Evaporative Coolers FAQs

What is a evaporative cooler?

Evaporative coolers are a practical and cost effective alternative to air conditioning. In order to be comfortable in summer, you typically only need to reduce the air temperature by a few degrees to make a tangible difference between the heat of outdoors and the cool comfort of indoors and sometimes the cooling effect of air conditioning can be too much. Evaporative coolers are much simpler than air conditioners and don't need exhaust hoses routed through walls, or windows and they don't need a condenser placed outside.  They are ideal for applications where using an air conditioner would be difficult (for instance where there is no easy access to outside air), or cost prohibitive, or where only moderate cooling is required.

How do they work?

In the same way that the evaporation of sweat on skin cools the skin, or where breezes coming from the sea are noticeably cool, evaporative coolers work by evaporating water from a substrate material whilst blowing air through the material. The air movement through the material aids evaporation and cools as it does so. A simple and reliable mechanism within the unit ensures that the substrate material (pad) is kept damp and a prefilter keeps dust off the pad. 

How effective are they?

The performance of evaporative coolers depends on the ambient temperature and the percentage relative humidity (%RH). If say the ambient temperature is say 25°C, which would be a typical uncomfortable indoors temperature during summer and the relative humidity is say a typical summer level of 40% then you could expect the outlet temperature from a evaporative cooler to be between a comfortable 18 and 19°C. It will obviously vary from one model to the next, but it is true to say that the lower the ambient relative humidity then the more they will cool. It is also the case that the greater the ambient temperature then the greater the degree of temperature drop. Evaporative coolers do not have the same cooling power as air conditioning and buyers used to air conditioning need to adjust their expectations of accordingly. Whilst they cannot provide the harsh cooling of an air conditioner, evaporative coolers, take the 'uncomfortable edge' of the very hot days.  The following table provides a reasonable guide to the cooling capacity typical of most evaporative coolers.

What else affects their performance?

As well as the ambient temperature and the relative humidity, their performance is affected by the temperature of the water in the tank. Some units can take ice as well as water, which will enhance the performance. If the prefilter becomes blocked then this will restrict airflow and impair performance, and for this reason, units fitted with washable filters will require their filter periodically washed and those with disposable filters will require occasional filter changes.

What other effects do they have?

Because they work by evaporation they have the inevitable consequence of increasing the relative humidity in the room, so acting in the same way as a humidifier. Also, because they pass air through both a prefilter and then a damp pad, they also act as an air cleaner, and should certainly trap larger particles such as pollen; a bonus for hay fever sufferers. It is also easy to dose the water with various fragrances to add pleasant smell to the air. So long as the fragrances are not oil based and mix easily in water there should not be a problem. Some units will be fitted with a heater element which means that they are a useful 'year round' appliance, rather than just summer.

What advantages does evaporative cooling have over air conditioning?

Because they are so much simpler and use a fraction of the electricity, evaporative coolers are substantially cheaper to buy and operate compared to a similar size air conditioner. Also evaporative coolers do not rely on refrigerant gasses (CFCs) to operate and they pose no risk of leakage of these gases. 

Should the doors and windows be closed when using a evaporative cooler?

No. The room that you are cooling should be open and well ventilated so far as possible, to ensure that relatively fresh air is taken through the wet pads in the machine. This reliance on fresh air makes the evaporative cooler a healthier cooling system compared to air conditions because sealed rooms such as those that are typically air conditioned are inevitably more polluted than well ventilated rooms. To use an evaporated cooler in a unventilated room increases the humidity of the air in the room and will ultimately inhibit the effectiveness of the cooler.