could ease the transition for those wishing to change to R 152a Other than system control settings the only modification foreseen at this time is changing the desiccant The environmental acceptability and the increase in cooling performance could be further improved with more efficient compressors more effective heat exchangers and higher quality fittings to reduce leakage On the system operating side the adoption of an energy efficient system 5 is highly recommended There are significant environmental and economical values in carrying such improvements WARNING HFC 152a is a flammable refrigerant and should not be used in systems unless specifically designed for its use LCCP Analysis Comparison of R 134a R 134a enh R 152a and R 744 Vehicle A C Systems Versus Climate 01000200030004000500060007000 R134a R134a enh R152a R744 R134a R134a enh R152a R744 R134a R134a enh R152a R744 Direct emissions Indirect emissions Frankfurt Phoenix Tokyo LCCP kg of Equivalent CO2 Figure 6 LCCP Analysis Vehicle A C Systems Versus Climate SAFETY CONSIDERATIONS R 152a is mildly flammable and is listed by the American Society of Heating Refrigerating and Air Conditioning Engineers ASHRAE as a Class A2 refrigerant defined as being of low toxicity and lower flammability than Class A3 which comprises hydrocarbons such as propane As a reference R 134a is Class A1 low toxicity and non flammable Since there is no prior experience in employing R 152a as a refrigerant in mobile air conditioning systems practices from other applications of R 152a were examined In particular the release of R 152a used in aerosol products is comparable to the quantity and rate of leakage that could occur in a failed or damaged mobile air conditioning R 152a referred to by aerosol product manufacturers as HFC 152a or 1 1 difluoroethane is commonly used as a propellant and solvent ingredient in aer