HVAC Glossary of Terms

[A]

Absolute Humidity:

The amount of water vapor per square foot.

Absorption Cycle:

Absorption cycle utilizes a thermal or chemical process to produce the refrigeration effect.

Accumeter:

An accumeter is a flow control device within a carrier centrifugal chiller. It feeds the cooler with liquid refrigerant, which has a greater cooling capacity than a gas refrigerant.

Accurator:

An accurator is a metering device that provides the correct amount of liquid refrigerant into the evaporator.

Air Change:

The volume of air necessary to completely replace the air in an enclosed space.

Air Conditioner:

Equipment that controls air temperature, relative humidity, purity, and motion.

Air Cooled:

Removes indoor heat by moving heat from a condenser coil to the outdoors with the use of a fan.

Air-Cooled System:

Utilizes refrigerant and air as a condensing medium.

Air Diffuser:

Equipment that directs airflow into a desired pattern.

Air Flow:

Movement of air.

Air Handler:

The part of a central air conditioner that moves cooled air through the duct system.

Annual Fuel Utilization Efficiency (AFUE):

A rating that measures the amount of heat per dollar that the heating equipment provides. This rating is calculated in accordance with the Department of Energy test procedures.

ARI (Air-Conditioning and Refrigeration Institute):

Non-profit organization for heating, air conditioning, and refrigeration manufacturers. They publish standards for testing and rating heat pumps and air conditioners, standardizing a measure of comparison.

Atmospheric Pressure:

The measure in weight of a 1 square inch column of the atmosphere.

Auto Changeover:

Automatic switch to a back up air conditioning system in the event of a failure.

[B]

Balance Point:

Between 30 and 40 degrees, an outdoor temperature that equals the heating needs of the home without the need for supplemental electric resistance heat.

Bimetal:

Used to open or close a switch or valve, bimetal is comprised of two metals with different rates of expansion that are secured together. When heated or cooled, they will warp and open the valve/switch.

Blower:

Device that moves air in a distribution system.

Boiling Point:

Temperature in which a liquid will turn to a vapor.

BTU (British Thermal Unit):

The rate that measures the amount of heat needed to raise the temperature of a pound of water by one degree Fahrenheit.

BTU/hr:

The rate of measurement that raises the temperature of one pound of water by one degree Fahrenheit per hour.

[C]

Capacity:

The amount of space a heating or cooling system can heat or cool. Heating ability is expressed in BTUs and cooling ability is expressed in tons.

Carbon Monoxide:

Colorless, odorless gas produced from burning any fuel.

Central Air Conditioner System:

Air is cooled at a central point and distributed through fans and ducts.

Centrifugal Compressor:

A compressor that uses a rotating impeller to compress the refrigerant vapor. The vapor is drawn into the impeller axially, energy is added to the vapor, and then it is discharged.

Centigrade (Measure of Temperature):

A temperature scale that measures the boiling point at 100 degrees and the freezing point at 0 degrees (sea level).

CFM (Cubic Feet per Minute):

Cubic feet per minute - the measurement for the rate of air flow in an air conditioner.

Charge:

The charge is the total refrigerant in a system.

Chilled Water System:

Utilizes a separate chiller that houses the refrigerant. It cools the water and pipes it to the air conditioner.

Comfort Air Conditioning:

Designed for the comfort of people. People generate humid heat. Comfort air conditioning systems remove 60-70% dry/sensible heat and 30-40% of humidity.

Compressor:

Cycles refrigerant from the indoor evaporator to the outdoor condenser and back to the evaporator.

Compression:

Mechanically reduces the volume of vapor or gas.

Compression Ratio:

Discharge pressure divided by suction pressure.

Condensation:

Through heat removal, gas is changed into a liquid.

Condensation Point:

If the temperature were reduced below this point it would change the vapor to a liquid.

Condenser:

A condenser disposes of unwanted heat. The three types of condensers are air-cooled, water-cooled, and evaporative.

Condenser Coil:

A network of tubes filled with refrigerant. It removes heat to make the gaseous refrigerant a liquid again.

Condensing Unit:

A refrigerant mechanism that pumps vaporized refrigerant from the evaporator, compresses it, liquefies it, and returns it to the refrigerant control.

COP (Coefficient of Performance):

The COP measures how energy efficient a chiller operates.

Cooling Anticipator:

A heater that is parallel to the cooling circuit and shortens the off cycle.

Cooling Capacity:

Measures the ability of a unit to remove heat from a room or building.

Cooling Load:

Based on an engineering space analysis, the amount of conditioned air needed to cool a space.

[D]

Damper:

Movable plates within the ductwork that are used in zoning to regulate airflow to certain rooms.

