[Greenbuilding] thermosiphon questions

[Norbert Senf]

Nick's result was around 3/4", but I believe in his example the height was
16'.
Off the top, 35' is a very long run, and the rise is low. You definitely
want to minimize friction - I'd go to 1" smooth (copper) pipe, minimum, as
a precaution.
With the situation you describe, I would not expect much heat
transfer................Norbert

On Sat, Nov 1, 2014 at 6:10 PM, Reuben Deumling <9watts at gmail.com> wrote:

> Is that what Nick's numbers suggested? I tried to follow but got lost
> somewhere.
> The tubing is 3/4", the run is 35', the rise is 5' from top of tank to top
> of tank. The water temperature from the originating tank (heated by solar
> thermal panels) can be expected to be 120F - 150F. House pressure is I
> think 60psi.
>
> On Sat, Nov 1, 2014 at 1:20 PM, Norbert Senf <norbert.senf at gmail.com>
> wrote:
>
>> In other words, the pipe should be 3/4" or
>> larger.......................Norbert
>>
>> On Sat, Nov 1, 2014 at 3:46 PM, <nick_pine at verizon.net> wrote:
>>
>>> One way to design a thermosyphoning system:
>>>
>>> 1. Calculate the required water flow, approximately G = 0.04A gpm for an
>>> A ft^2 collector, eg G = 1.28 gpm for a 4'x8' collector.
>>>
>>> 2. Calculate the available thermosyphoning head, Ha = H(62-61.71)/144 =
>>> 0.002H psi, based on a 10 F temp diff at 100 F and an H foot height
>>> difference, eg Ha = 0.002x8 = 0.016 psi with H = 8'.
>>>
>>> 3. Calculate the minimum supply and return pipe inside diameter d in
>>> inches, given their total length L in feet.
>>>
>>> http://www.calctool.org/CALC/eng/fluid/hagen-poiseuille says dP =
>>> 32MuLV/d^2, where V is a velocity and d a diameter. A G gpm flow rate makes
>>> V = cG/d^2 for some constant c, ie dP = kLG/d^4 for some constant k.
>>>
>>> Plugging L = 8' and d = 1" and G = 1.28 gpm into the website makes dP =
>>> 0.001775 psi = k8'x1.28gpm/1^4, so k = 1.73E-4.
>>>
>>> In the example above, d = (kLG/Ha)^0.25 = (1.73E-4x16'x1.28gpm/0.016psi)^0.25
>>> = 0.69" for L = 16'.
>>>
>>> Nick
>>>
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>>
>>
>>
>> --
>> Norbert Senf
>> Masonry Stove Builders
>> 25 Brouse Road, RR 5
>> Shawville Québec J0X 2Y0
>> 819.647.5092
>> www.heatkit.com
>>
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>
>
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-- 
Norbert Senf
Masonry Stove Builders
25 Brouse Road, RR 5
Shawville Québec J0X 2Y0
819.647.5092
www.heatkit.com
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