THERE'S an ongoing argument online among car fans on whether it is more fuel-efficient to drive with your air-conditioning on or to lower your windows.
This surprisingly contentious debate has been raging ever since the first car rolled off the production line with modern air-conditioning (incidentally, it was the 1953 Chrysler Imperial).
Prior to that, the now-defunct car maker Packard began offering an option of retrofitting air-conditioners in their vehicles in 1939, huge machines that took up half the car's boot space.
So, is driving with the windows down more fuel-efficient than having them up with the air-conditioning on?
Verdict:
TRUE – at least, mostly
In 2013, the Society of Automobile Engineers (SAE) tested the theory and found that for both sedan cars as well as sports utility vehicles (SUVs), it was more fuel-efficient to drive with the air-conditioning off and windows down at any speed.
They tested two cars, a 2009 Ford Explorer (SUV) and a 2009 Toyota Corolla (sedan), both on the road and in a wind tunnel.
At steady speeds between 64kph and 113kph, both vehicles consumed more fuel with the air-conditioner on, versus off with the windows down.
The argument was that leaving the windows down would mess with the vehicle's aerodynamics, making it consume more or at least the equivalent amount of fuel as compared to running the air-conditioner. However, SAE's test proved that this was not the case.
The caveats are that the SAE's tests were done on only two vehicles out of all the different models ever made with air-conditioning.
Furthermore, there have been vast strides in engine efficiency and air-conditioning technology over the last decade or so since the tests were run, so perhaps the fuel efficiency would not be so heavily impacted if the same test were conducted with today's cars.
The Idaho National Laboratory did test the range impacts of auxiliary systems (including a car's air-conditioning) on electric vehicles (EV).
What it found was that air-conditioning impacted an EV's range far more than vehicles with an internal combustion engine.
Its test found that using an air-conditioner could decrease an EV's range by up to 30%.
References:
1. https://www.sae.org/publications/technical-papers/content/2013-01-0551/
2. https://avt.inl.gov/sites/default/files/pdf/fsev/auxiliary.pdf
3. https://autospark.com.au/a-brief-history-of-car-air-conditioning/
4. Langworth, Richard M. (1994). Chrysler and Imperial: The Postwar Years. Motorbooks
