EVALUATION OF A VARIABLE SUCTION GAS HEAT EXCHANGER IN A LIQUID CHILLER SYSTEM USING CARBON DIOXIDE AS REFRIGERANT

摘要

A prototype refrigerated seawater (RSW) system using carbon dioxide (CO_2) as the refrigerant in a transcritcal process has been designed, built and tested experimentally. The system was equipped with a variable capacity suction gas heat exchanger (SGHX) which allowed operation at optimal evaporator refrigerant charge. A simulation program for finding the optimum SGHX capacity at different operating conditions has been developed and used. Steady state experiments were done in both cooling and combined cooling / water heating mode at discharge pressures between 50-90 bar and cooling water temperatures between 10-25°C. Measured cooling capacities at steady state varied between 17-38 kW depending on the ambient cooling water temperature. Highest cooling capacity was measured at 10°C cooling water temperature and 70 bar discharge pressure. The optimum coefficient of performance (COP) was measured at 60-70 bar discharge pressure for cooling water temperatures below 20°C and 80 bar above. In hot water heating mode water temperature of 80°C was achieved without problems but with low efficiency due to a gas cooler not designed for this operation. This work indicate that a variable capacity SGHX concept appears not to be beneficial with cooling water temperatures below 25°C, but could have a potential at higher temperatures. Generally, the prototype CO_2 liquid chiller system worked stable and well.