A term that stands for Heating, Ventilating, Air Conditioning, and Refrigeration

Air Conditioner

A system of components that control air temperature, relative humidity, air filtration, air sanitization, and airflow in a conditioned space.

Air Cooled System

A type of cooling system that uses air to cool a condensing coil in which refrigerant vapor is condensed into a liquid.

Air Handling Unit (or Air Handler)

The portion of the central air conditioning system that moves heated or cooled air throughout the ductwork


The fan that circulates the indoor air through the system


A unit that heats the water. A boiler does not boil water unless it is a steam boiler


A British Thermal Unit is the amount of heat required to raise the temperature of 1 Lb. of water 1 degree Fahrenheit


The total amount of heat required to be added or removed from a space in a one-hour period to maintain space temperature. The amount of heat or cooling a system can generate in a one-hour period

Capacity Control

A means of reducing the effective amount of heat transfer of a system


The quantity of refrigerant in the refrigeration system


A unit that cools water to be distributed to water-cooling coils


A pump that moves water around in a loop through a closed system


A portion of the refrigeration system that transfers heat to or from the refrigerant in the refrigeration system using air, water, glycol, or any other media that is at a different temperature

Cooling Tower

An outdoor heat rejection unit that removes heat from water by evaporation


A device that compresses a low-pressure, low-temperature, superheated refrigerant vapor and transforms it into a high-pressure, high-temperature, superheated vapor

Condenser Coil

A coil is used to reject heat from the refrigeration system by removing heat from the refrigerant and converting the refrigerant from a high-pressure, high-temperature, superheated vapor into a high-pressure, medium-temperature, subcooled liquid

Condensing Unit

A unit that contains a compressor, condenser coil, condenser fans (air-cooled system), and electrical control components


A device that removes humidity from the air


Any pipe or closed chamber, usually made of sheet metal or fiberglass, that is used for transferring air through an air handling unit to and from a conditioned space

Ductless Split System

A type of air conditioning system that does not use ducts to transfer cool air and instead the outdoor unit is connected directly to one or more indoor air handler that delivers air directly to the conditioned space

Dual Fuel System

A heating system capable of using two types of fuel to supply heat


A set of dampers with controls that offer free outdoor air cooling when the outdoor conditions are low enough. Economizers are also capable of supplying ventilation for fresh air to the space

EER (Energy Efficiency Ratio)

A ratio to determine the energy efficiency of an air conditioner. The higher the EER rating, the more efficient the unit


A measure of the energy supplied to the system that is used without being wasted to effectively condition the space

Electronic Expansion Valve

A refrigerant metering device controlled by an electronic control and used to control the system superheat

Evaporator Coil

A coil that absorbs heat from the surrounding media in which liquid refrigerant vaporizing

Evaporator Pressure Regulator (EPR) Valve

A mechanical or electrically controlled valve is used to prevent the refrigeration system evaporator from going below a set pressure

Fresh Air Intake

An opening through which outdoor air is drawn into a system


A unit that adds heat to the air by burning fuel in a heat exchanger

Head Pressure Regulator

A device that prevents the high-pressure side of a refrigeration system from going below a set point

Heat Pump

A refrigeration system that uses a reversing valve to allow the outdoor coil to absorb heat from the outdoor air and reject that heat into the indoor air

Heat Recovery Valve

A device used to transfer heat that would have been wasted to warm another medium such as water or air steam and thereby saving energy


A device that adds moisture to the air through evaporation


The Heating Seasonal Performance Factor is a measure of efficiency for air source heat pumps. A higher number represents higher efficiency

Indirect Water Heating Tank

A domestic water heating tank that has a coil which boiler water flows through to heat the water

Load Calculation

A calculation to determine the amount of heat gained into or lost out of a structure at a specified outdoor temperature

Low Ambient Operation

Controlling a system to operate a lower outdoor temperature

Oil Management System

A means of controlling the proper oil level in a refrigeration compressor

Packaged Unit

A unit that has all the components to condition a space in one unit

Plasma Air Purifier

Kills bacteria and viruses.  Eliminates odor and smells


A device that moves water for an open water system


A chemical that can be used in a mechanical system to produce a heat transfer effect while changing the pressure of the refrigerant and thereby changing the state from liquid to vapor and back to liquid. Refrigerant changing state from liquid to vapor absorbs large amounts of heat and when changing from vapor back to liquid rejects a large amount of heat

Refrigerant Metering Device

One of four essential components of a refrigeration system that cause a rapid drop in pressure of a high-pressure liquid refrigerant causing it to be transformed into a low-pressure vapor and in the process absorbing large quantities of heat


A grille and damper assembly that covers the opening or end of an air duct

Relative Humidity

The ratio of the amount of moisture in the air compared to the amount of moisture the air could hold at the current temperature expressed as a percentage

Return Air

The air is drawn back into the air handling unit from the conditioned space


A Rooftop Unit is a packaged unit that contains and fan and filter section and may contain heating and cooling equipment


Seasonal Energy Efficiency Ratio is a rating that expresses the efficiency of air conditioning equipment throughout an entire average cooling season. The higher the SEER rating, the more efficient the system

Solenoid Valve

A device with an electrically energized coil that causes a magnetic field to open a valve that allows flow through a system when powered and stops the flow when de-energized

Split System

A system whose components are in separate places. Usually an evaporator and air handler or furnace indoors and a condensing unit outdoors

Steam Boiler

A boiler that converts water to steam


A temperature-actuated switch

Thermostatic Expansion Valve (TXV)

A mechanical refrigerant metering device that senses low side pressure, and suction line temperature and employs a spring to control the system superheat


A unit of measure used to describe the cooling capacity of an air conditioning system.  One ton of cooling is the amount of heat needed to melt a one-ton block of ice in a 24-hour period. One ton of cooling is equal to 12,000 BTUs per hour

UV Lamp

A light to kill or inactivate microorganisms

Variable Air Volume

A system using constant system airflow that varies the amount of air delivered to each space depending on the room load


Variable Refrigerant Flow (VRF) systems vary the flow of refrigerant to indoor units based on demand. The ability to control the amount of refrigerant that is provided to fan coil units located throughout a building makes VRF technology ideal for applications with varying loads or where zoning is required


Variable Refrigerant Volume (VRV) systems are multi-split type air conditioners for commercial buildings that use variable refrigerant volume control originally developed by Daikin to provide the ability to maintain individual zone control in each room and floor of a building. All other manufacturers refer to this as VRF

Water Source Heat Pump

Water source heat pumps operate much like a traditional air source heat pump except that it extracts and rejects heat through the water instead of air

Water Source Heat Pump System

A system that uses several water source heat pumps connected to a water loop circulated to transfer heat between units via the water flow. Heat is added to the water system when needed usually by a boiler. Heat is rejected from the system when needed through an outdoor cooling tower


A method of providing independent heating or cooling to different areas or rooms within a building. Typically controlled by separate controls or by opening or closing the vents and ducts in each zone