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Author Topic: Solar + wood burning + mains gas - where to start?  (Read 9981 times)
ringsoft
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« on: June 22, 2010, 01:41:26 PM »

Our current systems (inherited from previous owners) are solar thermal panels for domestic hot water and a gas-powered warm-air system for heating. The solar panels work very well. The warm-air system is horribly expensive to run and doesn't heat the house evenly. Cavity wall and loft insulation is installed.

My dream is to take away the warm-air system and replace it with a radiator-based system and to drive this with a mixture of a conventional mains gas boiler and a wood-burning boiler. Is this at all feasible and if so what type of supplier should I try to find to take the project forward? Most local suppliers (GU4) I have identified so far only deal in one type of equipment and mixing them seems to be in the "too difficult" category.

Any advice appreciated.

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martin
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« Reply #1 on: June 22, 2010, 01:46:30 PM »

Whereabouts are you? (roughly?)   I'm sure you'll soon be inundated with advice, and there may well be someone in your area who could do the job for you.......... Smiley
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KenB
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« Reply #2 on: June 22, 2010, 02:25:03 PM »

Ringsoft,

Do you mean a wood burning stove with a back boiler, or a dedicated wood-burning boiler?

The former is likely to be a traditional stove fitted with a back boiler, intended mainly for heating the room in which it is installed and contributing to domestic hot water.  The dedicated wood burning boiler is often located in a utility, garage or outbuilding and is intended to drive the entire CH and DHW systems.

I have combined a traditional stove with back boiler in my living room, with a condensing gas boiler in the kitchen.   The traditional stove heats the living room directly and the room above, by way of the heat-leak radiator. It also contributes to the domestic hot water, but the total output from the back boiler is not really sufficient to drive the 7 remaining radiators around the house.

The back-boiler is a gravity fed system and is linked to the gas boiler (which is a pumped system) by way of a unit called a "systemzone".   This is a rectangular tank about the size of a biscuit tin, located in the airing cupboard, which couples the two systems together and allows them to individually circulate. There is a similar product made by Dunsley Baker, known as a neutraliser.

I took this route, because my hot water cylinder only has 1 coil, so it would not be possible for me to link the wood burning back-boiler into a "spare" coil.  If you are doing a complete new system, then the multi-coil cylinder might be a worthwhile approach, where solar, gas and wood sources all contribute to your DHW.

There is considerable variation between the efficiency of woodstoves. For many, the inclusion of the back boiler puts a significant load on the heatsource, and may lead to excessive cooling of the flame temperature. If you look at the new generation of gasifying woodstoves - these use a 2 stage combustion process and do not have the same limitations as the traditional type.  The efficiency is considerably raised - and so you don't have to burn so much wood or sweep the flue so often.  Have a look at the Dunsley Yorkshire, which is a 2 stage stove, and gets a much better balance between heat into the room and heat into the water - the living room is not overheated, and the boiler makes a significant (9kW) contribution to the central heating system.  It is also permitted for wood use in otherwise smokeless zones.  It will cost you about 2K, but may in the long run prove to be a better investment than a simpler traditional stove.  Similar stoves exist from other manufacturers (I'm not biased) - just that the Dunsley Yorkshire was the first on the UK market, and is worth a look, if you want to invest in a better product.  I went for a low cost product - because money was tight.

When it comes to installation, find an installer who is fully experienced with solid fuel (wood) stoves when combined with gas installation.  As wood is still common in Sussex, Surrey and Hampshire - you should be able to find a reputable local installer close to GU4, with HETAS accreditation.

Attached is a picture of the systemzone in my airing cupboard, just to give you some idea what's involved.  Basically its a tank with 4 pairs of ports, each a flow and a return. The WBS is connected to the LHS and the gas boiler to the RHS.  Two further ports connect to the flow and return of the heating system, and there are two spare for later expansion.
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Most of the heat from the WBS goes to the 1000mm double convector (heat leak) radiator in my 14'x12' work room - keeping it cosy. On the top of the systemzone is a tankstat, which when the systemzone gets up to about 60C, starts a pump which moves the excess heat into my DHW heating coil. Whilst this proved OK for last winter, I am now going to slightly reconfigure the system so more of the heat contributes to the hot water, making it unnecessary to fire up the gas boiler just to heat the hot water.



Ken


* systemzone.jpg (106.86 KB, 800x600 - viewed 2510 times.)
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ringsoft
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« Reply #3 on: June 22, 2010, 03:58:11 PM »

We are near Guildford, Surrey (postcode GU4).
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ringsoft
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« Reply #4 on: June 22, 2010, 04:06:37 PM »


Do you mean a wood burning stove with a back boiler, or a dedicated wood-burning boiler?


