VI 히트펌프 사이클의 고효율화에 관한 연구

Abstract

It has been found that the VI(vapor-injection) heat pump cycle can compensate for decrement of cooling capacity and coefficient of performance of heat pump caused by outdoor temperature increase of summer. However, these research is not use a heat exchanger for medium-low temperature refrigerant, and performance enhancement of conventional heat pump with VI cycle was expected by using heat exchanger for medium-low temperature refrigerant. Thus, in this study, performance characteristics of the VI cycle heat pump when the heat exchange was occurred between medium temperature refrigerant comes from economizer and low-temperature refrigerant comes from evaporator at the re-cooler was investigated. In addition, in the winter, coefficient of performance for heating is reduced because of liquid compression caused by reduce of evaporation of wet steam refrigerant evaporated in the outdoor unit in air source heat pump. So, recently, many research about VI cycle heat pump have been studied for preventing these problems, but experimental study about these system is insufficient yet. Thus, this study investigate the thermal performance characteristics of VI cycle heat pump when suction refrigerant was reheated by refrigerant that was discharged from compressor by re-heater experimentally. Also, in the past, heat pump was used as a sub system of solar thermal system. But these systems fail to obtain the desired thermal energy for heating water in thermal storage tank according to weather. So, in this study, performance characteristics of VI cycle heat pump was investigated experimentally when the re-heater was used with solar thermal as auxiliary energy. All of experiment conducted on the constant outdoor air temperature for comparing heating and cooling performance by using re-heater, re-cooler and solar thermal energy. As a results, on the cooling mode, performance was shown highest value when VI cycle and re-cooler were used simultaneously, while the heat pump cycle without VI system and re-cooler was shown lowest value. Also, average cooling coefficient of performance(COPc) was shown 3.2 when the re-cooler was used with VI system, which was 8.6% higher than VI system without re-cooler and 33% higher than heat pump cycle withou VI system and re-cooler. When the system operating on heating mode, heating coefficient of performance(COPh) was shown about 2.86 on VI heat pump cycle with re-heater which was 4% higher than VI heat pump cycle without re-heater and from these results, it was confirmed that the improvement of heating performance of heat pump with VI cycle can be achieved by applying re-heater. When driving solar assisted heating mode, coefficient of heating performance(COPh) of VI heat pump cycle with re-heater and solar thermal energy was improved by 13.6% higher than the performance of VI heat pump system with re-heater shown the average COPh of 3.408 and by 18.9% higher than the performance of VI heat pump cycle without re-heater shown the average COPh of 2.86. From these results, it was confirmed that the performance of heat pump system with refrigerant re-heater and VI cycle can be improved by applying solar thermal energy as an auxiliary heat source. Also, 2m2 of flat plate solar collector was shown that supplying thermal energy fully to heat pump that has 2.5kW(3.5HP) compressor as auxiliary heat source, but system capacity is changed by heat load, heating and cooling time. So, further experiments on more strict conditions is needed to conducted for standardization and commercialization of heat pump.