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HVAC Abbreviations Directory
American National Standards Institute. A set of specifications (envelope dimensions) for centrifugal pumps manufactured in the United States
Reduction or removal of a contaminant.
filter having an efficiency of 99.90% or higher, capable of dealing with particle sizes down to 0.01 micrometre; a HEPA filter.
Absolute humidity (vapor concentration; water-vapor density number)
a mixture of water vapor and dry air, the mass of water vapor in a specific volume of the mixture.
pressure above a perfect vacuum; the sum of gage pressure and atmospheric pressure.
Absolute temperature (thermodynamic temperature)
temperature as measured above absolute zero.Degrees Rankine, where absolute 0°R. = -459.7°F, degrees Kelvin where absolute 0°K = -273.1°C.
space totally void of matter (theoretical).
Absolute viscosity (dynamic viscosity)
force per unit area required to produce unit relative velocity between two parallel areas of fluid unit distance apart, also called coefficient of viscosity.
Absolute Zero Temperature
Temperature at which all molecular motion ceases (-460o F. and – 273o C.)
that substance absorbed by an absorbent.
A material which, due to an affinity for certain substances, extracts one or more such substances from a liquid or gaseous medium with which it is in contact and which changes physically or chemically, or both, during the process. Calcium chloride is an e
device containing fluid, or other material, for absorbing refrigerant vapor or other vapors; chill factor part of the solar collector receiving the incident radiation energy and transforming it into thermal energy. It may possess a surface through which e
Absorber area (in a solar collector)
total heat transfer area from which the absorbed solar irradiance heats the transfer fluid; area of the absorber medium if both transfer fluid and solid surfaces jointly perform the absorbing function; i.e., total area onto which incident solar radiation
absorbed portion of the radiant energy striking a surface;ratio of the radiant flux absorbed by a body to that incident upon it.
process whereby a porous material extracts one or more substances from an atmosphere, a mixture of gases, or a mixture of liquids; transformation of radiant energy to a different form of energy by interaction with matter; absorption of acoustical energy b
Absorption chillers differ from mechanical vapour compression chillers in the fact thatthey utilize a thermal or/and chemical process to produce the refrigeration effect necessary to provide chilled water. There is no mechanical compression of the refrige
ratio of the radiant flux absorbed by a body to that incident upon it.
Absorption hygrometer (chemical hygrometer)
instrument in which the relative humidity is determined from the absorption of water vapor by a hygroscopic material; chemicals impregnated into small paper cards that change color with specific relative humidities.
Refrigerator which creates low temperature by using the cooling effect formed when a refrigerant is absorbed by chemical substance.
Absorption-type refrigerating system
refrigerating system in which refrigeration is created by evaporating a refrigerant in a heat exchanger (evaporator), with the vapor then absorbed by an absorbent medium from which it is subsequently expelled by heating at a higher partial vapor pressure
absorbed portion of the radiant energy striking unit area of a substance.
AC (Alternating Current)
The commonly available electric power supplied by an AC generator and is distributed in single or three phase forms. AC current changes its direction of the flow (cycles).
A motor (see motor definition) operating on a-c current that flows in either direction (AC current) there are two general types: induction, and synchronous.
Acceleration due to gravity
rate of increase in velocity of a body falling freely in a vacuum; its value varies with latitude and elevation. The International Standard, derived from the value at sea level and 45 degree latitude, is 9.806 65 meters per second per second (m/s2), or 32
The energy required to induce air to move at the entry to a system.
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.
performance of a component or system that meets specified design parameters under actual load.
Acceptable thermal environment
environment in which 80% of normally clothed men and women living in the United States or Canada, while engaged in indoor sedentaryor near sedentary activities, would express thermal comfort.
angular zone within which radiation is accepted by the receiver of a concentrator. Radiation is said to be accepted if radiation incident within this angle reaches the absorber after passing through the aperture.
Method for determining or restricting access to system and network resources.
Access control system
A dedicated special system for security.
A door provided in a unit casing, wall, floor, ceiling, duct, etc., to permit inspection, entrance, or availability to concealed parts or devices.
Opening in natural draft tower used for access to the cold water basin. It can be large enough for a man only, or large enough for mechanical equipment.
(as applied to equipment) equipment is accessible when close approach is not prevented by locked doors, elevation, or other effective means.
Accessible hermetic (semihermetic) refrigerant compressor
hermetic refrigerant compressor whose housing is sealed by one or more gasketed joints and is provided with means of access for servicing internal parts in the field.
part or assembly that aids the effectiveness of equipment without changing its function.
vessel for storing low-pressure-side liquid refrigerant; also known as a low-pressure receiver, surge drum, surge header, or surge tank; pressure vessel whose volume is used in a refrigerant circuit to reduce pulsation; pressure vessel connected to more t
conformity of an indicated value to an accepted standard value, or true value. Quantitatively, it should be expressed as an error or an uncertainty. The property is the joint effect of method, observer, apparatus, and environment. Accuracy is impaired by
welding using an acetylene-gas torch for fusing a selected metal (welding rod) in such a position as to fill the space where a junction is to be made.
Actual cubic feet per minute; the quantity or volume of a gas flowing at any point in a system. Fans are rated and selected on the basis of ACFM, as a fan handles the same volume of air regardless of density.
Air Changes per Hour. The number of times that air in a house is completely replaced with outdoor air in one hour.
Any substance that donates a proton (H+) when dissolved in a solution. In water treatment, it usually means circulating water with a pH of less than 7.0. Sulphuric acid is the most common acid used to control cooling water pH.
The recognition and/or registration of an event (e.g. alarm) by an operator.
