relative heights in thermosyphon

[jus]

Hello everyone. Is there an optimal ratio between rise and run in a gravity loop (thermosyphon) between a wood burning stove and a cylinder? Ive heard it said that 1 in 5 is the minimum advisable for a reasonable flow rate. Is this true? And if I have an insulated flow pipe going up 20 feet and then back down 15 to the cylinder should I assume the rise to be 20 foot or 5 foot? (come to think of it would there be any other advantage in this setup?) Also is there an optimal pipe size for gravity flow systems? Any help with these questions would be greatly appreciated.

 

[keego]

If I've pictured this right then a 20ft rise followed by a drop of 15ft will never work on a gravity system. We have had instances were when a cylinder has been changed the pipework has dropped a few inches & the system will airlock on a regular basis requiring it to be boiled to get it going again, only to lock up again the next day.
If that is the only way you can run the pipework the you will have to pump it.

 

[jus]

Well actually no, I can run the pipes by a much more direct route, but would you believe it I thought that there might actually be some advantage in it. Obviously high points are bad!
I have other options (unfortunately with more mess and ancillary work but there you go) the one I'm most concerned about, but which would make most sense in terms of avoiding cold legs etc, would involve firstly a vertical rise of about 7 foot and then a run of about 30 foot with a possible rise of 2 foot over this second stretch of pipe, that is assuming the flow is going to the top of the cylinder. The return pipe would begin with a vertical drop of say 6 foot and then a completely level run of 30 foot to just below the burner (I'm guessing that a big thermal store would have a distance of around 4 foot between flow and return).
Does this seem feasible?
Jus.

 

[doitall]

A gravity circuit can rise as high as you like, in more or less a continous climb.

Return is the important bit and must, fall from the highest point back to it's heat source.

To stop any confusion it can pick up the rads, cylinder etc on the way, up or down, provided the returns are connected in the correct positions

 

[brumylad]

if your going to run a thermal store I would have thought the heat recovery period (heat exchanger design) would be based on a pumped primary flow.

 

[doitall]

if your going to run a thermal store I would have thought the heat recovery period (heat exchanger design) would be based on a pumped primary flow.

Most of the new HE cylinders and stores say not suitable for gravity primaries.

 

[kevplumb]

honest

 

[jus]

OK, so if I were to use a more traditional style of cylinder that will work in a gravity circuit and the rise of the flow pipe totals 9 foot how much of a horizontal run could I get away with? Would 30 foot be too much?
jus.

 

[doitall]

OK, so if I were to use a more traditional style of cylinder that will work in a gravity circuit and the rise of the flow pipe totals 9 foot how much of a horizontal run could I get away with? Would 30 foot be too much?
jus.

I think before you/we continue you should read the link and download the pdf file.

There are safety issues that must be taken into consideration, DIY is not adviced

http://www.solidfuel.co.uk/frame/main.html

http://www.solidfuel.co.uk/pdfs/design_guide.pdf

 

[jus]

Fear not, I'm not going to play at plumbers but rather I'm going to employ a professional one when the time comes. At present I'm at the planning stage of a refurbishment and not having even decided on the type of heating (woodfired? Pellet stove? Kerosene? Accumulator tank? Electricity dependent? Magnox Reactor?), I'm trying to fit together the puzzle of what will go where in the limited space we have. In order to do this I need to try to find out what the limitations of certain types of system are so I can tie them in with kitchens, airing cupboards, bunded kerosene tanks, existing fireplaces, planning applications for new stainless flues etc. etc. etc. But certainly I can not afford to pay someone to advise me on all of this therefore I'm doing my own research. My aim is to present the plumber with some kind of coherent general plan which he can build on or transform as necessary, and hopefully it will tie in well with the plans for other aspects of the house.
I'll chek out the publications you recommend before proceeding. Cheers for now.