Evaporative Cooling & How Much Cooling You Really Get
Cools dry air
“The best tip on this tool is probably in the comments already.
Enter dry-bulb and wet-bulb temperatures and pad saturation efficiency to get the temperature dropand the cooled outlet temperature — it works best in hot, dry air and barely in humid air.
Size your evaporative cooler
Next: expect about 28 °C off the pad — a 12 °C drop; keep pads fully wetted and replace clogged media to hold efficiency near 80%.
Evaporative cooling only works while air is dry (large wet-bulb depression). In humid weather the achievable drop shrinks toward zero.
Evaporative cooling — key facts
- Temp drop
- depression × efficiency
- Depression
- dry-bulb − wet-bulb
- Outlet temp
- dry-bulb − drop
- Floor
- the wet-bulb temperature
- Pad efficiency
- ≈ 70–90%
- Best in
- hot, dry air
- Poor in
- humid air
- Privacy
- Runs in your browser; nothing uploaded
Cooling toward the wet-bulb, as far as the pad allows
Evaporative cooling is the cheapest way to drop air temperature for produce storage, but how much it actually cools depends entirely on the air. The theoretical floor is the wet-bulb temperature, and the most you can gain is the wet-bulb depression — the gap between ordinary air temperature and the wet-bulb. A pad never reaches the wet-bulb fully; its saturation efficiency sets how much of that depression you capture.
This tool gives the temperature drop, outlet temperature, wet-bulb depression and the efficiency you are using, so you can see realistic cooling for your climate before building or running a cool chamber. In dry heat the gains are large; in humid air they shrink fast. Pair it with the Evaporative Cool Chamber, Cold Room Cooling Load and Storage Humidity (VPD) calculators to plan post-harvest storage.
Know your climate
See real cooling for hot, dry or humid air.
Size the store
Check the outlet temp before you build.
Skip refrigeration
Cool produce cheaply where the air allows.
Tune the pad
Lift efficiency to get closer to wet-bulb.
Frequently Asked Questions
What is evaporative cooling?+
Evaporative cooling drops air temperature by evaporating water into it. As water turns to vapour it absorbs heat from the air, so the air leaves cooler and more humid. It is used in cool chambers, pad-and-fan stores and swamp coolers to keep produce fresh without refrigeration.
How is the temperature drop calculated?+
Temperature drop = wet-bulb depression × saturation efficiency, where the wet-bulb depression is the dry-bulb temperature minus the wet-bulb temperature. A pad at 80% efficiency in air with a 10°C depression gives an 8°C drop, and the outlet temperature is the dry-bulb minus that drop.
What is wet-bulb depression?+
It is the gap between the dry-bulb (ordinary) air temperature and the wet-bulb temperature, which is the lowest temperature evaporation could reach in that air. A big depression means hot, dry air with lots of cooling potential; a small one means humid air with little room to cool.
What is saturation efficiency?+
Saturation efficiency is how close the cooler brings the air to the wet-bulb temperature, as a percentage. A perfect cooler (100%) would reach the wet-bulb; real pads manage roughly 70–90% depending on pad type, thickness, water flow and air speed. It is the share of the depression you actually capture.
Why does it work best in hot, dry air?+
Cooling is the depression times the efficiency, and the depression is large only when air is hot and dry. In humid air the wet-bulb sits close to the dry-bulb, so even a perfect pad has little depression to work with and barely cools — which is why evaporative cooling shines in dry climates and struggles in muggy ones.
Can it cool below the wet-bulb temperature?+
No — the wet-bulb temperature is the theoretical floor for evaporative cooling. The outlet can approach it as efficiency rises but never goes below it. To get colder than the wet-bulb you need mechanical refrigeration, not evaporation.
How does this help with produce storage?+
Cool chambers and pad-and-fan stores rely on evaporative cooling to lower temperature and raise humidity, both of which slow ripening and water loss in fruit and vegetables. Knowing the realistic outlet temperature for your climate tells you whether a chamber will hold produce well or whether you need refrigeration.
What raises the saturation efficiency?+
Thicker, well-wetted pads, even water distribution, the right air velocity through the pad, and keeping pads clean all push efficiency up. Channelling, dry spots, scale or too-high air speed drop it. Higher efficiency means the outlet air gets closer to the wet-bulb.
Are the figures exact?+
The arithmetic is exact for the temperatures and efficiency you enter. Real performance shifts with pad condition, airflow, water temperature and changing weather through the day. Measure dry- and wet-bulb on site, use a realistic efficiency, and treat the result as a sound planning estimate.
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