Characterization, Scroll compressor, Vapor-injection, Calorimetric bench
Vapor-injection compressor technology is being used in refrigeration systems and heat pumps working at large differences between evaporating and condensing temperatures. However, there are no published standards for the characterization of this kind of compressors. Calorimetric benches are widely used to characterize compressors, nevertheless, the calorimetric benches, as known, cannot be used directly to characterize vapor-injection compressors, since the refrigerant conditions at the injection port are defined by the injecting temperature and the intermediate pressure. In addition, these intermediate conditions depend critically on the way in which the injection is performed (economizer, flash tank, liquid injection, etc.). Therefore, the characterization process of this type of compressors is more complex. In this paper, a methodology for characterizing vapor-injection compressors is proposed. The method allows measurement of vapor-injection compressors in a typical calorimetric test bench after implementing some minor modifications in order to incorporate the injection line. With these modifications, the system is capable of independently controlling the intermediate pressure and the injection temperature. The proposed methodology has been evaluated with a vapor-injection scroll compressor (of 17.1 m3/h) using R407C as a refrigerant. The measurement results and the performance parameters of the vapor-injection scroll compressor are presented. A simple correlation to estimate the injection mass flow rate as a function of the intermediate pressure has been found, that can be used to correlate the experimental results with high accuracy for several operating conditions. The advantages of the proposed methodology are the better control of the intermediate compression conditions and the possibility of testing vapor-injection compressors in a wide range of operating conditions.