Solar & Wood Burner

[UlsterRugby1999]

Hi all - Having read some previous posts on the topic of vented and non vented systems I'm left with a headache, mainly as I dont understand the technical arguments you guys submit. [:D] I want to install a solar panel (evac tube type) system to produce some of our hot water. Coupled to this, I had hoped to be able to install a wrap around wood burning stove for added umph to our water in the winter. From the same wrap around I had intended to heat a few rads too.

The tanks that are available here in France, and also many in the UK, are for closed (I think pressurised - non vented) systems. Is there a safe way of connecting the wrap around to the tank so that if it over pressures it wont blow up? I dont have space for header tanks etc.

I do intend to install the system along with a local electrician and plumber (one of whom is Dutch and the other Belgian) so absolute knowledge of the French system may not be guaranteed. What do you think (in Numpty English please [:D])

[crossy67]

I might be wrong with all this but as far as I can understand you can't use header tanks in France, you are not allowed to store water other than in closed circuits. 

In general an accumulator is used to store the extra pressure created by expansion in a closed circuit caused by heating, not 100% but I recall them being called a Ballon.  I have only ever seen one and it's an old one, not in use any more in our basement.  It's a red cylinder about10" diameter and about 12" long.  They usually have a bladder in a steel cylinder that is pressurised with nitrogen gas, as the water expands it forces water into the bladder compressing the gas, when the pressure reduces the gas can expand, forcing the water back into the system. 

You would need a blow off safety valve plumbed into a drain in case the pressure and/or the water that needs to be displaced exceeds the accumulators capacity.

[Dog]

If you buy the solar heater from the Caribbean Magician (Leroy Merlin) or even if you don't they have DIY guides that are simple and they sell the stuff in a kit form. Yes you need a special water cyclinder - but it does mean it can also be electrically heated.

I personally do not like the complexity of using a wood burner with a back boiler (although I bet there are some happy cusatomers). In my experience they suck all the warmth out of the woodburner.

If you want to know how to make a wood oven just ask - though last week in the Troc in Perigueux there was a lovely cast iron wood burning cooker - propably 1960's it was very clean and only 60 euros.

Good luck.

[UlsterRugby1999]

Cheers folks for the replies. Ive been searching the web for a while too. The wood burner "claims" to have 14kw for the boiler and 8kw for the fire. That would be enough for what we want. Making my own was never in my plans Dog but.............. Crossy67 the solar kits that I am looking at all come with an expansion vesel which is waht, I guess, you mean.

What worries me most is that in some previous threads several times the discussions have centred on unsafe installations and even explosions. Yikes. I dont want that.

[Dave&Olive]

hi ok

             You need to read the small print for the claims on wrap around tanks ....say you have a 30 kw wood burner  just the act of fitting a tank will take 10 kw away by the room it takes up ....then say 12- 14 for the hot water so you are left with an 6kw wood burner ... for more details on how to fit one best bet is to read back posts here or ask

              http://www.navitron.org.uk/forum/index.php

                           Dave

[fisherman]

No you don’t want an explosion. However just ensure that an adequately rated safety valve is fitted. This should be on a reasonable diameter pipe line to allow rapid steam flow in the event of overpressure. I know that on marine boilers the safety valves are fitted directly to the steam drum but they are designed to do so. However I would not have the confidence that commercially available safety valves for domestic use would have the same reliability and I would personally probably mount the valve fairly near to the boiler on a short spur so the it is slightly cooler than the heated steel of the boiler. In addition without doing any detailed research I don’t think it would be wise to just rely on the pressure valve fitted to the accumulator I would not think that the bore would be sufficient.

Gas / oil boilers have several layers of safety systems to keep them safe however generally speaking wood / coal boilers do not have the same level of sophistication. However that is not to say they are unsafe and I would have no problems in having one if the occasion arose just ensure that a safety valve is fitted.

