Air Conditioners and Refrigerators

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The second law explains how the Universe is continuously slipping into chaos. This does not mean that there cannot be (on a local scale) a transformation from chaos to order. In fact, this is the main mechanism by which we can defy nature. When we build houses, we change the randomly distributed bricks, lumber, and clay into structured walls of living rooms, bedrooms, and kitchens. We bring order into our house by cleaning it. What the second law precludes us from doing is not creating order, but creating order without causing even more disorder somewhere else (usually in the neighborhood).

Figure 1: Refrigerator

Air conditioners and refrigerators are devices that move heat away from a space in defiance of the common perception that heat moves from a higher to a lower temperature. The price is of course the expenditure of additional energy in terms of electricity and creation of disorder outside the immediate neighborhood of these devices.

The operation of these devices can be best described as the heat engines operating in reverse. Heat is removed from the space (inside the refrigerator or air-conditioned room) and dumped into a second reservoir at a higher temperature. In the case of the household refrigerator, the second reservoir is the kitchen. In the case of the air-conditioner, it is the outside air. Energy input in the form of electricity or heat is needed to make the uphill transfer of heat possible (Figure 1).


(1) Toossi Reza, "Energy and the Environment:Sources, technologies, and impacts", Verve Publishers, 2005

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