A function that allows a destination node to inform a sending node of the receiptof a protocol-data-unit.
device to sense velocity of air at a point by use of the Doppler Effect on the velocity of sound. It may also sense temperature.
Acoustical Doppler Effect
change in pitch of a sound observed when there is relative motion between source and observer. Note: Results are different when the source moves relative to the listener who is fixed in the medium (atmosphere), compared with the listener moving relative t
one that evaluates temperatures from the measurement of the speed of sound in a gas; used for very low temperatures.
science of the production, transmission, and effects of sound; characteristics of a room that determine the qualities of sound therein, relative to hearing.
word formed from the initial letter, or groups of letters or words, in a set phrase.
A term used to identify the level of indoor radon at which remedial action is recommended.
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
It is a form of aluminum oxide, which absorbs moisture readily and is used as a drying agent.
Activated alumina desiccant
form of aluminum oxide, readily used as a drying agent, which absorbs moisture;phosphorous pentoxide desiccant (P2O5) although an effective drying agent, it becomesgummy on reacting with moisture so is not used as a drying agent in refrigerating systems.
It is a form of carbon made porous by special treatment by which it is capable of absorbing various odours, anesthetics, and other vapours.commonly used to clean air.
The amount of steel (iron) in the stator and rotor of a motor. Usually the amount of active iron is increased or decreased by lengthening or shortening the rotor and stator (they are generally the same length) .
Active tracer gas release
Controlled release of a tracer gas by a pressurized system or pump.
Device, either electrically, pneumatically, or hydraulically operated, that acts as a motor to change the position of movable devices such as valves or dampers.It influences the mass flow or energy flow
Connects and aligns the power end of an ANSI pump to the wet end.
Add On Heat Pump
Installing a heat pump in conjunction with an existing fossil fuel furnace. The result is a dual fuel system.
set of revisions to a standard in the form of a supplement.
Unique object identifier and/or device identifier within a system or combined systems.
Unique structured method for data point identification to address the information provided in BACS, consisting of a scheme and the semantics of the elements.
Compression of a gas during which no heat is exchanged with the surroundings.
Efficiency with which work is done with respect to heat gains or losses; (indicated efficiency) ratio of the work absorbed in compressing a unit mass of refrigerant in a compressor to the work absorbed in compressing the same mass in an ideal compressor.
Expansion of a fluid during which no heat is exchanged with the surroundings.
Exponent k in the equation pvk = constant, representing an adiabatic change (k is the ratio of the specific heat at constant pressure to the specific heat at constant volume).
It is a thermodynamic process during which no heat is extracted from or added to the system.
Adjustable capillary valve
having male threads on a stem that fit female threads in the solid body, leaving a capillary channel between the threads regulated by the number of threads engaged.
louver in which the blades may be operated manually or by mechanical means.
Adjustable speed drive
A mechanical, hydraulic or electrical system used to match motor speed to changes in process load requirements.
Adjustable-frequency drive (AFD)
electronic device that varies its output frequency to vary the rotating speed of a motor, given a fixed input frequency. Used with fans or pumps to vary the flow in the system as a function of a maintained pressure.
air diffusion performance index.
It is a material which has the ability to cause molecules of gases, liquids, or solids to adhere to its internal surfaces without changing the adsorbent physically or chemically. Certain solid materials, such as silica gel and activated alumina, have this
Substance with the property to hold molecules of gas or fluid without causing a chemical reaction.
process in which fluid molecules are concentrated on a surface by chemical or physical forces, or bothsurface adherence of a material in extracting one or more substances present in an atmosphere or mixture of gases and liquids, unaccompanied by physical
The binding of gases to the adsorbent surface through chemical reaction after thephysical adsorption.
Physical adsorption resembles the condensation of gases to liquids and depends on the physical, or van der Waals, force of attraction between the solid adsorbent and the adsorbate molecules.
Blowing or mixing of air through water to sweep out other dissolved gases and to equilibrate the water with primarily nitrogen, oxygen and carbon dioxide.
An organism that grows only in the presence of free (molecular) oxygen.
time varying loads acting on the blades of a fan due to nonconformities of the air flow.
It is an assemblage of small particles, solid or liquid, suspended in air. The diameters of the particles may vary from 100 microns to 0.01 micron or less; that is dust, fog, smoke.
Fan wheel design with airfoil-shaped blades.
They predict how capacity, head and horsepower are affected by changes in the centrifugal pump impeller diameter or shaft speed.
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
annual fuel utilization efficiency.
American Gas Association.
Age of air, local mean
The mean time it takes for supply air to reach a certain indoor point.
Age of air, room mean
Mean of all the local mean ages of air. symbol α.
Device to create turbulent motion in a fluid, usually inside a vessel.
Air Handler Unit. The air handler unit generally includes a blower or fan, heating and/or cooling coils, and related equipment such as controls, condensate drain pans, and air filters.
the atmosphere; the mixture of invisible, odorless, tasteless gases (nitrogen, oxygen, and others) that surrounds the earth.
Air agitating system
Combination consisting of a blower, distributing piping, and flexibly connected fittings for delivering air to the water in ice cans to agitate the water and promote production of clear ice.
It is a device which automatically switches the air from one side of the ice tank to the other.
Introduction of new, cleansed, or recirculated air to conditioned space, measured by the number of complete changes per unit time.
The amount of air required to completely replace the air in a room or building; not tobe confused with recirculated air.
Air change rate
Ventilation air flow rate divided by room volume. It indicates how many times, duringa time interval, the air volume from a space is replaced with outdoor air.
Air change rate, nominal
The nominal air change rate is equal to the ventilation flow rate divided by the roomvolume.
