Glossary of HVAC Terms

AFUE (Annual Fuel Utilization Efficiency) - A rating that denotes the efficiency of gas heating equipment. It is the amount of heating your equipment delivers for every dollar spent on fuel. A higher rating indicates more efficient equipment. This rating is calculated in accordance with the Department of Energy test procedures.

Ambient Temperature - The temperature, usually of the air, that surrounds operating equipment.

BTU (British Thermal Unit) - The standard of measurement used for measuring the amount of heat required to raise the temperature of one pound of water by one degree (Farenheit).

BTUH - The number of BTUs in an hour.

Compressor - A machine used to compress gasses. The function of the compressor is to maintain a pressure difference between the high and low sides of the system. It is considered the heart of an air conditioning or heat pump system. The compressor is the part of the outdoor equipment that pumps the refrigerant. On the cooling side, it draws in the low-pressure refrigerant and compresses it into high-pressure on the condensing side of the cycle. The compressor maintains adequate pressure within the system to cause refrigerant to flow in sufficient quantities to meet the cooling requirements. There are four types of compressors: reciprocating, rotary, scroll, and centrifugal. Most residential systems have reciprocating or scroll compressors.

Condenser - A device that transfers unwanted heat out of a refrigeration system to a medium (either air, water, or a combination of air and water) that absorbs the heat and transfers it to a disposal point. There are three types of condensers: air-cooled condensers, water-cooled condensers, and evaporative condensers. The evaporative condenser uses a combination of air and water as its condensing medium. Most residential systems have an air-cooled condenser.

DOE -The Department of Energy. A federal agency that sets industry efficiency standards and monitors the use of various energy sources.

Enthalpy - Heat content or total heat, including both sensible and latent heat. The amount of heat contained in a refrigerant at any given temperature with reference to -40°F.

Evaporator - Absorbs heat from the surrounding air or liquid and moves it outside the refrigerated area by means of a refrigerant. It is also know as a cooling coil, blower coil, chilling unit or indoor coil.

HVAC - Heating, ventilation, and air conditioning.

Insulation - Any material that slows down the transfer of heat.

(K) Factor - The insulating value of any material. Also known as conductivity.

Kilowatt (KW) - Equal to 1,000 watts.

Kilowatt-hour (KWH) - A common unit of electrical consumption measured by the total energy created by one kilowatt in one hour.

Latent Heat - The heat energy needed to change the state of a substance (i.e.: from a liquid to a gas) but not it's temperature.

SEER-(Seasonal Energy Efficiency Ratio) - A rating that denotes the efficiency of air conditioning equipment. It is the amount of cooling your equipment delivers for every dollar spent on electricity. It is the ratio of cooling delivered by a system, measured in BTUs, to the dollar cost of the electricity to run the system, as measured in watt-hours. This ratio is determined using specified federal test procedures.

Sensible Heat - Heat energy that causes a rise or fall in the temperature of a gas, liquid or solid when added or removed from that material. Sensible heat changes the temperature by changing the speed at which the molecules move.

Split System - A refrigeration or air conditioning system that consists of a "hot" side, or the condensing unit-including the condensing coil, the compressor and the fan-which is situated outside your home. The hot side is connected to the "cold" side-located inside your home-via supply and return refrigerant lines. The cold side consists of an expansion valve and a cold coil, and it is usually part of the furnace or some type of air handler. The furnace blows air through an evaporator coil, which cools the air. Then this cool air is routed throughout your home by means of a series of air ducts. This type of set up is also used with heat pump installations.

Supercooled Liquid - Liquid refrigerant cooled below its saturation point.

Subcooling - Creating a drop in temperature by removing sensible heat from a refrigerant liquid.

Superheated vapor - Refrigerant vapor heated beyond its saturation point.

Superheating - Creating a rise in temperature by adding heat energy to a refrigeration vapor.

Ton - A sizing measure for the capacity of air conditioners and heatpumps. A ton is the total BTU capacity of a system. One ton is equal to the BTU's required to melt one ton of ice in a 24 hour period. There are 12,000 BTU's in a ton, a 2 ton air conditioner will produce 24,000 BTU's, a 3 ton will produce 36,000 BTU's and so on... The size of the area to be cooled will determine the correct size of the system in tons. Published capacity ratings are based on ARI standard temperatures of 95°F, outside and 80°F inside, but the actual capacity of a system changes with outdoor and indoor temperatures.

Watt - A unit of power that equals one joule per second. Named after James Watt.