The specific approach of this study is the ex post evaluating data records of refrigerant losses of passenger cars actually driven on roads. Overall R-134a emissions are broken down into three types: Normal (bit by bit release through seals), irregular (abrupt, in case of accidents, stone hits etc), disposal emissions (End-of-life sucking out not occurring).
Based on 1000 A/C units opened and recorded by 9 garages in 2000 (three different German car makes), the rate of normal loss is assessed at 6.3 % per year (25% tolerance band) over the first seven years of ex work A/C systems' use phase. Normal loss is considered any refrigerant deficiency of about 40 % compared to the first fill. The losses below 40 % as recorded by the garages are taken as an unintentional sample survey of the normal emissions. The basic assumption is that a 40 % refrigerant loss still allows the A/C system to work just properly.
Irregular losses are all the losses over 40 %. They are mostly caused by external events like accidents, stone hits and suchlike. Therefore the most defective single circuit component to replace is by far the condenser. The rate of irregular emissions amounts to almost 2 % per year (347 kg from all the 21,300 once a year inspected cars equipped with an R-134a ex-work A/C system).
Future disposal emissions are estimated at 2 %. This is why the assumed 25 % one-off disposal emissions are split into 12-13 usage years of the A/C system.
Thus, the overall emissions range around 10 %/yr. This rate is equivalent to a loss of roughly 88 grams per year and car (average first fill of 0.850 kg).
Emission of Refrigerant R-134a from Mobile Air-Conditioning Systems
Annual Rate of Emission from Passsenger-Car Air-Conditioning Systems up to Seven Years Old
Different from stationary refrigeration and air conditioning, the refrigerant circuit in MAC systems for road vehicles is unstable mainly due to the specific conditions in a vehicle. Firstly, the compressor is driven by the engine and inevitably not hermetically closed. Secondly, all components and connecting lines are exposed to the vibrations of the engine and the heat developed by it. In addition, the pressure inside the A/C system is permanently high, not only in the running times of the engine (ca. 450 h/yr) or of the A/C unit (ca. 150 h/yr) but during the whole life time of the system. Losses of gaseous refrigerant are "normal" and generally accepted by car manufacturers within certain specified limits. Basically, there are three weak spots regarding the tightness of car A/C systems: 1. The rotating shaft seal of the compressor. 2. The flexible hoses between the components. 3. The O-rings sealing the component connections.This study carried out on behalf of the Germany EPA (UBA) by Oeko-Recherche, Frankfurt, is the first attempt to find out rate and amount of refrigerant losses based on field data of a larger population of vehicles and not only by experts' estimations or laboratory based calculations. The data have been taken from the handwritten records of nine garages in the Rhein-Main and Nuernberg areas comprising more than thousand service processes of refrigerant charging by means of charging (recovery/recycling) stations. Three German car brands were covered over the periods 1999, 2000 and 5/2000-5/2001.
Chapter A presents and discusses the data base of the study consisting of about 1.000 recorded refrigerant charging processes carried out by nine garages of three different German car manufacturers from 1999 to 2001, May.
Chapter B deals with the recovery/charging stations in order to check the measure exactness of the quantities sucked out and filled in, as well as to limit the margins of error and to introduce correction factors.
In Chapter C the causes of the refrigerant losses detected on the opening of the A/C systems are analysed. Total losses (roughly 40 % of the cases) turn out to have other, mostly external, causes than losses below 40 % representing the same amount of overall cases. A refrigerant deficiency of 40 % in relation to the norm fill is considered as the upper limit within an A/C system just properly works (no gaseous refrigerant [flash gas] but only liquefied refrigerant in the line from receiver to expansion valve), and basically achieves the same cooling performance as a full system. Refrigerant losses below 40 %, unless occurring in the initial use phase of the A/C system, are principally results of normal bit by bit release, not of irregular events (accidents, stone hits etc) - the latter usually causing higher losses. From that is derived the basic distinction of this study between normal and irregular emissions. Refrigerant losses below 40 % represent normal release, especially through the seals and hoses. Losses over that limit are considered to have irregular causes. Admittedly, some time or other the normal refrigerant release will exceed a deficiency of 40 %, too. But vehicles younger than six/seven years, constituting the mass of the present sample, are not assumed to have reached that time up to now, already. Provisionally, refrigerant losses below 40 % found out and recorded by the garages are treated as equivalent to normal refrigerant release.
