INTEGRATION OF A TWO-PHASE EJECTOR INTO A COMPACT, LIGHTWEIGHT UNITARY-TYPE AIR-CONDITIONER USING R744 FOR ENERGY EFFICIENT OPERATION IN HOT CLIMATES

摘要

Transcritical R744 technology was used to design a compact, lightweight unitary-type air-conditioner forrnmilitary shelter cooling. In the past, U.S. Army has funded a series of research projects aimed at convertingrnexisting Environmental Control Units (ECUs) that use H/C/FC refrigerants to transcritical R744. However,rnfor the nominal cooling capacity of 35 kW no baseline system that uses a conventional refrigerant exists.rnTherefore, a trailer-mounted R744 ECU air-conditioner had to be designed and built from ground up. Thisrnmade it possible to focus the design considerations on achieving high energy efficiencies during operation inrnhot ambient temperatures. R744 ECU systems show large improvement potentials due their use at very highrnambient conditions that are generally difficult for the transcritical cycle. Throttling losses are large, creatingrnan ideal application for the use of expanders or ejectors. The performance, and in particular the energyrnefficiency of the system was further improved by implementing a two-phase ejector designed for use inrntranscritical R744 systems. While two-phase ejector technology has previously been used in a variety ofrndifferent mobile and stationary applications, the present study utilizes a transcritical R744 two-phase ejectorrnthat is among the largest ever reported in the open literature. Up to 7 % higher COPs can be achieved inrncomparison to the baseline case with expansion valve. Another important finding of the study points towardsrnthe importance of the vapor-liquid separator that is required in the standard two-phase ejector cycle. Lessrnthan perfect vapor and liquid separation efficiencies can have dramatic impact on the performance of thernejector cycle. Therefore, the subject has been studied in more detail and different separator designs andrnseparation approaches that yield high separation efficiencies are presented.