MODULE III
Air-conditioning and Cooling technology Page 26

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The quantity of outside air may be reduced in comfort plants for outside temperatures under 0C in order to avoid excessively large air heaters and, thereby, uneconomical heating operations. In most plants, a portion of already heated room air (V1, t1) is therefore mixed with the outside air (V3, t3) (see Fig. 21). The temperature t4 of the air mixture is determined from:

Fig. 21 Room air renewal with return air mixing




English translation of technical terms and sentences in Fig. 21:

Mischluftmenge
= air mixture volume
Mischlufttemperatur = air mixture temperature

Room air heating

As we have already seen from point 1.4.2 (Basic load heating), it is possible to cover the whole or just a part of the transmission heat requirement using the ventilation plant.
If the required heat output Q of the ventilation plant, as well as the difference between the maximum supply air temperature t2 and the desired room temperature t1 is known, the air quantity can be calculated as follows:



If this plant serves simultaneously for the renewal of air in the relevant room, the calculated air volume must also correspond to the entries made under point 1.4.1.
For a given air volume V, the temperature difference between the supply air temperature t2 and the desired room temperature t1 necessary for attaining a specified heat output Q, can be calculated as follows:



For a given air volume V in m3/s and an established difference between the supply air temperature t2 and the desired room temperature t1, the necessary heat output will be:

Q = V x p x c (t2 - t1)


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