PRACTICAL EXPERIENCE WITH AN ALTERNATIVE TO R-22 BASED ON R-32lR /R a. R E Low, B E Gilbert, T W Dekleva.

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1 PRACTICAL EXPERIENCE WITH AN ALTERNATIVE TO R-22 BASED ON R-32lR /R a R E Low, B E Gilbert, T W Dekleva IC1 Klea ABSTRACT IC1 Klea has developed HFC alternatives to R-22 and R-502 which include ternary mixtures ( R-32, R-125 and R-l34a. Performance of these refrigerants has been evaluated by theoretical studies, calorimetry, field trials and retrofits. The paper covers the topics of blend design, theoretical and practical performance data, and practical experience of retrofitting systems to the alternatives. The paper illustrates the importance of considering behavior of alternative refrigerants in all parts of a refrigeration system, as opposed to relying on a single test method or rating point in isolation. The issues of temperature glide and servicing of zeotropic refrigerants are discussed. Studies on system leakage are used to illustrate that these refrigerants can be used and serviced with minimal alterations to existing practices. INTRODUCTION The need for alternatives to the CFC refrigerants R-12 and R-502 is well understood; complete phaseout of these refrigerants will occur in Europe at the end of The replacement for R-12 in most applications is now accepted as R-134a7 however there is no singlc fluid which directly replaces R-502. This has resulted in the development of a number of alternatives to R-502, including the single refrigerants R-22 and R-717. Legislation is now also in place in several countries to control the production and use of HCFC refrigerants; of which the most common is R-22. The range, diversity and variation in si2 of equipment using R-22 is considerable, and as a result R-22 will play an important and valuablt role for some years to come. Nonetheless it should be realized that eventually HCFCs too will t- phased out; in this context it is prudent to develop alternative medium-temperature refrigerant options now. IC1 Klea has developed a range of zeotropic or blended HFC refrigerants as long-term alternatives to R-502 and R-22. This paper discusses the design, performance and experience of working with these HFC refrigerants; it is demonstrated that they offer viable and energy eficier options to refrigeration and air conditioning system designers. 154

2 DESIGN OF ALTERNATIVE REFRIGERANTS ICI Klea has developed three refrigerant blends as alternatives to R-502 and R-22 with the aim of providing HFC refrigerants with a close match of properties to the existing fluids. This approach is intended to give the industry refrigerants which require little or no redesign for their use, and also to provide the ability to retrofit systems, should if required. The refrigerants are GEA 407A and KLEA 407B for traditional R-502 applications and KLEA 66 in traditional R-22 applications. (The ASHRAE SSPC-34 recommendation that the blend marketed as KLEA 66 be designated R-407C is currently in public review.) The key characteristics to be matched by an alternative refrigerant are many: capacity, energy efficiency, compressor discharge temperature, pressure levels, toxicity and nonflammability. The effect of the components in a mixture are summarized, relative to R-22, in the following table: I Component lir-134a Flammability,Capacity Energy Discharge Efficiency Temperature Higher Comparable Comparable Comparable Lower Lower (No Lower Higher Lower Condenser Pressure Higher Comparable Lower Table I: Effect of Rtfrigerzrtit Coniporietits oti Zwtropc Propertics Relative lo R-22 It is readily seen that a mixture of all three components is required to achieve a match to the properties of R-22. COMPARISON OF REFRIGERANT PERFORMANCE There are four basic ways of comparing performance of different refrigerants in a given application: Theoretical studies (using thermophysical tables and computer simulation) Compressor calorimetry System calorimetry Field tests (in a specific application) All four methods are required in order to build up a complete picture of the relative performance of refrigerants in differing duties and equipment designs. The theoretical comparisons are most useful for identifjing ways to optimize performance by showing the sensitivity of refrigerant performance to parameters such as subcool and pressure ratio. Compressor calorimetry provides a picture of the compressor efficiency however it does not reveal how a system design will behave using different refrigerants. The most accurate "spot" representation of a unit's performance is in a system calorimetry test; however yet another dimension of knowledge is provided by a field trial. In a field trial the 155

