| Solar Cooling |
| Friday, 05 September 2008 20:11 |
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Sunny summer days are beautiful, yet in the office a hot day can be altogether stressful. Because productivity can suffer under such conditions, more and more buildings are being fitted with air-conditioning systems. In fact, since the early 90s the number of air conditioning units in Malta has increased dramatically. This is reflected in the consumption patterns records at Enemalta. In fact, since 1997 there was a higher demand for electricity during the months of July and August, whereas in the previous years, the peak demand was during the cold months of December and January. It might sound like a strange idea to think of using the sun to cool your home or office, but in fact, absorption cooling was the first type of air conditioning. Absorption cooling is still practical for remote homes in places where there is an excess of heat energy available. This is definitely the case for the hot and sunny Maltese summers. Although still in its infancy, this solar cooling technology is making a comeback and hopefully during the next few years it will become more widespread throughout the country. There are several basic types of solar cooling technologies. Absorption cooling, which can use solar thermal energy to vaporize the refrigerant; desiccant cooling, which can use solar thermal energy to regenerate (dry) the desiccant; vapour compression cooling, which can use solar thermal energy to operate a Rankin-cycle heat engine; evaporative cooling; and heat pumps and air conditioners that can be powered by solar photovoltaic systems. In absorption cooling, heat drives the system, instead of electricity. There are two basic types of systems. The single-stage systems, are driven by any warm fluid (not necessarily water) heated to around 100 degrees Celsius. On the other hand the two-stage systems work at around 120 degrees Celsius. These can use low temperature solar energy to "pre-heat" the air. A high-temperature energy source (e.g. natural gas or oil) is used in the second cooling stage. Desiccant coolers are the other very popular style of solar cooling. Desiccant coolers remove moisture from air. This does not actually cool the air but reduces the humidity, making it seem cooler. These are often used in combination with other types of solar coolers such as vapour compression or evaporative, which really do lower temperature. Vapour compression cooling uses solar thermal energy to operate a Rankin cycle heat engine, whilst the evaporative cooling method uses a mechanical device that takes the heat from the outside air and uses this to evaporate water held in pads inside the cooling unit. This 'sucks' heat out of the air and the cooled air is blown into the home by a fan. Solar cooling saves electricity and unlike solar heating it has absolutely no storage needs as the need for cool air is almost exactly in-sync with available solar energy. |
