Glossary of Heating, Ventilation and Air Conditioning (Part One A-K)

A.

AC or DC Abbreviation for equipment capable of operating on alternating or direct current.

AFUE Annual Fuel Utilization Efficiency. A measure of a gas furnace’s efficiency in converting fuel to energy. The higher the rating, the more efficient the unit.

Air Conditioner Any device that can change the temperature, humidity or general quality of the air.

Air Cleaner Any device that removes undesirable particles from moving air.

Air Handler An air moving and/or mixing unit. Residential air handlers include a blower, a coil, an expansion device, a heater rack and a filter. Heaters for air handlers are sold as accessories. In some models heaters are factory installed.

ARI Air Conditioning & Refrigeration Institute.

ASHRAE American Society of Heating, Refrigeration and Air Conditioning Engineers.

B.

BTU British thermal unit. The amount of heat required to raise or lower the temperature of one pound of water one degree Fahrenheit. The heat extracted from your home by an air conditioner is measured in BTUs.

BTUh British thermal units per hour. 12,000 BTUh equals one ton of cooling.

C.

Capacity The output or producing ability of cooling or heating systems. Cooling and heating capacities are referred to in British thermal units (BTUs) per hour.

Celsius The metric temperature scale in which water freezes at zero degrees and boils at 100 degrees, designated by the symbol “C”. To convert to Fahrenheit, multiply a Celsius temperature by 9, divide by 5 and add 32 (25 x 9 equals 225, divided by 5 equals 45, plus 32 equals 77 degrees Fahrenheit).

Compressor This is the heart of an air conditioning or heat pump system. It is part of the outdoor unit and pumps refrigerant to meet the cooling requirements of the system.
CondensateVapor that liquefies due to the lowering of its temperature to the saturation point.

Condenser Coil (or outdoor coil) In an air conditioner, the coil dissipates heat from the refrigerant, changing the refrigerant from vapor to liquid. In a heat pump system, the coil absorbs heat from the outdoors.

Condenser Fan The fan that circulates air over the aircooled condenser.

D.

DC Direct current electricity. This type of electricity (as opposed to Alternating Current, or AC) flows in one direction only, without reversing polarity.

Damper Found in ductwork, this movable plate opens and closes to control airflow. Dampers can be used to balance airflow in a duct system. They are also used in zoning to regulate airflow to certain rooms.

Dehumidifier An air cooler that removes moisture from the air.

Diffuser A grille over an air supply duct having vanes to distribute the discharging air in a specific pattern or direction.

Ductwork A pipe or conduit through which air is delivered. Ducts are typically made of metal, fiberboard or a flexible material. In a home comfort system, the size and application of ductwork is critical to performance and is as important as the equipment.

E.

EER Energy Efficiency Ratio (steady state).

ENERGY STAR® Trane high efficiency systems carry the ENERGY STAR label which is the result of Trane’s partnership with the U.S. Department of Energy and Environmental Protection Agency (EPA). ENERGY STAR products are more energy efficient and help reduce our whole earth’s pollution problems. Choosing a Trane ENERGY STAR Comfort System assures homeowners of lower energy bills and improved indoor air quality for their home.

EPA Environmental Protection Agency.

Expansion Valve A refrigerantmetering valve with a pressure or temperature controlled orifice.

Evaporator Coil (or Indoor Coil) The other half of an air conditioning system, located inside your home in the indoor unit. This is a tubing coil in which a volatile liquid evaporates and absorbs heat. This is where the refrigerant evaporates as it absorbs heat from the indoor air that passes over the coil.

F.

Fahrenheit The temperature scale on which water freezes at 32 degrees and boils at 212 degrees; designated by the letter F. To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit number, multiply by 5 and divide by 9 (77 32 equals 45, times 5 equals 225, divided by 9 equals 25 degrees Celsius).

Fan Any device that creates air currents.

Filter Any device that removes impurities through a straining process.

Furnace That part of the heating system in which the combustion of fossil fuel and transfer of heat occurs.

H.

Heat Exchanger An area, box or coil where heat flows from the warmer to the colder fluid or surface.

Heat Gain Heat added to the conditioned space by infiltration, solar radiation, occupant respiration and lighting.

Heating Coil Any coil that serves as a heat source.

Heat Loss The rate of heat transfer from a heated space to the outdoors.

Heat Pump A mechanicalcompression cycle refrigeration system that can be reversed to either heat or cool the controlled space.

Heat Transfer The movement of heat energy from one point to another. The means for such movement are conduction, convection, and radiation.

HSPF Heating Seasonal Performance Factor. This rating is used in measuring the heating efficiency of a heat pump. The higher the number, the more efficient the heat pump system.

Humidifier A machine that adds water vapor to the air to increase humidity.

Humidistat A humiditysensing control that cycles the humidifier on and off.

Humidity The presence of water vapor in the air.

Humidity, Absolute Weight of water vapor per cubic foot of dry air, expressed as grains of moisture per cubic foot.

Humidity, Relative The amount of moisture in the air expressed as a percentage of the maximum amount that the air is capable of holding at a specific temperature.

HVAC Heating, Ventilating and Air Conditioning.

K.

Kilowatt (kW) 1,000 watts.


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