water pressure problem

[bob golding]

hi all,

i have a solar  panel i want to use for hot water. it has 10mm bore copper tubing,and i want to use it with a tank fitted above it so that it will thermo-syphon. i estimate there is around 10 metres of tubing in the panel plus 4 metres to the tank. what i want to know is how big does the tank have to be to gaurantee it will thermo-syphon? i want to avoid having to use a pump so i can keep it simple. i could go up to 2 metres above the panel. i plan on using a pump to keep the tank topped up.

cheers

bob golding

[wpowokal]

Bob,

     The tank need only be just above the collector, the outlet from the collector returns to the top of the tank while the "cold" water pipe leaves the bottom of the tank.

The collector tubes must all have a continual upward incline so air will not be trapped and interrupt the siphon, and the panel a slight incline say 10 deg so the water doesn't get confused as to which way to expand too.  

allan down under

[rossw]

One more thing: once the syphon starts, it tends to "self-perpetuate". As hot flows out the panel and into the header tank, that tends to "push" water out the bottom of the header tank, which in turn "pushes" water into the botom of your panel.

I've seen systems with high differential temperatures (wood fired boiler) with 1" pipes (not withstanding nearly 100 feet of pipe between the tank and the boiler) making flow rates of over 60 litres/minute without any active pump!