How air conditioning works

Air Conditioning is the process of supplying an internal space with cooled and filtered air at the specified temperature and humidity. The term usually describes a refrigeration system designed to cool the air supplied into the space via ductwork within the building. The air conditioning process removes moisture from the air in the evaporator coils and the required amount is then added to control humidity which is important to comfort of occupants and prevention of undesirable effects such as static. Auxiliary filters will remove pollen, dust and other pollutants from the air. Entire buildings are designed so that air temperature, humidity, and freshness are controlled by a single, central air conditioner. There are many different types and different manufacturers of air conditioners and of all these types’ people in the UK are mostly familiar with the type known as a "split system". This is an indoor fan coil unit connected via pipe work to an outdoor condensing system. The simple split system is ideal for fitting during building occupation but it is not full air conditioning as only air temperature is controlled.


The key element of the air conditioner is the refrigerant, usually a fluorocarbon that flows constantly through the conditioners mechanisms. Refrigerants have compression and expansion characteristics suitable for the transfer of latent heat from the evaporator coil to the condenser coil. When compressed is gives off heat and when evaporated it absorbs heat. The mechanisms that evaporate and compress the refrigerant are divided into two areas, an indoor air filter fan and cooling coil. And outdoor comprising of a compressor, condenser coil and fan.


In the room unit warm humid air is drawn from the room through the filter and over the cooling coil by a fan. This coil contains a refrigerant which has a very low boiling point, i.e. it will evaporate at room temperature. The warm air gives up its heat to the refrigerant and in the process, causes the refrigerant to vaporize. The air passing over the cold coil will reduce in temperature to below the dew point and moisture will condense onto the coil and drip into a collection tray, so dehumidifiying the air. Cooled dehumidified air is passed back into the room. The vaporized refrigerant passes through the interconnecting piping to the compressor, which pumps it under pressure to the condenser coils. Here its heat is transferred by fan to the outside, and it is returned to the cooling coil as a liquid. Electric motors drive the compressor and both fans. Thermostatic control the compressor motor, turns it off when the room temperature reaches the desired level and restarting it as the room heats up.


Buildings which are designed for air conditioning at construction can be centrally air conditioned if they have a forced air conditioning system, which utiises a blower fan and ducts to distribute conditioned air throughout the building. During the summer months these ducts will carry cooled air. In the winter warmed air which has had moisture added to achieve around 50% relative humidity will be circulated. For most centrally air conditioned buildings, the condenser and compressor are built into an enclosed housing outdoors, and the cooling coil is mounted in the main duct near the blower fan. Insulated tubing carries the refrigerant between components.


A large building may have several cooling units mounted on its roof or placed beside it. In some air conditioning systems, a fresh air intake mixes fresh outside air with the inside air. This mixture is sent through several filters that remove airborne particles. The cleaned air is then passed through the coils of a cooling unit. In cases where the air is too dry and needs moisture adding, it may be forced through ducts containing a water spray. Finally the cooled air is ducted into the rooms or offices in the building.


Indoor units come in various shapes and sizes. They can be mounted on the floor, on a wall, or below or within the ceiling. The size of the indoor unit normally indicates the capacity i.e. the quantity of cooling or heating. Outdoor units generally look the same although varying in size.


Primitive 19th century air conditioning systems utilised the evaporation of ice to cool the air. Willis Carrier was credited with the design of the first practical air conditioning system. He was the inventor, who designed a mechanical air conditioner in 1911 and began manufacturing conditioners in 1915.


It was in the 1930's however, that air conditioning systems started to be installed in office buildings, hospitals, apartments, buses & trains. Today, most large buildings are constructed with air conditioning. Large systems are controlled by computers to ensure efficient operation of heating and conditioning systems.


In the 21st century there is pressure to reduce the carbon footprint of buildings and buildings have been built without air conditioning as described above. Careful control of solar gain, use of thermal inertia and ventilation control to stabalise temperatures has been used to achieve comfortable working conditions without the electrical load associated with air conditioning. These low energy buildings employ a range of technologies to achieve adequate environmental control and they generally operate with a wider allowable range of internal temperature.


Portable air conditioning hire, by Aircon Hire Ltd, serving London and South East England.