3 "real world" effects of seasonal performance, load variations and stability of operation can all be assessed. It is accepted that the accuracy of measurement will generally be lower for this testing. Although all of these tests are equally important, this paper will focus on field trial results; laboratory calorimetry results are available from the AREP testing program or from compressor manufacturers' rating tables. EFFECT OF ZEOTROPIC TEMPERATURE GLTDE ON PERFORMANCE The temperature glide effect characteristic of zeotropes was thought by some to make the use of such refrigerants difficult, in fact this has been found to be untrue in the course of ICI's trialing program. The observed temperature glide in a system heat exchanger is a function not only of the properties of the mixture but also of pressure drop and of the heat exchanger geometry. These last two effects will also affect the evaporation temperature of single fluids, in fact it has been possible to measure distinct temperature glides with R-22 because of these effects IC1 has experienced no problems caused by temperature glide in the course of field trial work providing the presence of glide is recognized and allowed for in selecting subcool and superheat values All major refrigerant manufacturers including IC1 now supply zeotropic refrigerants to the industry, in large part as service refrigerants. In the US alone, thousands of technicians are trained in safe handling ofzeotropes A growing quantity of information is available in the technical literature to enable service engineers and system designers to accommodate the glide in their work. The utilization of temperature glide of refrigerants to enhance cycle efficiency offers some promise; this is the subject of active research by many and will be discussed in future papers. HANDLING AND SERVICING OF ZEOTROPIC REFRIGERANTS Handling Of Zeotropic Refrigerants While we have been involved in several high profile new installations (such a Cadbury's limited 3.5MW refrigerated warehouse in Bournville, England), the majority of field trials carried out in ICI's trial program have involved the retrofit of existing systems from R-22 to the HFC alternatives. Wherever possible the handling of refrigerant has been entrusted to service personnel rather than IC1 technicians. This exercise has enabled an assessment of the degree of difficulty posed in the handling techniques required for correct use of zeotropes. The major difference in handling zeotropes is that the refrigerant should be transferred from the storage cylinder to the system from the liquid side. This is important in order to preserve the composition ratio of the refrigerant in the cylinder and in the system. If an intermediate charging vessel is used to hold the whole charge for a system then this may be charged in as vapor, providing that the entire contents of the intermediate cylinder are charged to the system. Charging to the suction line should be carried out with care, using a needle valve, restrictor device or capillary tube to ensure vaporization of the liquid from the liquid side of the cylinder. These techniques have been proven acceptable in field trials. 156

4 Condenser pressure P a Evaporator pressure Pressure ratio PSig Differential Leakage A major concern shared by many about the introduction of zeotropic refrigerants was the potential for the mixture to change composition in a system. It was thought that any change in composition would lead to significant loss of performance and difficulty in servicing,, ICI has developed a refrigeration system model which enables estimation of the refrigerant composition circulating in a system from knowledge of the charge size, system dimensions and operating conditions. Details of the basic model have been described previously. This model has further been extended to allow estimation of the effect of so-called "differential leakage" on system performance. Studies carried out using this model, supported by our own laboratory trials and the trials of others, have shown that for direct-expansion evaporator systems where no accumulator is present there is little composition shift during operation. The presence of a suction accumulator can however act to enrich the circulating composition in R-32, leading to a slightly higher capacity than would otherwise be expected. The only modes of leakage which will produce a selective leak of R-32 and R-125 are: selective leak of accumulator vapor, or a static vapor leak durinz shutdown. The effect of leakage in both modes is to reduce capacity of the refrigerant by 3-9% depending on the number of leakhecharge cycles. In this scenario energy efficiency, discharge temperature and pressure ratio are essentially unaffected by these leaks. The result of an evaporator vapor leak for a typical DX systetn running with KLEA 66 is shown in Figure 1. Here the conditions have been chosen to exaggerate the fractionation by using a low evaporator temperature (-22 F) and a very high subcool. The simulation progressively removes mass from the system until the condenser is wholly depleted of liquid, then recharged with original composition refriserant. Table 2 presents the calculated performance data before and after the leak. Composition II I 1 23/25/ /23.3/55 I (R-32/R- 12" 134a) 22/24154 I/ 29 I Energy Eficiency Ratio BTUIW. hr Refrigeration Capacity 100% 97.1% 98.1% Power Consumption Discharge Temperature OF 100% % %

