It’s helpful to consider the air as a sponge to understand the principles behind Evaporative Cooling. When air is in contact with water, it absorbs the water and turns into the humidor damp air. The amount of water the air can absorb will depend on the amount of water already present in the air. A dry sponge will absorb more water than a wet sponge. The term “humidity”, which is used to describe the level of water in the air, is generally used. If 20% of the mixture is water, the humidity would be 20%. If humidity is 100%, it would mean that the air has retained all of the moisture it can. This could indicate that it is either raining or very damp.
The humidity is a function of how much air there is. The lower the humidity, the more water can be evaporated and the more space there will be.
Remember that portable evaporative cooler is powered by the cooling power of evaporation. When describing the moisture content of the air, we use the term “relative humidity”. Temperature affects the air’s “sponginess”. The air becomes more spongy when it is warmer and can hold more water. We must refer to the humidity of temperature. This affects the sponginess or absorbability’ of the air. A room with 50% humidity will retain more water at 80 degrees F than at 50 degrees.
How Is Cooling Produced?
To evaporate water, energy in the form of heat is needed. To evaporate a gallon of water, you need 8,700 British Thermal Units (BTUs) of heat. Heat comes from anything the water is in direct contact with, which could include a building, your body, or a tree. The temperature of the heat-source decreases as the heat comes in contact with water.
It is important to remember that water temperature does not affect the cooling caused by the evaporation process. A gallon of water heated to 50 degrees F would cool a pavement at 90 degrees F. It would produce 9,000 BTUs. A gallon of water at 90 degrees F would create 8,700 BTUs of cooling. This is only a 3% increase. Imagine being sprayed by water at these temperatures on a hot summer day. You would feel cooler as the water evaporates off your skin.
An evaporative cooler is constructed so that the filter pads are placed at the back, sides, or both of the machine. The warm air surrounding the machine is then sucked into it through the pads. Water is pumped through the pads to keep them damp from either an external source or an internal reservoir. The heat is removed from the air by the water evaporated as the warm outside air flows across the damp pad. The air that exits the machine is therefore in a cooler condition than it was when it entered it.
The most efficient Evaporative Coolers can provide the greatest surface area for the air to travel and evaporate water. The machine should draw in as much warm and humid air as possible.