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
Normal manufacturing
eg Machine shop, assembly area
Heavy manufacturing
eg Injection moulding, welding shop
Extreme conditions
eg Bakery, forge


Air changes per hour

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.


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