A Refrigerator For Your Window

At one point or another, I'm sure we've all stuck our heads in the refrigerator or freezer to get a burst of cool air on a hot day. It wasn't until I learned a few of the basics behind refrigeration that it became clear to me just how bad of an idea this is. If you've ever been silly enough to run a window air conditioner in a closed room, the unit, say, just sitting there on the floor, you might get some idea as to why the above refrigerator scheme doesn't quite play out.

You see, air conditioning is all about an exchange of energy, with the front part of your AC generating cool air and the back part (that's ideally hanging out the window) expelling hot air. If the unit's just sitting there in the room, then all the hot air stays there with you. Open a refrigerator door, and the hot and cold in the room will only balance out, if not lean hotter.

There are two sets of coils in a window AC unit, one in the front and one in the back. The set of coils in the back circulates a heated refrigerant that gets compressed into gas on its way to the coils in the front. That process cools the refrigerant significantly because of Amonton's Law of Pressure Temperature, which states that a decrease in pressure will result in a decrease in temperature. When the liquid refrigerant transforms into a gas, its pressure drops, and so, too, does its temperature.

It's the same reason that a can of compressed air starts to feel cold as you spray it; as the liquid, you can hear if you shake the can turns to gas, it loses pressure and gets colder. That's also why low-pressure weather patterns bring cold air.

Then, it's simply a matter of blowing a fan against the cooling coils and sending that air out into the room. The refrigerant then travels back through the unit's compressor where it's returned to its much warmer, liquid form.

The British Are Coming!

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Even though the air conditioner was invented in America (more on that later), the people who sell these things still insist on measuring their efficiency in BTUs, or British Thermal Units. A BTU is the amount of energy in joules (that familiar measure!) needed to raise the temperature of one pound of water by one degree Fahrenheit. It's possible there's supposed to be a cow sacrifice and a rain dance in there somewhere; you never know with the Imperial system.

Whatever the case, before you buy your AC, you ought to figure out just how many BTUs your unit will need to cool the room or rooms in question.

The lowest BTU rating among the air conditioners on our list is 6,000 BTUs. That's good enough to cool about 150-200 square feet of space. According to the National Association of Home Builders, the average master bedroom in a 2,000-2,999 square foot home was 271 square feet in 2013. That's a big bedroom: 27 feet long by ten feet wide. Get up from your computer and walk that out. You can cool all that space with only 8,000 BTUs.

The most powerful AC on our list pumps at 25,000 BTUs, more suited to a 900 square foot space. You very well may have a great-room configuration combining your kitchen, foyer, living room, and more into one space, and if you only want to have one AC unit running, that beast may be for you.

In short, measure your space and consult this handy chart and calculator. It'll tell you all you need to know about how many BTUs your room needs to stay cool.

Rebels Are Rarely This Cool

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I recall a movie about gorillas and diamonds and lasers set in Africa. It was called Congo, and among all the amazing pillars on which the film was built, one thing stays with me above all else. The scientists had little baby air conditioners for their tents!

But just moments ago, we talked about the air conditioner being invented in America. The inventor himself was a man named Willis Carrier, an engineer specialized in heating. I guess that would make him, like so many iconic Americans before him and to come to a rebel.

In 1902, Carrier got a patent for what would become the first prototype AC, though it would be another 13 years before a commercial unit hit the market. This original unit of 1902 was designed as a humidity reduction device for a printing company in Brooklyn whose inks would not dry efficiently in the muggy air. By forcing the humid air over coils containing a coolant (sound familiar?), Carrier was able to remove the excess moisture from the environment and solve the problem.

Industrial applications abounded, and in a short time, the air conditioner found its way into people's homes, putting an ever-increasing strain on our cities' power grids ever since.