I thought I meant a dedicated boiler, but after reading your post I am not so sure. A local supplier of wood-burning stoves informed me that the back-boiler water temperature was uncontrolled and therefore unsuitable for feeding water into the domestic hot water supply. And remember that we have got solar panels heating the domestic hot water. I'm trying to gauge whether what I want is at the "bleeding edge" of what is feasible or not. If it is, then a simpler approach may be preferable.
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martin
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« Reply #5 on: June 22, 2010, 04:27:53 PM »

The supplier of woodburners is talking through his................ whistlie
A woodburner/back boiler/solar system is an excellent one - simple, low tech, clutter all to go wrong, and relatively inexpensive - easy way to tie it all together is have one vented store with coils for boiler, back boiler etc......... easy peasy! (when the sun's heating the solar hot water system, the woodburner will be out/used intermittently)
I like simple straightforward systems like that........ Wink
(not at all "leading edge", far more "low tech and easy")
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KenB
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« Reply #6 on: June 22, 2010, 05:51:58 PM »

martin,

I tend to agree with you.  Try to keep the system simple - gravity feed with suitable sized heat leak radiator.

However, if you are combining a modern gas boiler, plus solar, plus a wood burner,  then would you specify the woodburner with sufficient boiler output to heat the whole house - especially if you already have an 800 gas boiler perfectly capable of doing that task.  It might be overkill if you are on a tight budget.

I found last winter that purchasing logs in Surrey was a bit hit and miss.   They were 100 a load and tended to be less than fully seasoned and all needed additional splitting with the maul to get them to a sensible size to fit in the stove.  Choose your log supplier with care.  Remember that even in the cruel January we had this year that 100 buys a lot of gas at 3.25p per unit. - about a month's worth.


Ken
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dhaslam
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« Reply #7 on: June 22, 2010, 07:07:46 PM »

What way is the heat distributed  by the present warm air system?    It might be possible to change  to a wet system  that uses finned  pipes as heat exchangers.       Water is easier to control and water  carries much more heat for a given pipe size.   
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Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
ringsoft
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« Reply #8 on: June 22, 2010, 08:03:46 PM »

What way is the heat distributed  by the present warm air system?    It might be possible to change  to a wet system  that uses finned  pipes as heat exchangers.       Water is easier to control and water  carries much more heat for a given pipe size.   
Via hefty ducting running at ceiling level in the basement (where the warm-air boiler is), under floors on the ground floor and in loft space around the first floor.
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desperate
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« Reply #9 on: June 22, 2010, 08:25:00 PM »

Ringsoft

If you want to see a system in the flesh so to speak, we are in worcester park, solar,WBS with boiler and gasser all linked up.

Desperate
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jamesg
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« Reply #10 on: December 16, 2011, 04:34:18 PM »

Excellent threads so far. I'm in a very similar situation needing advice;

At Present my situation is; 3 bed 1978 semi, cavity filled + topped up loft insulation, on mains gas.
No radiators in house, just a woodburner(without backboiler) in open plan downstairs room, & an old instantaneous gas water heater for tap hot water. No header tank in loft, no hot water storage cylinder.

Want to replace old gas water heater for a modern combi or condensing boiler, to run my newly installed underfloor heating circuit in the kitchen/dining extension, and 3 radiators to distribute heat upstairs better than the woodburner does.

Later(in a few years when gas increases in cost) want to replace current woodburner with one that has an integral boiler, and have this plumbed into the underfloor heating, and 3 radiators, via a storage tank with coils.
Also want the option of introducing solar thermal into system as well (the solar thermal panels will be on a lower extension roof, so a feeder tank in the loft is possible for a vented system)

I don't want to buy the thermal storage tank now, only when I decide to introduce the wood stove boiler and solar later. I don't mind buying a feeder tank for the loft if a vented system is better.

Question is ?  What type of gas boiler should I have installed now.?
An open vented type, with a feeder tank in the loft (is that a condensing boiler?), or a combi sealed boiler ?
or any other type of gas boiler that suits this scenario.

Many thanks if anyone has a similar future proofing situation, or can help. Am in Mid Somerset.
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desperate
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« Reply #11 on: December 16, 2011, 04:58:05 PM »

Yo James welcome...............

check out my CRAC thread on the show us yours board, we have a solar/woodburner/gasser system that works quite well, gas bill gone down from 900/yr to 200/yr.
We used a Worcester Bosch system boiler, that is a sealed pressurised ch and hw system. All domestic boiolers are condensing nowdays the difference is the plumbing system attatched to it, a combi supplies instant hot water on demand, a regular boiler supplies heat to a hot water cylinder and ch, and has an open vented system, a system boiler supplies a hot water cylinder and ch with a pressurised system.

Personally I think a combi would struggle to satisfy the hot water needs in a 3 bed house,, multiple demand leads to low flow situaations sometimes, and are difficult to integrate with a solar system, but they are the simplest and cheapest systems to fit. A system boiler with a hot water cylinder give you the most possibilities for unstandard plumbing designs such as wood burners and solar panels.

Lots of design work needed
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