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HVAC Terminology

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

Reduction or removal of a contaminant.

Absolute Humidity
It is the ratio of the mass of water vapor to the unit volume of moist air represented in grams per cubic foot (g/ft3).

Absolute Zero
Temperature at which all molecular motion ceases (-460 F. and -273 C.).

Absorption Refrigerator
Refrigerator which creates low temperature by using the cooling effect formed when a refrigerant is absorbed by chemical substance.

Air Conditioning Contractors of America - a leading HVAC/R Association.

Acceptable indoor air quality
Indoor air that does not contain harmful concentrations of contaminants; air with which at least 80% of building occupants do not express dissatisfaction.

Storage tank which receives liquid refrigerant from evaporator and prevents it from flowing into suction line before vaporizing. Tank on the suction side of a system that holds excess refrigerant to prevent slugging the compressor with liquid.

Air Changes Per Hour. The number of times that air in a house is completely replaced with outdoor air in one hour.

Acid Condition In System
Condition in which refrigerant or oil in system is mixed with fluids that are acid in nature.

ACR Tubing
Tubing used in air conditioning and refrigeration. Ends are sealed to keep tubing clean and dry.

Activated Carbon
Specially processed carbon used as a filter drier ; commonly used to clean air.

That portion of a regulating valve which converts mechanical fluid, thermal energy or electrical energy into mechanical motion to open or close the valve seats.

Adiabatic Compression
Compressing refrigerant gas without removing or adding heat.

Adjustable Grille
A grille with linear blades which can be adjusted to vary the direction of the discharged air. The linear blades are normally either vertical or horizontal, or both horizontal and vertical.

Substance with the property to hold molecules of fluids without causing a chemical or physical damage.

Act of combining substance with air.

AFLU (Annual Fuel Utilization Efficiency)
A rating that reflects the efficiency of a gas furnace in converting fuel to energy. A rating of 90 means that approximately 90% of the fuel is utilized to provide warmth to your home, while the remaining 10% escapes as exhaust.

AFUE (Annual Fuel Utilization Efficiency)
This number represents how efficiently a furnace converts fuel to energy. The ratio of annual output of useful energy or heat to the annual energy input to the furnace. The higher the AFUE, the more efficient the furnace -- higher efficiency translates to more savings on fuel bills. This will range from 80% to 95%. Percentage of fuel used for heating. A measure of heating efficiency, in consistent units, determined by applying the federal test method for furnaces. This value is intended to represent the ratio of heat transferred to the conditioned space by the fuel energy supplied over one year.

Air Conditioner
Device used to control temperature, humidity, cleanliness and movement of air in a confined space.

Air Conditioning
Control of the temperature, humidity, air movement and cleaning of air in a confined space.

Air Diffuser
Air distribution outlet or grille designed to direct airflow into desired patterns.

Air Exchange Rate
The rate at which outside air replaces indoor air in a space. Expressed in one of two ways: the number of changes of outside air per unit of time in air changes per hour (ACH); or the rate at which a volume of outside air enters per unit of time - cubic feet per minute (cfm).

Air Handler
The portion of the central air conditioning or heat pump system that moves heated or cooled air throughout a home's ductwork. In some systems a furnace handles this function.

Allergens and Pathogens
Biological material, including bacteria, viruses, fungi, mold spores, pollens, skin flakes and insect parts are ubiquitous in indoor environments. These particulates range from less than one to several microns in size. When airborne, they are usually attached to dust particulates of various sizes so that all sizes of airborne particulates may include them.

The surrounding atmosphere; encompassing on all sides; the environment surrounding a body but undisturbed or unaffected by it.

Ambient Air
The air surrounding a building; outside air.

Ambient Air Temperature
Surrounding temperature, such as the outdoor air temperature around a building.

Ampere (A or Amp)
The primary unit of measurement of electrical current. Amps multiplied by Volts determines Watts. Electricity bills are based on watts or kilowatts (a thousand watts) per hour.

