A COOLER HOME

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Approximately 57 million U.S. households (roughly 60%) have air conditioners, with an energy consumption equivalent to the output of seven large coal power plants, and at a cost to homeowners of $9.8 billion. That amount of electric energy results in the release of about 100 million tons of carbon dioxide per year, or a little under two tons per year on average for every home with air-conditioning. Furthermore, airconditioner use in the United States has increased more than 20% since 1984. Seventy-five percent of new homes are being outfitted with central air-conditioning systems, reports Air Conditioning, Heating, and Refrigeration News, including over half the homes in the Northeast. A switch to high-efficiency air conditioners and measures to reduce cooling loads in homes can reduce this energy use by 20-50%.

Air-Conditioning Basics

Air-conditioning, or cooling, is more complicated than heating. Instead of using energy to create heat, air conditioners use energy to take heat away. The most common air-conditioning system uses a compressor cycle (similar to the one used by your refrigerator) to transfer heat from your house to the outdoors. How is this done? A compressor is filled with a special fluid called a refrigerant (usually HCFC 22, one of the environmentally notorious chlorofluorocarbons).
One of the chemical's properties is that it can change back and forth between liquid and gas. As it changes, it absorbs or releases heat. Thus, it is used to "carry" heat from one place to another, such as from the inside of a refrigerator to the outside, or-using an air conditioner from the inside of a house to the outside. Simple, right? Well, no. And the process gets quite a bit more complicated with all the controls and valves involved.

But its effect is quite remarkable. An air conditioner takes heat from a cooler place and dumps it in a warmer place, seemingly working against the laws of physics. What drives the process, of course, is electricity-quite a lot of it, in fact.

Types of Air Conditioners

There are three common types of air conditioners: separate room air conditioners, central air conditioners, and electric heat pumps. Both central and room units work the same way, with the compressor located outside. Room air conditioners are sized to cool just that one room, so a number of them may be required for a whole house. Central air conditioners are designed to cool the entire house. The large compressor unit is located outside, and the inside coils cool air that is distributed throughout the house via ducts.

Often, the same duct system is used for forced, warm air heating systems and central air conditioners. Heat pumps are like central air conditioners, except that the cycle can be reversed and used for heating during the winter months. In addition to these common types of air conditioners, there are several other types used very successfully in certain parts of the country. Evaporative coolers are practical in very dry areas, such as the Southwest.

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