Gravity Feed Custom Radiator Question

[Keajre]

Dear Friends,

 

I am creating a gravity fed heat sink for my new stove back boiler. Thanks to help on this site, I have ironed out many of the questions I needed answer to. However one still remains.

 

For the heat sink aspect of a gravity fed system, would a 10 - 12 meters of 22mm cooper pipe made into a sort of towel rail allow water to thermosyphon. Would be using a pipe bender not joints to keep joint restrictions at near zero. There would be a lot of horizontal pipes in this design idea, which is a concern, I don't have enough experience to know if gravity circulation would function enough under these conditions.

 

Would use mounts all the way along to support the pipe. Haven't done the maths yet, in terms of how much heat would be displaced, but will get back to that after, once I know this design will work.

 

Please enjoy my wonderful diagram which hopefully will assist the explanation :-)

[FadeToScarlet]

You'll need a header tank, with a feed from the highest point so the system can self bleed- otherwise, you've created a bomb.

[Keajre]

Yes, I am aware of this, the system has many other elements which I have not mentioned here, one of the elements is a vented F&E tank at the highest point.

 

The reason for the post, was to try and understand if a thermosyphon process would be able to circulate the water given the number of horizontal pipes. Typically it is my understanding that it is preference to keep the hot /feed pipes on a rising angle.

 

The boiler is 1.4KWH

 

Thanks

Edited August 25, 2016 by Keajre

[Tony Brooks]

As you intend to use a pipe bender they will only be truly horizontal if you make it that way. AS long a sit was not on full and open view I would tend to under bend each of the ends so there is a slight fall. You may also have to take account of how the boat sits so you still have some fall on each leg but the whole thing looks true to the boat.

 

If I had to guess I would say that it will work because water would cool in each led and drop to the bottom of the horizontal run and then "spill over" into each bend section but on no account take that as gospel.

[Keajre]

The other items I should mention probably are:

 

- The 'custom towel rail' will be mounted to a wall (so virtual)

- The 'custom towel rail' will be 1 - 1.5 meters above the boiler approximately

- The feed (hot) pipe will rise at a 45 degree angle approximately to the top of the 'custom towel rail'

- The output of the boiler is 3/4BSP converted to 22mm cooper pipe, the entire 'custom towel rail' is constructed of a single piece of pipe (with some joins)

- Full bore valves will be used to endure no constriction of the pipe / flow

As you intend to use a pipe bender they will only be truly horizontal if you make it that way. AS long a sit was not on full and open view I would tend to under bend each of the ends so there is a slight fall. You may also have to take account of how the boat sits so you still have some fall on each leg but the whole thing looks true to the boat.

 

If I had to guess I would say that it will work because water would cool in each led and drop to the bottom of the horizontal run and then "spill over" into each bend section but on no account take that as gospel.

 

Thank you for your reply. Good idea, so make the horizontal pipes slop down slightly that makes sense. My boat is lower at the back due to the weight of the engine, as many are. Will take that into account, though hmm it might not look very good visually like that (but of course I probably have no choice if I want it to work!)

Edited August 25, 2016 by Keajre

[Tiggs]

Can you bend 22mm pipe tight enough so as not to make the whole thing too tall?

[Keajre]

not sure, never done pipe bending before

[Tony Brooks]

Well for goodness sake do not try to use a 22mm spring, I assumed that you had a suitable pipe bending machine. If you try it with a spring I suspect that you may waste a lot of copper and ruin a number of springs where the pipe eventually kinks and traps the spring.

 

If I was doing it I would probably use a 22mm header and footer tube more or less horizontal and a number of uprights T'd off with solder feed fittings. I would try 15mm verticals and the solder on some horizontal "pipes" on stand offs to put the towels on. I would not attempt to get water into the towel rail bits.

[OldGoat]

Unthought things through, how's about -

using a quantity of 28mm 'slow bend' elbows and arrange a gentle bend in each pipe run using the spring to give that slight curve?

