There is hardly any seminar today, focused on the themes of energy conservation and sustainability, which goes without reference to air conditioning (A.C.). Considered to be among the fastest expanding human needs, just like flights, phones or cars, air conditioned indoors are on a fast track in every developing country, while the affluent nations have already conditioned most of their indoors.
Impacts of air conditioning on green living is much debated, ironically, most often sitting inside A.C. rooms, suggesting how inseparable it has become from our routine urban lives. The need of the hour is to understand the problems and potentials of the technology behind A.C. Human attempts to control the indoor air must have started right when our ancestors stopped their nomadic lifestyle and became settlers. Mere wrapping up of the body was not adequate to protect us from heat and cold, especially in climatic zones with extremities of temperature. There are records to prove that as early as 2 century A. D. the Chinese were trying to cool the indoors using ingenious ideas. St. George’s Hall in Liverpool, England, built in 1854, is believed to be the first air conditioned building in the modern era. The credit of adopting modern technology, using electrical energy, for air conditioning goes to Willis Carrier, who in the early 1900s started the trend of air conditioned buildings in the U.S. So, the urge to condition the air has been both historic and human, and cannot be wished away now a century later.
As heat would naturally flow in the opposite direction, we need machines to achieve this. Air conditioning happens by a simple rule of physics which states that liquid absorbs heat when changed from liquid to gas and gases give off heat when changed from gas to liquid. The system follows cycles of expansion, evaporation, compression and condensation, all inside a closed loop. First, the refrigerant liquid is expanded at low pressure and is let into the indoors. In contact with the indoor air, this low pressure liquid absorbs heat, becoming low pressure gas, in the process resulting in lower temperature inside. This heat laden low pressure gas is collected and goes through compressors to become high pressure gas. This hot gas is passed thorough condensers, releasing the heat to outside, becoming high pressure liquid. This pressurized liquid is expanded to become the low pressure gas, repeating the cycle already explained.
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In principle, it is the same refrigerant that moves from one machine to another, passing through hot indoors, cooling it and releasing the heat to outside. If we try standing near these machines outside, we can feel the heat being released, so too while crossing a jammed road with majority of air conditioned cars around. So, in the name of air conditioning, while we are cooling the indoors, we are actually heating the outdoors!