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Evaporative air conditioning

The Basic Principals

To understand how an Evaporative Air conditioner works, it is necessary to understand something about the properties of heat, air and water vapour.

Evaporative Air Conditioners are often called Evaporative Air conditioners and desert coolers. The most common type of Evaporative Air Conditioner is the direct type in which the hot outside air is cooled within the machine and forced into the building and exhausted to outside again.

What is Heat?

Cold is only the absence of heat so to discuss cooling we first need to understand more about heat. Heat has two forms:

  1. Sensible Heat – which as the name suggests you are able to sense or feel this type of heat. This is the heat produced by nature and can be measured with a thermometer, examples of sensible heat would be a cooker, a hair dryer and the sun heating the pavement.
  2. Latent Heat – This type of heat is unable to be detected by touch or a thermometer and therefore is hidden. Latent heat of evaporation is what happens when water is heated and forms vapour. Water vapour absorbs the heat from the surrounding area, which does not increase the temperature but heat and energy is absorbed and is contained within the molecular structure of the vapour. The natural phenomenon of latent heat, this is the reason why Evaporative Air Conditioning is possible.

Where Does Latent Heat Come From?

Latent heat comes from the surrounding air and materials. If a substance changes from its solid state to vapour it absorbs heat from the surrounding area which means objects within that area become cooler as they give their heat to help with the melting or evaporating process.

The Basic Principals Principals

Total Heat

Total heat is the sum of latent and sensible heat. The total is made up from the heat in a room you can feel and the heat you can’t.

Total heat is measured in Kilojoules (KJ) 1000KJ is approximately 1000 BTU’s. It takes approximately 2000KJ to complete the evaporation of one litre of water.

The evaporation of the water occurs without the intervention of external energy hence why Evaporative Air Conditioners only use a small amount of electricity to operate. The only power that is required is for the driving of the fan & pump.

The Evaporative Air Conditioning Process

In direct Evaporative Air Conditioning machines use a water pump to deliver water to heat exchanging media panels and a motor driven Fan which forces hot outside air through the media panels.

These Components combine to accelerate the natural heat exchange process. The process takes sensible heat and turns it into latent heat when the water in the evaporation air conditioner is changed into water vapour.

This allows the hot air to become colder and the air temperature falls. The cold air is pumped around the area and exhausted back outside therefore never re-circulating old air, it is always fresh air.

Depending on the amount of water vapour or humidity there is in the outside air depends on how much evaporation can take place. If the humidity is too high then not much evaporation can take place, this decreases the units cooling capacity. Therefore Rapid Heatbusters suggest that the Evaporative Air Conditioner is used mainly in hot and dry climates.

Evaporative Air Conditioning Capacity

To use the Evaporative Air Conditioner effectively you need to know three pieces of data:

  1. The ambient dry bulb temperature
  2. The ambient wet bulb temperature
  3. The saturation efficiency of the machine

The way of calculating the two bulb temperatures is done by a combined thermometer with a dry bulb and a wetted bulb. The Wetted bulb is a dry bulb with a wetted sock over it and the temperature is taken by using an instrument call a psychrometer.

Saturation efficiency for the equipment should be available from the manufacturer but working on about 80% is a good average.

The superior designs of Rapid Heatbusters Evaporative Air Conditioners yields a much higher efficiency up to 94% saturation which delivers larger temperature reductions.


TO CALCULATE YOUR COOLING REQUIREMENTS CLICK HERE.