[Greenbuilding] thermosiphon questions
Norbert Senf
norbert.senf at gmail.com
Sun Nov 2 19:09:39 CST 2014
Thanks, Frank - very interesting observations and information.
We did some testing on our shop heater, and found that in a simulated
emergency (no power to the circulation pump), on a pumped system we could
get flow by installing a swing check valve, horizontally on the cold inlet
side to the coil. When the water first boils, you get individual steam
bubbles, which produce pressure pulses. The pressure pulse hits the swing
check valve, and causes it to bounce, letting in a small amount of water.
It begins to act like a pump, in a similar fashion to how ram pumps work.
The main downside is that it gets noisy as the boiling increases,ie. with a
hot fire. However, interesting as a backup alternative to using a 12V pump
with battery backup..............Norbert
On Sun, Nov 2, 2014 at 7:54 PM, Frank Tettemer <frank at livingsol.com> wrote:
> Just to add to Norbert's thorough thinking, I agree on the 1" dia.pipe as
> being relevant, given that your rise to run ratio is way less that 1 to 2.
>
> I've worked on three homes that use an ESSE cookstove, (must be similar to
> your Ireland description, Norbert.)
>
> In one home, the stove is on a lower level, and heats radiators in distant
> rooms that are only five steps up. This one stove heats 2,400 sq, ft. of
> well insulated home, through direct radiant heating when in the kitchen,
> air circulation heating, and water circulation heating through three iron
> radiators.
>
> It does this all using gravity flow circulation, which draws the cold
> water return from the rads, right back down to the stove. Total height is
> only four feet. from bottom of stove to bottom of radiator. The furthest
> rad is about 45 feet away from the stove, with a 60 gallon storage tank
> somewhere in middle of the supply run. Works good, with 1" copper, and high
> temp (Boiler pipe insulation) wrapped on both lengths of pipe. However,
> they have a sensor and some automatics involved, to deal with too high
> temperatures. There is a pump that starts a side circulation loop, that
> dumps the excess heat outside under the ground, until the tank temperature
> returns to under 60C..
>
> Considering the caution needed in dealing such high temperatures, there
> was some additional safety added. The problem to solve was that with no
> fire going, there is no circulation. So the beginning of the fire building
> in the stove, with no circualtion, the water begins to boil in the stove's
> heat exchanger. On the output pipe, on the side of the Esse, is mounted a
> short leg of pipe with a large brass Maid'O'Mist air evacuator valve. This
> lets out any air or steam that develops during the morning's initial wood
> fire, that heats the pipes up near boiling temperatures, just before the
> beginning of a good circualtion flow. This brass Maid'O'Mist hisses and
> sputters for a few minutes each morning, letting air out, until a
> reasonable flow develops in the circulation loop.
>
> Not that you'll need that, but I included the detail FYI, in that the Esse
> cook stove is not considered just a cooker and a water heater. The heat
> exchanger along side the firebox is so efficient at drawing heat to the
> water that the company describes this stove as a Boiler. Thus, it needs to
> have overheating conditions dealt with right from the get go, through
> careful consideration and thoughtful design.
>
> Frank
>
>
> On 02/11/2014 11:34 AM, Norbert Senf wrote:
>
>> 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
>> <mailto: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 <mailto: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 <mailto: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 <mailto: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
>> <mailto: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
>>
>
> --
> Frank Tettemer
> Living Sol ~ Building and Design
> www.livingsol.com
> 613 756 3884
>
>
>
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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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