Potential for expanders in a mobile carbon dioxide air-conditioning system

Abstract

Abstract

Three possible automotive CO₂ air-conditioning system configurations were simulated over the full range of vehicle operating conditions. These include a baseline cycle with an internal heat exchanger (IHX), an expander cycle, which is simply a baseline cycle without an IHX and with a turbine replacing the expansion valve, and finally an expander cycle with an IHX. It was found that the highest coefficient of performance was achieved using the expander cycle, with 30–45 per cent improvement over the baseline cycle, followed by the expander cycle with the IHX, and then the baseline cycle. However, when the capacity was investigated, the expander cycle resulted in the lowest capacity for all gas cooler refrigerant outlet temperatures. The cycle with the IHX and the work-recovering expander had the highest capacity followed by the baseline cycle. Based on the above, the IHX is a fundamental component in the CO₂ systems and cannot be simply eliminated if an expander is used in the system. It was also found through simulation that up to 57 per cent of compressor work can be recovered in cycle 2, and 30 per cent in cycle 3 using an expander, compared with only 18 per cent in current production R-134a systems.