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Air-conditioning facts and myths

Using your AC can affect both fuel-consumption and CO2 emissions

Published: May 22, 2013, 4:00 PM
Updated: October 15, 2018, 3:45 AM

Woman enjoying air-conditioning

With warmer weather now upon us, the air-conditioning systems in our cars and trucks are once again getting a workout.

But, given some of the rhetoric you may have heard about the impact of AC use on the environment, you may feel guilty about using it.

It can have an effect on the environment, but chances are that effect is different from what you may have been led to believe.

Here are some facts about the use of air-conditioning in your vehicle and its impact on ozone depletion, global warming and fuel-consumption.

Ozone depletion

Back in the 1970s it was discovered that some man-made chemicals, including the refrigerant used in automobile air-conditioning systems (called Freon 12 or R12), were having a deleterious effect on the earth's ozone layer, which helps protect us from damaging ultraviolet-B (UVB) radiation from the sun.

At that time, it was common practice for refrigerant to be released into the atmosphere when AC systems were being serviced, allowing it to migrate to the stratosphere where it contributed to ozone depletion.

In 1987, most of the world's industrialized nations signed onto the Montreal Protocol on Substances that Deplete the Ozone Layer, which resulted in eradication by the year 2000 of major ozone-depleting chemicals, including R12.

New regulations also mandated that R12 be recovered rather than released when AC systems were serviced and that it be replaced, both in older vehicles being serviced and in new vehicles, with a new refrigerant called HFC 134a (R-134a), which was benign to the ozone layer.

During that transition, some well-meaning but ill-informed environmental advocates urged people to stop using the air-conditioning in their cars and trucks to help protect the ozone layer.

What they failed to understand is that as long as the refrigerant stays within the closed system of the vehicle, it can do no harm.

So, simply using a properly functioning air-conditioning system plays no role in ozone depletion.

Global warming

By the end of the century, after the entire new vehicle fleet had adopted R-134a as its AC refrigerant. environmental attention had refocused on global warming and climate change. And R-134a, although benign to the ozone layer, was found to be be a global warming gas (GWG), with a relatively high global-warming index.

Given that all refrigerants must now be recaptured during system servicing and vehicle disposal, the amounts of the refrigerant released into the atmosphere are relatively low so its impact is quite small.

Nevertheless, industry has once again undertaken to find a new refrigerant that is both ozone-friendly and has a low-impact on global warming.

That work is still in progress, although one vehicle – the Cadillac XTS – has already adopted a next-generation refrigerant, called R-1234yf, which satisfies those criteria.

From a consumer perspective, however, whatever refrigerant your vehicle uses, it has no impact on global warming as long as it stays within the closed system of a properly functioning air-conditioning system.

Fuel-consumption

Air-conditioning use can contribute to global warming indirectly, however, as it requires some additional fuel use by the engine to power the refrigerant compressor when the system is in use.

The amount of carbon-dioxide (CO2) produced in a vehicle's exhaust is proportional to the amount of fuel used and CO2 is also a global warming gas.

Just how much additional fuel the use of air-conditioning requires varies dramatically with such factors as the vehicle itself, driving speed, wind conditions and temperature.

Various studies suggest the range of that effect is typically between 1 and 10 percent, with the greatest increase in consumption in urban stop-and-go driving and the least effect at expressway speeds.

Rolling the windows down rather than using the air-conditioning also has a negative effect on fuel-consumption at higher speeds, because of the additional aerodynamic drag created so may or may not be a worthwhile alternative.

Whether or not to use your air-conditioning comes down to a choice between personal comfort and a modest increase in fuel-consumption and consequent CO2 production.