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This paper presents an experimental performance investigation and exergy analysis using R1234yf in an automotive air conditioning system. The R1234yf system with an internal heat exchanger (IHX) was compared with an R1234yf system without the IHX and an R134a system. The R1234yf system had 4.0–7.0% smaller cooling capacity and 3.6–4.5% lower COP compared to the R134a system. With the IHX, the R1234yf system showed almost equivalent cooling capacity to the R134a system. The COP of the R1234yf system with the IHX is lower than that of the R134a system by 0.3–2.9% for a compressor speed of 800–1800 rpm. The COP increased by 0.9% at a compressor speed of 2500 rpm. The second law efficiency of the R1234yf system was 3.4–4.6% lower than that of the R134a system at all compressor speeds. The second law efficiency of R1234yf with the IHX was improved by 1.5–4.6% compared to the R1234yf system without the IHX. The EDR of the R1234yf system was 0.5–3.3% higher than that of the R134a system in the range of 800–1800 rpm. However, the R1234yf system with the IHX had 1.2% lower EDR than the R134a system at a compressor speed of 2500 rpm.

This paper presents a numerical study on the performance of a vapor compression cycle equipped with an ejectoras an expansion device to improve the COP by reducing the expansion loss and compressor work. The simulation is carriedout using a model based on the conservation of mass, energy and momentum in the ejector. From the results of the simulation,the vapor compression cycle equipped with an ejector showed a maximum COP improvement of 14.0% when using R134a refrigerant and 16.8% when using R1234yf. In addition, the performance of the system with an ejector represents the increasedperformance as the temperature difference between condensing and evaporating increased. Key words Ejector(이젝터), Entrainment ratio(유입비), Area ratio(면적비), R1234yf(R1234yf), GWP(지구온난화지수), COP(성능계수)†Corresponding author, E-mail: cspark@hoseo.edu 기호설명 A ： 단면적 [m 2 ] COP ： 성적계수 h ： 엔탈피 [kJ/kg]  ： 질량유량 [kg/s] P ： 압력 [kPa] Q ： 냉방용량 [kW] S ： 엔트로피 [kJ/kg ℃ ] V ： 속도 [m/s] W ： 압축기 소요동력 [kW] x ： 건도그리스 문자  ：

The objective of this study is to investigate the influence of the cooling performance for a water-to-water ground source heat pump (GSHP) by using the counter flow and parallel flow methods. The GSHP uses R-410A as a refrigerant, and its main components are a scroll compressor, plate heat exchangers as a condenser, an evaporator, a thermostatic expansion valve, a receiver, and an inverter. Based on our modeling results, the heat transfer rate of the counter flow evaporator is higher than that of the parallel flow evaporator for a heat exchanger length greater than 0.42 m. The evaporator length of the GSHP used in this study was set to over 0.5 m. The performance of the water-to-water GSHP was measured by varying the compressor speed and source-side entering water temperature (EWT). The cooling capacity of the GSHP increased with increased compressor RPMs and source side EWT. Also, using the counter flow method, compared to the parallel flow method, improves the COP by approximately 5.9% for an ISO 13256-2 rated condition.

The present study investigated a two-stage compression heat pump system for district heating utilizing waste energy. An evaporator and condenser exhibit a large difference in temperature when hot water is produced for heating by a heat pump. With single-stage compression, this causes a dramatic drop in the compressor efficiency and lowers the system performance; so, in the present study, a two-stage compression heat pump system comprising an intercooler and flash tank was designed, and the performance characteristics under various operating conditions were tested. When the heat source temperature was raised from 10 °C to 30 °C, the COP (coefficient of performance) was improved by up to 22.6%. As the superheating at the low-stage compressor was increased from 2 °C to 11 °C, the refrigerant flow rate and heating capacity decreased by as much as 7.6% and 2.2%, respectively, but there was no major impact on the temperature of the hot water produced nor on the system performance. Controlling the frequency of the high-stage compressor to control the intermediate pressure resulted in the ability to improve performance by as much as 5.2% under identical heat source conditions.

The objective of this study is to investigate the performance of a two-stage com-pression heat pump system for district heating. The experimental setup of heat pump consists of compressor, condenser, evaporator, expansion device, intercooler, flash tank, oil separator and accumulator. The experimental evaluations on the two-stage compression cycle were carried out under various operating conditions which were heat source temperature, the degree of compressor inlet superheat, and intermediate pressure. The temperature ranges of unutilized energy as the heat source were used in the test conditions. As the heat source temperature increased from 10℃ to 30℃, the COP and heating capacity of the heat pump system increased by 22.6% and 45.8%, respectively. The performance of the two-stage heat pump system increased by 5.2% with the variation of the intermediate pressure in the same heat source temperature conditions.Keywords:District heating(지역난방), Intermediate pressure(중간압), Two-stage compression heat pump(2단 압축 히트펌프), Unutilized energy(미활용에너지)

A simulation study on the performance of the solar and geothermal hybrid heat pump system by using R22 was carried out with a variation of operating conditions. The system was consisted of solar system (concentric evacuated tube solar collector, heat storage tank) and geothermal heat pump system (double pipe heat exchanger, electric expansion valve and compressor). As a result, the heating capacity is linearly decreased from 13.2 kW to 11 kW as the heat pump operating temperature increases from 40 o C to 48 o C. Besides, the heating COP decreases by 13.6% from 4.4 to 3.8 when the ground temperature raises 13 o C to 17 o C. The heating capacity is increased by 4.7% from 11.5 kW to 12.2 kW and the heating COP rises by 19% from 4.7 to 5.6.