How an Evaporative Cooler Works
In the Arizona desert in the 1920s, people would often sleep outside on screened-in sleeping porches during the summer. On hot nights, bed sheets or blankets soaked in water would be hung inside of the screens. Whirling electric fans would pull the night air through the moist cloth to cool the room.
That concept, slightly more refined, became the evaporative coolers that to this day provide a low-cost, low-technology alternative to refrigerated air conditioning.
An evaporative cooler produces effective cooling by combining a natural process - water evaporation - with a simple, reliable air-moving system. Fresh outside air is pulled through moist pads where it is cooled by evaporation and circulated through a house or building by a large blower.
Probably because evaporative coolers add moisture to the air and blow it around, they are sometimes knows as "swamp coolers." Evaporative coolers can work wonderfully well, provided the outside air they are drawing in is dry and desert-like and that is why they are popular in parts of Australia. As the humidity increases, however, the ability for them to cool the air effectively decreases. Simply put, swamp coolers were not designed to work in swamp-like conditions or where you have high humidity.
Many people buy evaporative coolers because they are less costly than a portable air conditioner that operates on a refrigeration process. However they don't always appreciate that for the cooler to work effectively you will for example require an intake of dry air from an open door or window at one end of a room. This dry air passes through the cooler and should then be allowed to exit the room from an open window or door at the opposite end of the room.
Unfortunately this method of using a cooler is not always possible and therefore the result is you are likely to experience an increase in humidity as the water in the cooler evaporates. This can make your actual comfort conditions worse. Using a proper air conditioner whether portable or fixed will actually cool your home or office by properly reducing the actual temperature, while at the same time it will dehumidify and lower the moisture content thus making conditions far more comfortable than with using an evaporative cooler.
Keeping a house cool with a swamp cooler depends on the temperature and humidity of the air coming into the cooler. The higher the outside temperature, the lower the humidity must be to drop the house temperature. This is not always possible, for example in the UK during summer months we can experience high temperatures accompanied by high relative humidity levels due to rainfall and therefore the evaporative cooler will not operate effectively.
England is not like Arizona or Australia and therefore if you buy an evaporative cooler don't be surprised if you feel little benefit and beware, if you don't extract the air, your room or office could end up feeling like a greenhouse.
If you want proper cooling an comfortable conditions then use a proper air conditioner.