Air-con on in the sun?

In the knowledge that the readership of this newsletter extends far beyond those of us expecting a traditionally wet British summer, this issue looks at air conditioning and its impact on fuel economy.

From our test centre in Los Angeles, where they are lucky enough to need air conditioning most of the year, we test elements of the cycle twice; once with the air conditioning switched on, and again with it switched off. We have looked at the data from over 100 passenger cars and this is what we have found.

April chart

With the air-con fully on there is a larger effect on MPG in the city (-5.4%) than in highway driving (-2.7%).

When you look at the data in more detail the effect of air-con on fully on MPG, by fuel type and cycle shows some noticeable differences:

April 14 chart 2

Hybrids suffer a significant reduction in fuel economy with the air-con on in cities, so if you drive one of these it is perhaps better to wind down the windows in town as the aerodynamic penalty may be less.

And when you look at the spread of values in the table below, you can see the effect of air-con differs quite a lot from vehicle to vehicle. So if you live in a hot country and are thinking of buying a car, it pays to investigate your options.

April 14 chart 3

 The average effect of air-con on MPG on passenger cars tested in the US is -4%, which equates to 14 g/km of CO2.  The average CO2 emissions of our real-world tests in the UK is 160g/km. Thus if the air-con has the same load on a European car then the effect would be an 8% reduction in MPG. However, it’s raining as I write this so perhaps not overly worrying for us Brits!