That could / should give a compact assembly, but with a reasonable gradient?

 

(Folks who have done it may be able to refine the process?)

 

My mind goes back to the days when motor vehicle engine were cooled by thermo-syphon - but the main pipe run was tapered to get the flow right - but the idea stick in the mind....

[Joe the plumber]

It might be worth you buying a conventional towel rail radiator and trying it first as they're not that expensive and it will save you a lot

of time and effort if it does the job.

 

Bending 22mm pipe with a proper bender will leave you a lot of space and not much pipe due to the 4" (+/-) radius,

so it won't be very efficient. For example a 40" high radiator will only have six horizontal pipes.

 

Mind you, if it goes wrong, buy a mouthpiece, call it a 'Serpent' and you can set up an Early Music group with it...!

 

https://en.wikipedia.org/wiki/Serpent_(instrument)

[Keajre]

It might be worth you buying a conventional towel rail radiator and trying it first as they're not that expensive and it will save you a lot

of time and effort if it does the job.

 

Bending 22mm pipe with a proper bender will leave you a lot of space and not much pipe due to the 4" (+/-) radius,

so it won't be very efficient. For example a 40" high radiator will only have six horizontal pipes.

 

Mind you, if it goes wrong, buy a mouthpiece, call it a 'Serpent' and you can set up an Early Music group with it...!

 

https://en.wikipedia.org/wiki/Serpent_(instrument)

 

 

But a towel rail as perfectly horizontal bars, surely that would not be good for circulation or might even stop it completely? I am speaking from zero experiene here only going off what others have said above (Tony Brooks)

 

I was going to use this:

 

https://www.amazon.co.uk/Silverline-MS124-Bender-Guide-Heavy/dp/B000LFVEZO/ref=sr_1_1?ie=UTF8&qid=1472194167&sr=8-1&keywords=pipe+bending

 

Its a 22mm pipe bender, was not going to use the spring method.

 

Tony Brook, why use 15mm verticals instead of 22? I believe larger vertical pipes provide a better thermosyphon effect is that not the case?

Joe:

Bending 22mm pipe with a proper bender will leave you a lot of space and not much pipe due to the 4" (+/-) radius,

so it won't be very efficient. For example a 40" high radiator will only have six horizontal pipes.

 

Me: Never used one before, ok 4" radius hmm. Well its more about leaking heat than being perfectly functional. Its going above the stove (to the right) on the wall, so its going to look weird anyway. So might as well make it look vaguely artistic than just a cheap b&q towel rail. That was my thinking. If it stops the boiler boiling in the event of circulation pump failure I'll be happy.

 

So what I am trying to get to, is, will it work! Or will horizontals def not work.

[Rizzo]

How about these 180 bends

http://www.ebay.co.uk/itm/15mm-22mm-copper-180-degree-return-bend-plumbing-diy-new-u-bend-/161161553662

[spadefoot]

Don't worry about the horizontals, they won't actually be horizontal on the boat, unless you set them so with a spirit-level.

Try it with the towel-rad first. If you've never done pipe-bending, you'll likely just end up with several feet of twisted, bent, kinked copper pipe.

[Keajre]

Ah I see, since the boat is lower at the bow, if I offer this up so its straight on the wall, then it will look straight but will be sloping in favor of the gravity flow thanks to the boat not being level.

 

I have never done pipe bending, I have done most of the plumbing on the boat, all self taught, reckon I could learn how to bend pipes without wishing to sound big headed.

 

That being said, thanks for the link Rizzo, that looks good, what do you think Spadefoot?

[Tony Brooks]

 

 

 

But a towel rail as perfectly horizontal bars, surely that would not be good for circulation or might even stop it completely? I am speaking from zero experiene here only going off what others have said above (Tony Brooks)

 

Tony Brook, why use 15mm verticals instead of 22? I believe larger vertical pipes provide a better thermosyphon effect is that not the case?

