HVAC Glossary

Alternative HVAC Solutions would like to offer the following HVAC Glossary as a helpful tool for you, our customer, to help with the various terms and technical definitions for the heating, cooling and indoor air quality industry.

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Abatement -  Reduction or removal of a contaminant.
Absolute Humidity -  This is often confused with mixing ratio. It is the ratio of the mass of water vapor to the unit volume of moist air. Vaisala products give this output as grams of water per cubic metre of air (g/m3).
Absolute Pressure -  Gauge pressure plus atmospheric pressure (14.7 lb.per sq.in.) equals absolute pressure.
Absolute Temperature -  Temperature measured from absolute zero.
Absolute Zero Temperature -  Temperature at which all molecular motion ceases (-460 F. and -273 C.)
Absorbent -  Substance with the ability to take up or absorb another substance.
Absorption Refrigerator -  Refrigerator which creates low temperature by using the cooling effect formed when a refrigerant is absorbed by chemical substance.
ACCA -  A leading HVAC/R Association - http://www.acca.org/
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.
Accessible Hermetic -  Assembly of a motor and compressor inside a single bolted housing unit.
Accumulator -  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.
ACGIH -  American Conference of Governmental Industrial Hygienists.
ACH -  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.
Action Packet -  In reference to the indoor air quality Tools for Schools Kit. The packet contains three components - an introductory memo, IAQ Backgrounder, and IAQ Checklist - to assist school personnel to implement an effective yet simple indoor air quality program in their school.
Activated Alumina -  Chemical which is a form of aluminum oxide. It is used as a drier or desiccant.
Activated Carbon -  Specially processed carbon used as a filter drier ; commonly used to clean air.
Actuator -  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.
Add On Heat Pump -  Installing a heat pump in conjunction with an existing fossil fuel furnace. The result is a dual fuel system.
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.
Adsorbent -  Substance with the property to hold molecules of fluids without causing a chemical or physical damage.
Aeration -  Act of combining substance with air.
Aerosol -  A suspension of liquid or solid particles in 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, 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 Change -  The amount of air required to completely replace the air in a room or building; not to be confused with recirculated air.
Air Cleaning -  An indoor air quality control strategy to remove various airborne particulates and/or gases from the air. The three types of air cleaning most commonly used are particulate filtration, electrostatic precipitation, and gas sorption.
Air Coil -  Coil on some types of heat pumps used either as an evaporator or condenser.
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 Cooler -  Mechanism designed to lower temperature of air passing through it.
Air Core Solenoid -  Solenoid that has a hollow core instead of a solid core.
Air Device, Lighting Troffer -  An air device, usually in the form of a slot or combination of slots, designed for use with a troffer unit.
Air Device, Linear -  Air device (grille) with an aspect ratio of 10: 1 or more.
Air Device, Slot -  A device with one or several slots with an aspect ratio of 10: 1 or more for each slot (the aspect ratio is the ratio of the length to the width of the closed rectangular opening). A slot may or may not have an adjustable member to vary the direction of the air jet(s) or air flow rate.
Air Device, Supply -  An air device through which air enters a treated space. It usually consists of one or several deflecting members which ensure reduction of the air velocity in the occupied zone as well as efficient mixing of the supply air with the air in the treated space. Moreover supply air devices usually the direction of the air jet(s).
Air Diffuser -  An air distribution outlet or grille designed to direct airflow into desired patterns. Supply air teRebholtz Mechanicalnal device, designed to direct airflow into desired patterns, usually placed in the ceiling, generally of circular, square or rectangular shape, and composed of divergent deflecting members.
Air Diffusion -  Distribution of the air in a space, called the treated space, by means of devices, called air teRebholtz Mechanicalnal devices, in a manner so as to meet certain specified conditions, such as air change rate, pressure, cleanliness, temperature, humidity, air velocity and noise level.
Air Distribution -  The transportation of a specified air flow to or from the treated space or spaces, generally by means of ductwork.
Air Exchange Rate -  The rate of air flow moving through a space, usually expressed in terms of room volume units per unit of time such as room air changes per hour.
Air Gap -  The space between magnetic poles or between rotating and stationary assemblies in a motor or generator.
Air Handler -  fan-blower, filter and housing parts of a system. Fan-blower, filter, heat transfer coil, and housing parts of a system. Also known as the blower section and part of the split system, this unit is commonly in your home or attic and blows the air through your house. This has to be matched with the condenser properly to assure maximum efficiency. This will contain your heating and evaporator coil.
Air Infiltration -  Leakage of air into rooms through cracks, windows doors and other openings.
Air Quality Standard -  A government-mandated regulation that specifies the maximum contaminant concentration beyond which health risks are considered to be unacceptable.
Air Source Equipment -  Heat pumps or air conditioners that uses the outdoor air to transfer heat to and from the refrigerant in the unit.
Air Technical Device -  A device located in an opening provided at the boundaries of the treated space to ensure motion of air in this space.
Air-Cooled Condenser -  Heat of compression, plus the heat of absorption, is transferred from refrigerant within coil to surrounding air, either by convection or fan or blower.
Ak value (of an air device) -  Quotient obtained by dividing a measured air flow rate by a measured air velocity according to a specific process and a specific instrument.
Algaecide -  Normally in tablet form, placed in evaporator drain pan. Used to help slow the growth of bacteria.
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.
Alternating Current (AC) -  Flow of electricity that constantly changes direction between positive and negative sides. Almost all power produced by electric utilities in the United States moves in current that shifts direction at a rate of 60 times per second.
Ambient -  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. One ampere of current is produced in a circuit by 1 volt acting through a resistance of 1 ohm.
Amplification -  An increase in the numbers or concentration of a microbe or its products through reproduction and growth of the microbe.
Annual Effects -  The total effects in energy use (measured in megawatthours) and peak load (measured in kilowatts) caused by all participants in the DSM programs that are in effect during a given year. It includes new and existing participants in existing programs (those implemented in prior years that are in place during the given year) and all participants in new programs (those implemented during the given year). The effects of new participants in existing programs and all participants in new programs should be based on their start-up dates (i.e., if participants enter a program in July, only the effects from July to December should be reported). If start-up dates are unknown and cannot be reasonably estimated, the effects can be annualized (i.e., assume the participants were initiated into the program on January 1 of the given year). The annual effects should consider the useful life of efficiency measures, by accounting for building demolition, equipment degradation and attrition.
Antimicrobial -  Agent that kills microbial growth.
Appliance Efficiency Standards -  California Code of Regulations, Title 20, Chapter 2, Subchapter 4: Energy Conservation, Article 4: Appliance Efficiency Standards. Appliance Efficiency Standards regulate the minimum performance requirements for appliances sold in California and apply to refrigerators, freezers, room air conditioners, central air conditioners, gas space heaters, water heaters, plumbing fittings, fluorescent lamp ballasts and luminaires, and ignition devices for gas cooking appliances and gas pool heaters. New National Appliance Standards are in place for some of these appliances and will become effective for others at a future date.
APR -  Air Purifying Respirator
ARI -  (Air-Conditioning and Refrigeration Institute) 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.
Asbestos -  A class of silicate minerals composed of long, thin fibers.
ASHRAE -  A leading HVAC/R Association - American Society of Heating, Refrigerating and Air Conditioning Engineers - http://www.ashrae.org/ The trade association that provides information and sets standards for the industry.
ASTM -  American Society for Testing and Materials.