Performance simulations of twin-screw compressors with economizer

In a compressor refrigeration plant with an economizer system, the regular expansion valve is replaced by two valves and an intermediate pressure vessel. The refrigerant which is vaporized after the first valve is injected via the compressor economizer inlet to a thread under compression. The economizer arrangement increases the refrigeration capacity and improves the coefficient of performance (COP). In this paper a performance simulation computer program for twin-screw compressors with an economizer arrangement is presented. Comparisons of economizer performance for different arrangements are often difficult to carry out if real tests have not been run, as the performance is dependent on the intermediate pressure and this pressure is not the same for different arrangements. Such comparisons can be made with the simulation program. Examples are presented for an economizer arrangement combined with external liquid subcooling and for a two-stage economizer arrangement.