 

 

1. I said that my guess was that horizontal 22mmlegs would work and explained why. I did not say it definitely would not work.

 

2. As such a setup will require fittings I feel 22mm verticals would look rather heavy. I feel the contrast between 22mm horizontal headers and 15mm verticals more aesthetically pleasing. I think the 22mm bit is for near horizontal runs. All the rads on my gravity system had 15mm feed and return legs and that worked well. My domestic single pipe central heating system used to gravity circulate in 15mm without the pump running but then it did have rather a lot of vertical run close to the stove.

 

 

 

 

I suspect that any DIY job is going to end up with lots of fittings and compre3ssion ones would look horrible, even push fit brass with plastic parts would still look horrible so you will be into a lot of cleaning, fluxing, soldering and washing off. Unless you have use end feed fittings or even Yorkshire fittings before it is likely that you will get a leak or three and maybe blobs of solder hanging off a joint. Try it with a cheap ready made rail first.

 

 

[Keajre]

Hi Tony,

 

Shame, truth be told I was looking forward to having a tinker around with a pipe bending machine. I respect your experience in this since its vast in comparison to my own. I will check out some towel rails for the time being, then perhaps a project for next year, see if I can build a towel rail from 22mm cooper pipes joined together and make it look aesthetically acceptable.

 

The back of the boiler is 3/4" BSP. I was planning to convert that to 22mm (3/4" female to 22mm coupler) and then I'd run that to the radiator some 1.5 meters above the boiler (above and to the right in fact). That sound ok?

Edited August 26, 2016 by Keajre

[Joe the plumber]

If all you want to do is dissipate some heat, your cheapest bet will be to forget the towel rail and just buy a small single panel radiator to try. You should get one for under £30, or possibly even under £20. Assuming it works (and the tubes are pretty much vertical) , you can then paint it whatever colour you like if you want it to look a bit different.

 

For example:

 

http://www.screwfix.com/p/kudox-premium-type-11-single-panel-single-convector-convector-radiator-white-300-x-600mm/76575

 

The heat output from a small conventional radiator will be more than from a larger towel rail due to the greater surface area. If the 'landscape' shape, above, is no good, other places will sell you a 'portrait' one (eg 600mm high, 300mm wide) although it will probably be a bit more expensive.

 

I'm not experienced enough in central heating design to be able to say for definite what will work I'm afraid, but an ordinary radiator will certainly be THE cheapest and quickest way to experiment.

[Bod]

The other items I should mention probably are:

 

- The 'custom towel rail' will be mounted to a wall (so virtual)

- The 'custom towel rail' will be 1 - 1.5 meters above the boiler approximately

- The feed (hot) pipe will rise at a 45 degree angle approximately to the top of the 'custom towel rail'

- The output of the boiler is 3/4BSP converted to 22mm cooper pipe, the entire 'custom towel rail' is constructed of a single piece of pipe (with some joins)

- Full bore valves will be used to endure no constriction of the pipe / flow

 

Thank you for your reply. Good idea, so make the horizontal pipes slop down slightly that makes sense. My boat is lower at the back due to the weight of the engine, as many are. Will take that into account, though hmm it might not look very good visually like that (but of course I probably have no choice if I want it to work!)

 

NO valves, or remove handles and wire open.

A closed valve on this type of system will cause problems.

2 closed valves will create a time bomb! Literally the system could blow up releasing high pressure steam, and boiling water.

 

Bod

[Joe the plumber]

Just to add, you get a free valve set (add code 53581 to the order) with the Screwfix radiator. If you do get it, don't for goodness sake fit the thermostatic valve or it could close off and cause serious overheating in the stove/boiler.

[Keajre]

I chickened out in the end! Decided the extra grand in 'stuff' to make this happen would take years to get a ROI based on 10p per kwh I pay for the good old immersion!

 

Do really appreciate everyones input here, it helped me come to my ultimate conclusion and saved me a lot of stress in the end.