Defrost Cycle:

During the heating season, the procedure to remove frost/ice build up from the outdoor coil.

Dehumidification:

Removal of water vapor from the air by either cooling the air below dew point or by chemical means.

Department of Energy (DOE):

A government department dedicated to monitoring energy use and setting industry efficiency standards.

Direct Expansion Systems:

A type of basic cooling media that uses Freon for cooling and dehumidification; the three most common methods of heat rejection are air cooled, water cooled, and glycol cooled.

Direct Vent:

Uses outside air for combustion and then vents the resulting gases back outside.

Downflow:

Used most often in computer rooms and modern office spaces, a type of precision air conditioning system that discharges air directly beneath a raised floor.

Downflow Furnace:

A furnace that inhales return air from the top and exhales warm air at the bottom.

Duct:

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

Ductwork:

Channels used to move air throughout a building.

[E]

Economizer:

In terms of HVAC, an economizer is a mechanical device that is used to reduce energy consumption.

Efficiency:

The cooling and heating equipment rating that judges the cost-efficiency of the system.

Electronic Air Cleaner:

Equipment that filters particles and contaminants from indoor air.

Emergency Heat (Supplemental or Auxillary Heat):

Supplementary heat in a heat pump system, used in an emergency situation.

Energy Efficiency Ratio (EER):

Ratio of the cooling capacity of an air conditioner in BTUs to electrical input in watts (API-specified test conditions).

Enthalpy:

The total heat contained in a refrigerant at any given temperature.

Evaporator:

Absorbs heat and moves it outside the refrigerated area.

Evaporator Coil:

A series of refrigerant filled tubes that take heat and moisture out of indoor air.

[F]

Fahrenheit (Represented as degrees "F"):

United States of America's unit of temperature measurement.

Filter:

Removes dust/particles from the air to reduce the load on the respiratory systems and HVAC equipment.

Free Cooling System:

Water cooled or glycol cooled system with an added coil that provides chilled water cooling when the outdoor temperature is cold.

Free Delivery:

A system that doesn't use ducts.

Freon:

Describes a group of halogenated simple hydrocarbons containing fluorine, chlorine, or bromine (used as refrigerants).

Furnace:

Equipment that convert gas, oil, electricity, or other fuel into heat.

[G]

Generator:

The container in which the lithium bromide solution is boiled and re-concentrated.

Glycol-Cooled System:

An air conditioning system that uses Freon as a refrigerant and water/glycol as a condensing medium.

Ground Water-Source:

Underground well water is used as a heat source for a heat pump.

[H]

Heat Exchanger:

Transfers heat energy from the source to the medium.

Heat Gain:

The amount of heat that enters an indoor area during the air conditioning season, measured in BTUs.

Heat Loss:

The amount of heat that is lost from an indoor area during the heating season, measured in BTUs.

Heat Pump:

A system that has a valve that allows it to alternate between heating and cooling.

Heat Source:

The heat source that the heating system uses to warm an indoor area.

Heat Transfer:

The movement of heat from one area to another.

Heating Capacity:

The rating that judges how much heat a device can provide.

Heating Seasonal Performance Factor (HSPF):

Total heat pump output in BTUs divided by total electrical input in watt-hours during normal usage period.

Horizontal Furnace:

A furnace that pulls return air in on one side and expels warm air on the other side.

HVAC:

Heating, Ventilation, and Air Conditioning.

Humidification:

The method of adding moisture to the air.

Humidistat:

Equipment that regulates humidity input by reacting to moisture changes in the air.

Humidity:

Humidity is the amount of moisture in the air.

[I]

Indoor Unit:

Contains the indoor coil, fan, motor, and filtering device.

Indoor Coil:

Tubing containing refrigerant.

Infiltration:

Air flow leaks into a living space.

Insulation:

Slows down the transfer of heat.

Integrally Controlled Motor (ICM):

An efficient, variable-speed motor.

Isolation Valves:

Valves that transfer and isolate refrigerate charge in the cooler or condenser.

[J]

No Definitions at this time.

[K]

(K) Factor:

(k) Factor is the insulating value.

Kilowatt (kW):

A unit of electrical consumption that equals 1,000 watts.

[L]

Latent Cooling Capacity:

The capability of an air conditioner to remove moisture from the air.

Latent Heat:

The amount of heat energy needed to change a substance from a liquid to a gas.

LCD:

Liquid Crystal Display

Load Calculation:

A design tool that measures the heat gain and loss in a building; it helps determine the proper air conditioning/heating equipment size.

[M]

Matched System:

A heating/cooling system that is equipped with products that have been certified to perform optimally together.

