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. 0ºK is equivalent to -273.16º Celsius.


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.


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


air handling unit - name given to an air conditioning unit that is normally custom built to suit the building requirements, commonly found in large buildings.


instrument used to measure air velocity (speed).


used in your drip tray to keep condensate trays and drains clean - also sometimes referred to as tabs.


branch take off - normaly forms part of a flexible duct where one duct splits into two ducts. Can be made from metal or plastic.


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.


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.


a device to meashure water flow.


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


see Celsius, it's effectively the same.


the most common area where diffusers are installed.


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


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


a machine that uses refrigeration to produce chilled water.

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 artifacts.


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.


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.


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.


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


the property or power of conducting heat.


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.


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.


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.


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


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.


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

drift eliminators

water drift are droplets that are carried out of the cooling tower with the exhaust air. The drift rate is typically reduced by employing baffle-like devices, called drift eliminators, through which the air must travel after leaving the fill and spray zones of a cooling tower.

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.


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


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

energy labeling

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


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.


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.


a device used to move or circulate volumes of air.

fan coil unit

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


the imperial measurement of temperature.


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!

flow hood

a device to meashure air flow.


flexible ductwork - see duct.


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


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.


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.


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.


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


hydro chlorofluorocarbon - 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.


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.


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


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

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.


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.


see absolute.


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


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


same as kw above.


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.

k factor

used to convert l/s to m/s or vic versa.


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.


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.


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.


a measurement of air velocity or speed - litres per second.


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.


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


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


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


a measurement of air velocity or speed - metres per second.


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


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 AUS.


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.


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.


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


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


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.

package systems

an air conditioner that is compleate, very common and ideal for most buildings, the evaporator & fan coil is connected to the condensing unit and comes as one unit.


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


as for mobile air conditioner.


the fitting used to connect flexible duct to soilid or ridge duct. Normaly made from metal and could have a damper fitted to adjust the airflow to the diffuser.


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.


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.


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


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


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


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


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


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


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.


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.

spiral duct

see duct.


see biocide.


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


an instrument for measuring the temperature.


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


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.


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




volume control damper - used to manual or automatically control distribution of airflow.


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


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.


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.


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! Hope you liked it.