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How Do Air Conditioners Work

The Basic Idea

An air conditioner is basically a refrigerator without the insulated box. It uses the evaporation of a refrigerant, like Freon, to provide cooling. The mechanics of the Freon evaporation cycle are the same in a refrigerator as in an air conditioner. According to the Merriam-Webster Dictionary Online, the term Freon is generically “used for any of various nonflammable fluorocarbons used as refrigerants and as propellants for aerosols.”

This is how the evaporation cycle in an air conditioner works:

  1. The compressor compresses cool Freon gas, causing it to become hot, high-pressure Freon gas (red in the diagram above).
  2. This hot gas runs through a set of coils so it can dissipate its heat, and it condenses into a liquid.
  3. The Freon liquid runs through an expansion valve, and in the process it evaporates to become cold, low-pressure Freon gas (light blue in the diagram above).
  4. This cold gas runs through a set of coils that allow the gas to absorb heat and cool down the air inside the building.

Mixed in with the Freon is a small amount of a lightweight oil. This oil lubricates the compressor.

Window Units

These air conditioning units take up a very small place. The units are made small enough to fit into a standard window frame. You close the window down on the unit, plug the unit in and turn it on to get cool air. If you take the cover off of an unplugged window unit, you will find that it contains:

  • A compressor
  • An expansion valve
  • A hot coil (on the outside)
  • A chilled coil (on the inside)
  • Two fans
  • A control unit

The fans blow air over the coils to improve their ability to dissipate heat (to the outside air) and cold (to the room being cooled).


Most air conditioners have their capacity rated in British thermal units (BTU). Generally speaking, a BTU is the amount of heat required to raise the temperature of one pound (0.45 kg) of water 1 degree Fahrenheit (0.56 degrees Celsius). Specifically, 1 BTU equals 1,055 joules. In heating and cooling terms, 1 “ton” equals 12,000 BTU.

A typical window air conditioner might be rated at 10,000 BTU. For comparison, a typical 2,000-square-foot (185.8 m2) house might have a 5-ton (60,000-BTU) air conditioning system, implying that you might need perhaps 30 BTU per square foot. (Keep in mind that these are rough estimates. To size an air conditioner for your specific needs, contact an HVAC contractor.)

The energy efficiency rating (EER) of an air conditioner is its BTU rating over its wattage. For example, if a 10,000-BTU air conditioner consumes 1,200 watts, its EER is 8.3 (10,000 BTU/1,200 watts). Obviously, you would like the EER to be as high as possible, but normally a higher EER is accompanied by a higher price.

Let’s say that you have a choice between two 10,000-BTU units. One has an EER of 8.3 and consumes 1,200 watts, and the other has an EER of 10 and consumes 1,000 watts. Let’s also say that the price difference is $100. To understand what the payback period is on the more expensive unit, you need to know:

  1. Approximately how many hours per year you will be operating the unit
  2. How much a kilowatt-hour (kWh) costs in your area

Let’s say that you plan to use the air conditioner in the summer (four months a year) and it will be operating about six hours a day. Let’s also imagine that the cost in your area is $0.10/kWh. The difference in energy consumption between the two units is 200 watts, which means that every five hours the less expensive unit will consume 1 additional kWh (and therefore $0.10 more) than the more expensive unit.

Cut 50% Off Your Energy Bill

During the hot summer months the average American family pays about 40% of their energy bill for air conditioning of their house, but this is not necessary. Use the following simple tips to help you keep your house cool and reduce your energy bills at the same time:

  1. During the day keep all windows closed. At night you can open them for ventilation and switch on a fan instead of an air conditioner.
  2. If you need to cool only one room, don’t use your central air conditioning. Invest in a portable air conditioner, instead. Modern portable units have a very high energy efficiency rating, so it will cool your room effectively and save you a lot.
  3. Install mini-blinds or white window shades. Mini-blinds can be very effective and
    can reduce heat gain from direct sunlight by 40-50 percent. You can also hang bamboo shades or tightly woven screens outside your windows. This will stop up to 80 percent of the sun’s heat from getting through your windows.
  4. If you are using a mini split air conditioner, make sure that the outside compressor is well shaded. However, trees and shrubs shouldn’t be planted right next to it; it needs some room for air flow.
  5. It is best to clean or replace your air conditioner filter at least once a month. Dust build-ups can significantly reduce air flow.
  6. When buying an air conditioning unit, make sure that it is the right size for your room. A unit that is too small will not cool your room effectively, and an A/C that is too large will consume much more energy than necessary. See recommendations for proper window air conditioner sizes for your room.
  7. If you use central air conditioning, seal all A/C ducts. Insulate ducts that run through rooms that don’t need cooling, like the basement or the attic.
  8. If your air conditioner is old, consider replacing it with a modern high efficiency unit. Older A/C systems have a SEER (seasonal energy efficiency ratio) of only 6 or 7, while the best air conditioners on the market today offer SEER as high as 13. That means that it will consume almost 50% less energy.
  9. Cooking, drying clothes or dishwashing generates a lot of heat. Try to delay these activities until the evening, when it gets cooler.

Generally, people just switch their air conditioners on and set the desired temperature. This will cool your room, of course, but it will cost you, too. Furthermore, excessive energy consumption is not environmentally friendly, so by following our simple advice you could not only save on your bills, but you could also help to reduce pollution in your area.

How To Choose The Right Air Conditioner Filter

stock-photo-19156539-clean-air-conditioner-filterThe air filter in an air conditioning system keeps the cooling coils and air inside the room clean and free from all pollutants, pet dander, ozone emissions and airborne particles.

There are many different kinds of air filters available today, such as HEPA, standard, pleated, electrostatic and electronic filters. Of these, standard, pleated and electrostatic filters are the most common types of filters that are used in air conditioners. Generally these filters are located in walls, ceilings, furnaces, or in the air conditioner itself.

Standard air filters, having the capacity of removing 10 percent of the airborne pollutants, are made of spun fiberglass with cardboard frames. . They should be changed once a month.

Pleated air filters catch around 35% to 40% of the particles in the air. Owing to their greater surface area with filter material folded back and forth like a paper fan, manufacturers claim that they can last from two to four months. The cost of these filters ranges from $5 to $20 which is slightly more than that of standard filters.

Electrostatic filters use filter media, which use an electric charge to attract the dirt particles in the air. These filters may have electric charge built-in, or else the air moving through the layers of the system creates electric charge. They may cost from around $20 to over $100 each. These filters only need to be changed once a year.

Sometimes people with allergies may consider the usage of an electronic air cleaner in the air conditioner, which works on the same principle as that of electrostatic filter. However, it is far more effective than electrostatic filter and does not hinder the flow of air inside the air conditioning system. Whatever type of air conditioner filter you use, it is advisable to check the cleanliness of the coils of the filter by a contractor at least once in a month.

Perhaps the most important measure that will ensure the efficiency of an air conditioner is frequent replace of its filters. One should change the air conditioner’s filter regularly, as clogged, dirty filters block normal air flow and reduce the system’s efficiency significantly by impairing the coils’ heat-absorbing capacity.