2. The spiral heater
You can make a 30 cm diameter spiral of thin cupper pipe. This solar spiral heater consists of two spiral pipes connected to each other. It is not that difficult to make. Just buy a 30 meter roll of cupper pipe 6 mm that a plumber uses for oil and butane gas lines. This pipe is rather flexible and with a bit of feeling for the material you ‘mould’ the line in a spiral without kinks. Connect the outside end of one to the outside end of the other, and the flow of the one runs against the flow of the other, which is most effective. In the middle you have to ends: one is the inlet and one is the outlet.
How the system schematically works, with the spiral heater, boiler and taps, is shown in this film.
Interested? Here is the schematic drawing and the description of the complete system.
We start under with the water tank containing water.
A pressure pump pumps water in the system: the water lines, the spiral and the boiler. From now you can use the cold water tap and the hot water tap (although the latter one is still cold now, but wait).
Then, a little circulation pump pumps the water into the spiral heater. The sun heats the spirals, so the water gets hot.
The water leaves this spiral heater through a line going along the hot water tap further to the boiler. It will be led into the top of the boiler. Hot water is lighter than cold water, so the hot water will be stacked on top. The cold water goes downwards. Down in the boiler there is the outlet, so from there the cold water will be sucked up by the circulation pump. Then the water is pumped to the spiral heater for a new circulation. Easy.
Only one safety issue. If water becomes hot, it expands. The pressure would get too high and it would damage the system. Therefore, there is an overpressure valve mounted in the system. It opens when the pressure becomes too high. Mount it just after the pressure pump. The water coming out, can be led to the water tank, or directly before the pressure pump. (this is not drawn here).
Regulating the heat of the water
The pressure pump has a pressure regulation: if the pressure drops, the pump starts running till the pressure is (mostly) about 2 Bar, the minimum water pressure for drinking water.
The spiral heater and the boiler each have a temperature sensor:
- If the temperature of the heater is higher than the temperature of the boiler, the circulation pump will start running.
- If the temperature of the heater is lower than the temperature of the boiler, the circulation pump will stop running.