Air-conditioning and Cooling technology Page 5

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Thus we can state that the average value of room air temperature and the average temperature of all the surrounding surfaces (incl. radiators) is decisive for comfort, in so far as temperature factors come into play. This is also known as "perceptive room temperature" or "resulting room temperature". The less these two temperatures deviate from one another, and the closer they are to 20 ...22C, the more stable will be the heat dissipation of the human body. The difference should not amount to more than 2 K. In addition, there should not be any great differences between the temperatures of the individual surrounding surfaces.

1.1.3 Relative air humidity

Atmospheric air always contains a certain proportion of water in the form of water vapour. This water quantity in grams per kilogram of air is expressed as absolute humidity x. However, air at a certain temperature can only absorb a very particular maximum amount of water (saturation, 100 % relative humidity). The higher the temperature, the higher the possible moisture content of the air. This relationship is represented in Fig. 4 as a diagram.
Relative humidity determines the actual moisture content at the given temperature in relation to the maximum possible moisture content, and calculates it as follows:

Relative humidity = actual moisture content x 100/moisture content at saturation point in %

1 kg of air at, for example, 25C can absorb approximately 20g of water at sea level before reaching its saturation point (saturation line phi = 100 %). However, if the absolute humidity of this air were now only 10 g/kg, only 50 % of the maximum possible moisture content would be present. This means that relative humidity of the air is 50 % (see Fig. 4).

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