HVAC Terminology
A comprehensive glossary of 324 HVAC terms and definitions to help you prepare for certification exams.
Filter by letter:
A-Coil
This heat exchanger depends on two coils, placed diagonally and then connected in the middle. The result is a coil that looks like the letter “A”.
Absolute Humidity
The humidity of the air measured by the number of grains of water vapor present in one cubic meter of air.
Absolute Pressure
The sum of gauge and atmospheric pressure (psia).
Absolute Temperature
The temperature measured on the Kelvin scale.
Absolute Zero
The lowest temperature theoretically attainable on the Kelvin scale (approximately 273.16° C).
Absorbent
A material that extracts one or more substances from a fluid (gas or liquid) medium on contact, and which changes physically and/or chemically in the process. The less volatile of the two working fluids in an absorption cooling device.
Absorption
In physics, the taking up of light, heat, or other energy by molecules. The absorbed energy is converted into heat. Absorption in chemistry is the taking up of one substance by another. For example, a gas such as oxygen may be absorbed, or dissolved, in water. In the HVAC industry heat energy is absorbed from the medium being cooled and transferred in the refrigerant.
Absorption Chiller
A type of air cooling device that uses absorption cooling to cool interior spaces.
Absorption Cooling
A process in which cooling of an interior space is accomplished by the evaporation of a volatile fluid, which is then absorbed in a strong solution, then desorbed under pressure by a heat source, and then condensed again at a temperature high enough that the heat of condensation can be rejected to a exterior space.
Absorption Refrigeration
A system in which a secondary fluid absorbs the refrigerant, releasing heat, then releases the refrigerant and reabsorbs the heat. Ammonia or water is used as the vapor in commercial absorption cycle systems, and water or lithium bromide is the absorber.
ACCA
ACCA is a non-profit association whose membership includes more than 60,000 professionals and 4,000 businesses in the indoor environment and energy services community.
Accumulator
A shell device installed in the suction line of a HVAC system to prevent liquids from entering the compressor.
Acoustical
Relating to sound, the science of sound, or a sense of hearing.
Activated Carbon
Processed carbon used in filter driers and commonly used in air filters to clean the air.
Active Cooling
HVAC term for compressor driven air conditioning.
Active Power
The power (in Watts) used by a device to produce useful work. Also called input power.
Actuator
A mechanical device for moving or controlling a mechanism or system.
Adiabatic
A change in gas condition where no heat is added or removed except in the form of work.
Adiabatic cooling
Adiabatic cooling is the process of reducing heat through a change in air pressure caused by volume expansion.
Adjustable Speed Drive
An electronic device that controls the rotational speed of motor-driven equipment such as fans, pumps, and compressors. Speed control is achieved by adjusting the frequency of the voltage applied to the motor.