Solar air conditioning & House Space Cooling

Until now solar systems are mostly limited to heating purposes and to PV solar electricity, and it may sound rather strange to use the sun energy in house cooling goals. And yet it’s possible, though in non-competitive terms.

Solar powered air-conditioning systems

Solar home space cooling systems are part of the Thermally Activated Cooling Systems (TACS), and for some enthusiasts of solar energy, they are an environmentally-friendly technique with a promising future.

Some gigantic facilities as the Los Angeles Audubon Nature Center - a 5,026-square-foot facility devoted to enjoyment and education – has a fully solar-powered air conditioning system (heating and also cooling).

Solar air cooling systems: possible but expensive

Today’s solar air conditioning systems aren’t competitive, mainly in stand-alone applications. Solar cooling is rarely used because of the high initial costs.

Only when combined with solar home water heaters and space heating systems solar cooling may become more competitive. Most stand-alone solar cooling systems are quite expensive investments: solutions of $4000 - $8000 per ton are very common.

Implementing a solar house cooling solution

Since solar cooling systems demand expensive investments, it's advantageous to develop combined air conditioning systems (dual systems) in order to use the same basic equipment/collectors to cooling goals during some months or even parts of the day, and for heating goals in others...

solar air conditioning Market

Solar home space cooling solutions have to be studied and implemented in conjunction with solar heating technicians and experts on common gas cooling systems. There isn't, currently, ready-to-use solutions.

A partial solution

Most solar air conditioning systems are sized to provide up to 40% to 70% of the building cooling requirements (the remainder are usually fueled by natural gas or other means).

Technologies available

Technologies available for solar-driven cooling include....

1) advanced absorption systems and
2) desiccant cooling systems.

Solar absorption technology

Absorption technology demands high temperatures and collectors capable of producing them: evacuated-tube and concentrating type solar collectors… The energy from these solar collectors is used to separate a tank liquid mixture that includes an absorbent (lithium bromide salt, for instance) and a refrigerant fluid (often the water). The refrigerant (water vapor) is then condensed and eventually evaporated to produce the desired cooling effect.

In the Audubon Nature Center case, cited above, the thermal energy from the solar collectors is driven to a 1,200-gallon insulated high-temperature hot water storage tank. When the stored hot water reaches the right temperature (180º F), it is pumped through a generator into a chiller containing a lithium bromide salt (the absorbent) which yields water vapor (the refrigerant) that subsequently is condensed to produce chilled water. In its terminal phase, the system use fan coil units to drive the indoor building air across the coils containing the chilled water, causing its cooling.

Solar desiccant technology

Solar desiccant technologies use… desiccants - substances like silica gel, calcium sulfate, etc. to absorb the air humidity and to cool it. Desiccants are commonly solids, but may also be liquids. Both technologies are very similar in their implementation.

In the case of the solid desiccant system, as the air passes through the desiccant (usually located on a wheel rotating into the air stream going into the rooms) the moisture is removed from the air, causing the humidity level and the temperature of the air to drop. At the same time the thermal energy from the solar collectors is used to dry the desiccant, driving off the absorbed water (as it rotates out of the air stream).