Performance evaluation of hot-gas by-pass capacity control schemes for refrigeration and air-conditioning systems

The capacity control of a vapor-compression refrigeration system is investi gated by injecting hot gas and liquid refrigerant into the suction side of the compressor. Three different possibilities for the by-pass schemes are i nvestigated for HFC-134a by considering finite size of the components that are used in the refrigeration systems. The model considers the finite-tempe rature difference in the heat exchangers, thus allowing the variations in t he condenser and evaporator temperatures with respect to capacity and exter nal-fluid inlet temperatures. It is demonstrated that the compressor discha rge temperatures increase significantly when the hot-gas from the compresso r discharge is extracted and injected (without any liquid injection) direct ly into the suction side of the compressor. A comparative study is also per formed of these schemes in terms of the system coefficient of performance ( COP), operating temperatures and the refrigerant by-pass fraction as a func tion of the percentage capacity reduction. (C) 2000 Elsevier Science Ltd. A ll rights reserved.