Solar cooling, at first, sounds like a paradox. How can something so hot be responsible for producing cold? Through careful exploitation of thermodynamic principles, these systems utilize solar heat energy to fuel a cooling process. Energy is always lost to the surroundings whenever it changes form. So instead of transforming solar heat energy into electricity, one may cool with solar heat energy and reap the benefits of an efficient solar power system.
Two main ways solar thermal energy can be used for cooling involve sorption processes. Both processes have very similar names; one must be careful not to confuse the two. Absorption is the process of incorporation of a substance of one state into a different substance existing in another state. (i.e. gases absorbed into a liquid). Adsorption is the process of molecular bonding or physical adherance onto the surface of a substance in a different phase. Both of these processes can be exploited for cooling.
Absorption chillers use a thermal compressor instead of the mechanical style compressor in traditional compression refrigerators. There are three phases to the absorption chilling process: evaporation, absorption and regeneration. The first stage involves liquid form refrigerant evaporating low partial pressure surroundings, thereby extracting heat from its environs. The environment in this case is the refrigerator, or space to be cooled. Following this, the refrigerant is absorbed, while in gaseous form, reducing the partial pressure in the evaporator chamber and allowing for more liquid evaporation. Finally, to regenerate the cycle, the refrigerant solution is heated, evaporating the refrigerant and replenishing the evaporating chamber.
For this cycle to proceed efficiently, the absorption chiller requires water at temperatures of at least 88oC/190 oF. Solar thermal energy is the best way to fuel an absorption chiller. One such device, the SolarBeam Concentrator, is a solar thermal collector capable of fueling a solar hot water system at temperatures over 93oC/199oF. With its mechanics, it takes up a minimal amount of space and is the most efficient system on the market. Its solar heat output can be easily routed to an absorption cooler and when the season does not require cooling, the solar thermal energy is available for heating purposes.
A method comparable to the absorption chiller is the adsorption chiller. Absorption chillers use Lithium Bromide (LiBr) as their refrigerant; this requires high maintenance costs. With LiBr there are risks of crystallization, corrosion and chemical leaks. Instead adsorption chillers use silica gel as the adsorbent. They have the advantage of being very low maintenance, with little vibration or noise during their operation.
Neither of these systems are as prevalent as they should be. They are a much more efficient way to provide cooling than traditional compression refrigerators or air conditioners. Combined with a solar thermal energy collector such as the SolarBeam Concentrator, the potential expands beyond cooling into the realms of space heating, electricity production and process heat. This can all be done while saving money, space and energy; a win for everyone involved.
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