Performance at Colombo, Ceylon, of a pressurised solar water heater of the combined collector and storage type

Abstract A solar water heater combining collection and storage has been tested in Ceylon. The heater consists of a square coil of 3 in. diameter pipe, 44·3 ft in length, in a wooden box with heat insulation at the bottom and two glass covers. The glass surface is 20 ft2 in area. If water is drawn off whenever the water reaches 120°F, it is possible to obtain 30–50 gal of water a day, the first draw-off being made about noon. The efficiency of collection based on the exposed glass area on the top of the box (which was 1·55 times larger than the horizontally-projected area of the pipe surface) is around 46 per cent. An equation for the performance of the heat collector over the day was devised, and this was applied by means of a computer program to solar radiation data for the whole year. The results showed that no heat could be collected for less than 10 per cent of the year. The total energy collection for the year was about 1250 kWh. Another computer program compared the performance of the heaters made up of 2, 2 1 2 , 3, 3 1 2 and 4 in. diam pipes respectively. This study indicated that a heater of 2 1 2 to 3 1 2 in. diam pipe would provide the best performance for most purposes.