Establishing the Leakage Rates of Mobile Air Conditioners

Establishing the Leakage Rates of Mobile Air Conditioners

A Study Prepared for the European Commission (DG Environment)
by Oeko-Recherche and Ecofys in 2003

Summary

The purpose of the study is to - based on field measurements - determine the average annual leakage rate of HFC-134a from MACs in the European Union of a “second generation” air conditioner. By "second generation" implies that the teething problems of the "first generation" HFC based air conditioners have been sorted out. According to experts this took place in the EU in 1996-7.

From November 2002, to January 2003 300 measurements of HFC-134a leakage were carried out on air conditioners of cars up to seven years age. The measurements were carried out on vehicles of all EU relevant makes at 19 garages in Germany (Osnabrück), Portugal (Rio Maior) and Sweden (Helsingborg) reflecting different climatic conditions. Prior to these measurements 140 vehicles had been tested in a separate project funded by the Dutch Energy and Environment Agency (NOVEM) in October 2002. These measurements helped to test and refine the methodology.

Industrial experts from car manufacturers and component suppliers played a key role in the Contact Group that was established for this exercise by DG Environment of the European Commission. These experts helped to solve many important questions relating to measurement accuracy. The Contact Group helped in defining a measurement protocol to ensure the accuracy of measurements. 

This study focused entirely on "regular leakage", which takes place gradually from undamaged, functioning air conditioners. This is quite different to the "irregular emissions", attributable to system failures caused by internal and external reasons, mostly by accidents or stone impacts. Irregular emissions mainly result in total refrigerant loss, which is noticed by the driver and usually leads to a repair. 

The main results of the study are:

Figure 1: The 276 regular annual leakage rates in 20-gram-sections, by frequency and weighted by real make shares. The average of the scattered leakage rates amounts to 53.0 grams.

1. Based on the measurements, the EU wide average (un-weighted) leakage rate is estimated to be 52.4 grams per year. This equals 6.9% per year. If the leakage rates are weighted to reflect the vehicle composition in the EU, the leakage rate was estimated at 53.0 grams per year. Weighting the leakage rates by the age of the vehicle, the weighted average leakage rate was estimated at 53.9 grams per annum.

2. There was a wide distribution of leakage among different vehicles makes ranging from 28.8 grams (or 5.3%) to 81.9 grams (10.6 %) per year. Perhaps unexpectedly, the leakage rate was found to be higher for cars that were under 2 years of age. As it is unlikely that the air conditioning design or the components of the air condition system have suddenly deteriorated in 2001-02, this issue warrants further investigation.

Figure 2: Regular annual leakage rates by makes (coded). The 12 different makes or make-groups show significant differences from each other. Car manufacturer 15 shows the lowest average annual leakage rate of 28.8 (±5.3) grams/yr, while car manufacturer 5 has the highest 81.9 (±24.4) grams/yr.

3. Climatic conditions seem not to influence much the leakage rate. There was some evidence supporting the hypothesis that the more the air conditioner prone to corrosion due to winter conditions the higher the leakage rate, as the leakage rate found in Sweden (54.3 grams or 7.0% per year) was higher than in Germany (48.7 grams or 6.2% per annum). However, it also seemed that the more the air conditioner is operated the higher the leakage rate, as the leakage rate of air conditioners measured in Portugal (54.0 grams or 7.5% per year) were higher than in Germany (48.7 grams or 6.2% per annum). All in all the differences were fairly small.

4. Smaller charged MACs (mean fill 684 g) were found to have a smaller leakage both in absolute (44.2 grams per year) and relative (6.5% per year) terms. Larger sized MACs (mean fill 883 g) had an annual leakage rate of 66.9 grams or 7.7% per year.

The main finding of this study is that the annual weighted average “regular” leakage rate for a “second generation” mobile air conditioners is 53.0 grams per annum. (The European car fleet with mobile air conditioner was used as the weight in order to correct the over and under representation of some makes in the sample of measured air conditioner). This needs to be compared with the other HFC-134a emissions that occur during the lifetime of the air conditioner. These emissions are (i) before taking the car into use, (ii) “irregular” emissions due to accidents, stone hits, component failures, (iii) emissions during service and (iv) emissions at the end of life of the vehicle. In another study (Öko-Recherche 2001) it was estimated that the “irregular” losses were about 16.3 grams per annum. Adding the regular and irregular emissions and assuming that the expected lifetime of a vehicle is 14 years, the expected greenhouse gas emission from a mobile air conditioner of an average in the EU is about 1,3 tonnes of CO2 equivalent.
 

Table: The make-weighted average regular leakage rate is 53.0 grams per year. As percentage of the norm charge the weighted leakage rate amounts to 7.1 percent.

To understand the full climatic impact of the mobile air conditioner, the lifetime emissions of about 1,3 t CO2 eq. need to be complemented by HFC-134a emissions before the vehicle has been taken into use, the service emissions and the end-of-life emissions, as well as CO2 emissions due to the increased fuel consumption as a consequence of operating the air conditioner.