Components of Solar Water Drain-Back System
The components of both types of solar hot water system are the same.
This component is used to collect solar energy to heat water. A flat plate collector is commonly used for such systems. It is made up of metal or plastic box, which is insulated and weatherproofed. It contains an absorber plate beneath a tempered translucent cover. Copper piping is added in an S-shape between the absorber plate and translucent cover. This copper piping carries a heat exchanger (fluid).
Metal collectors are somewhat better than plastic collectors because they are sturdier and provide better fire resistance. However, they are heavy and more expensive than plastic collectors.
This is another main component of this system. It is used to collect hot water, and cold water is also passed to solar collectors from it. The size of the tank used in drain back system is significantly larger than that used closed loop system.
Thermostat Element (Controller)
The thermostat element is a differential temperature controller that controls the circulator and maintains the temperature of hot water. When the temperature of the tank is lower than the collector it senses the situation and turns the circulator on. Due to this, the heat transfer fluid starts moving and the procedure of heating water starts again.
At the time of its failure in drain-back system, the circulator doesn’t start at the right time. Therefore, the water is not circulated for further heating, and remains inside the tank.
The circulator uses a pump that sends the heat transfer fluid from tank to collector.
Inlet and Outlet
They are two valves present on the boundary of the tank. The inlet valve is used for sending cold water to the tank, and the outlet valve is for receiving hot water from the tank.
A heat exchanger is also used in this system to transfer heat from working fluid to the water present in the tank. It is a series of copper coils, and submerged in the water tank.
This component has different structures for drain-back solar systems and closed loop solar systems.
In drain-back system, a couple of pipes are used for transferring cold and hot water separately. One end is connected to the collector and the other end is to the tank.
In closed loop system, a closed loop piping is used between the collector and the tank, in which the mixture of water and glycol is circulated.