Sun power for your shower – The spiral heater

Last week you read about the shower bag. Now we describe a system with the Spiral Heater that you can build in on board, even by yourself.
It is a rather simple system, with some technical things, so sometimes boring. But we have a cliff hanger: would the story end up with a beautiful model under the shower head? Male or female?

2.    The spiral heater

The cupper spiral is just visible through the double skinned insulation plastic, that prevents that the heat gets lost.. The sunrays go through it, heat the spiral and the water circulatiing through it.

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.

In general: the Pressure pump keeps the water system under pressure, so the (cold and hot water) taps can give water. The circulation pump circulates the water first through the spiral heater, to the hot water tap and into the top of the boiler, pushing the cold water under into the circulation 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).

 This pump is a typical robust circulation pump. It works on 12 Volt. It switches on when the temperature of the boiler is lower than the temperature of the spiral heater.

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.

The shower test

It works!