Which is economical? Air Con or window open on motorway?

wazza

We know that the air conditioning unit in the car affects the fuel economy when in use. Have seen cars on the motorway with windows open travelling at 50+mph. I thought it would be more economical to use an air con frugally compared to having a window open which causes a drag which affects the aerodynamic of the car hence using more fuel.

I tend to use the air con, with the recirculating button on, for around 5mins then put it back on when it gets warmer.

What do your views?

Kingsd316

I pretty much have my air con on every time im in the car, even in the winter, (as air con is not just for cooling the car) and ive not noticed any massive affect on fuel

nobby24

It's far too noisy if you have your windows open on the Motorway.

steveo3002

cant see either way making a big enough differance to care about

use the a/c so it doesnt sieze up and cost you £££

Premier_2

Using the air con will be cheaper at higher motorway speeds as an open window will significantly increase drag.

At lower speeds, then an open window would be more economical than using the air con (but may not be as comfortable).

You shouldn't run the aircon for short periods if it can be avoided - about 20 minutes minimum is best.

Remember, not all cars have air con, hence why you may see so many on a motorway with their windows open this time of year.

savemoney

I seem to recall reading somewhere that its wise to sue it every few months just so that doesn't happen

steveo3002 wrote: »

cant see either way making a big enough differance to care about

use the a/c so it doesnt sieze up and cost you £££

vikingaero

One car mag did a test on this. At the time everyone thought it would be more economical use the a/c. They drove the vehicle with the windows closed and a/c off as control. Depending on the vehicle, using a/c increased fuel consumption by 5-8%. And opening the windows increased fuel consumption by 3% due to the increased drag.

Premier_2

Some varying answers to support whatever your point of view here

http://www.newscientist.com/article/mg18925432.200

...There have been a number of studies on the efficiency of cars in relation to open windows and air conditioning. In 1986, Cecil Adams of the newspaper column "The Straight Dope" attempted to test this (www.straightdope.com/classics/a2_393.html). Driving a four-door Pontiac 6000LE he drove 500 kilometres at an average speed of 96 kilometres per hour (60 miles per hour).

His results showed that he could achieve 12.4 kilometres per litre (35 miles per US gallon) with the air conditioning off and the windows up, 12.2 km/l with the windows up and air conditioning on, and 12.0 km/l with four windows down and the air conditioning off, showing it to be more fuel efficient to have the air conditioning on and the windows up. This study was conducted in Ohio in May.

An investigation by the Florida Solar Energy Center reached a different conclusion. Conducted with a Volkswagen GTI, this test found that at 108 km/h the increase in consumption was 3 per cent with the windows down, whereas with the air conditioning on it was 12 per cent. This study was conducted in July in Florida...

...The American TV show Mythbusters tested this using identical cars with the same amount of fuel. It found that at speeds up to 80 km/h it was more efficient to leave the windows open, and at higher speeds it was better to use air conditioning....

...A study in 2004 for the US Society of Automobile Engineers shows just how difficult this question is to answer (www.sae.org/events/aars/presentations/2004-hill.pdf). It looked at the impact of air conditioning on the fuel efficiency of a large family car and an SUV. Tests carried out at General Motors' desert proving ground in Mesa, Arizona, showed that at speeds above 56 km/h winding down the windows is preferable to switching the air conditioning on (see Graphs).
The results need to be interpreted with caution however, as they were sensitive to a variety of factors including external wind speed and direction and ambient temperature. ...

iolanthe07

I know A/C must increase fuel consumption, but only by a tiny amount. I notice no difference at all. Slowing down is a far better way of saving fuel, if you can stand the boredom!

Viper_7

Depends if it's air-con or Climate control?
Is it an "always on system" or regulated so it only comes on/ it's cooling efficiency is only as required.

Generally opening the window causes more drag and uses more fuel and the noise drowns out Abba.

Climate control systems should be left on permanently, they will last a life time.
air-con untils should be used for at least 15 minutes every week, or the seals degrade and you lose the coolant and also looking at new seals and compressor.
As said driving more efficiently totally outweighs caring about an open window or the air-con.

Bongedone

Straightdope also covered this question. He went out and carried out some experiments:

http://www.straightdope.com/columns/read/1010/what-gets-the-better-gas-mileage

Ah, I see that Premier's post mentions the column.