Air-Conditioning and Refrigeration Institute is a nonprofit, voluntary organization comprised of heating,air conditioning and refrigeration manufacturers. ARI publishes standards for testing and rating heat pumps and air conditioners to provide you with a standardized measure of comparison. So, ARI ensures a level of performance within the industry.

A leading HVAC/R Association - American Society of Heating, Refrigerating and Air Conditioning Engineers - The trade association that provides information and sets standards for the industry.

American Society for Testing and Materials.

[ B ]

Balance Point
An outdoor temperature, usually between 30° F and 45° F, at which a heat pump's output exactly equals the heating needs of the home. Below the balance point, supplementary electric resistance heat is needed to maintain indoor comfort.

An air handling device for moving air in a distribution system.

Boiling Point
The temperature at which the addition of any heat will begin a change of state from a liquid to a vapor.

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 (Fahrenheit). BTUH - The number of BTUs in an hour.

The abbreviation for British thermal units per hour. The amount of heat required to raise one pound of water one degree fahrenheit per hour, a common measure of heat transfer rate.

Building Envelope
Elements of the building, including all external building materials, windows, and walls, that enclose the internal space.

[ C ]

The ability of a heating or cooling system to heat or cool a given amount of space. For heating, this is usually expressed in BTU's. For cooling, it is usually given in tons.

Central Air Conditioner System
System in which air is treated at a central location and carried to and from the rooms by one or more fans and a system of ducts.

Centrifugal Compressor
A type of compressor used in vapor compression refrigeration cycles where a rotating impeller is the device which compresses the refrigerant vapor. The vapor is drawn into the impeller axially, and is discharged radially after energy is added to the vapor within the impeller.

CFM (Cubic Feet per Minute)
The abbreviation for cubic feet per minute, commonly used to measure the rate of air flow in an air conditioning system.

Amount of refrigerant in a system.

Comfort Air Conditioning
Comfort air conditioning systems are designed for the comfort of people, not the protection of computer-based electrical systems. Unlike people, computers generate dry (sensible) heat, but not humidity. Only about 60-70% of a comfort system's total capacity is dedicated to the removal of sensible heat, while 30-40% is for dehumidification. With a large percentage of their total capacity devoted to the removal of moisture, comfort systems can lower room humidity far below acceptable standards. A larger comfort system is required to obtain the same sensible capacity as a precision cooling system.

The pump that moves the refrigerant from the indoor evaporator to the outdoor condenser and back to the evaporator again. The compressor is often called "the heart of the system" because it circulates the refrigerant through the loop.

The process by which a gas is changed into a liquid at constant temperature by heat removal.

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.

Condenser Coil
A series or network of tubes filled with refrigerant, normally located outside the home, that removes heat from the hot, gaseous refrigerant so that the refrigerant becomes liquid again.

Condensing Unit
Part of a refrigerating mechanism which pumps vaporized refrigerant from the evaporator, compresses it, liquefies it in the condenser and returns it to the refrigerant control. The outdoor portion of a split system air conditioner contains the compressor and outdoor coil ignoring the reverse cycle operation, also the outdoor in a heat pump system.

Cooling Capacity
A measure of the ability of a unit to remove heat from an enclosed space. COP - Coefficient of Performance of a heat pump means the ratio of the rate of useful heat output delivered by the complete heat pump unit (exclusive of supplementary heating) to the corresponding rate of energy input, in consistent units and under operating conditions.

Cooling Load
Heat which flows into a space from outdoors and/or indoors.

[ D ]

Found in ductwork, this movable plate opens and closes to control airflow. Dampers are used effectively in zoning to regulate airflow to certain rooms.

The reduction of water vapor in air by cooling the air below the dew point; removal of water vapor from air by chemical means, refrigeration, etc.

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

Direct Vent
Pulls outside air for combustion and vents combustion gases directly outside.

A pipe or closed conduit made of sheet metal, fiberglass board, or other suitable material used for conducting air to and from an air handling unit.

Pipes or channels that carry air throughout a building

[ E ]

Electronic Air Cleaner
An electronic device that filters out large particles and contaminants in indoor air. It then electronically pulls out tiny particles that have been magnetized, such as viruses and bacteria, drawing them to a collector plate.