A method of expressing the amount of air leakage into or out of a building or room in terms of the number of building volumes or room volumes exchanged.
Air changes per hour (ACH)
Ventilation air flow divided by room volume. It indicates how many times, during onehour, the air volume from a space is replaced with outdoor air.
motion of air, either natural or induced.
Air circulation rate (air circulation ratio)
volume of air circulated within a closed space per unit time divided by the volume of the space.
Device used for removal of airborne impurities; A device that actively removes impurities from the air, including forced air filtration systems and electronic air cleaners; Air cleaners may be added to HVAC systems or stand-alone room units.
It is a device used to remove airborne impurities.
Air cleaner, electrostatic
A device that uses an electrical charge to trap particles traveling in the air stream.
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 cleaning system
A device or combination of devices applied to reduce the concentration of airbornecontaminants, such as microorganisms, dusts, fumes, respirable particles, other particulatematter, gases, and/or vapours in air.
Coil on some types of heat pumps used either as an evaporator or condenser.
assembly of equipment for the simultaneous control of air temperature, relative humidity, purity, and motion.
Device used to control temperature, humidity, cleanliness and movement of air in a confined space.
Air conditioner capacity
useful (net) available refrigerating capacity of an air conditioner for removing sensible and latent heat from the space being conditioned.
Air Conditioner, Room
It is a factory-made, encased assembly designed as a unit primarily to provide free delivery of conditioned air to an enclosed space, room, or zone. It includes a prime source ofrefrigeration for cooling and dehumidification and means for circulating and
It is the process of treating air so as to control simultaneously its temperature, Humidity, cleanliness and distribution to meet the requirements of the conditioned space.
Air conditioning process
in enclosed spaces, combined treatment of the air to control, as specified, temperature, relative humidity, velocity of motion, and radiant heat energy level, including consideration of the need for removal of airborne particles and contaminant gases. So
Air conditioning system
A combination of all components required to provide a form of air treatment in whichtemperature is controlled or can be lowered, possibly in combination with the control ofventilation, humidity and air cleanliness. (EPBD, 2002/91/EC)
Air Conditioning Unit
It is an assembly of equipment for the treatment of air so as to control simultaneously its temperature, humidity, cleanliness, and distribution to meet the requirements of a conditioned space.
Air Conditioning Unit, Cooling (Heating)
It is a specific air-treating combination, consisting of means for ventilation, air circulation, air cleaning, and heat transfer, with control means for cooling (or heating).
Air Conditioning, Comfort
It is the process of treating air so as to control simultaneously its temperature, humidity, cleanliness, and distribution to meet the comfort requirements of the occupants of the conditioned space.
Air Conditioning, Complete
It is the process of air conditioning in which the temperature and humidity are independently controlled.
Air Conditioning, Industrial
It is the process of air conditioning for other uses other than comfort.
Air Conditioning, Summer
It is the comfort air conditioning carried out primarily when outside temperature and humidity are above those to be maintained in the conditioned space.
Air Conditioning, Winter
It is the process of heating, humidification, air distribution, and air cleaning, where outside temperatures are below the inside room temperature.
Air Conditioning, Year Round System
It is a complete system, which ventilates, heats and humidifies in winter, cools and dehumidifies in summer, the air in the spaces under consideration and provides the deserved degree of air cleanliness and motion.
maximum rate at which air is consumed, under steady-state conditions, by a device operating within its design limits.
Any material in the atmosphere that affects persons and their environment (pollutantincludes materials such as liquids, solids, aerosols, gases and odours). Term is used interchangeably with air pollutant.
It is a factory-encased assembly of element whereby the temperature of air passing through the device is reduced
Air Cooler Unit
It is specific air-treating combination consisting of means of air circulation and cooling.
Air Cooler, Dry
It is an equipment that removes sensible heat from the dehydrated air whenever it leaves the dehydrator at an elevated temperature
Air Cooler, Dry-Type
It is a forced circulation air cooler wherein heat transfer is not implemented a liquid spray during the operating period.
controlled stream of air moving across the height and width of an opening with sufficient velocity and volume to reduce the infiltration or transfer of air from one side of the opening to the other; and to inhibit insects, dust, and debris from passing th
Air cycle refrigeration
consists of four stages: compression of air, cooling the air down to ambient temperature, expansion of the air, and heating of the cold air by heat absorption in the space to be cooled.
mass per unit volume of air.
An air distribution outlet or grille designed to direct airflow into desired patterns. Supply air terminal device, designed to direct airflow into desired patterns, usually placed in the ceiling, generally of circular, square or rectangular shape, and com
Distribution of the air in a space by means of air terminal 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 diffusion performance index (ADPI)
single number rating of the air diffusion performance of a system of diffusers, as installed, at a specified air delivery rate, temperature, and moisture content.
Air diffusion, displacement
Air diffusion where the mixing of supply air and indoor air is very low. Usually supplyair is a few degrees cooler that room air and supply velocity low.
Air diffusion, mixing
Air diffusion where the mixing of supply air and room air is intended
Air discharge coefficient
ratio of the net area at vena contracta of air flowing through an orifice to the total free area of the opening.
The transportation of a specified air flow to or from the treated space or spaces,generally by means of ductwork.
Air distribution envelope
surface or locus of points of equal velocity which describes an air distribution profile.
A jet of air at specific conditions discharged at low velocity in a space in order to provide locally needed conditions.
vertical distance between the base of an air outlet and the bottom of the airstream at the end of the air throw. Note: Drop occurs from the natural expansion of the airstream.
tube or conduit for conveying air. Note: Air passages of self-contained systems are not recognized as air ducts.
