AIR CONDITIONING

A brief but easily read description of air conditioning.

With the hot spell of weather experienced at the time of writing thoughts turn to air conditioning. Many people now have the luxury of air conditioning in their cars and would like to achieve the same comfort in their homes, but it is not that simple. It is possible, of course, to purchase free standing units to place in a room, but such devices can only succeed in reducing humidity, a welcome benefit no doubt, but they are not able to reduce the temperature.

The basic operating cycle for any refrigeration plant for air conditioners, freezers or refrigerators consists of an electrically driven compressor which compresses the vapour of the refrigerant which, at this point is at a higher temperature than the environment. The refrigerant is then passed through a condenser where it loses heat to the environment and condenses the vapour into a liquid. This liquid is then passed through a throttle valve which causes the pressure to drop so that the liquid is transformed into a wet vapour at a temperature below that of the environment. This wet vapour is then passed through a heat exchanger which takes heat from its environment, this heat evaporates the liquid in the wet vapour of the refrigerant before returning it to the compressor. The evaporator heat exchanger is the actual cooling component.

In most applications the condensing heat exchanger that is transferring heat to the environment is situated away from the cooler e.g. at the back of the refrigerator or in front of the car engine. In a free standing unit, however, the condenser and the evaporator are situated in the same room so that, as fast as the evaporator is extracting heat from the room, the condenser is putting the same amount, plus the heat equivalent of the electrical energy put into the compressor, back into the room so that the unit is unable to produce a net cooling effect. If the air in the room is humid there will be considerable condensation on the evaporator which removes water from the air and reduces the humidity making the room more comfortable if no cooler. Unfortunately, unless the room is sealed, the tendency will be for the humidity to return to the outside value and the cooler will be fighting a continuos battle in its efforts to remove water from the air in the room.

Ron Watts