The Physiological Basis for Air conditioning

The physiological basis for air conditioning

Seasonal extremes of heat and cold are more than most people can endure, even in the temperate zone, in which large areas of the United States and Canada are located. Winter temperatures in some areas may run as low as minus 46°C. On the other hand, summer temperatures can often exceed 40°C and in many parts of Australia.

The temperature range within which people feel comfortable depends to a considerable degree on the clothing worn, the degree of physical activity, and the amount of moisture in the atmosphere, but for people indoors engaged in light activity the general accepted temperature in summer is about 24°C and winter being 21°C.

The fact that the ranges are different for summer and winter is in part due to the different clothing worn and in part due to an actual change in the body metabolism from winter to summer.

There are probably very few areas in Australia which air conditioning of some kind (winter heating or summer cooling) is not required.  Summer cooling, though not absolutely essential for existence, is necessary in many regions of the world for comfort and health. Nations located in tropical zones, where both temperature and humidity are high, are in constant need of air conditioning.

Tourism is an important industry in many of these countries, and the number of air conditioning systems will increase markedly in response to tourist demand, unless energy shortages curtail development in these regions.

Air conditioning, as the term is correctly used, implies a great deal more than mere temperature control. There are four atmospheric conditions which affect human comfort. These are:

  1. The temperature of the surrounding (ambient) air. This is measured in degrees Celsius (°C) or degrees Fahrenheit (°F) in the USA.
  2. The humidity of the air. Humidity means moisture content, and its relation to human comfort.
  3. Air Purity. People are not comfortable when breathing contaminated air even if it is within acceptable temperature and humidity ranges.
  4. Air movement. Even if temperature, humidity, and air purity are satisfactory, a small amount of air motion would be necessary for human comfort.

True air conditioning implies that all four of these atmospheric conditions for human comfort are being

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