Comparative study of the thermal behaviour and performance of two Egyptian style compact solar water heaters

Two thermosyphon, non-pressurized and pressurized type compact solar water heaters are designed, manufactured and tested under the local meteorological conditions of Assiut city (27 degrees north latitude and 31 degrees east longitude). The two heaters are manufactured having the same collector aperture area of 1.8 Square meter and a water storage capacity of 175 liters. The absorber of the non-pressurized heater is a hybrid of two parallel aluminum sheets pipeless type flat plate absorber, painted with normal black paint. The pressurized heater is built into one unit in construction profile that can withstand water pressure. The water flow channel is formed between a concave stainless steel sheet attached to an acrylic sheet using a modern technology. The temperature fields both on the absorber surfaces, inside the flow channels and storage tanks are monitored. The temperature distribution in the two thermosyphon loops of both heaters for different tanks stratification are also plotted and analyzed. The results show that a linear temperature distribution along the absorber plates as well as inside the flow channels is obtained. The water temperature is found to be very close to the metal temperature and follows it almost with no time delay. It is found also that the non-pressurized heater has a slightly better performance characteristics when compared with the pressurized one. According to the experimental analysis, the absorber heat removal factor and overall heat loss coefficient are found to be 0.92 and 5.11 W/m(2) degrees c for the non-pressurized heater and 0.90 and 5.20 W/m(2) degrees c for the pressurized one.