Climate control

Humans (at least, this human) are creatures of comfort; and the story of civilization is, to a certain extent, the quest to keep from being either too hot or too cold.

The earliest form of climate control was the fire. Room temperature was controlled by adding (or having the servants add) more wood or coal to the fire or letting it die down. You fine-tuned your comfort by moving closer to or further from the blaze.

Nowadays most homes are still heated by combustion, but modern heating systems allow you to burn fuel in one location and convey the heat somewhere else.

In the common forced-air system, heated air from an oil, gas or electric furnace is blown into a room by a fan. Return air is taken from the room, mixed with outside air, filtered and sent back to the furnace. A thermostat controls the system.

Another form of heating is the radiant system, in which hot water, air or steam is circulated through radiators, pipes or ducts hidden in the floor, ceiling or walls. In electric heating, electrical resistance heats wires in the walls (think of a giant toaster).

Finally, solar heating uses the energy of the sun, either letting it pour through big glass windows or soaking it up with a dark surface, under which run water pipes, providing hot water for radiant heating or, if you prefer, a shower.

Heat is our primary concern in Saskatchewan for far too many months of the year, but come summer our thoughts turn to keeping cool. It’s one thing to burn something to put heat into a room, but how do you take heat out?

The first attempts, in the 19th century, involved circulating air over blocks of ice. More sophisticated attempts had to await the invention of mechanical refrigeration.

Refrigeration is based on the fact that liquids absorb heat from their surroundings when they evaporate or boil . By controlling the liquid’s pressure, you can control the temperature at which this happens: the higher the pressure, the higher the boiling point.

Way back in 1748 William Cullen of the University of Glasgow demonstrated refrigeration using this principle, but it was 86 years before Jacob Perkins patented the first practical ice-making machine in London. Air conditioning waited until 1911, when Willis Carrier invented a system in the United States. By 1915 he was manufacturing it.

In both a refrigerator and an air conditioner, a liquid is boiled in an evaporator, absorbing heat as it expands. The warmed vapor that results is then compressed, which makes it even hotter (you’re packing the same amount of energy into a smaller space), and piped outside, where it radiates that heat away. No energy is lost; it’s just transferred from the place you want cool to a place where you don’t mind a little heat. Devices called heat pumps, used in many modern buildings, make this process reversible, so one unit can both cool and heat a room.

The first refrigeration system invented in the United States, in 1844, used air as its refrigerant, alternately letting it expand and compressing it, for the same effect as boiling and compressing a liquid. Another kind of refrigerator invented in France at about the same time (and still used in some large air conditioning systems) is called the absorption type, and uses water, boiling it in a partial vacuum.

The most common refrigerant, however, is Freon or one of its variants. Introduced in 1930, these chlorofluorocarbons have recently been implicated in the depletion of the Earth’s ozone layer; ironically, they were developed because of the need for something safe to replace the hazardous refrigerants of the day, such as sulfur dioxide. Stable, incombustible and non-toxic, Freon made air conditioning practical in office buildings, hospitals, apartments, trains and buses, and, by 1950, even in automobiles.

Today, you can hardly find a large building that isn’t heated and air conditioned to perfection under the careful control of computers programmed to ensure maximum effeciency and comfort.

Which just leaves one question: how come, in any room containing two people, one is always too hot and the other too cold?

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