[Greenbuilding] thermosiphon questions

[Norbert Senf]

Hi Reuben: That's not to say that it can't be done. In Ireland, I saw wood
fired cookstoves with a water jacket apparently running a bunch of
radiators, pretty much at the same elevation and with no apparent
circulation pump. Wish I'd had time to investigate further. We have one
client who has a masonry heater with a water coil in the firebox,
thermosyphoning into a regular hot water tank behind the heater, only
slightly elevated off the floor. Works fine. With the large horizontal run,
your enemies are friction and heat loss. You can insulate the heck out of
the supply line, and use a large diameter pipe to cut the friction. If you
can afford the loss, leaving the return line uninsulated would give you
more temperature differential for thermosyphoning.  Studying how those
systems in Ireland work, would be useful...............Norbert

On Sun, Nov 2, 2014 at 9:21 AM, Reuben Deumling <9watts at gmail.com> wrote:

> Thanks, Norbert. That is what I'm fearing.
>
> On Sun, Nov 2, 2014 at 6:06 AM, Norbert Senf <norbert.senf at gmail.com>
> wrote:
>
>> 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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>
>
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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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