[Greenbuilding] thermosiphon questions for the solar DHW experts

Topher topher at greenfret.com
Fri Oct 31 16:28:04 CDT 2014


On 10/31/2014 2:38 PM, Reuben Deumling wrote:

> (1) Does it seem reasonable to assume that this system will adequately
> thermosiphon itself without the need of a pump? We have a spare pump but
> would prefer not to use it.

I would calculate the effective length of pipe (i.e. adjust for elbows
etc.) and then determine the pressure due to temperature difference, and
flow rate for that pressue.  That should get you there.

> (2) My question is whether I should install shutoff valves at both ends of
> the two 35' runs connecting the two tanks, or just at one end, and if just
> at one, which one?

I am a huge fan of shut-offs and unions.  Be able to replace anything
which breaks without draining the entire system.


 My thinking is that with 70' of  3/4" that is a lot of
> potential hot water we might as well not be heating.

The problem isn't the capacity of the pipe, but rather the surface area
of the pipe.  70 feet of 3/4" PEX holds 1.3 Gallons, at a temperature
difference of say 60°F is 641 BTUs.  The heat loss through the insulated
pipe on the other hand is 183 BTU/hour.

Thank You Kindly,

Topher

-- 
Topher Belknap
Green Fret Consulting
Kermit didn't know the half of it...
http://www.GreenFret.com/
topher at greenfret.com




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