Air-conditioning and Cooling technology Page 27

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We stress here once again that the just calculated heating output Q is only that output which influences the temperature conditions in a room. For the specification of the air heater output, however, a certain capacity for the purpose of heating the drawn upon outside air volume V3 with the temperature t3 to the desired room temperature t1 must be added to it. For a complete outside air operation, the outside air volume corresponds to the volume of supply air. Heat loss through the walls of the air ducts are not taken into account here:

Air heater output = Output for room air renewal + output for room air heating

Room air cooling

For a given cooling load Q of a room and an established temperature difference between the desired room temperature t1 and the supply air temperature t2, the supply air volume V in m3/s necessary for the removal of heat can be calculated from the following equation:

Because dehumidification (removal of a part of the water vapour contained in the air, whereby additional condensation heat is also released) usually accompanies the cooling of air, and warmer outside air must be cooled to the desired room air temperature, the necessary air cooler rating is comprised of the following:

Air cooler rating = Dry cooling load (cooling) + humid cooling load (dehumidification) + outside air cooling and dehumidification

The simplest method of calculating the air cooler rating is to use the Mollier or Carrier charts.

Room air humidification

The water quantity x (g/s) to be absorbed by air per second in a humidification plant is calculated as follows:

x = V o p(x1 - x4) + x

This means:

x1 = Desired moisture content of room air in g/kg
x4 = Moisture content of air before the humidifier
x = Moisture content absorbed in room in g/s. (Generally not taken into account. Only a factor for rooms in which very hygroscopically sensitive goods are processed.)

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