comfort - controlling your environment at a touch Air conditioning in the office, in the home, out and about
A-Z of Air Conditioning

Note: These definitions are for guidance of users and we appreciate engineers could argue that some descriptions could be more accurate. If you think we may have seriously misled anyone, please e-mail us with your argument or correction and we will add or edit. The terms are to help lay persons understand air conditioning terminology without getting too technical or theoretical.

absolute

as in absolute freezing point which is minus 273 degrees Kelvin - the Kelvin temperature scale developed by Lord Kelvin in the 1800's is also known as the absolute temperature scale. It is a scale mainly used by scientists and the zero point is considered the lowest temperature of anything in the universe. 0K is equivalent to -273.16 Celsius.

acrib

acronym for air conditioning refrigeration industry board

air

we all need it to breathe, sometimes it is dirty and polluted, sometimes it is clean and fresh

air conditioner

term used to describe a packaged (complete) air conditioning unit in one box, as in mobile, portable, window, console or rooftop

air flow

as in volume air flow rate needed to transfer heat

ammonia

a very toxic, slightly flammable substance that can be used as a refrigerant.

anemometer

instrument used to measure air velocity (speed)

ari

a standard test condition but does not relate to UK design conditions - see nominal duty

biocide

used in your drip tray to keep condensate trays and drains clean - also sometimes referred to as tabs, Comfort use them for maintenance contract customers.

Btu

a measurement of heat, the British thermal unit, as heat flow rate = Btu/hr. Put simply, one Btu is the amount of heat required to raise the temperature of 1 lb. of water 1 degree Fahrenheit. Heat flow rates are now measured in watts or kilowatts.

cassette

a fan coil unit that fits mainly in the ceiling void with only a diffuser plate visible, diffuses conditioned air in one, two, three or four directions

Celsius

the correct metric unit of temperature measurement 0 degrees Celsius is freezing point and 100 degrees Celsius is boiling point for water

centigrade

see Celsius, it's effectively the same

cfc

a chlorofluorocarbon that is now not allowed to be used as a refrigerant, typically R11 or R12

cfm

an imperial measurement of air flow rate - cubic feet per minute

chiller

a machine that uses refrigeration to produce chilled water

cibse

acronym for the chartered institute of building services engineers - UK authority on design matters

close control

commonly means air conditioning to precise control requirements of air temperature, humidity and cleanliness - very expensive to own and run and wastes energy but is sometimes necessary for machines, processes and historical archives or artefacts

comfort

our namesake but what we all strive to achieve, air conditioning provides this by altering the environment served

comfort cooling

often derided by some engineers (who should know better) as not being air conditioning, is a common term to describe cooling for comfort as opposed to close control. Modern comfort air conditioning systems control temperature very accurately but not humidity, as it would be an unnecessary waste of energy to do so, purely for human comfort.

compressor

at the heart of most air conditioning systems there has to be a refrigeration compressor. With current technology without a compressor, there would not be enough cooling for most applications

condenser

a device used to condense a refrigerant thereby rejecting the heat to another source, typically an air cooled or water cooled condenser

condensing unit

a machine comprising a compressor, condenser and if air cooled, a fan, used to reject heat

condensate

water, or the moisture removed from the air when the air is cooled

conductivity

the property or power of conducting heat.

cooler

a machine, commonly using water, a fan and a coil or mesh to provide evaporative cooling - very effective and cheap to run in hot dry climates, but not so effective in humid climates, such as the UK. It is now illegal to refer to them as air conditioners.

cooling

a process of which there are many to remove either sensible or latent heat, or both, which is then referred to as total heat

cooling tower

a device, commonly used in larger buildings to reject heat from a chiller to the atmosphere via water and forced air. They have to be regularly cleaned and maintained, particularly to prevent legionella bacteria forming within the water. It is probably preferable to use air cooled condensers now.

cop

the coefficient of performance, used to determine how efficiently a heat pump operates. It is now common for modern systems to exceed 3 to 1, whereby for every 1kw of electrical power used by the unit 3kw of heat will be provided. Latest systems can exceed 4 to 1, but note that the COP is related to external and internal temperatures.