Microprocessor Controls:

Uses computer logic to operate and monitor air conditioning systems.

[N]

Natural-Draft Furnace:

A furnace that utilizes the natural flow of air around the furnace to provide air to support combustion.

NFPA:

National Fire Protection Association.

[O]

Operating Cost:

The cost of running the air conditioner/heater in a space.

Outdoor Coil/Condensing Unit:

Collects heat and moves it to the outdoor air.

[P]

Package System:

A system where all air conditioning and heating equipment is located in one cabinet.

Packaged Unit:

A self-contained heating and/or air conditioning system.

Payback Analysis:

It is a measure of the value of a home comfort system; combining your purchase price and operating cost, the payback analysis determines how many years it takes to offset the purchase price.

Precision Air Conditioning:

Pre-packaged systems designed to cool electronic equipment.

Purge Device:

Equipment that removes air and water vapor from the refrigerant of a negative pressure designed chiller.

[Q]

No Definitions at this time.

[R]

Refrigerant:

A substance that provides a cooling effect by expanding or vaporizing.

Refrigerant Lines:

The connection between an outdoor and indoor unit made of two copper lines.

Register:

Covers an air opening or the end of an air duct; it is a combination of a grille and damper.

Relative Humidity:

Given a certain temperature, the amount of vapor in the air divided by the largest amount of vapor that could be contained in the air.

Return Air:

The air drawn into the heating unit after circulating from the heater's output supply.

Reversing Valve:

The device within a heat pump that reverses the refrigerant flow and switches the equipment from cooling to heating.

[S]

SEER (Seasonal Energy Efficiency Ratio):

The Seasonal Energy Efficiency Ratio measures the energy efficiency of air conditioning equipment.

Sensible Cooling Capacity:

The air conditioner's ability to remove heat from an area.

Sensible Heat:

Heat energy that changes the temperature of a gas, liquid, or solid when added or removed.

Setpoint:

The ideal thermostat temperature.

Single Package:

A year-round heating and air conditioning system that is contained in a single package.

Split System:

The most common system installed in homes, it is a central air conditioner that contains a compressor and condenser installed outdoors and a non-compressor installed inside the building.

Storage Tank:

The refrigerant temporarily is stored here while being serviced.

Supercooled Liquid:

Liquid refrigerant cooled below its saturation point.

Subcooler:

Some condensers contain this section, which reduces the temperature of the condensed refrigerant liquid, improving energy efficiency.

Subcooling:

Removes sensible heat from a refrigerant liquid by dropping the temperature.

Superheated Vapor:

Refrigerant vapor heated beyond its saturation point.

Superheating:

Adds heat energy to a refrigeration vapor by creating a rise in temperature.

Supplementary Heat:

Emergency heat, available at temperatures below a heat pump's balance point.

Switchover:

Equipment that switches the heat pump from cooling to heating by changing the flow of refrigerant.

[T]

Temperature:

The measure of heat matter contains.

Thermidistat:

A sophisticated thermostat that measures the outdoor temperature, indoor air temperature, and indoor relative humidity. A microprocessor communicates with the temperature control equipment to determine the most efficient method of achieving an optimal temperature.

Thermostat:

A temperature control device that monitors the control functions of temperature control equipment.

Tonnage:

In cooling systems, the unit of measurement that describes the cooling capacity.

[U]

Upflow:

An air conditioner that discharges cool air through a top-mounted discharge plenum or overhead duct.

Upflow Furnace:

A type of furnace that expels warm air at the top and expels return air at the bottom.

[V]

Vacuum Pump:

Removes air and water vapor from a refrigeration system below atmospheric pressure.

Vapor Barrier:

A moisture-proof layer, preventing the travel of water vapor.

Vapor Seal:

A vapor seal is a critical component of sealing moisture out of a sensitive room. The seal barricades air, moisture, and contaminants from moving through small cracks or pores in the walls, floor, or ceiling into the contaminant-sensitive area.

Ventilation:

Adding or removing air by either natural or mechanical means to or from any space.

Ventilator:

Removes stale indoor air and transfers it to fresh incoming air.

[W]

Water Cooled System:

An indoor cooling unit that utilizes Freon and water as a condenser. Water is piped to the unit from a suitable source.

Water Source:

Water is a heat source for the heat pump.

Watt:

A unit of power.

[X]

No Definitions at this time.

[Y]

Year-Round:

A gas or oil fueled air conditioner.

[Z]

Zone System:

A system that divides a space into zones and provides the ability to control the temperature for each zone separately.

Zoning:

The act of providing independent heating and cooling options to different zones of a structure. This practice uses a system controller, zoning dampers, and a bypass damper.

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