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Solar Air-Conditioning

How to make cool air on hot days

The need for better cooling

The Queensland Government's "Improving sustainable housing in Queensland" discussion paper notes, "In recent years, the amount of electricity used in a typical Queensland home has increased by an average of 10 per cent per year. This is due to an increased reliance on air-conditioners".


Sorption chillers

Sorption chillers are closed loop systems that can use one of two processes, either Absorption or Adsorption. The distinction between the two beyond the scope of this page but The Solar Guys will be concentration Absorption chillers for technical reasons.

An absorption chiller is similar to a regular compressor air-conditioner in that the refrigeration takes place by evaporating a liquid with a very low (sub-zero) boiling point. In both cases, when a liquid evaporates or boils, it takes some heat away with it.

The difference between the two is how the gas is changed back into a liquid so that it may be used again. A regular air-conditioner regenerates the gas back into a liquid by using a compressor to increase the pressure on the gas, and then condenses the higher pressure gas back to a liquid by heat exchange with a coolant (usually air).

An absorption chiller uses heat energy requiring no moving parts to condense the higher pressure gas back into a liquid. Absorption chillers have the advantage of using either solar heat inputs or waste energy inputs and have very low electricity consumption (typically just small pumps to move the liquids around).

For more information please see the original

Wikipedia page.

Desiccant coolers

These coolers work by extracting the humidity out of the air by passing the air through a liquid spray of the desiccant. Solid desiccants can also be used to extract the moisture and make the air more comfortable.

Interestingly, by adding a small amount of water back into the air after the humidity has been extracted, the air temperature rapidly falls. This is known as a combined desiccant / evaporative cooler.

Once the desiccant has been saturated with the humidity it must be regenerated by heating it up, which can be achieved by using solar thermal energy in a cost-effective, low-energy-consumption, continuously-repeating cycle.

Solar Collectors

For small to medium solar air-conditioning systems, evacuated tubes make excellent solar collectors due to their low cost and high efficiency at high temperatures (80°C - 100°C). Evacuated tubes also have virtually no maintenance or running costs.

For larger solar air-conditioning systems, solar parabolic trough collectors are often employed. These can produce higher efficiency and temperatures than the evacuated tubes but require active tracking systems, which have higher running and maintenance costs.