dBA

a unit for measuring sound power or pressure, deciBel on the A scale

de-humidify

to remove moisture from the air, achieved by mechanical cooling

dew point

the temperature at which the moisture in air condenses from a vapour back to a liquid. As in the condensation that forms on a cold surface relative to air temperature, i.e. glazing or un-insulated ducts or pipes.

diffusion

the art or science of delivering air to achieve cooling or heating with good air distribution without causing discomfort or draughts, uses a diffuser

diffuser

a device forming part of an air conditioning unit or duct system to deliver and diffuse air efficiently without causing discomfort or cold draughts

drip tray

a component of most air conditioning units and fan coil units to collect the condensate water removed from the air whilst cooling

dry bulb

the dry air temperature - relative to the wet bulb temperature - see wet bulb.

dry cooler

similar to a condenser

duct

a pipe or tube made from various materials either rectangular, circular, oval, flexible, vapour sealed or and insulated used to convey air.

eer

energy efficiency ratio - a factor calculated to determine how efficient a unit/system is.

energy labelling

a system commonly used from 2003 to show how energy efficient a unit or system is.

enthalpy

a term used to determine the amount of moisture held by a specific volume of air at a certain condition.

evaporative cooling

cooling effect caused by air blowing across a moisture laden surface - see cooler - but also is the effect you feel if air is blown across your skin. Try it now, you have moisture on your skin and by blowing on it you will feel the cooling effect.

evaporator

commonly the room unit of an air conditioning unit, that gives off cooling by typically evaporating refrigerant from a liquid to a gas. This action causes a refrigerated cooling effect and the heat within the room air is transferred to the refrigerant. Also a component part of a chiller.

fan

a device used to move or circulate volumes of air

fan coil

a device commonly having a fan and a coil located within a room to provide local cooling or heating

Fahrenheit

the imperial measurement of temperature

filter

a device of varying types and qualities used to remove impurities from air, gases or liquids. Always keep your filters clean! Dirty air conditioning filters can be the largest cause of unnecessary breakdowns!

freezing

the process of converting a liquid or gas to a solid state

gas

common term used to refer to some refrigerants, which are at sometimes in a gaseous state - otherwise any substance that is freely moving but is neither a solid or a liquid.

grille

not to be confused with a diffuser, a grille is device supplying or returning air, commonly a grille is never used for supplying air from a ceiling, as it cannot diffuse the air. It should only be used in a sidewall application or for vertical discharge.

gwp

global warming potential - is a measurement of how much effect any given refrigerant will have on global warming in relation to carbon dioxide. This is usually measured over a 100 year period. The lower the value of GWP the better the refrigerant is for the environment.

hc

hydrocarbon, amongst other applications also a highly flammable refrigerant - propane

hcfc

hydrochlorofluorocarbon - a refrigerant, typically R22 - see refrigerants

heat pump

a machine similar to a condensing unit but can reverse it's refrigeration cycle and extract heat from an external source, air or water and then pump it back in to a building to provide heating. Very efficient because even when it is -15ºC outside there is still heat in the air and a heat pump can extract this heat, upgrade it and use it.

hfc

hydrofluorocaron - a refrigerant, typically R134A, R407C, R410A - see refrigerants

heat gain

the heat a building or room gains causing possible discomfort, this can be from many sources including solar gain (heat radiated from the sun), conduction gain, (heat transmitted to a space due to the difference between the inside and outside temperatures), lights, people, machines, fresh air etc.

heat loss

The heat a building or room loses causing possible discomfort, this can be primarily due to the difference between internal and external temperatures, but also the amount of cold air used for ventilation.

hi-wall

a term used to describe a room fan coil unit mounted at high level on a wall

humidistat

a control switch used to operate (turn on and off) another device based on pre-set humidity conditions

humidity

or relative humidity, the measurement of how much water vapour is contained within the air - i.e. 50% is considered acceptable comfort, 20% would be an uncomfortable dry condition and 100% means it's probably raining!

hvca

acronym for the heating and ventilating contractors association

hygrometer

an instrument used to measure the relative humidity

ice

solid water at 0ºC, -32ºF

internal heat gain

the heat produced by internal rather than external sources, can be people, lights, machines, computers, electronics, cooking, TV's, hot meals, etc.

inverter

an electrical device that allows the frequency of the electric supply to be varied from it's standard 50Hz, thereby allowing motors (compressors) to be run at variable speeds. This in turn allows more precise delivery of energy to match the required load at any one time, rather than a constant delivery, which may not match. The result is an extremely controllable and energy efficient system that is not only cheaper to run but also needs a smaller power supply.

