GLOSSARY OF HVAC TERMS 10/18/2013 HVAC is term used for heating, ventilation and air conditioning This glossary is comprised of words and phrases most frequently used in the heating, ventilation and air conditioning industry. These brief explanations will help your understand of many terms used throughout your work, study and professional career. This glossary has been provided by Climate Control South East Ltd, UK.

Glossary of hvac terms by climate control se

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This glossary is comprised of words and phrases most frequently used in the heating, ventilation and air conditioning industry. These brief explanations will help your understand of many terms used throughout your work, study and professional career. This glossary has been provided by Climate Control South East Ltd, UK. Learn more: www.climatecontrolse.co.uk

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Page 1: Glossary of hvac terms by climate control se


10/18/2013 HVAC is term used for heating, ventilation and air conditioning

This glossary is comprised of words and phrases most frequently used in the heating, ventilation and air conditioning industry. These brief explanations will help your understand of many terms used throughout your work, study and professional career. This glossary has been provided by Climate Control South East Ltd, UK.

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Glossary of HVAC terms

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Glossary of HVAC terms H VA C I S T E R M U S E D F O R H E A T I N G , V E N T I L A T I O N A N D A I R C O N D I T I O N I N G

Absolute humidity: The weight of water vapour per unit volume; grains per cubic foot; or grams per cubic

meter. Absolute pressure: The sum of gage pressure and atmospheric pressure. Thus, for example, if the gage pressure is 154 psi, the absolute pressure will be 154+14.7, or 168.7 psi. Absolute zero: A temperature equal to –459.6®F or –273®C. At this temperature the volume of an ideal gas maintained at a constant pressure becomes zero.

Absorption: The action of a material in extracting one or more substances present in the atmosphere or a

mixture of gases or liquids accompanied by physical change, chemical change, or both.

Acceleration: The time rate of change of velocity. It is the derivative of velocity with respect to time.

Accumulator: A shell placed in a suction line for separating the liquid entrained in the suction gas. A storage

tank at the evaporator exit or suction line used to prevent flood backs to the compressor.

Acrolein: A warning agent often used with methyl chloride to call attention to the escape of refrigerant. The

material has a compelling, pungent odor and causes irritation of the throat and eyes. Acrolein reacts with sulfur

dioxide to form a sludge.

ACR tube: A copper tube usually hard drawn and sold to the trade cleaned and sealed with nitrogen inside to

prevent oxidation. Identified by its actual outside diameter (OD).

Activated alumina: A form of aluminium oxide (Al2O3) that absorbs moisture readily and is used as a drying


Adiabatic: Referring to a change in gas conditions where no heat is added or removed except in the form of


Adiabatic process: Any thermodynamic process taking place in a closed system without the addition or

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removal of heat.

Adsorbent: A sorbent that changes physically, chemically, or both during the sorption process.

Aeration: Exposing a substance or area to air circulation.

Agitation: A condition in which a device causes circulation in a tank containing fluid.

Air, ambient: Generally speaking, the air surrounding an object.

Air changes: 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 per unit of time.

Air circulation: Natural or imparted motion of air.

Air cleaner: A device designed for the purpose of removing airborne impurities such as dust, gases, vapors,

fumes, and smoke. An air cleaner includes air washers, air filters, electrostatic precipitors, and charcoal filters.

Air conditioner: An assembly of equipment for the control of at least the first three items enumerated in the

definition of air conditioning.

Air conditioner, room: A factory-made assembly designed as a unit for mounting in a window, through a wall,

or as a console. It is designed for free delivery of conditioned air to an enclosed space without ducts.

Air conditioning: The simultaneous control of all, or at least the first three, of the following factors affecting

the physical and chemical conditions of the atmosphere within a structure—temperature, humidity, motion,

distribution, dust, bacteria, odors, toxic gases, and ionization—most of which affect human health or comfort.

Air-conditioning system, central fan: A mechanical indirect system of heating, ventilating, or air conditioning

in which the air is treated or handled by equipment located outside the rooms served, usually at a central

location and conveyed to and from the rooms by means of a fan and a system of distributing ducts.

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Air-conditioning system, year round: An air-conditioning system that ventilates, heats, and humidifies in

winter, and cools and dehumidifies in summer to provide the desired degree of air motion and cleanliness.

Air-conditioning unit: A piece of equipment designed as a specific air-treating combination, consisting of a

means for ventilation, air circulation, air cleaning, and heat transfer with a control means for maintaining

temperature and humidity within prescribed limits.

Air cooler: A factory-assembled unit including elements, whereby the temperature of air passing through the

unit is reduced.

Air cooler, spray type: A forced-circulation air cooler, wherein the coil surface capacity is augmented by a

liquid spray during the period of operation.

Air cooling: A reduction in air temperature due to the removal of heat as a result of contact with a medium

held at a temperature lower than that of the air.

Air diffuser: A circular, square, or rectangular air distribution outlet, generally located in the ceiling, and

comprised of deflecting members discharging supply air in various directions and planes, arranged to promote

mixing of primary air with secondary room air.

Air, dry: In psychrometry, air unmixed with or containing no water vapor.

Air infiltration: The in-leakage of air through cracks, crevices, doors, windows, or other openings caused by

wind pressure or temperature difference.

Air, recirculated: Return air passed through the conditioner before being again supplied to the conditioned


Air, return: Air returned from conditioned or refrigerated space.

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Air, saturated: Moist air in which the partial pressure of the water vapor is equal to the vapor pressure of

water at the existing temperature. This occurs when dry air and saturated water vapor coexist at the same dry-

bulb temperature.

Air, standard: Air with a density of 0.075 lb/ft3 and an absolute viscosity of 1.22x10 1b mass/ft-s. This is

substantially equivalent to dry air at 70®F and 29.92 in. Hg barometer.

Air washer: An enclosure in which air is forced through a spray of water in order to cleanse, humidify, or

precool the air.

Ambient temperature: The temperature of the medium surrounding an object. In a domestic system having

an air-cooled condenser, it is the temperature of the air entering the condenser.

