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Air Conditioning Systems Explained
Packaged (Simple) Cooling Systems
Simple cooling systems are usually indoor units that comprise of refrigerant-to-air heat exchangers and an integral air circulation fan. They generally fall into one of the following categories:
- Single Packaged Units: The indoor and outdoor units are both contained in a single (unitary) housing and are usually installed as 'through the wall' units.
- Split Packaged Units: A single indoor unit (floor, wall or ceiling mounted) connected to a single outdoor unit by refrigerant pipework.
- Multi-Split Packaged Units: A number of indoor units (floor, wall or ceiling mounted) with dedicated refrigerant pipework connected to a single (common) outdoor unit.
- Variable Refrigerant Flow Systems (VRF): A number of floor wall or ceiling mounted indoor units connected to a common outdoor unit by refrigerant pipework.
Some simple packaged systems are reversible allowing them to work as heat pumps.These systems generally have self contained controls for temperature and may include a function for timed control.
Centralised (Complex) Cooling Systems
Centralised air conditioning systems are more extensive (complex) and generally utilise water or air distribution systems to deliver cooling to conditioned spaces by way of various terminal units. The conditoned spaces maybe seperated into zones by distibuted control systems which allow differing parameters to be applied to each zone. The controls could be integrated into a building management system. Centralised systems fall into the following categories:
- Centralised Air Systems: An air handling unit (AHU) containing a cooling heat exchanger produces cooled air which is distributed via ductwork to conditioned spaces and is expelled through grilles or diffusers or other terminal devices in the conditioned area. These systems could comprise of centralised ductwork where the air is cooled at the conditioned space by a terminal unit.
- Centralised Cooled Water Systems: Water is cooled by a centralised system and distributed to terminal units in the conditioned spaces. Terminal units may cool recirculated air from the room, fresh air drawn from outdoors or air supplied by centralised ducted systems.
- Water Loop / Reversible Heat Pump Systems: comprising of individual reversible water to air heat pumps situated in each conditioned space, heat is drawn from or returned to a common temperature controlled water loop. A cooling tower is used to dissipate excess heat.heat in the loop is provided by a central heat generator such as a fossil fuel burner or electric flow boiler.
- Additional Systems: Complex systems may also incorporate simple cooling systems (unitary packaged units, split ot multi-split systems) to serve certain conditioned spaces.
What does air conditioning do?
- Cooling - Air conditioners offer precise temperature control. You can always create a comfortable climate, with the right temperature. Not only does it create comfort, it makes you feel fresh and active whatever the conditions outdoors.
- Heating - Air conditioners can also provide heating. You can enjoy a constant temperature all year round, no matter what the outside temperature. It is an environmentally friendly alternative to traditional heating because it takes energy from the outside air and brings it inside.
- Cleaning - Air conditioners produce clean, healthy air. Indoor units are equipped with filters that take dust, pollen, smoke and other allergens from the air. The level of filtration can be increased if required.
- Dehumidifying - In cooling mode an air conditioner dehumidifies the air. Correct humidity levels limit the growth of dust mites and moulds, which has a positive effect on allergy sufferers. 40% to 60% humidity is a comfortable level for humans, which also ensures a longer life of your house and appliances.
- Ventilating - Ventilation can be integrated in to the air conditioning system. It extracts the inside air and pushes in fresh, conditioned air from outside. When the air conditioning is turned off, the ventilation can work independently. Ventilation systems can also be installed without the air conditioning installation.
How does it cool?
In simple terms air conditioning works by absorbing energy in one place and releasing it in another place.
The process requires an indoor unit and an outdoor unit with copper piping connecting the two. Refrigerant flows through the pipes between the units. The refrigerant absorbs the energy in one unit and transfers it to the other unit for release.
- Indoor unit - A fan blows hot indoor heat over a heat exchanging coil containing refrigerant. The cold refrigerant absorbs heat from the air and cooled air is blown in to the room.
- Copper Piping - Refrigerant circulates through the system via the copper piping, transferring the heat from the indoor unit to the outdoor unit.
- Outdoor unit - Through compression, the refrigerant is heated and its boiling point increases. In the outdoor unit, the obtained heat is released to the outdoor air by a fan which blows the outdoor air over a heat exchanger.
- Refrigerant - The liquid refrigerant flows back to the indoor unit.
- Back to the Indoor unit - The refrigerant is decompressed which enables it to absorb heat from the indoor air and the cycle starts over.
How does it heat?
By use of an air source heat pump, the cooling cycle of the air conditioning unit is reversed. The outdoor unit absorbs heat from the outside air (heat exists in all air down to -273 °C) which is transferred through the system and is released indoors, therefore providing heating. Typically for each kilowatt of electricity used, 3-5 kilowatts of heat is generated.
