2ND-LAW-BASED THERMODYNAMIC ANALYSIS OF HOT-GAS, BYPASS, CAPACITY-CONTROL SCHEMES FOR REFRIGERATION AND AIR-CONDITIONING SYSTEMS

The automatic hot-gas by-pass technique is applied to reduce the capac ity of refrigeration and air-conditioning systems when operating at pa rt load. In this scheme, hot gas from the compressor is extracted and injected into the suction side of the compressor through a hot-gas by- pass valve. Thus, the refrigerant gas by-passes the evaporator and red uces the system capacity. In this paper, three hot-gas, by-pass scheme s for HFC-134a are discussed and analyzed on the basis of the first an d second laws of thermodynamics. A comparative study is performed of t he schemes in terms of the system coefficient of performance (COP) and irreversible component losses. Second-law-based thermodynamic analysi s indicates that the total irreversible losses of the by-pass valve in crease substantially as the capacity decreases.