Solar water heating is one application of the Solar Thermal. Solar Water Heaters (SWH) are of two types; one is non-pressurized solar water heating (SWH) and other is Pressurized Solar Water Heating. In non-pressurized solar water heater, the collector (Vacuum tubes or flat plate) and tank are mounted on one fixture and are in one integrated unit. Tank is mounted at top of the collector. There is no pump used in this type of system. This system works on flow of water through gravity from overhead tank to solar water heater tank (stainless steel tank with 55 mm poly-urethane insulation) and from this tank onward to vacuum tubes and by natural convention process, the hot water circulates and heats up the whole tank. It usually takes four hours to heat up the water of 300 litters up to 50 Degree in peak winter season and 60 Degree in moderate season and 90 degree in peak hot season. So the temperature of water varies as per ambient temperature. Usually 50 Litters per person per day is taken while designing the system for domestic use. For industrial application of washing and cleaning, the total water load in terms of flow is calculated to design the system. The total number of solar water heaters connected in parallel or series depends upon the daily water consumption and temperature requirement.
The collectors used in Pressurized Solar Water Heaters can be flat plate or vacuum tubes. In pressurized solar water heaters, the tubes are made of copper and these are closed tubes and the upper top has bulb dipped in water tank through which heat radiates into the water in tank. The copper tubes are filled with ether which expands quickly when sun radiations fall at tubes. So in this type of system water does not enter into the copper tubes and therefore no chance of rusting. In pressurized systems, tank is separate than the collector unit and no gravity is required. There are two circuits one is primary circuit and other is secondary circuit. In primary circuit the glycol moves through circulatory pump by controller and in secondary circuit the water moves through pump or without pump to end points.
The tanks in pressurized systems can have one cooper coil or two coils depending upon the type of applications. In large systems where quick heat exchange is required, the heat exchangers are also used.