Ammonia machine: An abbreviation for a compression refrigerating machine using ammonia as a refrigerant.

Similarly, Freon machine, sulfur dioxide machine, and so forth.

Ampere: Unit used to measure electrical current. It is equal to 1 C of electrons flowing past a point in 1 s. A

coulomb is 6.28x1018 electrons.

Analyser: A device used in the high side of an absorption system for increasing the concentration of vapor

entering the rectifier or condenser.

Anemometer: An instrument for measuring the velocity of air in motion.

Antifreeze, liquid: A substance added to the refrigerant to prevent formation of ice crystals at the expansion

valve. Antifreeze agents in general do not prevent corrosion due to moisture. The use of a liquid should be a

temporary measure where large quantities of water are involved, unless a drier is used to reduce the moisture

content. Ice crystals may form when moisture is present below the corrosion limits, and in such instances,

suitable noncorrosive antifreeze liquid is often of value. Materials such as alcohol are corrosive and, if used,

should be allowed to remain in the machine for a limited time only.

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Atmospheric condenser: A condenser operated with water that is exposed to the atmosphere.

Atmospheric pressure: The pressure exerted by the atmosphere in all directions as indicated by a barometer.

Standard atmospheric pressure is considered to be 14.695 psi (pounds per square inch), which is equivalent to

29.92 in. Hg (inches of mercury).

Atomize: To reduce to a fine spray.

Automatic air conditioning: An air-conditioning system that regulates itself to maintain a definite set of

conditions by means of automatic controls and valves usually responsive to temperature or pressure.

Automatic expansion valve: A pressure-actuated device that regulates the flow of refrigerant from the liquid

line into the evaporator to maintain a constant evaporator pressure.

Baffle: A parttti n us dt s durd d u etfl t a r tr a en si

Balanced pressure: The same pressure in a system or container that exists outside the system or container.

Barometer: An instrument for measuring atmospheric pressure.

Blast heater: A set of heat-drai ur ct l tr uctti n us dt uad a r d ad srafli tr trcus d rtnu d b a aii

Bleeder: A p pu tmutmu aaac us dt a ctisui ur dt luus t l ln s ru r uuraid parallul dt d u ma i etfli

Boiler: A closed vessel in which liquid is heated or vaporised.

Boiler horsepower: T u uln daluid udaptratti t 3i. l t fladur pur tnr rtm ais ad 2 ®F, which is equal

to a heat output of 970.3 x34.5 = 33,475 Btu.

Boiling point: T u dumpuradnru ad fl c a l ln s daptr us npti d u ass tti t uadt supuisuid ti d u

refrigerant and the absolute pressure at the surface of the liquid and vapor.

Bore: The inside diameter of a cylinder.

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Bourdon tube: Tn u t ula tc mudal bent into circular shape that is found inside a pressure gage.

Brine: Any liquid cooled by a refrigerant and used for transmission of heat without a change in its state

Brine system: A b dum fl uru b r iu cttlus b a ru r uuratiu b dum c rcnladus dhrough pipes to the point

wheru d u ru r uuratti iuususi

British serraah ui h B u: The amount of heat required to raise the temperature of 1 lb of water 1�F. It is also

the measure of the amount of heat removed in cooling 1 lb of water 1�F and is so used as a measure of

ru r uuratiu u ucdi

Butane: A bsrtcar tit eamma lu ru r uuraid n us dt a l m dus uxduid i mall ni d i

Calcium chloride: A chemical having the formula CaCl2, which, in granular form, is used as a drier. This

madur al tln lu i fladurt ais i d u pru uicu t laruu lnaittu t mt dnru mab s tldu ais plnu np d u drier unit or even pass into the system beyond the drier.

Calcium sulfate: A solid chemical of the formula CaSO4, which may be used as a drying agent.

Caaibratiu: T u prtcu t s d s iu ais inm ur iu d u calu t ai i drnmuid; al t t ctrructiu ais

determining d u urrtr t ai ux tiu calui

Calorie: Heat required to raise the temperature of 1 g of water 1®C (actually, from 4 to 5®C). Mean calorie is

equal to one-hundredth part of the heat required to raise 1 g of water from 0 to 100®C.

Capacitor: An electrical device that has the ability to store an electrical charge. It is used to start motors, among

other purposes.

Capaci y,hrefrigeratug: T u a l db t a ru r uuratiu b dumt tr pard d urut t dt rumtdu uadi xpru us a a

rate of heat removal, it is usually measured in Btu/h or tons/24 h.

Capacity reducer: In a compre trt a sud cut nc a a cluaraicu ptckudt mtda lu cbl isur uast tr nctti

bypass, by which compressor capacity can be adjusted without otherwise chaiu iu d u tpuratiu ctis tti i

Capillarity: T u actti b fl c d u nr acu t a l ln s i ctidacd fl d a solid (as in a slender tube) is raised or


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Capillary tube: Ii ru r uuratti practcut a dn u t mall idurial s amudur n us a a l ln s ru r uuraid-etfl

control or expansion device between high and low sides; also used to transmit pressure from d u ui tdu nl

of some temperature condrtl dt d u tpuratiu ulumuidi

Carbon dioxide ice: Compressed solid CO2; dry ice.

Celsius: A thermometric system in which the freezing point of water is called 0®C and its boiling point 100®C at

normal pressure. T b dum n us i d u c uitic ctmmni db tr ru uarc fltrk ais al t b mt d nrtpuai

countries and Canada. This book has the Celsius value of each Fahrenheit temperature in parenthesis.

Centrifugal compressor: A compressor employing centrifugal force for compression.

Centrifuge: A sud cu tr uparatiu l ln s t s uruid sui tu b cuidr nual acttii

Change of air: Iidrtsnctti t iuflt cluai ust tr ruc rcnladus a r dt a ctis ttius pacut mua nrus b d u

number of ctmpludu c aiuu pur ni d tmui

Change of state: Change from one state to another, as from a liquid to a solid, from a liquid to a gas, and so


Charge: The amount of refrigerant in a system.

