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3.1.3. Compressor The correlation for the isentropic efficiency has been found by fitting of data obtained from the compressor manufacturer (Emerson climate technologies, 2015). A large number of values were available for several combinations of evaporation and condensation temperatures. For the same combinations the pressure ratio was defined and a diagram of the efficiency vs. the pressure ratio was thus obtained Figure 3.4. The fitting polynomial (3.18) was then extracted. The values obtained with (3.18) were compared with the experimental data available, and a relative difference between the two set of values calculated The calculated difference above mentioned allowed to obtain values closer to the real case, from the manufacturerβs data. It is assumed to be applicable to the alternative refrigerants as well. Hence, the provided correlations for R1234yf, R290, R1270 and R152a β obtained for other operating conditions β could be adjusted to be applied to the studied heat pump case. The resulting correlations for the available refrigerants, function of the pressure ratio, can be seen in Figure 3.4. π =0.0024βπ 3 β0.0363βπ 2 +0.1377βπ +0.5531 ππ πππ‘ππ πππ‘ππ πππ‘ππ (3.18) 0.80 0.70 0.60 0.50 0.40 0.30 0.20 0.10 0.00 R410A R1234yf R290 R1270 R152a Isentropic efficiency vs. pressure ratio 123456789 Pressure ratio Figure 3.4. Isentropic efficiency of compressor for different refrigerants For the refrigerants for which the correlation was not available to start with, assumptions were made. Specifically, it was assumed that R32 could operate with the same compressor efficiencies as R410A, due to its similarities in temperature and pressure levels. Concerning R1234ze(E), it was assumed to operate with the same correlation as R1234yf. -26- Ξ·isPDF Image | Next generation of refrigerants for residential heat pump systems
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