Air Conditioning Lingo

Air handler In any forced-air cooling or heating system, the air handler contains a powerful fan that blows conditioned (cooled or heated) air through supply ducts for distribution throughout the living space. The same fan pulls air back through return ducts to be reconditioned.

Coil The coil in an AC system is like the radiator in a car; it's a place where heat is transferred. The coil consists of a serpentine run of tubing where refrigerant circulates. When a heat pump is operating in cooling mode (air conditioning), the condensing coil (condenser) is located outside, while the evaporating coil (evaporator) is located inside, in the system's air handler. In both locations, fans blow air across the coil to facilitate heat transfer.

Compressor Essentially a specialized pump, the compressor moves the refrigerant through the cooling or heating cycle. When the refrigerant is put under pressure, its temperature increases. When pressure is reduced (see "Expansion Valve," below), the refrigerant cools.

Condenser This outdoor coil allows the refrigerant to condense (change from a gas to a liquid), thereby transferring its heat to the outdoors.

Ductless mini-split system As the name suggests, this type of air conditioning system doesn't distribute cooled air through ductwork. Instead, the system's air handler unit is mounted on a wall or ceiling and blows conditioned air directly into the room.

Evaporator Sometimes called the evaporator coil (see "Coil," above), this part of the AC system allows the liquid refrigerant to boil or evaporate, turning into a gas. With this phase change, the refrigerant removes unwanted heat from the house.

Expansion valve Putting refrigerant under pressure increases its temperature. The expansion valve removes this pressure, allowing the refrigerant to cool before entering the outdoor condenser coil.

Refrigerant This chemical compound changes from a liquid to a vapor (a phase change) at a very low temperature, a characteristic that is ideally suited to absorbing and releasing heat in heat pump and air conditioning systems.

SEER rating The Seasonal Energy Efficiency Ratio is a standard measure of air conditioning efficiency during a "normal" annual cooling season. More specifically, SEER is the system's total cooling output in BTUs divided by the unit's total energy input in watt-hours. NOTE: The EER (Energy Efficiency Ratio) is a similar rating that is based on the unit's performance during peak cooling conditions (typically 95°F). The higher a unit's SEER or EER, the more efficient the unit. The minimum permissible SEER for residential split-system air conditioners is 13.0.

Ton This measure of air conditioning capacity originated back when people purchased ice to keep cool. A "ton" of cooling capacity equals the amount of heat absorbed by one ton of ice melting over 24 hours. One ton of cooling capacity is equal to 12,000 Btu/h.

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