A Simple DIY Thermosyphon Solar Water Heater for the Tropics
Peter lives in a remote and beautiful area of Costa Rica and was looking for a simple solar water heating system that could be built with locally available and affordable materials.
He worked out a simple thermosyphon collector design that heats water in an elevated tank. The tank gravity feeds to showers. A float valve arrangement at the tank automatically keeps the tank topped up with water.
Because copper is very expensive locally, he used CPVC pipe for the collector. Normally CPVC would not be a good choice for a glazed collector that sees this much sun because of the potential for overheating damaging the CPVC pipe, but Peter has worked out a couple of reliable mechanisms to keep the collector temperatures down. He allows for some circulation of air under the collector glazing, and the thermosyphoning of water from the collector to the un-pressurized tank insures that the water temperature will not exceed 212F. Both of these protection methods are reliable and don't depend on electrical power or pumps or controllers (which are all subject to failure).
The CPVC collector absorber in work and before paintinig.
This is a non-pressurized system in which the collector heats the water in an elevated tank. Water in the tank gravity feeds to showers, and the tank is automatically kept topped up via a float valve in the tank that allows new cold water into the tank.
The heated water storage tank with float valve to keep it filled.
The completed system in operaftion.
Really a nice simple and effective design for situations where freeze protection is not required, or where the system could be drained during freezes.
Thanks very much to Peter for working out this design and sending in the details!
One Year Update On System From Peter:
Thanks very much to Peter for providing this one year update on the system, and some hints for even better performance:
The system has performed admirably through about a year of operation. On a typical wet-season day with alternating sun and clouds on and off all day, there is water enough for two or three good, substantial, warm showers. On a day that is mostly bright, the water is near scalding, and needs a little tempering with cold. On a hot, dry-season day it is scorching. I have never had the need for more than three showers a day at the house, but on one of those hot, clear days the capacity would seem nearly limitless. On an unusually consistently rainy, overcast day, the sun struggles to get much heat through. I tend to avoid taking showers on those days, but when I have the water is at least no more chilly than from the suicide electric showers.
Some tips and observations.
The moist weather in the cloud forest has resulted in a mildew buildup on the underside of the glazing. I may opt to remove it at some point as dirty glazing is probably more hindrance than help. Given my experience with this system I would not use any glazing in future in these conditions.
The only consistent problem has been the tank-fill valve. Because the diameter of the tank is small, I had to use a shorter float arm than recommended. This does not generate adequate force to keep the valve tightly sealed, and the tank has a tendency to overflow. I have taken to letting it fill after taking a shower and then shutting off the water supply until the next shower. I am getting a little tired of this, and am starting a hunt for a different variety of valve that will control the water level in the narrow tank.
The UV is hard on exposed cpvc pipes and the tank insulation, and getting them painted helps.
Building the collector with a drain valve at the low point was great, since it makes it easy to drain everything completely when I need to for any reason.
There is about a three-foot difference in height between the two showers in the house, and man does it make a difference in the effective water pressure. I may try to raise the tank slightly to get a bit more pressure to the 'upstairs' shower.