Chapter D takes the A/C systems with losses below 40 % having been opened by several reasons but not due to less refrigerant as an (unintentional) sample survey of the normal emissions, and relates these cases of small losses to the time in months gone by since the first registration of the vehicle. First there is no obvious connection between the amount of the refrigerant loss and the vehicle age, mainly due to numerous unexpectedly high losses during the first 18 operation months of the car. Because such cases of extraordinary high losses are assumed to have irregular instead of normal causes, they are excluded from the further consideration of the normal emissions. After filtering the sector of refrigerant losses below 40 % by removing these emission cases, the remaining 216 A/C systems (losses below 40 %) show an average annual refrigerant loss of 6.3 percent (52 grams) per year during the first seven operation years. This is the rate of normal emissions. The average emission rate varies among the car brand by roughly ten percent. The average normal loss of 52 grams per year does not go beyond the scope of the car manufacturers tolerance per A/C system of 34 - 83 grams.
Chapter E: The normal emissions are determined indirectly from the charging records of the garages by application of the emission behaviour of these A/C systems opened in the repair shops to the emission behaviour of the totality of the car A/C systems - up to seven years operating time. Compared with that the irregular emissions are found directly from the garage records. The total of the refrigerant losses detected and recorded in kilograms by a garage in the course of one year is related to the total number of A/C equipped cars inspected by this garage in the same year. Through several intermediate stages (e.g. A/C ratio of the regularly inspected cars by brand) it turns out that the air-conditioned cars regularly serviced by the nine garages, lost 1.9 percent/year of their refrigerant in an irregular way, in the period from 1999 to May 2001. Depending on the car brand this figure varies from 1.5 to 2.2 percent.
In chapter F total use phase emissions are discussed adding up to the annual rate of emissions of 8.2 percent, varying from 7.7 to 9.2 percent depending on the car brands. In order to take into account that deviations between the brands as well as the immanent measure imprecision of the charging stations, an uncertainty of 25 percent to that figure of 8.2 percent is provided. Consequently, the annual rate of the total refrigerant emissions from car air-conditioning systems is in the range from 6.2 to 10.3 percent. It should be pointed out, that even this statement applies to A/C systems up to seven years old, only. In addition, the emission estimates do not yet include the disposal emissions. Subsequently, the overall operating emissions of R-134a from passenger car air-conditioning systems in Germany figure between 685 (minimum) and 1140 (maximum) tonnes, in the year 2000 - corresponding emission rates of 6.2 % or 10.3 % related to the overall refrigerant stock in personal cars of 11.050 tonnes. The basic parameters of this estimation are: 13 million air-conditioned passenger cars (30 % of the total fleet) and 850 g average charge of the existing A/C units.
If the disposal emissions are taken into account and divided into the 12 or 13 single years of the A/C system service life, the - average - annual rate of refrigerant emissions will rise over ten percent because the suction extraction of refrigerant in scrapping is not expected to occur in more than a half of the cases for the next time.
The final chapter G elaborates on the question whether regular inspection and maintenance of car A/C systems prevent refrigerants from being released in the environment. Basically, preventative checks may increase the reliability and operation safety of the A/C system and furthermore drop the fuel consumption (as a result of cleaning condensers etc.). However, a reduction of (1) disposal, (2) irregular, or (3) normal refrigerant emissions does not seem possible via this route. A mandatory maintenance only to reduce direct R-134a emissions is not considered to be useful from the view point of this study.