Although conventional portable evaporative coolers sell in reasonable quantities, they are very much bought as a cooler of last resort and are rarely satisfactory. The reasons include:
For a portable cooler to give comfort, everything must be arranged to maximise cooling. Some of the information given by salespeople and in instructions is partially correct but doesn't give the full story. To get more comfortable see Getting the most from your portable evaporative cooler.
Unless the portable evaporative cooler has a decent airflow, it hasn't got a chance of keeping you cool. Each bit of air can only remove a small amount of heat, so to remove enough heat to make you comfortable you need the largest airflow cooler you can find.
Recirculation occurs when the air coming out of the cooler, has come from the room and not directly from outside. Because the air comes from the room it has already got extra moisture from the air that has passed through the cooler. This means it doesn't cool effectively.
Because the cooler is located in the room, a certain amount of recirculation is inevitable. Conventional windowsills in residential buildings are typically around 760mm or higher above the floor. Typical small freestanding portable coolers are around 760mm high which means that in most cases the top of the unit is below the windowsills. Because the unit is below the windowsill, approximately 85% of the air is drawn from within the room. This air is already humid because it has already passed through the wet filter pads of the cooler. This reduces the efficiency of the unit because it is being operated under humid conditions.
Another limitation of having the cooler in the room, near an open window is that when the wind blows air into the room, it doesn't necessarily go through the cooler, but can go straight into the room making the room hotter. This is called air bypass.
Because conventional mobile evaporative cooler units have to be placed near an opening, such as a window, and the discharge grilles or vents only allow the air to bend a small amount, the effectiveness of the unit is further reduced. With a portable evaporative cooler, you only get comfortable if you are in the direct airflow.
A portable evaporative cooler can only achieve comfort when everything is just right. This means that most of the time in a humid environment like Sydney or Brisbane, the cooler doesn't give much comfort. In these areas, you are probably better off buying a decent pedestal fan if you can't get air conditioning. For more information visit what climates are suitable?