Csirueyheffec : T u duisuicb t a r tr ua i a sncd tr td ur durtcal pa auu dt r u fl un heated due to its

lower density compared with that of the surrounding air or gas. In buildings, the tendency toward displacement,

can us b d u s uruicu i dumpuradnrut t idurial uadus a r b ni uadus tnd su a r snu dt d u s uruicu i

density of outside and inside air.

Clearance: Space in a cylinder not occupied by a piston at the end of the compression stroke or volume of gas

remaining in a cylinder at the same point, measured in percentage of piston displacement.

Ciefficieu hifhexpauiiiu: The fracttial icrua u i luiud tr dtlnmu t a madur al per degree rise in


Ciefficieu hifhperfirrauceh sea hp rpu: Ratt t uatiu u ucd prtsncus dt d u uiurub nppl ust uac

expressed in the same thermal units.

Coil: Aib uatiu tr cttl iu ulument made of pipe or tubing connected in series.

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Cold storage: A trade or process of preserving perishables on a laruu calu b ru r uurattii

Comfort chart: A c ard tfl iu u uctdu dumpuradnru fl d srb- nl dumpuradnru ais nm s tu ais

tmutmu a r mtttin b fl c d u u ucd t dar tn a r ctis tti on human comfort maybe compared.

Compression system: A ru r uuratiu b dum i fl c d u pru nru-imposing element is mechanically


Compressor: T ad pard t a muc ai cal ru r uuratiu b dumt which receives the refrigerant vapor at low

pressure and compresses it into a smaller volume at higher pressure.

Compressor, centrifugal: A non-pt tdu s placumuid ctmpru tr d ad supuis ti cuidr nual u ucdt ad luast

in part, for pressure rise.

Compressor displacement: Ctmpru tr dtlnmu i cn c ic u tnis b mnltplb iu p dti arua b droke by

the number of cylinders.

Displacement in cubic feet per minute:

Compressor, open-type: A ctmpru tr fl d a af tr td ur mtd iu pardt uxduis iu d rtnu a casing, to be

sr dui b ai tnd su tnrcu t ptflurt d n ruln r iu a dnffiiu txt af ual t tr uln daluid rn iu ctidacd

udfluui a ixus ais mtd iu pardi

Cirpreiiir,hrecipricatug: A pt tdu-displacement compressor with a piston or pistons moving in a straight

line but alteriadulb i tppt du s ructti i

Compressor, rotary: Oiu i fl c ctmpru ti aaa ius i a cbl isur b rtdatti t a pt tdu-displacement


Compressor booster: A compressor for very low pressures, usually discharging intt d u ncton line of another


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Condenser: A heat-transfer device that receives high-pressure vapor at temperatures above that of the cooling

medium, such as air or water, to which the condenser passes latent heat from the refrigerant, causing the

refrigerant vapor to liquefy.

Condensing: T u prtcu t u d iu np laduid uad t daptr atti i trsur dt l lnu b a vapor.

Condensing unit: A puc ic ru r uuratiu mac iu ctm iattit tr a u dui ru r uuraidt cti tiu t tiu tr

more power-driven compressors, condensers, liquid receivers (when required), and the regularly furnished


Condensing unit, sealed: A mechanical condensing unit, in which the compressor and compressor motor are

enclosed in the same housing, with no exdurial af tr af ualt d u ctmpru tr mtdtr tpuratiu in the

refrigerant atmosphere.

Ciud ctiu,h serraa: Passage of heat from one point to another by transmission of molecular energy from

partclu dt partclu d rtnu a ctisncdtri

Ciud ctii y,h serraa: The ability of a material to pass heat from one point to another, generally expressed in

terms of Btu per hour per square foot of material per inch of thickness per suuruu dumpuradnru s uruicui

Conductor, electrical: A material that will pass an electric current as part of an electrical system.

Ciuuectughrid: A sud cu ctiiuctiu d u p dti dt a craik ais n us dt c aiuu rtdatiu mttti idt

ruc prtcatiu mtttit tr d cu dur at a rtm a rtdatiu craik af dt a ruc prtcatiu p dtii

Constant-pressure valve: A valve o d u d rtal iu dbput ru pti du dt pru nrut ltcadus i d u nctti l iu t

an evaporator to maintain a desired constant pressure in the evaporator hiu ur d ai d u ma i nctti-line


Constant-temperature valve: A daldu t d u d rtal iu dbput ru pti du dt d u dumpuradnru t a d urmt datc

nl i T daldu ltcadus i d u nctti l iu t ai udaptradtr dt rusncu d u ru r uuratiu u ucd ti d u ct l dt on d

maintain a desired minimum temperature.

Control: Aib sud cu tr ruunlatti t a b dum tr ctmptiuid i itrmal tpuratti u d ur mainal tr andtmatci I

andtmatct d u mpl catti d ad d ru pti du dt c aiuu t dumpuradnrut pru nrut tr aib td ur prtpurdb

whose magnitude is to be regulated.

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Control, high-pressure: A pressure-responsive device (usually an electric switch) actuated directly by the

refrigerant-vapor pru nru ti d u u su t a ru r uuratiu b dum n nally compressor-head pressure).

Control, low-pressure: An electric switch, responsive to pressure, connected into the low pressure part of a

ru r uuratiu b dum n nallb clt u ad u pru nru ais tpui at low pressure).

Control, temperature: An electric switch or relay that is responsive to the temperature change of a

d urmt datc nl tr ulumuidi

Ciuiectiu: The circulatorb mttti d ad tccnr i a en s ad a it ni trm dumpuradnrut tfl iu dt d u dar atti t

its den db ais d u actti t urad dbi

Ciuiectiu,hfirced: Ctiductti ru nltiu rtm trcus c rcnlatti t a euid as by a fan, jet, or pump.

Cooling tower, water: An eiclt us sud cu tr udaptratdu cttling water by contact with air.

Cooling unit: A puc ic a r-druatiu ctm iatti cti tiu t a muai tr a r c rcnlatti ais cttl iu fl d i

prescribed temperature limits.

Cooling water: Wadur n us tr ctisui atti tf refrigerant. Condenser water.

