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Dr. Christopher S. Baird

What are some other ways to save energy in a car besides turning off the air conditioner and rolling down the windows?

Category: Physics      Published: December 12, 2012

speeding car
Public Domain Image, source: Christopher S. Baird.

Turning off the air conditioner in a car and rolling down the windows actually uses more energy than driving with the windows up and the air conditioner on, if you are driving on the highway. The air conditioner uses very little energy. On the other hand, rolling down the windows introduces significant air resistance that the motor must use energy to overcome. The energy lost to drag is higher than to the air conditioner when driving at highway speeds. As reported by the Chicago Tribune in August 2010, "An SAE study conducted at the GM Proving Grounds and in a GM wind tunnel on a full-size car and a large SUV showed that increased wind resistance from running with windows down at more than 55 mph cuts gas mileage by 20 percent, while running the air conditioning cuts gas mileage by 10 percent." In other words, having the windows down worsens gas mileage twice as much as having the air conditioner on at highway speeds. Below speeds of 40 mph, the drag due to air resistance lowers enough that the air conditioner becomes more energy consuming.

Topics: air conditioner, car, car mileage, driving, efficiency, energy, save energy