Air duct (trunking)
major conduit in an air-conveying system, usually rectangular or circular in cross section.
rapid falling of cold air that occurs when a variable air volume (VAV) box or other device reduces airflow, and the supply air leaves the diffuser at very low velocity.
Air eliminator (air vent)
in a steam or water distribution system, a device which closes if either steam or water is present in the vent body, and opens when air or noncondensables reach it.
capture of part of the surrounding air by an airstream discharged from an outlet; sometimes called secondary air motion.
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 f
air leaking outward.
Air extract, mechanical
The process of extracting air with the aid of powered air movement components,usually fans.
Air extract, natural
The process of extracting air by means of wind forces or density differences or acombination of the two.
Total amount of dry air and associated water vapor flowing through the tower, measured in cubic feet per minute at the exhaust from the tower and converted to standard air which has a density of 1.20 kg/m3.
Air flow rate, mass
Mass flow of air over specified time, usually expressed in kg/s or kg/h.
Air flow rate, volumetric
Volumetric flow of air over specified time, usually expressed in l/s or m3/h.
The space between magnetic poles or between rotating and stationary assemblies in a motor or generator.
Air gas ratio
ratio of the air volume to the gas volume. A specified ratio is necessary to achieve a desired character of combustion.
An-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 yo
Air handling unit
Assembly consisting of sections containing a fan or fans and other necessary equipment to perform one or more of the following functions: air circulation, filtration, heating, cooling, heat recovery, humidifying, dehumidifying and mixing of air, and neces
Air heater, forced convection (unit heater)
assembly of a heating element and a distribution fan.
The measure of useful power required to move a given air rate against a given resistance. The ratio of air horsepower to fan input horsepower is the measure of fan efficiency.
Air infiltration (building)
uncontrolled inward leakage of air (that may contain entrained water vapor) through cracks and interstices in any building element and around windows and doors of a building, caused by the pressure effects of wind or the effect of differences in the indoo
Air is coming into the stuffing box because of a negative suction pressure
device or opening through which air is withdrawn from or discharged into a conditioned space (grilles, registers, diffusers, and slots may be used as air inlets).
Air inlet core area
total plane area of the portion of a grille, face, or register bounded by a line tangent to the outer edges of the outer openings through which air can pass.
Air inlet free area
total area through which air can pass in a grille face or register; actual open area between the fins of a grille or register.
It is a pipe which supplies the air requirements of the conditioned space; to the ice cans contained in the freezing tank.
Air leakage factor
The air leakage per unit envelope area.
Air leakage, internal
Air leakage between two air streams in an air handling component like heat recovery unit.
compartment whose purpose is to control air exchange into or out of a conditioned space. Two individual closures usually are used to restrict air transfer by keeping one of them closed.
supply line from air compressor or central pressure-reducing station to branch feeder in a pneumatic control installation; tube carrying the supply of compressed air to the components of a pneumatic control system; pipe carrying air to the laterals supply
totality of gas molecules in a defined volume of air.
Air mass ratio
ratio of the mass of atmosphere in the actual earth-sun path to the mass which would exist at sea level if the sun were directly overhead.
device which converts compressed air into mechanical force; air-operated device that is used primarily for opening or closing dampers; pneumatic operator, a final control device that assumes a position as directed by an input-pressure signal.
Result of the presence of air pollutants in the atmosphere.
Air power (operational)
power required to move air at a given rate of flow against a given resistance. The ratio of air power to input power of a fan or blower is termed “efficiency.”
Air power (theoretical)
power required to drive a fan or blower as though there were no losses in the fan or blower (100% efficiency).
Air Pressure Switch
Used on motors with blowers to measure the difference in pressure across the filter so as to detect a clogged filter.
Air Quality Standard
A government-mandated regulation that specifies the maximum contaminant concentration beyond which health risks are considered to be unacceptable.
Air quality, indoor (IAQ)
IAQ deals with the health and comfort of the air inside buildings and characterize theindoor climate of a building, including the gaseous composition, temperature, relative humidity, and airborne contaminant levels. IAQ is the expression for both the conc
Air quality, perceived (PAQ)
Perceived air quality is an indoor air quality as it is perceived by humans.
Air separation (air fractionation)
separation of the various components of air through distillation at very low tempera-ture.
Air separation unit
device used to remove air from another fluid stream.
Air Source Equipment
Heat pumps or air conditioners that uses the outdoor air to transfer heat to and from the refrigerant in the unit.
blade or blades fitted across an air duct to divide the airstream into a number of streams in parallel.
divergence of an airstream after it leaves an outlet.
The layering of air within a space, due to density differences caused by temperaturedistribution of the air
Air supply fixtures
devices or openings through which air flows into a room.
Air supply, displacement
Air supply where the mixing of supply air and indoor air is at a minimum
Air supply, mechanical
The process of supplying air with the aid of powered air movement components,usually fans.
Air supply, mixed
The supply of mixed air.- see also mixed air
Air supply, natural
The process of supplying air by means of wind forces or density differences or acombination of the two.
Air Terminal Device
A device located in an opening provided at the boundaries of the treated space to ensure a predetermined motion of air in this space.
Air Terminal 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 t
The distance an air jet travels upon leaving a diffuser before its velocity is reduced to a specific value, usually to the velocity which does not cause draft, 0,15-0,25 m/s depending on the temperature
qualitative term describing the integrity of the building envelope relative to air permeation; the resistance of the building envelope to the flow of air and entrained moisture.
