Air-conditioning and Cooling technology Page 3

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1. Introduction to ventilation and air conditioning technology

1.1. Comfort

Room climate plays a significant role in the well-being and working capacity of human beings. Observation has revealed an air quality range within which people generally feel at their best. This range is known as the comfort range and is mainly characterised by the components represented in Fig. 1.

Fig. 1 Most important components of comfort

t1 = Room air temperature
t2 = Radiation temperature
= Air humidity
v = Air velocity

Decisive for thermal comfort are not the individual components, but rather their "joint effect". In this way air temperature and heat radiation (wall temperature) can to some extent mutually compensate for one another, or a relatively high ambient temperature can be made tolerable by a light increase in air velocity, etc.
In addition to those mentioned above, many further factors influence comfort. Some examples include air purity, noise level, electrostatic state of air and clothing, age, gender, habits, type of work, etc. Thus we can see that no strict boundaries can be plotted for the comfort range. Nevertheless, for normally clothed, seated persons, or those undertaking only light physical activity, certain average values have been determined. Some of them will be clarified in the following.

1.1.1 Room air temperature

For our central European climate, hygiene specialists generally recommend a most favourable room air temperature for normally clothed, seated people not carrying out physical labour, of 20 ... 21C in winter, and of 21 ... 22C in summer at an average outside temperature (ca. 24C). The reason for the higher temperature in summer is that people generally dress more lightly at this time, and thus require a higher ambient temperature at the same body surface temperature in order to maintain the same amount of heat dissipation to the surroundings.
The room air temperature of 20 ... 21C in winter can only be regarded as a rough average, and only applies where their is no room air movement. Where the air is in movement, which is always the case in ventilated areas, this results in a cooling effect, which can be unpleasant. Thus, a room temperature of 22C is recommended. Experience also shows again and again that women feel the cold more readily than men. The same applies to older people (over 40 years) in comparison to younger. It is thereby advisable, under certain circumstances, to heat rooms primarily frequented by women or older people at a temperature which is 1 K higher.
On hot summer days, when the outside temperature climbs to 28 ... 32C, and when people clothe themselves more lightly, a room temperature of 21 ... 22C will generally be found to be too cold. This is especially the case when one only stays in such areas (department stores, theatres, assembly halls, etc.) for a short time. On hot summer days it is therefore recommended to raise the room temperature in relation to the outside temperature (see Fig. 2).

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