If you are in the market for a solar water heater, you might be confused between the different types of solar water heaters available in the market. Solar water heaters can be categorized differently based on how they operate.
The working principle of a solar water heater is simple. The collectors installed on the roof collect solar energy which is used to heat the water. However, there are two ways this can be done which leads to two types of solar water heaters.
The two first types of solar water heaters you will encounter are the direct and indirect solar water heaters. In the direct solar water heaters, the water is heated directly in the tubes underneath the collectors. The water circulates from the tank to the collectors and back. This system is also called the open loop system.
The indirect system is different because the heat from the sun is used to heat up a liquid. The circulation system then moves the heated liquid to the heat exchanger where the liquid transfers it’s energy to the water in the tank. The water tank is insulated to ensure the water remains hot for a long time. To move the heat transfer liquid, a pump is used. The liquid is stored in a drainback reservoir when the pump stops.
The indirect system is ideal for places where the conditions can get really hot or very cold. This is because the heat transfer liquid prevents overheating or freezing and therefore the system is always maintained at optimal conditions.
The other types of solar water heaters you will encounter are passive and active solar water heaters. The categorization here is done based on whether an external force is used in the circulation system. Active solar water heating systems use pumps to circulate water in the system or the heat transfer liquid.
These systems also use electronic controllers to regulate the whole system. The temperature controllers check the temperature differences between the heat transfer liquid and water in the tank and start the pump automatically when there is a pressure difference to move the liquid through the system and heat up the water. The pump automatically stops when the temperature difference is reduced to about 3 – 4 degrees Celsius between the water and the transfer liquid.
Passive solar water heaters on the other hand do not use pumps to circulate the water or heat transfer liquid throughout the system. They depend on convention currents to move the hot water and gravity to move water from the tank to the rest of the taps for use. In these systems, the storage tank is always placed above the collectors to ensure the hot water rises to the tank.
Passive solar water heating systems are usually very affordable, easy to install and require little to no maintenance as compared to the active systems. On the other hand, active systems offer more freedom in terms of installation design and allow for precise temperature control. They also do not overheat or freeze.
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