Inefficiency Comparison of Car Air Conditioning vs. Open Windows

Question

On a recent long, hot journey in Spain, I was pondering which was the most efficient way of cooling the car. Which of these would be the most effective?

1. Switching on the air conditioning, thereby consuming more fuel
2. Winding down the (both driver and passenger) windows, thus disrupting the airflow around the car and ostensibly creating extra drag

Let's assume I'm travelling at 100km/h on level road, in a 1.2 litre Fiat 500. (It's a valid assumption, because it was true). Let's also assume that both methods cool me down equally as well.

For what's worth, I went with option 2.

Answer 1

Let´s assume... it´s not valid at all. It depends completelly on many factors: interior T, exterior T, performance of your AC equipment, your "feeling"... From my point of view, of course you can reach the outside T of the car, which could be -10°C if you want (in winter)... and your AC won´t be able to reach that T for sure.

But in summer, with 30°C outside, there´s no way for you to have better results by opening the windows: you need to turn on your AC, so spend some money in gas, if you want to have less than 30°C in your car.

For your information, cars are equipped with AC capable to reach a confort T (let´s say around 25°C in heads). But that´s a little bit tricky too: Many people prefers to "feel" more than that or more, so they control the AC in different ways. You can only control the epperture of windows, more o less, but you´ll never be below the out T. Just an opinion, but your question and assumption is kind of lazy. Best regards,