Heating controls for multiple heating sources

[nads1978]

In short, is there a controller on the market that will allow me to utilise a wood burner boiler instead of the oil boiler, and vice versa. So at the flick of a switch I can isolate the oil boiler, and keep the pumps running for my wood burner boiler.

Would it be easier to configure a separate control system, that can operate the TWV for DHW/CH and run the pumps, or would they conflict?

If I had the time, I'd wack a PLC in there and control the lot, but winter is approaching and I have other priorities right now!

 

[RickMoore]

It's usually done with gravity open vent for the stove and a twin coil cylinder. The time/temperature controls for the boiler can then be set so that the boiler suppliments the stove rather than the other way around.
A thermal store would be well worth considering.
Alot depends on what the stove can work with too. Its hard to give generic advice on it.

 

[Agile]

A multi pole switch or a simple switch and a relay!

They can be mounted in a Tupperware box to make them look neat and tidy!

Tony

 

[Norcon]

It will depend on what type of wood burner you have fitted and the plumbing layout.

The electrics then work back from that. It might be that all you need are hi-lo stats.

 

[nads1978]

My wood burner is a Hunter Herald 6 7kW with clip-in boiler option. Multi-fuel
My Oil boiler is a HRM Wallstar 20/25 (Non condensing)

Below is a rough drawing of my HW/CH system. Electrics not yet drawn.

I only just moved into the house, and some things need changing; the log burner is acting as a radiator, probably needs a motorised valve in its feed or return. The controls are ancient and in the attached garage so need to be replaced and relocated (through party wall, easy). The underfloor heating (master bed) is run off the CH loop, but is controlled by its own thermostat in the bedroom, this activates the pump 24/7 no mater if CH is on or off!

 

[Onetap]

the log burner is acting as a radiator (1) , probably needs a motorised valve in its feed or return (2) . The controls are ancient and in the attached garage so need to be replaced and relocated (through party wall, easy).

1) It would do. As a matter of interest have a Google for the Hetas link-up leaflet. It needs some hydraulic separation and hasn't got any at the moment.

http://www.solidfuel.co.uk/pdfs/link_up.pdf

2) Not a good idea, a closed valve would isolate the woodburner from the cold feed or the open vent. besides that, you don't need one.

The woodburner should have gravity circulation to a heat-dump radiator.

I can understand that you are anxious to get the controls sorted, but your system is in need of some major plumbing alterations to make it work efficiently.

 

[matt1e]

In short, is there a controller on the market that will allow me to utilise a wood burner boiler instead of the oil boiler, and vice versa. So at the flick of a switch I can isolate the oil boiler, and keep the pumps running for my wood burner boiler.

Would it be easier to configure a separate control system, that can operate the TWV for DHW/CH and run the pumps, or would they conflict?

If I had the time, I'd wack a PLC in there and control the lot, but winter is approaching and I have other priorities right now!

1 Yes, most likely
2 yes most likely the cheaper option,and no not if done correctly
3 as Onetap has already stated, sort out the plumbing issues first before thinking about a control strategy

Matt

 

[Norcon]

Plumbing is crazy on that and deviates completely from the MI's.

It looks like someone just T'd it into the oil boiler primaries without a moments thought.

 

[nads1978]

Thanks for the info and links, much to think about.

If we ignore the log burner for now, is the rest of the system okay? Plumbing wise, not controls.

 

[dcawkwell]

A wood burner is an uncontrolled heat source.
More trouble than it is worth.

 

[Norcon]

A wood burner is an uncontrolled heat source.
More trouble than it is worth.

It's classed as an uncontrolled heat source but certainly not uncontrollable.

The cowboy who did the bodge job above certainly left it uncontrollable!
One of yours maybe?

PLC indeed.

 

[SimonH2]

Ideally you need a neutral point (buffer tank) to take everything to. This can just be a modest size cylinder, or a larger one (such as a thermal store suggested as an option).

The wood burner should do nothing but heat this buffer - preferably by gravity, but I believe there are ways to do it pumped.
The boiler should also heat the buffer.
Both these can be direct, or indirect with coils - there is "much debate" about the merits of the two options.

Then draw the CH off the buffer with one pump. And draw off for the UFH separately with it's own pump and it's own TMV which is missing from your diagram. Ie the CH and UFH should ideally have separate tapping on the buffer - but if you share tappings, you should tee between the buffer and any pumps/valves and you will probably need motorised valves or check valves to prevent incorrect flows when only one circuit is running.

DHW can come from a coil in the buffer (as a thermal store), or via an external PHE (as a heat bank).

The above will allow for an "any supplies any" setup. But there are many other ways of plumbing it - generally not allowing for any source to supply any load. Whatever you decide, you are going to have to fix the system as it's got several serious faults - some of them dangerous.

 

[nads1978]

Some really good info there Simon, thanks. I have been pondering & unless I can share the header between the wood burner boiler and the oil boiler, then I don't have much option (don't want to take another pipe up through house). But this presents the problem of the systems being linked. I have now been looking at the Dunsley Baker Neutraliser as a way to solve this. It looks to be an 'off the shelf' solution.

Any opinions?
Here is a pic from the manufacturers website:

 

[Onetap]

The buffer vessel/ neutraliser is effective, but all the circuits from it need their own pump, excluding the woodburner IF the gravity circulation can achieve adequate flow.

You could connect the woodburner to the CH return, if the return passes close above the woodburner. You'd increase the size of the return (giving negligible head losses along it, making it a LLH and so the CH pump induces no nuisance flow through the unfired woodburner).

When the woodburner is on, gravity circulation causes water flow from the inlet end of the LLH to the outlet end. The oil burner is controlled by it's own thermostat, which will prevent it firing if the water, from the wood burner is hot enough.

The CH (primary) pump has to run if either boiler is firing. The flow through the unfired oil boiler shouldn't cause any significant heat loss, assuming it's a fanned flue; otherwise it has to be connected as a secondary sub-circuit with it's own pump.

You need to check the pipe sizes can achieve adequate flow through the woodburner. You can fit a pump, but it needs to have a minimum run timer or be speed controlled; a simple clamp on thermostat will rapidly switch the pump on/off/on/off as the woodburner heats up, pump starts and a slug of cold water passes through. The heat dump rad is still required to operate solely undfer gravity circulation.

 

[Norcon]

Also check out system link....
http://www.systemlink.ie/

They provide wiring centres with their kit so its simplifies installation.
PHE options are available also.
Their manifolds are a lot cheaper than dunsleys neutralizers btw.

Their latest header has a twin helical spiral inside to direct water flow which they hold a patent for.

http://www.systemlink.ie/products-59/spirozone.html

Looks like another good invention and innovative product from the Irish.