[BIG MAC]

The removal of 10kw of performance from the fire is not the whole picture as of course you could have underfloor or  rads in the same room putting some of the energy back. If you install a brine filled thermal store then you will optimise the burn cycle, retaining heat energy for when the fire is on the wane. It should not be beyond the ken of man to set the system to circulate on a gravity primary first which charges the thermal store and mains pressure cylinder on a sealed sytem with appropriate blow by and pressure vessels. A conventional sealed heating system can then draw on the thermal store (like a boiler if you will)  if you set the heating to come on only when the thermal store reaches a 'set point' then the system  should be ok...of course you could also charge the thermal store on heures creuses (sp?) off peak electric at night when the fire is damped down or out.....toastie in the morning....theoretically at least.

I suspect initial cost may be an issue though.

[UlsterRugby1999]

OMG I'm confused already [;-)] [:D].

Here is an extract from an email I received from the company who makes the stove I had hoped to include in the system.

"You can’t put a boiler stove into a pressurised system – only open vented and non pressurised. There is a high risk of explosion in a pressurised system and the stoves are not designed for that."

So, can I or cant I. I am really confused. Sorry to be thick. You guys have offered great advice and thank you for that.

The link is to the stove but I would have thought that they were much of a muchness.

http://www.naturalheating.co.uk/titan-wraparound-boiler-stove-22kw-limited-stocks-p-1058.html

[idun]

Our Turbo Fonte insert fire in France heated radiators and we had a non pressurised system. Eventually when gas came to the village we had our central heating was linked into the exixting pipework and we had no problems. Well apart from when there were power cuts as, unlike our neighbours we could not depend on our woodburner as it was always so hot that it still sounded like it was going to explode and my little theory is that if something very hot is making that much noise, then to turn it off.

[BIG MAC]

That's sounds very like a system without gravity circulation on the primary and a bypass

[Oracle]

 

UlsterRugby

Everything you want to do is certainly do-able, so long as the components of the system are designed and compatible for the type of system.

You simply cannot for example hope to connect a back boiler wood fire designed for open vented system to a French Pressurised system - common sense would answer that question without too much research. Now there are some folk who have done just that I have to say, but they, by an large have the skills in engineering to accommodate the special provisions necessary to prevent system failure. Whereas I get the impression that you are not so interested in the 'wheel reinvention' approach, so keep it simple.

So, it follows that you are in France and should therefore follow French plumbing norms, without which there will surely be implications of some kind later on (insurance et al;). Hence the best approach from a guidance point of view would be to abandon thoughts of duplicating an UK configuration and adopt European (pressurised) - you may not know, but the Scandinavians have been doing this for many, many decades and are probably the world leader in wood fuel heating systems so why not copy them and use components which are made there.

Their approach is simple, nearly all systems involve a pressurised thermal storage - as big as possible, something like a multiple of 10 x your floor area (in litres) say 100m2 house, then that is 1000lt Thermal store, its not definitive but its a starting point. Then connect your stoves, solar panels, heat pump and every other heat generation or collection source you have. Likewise connect your rads, underfloor circuit, DHW whatsoever to take the heat out to where and when you want it and there you have it.  The system runs on about 1,5 bar and there is pressure relief in the form of expansion vessels, and as a last resort, over pressure valves to dump excessive pressure if it all gets too hot. As the water inside is deoxygenated, then you have no problem with corrosion and so the components should last for many decades. Its really not complicated and any decent local plumber can fathom it once the schematic has been designed. (therein lies the rub - it needs to be designed)

On the wood stove side, the essential component is a Laddomat, which is a device to solve the problems to which Big Mac was eluding. That is, you cannot hope to run a wood fire efficiently if you're harvesting heat constantly - it just put the fire out. So its essential for a modern 'hands off' system to have the control automated to some degree - which means a Laddomat (PM me if you want more info on these things). Solar likewise has to be designed and certainly I would encourage anyone to always included solar into any system design as its relatively simple and the energy collected is free both in money and labour terms which is unique to Solar.