5 The effect of repeated leakhecharge cycles on KLEA 66 is illustrated in Figure 2. This shows the change in capacity as a result of repeated 50% system vapor leakage at ambient temperature. This simulates the effect of a leak when shut down. The calculation is conservative because the assumption is made that the system is 90% fill of liquid; in practice the liquid volume fraction of a system will be lower (maybe as low as 10%) and this will lessen the effect of the leak. The capacity drops on repeated leakhecharge cycles approaches an asymptotic value of approximately 91% of the original performance. As in the previous study the energy efficiency, discharge temperature and pressure ratio are unaffected. The reason for the asymptote is understood; eventually the refrigerant composition is altered so that the vapor leaking is of the same composition as the original blend composition. By comparison, at a liquid volume fraction of 20% the asymptotic capacity is 92-93%. Practical measurements of leakage effects have been carried out which validate the results of this model. Further details are published in the IC1 technical literature [2]. PERFORMANCE OF KLEA 66 IN FIELD TRIALS KLEA 66 has been installed in a wide range of field trials covering all major refrigeration and air conditioning applications. Some detailed analyses of differing blend formulations and the effect of composition on performance have been published previously. A preliminary report on progress of field trials using these zeotropes has also been published. In this paper some of the more noteworthy results of recent trials are summarized. Case Study 1 : Supermarket Refrigeration This installation was carried out in spring 1994 in the Netherlands, by the Dutch firm Hougkoeling. A new supermarket was designed around the use of KLEA 66 in both medium temperature and low temperature refrigeration packs, using semi-hermetic reciprocating compressors. The low temperature cabinets maintain -8 F space temperatures, while the medium temperature racks maintain space at 32 F. In total, three cold rooms and 10 display counters are maintained by the system; they continue to provide valuable data on the performance of the refrigerant. Full data will be published separately. Case Study 2: Fresh Produce Warehouse This installation is a produce distribution center in the United Kingdom. Owned by Woods Distribution, it provides storage facilities for all the major British food retailers, storing fruit and vegetables in a carefully-controlled climate with close temperature and humidity control. The refrigeration system is built around racks of Frascold compressors, with a total charge of approximately 2 tons of KLEA 66. The warehouse floor area is in excess of 80,000 ftz. The system was installed in February-March 1994 and is running within specification. Performance and condition of the refrigerant and polyol ester lubricant is now being assessed prior to publication of further results. 158

6 Study 3 : Water Chiller 7 'est - R-22 KLEA 66 (Mean) evaporator temperature (Mean) condenser lemperatnre OF "F Degree of liquid subcooling OF Measured capacity BTU/hr 05, ,300 Average power consumption' SIMILAR SIMILAR Evaporator pressure PSk Condenser pressure psig Table 3: Perfonmatice of Water Chiller in Test CONCLUSIONS ICI's refrigerant, KLEA 66 is now in use in a wide range of applications and system designs, where much valuable experience in the use of zeotropes is being gained. The value of field tests as an aid to the industry is shown by the resulting exposure of system design effects on refrigerant performance. The refrigerant has proven to be effective in service and robust towards leakage. Providing that the appropriate charging procedures are followed there is little difference between use of KLEA 66 and any single component refrigerant. IC1 will continue to progress field trials in new and existing equipment throughout the world in an effort to gain real world information in Support of the industries progression into the HFC alternatives for R-12, R-22 and R-502. References 1. Corr, S; Murphy, F T; Wilkinson, S; "Composition shifts of zeotropic H refrigerants in service", submitted to ASHRAE Transactions, June IC1 Klea: "KLEA 66 Case Study: Performance and Leakage Simulation, pub. IC1 Klea

7 ~~ - 3. Corr, S: Gilbert, B E; Dekleva, T W; Low, R E; Murphy, F T; Davies, G; "Trials with zeotropic refrigerants as replacements for R-22 in an instrumented glycol-water chiller"; Proceedings of the 1994 International Refrigeration Conference at Purdue University 4. Carpenter, N E; Low; R E; Lindley, A A; "Practical Experience with Zeotropic Refrigerants" in Refrigerants Beyorid the Crisis, pub. Institute of Refrigeration, London 1993 Figure 1: Variation of Charge Corn position Evaporator Vapor Leak Charge Weight Fraction Fraction of original charge Refrigerant: KLEA 66 Cycle conditions: -22/122"F 100 R R-134a -_t_ R-125 Figure 2: Repeated Leak/Recharge Effects KLEA 66: static lcak at 25 "C Capacity, Relative to 0 riginal Fill 1.05 I 1!- I 90% fill 0.8 n 75 - Original 1st leak 2nd leak 3rd leak 4th leak 5th leak Number of leaks Conditions: -1 0/45"C, 5 C superheat, 0 C subcooling As Charged: 23/25/52 wt%; 50% removal of chargc 160