Evaporative cooling uses the heat in the air to evaporate water. When hot air passes through wet cellulose pads, some of the water evaporates, and the energy that takes comes out of the air, so the air leaving the pads is cooler. It works best in hot, dry air and needs a way for warm air to leave the building.
The science in one paragraph
Turning water into vapour needs energy. In an evaporative cooler that energy comes from the air flowing through the wet pads. The air gives up heat, gets cooler and picks up moisture. It is the same reason you feel cold stepping out of water on a windy day.
Inside an industrial cooler
- A pump lifts water from the tank to a pipe above the pads.
- Water trickles down through cellulose cooling pads, wetting their honeycomb surface.
- The fan pulls outside air through the pads.
- The cooled air is blown into the building, directly or through ducts.
- Unevaporated water drains back to the tank; a float valve tops it up.
Why humidity matters
Dry air can take up a lot of water, so it cools a lot. Humid air is already close to full, so it cools less. That is why evaporative cooling performs very well in the hot, dry months across most of India and less well at the peak of the coastal monsoon.
Even on humid days, an evaporative cooler still brings in fresh air and keeps it moving, which helps comfort.
Why ventilation is essential
An evaporative cooler adds moisture to the air. If the warm, moist air cannot leave, humidity builds up and comfort drops. Keep doors, windows or roof vents partly open, or fit exhaust fans on the opposite side, so fresh cooled air keeps flowing through.
Where evaporative cooling works best
- Factories, workshops and warehouses
- Poultry houses and greenhouses (with fan and pad walls)
- Kitchens, canteens and dining halls
- Events, pandals and semi-open spaces
- Any space where doors stay open and AC would be wasted
Where it works least
- Sealed rooms with no exhaust
- Very humid locations when the air is near saturation
- Rooms that need dry air, such as server rooms and some storage
What affects performance
- Pad quality and thickness: good cellulose pads above 80% efficiency make a real difference; see our cooling pads guide.
- Even wetting: a weak pump or blocked pipe leaves dry patches.
- Clean water: scale and algae clog pads.
- Airflow matched to the space: see how many coolers you need.
See our industrial coolers.
Frequently asked questions
How does an evaporative cooler cool the air?
Water evaporating from wet pads takes heat out of the air passing through them, so the air leaving the cooler is cooler.
Do evaporative coolers work in humid weather?
They cool less in very humid air but still bring in fresh, moving air. They work best in hot, dry weather.
Does an air cooler need ventilation?
Yes. Warm, moist air must be able to leave through open doors, vents or exhaust fans, or humidity builds up.