Emergency Heat (Supplemental or Auxiliary Heat)
The back-up heat built into a heat pump system.

Energy Efficiency Ratio (EER)
Means the ratio of the cooling capacity of the air conditioner in British Thermal Units per hour, to the total electrical input in watts under ARI-specified test conditions.

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.

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

Evaporator Coil
A series or network of tubes filled with refrigerant located inside the home that take heat and moisture out of indoor air as liquid refrigerant evaporates.

[ F ]

A device used to remove dust and other particles from air for the purposes of reducing the load on the respiratory system and to protect the HVAC equipment. Filters vary greatly in particle arrestance; the higher the MERV rating, the better the filter.

Five-Two-One (5-2-1 Compressor Saver)
An electrical starting component that reduces air conditioner start-time by up to 50%. This helps lower energy bills and extend equipment life.

Free Delivery
There are no ducts and the unit may be installed in the field without ducts if needed. Ground-Source - The ground or soil below the frost line is being used as the heat source or heat sink for a heat pump.

A general term used to identify, any of a group of partially or completely halogenated simple hydrocarbons containing fluorine, chlorine or bromine, which are used as refrigerants.

That part of an environmental system which converts gas, oil, electricity or other fuel into heat for distribution within a structure.

[ G ]

In an absorption cycle, the vessel in which the lithium bromide solution is reconcentrated by boiling off the previously absorbed water.

Ground Water-Source
Water from an underground well is being used as the heat source or heat sink for a heat pump.

Glycol-Cooled System
A type of air conditioning system that uses freon as a refrigerant and a water/glycol solution as a condensing medium. Typically, the glycol-cooled condenser is located inside the air conditioner with the rest of the refrigeration components. Water/glycol is piped to the unit from a drycooler or other suitable source. The glycol keeps the solution from freezing during winter operation.

[ H ]

Heat Exchanger
A device for the transfer of heat energy from the source to the conveying medium.

Heat Pump
An air conditioner that contains a valve that allows it to alternate between heating and cooling.

Heat Source
A body of air or liquid from which heat is collected. With any heat pumps, the air outside the home is used as the heat source during the heating cycle.

Heat Transfer
The movement of heat from one place to another, between two substances, or within a substance.

Heating Capacity
The rate at which a specific device can add substantial heat to a substance, expressed in BTUh (British Thermal Units per hour)

Horizontal Furnace
A furnace that lies on its side, pulling in return air from one side and expelling warm air from the other

Heating, Ventilation, and Air Conditioning

The process of adding moisture to the air within a space

The amount of moisture in the air. Air conditioners remove moisture for added comfort

[ I ]

ICE 22
A premium, synthetic air conditioner oil that improves heat transfer capability and reduces wear and tear. Air conditioning systems produce cooler air, use less energy and last longer.

Indoor Unit
This is usually located inside the house and contains the indoor coil, fan, motor, and filtering device, sometimes called the air handler.

Indoor Coil
Refrigerant containing portion of a fan coil unit similar to a car radiator, typically made of several rows of copper tubing with aluminum fins.

Any material that slows down the transfer of heat.

Integrally Controlled Motor (ICM)
A variable-speed motor that operates at low RPM when possible for efficiency and quiet operation. ICM motors are more than 90% efficient versus 60% efficiency for conventional motors.

[ J ]

A unit of work or energy. It takes ~ 1,000 joules to equal a British thermal unit. It typically takes ~ 1 million joules to make a pot of coffee.

[ K ]

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.

kWh (kilowatt hour)
A kilowatt hour (kWh) is the amount of kilowatts of electricity used in one hour of operation of any equipment. The most commonly-used unit of measure telling the amount of electricity consumed over time. It means one kilowatt of electricity supplied for one hour. It is the basis for your electricity rate.

[ L ]

Latent Cooling Capacity
An A/C system's capability to remove moisture from the air.

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.

An abbreviation for a screen type - Liquid Crystal Display.

Load Calculation
A mathematical design tool used to determine the heat gain and heat loss in a building so that properly sized air conditioning and heating equipment may be installed.

[ M ]