This fan circulates air around a greenhouse
A small personal fan
Room sized pedestal fan
Domestic Air Conditioners:
These come in two types (if you want to know how they work look here)
A Fixed Air Conditioning Unit Fixed air conditioning units:
They draw in air from outside cooling it using a heat exchanger set outside of the building before blowing it into the room.
The vents for airflow are fixed in windows or walls.
Portable air conditioning units:
These are compact portable appliances which suck air from the room into the unit which contains a heat exchanger.
They draw heat out of the air and a fan then blows the cooled air back into the room. The hot air is exhausted out of a ducting hose which is usually hung out of a window.
Air conditioning units purify and dehumidify (remove the moisture from ) air passing through them, filtering out dust and blowing out cool, clean, dry air.
They all come with thermostatic controls to keep the room at a constant temperature and, like heaters, there are a range of extra options you can have depending on your needs.
Air conditioners were originally designed to remove moisture from the air and will dry out air in the room, they also need an external vent to get rid of waste heat (usually a flexible ducting hose).
Portable ones can be moved from room to room, in heatwaves you can use it in the lounge during the day and in the bedroom on those hot sultry nights.
During winter they can be used as dehumidifiers to remove dampness from the air, preventing mould, mildew and condensation problems.
Some have a heating function which you can use for all-year-round climate control.
Choosing a portable air conditioner
A too-small unit will burn excess energy as it will overwork to keep your room cool, and a too-large unit will keep switching on and off too quickly, either way, they will cost you more to run than the right-sized air conditioner for your space.
In the UK Air conditioners are usually rated in British Thermal Units (BTUs) 1 kW = 3,400 BTUs
Roughly calculated you will need about 30 watts (115 BTUs) for each cubic meter ( m3 ) of space.
We advise buying an air conditioner with a minimum output 7000 BTUs this is the minimum required to cool a small room (40m3) on a hot day.
Larger rooms up to 60m3 need around 10,000 BTUs and open plan rooms, lofts and office spaces up to 90m3 need at least 15000 BTUs.
Choose the right size for your room, then select the extra controls for your needs (remote control, timer etc...)
To see a range of options please visit our award-winning partners, the air conditioning experts at Airconcentre
Tip: If you have issues with dry air then a bowl of water placed across the room from your air conditioner and topped up regularly will keep the air moist.
How Air Conditioners work :
Air conditioning units were originally designed as dehumidifiers to remove moisture from the air to keep paper stock at a publishing company dry during humid summers.
Because cold air holds less moisture than warm air the warm moist air was cooled by blowing it across cold pipes. The cooled water condensed out of the air drying it, cooling the air was a fortunate side effect of the process.
An air conditioner does this by refrigerating the air using a technique known as phase conversion, this is a law of physics which states that when a liquid changes to a gas it absorbs heat, so air conditioners use a closed system of coils containing chemicals called refrigerants which constantly change from gas to liquid and back again.
When the fan blows warm air from the room over one set of coils (evaporator coils) the refrigerant changes from a liquid to a gas absorbing heat from the air, this cold air is channelled into the room cooling it.
The gas is then pumped into a compressor which 
pressurizes it causing it to turn back into a liquid. This now warm liquid flows through a second set of coils (condenser coils) and a second fan blows over these coils removing the warm air (which is channelled outside) and cooling the liquid, which is then routed back to the evaporator coils and the process starts all over again.
With portable air conditioning units, the hot air is vented out via a ducted hose which can be hung out of a window or attached to a wall vent, similar to the way a tumble dryer is vented.
For more info on buying and using air conditioners see the Air conditioner buying guide at aircon centre