There are other issues to discuss but to cover more than that here is too much typing.

Oracle

[UlsterRugby1999]

Good ness me its all gotten complicated. I think the first thing I need to do is source another stove as the one I had chosen, it would seem, isnat capable of running as I had hoped. Oracle your post is informative but I couldnt imagine having the space to put a 1900lt tank but I am encouraged by what you say.

Big Mac - thanks too for ypur posts but I am not altogether sure that I understand exactly what you have said. [:$]

[BIG MAC]

Pretty much the same as Oracle or rather Oracle interpreted what I was saying.

Hot water rises over cold on gravity so if you imagine a big 'loop' of pipework with an up and a down attached to your boiler then without the aid of a pump hot water will flow from the water jacket up the up and will return down the down. In a vented system this would be open to atmosphere by virtue of a flow and expansion tank high up in the building and pipework would run from this primary loop out to rads and to a hot water cylinder to create a heating system. This is not efficient and is against French codes. What is being suggested is that the primary heats an accumulator which is like a very well insulated hotwater cylinder and the heat from the 'up' flow passes through a coil in the accumulator and passes heat into the brine within. The accumulator will have other coils and possibly an immersion type electric heater. The accumulator 'accumulates heat from the available sources and puts it down into a take off coil which will more than likely be on a pumped circuit.

A gravity primary therefore should behave predictably and be designed to have sufficient expansion and make up (replenish) provision a pump failure would mean nothing as the system is operating on gravity and you can have a thermostatic damper installed if you want to be even safer - this restricts air supply to the fire and controls burn ....that's the basics

[UlsterRugby1999]

Thanks everyone for all your input and advice. I have ordered the solar system and this should arrive end of the July. What I need to source is an actual diagram of layout and parts required to link the soalr and wood burning elements to maximise security so if any of you guys can point me in the right direction I'd be eternally grateful. Many thanks to all. Cheers. Paul

[idun]

If I didn't make myself clear, we had a pump.  Our gas boiler and the whole system was linked, including our wood burner and it was not sealed/pressurised at all. We had a header tank in the loft.

Our neighbour had the same boiler and the part that deals with the pressure went twice. Ours ofcourse was not used.

[BIG MAC]

http://www.broseleyfires.com/Link-Up-Systems.html

[idun]

What a good idea, especially with the solar panels. Would they run electricity for the pump?

I only ask as for all it is great to get hot water from a wood burner, when the electricity goes off then I used to have to put my fire out. And this is the reason I have installed just wood burners now, that mean that I have independant heating and cooking as it happens now.

[The Riff-Raff Element]

[quote user="UlsterRugby1999"]Thanks everyone for all your input and advice. I have ordered the solar system and this should arrive end of the July. What I need to source is an actual diagram of layout and parts required to link the soalr and wood burning elements to maximise security so if any of you guys can point me in the right direction I'd be eternally grateful. Many thanks to all. Cheers. Paul[/quote]

In our set up the two circuits are not linked. We have a 300l HW tank with two seperate coils in it: one coming down from the panels, one fed from the back boiler, rather than a Broseley style thermal store.This simplifies the pipework considerably. There is an electric back-up in there somewhere too.

There is a four-way valve between the heating circuit and the hot water circuit from the back boiler that allows for basic control and if we are going out or to bed then we bias this to the heating since this will operate without the pump if necessary based on thermal cycling.

I must say it works vey well. We wash a family of five and heat 10 rads from a 33kW stove, though we have an insert for when things get really cold.

The installation diagram was supplied by Godin (who built the stove) but I can't find anything on their website, but it might be worth a more thorough search.

[UlsterRugby1999]

Brilliant Big Mac - actually to see it in diagram form makes way more sense to me. The Riff-Raff Element - thanks for the post. I havent explained myself well. The tank will have 2 coils, one for the solar set up and the second for the wood burner just as you describe.