 Are multiple room air conditioners causing your electric bills to skyrocket? Or, perhaps worse, is your house virtually unlivable during summer because of the heat and/or humidity? Maybe it’s time to consider central air conditioning.
Central air conditioning, also called “central air” in the United States and “air-con” in the United Kingdom, is a system that cools more than one room in a house or building (in most cases, the entire structure). A conventional air-conditioning system blows cooled and/or dehumidified air through ductwork to deliver it throughout the interior room spaces. In most cases, it employs an air handler (blower) and ductwork of a forced-air furnace for this cool-air delivery. This is, of course, different than a portable room or window air conditioner, which is meant to cool only a single room.
Air conditioners use refrigeration principles to cool the air. As discussed below a condenser, compressor, and evaporator work together to do this job. A typical split-system air conditioner has a compressor and condenser located outdoors and an evaporator unit mounted on the air handler or furnace. A package A/C system combines all of these components in one outdoor unit.
A central air unit draws room air through return-air ductwork, cools, dehumidifies, and filters it, and then blows it back into the rooms through air-supply ductwork. The A/C unit is controlled by a thermostat, which turns the unit off and on as needed. In most cases, the same thermostat doubles for both the air-conditioning and heating system.
Be aware that retrofitting an existing home with central air conditioning may not be an easy nor inexpensive project. Ductwork must run from the air handler to the rooms and, to do this, must usually be routed through the attic or under the floor. If your home is not suited to this type of installation, room air conditioners may be a better solution.
| How a Central Air Conditioner Works |  When the thermostat signals the air-conditioning system to lower air temperature, a whole sequence of events begins. The air handling unit kicks on, drawing room air in from various parts of the house through return-air ducts. This air is pulled through a filter, where airborne particles such as dust and lint are removed—in fact, sophisticated filters may remove microscopic pollutants as well. Then the air is routed to air-supply ductwork that carries it back to the rooms. Whenever an air conditioner is running, this cycle repeats continually. But how does the evaporator coil get cold in the first place? That happens through the magic of refrigeration. Every air conditioner has three main parts: a condenser, an evaporator, and a compressor.
With a typical “split system,” the condenser and the compressor are located in an outdoor unit; the evaporator is mounted in the air-handling unit, which is often a forced-air furnace. (With a “package system,” all of the components are located in a single outdoor unit that may be located on the ground or on the roof of the house.)
A refrigerant such as freon circulates through copper tubing that runs between these components. This refrigerant receives and releases heat as it raises and lowers in temperature, changing from liquid to gas back to liquid. The refrigerant is especially cold when it begins to circulate through the indoor coil. As the air handler pushes warm air across the coil, the refrigerant absorbs so much heat from the air that it turns into vapor. As a vapor, it travels to a compressor that pressurizes it and moves it through the outdoor coil, which jettisons the heat. A fan also helps to dissipate the heat. The refrigerant then passes through an expansion device that converts it to a low-pressure, low-temperature liquid, which returns to the indoor coil. And so the cycle goes.
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