Evacuated Tube Comparison

This is not an evacuated tube batch heater.

Can You tell why?

This is a thermo siphoning batch collector. It's a great improvement over the simple batch heater  because the heat storage area is separated from the heat collection area and the tank is insulated.  BUT this direct water heating system has a low heat storage capacity and a large capacity for freezing in a cold climate. It is also more difficult to build than the simple batch heater. also be difficult  to install for on a roof but if you have one it's a ideal for demonstrating the thermo siphoning phenomena. 

This evacuated tube batch heater may at first appear the same as the thermosyphoning batch, but  it's different. Thermosyphoning batch heaters are vulnerable to freezing and the evacuated tube batch heater is vulnerable to snow buildup.

If the evacuated tube tank is well insulated the water inside the tank will stay warm a long time since very little heat will be lost through the evacuated tubes. 

HOWEVER in snow belt areas snow remains on the evacuated tubes for a long time and blocks sunlight. The snow on these tubes does not melt easily since they are so well insulated. Pushing potable water through the evacuated tube batch heater tank is another problem that must be addressed. If you must use evacuated tubes use them in a areas with minimal snow use them in conjunction with a closed loop glycol system so you won't have to worry about freezing pipes. An alternative to the evacuated tube, direct connect, batch heater is the evacuated tube closed loop heat collection system.

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