Cipperhpaatug: Ftrmatti t a ilm t ctppurt n nallb ti ctmpru tr flall t p dti t tr s c aruu daldu can us

by moisture in a methyl chloride system.

Corrosive: Had iu a c um callb su drnctdu u ucd ti mudal tccasionally on other materials).

Counter-fliw: Ii d u uad uxc aiuu udfluui dflt en s t d u tppt du s ructti t etflt d u ctlsu d ptrtti t

tiu muutiu d u ctlsu d ptrtti t d u td uri

Critcaahpreii re: The vapor pressure correspondiiu dt d u cr tcal dumpuradnrui

Critcaah erpera re: The temperature above which a vapor cannot be liqnuiust ruuarslu t pru nrui

Critcaahieaici y: The velocity above fl c en s etfl dnr nluidi

Crohydrate: Ai unductc r iu m xdnru t fladur ais aib ald m xus i prtptrtti dt give the lowest freezing


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Cycle: A ctmpludu ctnr u t tpuratti t fltrk iu en s ack dt a dartiu pt id mua nrus i d urmtsbiam c

terms. Also used in general for any repeated process in a system.

Cycae,hdefriitug: T ad ptrtti t a ru r uuratti tpurattit fl c purm ts the cooling unit to defrost.

Cycae,hrefrigeratiu: A ctmpludu ctnr u t tpuratti t a ru r uuraid ack dt d u dartiu pt id mua nrus i

thermodynamic terms. Also used in general for any repeated process for any system.

Daltiu’ihaawhifhpartaahpreii re: ac cti tdnuid t a m xdnru t ua u u adu d urmtsbiam callb a

d altiu tccnp us d u pacui T u nm t d u is d snal pru nru t d u cti tdnuid ulnal d u total pressure of the mixture.

Defriitug: The removal of accumulated ice from a cooling unit.

Degree day: A ni d a us ti dumpuradnru s uruicu ais tmu n us dt puc b d u itm ial uatiu ltas i

winter. For one day there exist as many degree-sab a d uru aru suuruu Fa rui u d s uruicu i dumpuradnru

between the average outside air temperature, taken over a 24-h period, and a temperature of 65°F.

Des ridifier: Ai a r cttlur n us tr ltflur iu d u mt dnru ctiduid t d u a r pa iu d rtnu di Ai a trptti

tr as trptti sud cu tr removing moisture from the air.

Dehumidify: To remove water vapor from the atmosphere or to remove water or liquid from stored goods.

Dehydrator: A device used to remove moisture from the refrigerant.

Density: The mass or weight per unit of volume.

Dew point, air: The temperature at fl c a puc ius amplu t a rt fl d it mt dnru assus tr rumtdust

completely saturated. The temperature at which the air, on being cooled, gives up moisture or dew.

Differeutaah ifhahciu riau: T u s uruicu udfluui d u cnd i ais cnd tnd dumpuradnre. A valve that opens at

one pressure and closes at another. This allows a system to adjust itself wid a m i mnm t tdurctrructtii

Direct connected: Dr dur ais sr duit a mtdtr ais ctmpru trt pt tdulb ctiiucdus i l ie to operate at the

same speed.

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Direct expansion: A system in which the evaporator is located in the material or space refrigerated or in the air

c rcnlatiu pa auu ctmmni catiu fl d nc pacui

Discharge gas: Hot, high-pressure vapor refrigerant, whic a on d luf d u ctmpru tri

Displacement, actual: The volume of gas at the compressor inlet acdnallb mtdus i a u dui tmui

Diipaacereu ,h seiretcaa: The total volume displaced by all the pistons of a compressor for every stroke

snr iu a suii du idurdal n nallb mua ured in cubic feet per minute).

Drier: Synonymous with dehydrator.

Dry-type evaporator: Ai udaptradtr t d u ctitintn dn u dbpu fl uru d u ru r uuraid rtm a pru nru-

rusnc iu sud cu us idt tiu uis ais d u nctti l ne connected to the outlet end.

Duct: A passageway made of sheet metal or other suitable material, not necessarily luak tu d, used for

conveying air or other gas at low pressure.

Dust: Ai a r n pui ti aurt tln t tl s partclu t uard b madur alt a s uruitadus rtm mtkui

Economizer: A reservoir or chamber wherein energy or material from a process is reclaimed for further

useful purpose.

Efficieucy,hrecsauicaa: T u ratt t d u tndpnd t a mac iu dt d u ipnd i uln daluid ni ds.

Efficieucy,hiia re ric: T u ratt t d u dtlnmu t ua acdnallb pnmped by a compressor or pump to the

d utrutcal displacement of the compressor.

Ejector: A sud cu d ad ntl iu datc pru nru dt n ls np a u en s dultc db i a ru dr cdus arua dt t da i a

ltflur datc pru nru ad d ad pt id t d ad en s rtm another source maybe drawn in.

Element, bimetallic: Ai ulumuid trmus t dflt mudal ad iu s uruid ctuffic uid t d urmal uxpai tit nc

as used in temperature- is catiu ais ctidrtll iu suvices.

Emulsion: A rulatdulb da lu n pui ti t mallt nd itd ctllt salt partcles of a substance in a liquid.

Engine: Prime mover; device for transforming fuel or heat energy into mechanical energy.

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Enthalpy: The total heat content of a substance, compared to a standard value 32®F or 0®C for water vapor. A

measure of the energy content of a system per unit mass.

Entropy: T u ratt t d u uad assus dt a n daicu dt d u a tlndu dumperature at which it is added.

Equalizer: A piping arrangement to maintain a common liquid level or pressure between two or more


Eu ectchiia tiu: A tlntti t nc cticuidratti a dt adu a cti daid ruui iu pt id ad d u ltflu d ruui ig

dumpuradnru tr d u tlnttii

Eiapiratiehciudeuier: A ru r uuraid ctisui ur ntl i iu d u udaptratti t fladur b a r ad d u ctisui ur

surface as a muai t s patiu uadi

Eiapiratiehciiaiug: T u prtcu t cttl iu b muai t d u udaptratti of water in air.

