Page 133 - Industrial Ventilation Design Guidebook

4,2 STATE VALUES OF HUMID AIR; MOLLIER DIAGRAMS AND THEIR APPLICATIONS f 5

When the inlet air is well mixed with the room air, the humidity of the
outlet air (2) is the same as the room air humidity, so x 2 = 0.00736, and its
temperature is the same as the temperature of the room air, 9 = 20 °C.
The enthalpy of the outlet air h k2 = 1.006 • 20 + 0.00736 • 2501
+ 1.85 • 20 = 38.8 kj/kg . The enthalpy of inlet air h kl and its humidity x\
are determined by the energy and humidity balances:

The net heat power also includes the enthalpy flow, m hb h. Then

The corresponding air temperatures can be calculated with the equation

The result of Example 12 is illustrated in Fig. 4.17.

4,2.8 Example of Cooling Tower Dimensioning

Cooling towers are commonly used for water cooling, but they can also be used
for heat recovery from outlet air. If the water temperature is higher than the dew-
point of the air, water will cool in the tower. Cooling is caused by vaporization on
the surface of the water drops. The vaporization energy comes from the inner en-
ergy of the water and in a certain phase, when the water temperature is lower
than the dry bulb temperature of the air, also from the airflow. When the water
temperature drops to near the air wet bulb temperature at the observation point.