Solar Closed-loop Absorption and Adsorption Cooling
The following are common technologies in use for solar thermal closed-loop air conditioning.
- Absorption: NH3/H2O or Ammonia/Water
- Absorption: Water/Lithium Bromide
- Absorption: Water/Lithium Chloride
- Absorption: Water/Silica Gel or Water/Zeolite
- Absorption: Methanol/Activated Carbon
Active solar cooling uses solar thermal collectors to provide solar energy to thermally driven chillers (usually adsorption or absorption chillers). The solar energy heats a fluid that provides heat to the generator of an absorption chiller and is recirculated back to the collectors.The heat provided to the generator drives a cooling cycle that produces chilled water. The chilled water produced is used for large commercial and industrial cooling.
Solar thermal energy can be used to efficiently cool in the summer, and also heat domestic hot water and buildings in the winter. Single, double or triple iterative absorption cooling cycles are used in different solar-thermal-cooling system designs. The more cycles, the more efficient they are. Absorption chillers operate with less noise and vibration than compressor-based chillers.
Efficient absorption chillers nominally require water of at least 190 °F (88 °C). Common, inexpensive flat-plate solar thermal collectors only produce about 160 °F (71 °C) water. High temperature flat plate, concentrating or evacuated tube collectors are needed to produce the higher temperature water required. In large scale installations there are several projects successful both technical and economical in operation world wide including, for example, at the headquarters of Caixa Geral de Depósitos in Lisbon with 1,579 square metres (17,000 sq ft) solar collectors and 545 kW cooling power or on the Olympic Sailing Village in Qingdao/China. In 2011 the most powerful plant at Singapore's new constructed United World College will be commissioned (1500 kW).
These projects have shown that flat plate solar collectors specially developed for temperatures over 200 °F (93 °C) (featuring double glazing, increased backside insulation, etc.) can be effective and cost efficient. Where water can be heated well above 190 °F (88 °C), it can be stored and used when the sun is not shining.
The Audubon Environmental Center in Los Angeles has an example solar air conditioning installation. which failed fairly soon after commissioning and is no longer being maintained The Southern California Gas Co. (The Gas Company) is also testing the practicality of solar thermal cooling systems at their Energy Resource Center (ERC) in Downey, California. Solar Collectors from Sopogy and Cogenra were installed on the rooftop at the ERC and are producing cooling for the building’s air conditioning system. Masdar City in the United Arab Emirates is also testing a double-effect absorption cooling plant using Sopogy parabolic trough collectors, Mirroxx Fresnel array and TVP Solar high-vacuum solar thermal panels.
In the late 19th century, the most common fluid for absorption cooling was a solution of ammonia and water. Today, the combination of lithium bromide and water is also in common use. One end of the system of expansion/condensation pipes is heated, and the other end gets cold enough to make ice. Originally, natural gas was used as a heat source in the late 19th century. Today, propane is used in recreational vehicle absorption chiller refrigerators. Innovative hot water solar thermal energy collectors can also be used as the modern "free energy" heat source.
For 150 years, absorption chillers have been used to make ice (before the electric light bulb was invented). This ice can be stored and used as an "ice battery" for cooling when the sun is not shining, as it was in the 1995 Hotel New Otani in Tokyo Japan. Mathematical models are available in the public domain for ice-based thermal energy storage performance calculations.
The ISAAC Solar Icemaker is an intermittent solar ammonia-water absorption cycle. The ISAAC uses a parabolic trough solar collector and a compact and efficient design to produce ice with no fuel or electric input, and with no moving parts.
Providers of solar cooling systems include include SOLID, Sopogy, Cogenra, Mirroxx and TVP Solar for commercial installations and ClimateWell, Fagor-Rotartica, SorTech and Daikin mostly for residential systems. Cogenra uses solar co-generation to produce both thermal and electric energy that can be used for cooling.
Read more about this topic: Solar Air Conditioning
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