Air transport factor
ratio of the rate of useful, sensible heat removal from the conditioned space to the energy input to the supply and return fan motor(s), expressed in consistent units and within designated operating conditions.
device to control volume and flow in air distribution.
rate of motion of air in a given direction, measured as distance per unit time.
manual or automatic device for removing air from circulating hot or chilled water systems; also used for removing air from steam systems.
unit for spraying or atomizing clean water into an air supply system; capable of heating, cooling, humidifying, or dehumidifying the air, depending on whether the water is heated or chilled.
It is the air surrounding an object.
Air that has been heated, cooled, humidified or dehumidified to maintain an interiorspace within the "comfort zone". (Sometimes referred to as "tempered" air)
Air removed from a space and discharged to outside the building by means of mechanical or natural ventilation systems.
The air in an enclosed occupiable space.
Air volume or flow that is set into motion by the primary air supplied to a space
The mixture of outdoor air and recirculated return air.
Air taken from outside the building which therefore has not previously circulated through the ventilation system.
It is external air; atmosphere exterior to refrigerated or conditioned space and ambient (surrounding) air.
Conditioned and dehumidified outdoor air supplied to the terminal unit such as chilledbeam, induction unit etc. through a duct from the air handling unit.
It is the returned air passed through the conditioner before being again suppliedto the conditioned space.
A part of extract air which is not exhausted from the building, but it is recirculated back to spaces.
Air, Reheating of
In an air conditioning system, the final step in treatment in the event the temperature is too low.
It is the air returned from conditioned or refrigerated space.
It is the moist air in which the partial pressure of the water vapour is equal to the vapour pressure of water at the existing temperature. This occurs when dry air and saturated water vapour coexist at the same dry-bulb temperature.
Air volume flow rate extracted from a room and being supplied again to the same room after having been conditioned. (EN 13779) - also referred to as transfer air
It is the dry air at a pressure 760 mm Hg at 21°C temperature and with a specific volume of 0.833 m3/kg
Air delivered by mechanical or natural ventilation to a space, composed of any combination of outdoor air, recirculated air or transfer air.
Air moved from one indoor space to another
Outdoor air which is supplied to a room for ventilation purposes.
Air/cloth ratio (feet per minute)
value used in dust collector calculations to measure air velocity through the bag filter media. Note: Calculated by dividing active cubic feet per minute of airflow by the effective area (square feet) of the cloth media.
same as air/cloth ratio, but used where non-cloth bag media, such as paper cartridges, are the filter media.
cooling by forced circulation of air at high velocity.
Airborne particles (particulates)
impurities as solid or liquid particulate matter from whatever source.
sound which reaches the point of detection by radiation through the air.
introduction of air causing either a flow restriction or a malfunction of the system.
average age of air that exits a building via all routes, divided by the arithmetic average of the local ages of air, measured at breathing height.
assembly of equipment for air treatment to control simultaneously its temperature, humidity, cleanliness, and distribution to meet the requirements of a conditioned space.
Air-cooled air conditioner
one whose refrigerating system has an 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.
Air-cooled refrigerant condenser
refrigerant condenser in which heat removal is accomplished entirely by heatabsorption by the air flowing over condensing surfaces.
condensing unit which utilizes refrigerant-to-air heat transfer means.
value used in dust collector calculations to measure air velocity through the bag filter media. Note: Calculated by dividing active cubic feet per minute of airflow by the effective area (square feet) of the cloth media.
movement of air, usually within boundaries such as ducts.
deterrent (due to friction, change of direction, etc.) to the passage of air within a system of airways or an apparatus.
material or construction which adequately impedes transmission of air under specified conditions.
The secondary airflow from the room induced into a terminal unit such as chilled beam, induction unit etc. by the primary air.
fan shaped blade (backwardly inclined or forward curved) in a fan assembly to optimize flow, with less turbulence.
ratio of the air volume to the gas volume. A specified ratio is necessary to achieve a desired character of combustion.
Factory-made encased assembly consisting of a fan or fans and other equipment to circulate, clean, heat, cool, humidify, dehumidify or mix air.
Air-handling units, decentralized
In contrast to the central air-handling units, these units are allocated to a single roomor group of rooms, supplying secondary air or outdoor air to that room.
ratio of the mass of atmosphere in the actual earth-sun path to the mass which would exist at sea level if the sun were directly overhead.
Air-to-air energy recovery effectiveness
ratio of actual heat transfer to the thermodynamically limited maximum heat transfer possible in a counter flow exchanger of infinite transfer area.
Air-to-air energy recovery system efficiency
ratio of the apparent heat recovered to the sum of the thermodynamically limited maximum possible in a counterflow heat exchanger of infinite heat-transfer area; plus all external energy inputs including, but not limited to, fan energy, auxiliary heaters,
Air-to-air heat exchanger
exchanger that transfers heat from an exhaust airstream to a separated supply airstream. Note: Fixed plate, rotary wheels, heat pipes, runaround coil loops, and shell-and-tube are the most common types.
Ak value (of an air terminal device)
Quotient obtained by dividing a measured air flow rate by a measured air velocity according to a specific process and a specific instrument.
signal, either audible or visual or both, which alerts an operator to an off-normal condition which requires some form of corrective action; off-normal condition such as a pressure, temperature, etc., that has deviated above or below an established operat
that point in the range of a variable which is the threshold of an off-normal condition.
ratio of reflected solar radiation from a surface and the incident solar radiation.
bulb with a vertical capillary tube containing alcohol (colored) which expands or contracts with changes in temperature, having graduated markings so that the end of the alcohol column indicates the ambient temperature.
A low form of plant life containing chlorophyll that generally requires sunlight and air for existence. Many are microscopic but under favourable conditions can grow sufficiently dense to plug cooling tower distributors on the decks and to interfere with
A toxic material which will retard or prevent the growth of algae and slimes. Some of the more commonly used algaecides are chlorine, copper sulphate and phenolic compounds.
prescribed set of well-defined rules, or process, for the solution of a problem in a finite number of steps, e.g., a full statement of an arithmetical procedure for evaluating sine x to a stated precision.
