Establishment of Leakage Rates of Mobile Air Conditioners in Heavy Duty Vehicles Part 2 Buses and Coaches

On behalf of the European Commission, this study establishes empirically the annual leakage rate of mobile air conditioners (MACs) in buses and coaches for the use-phase of the vehicles. In buses, refills are carried out in relatively short service intervals to compensate for leakages whatever their nature. Such refills are recorded over a sufficiently long time and in appropriate detail in Sweden where annual inspection is mandatory for every installation with a refrigerant charge of HFCs more than 3 kg. The refill-based approach of this study consists in the analysis of approximately 2,000 report forms on inspections of mobile air conditioners (MACs) of buses and coaches in a specialised garage in SouthEast Sweden over the 1996-2005 period. Equating refills with emissions, the following conclusions on the annual leakage rate can be drawn. Over ten years, a total of 1,267 annual inspections were carried out on 309 different MACs in buses. For the ten-year period taken as a whole, the leakage rate per annually checked bus MAC averages 2.34 kg ± 0.26 kg. This leakage rate as a percentage of the full refrigerant charge amounts to 23%. These values still disregard any differences in type or design of the buses, and particularly in time of MAC installation. Further analysis reveals significantly higher leakage rates for articulated compared to single buses, and for gas compared to diesel driven buses. There were differences in leakage rate between particular bus and MAC makes, however, they depend on differences in leak tightness by bus design and fuel type. The analysis of age dependency splits the bus sample into three categories. MACs installed between1995-1999 show 2.1 kg/a within their first five inspection years and 2.9 kg/a in the next five years. New MACs, installed ex 2000 exhibit a leakage rate of only 0.9 kg/a over the 2001-2005 inspection period. These three figures indicate a double age-dependency. The leakage rates grow as the MAC systems age, and modern MACs are less leaky than older ones. This evidence might lend some support to the argument of MAC makers that there have been substantial improvements in leak tightness due to replacement of flexible hoses and to better connections.. As regards coaches, the average 1996-2005 leakage rate of the 308 annual inspections on 115 vehicles is 1.5 kg/a. This low value can be explained by the fact that all coaches are diesel-driven solo vehicles. The corresponding figure of MACs in …