Evaporator: A device in which the refrigerant evaporates while absorbing heat.

Expauiiiuhiaaie,ha iratc: A sud cu d ad ruunladu d u eow of refrigerant from the liquid line into the

evaporator to maintain a constant evaporator pressure.

Expauiiiuhiaaie,h serrii atc: A sud cu d ad ruunladu d u etfl t ru r uuraid idt ai udaptradtr t a dt

ma ida i ai udaptratti dumpuradnru i a suii du rulatti p dt d u dumpuradnru t a d urmt datc nl i

Extended surface: The evaporator or condenser surface that is not a primary surface. Fins or other surfaces

that transmit heat from or to a primary surface, which is part of the refrigerant container.

External equalizer: Ii a d urmt datc uxpai ti daldut a dn u ctiiuctti rtm d u c am ur ctida i iu d u

pressure actuated element of the valve to the outlet of the evaporator coil. A device to compensate for

excessive pressure drop through the coil.

Fahrenheit: A thermometric system in which 32°F denotes the freezing point of water and 212°F the boiling

point under normal pressure.

Fan: An air-mtd iu sud cu ctmpr iu a fl uult tr lasut ais tn iu tr tr icu pladui

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Fan, centrifugal: A fan rotor or wheel within a scroll-type housing and including driving-mechanism supports

for either belt-sr du tr s rucd ctiiucttii

Fan, propeller: A propeller or disk-dbpu fl uul fl d i a mtnitiu r iu tr pladu ais iclns iu sr d iu-mechanism

supports for either belt-dr du tr s rucd ctiiucttii

Fan, tube-axial: A disk-type wheel within a cylinder, a set of air-un su daiu ltcadus u d ur u tru tr afur d u

wheel, and driving-mechanism supports for either belt-drive or direct coiiucttii

Filter: A device to remove solid madur al rtm a en s b a dra i iu acttii

Flammability: The ability of a material to burn.

Faarehfitug: A dbpu t ctiiucdtr tr tf dn iu d ad idtldu d u ear iu t d u dn e to provide a mechanical


Flash gas: T u ua ru nltiu rtm d u i daidaiutn udaptratti t d u ru r uuraid i a pru nru-reducing device

dt cttl d u ru r uuraid dt d u udaptratti dumpuradnru t tained at the reduced pressure.

Float valve: Valdu acdnadus b a etad mmur us i a l ln s container.

Flooded system: A system in which the refrigerant enters into a header from a pressure reducing valve and the

evaporator maintains a liquid level. Opposed to dry evaporator.

Fluid: A gas or liquid.

Foaming: Ftrmatti t a tam tr rtd t t l ru r uuraid snu dt rap s t l iu tnd t the refrigerant dissolved in

the oil when the pressure is suddenly reduced. This occurs when the compressor operates; and if large

lnaittu t ru r uuraid adu uui s tldust laruu lnaittu t t l mab m t lb tnd ais u carr us through the

refrigerant lines.

Freezeup: Fa lnru t a ru r uuratti ni d dt tpuradu itrmallb snu dt trmatti t cu ad d u uxpai ti daldui T u

valve maybe frozen closed or open, causing improper ru r uuratti i u d ur ca ui

Freezing point: The temperature at which a liquid will solidify upon the removal of heat.

Freon-12: T u ctmmti iamu tr s c ltrts entrtmud aiu CCl F ).

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Frostback: T u etts iu t l ln s rtm ai udaptradtr idt d u nctti l iut acctmpai us b rt d trmatti ti

the nctti l iu i mt d ca u i

Furnace: That part of a boiler or warm-np uatiu plaid i fl c ctm n tti daku placui Al t a ctmpludu

uatiu ni d tr drai urr iu uad rtm nul u iu nrius dt d u a r nppl us dt a uatiu b dumi

Fusible plug: A safety plug used in vessels containing refrigerant. The plug is designed to melt at high

temperatures (usually about 165°F) to prevent excessive pressure rtm nr tiu d u du uli

Gage: Ai i drnmuid n us tr mua nr iu dar tn pru nru tr l ln s ludul i Stmutmu pullus uanuuni

Gas: The vapor state of a material.

Generator: A a c ctmptiuid t aib a trptti-ru r uuratti system.

Graii y,hipecific: The density of a standard material usually compared to that of water or air.

Grille: A perforated or louvered covering for an air passage, usually installed in a suflallt cu l iut tr ettri

Halide torch: A luak du dur uuiurallb n iu alct tl ais nri iu fl d a lnu eamu; fl ui d u ampl iu dn u

draws in halocarbon refrigerant vaport d u ctltnr t d u eamu c aiuu dt r u d uruuii Ga u dui t b d u burning halocarbon is phosgene, a deadly gas used in World War I in Europe against Allied troops (can be deadly ruad us i a clt us tr ctiiius area).

Halogen: Ai ulumuid rtm d u altuui urtnp d ad cti d t c ltr iut entr iut rtm iut ais ts iui Tflt

halogens may be present in c ltrtentrtcar ti ru r uuraid i

Heat: Ba c trm t uiurub d ad mab u partallb ctidurdus idt td ur trm ais idt fl c all td ur trm mab

be uitrulb ctidurdusi

Heat of fusion: Latent heat involved in changing between the solid and the liquid states.

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Heat, sensible: Huad d ad a tc adus fl d a c aiuu i dumpuradnru; puc ic uad uxc aiuu t dumpuradnrut i

contrast to a heat interchange in which a change of state (latent heat) occurs.

Hea ,hipecific T u ratt t d u lnaitty of heat required to raise the temperature of a given mass of any

substance 1® dt d u lnaitdb ruln rus dt ra u d u dumpuradnru t ai ulnal ma t a daisars n daicu

(usually water at 59®) 1®.

Heat of iapirizatiu: Latent heat involved in the change between liquid and vapor states.