The centerline of the pump is perfectly aligned with the centerline of the driver (usually an electric motor).
An expression of the total basic anions (hydroxyl groups) that is present in a solution. It also represents, particularly in water analysis, the bicarbonate, carbonate, hydroxyl and occasionally the borate, silicate, and phosphate salts which will react w
All-air air-conditioning system
air-conditioning system in which the thermal energy is carried from the central plant by the air itself as against those systems in which another fluid transmits its energy to the air at the points of usage.
A substance capable of causing an allergic reaction because of an individual's sensitivity to that substance.
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 atta
Alloy steel pipe
steel pipe with one or more chemical elements other than carbon, which give it greater resistance to corrosion and more strength than carbon steel pipe.
Alpha K factor
effective area of an air terminal, equal to the measured airflow rate divided by the velocity reading of a particular instrument used in a prescribed manner.
Character set that consists at least of decimal digits and letters.
replacement refrigerant that can accomplish the same task as the one being replaced, but may require that refrigeration or air-conditioning equipment be redesigned or replaced.
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.
Alternative energy sources
nondepletable sources alternative to energy derived from combustible waste or heat recovery processes.
The atmospheric altitude (height above sea level) at which the motor will be operating; NEMA standards call for an altitude not exceeding 3,300 ft. (1,000 meters),As the altitude increases above 3,300 ft. And the air density decreases, the air’s ability t
The atmosphere which is adjacent to but not affected by the cooling tower. Generally, this means upwind of the tower, and the other areas where other heat producing equipment is located that supplies extraneous sources of heat to the air coming to the tow
Immediate surroundings or vicinity.
surrounding air (usually outdoor air or the air in an enclosure under study).
Ambient air conditions
characteristics of the environment, for example, temperature, relative humidity, pressure, motion.
Ambient Air Temperature
Surrounding temperature, such as the outdoor air temperature around a building.
Ambient dew point
The ambient temperature in oF when dew begins to be deposited.
The heat or pressure in the area where the equipment is located.
environmental pressure in which a device operates; pressure of the medium surrounding a device.
The temperature of the surrounding cooling medium, such as gas or liquid, which comes into contact with the heated parts of the motor. The standard enema rating for ambient temperature is not to exceed 40 degrees Celsius
Ambient wet-bulb temperature
The wet-bulb temperature that is measured in accordance with the definition of ambient. Readings are obtained by means of a mechanically aspirated psychrometer.
one designed to negate the effects of ambient conditions surrounding the body of the control, thereby not affecting the control output.
Air Movement and Control Association.
A water-soluble, colourless, pungent gas with the formula NH3.
anhydrous ammonia (NH3).
Positive ion with the formula NH4+ that forms when ammonia dissolves in water. It adds non-natural alkalinity to the water.
ability of a wire to carry electric current safely without undue heating. Formerly current capacity.
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.
An increase in the numbers or concentration of a microbe or its products through reproduction and growth of the microbe.
circuit used to increase the power, voltage, and/or current level of a signal; device whose output is an enlarged reproduction of the essential features of an input signal and which draws power from a source other than the input signal; device that enable
An organism that can grow under either aerobic or anaerobic conditions.
An organism that grows only in the absence of free oxygen (e.g., sulphate reducing bacteria).
Continuous progression of a value with different point-by-point assignment of information.
data represented in a continuous form, as contrasted with digital data represented in a discrete (discontinuous) form; an analog of the variable represented.
display of analog data values; display of a physical variable in a continuous form
analog display; e.g., a meter, or gage, which shows an analog value to an operator.
a verifying quantity; e.g., pressure, voltage, or temperature, which can have any value between a minimum and a maximum, used as the initiating part of a control system; input of a physical variable in a continuous form such as a voltage input to a voltme
Part of the hardware pertaining to a control device for measuring or positioning.
continuous variable used to represent another; e.g., in temperature measurement, an electric voltage or current output represents temperature input; varying quantity, e.g., pressure, voltage, or temperature, which can have any value between a predetermine
Analog to digital converter
device that converts a signal that is a function of a continuous variable into a representative number sequence (digital format).
method by which analog values are transferred from the sensing location to a controlling location; sending of a continuously variable signal from one point to another.
Information containing a numerical represented quantity.
device in the high side of an absorption system for increasing concentration of refrigerant in the vapor entering the rectifier or condenser.
A threaded bolt embedded in a concrete basin or fitted to supported members, to which an anchor casting is attached.
A device for attaching the tower structure to the foundation; it does not include the anchor bolt. Also known as Column Anchor
device placed at the end of a test duct to prevent excessive reflection of the sound waves back into the test duct where they would interfere with the waves to be measured.
A device that reads air velocity, such as a wind vane. In fan applications, it is usually a spinning-vane-type instrument used to read low velocities at registers or grills.
thin, disc-shaped box or capsule, usually metallic, partially evacuated and sealed, held extended by a spring, which expands and contracts with changes in atmospheric or gas pressure.
Angle of discharge
largest included angle between centerlines of principal jets of primary air.
Angle of incidence
angle between the direct solar irradiance and the normal to the aperture plane.
valve in which the inlet and outlet are at an angle, usually 45 or 90 degrees.
ion that is negatively charged; e.g., chloride, silicate, sulfate.
