homework
This is the VOA Special English Technology Report. Solar water heaters are used around the world and are not difficult to build. The system we are going to describe is based on the design developed some years ago in Afganastan. Since then, it has been built and used in many countries. It can heat 70 liters of water to 60 degree Celsius, it can do this between sunrise and noon on the clear day with an average air temperature of 32 degree Celsius. There are two parts of the solar water heater, one part is made of the sheet of metal painted black. Black surfaces become hotter in the sun than surfaces painted in the other colour. This black metal plate is called a collector. The collector is places in contact with the water. There are several kinds of metal sheets that can be used for the collector. Chorogated metal will work very well. Choragited sheets are often used as roofs on the housing. Once the water is heater, it is kept hot with insulation material. This allows the water to stay warm for a long time. The second part of the solar water heater holds the water for the system. This storage tank can be a container that holds about 100 liters. Two rubber pipes are attached to the water storage tank, one pipe lets water flow into the system, the other lets water flow out. When the water heater is working correctly, water will flow from the storage tank to the collector and back again. You can use the hot water at the top of the tank for washing and cleaning. You can change the flow of water so that the temperature is hot or warm as designed. This solar water heater is easy to build and operate. It ** about two years before the rubber pipes need to be replaced. There is also something else you need to make the solar water heater work, the sun, as you might imagine the heater will heat water only on the sunny days. You can get more information about solar water heaters and other project from enterprise works **. This group works internaionally to fight poverty. The website is enterprisework.org. Choose the link for news and resources, then flick on publication. And that is the VOA Special English Technology Report. Tell us if you ever built the solar water heater or have ideas for improvements, post your comments at voaspecialenglish.com
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