Wood burner and unvented cylinders

[guydewdney]

I have searched and seen conflicting advice / comments.

Many people say that you are NOT allowed to connect a wood burner to an UVC, as its an 'uncontrolled' heat source. But isnt a thermosyphoning solar panel the same? And what if the boiler has a mechanical thermostat air control, that can shut the boiler down if the water temp gets above 80 degrees? (like the one Im looking at) http://www.broseleyfires.co.uk/catalogue.php?Level=3&CatPage=11&SubCatPage=27&ProductPage=106

so can I or can't I? (via a dunsley neutraliser or equivilant)

[sleepybubble]

and what if that mechanical thermostat fails and your not aware of it.....

Have you considered adding in a 3-port diverter valve and dumping the WBS to the CH if the cylinder hits target temperature.
Or better still if you already have a valve for existing setup e.g. gas or oil, with a bit of thought and some changeover relays so can actually use the stove to replace the 'other' boiler. Using a pipestat to provide heating and hot water calls to the valve via a relay which drops out the standard calls from the programmer. Another relay can disable the switched power to the other boiler, whilst still allowing power to trip in for the CH pump.

Of course you still have to factor for a blackout scenario, which is where another relay can switch over the power supply to the whole heating wiring circuit to a redundent supply, such as UPS or solar charged battery.

I have installed several wood burning stoves this year using this system, I keep meaning to modify Antmans wiring spreadsheet and asking him to post it with the other stuff as it is a very good system, all the relays, enclosure UPS etc come in for under £150

For my own house, I am in the process of putting in a both a rayburn range and solar, and all the controls for the four cylinders will be run off a few simple pipestats and a box full of relays.

[guydewdney]

Thanks SB - the 'what if' scenario would have to be:-
Power failure.
Middle of summer, drought (thus water wheel isnt working and making no power)
Lister engines arnt running on recycled veg oil.
WBS fully loaded. (It would take a fair bit of wood to heat a 300 litre tank to 80+ degrees - about 6kg of good wood I reckon)
Thermostat in WBS broken.
Temp and pressure relief valve in cylinder has jammed shut.
Secondary pressure relief valve has stuck as well.
Theres no one in the house.


really - is this possible? Technically, yes. If theres power - then the heat dump mode of the solar will kick in (runs CH system until temp drops from 75 to 74.5 IIRC).


I was plannign on using the WBS instead of the nice shiney new oil burner during the winter, and using solar with maybe a topup from the boiler during the summer.

And I have a few UPS's kicking about....

The question still arises - is this legal, and possible?

[sleepybubble]

Legally No....

as its a requirement that any heat source connected to an unvented cylinder must be thermostatically controlled and able to turn itself completely off.....

However, if that heat source is technically not supplying the cylinder but dumping via a valve elsewhere then it becomes a bit grey. Does that count as off, no. Is it off in terms of heat supply, yes.

Is it possible?  yes, but its so close not being legal, you have to make your own call.

[dhaslam]

One thing that happens to wood burners is broken glass it can then become a bit uncontrollable.    A bucket of ash can be useful.   

[JW]

... why not check out the European wood burning systems, in most of Europe a vented cylinder and open tank are illegal so systems for unvented with wood boiler are common place.

www.kotly.com is a good place for the basic info but there is loads of stuff on the net

[Ivan]

Yes, you're right about a thermosyphoning solar panel - you couldn't connect that to an unvented cylinder either. Standard pumped system which cannot heat cylinder by thermosyphoning is perfectly ok, however.

[lightfoot]

If your looking to use wood as your primary heat source, why bother with a unvented cylinder, dunsley neutralisers and UPS etc.  Just use an appropriately sized, combined (DHW & UFH/Rads), well insulated/stratified, thermal store.  It's simple, efficient, safe and legal.....and very commonly used in other European counties.

If it's sized correctly, you can burn the wood efficiently and store the energy to be used as and when required.  Connect the inputs and outputs directly (apart from the solar and DHW coils), use a loading valve/charging unit on the wood boiler/rayburn/larger stove circuits etc and a 3-port mixing valve (preferably weather compensating) on the UFH/rad circuits.  You can also connect the gas/oil boiler (preferably directly) to avoid them cycling during part load conditions etc.  You can also heat it with wind, hydro power etc.

It keeps the system simple and efficient....and they don't need to be made from expensive copper or stainless steel either !


Lightfoot.


http://www.termoventiler.se/default.asp?webb_ID=110&webbsida_ID=71
http://www.akvaterm.fi/eng/Accumulators/Akva.38.html

[guydewdney]

cos I have JUST bought (1 year ago?) a spangly dangly new 300L,solar coil equipped, UVC.... I was looking at a thermal store, but got persuaded by my plumber not to bother. 

 

An alternative idea:-
can I have the WBS feeding a load of radiators, with a fail safe valve feeding the cylinder? IE - if all else fals, I just have a rather warm bedroom? The two systems essentially separate, but the powered valve allows heat to enter the UVC if all other safe conditions are met? If I want the oil burner to heat the house, then I can swap some valves round, or somehow use the boiler to suppliment the WBS?

[ajstoneservices]

You could put the output from the woodstove through a buffer cylinder, connect the unvented via a 2 port valve and pump to the buffer which is then "a controlled heat source"

Tony

[guydewdney]

Ah - I see. Use the wbs to heat a big tank. then suck the heat from the tank and inject it into the UVC using a pump. Then run the system as if the pump were the one to the oil boiler....


simple - and cheap - I could even use the original oil burner circulating pump - I just need a changeover valve, and an efficient tank somewhere. But the tank needs to be sized to be able to absorb all the heat from the WBS.


Thanks Tony.

[ajstoneservices]

 

[lightfoot]

....I think the word your looking for is a Thermal Store 

http://www.navitron.org.uk/forum/index.php/topic,4177.msg40988.html#msg40988

Lightfoot.

[ajstoneservices]

nope,too expensive, simple direct cylinder with four bosses and a header tank, jobs done on the cheap

[lightfoot]

Ummm.....Isn't that just a thermal store