The process of relieving stress and brittleness in metals by heating.
process involving controlled heating and subsequent controlled, generally slow, cooling; applied usually to induce ductility in metals; treatment intended to remove internal stresses, alter mechanical or physical properties, produce a definite microstruct
The total effects in energy use (measured in megawatt hours) and peak load (measured in kilowatts) caused by all participants in the DSM programs that are in effect during a given year.
form of two-phase flow in a pipe where the gas forms the core and the liquid flows annularly against the internal walls of the pipe.
an “alert” to an operator. Not to be confused with alarm, the operator is informed of a change in a system. This change could require an alarm but not necessarily; displaying of a condition by a visual or audible means
positive electrode in an electrolytic system, such as applied in cathodic protection. The electrode at which oxidation or corrosion occurs, or from which the current is transmitted to the electrolyte.
Area on a metal surface where electrons are given up and metal dissolves (corrosion).
An electrolytic action of affixing a protective coating or film, usually applied to aluminum.
American National Standards Institute.
dense, hard coal with a very high percentage of fixed carbon, usually above 90%.
substance produced by a living organism (i.e., fungi, bacteria) that inhibits the growth of, or kills, another living organism.
one which, by artificial means, is actuated sooner than it would be without such means to produce a smaller differential of the controlled variable.
An agent that prevents foam from forming or reduces its presence.
An anti-friction bearing is a beating utilizing tolling elements between the stationary and rotating assemblies.
Agent that kills microbial growth.
valve or mechanical device that eliminates siphon flow.
American Petroleum Institute.
application part-load value
Apparatus dew point
dew-point temperature of the air leaving the conditioning apparatus, used interchangeably with maximum average coil surface temperature required to produce dew.
In an AC circuit, the product of Volts x Amperes supplying a single-phase motor, or 1.732 x Volts x Amperes supplying a 3-phase motor; expressed in either volt- amps (VA) or kilovolt-amps (kVA), where 1000 VA = 1 kVA. See also ‘‘Real Power’’ and ‘‘Power F
temperature of an object as determined from the measured radiance.
Apparent volumetric efficiency
on an indicator card, the ratio of suction line length to stroke.
piece of equipment that draws electric or other energy and produces a desired work-saving or other result, such as an electronic range, a radio, or an air conditioner.
flue within an appliance.
Appliance vent connector
portion of the venting system that connects the gas appliance or its draft hood to the chimney or vent terminal.
Appliance vent pipe
passage or conduit in a direct vent or direct exhaust system through which gases pass from the combustion chamber to the outdoor air.
A set of functions that, together, form a logical unit supporting a process.
Object located within the BACS device’s application process.
Application part-load value (APLV)
part-load value based on operation at actual design conditions; typically used in system design and specification.
rating based on tests performed at stated application conditions other than standard rating conditions.
Application rating conditions
rating conditions other than standard rating conditions.
digital controller dedicated to a specific application such as a VAV box or water-source heat pump.
Customized device fulfilling the requirements of a specified application.
In an evaporative cooling device, combination consisting of means of air circulation and the difference between the average temperature of the cooling; circulating water leaving the device and the average wet-bulb temperature of the entering air. In a con
Accessories added to a fan for the purposes of control, isolation, safety, static pressure regain, wear, etc.
Air Purifying Respirator
thermostat designed for use in water.
group of welding processes wherein coalescence of metal is produced by heating with an electric arc or arcs, with or without the application of pressure, and with or without filler metal.
a body immersed in a fluid undergoes an apparent loss in weight equal to the weight of the fluid it displaces.
Architectural area (of a building)
the sum of the areas of the several floors of the building, including basements, mezzanine and intermediate floored tiers, and penthouses of headroom height, measured from the exterior faces of exterior walls or from the centerline of walls separating bui
Architectural volume (of a building)
(cube or cubage) the sum of the products of the architectural areas (using the area of a single story for multistory portions having the same area on each floor) and the height from the underside of the lowest floor construction system to the average heig
Structure and means by which components and devices of a system are connected to intercommunicate.
It is the total plane area of the portion of a grille, face, or register bounded by a line tangent to the outer edges of the outer openings through which air can pass.
It is the total minimum area of the openings in an air inlet or outlet through which air can pass.
Area, gross floor
The total area of all the floors of a building, including intermediately floored tiers, mezzanine, basements, etc., as measured from the exterior surfaces of the outside walls of the building.
Area, internal gross
A term used in the United Kingdom, defined in the RICS Standard, for the area of a building measured to the internal face of perimeter walls at each floor level.
Area, net floor
A term used in the ISO standard to express the Interior Gross Area less the areas of all interior walls.
Area within the heated or cooled surface occupied for long periods. Normally the floorarea within 1,0 m from external walls-windows and HVAC equipment and 0.5 m from internal walls.
Area of a building, next to the exterior walls, which has a different heating or coolingload than the rest of the building.
Area/space, living floor
Total area of rooms falling under the concept of rooms. (OECD Glossary of statisticalterms)
Area/space, useful floor
Floor space of dwellings measured inside the outer walls, excluding cellars, non-habitable attics and, in multi-dwelling houses, common areas. (OECD Glossary of statistical terms)
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
Arithmetic mean temperature difference
in a parallel flow or counterflow heat exchanger, arithmetic mean of the temperature differences between the two fluids at both ends of the exchanger.
The portion of the magnetic structure of a DC or universal motor which rotates.
Armature Current, Amps
Rated full load armature circuit current.
Armature Inductance, Mho
Armature inductance in mill-henries (saturated).
The current that flows in the armature winding of a d-c motor tends to produce magnetic flux in addition to that produced by the field current. This effect, which reduces the torque capacity, is called armature reaction and can effect the commutation and
Armature Resistance, Ohms
Armature resistance is measured in ohms at 25 degree Celsius. (cold)
A measure of the ability of a device to remove ASHRAE standard test dust from testair. Also see ASHRAE dust.
