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Posted by GoodCooling Team

Evaporative Air Coolers and Humidity: When Evaporative Cooling Works

The most common question about evaporative air coolers is: does it work in muggy weather too? The honest answer: only to a limited extent. Evaporative cooling depends directly on humidity. Anyone who understands this can use an evaporative air cooler where it plays to its strengths, and avoid other places.

Why humidity is decisive

An evaporative air cooler cools because water evaporates and in doing so draws heat from the air. Dry air can absorb a lot of water vapour, a lot evaporates and the temperature falls noticeably. If the air is already humid, hardly any water evaporates and the cooling effect is small. At 100% relative humidity, no cooling would take place at all. This relationship is physical, not a shortcoming of a particular appliance.

What an independent test showed

The Swiss broadcaster SRF tested ten household evaporative air coolers as part of its programme Kassensturz. According to the report, cooling in the airflow reached 3.5 °C at most, and outside the airflow the effect was considerably smaller. In addition, humidity in the test room of around 66 m³ rose noticeably after three hours. The editorial team points out that too much moisture can damage furniture and encourage mould. We take such results seriously, because they show what matters when using the appliance. The test appliances were household units for small, enclosed rooms, and that is exactly where the limits of the technology are clearest.

Where evaporative cooling works well

  • Large, airy rooms: Halls, workshops and storerooms exchange air, so the moisture disperses. More in our article on hall cooling.
  • Outdoor areas: Terraces and beer gardens offer constant air exchange. Our article 5 Reasons for the Hospitality Sector fits well here.
  • Dry heat: The lower the humidity, the greater the effect.

Where you should be careful

  • Small, enclosed rooms: Humidity rises quickly.
  • Muggy days and thunderstorm weather: The cooling effect is then small.
  • Rooms prone to mould: Additional moisture is unhelpful here.

In such situations an air conditioner may be the better choice, see our comparison of evaporative air coolers and portable air conditioners.

How to avoid humidity problems

  1. Ventilate: For indoor use, open a window or door so that humid air can escape. For our Y5, the data sheet expressly points this out.
  2. Size correctly: An appliance that is too large for the room humidifies unnecessarily strongly.
  3. Measure humidity: A simple hygrometer shows whether the values in the room stay in a comfortable range.
  4. Look after the appliance: Clean water and a cleaned cooling pad prevent germs, see maintenance and care.

Frequently asked questions

At what humidity is an evaporative air cooler no longer worthwhile?

There is no fixed limit; the effect decreases steadily as humidity rises. As a rule of thumb: the muggier it is, the less the appliance achieves.

Can an evaporative air cooler cause mould?

If too much moisture builds up permanently in a small, poorly ventilated room, this can encourage mould. Regular ventilation and choosing a suitable appliance help prevent it.

Does an evaporative air cooler help without water?

Then it works only like a fan. The actual cooling comes from the evaporating water.

Conclusion

Evaporative cooling is not a miracle cure, but in the right situations it is an economical and effective solution. What matters are dry air, air exchange and an appropriately sized appliance. If you are unsure whether an evaporative air cooler is suitable for your room, we are happy to advise you, honestly, even when another solution suits better.

Sources

Further reading