Experimental study on system characteristics of vapor compression refrigeration system using small-scale, gas-bearing, oil-free centrifugal compressor

Small-scale refrigeration centrifugal compressors hold the potential for superior efficiency compared to currently used positive displacement compressors. However, traditionally, centrifugal compressors have been employed in large refrigeration systems with cooling capacity of several hundred kilowatts or more. Conversely, the application of small-scale centrifugal compressors in smaller refrigeration systems, with cooling capacity in the tens of kilowatts, has largely remained theoretical, lacking practical experimental studies. For a better understanding of the operational characteristics of such systems, this study constructed a 45 kW R245fa refrigeration system test bench based on the small-scale oil-free centrifugal compressor utilizing gas foil bearings. The experimental investigation analyzed the impact of refrigerant charge amount, compressor speed, and coolant flow rate on system performance. Results indicate that the system achieves its peak cooling capacity of 49.73 kW with a system COP of 3.64 at 65,000 rpm. Moreover, at 50,000 rpm, the system demonstrates its highest system COP of 4.23 with a cooling capacity of 26.07 kW. In comparison to traditional positive displacement compressor refrigeration systems, it exhibits higher energy efficiency. Additional simulation studies were conducted to evaluate the effects of substituting R1233zd(E) for R245fa on the system performance and to assess the feasibility of such a substitution.