Turbo Vent - Evaporative cooling: What is evaporative cooling?

Evaporative cooling: What is evaporative cooling?

What is evaporative cooling?

When air comes into contact with water, the water evaporates and absorbs heat thereby cooling the air. The drier the air, the faster the rate of evaporation and the greater the cooling effect.

Evaporative cooling, imitates this natural cooling process as follows...

Air from outside the building is drawn into a cabinet using a powerful fan.

The air enters the cabinet through water-saturated cooling pads which filter the air, substantially removing large particulate contaminants such as dust and pollen.

As the air makes contact with the water, it is cooled by evaporation to a degree dependent on the dryness of the air.

The resultant fresh, clean, cool air is then directed, via a duct system, into the interior of the building.

The effectiveness of this cooling process is determined by three key factors...

The drier the ambient air, the greater and faster the cooling. Humid ambient air is not conducive to effective evaporative cooling.

The availability of outlets for the air such as open windows, doors and or relief vents in the ceiling or roof.

The continuous, even distribution of water over the cooling pads. This ensures that all of the passing air comes into contact with the water. Any dry spots on the pads will result in an dramatic drop in cooling efficiency. This is because air passing through the dry spot will do so with less resistance and therefore a higher volume will pass through, none of which will be cooled.

Evaporative coolers have been used in warmer climates such as the USA, Australia and the Middle East for many years. As the effects of global warming are felt in cooler climates, such as Europe, the use of evaporative coolers is becoming more widespread.

On days when heat or humidity, or even excess pollen, causes discomfort, people often head off to lakes or the seaside in search of relief. Evaporative Air Cooling is, in many ways, simulating the cooler conditions so often found at or near large expanses of water. It makes it possible to effectively cool factories, warehouses, offices and many other areas.

As water is evaporated, energy is lost from the air reducing temperature. Two temperatures are important when dealing with evaporative cooling systems. The first is the dry bulb temperature. This is the temperature that we usually think of as air temperature, measured by a regular thermometer exposed to the air stream. The second air temperature, important in evaporative cooling systems, is the wet bulb temperature.

This is the lowest temperature that can be reached by the evaporation of water. The dry and wet bulb temperature can be used to calculate the relative humidity.

Evaporation will take place when the humidity is below 100% and the air begins to absorb water. Any given volume of air can hold a certain amount of water vapour and the degree of absorption will depend on the amount it is already holding. The term humidity describes how much water is already in the air, relative to the amount it is capable of holding. Air is saturated when it cannot hold any more water. Imagine it as a sponge, if the sponge held half as much water as it was capable of holding, it would be 50% saturated. In the case of air, we would describe the relative humidity as being 50%.

Energy is required to change water from liquid to vapour. This energy is obtained in an adiabatic process from the air itself. Air entering an evaporative air cooler gives up heat energy to evaporate water. During this process, the dry bulb temperature of the air passing through the cooler is lowered.