Carbon Conservation & Energy Efficiency

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Bruce Rowse & Team

Posts Tagged ‘multi stage evaporative cooling’

“Dry” evaporative cooler saves energy and eliminates the need for refrigerant based cooling

Monday, November 2nd, 2009

At the recent All Energy expo in Melbourne (early October) I came across the Coolerado cooler, distributed in Australia by Clear Solar. This is an ingenious, simple air cooler based on a combination of evaporative cooling and plate heat exchangers to deliver cooler air than is possible with conventional evaporative cooling but without the use of a refrigerant. It therefore has the energy efficiency of evaporative cooling, but with the performance of refrigerative cooling in dryer climates.

For a detailed explanation of how it works visit the Coolerado website. Below is a quick technical summary using the psychometric chart. You may prefer the Coolerado website if you don’t understand the properties of air at different moisture levels as displayed in the psychometric chart.

The unit splits air into two streams, either side of a plate heat exchanger. Moisture is added to one stream – the working stream. Its temperature drops using the evaporative process. This then sensibly cools the air on the other dry side of the plate, the process stream. Some of the process air is then split off and made into more working air. Moisture is added to this too. This then cools further, and through the plate heat exchanger it then further sensibly cools the process stream. By doing this multiple times the resultant process air exits at near the dew point temperature of the air. And around half of the total air going through the system ends up as useful process air. 

Psychometric chart showing how the Coolerado cools air

Psychometric chart showing how the Coolerado cools air. Click on chart to enlarge it.

The chart above shows the principal of operation marked on it assuming the process stream is split up 3 times and perfect evaporative cooling (ie to the wet bulb temperature). In the Coolarado 13 stages are used to get air down to near dry bulb temperature.

As you can see in the my chart below – for 35 degree air at 20% humidity (at sea level) with a conventional evaporative cooler we can get the temperature down to near the wet bulb temperature of 19 degrees, but at 100% relative humidity. With the Coolerado we can get the temperature close to the dew point of 9 degrees, or if we are only cooling to 19 degrees do so with a relative humidity of around 55%, which is perfectly comfortable.

A variable speed fan in the unit controls the air flow and thus the exit temperature and relative humidity of the air it supplies.

For hot dry climates the Coolarado can completely substitute conventional refrigerative air conditioning. And in more humid climates it extends the usefulness of evaporative cooling.

The Coolarado website also has a chart based on historical weather data for hundreds of sites world wide, showing its applicability, including several Australian cities. Or, if you know your local weather and can use a psychometric chart, its possible to figure out its suitability. In Australia for example the Coolarado is well suited for use in Adelaide.

I’m not sure of the maintenance regime for the heat transfer plates and cooling pads – presumably similar to those of a conventional evaporative cooler, and obviously the system whilst saving energy does use water.

In addition to the energy savings another advantage of the Coolarado is it doesn’t have any refrigerants in it, so you don’t need to worry about the global warming potential of any leaked refrigerant. And the only moving part is its fan, which is a high efficiency direct drive unit, reducing mechanical maintenance requirements. 

Innovations such as this are going to help enable a low carbon economy, and as prices drop will start drive it.