Sizing by airflow
Multiply the floor area by the ceiling height to get the volume of the space, then, as a rough guide, look for an airflow of 15 to 30 times that figure in cubic metres an hour. Desktop units cool one person at close range, floor standing models of around 1,500 to 5,500 cubic metres an hour suit a room, garage or small workshop, and commercial coolers of 7,000 to 48,000 cover warehouses, marquees and factory floors.
When evaporative cooling works
Evaporating water cools the air but also makes it more humid, so the drier the day, the bigger the drop: typically a few degrees, and much less in muggy weather. The moist air has to escape, so the space needs open doors or windows. A cooler therefore suits a workshop with the doors open, where an air conditioner would be cooling the street, but not a sealed office, where the air soon turns damp and clammy.
Water supply and maintenance
Smaller coolers are filled by hand, while larger ones can connect to a hose for a continuous supply, which matters when a big commercial unit can use up to 20 litres an hour. The cooling pads gradually scale up, faster in hard water areas, and need replacing once they stop soaking evenly. Drain and dry the tank whenever the cooler is not in use, and clean the tank and pads regularly so stale water does not start to smell.
