Life Cycle Climate Performance ( LCCP ) of Mobile Air-Conditioning Systems with HFC-134a , HFC-152a and R-744

Abstract

Life Cycle Climate Performance (LCCP) of mobile air-conditioning (MAC) systems have been calculated based on published performance data of enhanced HFC-134a systems achieved during the SAE AR CRP1 (2002), and measured performance data of an improved R-744 MAC system (Pilot 2002), results which are now also included in the SAE AR CRP. All experimental investigations were performed at equal conditions in the same test facility at the University of Illinois (ACRC). The NEDC driving cycle (93/116) was applied for the European countries, while the US FTP75 combined city & highway driving cycle was applied in combination with the measured performance data to calculate the energy consumption of the Air Conditioning system of mid size vehicles. Direct comparison of the two systems show that the COP of the R-744 system is equal or better than the efficiency of the enhanced HFC-134a system at the dominant operating conditions, i.e. moderate temperatures and high revolution speed of the compressor. At high ambient temperatures, where capacity is the most important parameter, the R-744 system can achieve a faster temperature pull-down, due to higher maximum capacity. The results of the LCCP investigations show 18 to 49 % reduction in LCCP based on a compact 2002 R-744 system (evaporator volume reduced to 76% of HFC-134a evaporator volume), indicating significant environmental improvements by a change to R-744 systems. Integrated seasonal data show that about 14 % reduction in energy (fuel) consumption can be obtained with R-744 in areas with moderate to hot climate. Even in a very hot climate (Phoenix), the 2002 R-744 system has equal energy consumption, when considering equal cooling capacities. The fuel consumption would be even lower with a 'full-size' R-744 evaporator, i.e. same size as for HFC-134a. The HFC-134a system has slightly better COP only at extreme operating conditions that seldom occur, and these conditions have no impact on annual energy (fuel) use. Preliminary data from the SAE ARCPR Phase II project has been applied in a separate analysis to calculate the LCCP for Best Technology (BT) HFC-134a and BT HFC-152a systems (SAE ARCRP, 2004). Although the test data can only compare R-744 systems with Phase I Baseline and Enhanced HFC-134a systems, and Phase II compares BT HFC-134a with BT HFC-152a systems, the results indicate that BT HFC-152a and 2002 R744 (from tests spring 2003) systems have approximately similar energy efficiency and LCCP profiles. The test data have reconfirmed that the COP is no argument against R-744. Fuel use of R-744 systems is significantly lower than with HFC-134a, even in the warm climates considered in the present comparison. Also taking into consideration the good properties R-744 offers for using the system as a heat pump in reversed mode and the potential for compact design, R-744 systems represent a very good alternative for the future.