A heat exchanger.

[happyhacker]

I have a solid fuel fire without a back boiler. Whenever we use it I put SS pans on it to provide hot water. What I need though is a larger water tank with a heat exchanger on the outside of the fire getting heat from the side(s) of the burner. Anyone got ideas about a design including the exchanger and tank?

[unsure]

take a look on youtube for engineer775 . he`s done some good stuff on this .

[lee3]

Hi I met someone who used one of these in his yurt however his stove had a small flue and this fitted around it so unsure if it would fit something larger

[triffid]

What volume of hot water are you looking for? Just enough for survival or enough to run a household?


Assuming, from your post, you want a household supply then a simple indirect immersion tank would suffice.
Hot water comes from your heat source passes through a coil in the immersion heater (heat is transferred from the pipe to the contents of the tank) and then the now cold(er) water recirculates through your heat source. You use the contents of the tank as domestic hot water.


How to extract the heat, in the form of hot water, from your stove?

[matthopkins]

Not sure of your system and if its mains fed, but i have found you have to run the burner alot hotter with these on the side type of boilers.
In tests i done whilst building boilers over the years, i found the best type is either the internal worm type ( running one of these myself) or run a worm around the flue like has been said before.
If you can email me a picture of your fire/burner please do and i will see if ive got any plans of a type that you may be able to mod to get it to fit.

Please bare in mind that doing a diy fitting on a woodburner or stove will most proberbly invalidate your home insurence should you need to make a claim (god forbid)
PM sent

Heres the guy unsure was talking about http://www.youtube.com/watch?v=b3i249KtB0o

[happyhacker]

Here is a pic. The gap between the RH fire side plate is about 15cm. I envisage a copper plate offered up to that side (which gets VERY hot) and on the side of that plate a "coil" of 22mm copper pipe soldered. Obviously as much pipe as possible here to maximise water in contact with heat. This will conduct up around the corner to a tank on the RH side of the fireplace which will have a lid to top up and a tap to take off hot water into a jug. Using this method I think th water could reach 75C.

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[Donquay]

Coil copper tube round the flue?

[matthopkins]

If i were in your shoes and doing it for myself to end up feeding a small tank as you desire, and not knowing the height you have on the rh side of your fire place i would go for the following.

The hottest place on the fire will be the top (excluding the flue) this is where a 15mm copper pipe coil (heat exchanger) would be wound round the flue 2 turns only. Both ends of the pipe coming out same side one above the other.

We will call the bottom pipe feed in, top pipe feed out.

Attach feed in to bottom of tank with feed out attached as high up the tank as possible. You will need to add a couple of bends to gain this height.
DO NOT MAKE THIS A SEALED SYSTEM keep the lid able to lift off if pressure builds.
The reason i would and do use 15mm pipe, is because there is a smaller amount of water in the pipe thats touching the stove and flue, it will heat QUICKER causing what is known as the thermosyphon effect.

Thermosyphon is the simple effect of the hotter water in the coil rising pulling behind it the colder water to take its place in the coil. The warmer water makes its way to the tank and sits on top of the cooler water in the tank.
As the water at the top cools it sinks and again is pulled by the hotter water in the coil and so the cycle of hotter water pulling cooler water through heat exchanger takes place, thermosyphon.

Very simple and this is a basic version of that which is on my boat, I run a shower and sink like this without any pumps.

I EXCEPT NO RESPONCABILITIE FOR ANY INJURY CAUSED BY TRYING THIS. I AM NOT A TRAINED PLUMBER OR HEATING ENGINEER AND AS SUCH YOU TRY THIS AT YOUR OWN RISK.
edited to add: have a look on youtube about thermosyphon

[poppypiesdad]

It might be prudent to braze the connection on any pipe you are using, solder melts around 450°c where as brazing is around 600°- 900° , which with the close proximity of the stove might not be a bad idea.

J

[poppypiesdad]

I did see somewhere that it is a bad idea to wrap the flue with copper tube to warm the water as it reduces the flue gas temperature which can lead to an increased deposits of soot and tar inside the flue increasing the chance of a fire , but however if you sweep it regularly what would be the problem ??

J