Condensation control in glazed flat plate solar water heaters

Flat plate solar thermal collectors are used around the world in both domestic and industrial fields as a simple and effective method to heat water. Avoiding condensation in solar collectors at night is a crucial issue in terms of their durability and performance. During the night the temperature of the collector will often drop below the ambient temperature due to thermal radiation in the cold air. In climates where the air at night becomes saturated with humidity, condensation will form both on the inside and outside of the collector glazing. Condensation on the glazing means energy is wasted in evaporating the moisture throughout the following day. If too much condensation occurs on the inside of the glazing, it will drip on to the absorber surface, which will consequently lead to long-term damage. The objective of this study was to undertake the development of a model, and to validate it. This will determine the frequency of condensation in glazed flat plate solar water heaters and the all parameters which are involved in this phenomenon. The numerical model showed that climatic factors including relative humidity, ambient temperature and wind speed determine the frequency of condensation for any given location. However, it also reveals that the frequency of condensation can be modified by altering the ventilation inside the collector, the slope of the collector and most significantly by using low emissivity coating on the glazing layer