Sizing of Evaporative Cooling Systems
Air Changes Method
This method calculates the number of coolers required based on the number of air changes per hour with a given working volume.
The working volume is that underneath the discharge of the plenum chambers as shown by the blue shaded area in the diagram below.
Typical air changes per hour are:
| Offices and Shops | 8 - 10 |
| Light manufacturing eg Warehouse, packing area |
10 |
| Normal manufacturing eg Machine shop, assembly area |
17 |
| Heavy manufacturing eg Injection moulding, welding shop |
25 |
| Extreme conditions eg Bakery, forge |
35 |
Example calculation
A bakery is 20m x 24m and it is proposed to fit ECP plastic external units with a minimum plenum discharge height of 3.5m.
Volume of working area: 20 x 24 x 3.5 = 1680m3
Target air changes per hour: 30
Target air flow per hour: 30 x 1680 = 50,400m3/hr
Air flow rate of ECP 13,000 m3/hr@150Pa
Nominal number of coolers required 50,400 / 13,000 =3.8 = 4 coolers
Therefore the proposal would be 4 ECP coolers together with balanced extract to maintain a small positive pressure.
