of outside air may be reduced in comfort plants for outside temperatures under
0°C 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
|Mischluftmenge||=||air mixture volume|
|Mischlufttemperatur||=||air mixture temperature|
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: