Frequently Asked Questions
Air conditioning (often referred to as aircon, AC or A/C) is the process of altering the properties of air (primarily temperature and humidity) to more favourable conditions. More generally, air conditioning can refer to any form of technological cooling, heating, ventilation, or disinfection that modifies the condition of air.
Air conditioning systems are designed to change the air temperature and humidity within an area and can be used for cooling and heating as required. A complete system of heating, ventilation and air conditioning is generally referred to as "HVAC".
Origins of Air Conditioning
The basic concept behind air conditioning is said to have been applied in ancient Egypt, where reeds were hung in windows and were moistened with trickling water. The evaporation of water cooled the air blowing through the window, though this process also made the air more humid (also beneficial in a dry desert climate).
In Ancient Rome, water from aqueducts was circulated through the walls of certain houses to cool them. Other techniques in medieval Persia involved the use of cisterns and wind towers to cool buildings during the hot season. Modern air conditioning emerged from advances in chemistry during the 19th century, and the first large-scale electrical air conditioning was invented and used in 1902 by Willis Haviland Carrier.
How does Air Conditioning work?
Air conditioners work on the same principals as a refrigerator - chilling indoor air, taking advantage of a remarkable physical law: When a liquid converts to a gas (in a process called phase conversion), it absorbs heat. Air conditioners exploit this feature of phase conversion by forcing special chemical compounds (refrigerants) to evaporate and condense over and over again in a closed system of coils.
The major parts of an air conditioner manage refrigerant and move air in two directions: indoors and outdoors:
Refrigerants have properties enabling them to change at relatively low temperatures. Air conditioners also contain fans that move warm interior air over these cold, refrigerant-filled coils. In fact, central air conditioners have a whole system of ducts designed to funnel air to and from these air-chilling coils.
When hot air flows over the cold, low-pressure evaporator coils, the refrigerant inside absorbs heat as it changes from a liquid to a gaseous state. To keep cooling efficiently, the air conditioner has to convert the refrigerant gas back to a liquid again. To do that, a compressor puts the gas under high pressure, a process that creates unwanted heat. All the extra heat created by compressing the gas is then evacuated to the outdoors with the help of a second set of coils called condenser coils, and a second fan. As the gas cools, it changes back to a liquid, and the process starts all over again.
How much does it cost to run?
Air conditioning units transfer heat between the two units and you pay for the electricity used to do this. Typical values in cooling are 3 to 1 which means you can transfer 3 Kw of heat with 1 Kw of electricity. In heating, typical values are even better 4 to 1. (Electricity is around 8.5 pence per kilowatt depending on your supplier).
Image source: Wikipedia