Kelvin

see absolute

kcal

a measurement of heat used in continental Europe, as 1000 calories - yes it's the same unit those diet people keep referring to.

kw

standard measurement of heat or power, 1kw = 1000 watts = 3412Btu/hr = 860kcal

kilowatt

same as kw above

Kyoto

protocol - we suggest you research this on the Internet, it covers the recommendations to reduce global warming and is a very complex subject. Air conditioning manufacturers and refrigerant producers are working hard to produce new and energy efficient products. Make sure you read it all though, don't believe everything you hear on the news or read.

joule

a measurement of energy

latent heat

the heat that does not change the temperature but does change the state of a substance when added to or removed from it.

liquid

a substance that is neither solid nor a gas

low ambient

term used to refer to a low external temperature, often an air conditioner or system will require low ambient controls to enable it to keep on cooling with low external temperatures

legionella

it's full name is Legionnaires' Disease (Legionellosis) and is a very uncommon form of pneumonia caused by a bacterium that when inhaled may have serious consequences. It is only possible to catch this via a water based aerosol and apart from natural sources the most likely way a single individual can catch this is from a little used shower head. Cooling towers that have not been correctly maintained more often causes larger public outbreaks.

mobile

as in a mobile air conditioner, you simply wheel it in, plug it in and turn it on, firstly having decided where you will put the condenser or how to discharge the flexible hose to external air. You can also have a split mobile where the room unit is connected by an umbilical to an external condenser.

monobloc

term used to describe a single packaged mobile or portable air conditioner, it will be a one piece unit normally with a flexible discharge hose, not a remote condenser.

Montreal

protocol covers the subject of substances that deplete the ozone layer.

mouth organ

slang term used to describe a horizontal ceiling suspend room fan coil unit, now you know why, it is similar to a mouth organ having slots on both sides through which air is blown. They normally do not make music or any noise if properly designed.

m3/hr

a measurement of air volume flow rate - cubic metres per hour

m3/s

a measurement of air volume flow rate - cubic metres per second

m/s

a measurement of air velocity or speed - metres per second

multi-split

a term used to describe a system where there is one outdoor unit connected to a number of room fan coil units

nitrogen

a constituent part of air - oxygen free nitrogen (OFN) an inert and safe gas is used to pressure test refrigeration pipework and is passed through the pipework when it is being installed. But only reputable companies do this.

nominal duty

the standard means of measuring the capacity of an air conditioner or unit, system etc., relates to conditions which mean nothing to UK

odp

ozone depleting potential - new refrigerants have zero odp and therefore, if released do not deplete the ozone layer. However, they still must not be released to atmosphere.

ofn

oxygen free nitrogen - used in brazing copper refrigeration pipes to prevent moisture and oxides collecting and remaining in the pipework during manufacture or on site installation. Failure to use it can have disastrous effects later, causing expensive failure of compressors.

oil

used to lubricate the compressor, can be mineral oil, but increasingly synthetic with new refrigerants

oxygen

we need it to oxygenate our bloodstream and live, therefore we have to ensure there is enough in the air we breathe.

ozone

as in that layer above earth that protects us from ultraviolet rays and other nasty things happening to our world. Some refrigerants are ozone depleting, which if they were released could possibly damage the ozone layer. New refrigerants are not able to deplete ozone.

physchrometrics

the art or science of the relationships between air, gas, liquids used to calculate air conditioning requirements

portable

as for mobile air conditioner

propane

or R290, although a naturally occurring substance that can be used as a refrigerant it is also a highly flammable gas and must be carefully used.

pressure

the changing pressure of a substance can affect it's state and hence properties. A compressor is used to change the pressure of a refrigerant and hence it's ability to absorb or transfer heat. The pressure a compressor, fan or pump is capable of producing will also affect how far a gas or liquid can be moved. The resistance to pressure a pipe or duct causes will also determine how far a gas or liquid can be moved.