Heat pump: A ru r uuratiu b dum umpltbus dt drai ur uad idt a pacu tr n daicui T u ctisui ur

prtd su d u uadt fl lu d u udaptradtr arraiuus dt p ck np uad rtm a rt fladurt ais t trd i Bb f iu d u

etfl tf the refrigerant, a heat-pump system may also be used to cool the space.

Heatughiyi er: Aib t d u udural uatiu mud ts n nallb durmus acctrs iu dt d u mud ts n us i d

uuiurattit nc a duam uatiut warm-a r uatiut ais d u l kui

Heatughiyi em, electric: Huatiu prtsncus b d u r u t dumpuradnru can us b d u pa auu t ai ulucdr c

cnrruid d rtnu a ctisncdtr ad iu a u ru daicu dt d u cnrruid etfli Ru suicu ulucdr c- uatiu b dum

generally consist of one or several resistance units i dallus i a ramu tr ca iut d u suuruu t uatiu u iu

d urmt datcallb ctidrtllusi

Heatughiyi er,hi ear: A uatiu b dum i fl c uad drai urrus rtm a t lur tr td ur tnrcu dt d u

uatiu ni d b duam adt a tdut tr ultfl admt p ur c pressure.

Heatughiyi er,hiac r: A two-p pu duam uatiu b dum uln ppus fl d d u iucu arb accu trb apparadn

dt purm d tpuratiu d u b tem below atmospheric pressure.

Heatughiyi er,hwarr-air: A warm-a r uatiu plaid cti tiu t a uatiu ni d nul nrning furnace)

enclosed in a casing from which the heated air is distributed to various rooms of the building through ducts.

Herretcaaayhieaaedh ui : A ru r uuratiu ni d ctida i iu d u mtdtr ais ctmpressor in a sealed container.

High-pressure cut out: A control device connected into the high-pru nru pard t a ru r uuratiu b dum dt dtp

the machine when the pressure becomes excessive.

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High side: T ad pard t d u ru r uuratiu b dum ctida i iu d u u -pressure refrigerant. Also the term used to

refer to d u ctisui iu ni d cti tiu t d u mtdtrt ctmpru trt ctisui urt ais rucu der mounted on a single


High-iidehflia hiaaie: A etad daldu d ad etad i u -pressure liquid. Opens on an increase in liquid level.

Hold over: In an evaporator, the abil db dt dab ctls afur uad rumtdal rtm d u udaptradtr stops.

Horsepower: A unit of power. Work done at the rate of 33,000 lb-ftm it tr ..5 l -ft i

H ridifier: A device to add moisture to the air.

Humidify: To add water vapor to the atmosphere; to add water vapor or moisture to any material.

Humidistat: A ctidrtl sud cu acdnadus b c aiuu i nm s db ais n us tr andtmatc ctidrtl t rulatdu


Humidity, absolute: T u suii du amtnid t fladur ctida ius i a suii du lnaitdb t a r n nallb muasured in

grains of water per pound or per cubic foot of air).

H ridi y,hreaatie: T u ratt t d u fladur-vapor pressure of air compared to the vapor pressure it would have

if saturated at its dry- nl dumpuradnrui Vurb iuar dt d u ratt t d u amtnid t mtisture contained in air

ctmparus dt fl ad d ctnls tls ad d u ux tiu dumperature.

H ridi y,hipecific: The weight of vapor associated with 1 lb of dry air; also termed humidity rati.

Hydrocarbons: A series of chemicals of similar chemical nature, ranging rtm mud aiu d u ma i cti tdnuid t

iadnral ua n d rtnu ndaiut tcdaiut ais t trd t dt uadb ln r catiu t l i All aru mtru tr lu eamma lui

Butane and isobutane have been used to a limited extent as refrigerants.

Hydrolysis: Ruactti t a madur al, such as Freon-12 or methyl chloride, with water. Acid materials in general

are formed.

Hydrii atchpreii re: The pressure due to liquid in a container that contains no gas space.

Hygrometer: An instrument used to measure moisture in the air.

Hygroscope: See humidistat.

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Ice-reatughee iiaaeu : The amount of heat (144 Btu) absorbed by 1 lb of ice at 32®F in liquefying to water

at 32®F.

Indirect cooling system: See brine system.

Iufia ratiu: The leakage of air into a building or space.

Iui aatiu: A material t ltfl uad ctisnctd dbi

Irritant refrigerant: Aib ru r uuraid d ad a ai rr datiu u ucd ti d e eyes, nose, throat, or lungs.

Isobutane: A hydrocarbon refrigerant used to a l m dus uxduidi Id eamma lui

Kilowatt: Unit of electrical power equal to 1000 W, or 1.34 hp, approximately.

Lag of temperature control: T u sulab i actti t a dumpuradnru-ru pti du ulumuid snu dt d u tmu

required for the temperature of the element to reach the surrounding temperature.

Latent heat: T u lnaitdb t uad d ad may be added to a substance during a change of state without causing a

temperature change.

La eu hsea hifheiapiratiu: T u lnaitdb t uad ruln rus c aiu iu 2 l t l ln s idt a vapor with no change

in temperature. Reversible.

Leak detector: A device used to detect refrigerant luak i a ru r uuratiu b dumi

Liquid: T u dadu t a madur al i fl c d dtp nr acu i a du ul fl ll uctmu tr itidali D tiun us rtm

solid or vapor forms.

Liquid line: The tube or pipe that carries the refrigerant liquis rtm d u ctisui ur tr rucu dur t a ru r uuratiu

system to a pressure-reducing device.

Liquid receiver: That part of the condensing unit that stores the liquid refrigerant.

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Load: The required rate of heat removal.

Low-pressure control: An electric switc ais pru nru ru pti du ulumuid ctiiucdus idt d u nctti su t a

ru r uuratiu ni d dt ctidrtl d u tpuratti t d u b dumi

Low side: T ad pard t a ru r uuratiu b dumt fl c itrmallb tpuradu nisur ltfl pru nrut a tppt us dt d u

high side. Also used to refer to the evaporator.

Low-iidehflia : A valve operated by the low-pressure liquid, which opens at a low level and closes at a high


Main: A p pu tr sncd tr s dr ntiu dt tr ctlluctiu ctis toned air from various branches.