The amount of particles of non-specific size captured by the filter; The arrestance describes how well an air filter removes larger particles (total mass) such as dirt, lint, hair and dust.
Artificial intelligence (AI)
capability of a device to perform functions that normally are associated with human intelligence, such as reasoning, learning, and self-improvement.
A class of silicate minerals composed of long, thin fibers.
As-built clean room
one that is complete and ready for operation, with all services connected and functional, but without production equipment or personnel within the room.
American Standard Code for Information Interchange.
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.
measure of the ability of a device to remove ASHRAE atmospheric dust from test air.
ASHRAE atmospheric dust spot efficiency
measure of the ability of a device to remove atmospheric dust from the test air.
ASHRAE synthetic arrestance dust
compounded test dust used for arrestance measurement and for loading filters.
American Society of Mechanical Engineers.
in any rectangular configuration, the ratio of the longer dimension to the shorter; ratio of the length to width of a rectangular air duct.
psychrometer having mechanical means for rapidly circulating air to be tested over dry and wet bulbs.
It is production of movement in a fluid by suction created by fluid velocity.
American Society for Testing and Materials.
substance or space that does not allow the passage of radiant heat.
Atmosphere of reference
reference atmosphere, the characteristics of which are defined by standards for given purposes.
condenser in which the pipes in open air are cooled by water flowing over them.
particulate matter naturally occurring in the air supplied to the test duct.
Atmospheric freeze drying
process in which the solid phase of the solvent is sublimed at atmospheric pressure.
One atmosphere is approximately 14.7 psi, 408″ water gauge at sea level. Airflow is the result of a difference in pressure (above or below atmospheric) between two points.
Atmospheric tower (natural-draft cooling tower)
one in which air movement through the tower occurs by aspiration or natural convection, as opposed to mechanical means.
A number given to each element representing the number of protons in one atom of that element.
Weight (in grams) of 6.02x1024 atoms of a particular element. The weight of an atom of any element compared with that of oxygen that is considered to be 16.
It is the process of reducing to fine spray.
to create a fine spray from a liquid.
At-rest clean room
one that is complete and has the production equipment installed and operating, but without personnel within the room.
Absorption of sound pressure. Attenuation reduces the amplitude only of a sound wave while leaving the frequency unchanged.
exhaust fan to exhaust air near the top of a building while air, generally cooler, is forced (drawn) in at lower levels.
introduction of cool outdoor air into an attic by exhausting its warm air to the outdoors.
Attic-type central furnace
one designed specifically for installation in an attic or in a space with low headroom, normally unoccupied.
Authority (of a controller)
ratio of effect on a manipulated variable of one input signal as compared to that of another.
Autogenous (spontaneous) ignition temperature
temperature of spontaneous ignition of a product in the absence of a flame, determined under standardized conditions.
changeover from one operation to another without operator intervention; e.g., a thermostat which changes from heat to cool without need for manual operation of levers or set points.
defrosting automatically at set intervals, based on time or temperature conditions, or both.
Automatic expansion valve
controlling device for regulating automatically the flow of volatile refrigerant into a cooling unit, actuated by changes in evaporator pressure. The basic response is to regulate evaporator pressure.
Automatic sequence control
one in which successive operations are carried out in a sequence either predetermined or resulting from the correct execution of each successive operation.
valve that automatically regulates the flow of a fluid as a function of temperature, pressure, etc.
Automatic-to-user load management
as a part of indirect load management, the automatic monitoring and control by a user of loads to take advantage of electric rate economic incentives.
implementation of process by automatic means.theory, art, or technique of making a process more automatic; investigation, design, development, and application of methods of rendering processes automatic, self-moving, or self-controlling.
The logical level on which the supervisory and processing functions for plant automation are performed. This level can also be assigned dialog-oriented operating functions.
An organism that is capable of producing its own food through the use of chlorophyll and light.
supply or supplemental air delivered to a laboratory fume hood to reduce room air consumption.
Auxiliary electrical system
assembly of electrical energy-using components necessary to make a main energy conversion function; such as a power burner, induced or forced-draft blower motor, ignition system (but not a resistance heating element supplied by the manufacturer as part of
Auxiliary thermal source
source of thermal energy, other than solar, used, for example, to provide service water heating; usually in the form of electrical resistance heat or thermal energy derived from combustion of fossil fuels.
energy in the form of shaft work or in a form completely convertible to shaft work by ideal processes.
Average age of air
average of local mean ages of air measured throughout an indoor airspace.
Average specific infiltration
value of the specific infiltration that is typical for an average climate in the United States or Canada.
Average temperature (mean temperature)
arithmetic mean of temperatures measured at a given point during a given lapse of time, or at a given time in various points of a space or body.
under the same conditions of pressure and temperature, equal volumes of all gases contain equal numbers of molecules.
Fan where the airflow through the impeller is mainly parallel to the axis of rotation. The impeller is contained in a cylindrical housing.
The force or loads that are applied to the motor shaft in a direction parallel the axis of the shaft. (such as from a fan or pump)
turbocompressor in which the com-pressed fluid flows generally in a direction parallel to the axis of rotation.
perspective drawing showing plan and partial elevations on the same drawing.
A mixture made up of two or more refrigerants with similar boiling points that act as a single fluid. The components of azeotropic mixtures will not separate under normal operating conditions and can be charged as a vapor or liquid.
temperature at which a liquid mixture boils and produces a vapor having the same composition as the liquid.
blend of two or more component refrigerants whose equilibrium vapor-phase and liquid-phase compositions are the same at a given pressure.
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