Test of 2 Thermosyphon Solar Water Heating Systems Using Homemade Collectors

I've been doing some simple testing of thermosyphon solar heating systems that make use of our two homemade collector designs.   The idea being to see how these collectors would perform in a thermosyphon system and just to learn more about thermosyphon systems.

For thermosyphon systems, the heated water storage tank is placed above the collector.  The inlet of the collector is connected to the bottom of the tank, and the outlet of the collector is connected to the top of the tank.

As sun heats the water in the collector, it becomes less dense and rises out the top of the
collector and into the tank.  The water leaving the collector is replaced by cold water from the bottom of the storage tank.   As long as the sun continues to heat the water in the collector, a circulation loop is setup in which water flows continuously out the bottom of the tank, through the collector, and then back into the top of the tank. 

When the sun goes off the collector, the water in the collector cools, and circulation no longer
occurs since the water in the collector is more dense than the tank water and naturally stays in the collector.

So, in this system, the circulation is all by natural forces -- no pumps needed.  And, the control is automatic -- no controllers needed. 

These systems are very simple and are widely used in some parts of the world.

The two collector configurations I tested include the collector that uses PEX tubing with aluminum heat transfer fins, and the configuration that uses copper tubing with aluminum heat transfer fins.  Here is the performance log for the copper tube collector (click for full size):

All the details on the test are here:

Details for the PEX tube collector thermosyphon system...

Details for the copper tube collector thermosyphon system...

Please read all the details from the links above if you have an interest in this, and maybe you can help answer some of the outstanding questions.

But, the tentative bottom line appears to be:

- The collector that uses the PEX tubes is probably a bad choice for this thermosyphon application.  The collector temperatures observed would likely result in a short life for the PEX tubing.

- The copper tube collector with the top/bottom manifolds and vertical risers worked well, and would likely be a good candidate for a homemade collector in a thermosyphon collector.  There were some anomalies that showed up in the performance logging -- maybe you have an idea what is causing these?

Gary

April 22, 2010