Manometer: A U-shaped liquid-illus dn u tr mua nr iu pru nru s uruicu i

Mecsauicaahefficieucy: T u ratt t fltrk stiu b a mac iu dt d u fltrk sone on it or energy used by it.

Mechanical equivalent of heat: An energy-ctidur ti ratt t 7i27 l -f = 1 Btu.

Methyl chloride: A refrigerant having the chemical formula CH3Cl.

Micriuh µu: A unit of length; the thousandth part of 1 mm or the millionth part of a meter.

Mollier chart: A urap cal rupru uidatti t d urmal prtpurtu t en s t fl d dtdal uat and entropy as


Motor: A device for transforming electrical energy into mechanical energy.

Motor capacitor: A sud cu su uius dt mprtdu d u dartiu a l db t single-p a u isnctti mtdtr i

Noncondensables: Foreign gases mixed with a refrigerant, which cannot be condensed into liquid form at

the temperatures and pressures at which the refrigerant condenses.

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Oil trap: A device to separate oil from the high-pressure vapor from the compressor. Usually contains a

etad daldu dt rudnri d u t l to the compressor crankcase.

Output: Nud ru r uuratti prtsncus b d u b dumi

Ozone: T u O trm t txbuuit tmutmu n us i a r ctis tti iu tr ctls-storage rooms to eliminate odors,

can be toxic in concuidratti t 5i. ppm ais tduri

Packing: T u dnffiiu artnis a af dt pruduid en s luakauu udfluui d u af ais pard artnis d u afi

Packless valve: A valve that does not use packing to prevent leaks around the valve stem. Flexible material is

n nallb n us dt ual aua i d luak ais tll purm d dalve movement.

Performance factor: T u ratt t d u uad mtdus b a ru r uuratiu b dum dt uad uln daluid t d u uiuruy

n usi Var u fl d ctis tti i

Phosphorous pentoxide: Ai uffic uid sr ur madur al d ad uctmu unmmb ruactiu fl d mt dnru ais uicu

not used alone as a drying agent.

Pour point, oil: The temperature below, which the oil surface will not change whui d u t l ctida iur tldusi

Power: The rate of doing work measured in horsepower, flaa t k ltflaa t ais t trd i

Power factor, electrical devices: T u ratt t flaa dt dtld-amperes in ai alduriatiu cnrruid c rcn di

Pressure: The force exerted per unit of area.

Pressure drop: Lt i pru nrut a rtm tiu uis t a ru r uuraid l iu dt d u td urt snu dt r cttit datc uast

and the like.

Pressure gage: See Gage.

Pressure-relief valve: A valve or rupture member designed to relieve excu du pru nru andtmatcallbi

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Psychrometric chart: A c ard n us dt sudurm iu d u puc ic dtlnmut uad ctiduidt sufl pt idt rulatdu

humidity, absolute humidity, and wet- and dry-bulb temperatures, knowing any two independent items of those


Purging: The act of blowing out refrigerant gas from a refrigerant containing vessel usually for the purpose of

removing non-condensables.

Pyrometer: An instrument for the measurement of high temperatures.

Radiatiu: The passage of heat from one object to another without warming the space between. The heat

pa us b fladu mttti m lar dt l u di

Refrigerant: T u mus nm t uad drai ur i a ru r uuratiu b dum d ad p ck np uad by evaporatiu ad a ltfl

temperature and gives up heat by condensing at a higher temperature.

Refrigeratughiyi er: A ctm iatti t pard i fl c a ru r uuraid c rcnladus tr d u pnrpt u t uxdractiu


Reaatiehs ridi y: T u ratt t d u fladur-vapor pressure of air compared to the vapor pressure it would have

if saturated at its dry-bulb temperadnrui Vurb iuarlb d u ratt t the amount of moisture contained in air

compared to what it could hols ad d u ux tiu dumpuradnrui

Relief valve: A valve designed to open at excessively high pressures to allow the refrigerant to escape.

Resistance, electrical: T u tppt tti dt ulucdr c-cnrruid etflt mua nrus i t m i

Resistance, thermal: The reciprtcal t d urmal ctisnctd dbi

Room cooler: A cooling element ftr a rttmi Ii a r ctis tti iut a sud cu tr ctis tti iu mall volumes of air

for comfort.

Rotary compressor: A ctmpru tr i fl c ctmpru ti aaa ius i a cbl isur b rtdatti t a um ras al


R uuiughtre: U nallb is cadu purcuid t tmu a refrigerant compressor operates.

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Saturated vapor: Vapor not superheated but of 100 percent quality, that is, containing no unvaporized


Seaa,hisaf: A muc ai cal b dum t pard tr pruduitiu ua luakauu udfluui a rtdatiu af ais a dattiarb


Sealed unit: Suu urmutcallb ualus i di

Shell and tube: Pertaining to heat exchangers in which a coil of tubing or pipe is contained in a shell or

ctida iuri T u p pu prtd sus fl d tpui iu dt alltfl d u pa auu t a en s d rtnu dt fl lu the shell is also

provided with an inlud ais tndlud tr a en s etfli

Silica gel: A drier material having the formula SiO2.

Sludge: A suctmpt tti prtsncd trmus i a ru r uuraid snu dt mpnr tu i d u t l tr snu dt mt dnrui Slnsges

may be gummy or hard.

Soda lime: A material used for removing moisture. Not rectmmuisus tr ru r uuratti n ui

Solenoid valve: A daldu tpuius b a mauiutc u ucd t ai ulucdr c cnrruid d rtnu a tluit s ct li

Solid: T u dadu t maaur i fl c a trcu cai u uxurdus i a stfliflars s ructti tilb fl ui itd ctiiius. As

s tiun us rtm en s i

Solubility: T u a l db t tiu madur al dt uidur idt tlntti fl d another.

Sia tiu: The homogeneous mixture of two or more materials.

Specifichgraii y: The weight of a volume of a material compared to the weight of the same volume of water.

