Air conditioning can control the physical conditions in a building namely temperature, cleanliness and humidity.
The air is cleaned by being passed through filters to remove dust, pollen, hair and other particles while it is being circulated by fans driven by electric motors.
The cooling system is very similar to the refrigerator in the way in which it operates. A refrigerant is circulated from an evaporator, through a condenser and then via an expansion valve by means of a compressor. This cycle is continuously repeated. The evaporator is positioned over a fan that extracts both humid and hot air from the room. It gathers the heat from the air and makes the moisture concentrate into water droplets by condensation. The cool waterless air then returns to the room via air vents. The fan transfers the heat from the condenser to the outside of the room.
Dehumidifying or humidifying is done by controlling the air temperature. If the air is warm it can hold more water vapour, and less if it is cold. If the air is not saturated it can be cooled and will become saturated. If it is cooled below a certain point then moisture will condense and it becomes less humid. Therefore the air can be dried just by cooling the air below the temperature at which it saturates. The process is the reverse for humidifying.
