Experimental Study on Automotive Cooling and Heating Air Conditioning System Using CO2 as a Refrigerant
This paper was presented at the IIR Gustav Lorentzen Conference in Glasgow (Sep. 2004). It presents an experimental study on automotive cooling and heating air conditioning systems using CO2 as refrigerant. Recently, as one of the countermeasures against the global warming and energy conservation problems, increasing attention is being paid to natural refrigerants such as CO2 as substitutes for HFCs in automotive air conditioning systems. Furthermore, because the heat release from the eco-car's engine decreases, present automotive heating air conditioning system can't provide sufficient heating capacity. Therefore, an electric heater is now used as an auxiliary heating method, but it causes a decrease in the energy efficiency. The study focused on the waste heat release of the heat pump cycle at the dehumidifying condition. By using the waste heat release as an auxiliary heating method instead of electric heat, the authors tried to develop a highly efficient automotive cooling and heating air conditioning system using CO2 as a refrigerant. In order to increase the energy efficiency of this CO2 system the following measures were taken. 1) construction of a CO2 heat pump system that uses the heat released at the dehumidifying condition which is used as the auxiliary heating method. 2) examination of the optimal method to control the amount of the CO2 refrigerant held under both cooling and heating conditions. 3) improvement of the elemental devices in CO2 heat pump cycle. The study resulted in the successful development of a prototype of a highly efficient CO2 automotive cooling and heating, air-conditioning system for medium-sized cars. According to the authors, this system can achieve a higher performance (relative heating/dehumidifying COP = 1.31) than that of the present HFC-134a system and the heat released during dehumidification can be used effectively as the source for auxiliary heating for improvements in energy saving. An intermediate pressure control method for adjusting optimum refrigerant amount was also established and maintained in the outdoor heat exchanger to avoid an unbalance in the optimum amounts of refrigerant for cooling and heating. Source: 6th IIR Gustav Lorentzen Natural Working Fluids Conference, Conference papers from Day 3 Sessions 5, 6&7, 7/A/14.00. Authors: Tomoichiro Tamura, Yuuchi Yakumaru, Fumitoshi Nishiwaki. You can order the proceeding CD-ROM of the Glasgow conference by clicking here.