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تاريخ التسجيل : 16/10/2010
 | | موضوع: What You Need to Know About A Solar Water Heater السبت أكتوبر 30, 2010 6:10 pm | |
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Cheaper energy... from the sun
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<H1>What You Need to Know About A Solar Water Heater</H1>
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There are two main categories of solar water heater, active and passive, and I will describe each briefly. In both categories the principle is the same, heat from the sun's rays is collected and transferred to the domestic hot water supply by means of a heat exchanger. Unlike solar swimming pool heaters, which use plastic or rubber as the material for heat exchange, the domestic solar water uses a metal, usually copper because of its high thermal conductivity, in a glass covered solar panel. Because the domestic water supply uses fresh water there is no fear of corrosion from chemicals as there is in the case of swimming pools.
In active solar domestic water heating there are five major components to look for, a collector (solar panel), a storage tank, a circulation system using electric pumps, valves and controllers, a backup heating system for extended periods with no sun, and a control system to govern the overall unit. The collector can either heat the domestic water directly or heat a suitable inert liquid such as antifreeze, oil or a completely separate sealed supply of distilled water in a heat exchanger. Glycol or a glycol/water mixture is especially useful in areas where the temperature drops below freezing for extended periods as water freezing in the collector could cause some very expensive damage. Systems that use glycol or oil have the disadvantage of having to be inspected every couple of years to ensure their viability.
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A very cost effective system is the drain back system. This often uses distilled water as the collector fluid. In these systems the collectors only have water in them when the pump is running and typically would contain no water at night when temperatures might drop below freezing.
A passive solar water heating system relies on the natural convection of hot water or on normal household water pressure to circulate water through a solar collector to the household storage tank. These are less efficient than active systems and are more useful in areas where there is no danger of freezing temperatures - such as summer camps and the southern United States.
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In all cases the collector tank should face the South and be tilted at the angle of latitude - care must be taken when mounting such a system as the collector can be quite heavy - the roof structure must be capable of bearing all the extra weight.
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Site copyright: Tony Roocroft (+27)(0)11-454-0105
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