R22

an hcfc refrigerant which from 2002 can only be installed new as small heat pumps

R407C

an hfc refrigerant that is non-ozone depleting, zero odp, commonly used in small air conditioning systems

R410A

an hfc blended refrigerant that is non-ozone depleting, zero odp, but operates at higher pressures than other hfc refrigerants.

R417A

the zero odp replacement, suitable for new equipment and as a drop-in replacement for existing R22 systems.

refcom

the register of companies assessed as competent to handle refrigerants

refrigerant

a substance used to absorb and transfer heat, can be air, water, gas or chemical.

refrigeration

the process of mechanical cooling

remote controller

a device that allows the remote operation or setting of another device, can be "wireless" as infrared or "hard wired" with a cable connecting - allows you to control your air conditioning

sensible heat

the heat which affects the temperature of a substance. e.g. there is no moisture change, such as heat from machines, lights or the sun etc.

sick building syndrome

often blamed on air conditioning, but is primarily due to insufficient or poor ventilation and also the chemicals used in manufacture of furniture, carpets and other office equipment or processes

sling physchrometer

looks like a football rattle (remember those!) but comprises two thermometers, one to measure dry bulb, the other wet bulb temperatures. has to whirled around to get air temperature and a correlation between the two temperatures gives us the relative humidity

solar gain

the heat gained by a building or room from the suns heat radiation.

sound

most air conditioning systems are relatively quiet and do not cause noise disturbance to users or the environment. It is common to illustrate equipment sound levels as either sound power, or sound pressure in dBA (deciBel on the A scale). This can be very confusing and the resultant room noise level is relative to many other factors, resulting in a room noise level, often expressed as a NR or NC level.

split system

an air conditioner that has been split, very common and ideal for most buildings, the room unit or evaporator, fan coil is split (separated) from the condensing unit, external or heat pump and connected by means of small bore pipes and cables.

tabs

see biocide

temperature

a measurement of how hot or cold a substance is. A comfortable summer internal temperature would be 24ºC, in Winter 21ºC

thermometer

an instrument for measuring the temperature

thermostat

a device for controlling or switching on or off another device based on a pre-set temperature.

ton

an imperial measurement of refrigeration heat - 1 ton = 12000Btu/hr or 3.517kw

total heat

the sum total of sensible and latent heat

u value

a calculated value used to further calculate the rate of heat flow through a structure, e.g. the heat conducted through a wall, roof or window

vav

variable air volume - a type of a/c system sometimes used in very large buildings

velocity

speed

vrf

variable refrigerant flow - a common type of air conditioning used in many buildings today, same as vrv
-

vrv

variable refrigerant volume, a protected trademark for the system developed by Daikin and now copied by many others who have to refer to it as vrf

vwt

variable water temperature, a water pipe loop system having both boilers to raise the temperature and dry coolers or cooling towers to lower the temperature, small heat pumps are commonly connected to the loop to either reject local heat to or extract heat from the loop.

vvt

variable volume and temperature - a small ducted air system that can vary both the volume of air and temperature to achieve either heating or cooling matched to the required capacity

water

we drink it, swim in it, pollute it and sometimes use it for air conditioning

water cooled

heat rejected from a building is transferred to water. Not advisable if you intend to use a cooling tower, unless you regularly maintain the system and ensure water treatment is maintained but can be very efficient if using ground water in conjunction with a heat pump, inverters and a vrf system

wet bulb

the air temperature measured with a wet bulb - a small fabric sleeve around the bulb of a thermometer and wetted

x factor

many x factors are used to calculate such things as the suns altitude, azimuth and angle of incidence to work out solar gains on buildings.

y factor

used with x factors as above.

z factor

if you have read the whole of this document you deserve to get some zzzzzzzzz!

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