A swamp cooler, an earthen pot for cooling drinking water, cooling tower, and human skin, work on the same principle. The principle is evaporative cooling. Water is broken down into smaller droplets and air forced through it. Heat transfer takes place from water to air or air to water depending on the design of the equipment. In human skin, the heat is taken away from the body when sweat on surface of skin evaporates.

Construction Of Swamp Coolers

The swamp coolers consist of a box and a fan is situated inside the box. On the suction side of fan, there are pads. These pads are made of wood shavings or PVC. A small water pump directs water on top of the pads. The construction of pads is such that the incoming water is broken down into small water droplets and air going to suction of fan goes through these small droplets. So in essence, it is just a box with a pump and a fan & lot of pads for breaking water into smaller droplets. The construction might also include a distributor for air delivery so that the air is equally distributed in all areas of the room.

Other variations include a common motor for pump and fan, thus further reducing construction complexity

The controls of swamp coolers include controls for fan speed, a float valve for maintaining water level in the basin of cooler and controls for air delivery. Some portable swamp coolers have water level indicators instead of float valve and water level has to be maintained by pouring water from outside.

Condition affecting performance

There are no controls for temperature of outgoing air since it cannot just be controlled. It is a "take it or leave it" type of machine with absolutely no control on the out let air temperature. The out let air temperature is the result of atmospheric air temperature and atmospheric humidity. The lesser the relative humidity, the higher is the performance for a given inlet temperature. At the same relative humidity, higher inlet temperature increases the cooling ratio. Therefore, you can see that the air-cooling cannot be controlled. If this is the case, why have a swamp cooler at all? The answer is, air conditioning was invented about in1902 and there was no choice before it. Now it is a question of money. If you wish to have a low initial cost and low operating cost solution, swamp cooler is the only alternative.

How to choose your swamp cooler

The capacity of swamp coolers is on cubic feet per minute (CFM) capacity of air delivery fan. If the room dimensions are 15 feet by 12 feet and 8 feet high, then room capacity will be 15*12*8 = 1358 cu ft. The fans are designed to have complete change of room air every 5 minutes. This means that the capacity of fans will be 1358 divide by 5, or approximately 280 CFM. This capacity is for a fan that draws cold air from the room. If the same swamp cooler is fixed in a window, the capacity will increase, as recirculation will be reduced to zero.