Some Thermodynamic Performance Test Results of Refrigerant 134a

As part of an ongoing investigation into environmentally acceptable alternatives to the CFC refrigerants a series of tests have been completed comparing the thermodynamic performance of Rl34a with Rl2. The tests were carried out under controlled conditions in a well instrumented water/water heat pump test facility, using an open-drive reciprocating compressor and counter flow heat e%changers. Based on the compressor design and chosen cycle conditions theoretical predictions of evaporator capacities for these two fluids indicate that a crossover point should occur at a particular evaporating temperature, with the corresponding capacity of Rl34a being less than Rl2 below that point and greater than R12 above the crossover. This prediction has been verified from the experimental test results. The test data are also used to compare other important performance characteristics of Rl34a and Rl2 including coefficients of performance (COPs), refrigerant mass flows, and volumetric refrigeration effects. The paper also includes a brief description of the test facility and the measurement techniques used. The test results are representative of various refrigeration cycle conditions and cover an evaporating temperature range from -4°F (-20°C) to 50"F (lO"C), with a constant condensing temperature of 122"F (50°C). The degree of subcooling and the superheat at compressor inlet were maintained constant throughout the tests. INTRODUCTION Some preliminary test measurements conducted at this laboratory and reported previously (Linton and Snelson 1989) indicated that lower overall cycle efficiencies should be expected for refrigerant Rl34a when considered as a drop-in substitute for R12. For convenience purposes those tests were carried out in a small prototype exhauSt air heat pump (EAHP) whose charge requirements were consistent with the small sample quantity of R134a available at that time. The design characteristics of the EAHP (Linton 1986) are such that the refrigerant evaporating temperature remained approximately constant over the range of ambient outdoor air temperatures used. Thus the early EAHP performance comparison tests were applicable over a very narrow band of evaporating temperatures around 40"F (4.4°C). · In the current series of tests reported here a highly instrumented water/water heat pump test facility was used to provide a more detailed comparison of the thermodynamic performances ofR12 and Rl34a. The flexibility oftbis equipment enabled the investigation to cover a broad range of evaporating temperatures representative of the normal span of conditions anticipated in refrigeration and air-conditioning system applications. Theoretical performance comparisons conducted by others (Wilson and Basu 1988)