Truth About Air Conditioning and Fuel Efficiency

Does Your Car's Air Conditioner Waste Gas?

I vividly remember the first time I experienced air conditioning in a car. I was a little kid sitting in the back seat between two of my brothers. It was a hot summer day and everyone was sweating buckets. Then my dad turned a button and we were suddenly cool. It was magical. Unfortunately it was a rental car. I asked my dad if we could get air conditioning. He shook his head no and said it wasted too much gas. Years have passed and it’s time to find out if my dad was right.

When I surfed the net for fuel saving tips, turning off the air conditioning was often listed as a good way to save gas. Since I didn’t see any data to back it up, I looked further. I found a 2005 study sited by many media sources done by a car sales and information site, Edmunds.com.[1] The test involved driving two cars on a 55 mile loop and a 20 mile loop at 65 mph; once with the A/C off and the windows down and once with the A/C on and the windows up. According to this test, there was no appreciable difference between keeping the windows down and turning up the A/C.

Why? Air conditioning burns a lot of gas, but if we roll down the windows when we are driving fast, there is an increase in drag on most cars. This wind resistance requires extra fuel so you end up burning almost equal amounts of gas.

An October 2000 study was published by the National Renewable Energy Laboratory stating that air conditioning does increase fuel consumption.[2] The study did not mention comparisons between open-window driving vs. air conditioning, but showed that air conditioning does use high levels of energy. It also states that the weight of the air conditioning unit adds to the car weight and thus adds to gas consumption year round. This study suggested design and regulatory changes that would make air conditioning units more efficient, allowing them to be lighter.

There may not be a significant energy savings from driving with your windows down and the air conditioner off when you are on the highway, however when you are driving slowly and drag is not a major factor, turning off the air conditioning will result in gas savings. Making sure your air conditioning is maintained will also improve fuel efficiency. Since almost all cars now have A/C units, the extra weight of the unit is a constant in most cars. Smaller units and more efficient systems will have a positive impact on reducing gas consumption.

 

Auto air conditioning gas saving tips

  1. Service your air conditioner once a year and keep it in good condition.
  2. Park your car in shady areas whenever possible.
  3. Turn off the A/C and open the window when you’re doing stop and go driving around the town.
  4. Turn off the A/C and open the windows when you are parked.





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References

1 What Really Saves Gas? And How Much?, Philip Reed & Mike Hudson, 2005. Retrieved May 30, 2010. http://www.edmunds.com/advice/fueleconomy/articles/106842/article.html#test4

2 Impact of Vehicle Air Conditioning on Fuel Economy, Tailpipe Emissions, and Electric Vehicle Range, R. Farrington and J. Rugh, 2000. Retrieved June 3, 2010. http://www.nrel.gov/docs/fy00osti/28960.pdf

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