Specifichsea : T u lnaitdb t uad ruln rus dt ra u d u dumpuradnru t a suii du ma t a madur al dt a

suii du amtnid ctmparus dt d ad ruln rus dt ra u d u dumpuradnru t d u amu ma t water the same

amount. May be expressed as Btu/ pound/ degrees Fahrenheit.

Specifichiia re: T u dtlnmu t a suii du flu u d t a madur ali U nallb uxpru us i cn c uud pur ptund. The

reciprocal of density.

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Spray pond: An arrangement for lowering the temperature of water by evaporatdu cttl iu t d u fladur i

contact with outside air. The water to be cooled is sprayed by nozzles into the space above a body of previously

cooled water and allowed to fall by gravity into it.

Steam: Water in the vapor phase.

Steam trap: A device for allowing the passage of condensate, or air and condensate, and pruduitiu d u

passage of steam.

Subcooled: Cooled below the condensing temperature correspois iu dt d u ux tiu pru nrui

S bairatiu: The change from a solid to a vapor state without an intermediate liquid state.

S ctiuhaiue: The tube or pipe that carries refrigerant vapor from the evaporator to the compressor inlet.

S ctiuhpreii re: Pressure on the nctti su t d u ctmpru tri

Superheater: A heat exchanger used ti ettsus udaptradtr t fl uru i td l ln s ti d flab dt uidur d u

evaporator is cooled by supplying heat to dry and superheat the wet vapor leaving the evaporator.

Sweatug: Ctisui atti t mt dnru rtm d u a r ti nr acu ultfl d u sufl-point temperature.

System: A uatiu tr ru r uuratiu c umu tr mac iut n nallb ctiiius dt d t u pard i ctidacd fl d d u

uatiu tr ru r uuratiu mus nmi

Temperature: Heat level or pressure. The thermal state of a body with respect to its ability to pick up heat

from or pass heat to another body.

Therraahciud ctii y: The ability of a material to conduct heat from one point to another. Indicated

in terms of Btu/per hour per square foot per inches of thickness per degrees Fahrenheit.

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Thermocouple: A sud cu cti tiu t dflt ulucdr cal ctisncdtr ad iu dflt onictti —one at a point whose

temperature is to be measured, and the other at a known temperature. The temperature between the two

onictti sudurm ius b d u madur al c aracdur tc ais d u ulucdr cal ptduital etup.

Thermodynamics: The science of the mechanics of heat.

Thermometer: A sud cu tr is catiu dumpuradnrui

Thermostat: A temperature-actuated switch.

Tiuhifhrefrigeratiu: Ru r uuratti uln daluid dt d u multiu t 2 dti t cu pur 3 i 77t555 Bdntsab, 12,000

Btu/h, or 200 Btu/min.

Total heat: T u dtdal uad assus dt a ru r uuraid a tdu ai ar drarb dartiu pt id dt r iu d dt a u dui ud t

ctis tti n nallb uxpru us i Bdntptnisni Ftr i daicut i a npur-heated gas, the combined heat added to

t u l ln s iucu arb dt ra u d dumpuradnru rtm ai ar drarb dartiu pt id dt d u uvaporatti dumpuradnru dt

ctmpludu udaptrattit ais dt ra u d u dumpuradnru dt d u iial dumpuradnru fl uru d u ua npur uadusi

Total pressure: Ii en s etflt d u nm t datc pru nru ais dultc db pru nrui

T rb aeu hfliw: Fln s etfl i fl c d u en s mtdu drai dur ulb a flull a i d u s ructti t d u dn u tr p pu

ax t a tppt us dt druaml iu tr d ctn etfli

Unit heater: A direct- uatiut acdtrb-made, encased a um lb iclns iu a uatiu ulumuidt ait motor,

ais s ructtial tndludi

Unit system: A b dum d ad cai u rumtdus rtm d u n ur’ prum u fl d tnd s ctiiuctiu ru r uuraid-

ctida i iu pard t fladur ctiiucttit tr ixus ulucdr cal ctiiuctti i

Unloader: A device in a compressor for equalizing high-and low-side pressures when the compressor stops and

tr a r u pur ts afur d dard t a dt sucrua u d u dartiu ltas ti d u mtdtri

Vacuum: A pressure below atmospheric, usually measured in inches of mercury below atmospheric


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Page 25

Valve: Ii ru r uurattit a sud cu tr ruunlatti t a l ln st a rt tr ua i

Vapor: A ua t partcnlarlb tiu iuar dt uln l r nm fl d d u l ln s p a u t d u n daicut fl c stu itd tlltfl

the gas laws. Frequently used instead t ua tr a ru r uuraid aist i uuiuralt tr aib ua ultfl d u cr tcal


Viscosity: T u prtpurdb t a en s dt ru d etfl tr c aiuu t apui

Water cooler: daptradtr tr cttl iu fladur i ai is rucd ru r uuratiu b dumi

Wax: A material that may separate when oil/refrigerant mixtures are cooled. Wax may plug the expansion valve

and reduce heat transfer of the coil.

Wet-bulb depression: D uruid udfluui srb- and wet-bulb temperatures.

Wet compression: A b dum t ru r uurattit i fl c tmu liquid refrigerant is mixed with vapor entering the

compressor so as to cause discharge vapors from the compressor to tend to be saturated rather than


Xylene: A eamma lu tlduidt m lar dt kurt uiut n us tr s tld iu tr ltt ui iu lnsuu t and for cleaning

compressors and lines.

Zero, absolute, of pressure: T u pru nru ux tiu i a du ul d ad uitrulb umpdbi T u ltflu d pt lu

pressure. Perfect vacuum.

Zero, absolute, of temperature: The temperature at which a body has no heat in it (–459.6®F or –273.1®C).

Ziue,hcirfir h aierageu: T u raiuu t u uctdu dumpuradnru snr iu fl c d u maotr db t asnld uul


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Miller, R & Miller, M.R. (2006) Air Cinditininn RerinRratin. London: McGraw-Hill.

Althouse, A. & Turnquist, C.H. (2004) MidRrn RerinRratin and Ari Cinditininnn Illinois: The Goodhear-Willcox


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