Air conditioners
Last updated: April 15, 2010.
What's the best way to cool down your kitchen on a hot summer's
day? If your immediate answer is "Open the refrigerator door," you're way off target!
Every bit of heat a refrigerator sucks in
through its cool box is pumped straight out of
the metal fins at the back. If anything, because of the sheer
inefficiency of the machine, you'll make the room even hotter.
But using a refrigerator to cool a home isn't such a mad idea as
it might seem: with a few slight modifications, it's almost exactly
how an air conditioner works. Let's take a closer look!
Photo: A typical air conditioner unit outside a restaurant. This is the fan that
blows away the hot air. There's another fan you can't see, circulating cool air inside the building. Most
air conditioners are permanently fixed in one place, but you can get small portable air-conditioning units too.
How not to cool your kitchen
A basic law of physics called the conservation of energy
says you can't make or destroy energy:
if you have some energy you don't want (such as heat in your kitchen),
you can't get rid of it completely. All you can do is change it into another form or move it to another place. If you
open your refrigerator door in the hope that you'll cool the kitchen,
all the heat that gets sucked in has to go somewhere else. The only
place it can go is out of the back of the machine. You may have
noticed that the grid of fins on the back of a refrigerator gets
pretty hot—and that's why: they're giving off all the heat that
would normally be inside. You can find out more in our article on
how refrigerators work.
Photo: Physics tells us you can't cool your kitchen by leaving the refrigerator door open!
How to build an air conditioner
But all's not lost! Instead of letting the power of science defeat us,
we just have to use it the right way.
Suppose you take a refrigerator and build your house around it, so
half the machine (the chiller cabinet) is inside your home and the
other half (the grid of hot fins at the back) is outside. Now if you
leave the door open, what you have in effect is a fully fledged air
conditioner. It sucks in warm air from inside your home and belches it
out again outside, gradually cooling your home in the process.
The simplest air conditioner units work in almost exactly this way, except they have
fans on both sides to circulate air more rapidly. They also have a
heating element in them so they can warm the air in a room on cold
days as well as cool it down on warm days. Machines like this are
sometimes called HVACs (heating and ventilation air
conditioning units). More elaborate air conditioners use long ducts to pipe
the warmed or cooled air throughout an entire building, but they
still work in essentially the same way.
Photo: This state-of-the-art HVAC (heating, ventilating, and air-conditioning) unit has huge pipes to blow hot or cold air around a large building. Photo by Warren Gretz by courtesy of
US Department of Energy/National Renewable Energy Laboratory (DOE/NREL).
How air conditioners can harm the environment
Photo: Air conditioners: they may be cooling you down, but they're heating up the planet!
These air conditioners are on a building in Bandung, Indonesia.
Photo courtesy of Ikhlasul Amal published on Flickr under a Creative Commons licence.
See more of Ikhlasul Amal's photos.
You probably love the feel of freshly chilled air on a hot day, but don't forget
that law called the conservation of energy! There's always a price to pay for getting something good in our universe. In this case, the price is the energy you have to use to run the air conditioning unit—and using energy means there's an impact on the planet too in the shape of environmental problems like global warming.
Next time you're thinking about switching on the air-con, why not simply open the window instead?
Every time you switch on the air conditioner in your car, you add an extra 10-20 percent to your fuel consumption (and an extra 10-20 percent to the price you pay at the gas station). At low speeds, opening a window instead is often a better option, though at higher speeds you create air resistance (drag) and waste more energy than you save (check out our fuel efficiency page for more tips on saving money as you drive). At home, using the air conditioner will add plenty to your electricity bill. You could try other strategies like opening your windows all night but shutting them tight first thing in the morning and throughout the daytime to keep hot air out of your home. You might be amazed at how well this can work—and how much money it helps you to save.
Air conditioning units used to have another very harmful effect on the environment as well. Until the late 20th century, most used coolant chemicals known as chlorofluorocarbons (CFCs), which were also used widely in refrigerators.
When old air conditioners were broken apart for scrap at the end of their lives, the coolant chemicals
escaped into the atmosphere. Floating up into the stratosphere (the upper atmosphere), they rapidly damaged Earth's ozone layer: the natural sunscreen that helps to protect us from the Sun's harmful ultra-violet rays. Most modern air conditioners avoid CFCs (now banned in many countries under a global agreement called the Montreal Protocol) and use alternative coolant chemicals instead (typically halogenated chlorofluorocarbons or HCFCs). If you look closely at our top photo, you can see that the fan has a green "Ozone friendly" label on it, which means there are no CFC coolants inside.
