Aircon or open window? Fuel cost

mistyarthur

It was a few years ago I read it maybe it was something like 1.9mpg. Thinking about it that would be worrying wouldn't it!!! lol.
I find when you get in a brand new car it is ice cold when you turn on the air con but in my car now 52 plate it is cool but not cool enough on the really hot days but I know it's not going to perform as brand new really.
I found something on it that suggests it is better to have the windows up and a/c on.
a/c vs. windows

tomstickland

I reckon I should open the windows at high speed and use the air con when driving slowly in town but what is the difference in fuel usage?

Other way round I'd say. Windows open at low speed costs nothing, only at high speed is there any drag influence worth worrying about.

my car has climate control and I'd say it doesn't use more fuel. Also what cost then would loud music and xenon lights be to you?

The power consumption of amplifiers and lights is very small compared to a compressor.

Personally I've never had air con and don't think I'm missing anything much.

tomstickland

This is quite useful too:

How Air Conditioning Affects Fuel Consumption

"Half a liter on 100 km" - "No", says someone else "one liter, I did an exact calculation." A third person needs even more and did also an exact calculation. What is correct?

All three are right, because fuel consumption per 100 km can vary substantially, depending on outside temperature and how long it takes to travel 100 km. For instance driving only 20 km in one hour, on a hot day, in sluggish traffic requires 0.4 liters of fuel for air conditioning, while the projected fuel consumption for 100 km is 2 liters. On the other hand, in highway conditions fuel consumption can go down to one third liter depending on driving speed. The consumption per hour on a hot day, in both cases is almost the same: 0.4 liters.

The hourly fuel consumption of an air conditioning cannot be directly compared with the overall fuel consumption of a vehicle which is expressed in liter per 100 km. Despite the difficulty in making a comparison it is possible to establish an estimate, if we assign an average distance, an average speed and a climate typical for Central Europe, as a basis. In this case the average yearly consumption is about 93 liters or 0.62 Iiters per 100 km. With vehicle fuel consumption of 8 to 12 liters per 100 km, the air conditioning consumes around 5-8 % of this amount. An acceptable expense, if you consider that your travel is not only more comfortable, but safer as well.

http://www.behrgroup.com/produkte/fahrzeug/klimatipps/text5.php

35mpg is around 8 L/100Km.

headcovers

mistyarthur wrote:

..................I find when you get in a brand new car it is ice cold when you turn on the air con but in my car now 52 plate it is cool but not cool enough on the really hot days but I know it's not going to perform as brand new really...........................

Air conditioning needs to be serviced annually. If you do this it will perform as it did when new, years into the life of a car.

If you don't service it.....it won't work as well. Makes sense really.

Wig

tomstickland wrote:

This is quite useful too:

http://www.behrgroup.com/produkte/fahrzeug/klimatipps/text5.php

35mpg is around 8 L/100Km.

"but safer aswell" ??? What? I suppose they mean you won't get any bee flying in through your open windows! :rotfl:

5 - 8% extra consumption is enough for me not to ever use it, I shouldn't have gone for a car with AC, next time I'll know better.

mistyarthur

headcovers wrote:

Air conditioning needs to be serviced annually. If you do this it will perform as it did when new, years into the life of a car.

If you don't service it.....it won't work as well. Makes sense really.

I get my car regular services and get the filters changed etc. but like a fridge and freezer the efficiency and the standard of the cooling deteriorates. A fridge after a few years doesn't cool as well and needs to be put on a lower setting.

moonrakerz

On a recent edition of "Mythbusters" they came to the conclusion that up to 50/60 mph you were better off with the windows open, above that speed the increased drag was more than the increased consumption used by the A/C.

Having said that I never noticed any difference in fuel consumption in my Mondeo with it on or off.

Lob_Rockster

my car has a uprated battery so in theory the extra power needed is provided by that battery. Plus with automatic climate control, it does not blow hard all the time ergo the battery can recharge efficiently.

So I say I see no difference in MPG.

plane_boy2000

Lob_Rockster wrote:

my car has a uprated battery so in theory the extra power needed is provided by that battery. Plus with automatic climate control, it does not blow hard all the time ergo the battery can recharge efficiently.

So I say I see no difference in MPG.

Its not electrical power used for Air con - the compressor runs from a belt driven by your engine hence the increase on fuel consumption as you are increasing the load on the engine.

plane_boy2000

mistyarthur wrote:

I get my car regular services and get the filters changed etc. but like a fridge and freezer the efficiency and the standard of the cooling deteriorates. A fridge after a few years doesn't cool as well and needs to be put on a lower setting.

Air con is not covered by standard servicing - its a specific task sperate to your anual service. If you have not specificaly asked your garage to re gas / service your air con then they havent done it. Changing of polen filters etc will have little effect to the cooling capacity of your air con.