wood burner and unvented cylinder

[Biggles..]

The dunsley doesnt show the secondary pump in their drawings feeding the cylinder i think, they appear to rely upon the heat leak radiator dissipating the heat and the 2 port ensuring the cylinder does not heat through the gravity flow or boiler flow.

Would having the 2 port satisfy the regs as this is turned off by a stat.?

 

[Onetap]

The dunsley doesnt show the secondary pump in their drawings feeding the cylinder i think, they appear to rely upon the heat leak radiator dissipating the heat and the 2 port ensuring the cylinder does not heat through the gravity flow or boiler flow.

Would having the 2 port satisfy the regs as this is turned off by a stat.?

http://www.dunsleyheat.co.uk/linkupsys.htm

They show the oil/gas boiler in series with the HWS cylinder and the pump on the return pipe from the neutralizer to the boiler. It's not a good arrangement, the water will tend to flow directly back into the neutralizer, rather than flow through the HWS cylinder coil.

You've got to use the 2-port (spring-return shut) zone valve that is supplied with the unvented cylinder. You need the secondary pump, or you'll get no flow through the secondary circuit. The 2-port zone valve is operated by the thermostat and the end-limit switch on the zone valve operates the pump when the valve is fully open.

 

[Balenza]

Onetap wrote

It's not a good arrangement,

Which is why its best to chuck the neutralizer and the unvented cylinder idea( and their myraids of controls) and just fit a decent (one size fits all) thermal store.

 

[Onetap]

Onetap wrote

It's not a good arrangement,

Which is why its best to chuck the neutralizer and the unvented cylinder idea( and their myraids of controls) and just fit a decent (one size fits all) thermal store.

I meant the arrangement of the pump and cylinder in the Dunsley diagram. If you want unvented HWS and a solid fuel boiler, the above is one way to do it. I would be very dubious about an average domestic plumber connecting an unvented HWS cylinder to a solid fuel boiler.

There's not many controls on an unvented cylinder.
Thermal stores have their own set of problems.

 

[htgeng]

I would also say that a thermal store would be the best solution in this case.

 

[billy bob]

Times have moved on, it is possible to now purchase solid fuel boilers that are designed to run unvented heating and can supply unvented cylinders have a look at www.windhageruk.com

 

[Balenza]

Times have moved on www.windhageruk.com

As have thermal stores.

 

[julybravo]

Hi, sorry I'm new to the site and only seen the topics today. This one very interesting as I am planning something similar and would appreciate any advice or comments.
I've no mains gas and fuel oil is expensive, hence want to rely on renewables (and a heat pump)
Central heating has a 213L vented heat store cylinder with a coil for solar. The WBS will be the main heat source. From the heat store the circuit pumps first thro the rads, then via the underfloor heating and back to the store. The heat pump is between the rads and the ufh so that when the fire is off first call for the heat pump is to the ufh with balance to the store. The rads will get a little warm until the fire is lit or the sun comes out. When the water in the circuit reaches 45 or 50C the heat pump will cycle off (so i'm told). The solar circuit will prioritise DHW then when this is 60C it will route to the heat store.
The DHW (unvented twin coil cyl)also has a pumped loop through a coil from the WBS. Reading all the comments I am now more confident that I have sufficient security if when the DHW reaches 60C, the circ pump will stop and the spring return valve will close. I was thinking about another safety angle to tee off another valve (power to close, power off open) which would vent the water from the WBS in event of a power failure, it would be replaced by cold water from the header tank. Would this be an overkill? Is my plan to route return from the rads into the underfloor heating circuit ok? (rather than a separate pumped system)[/img]

 

[julybravo]

sorry I'm having difficulty loading the picture. hope this is now OK and clearer

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• julybravo
• 10 Dec 2010
• 1

[/img]

 

[Norcon]

The connection between the stove and uv cylinder is a no no.
Read onetaps posts again.


I would integrate this system into viessmanns vitocall 300 design.
Page 29-system 2.
http://tiny.cc/13d2l

Only have an extra 3 port divertor fitted to facilitate operation when the store temp is above the heat pumps set point and hw calling to give priority to the sf and allow pump 4 to heat hw without the immersion operating.
After pump 7 use zone valves/manifold actuaters for radiators and ufh
Connect the solar to the lower coil for hw only and hp and sf to the upper coil.
Sf connected to extra tappings on the store with the usual venting arrangements.

You need a clear plan before undertaking a project of this nature or it will leave you with a severe headache.
You will have 4 separate heat sources for HW and 2 for the CH.
Look into Danfoss avta cooling valves integrated with a heat leak radiator or SCWS (safe cold water system) integrated with a coil to provide extra heat dissipation. Certain manufacturers integrate scws with their stoves. I would strongly recommend cad design for plumbing and electrics.

 

[GaytonTonner]

The Dunsley neutralizer is just a high-priced, low-loss header. A thermal store would achieve the same effect.

He is better off using a thermal store in this application. Safer, easier and perfect for mixed heat sources.

 

[Onetap]

Is my plan to route return from the rads into the underfloor heating circuit ok? (rather than a separate pumped system)[/img]

Strange; have you employed someone to design this for you?

The UFH will only work when the radiators are on. You'd usually want the UFH to be able to run when the rads are off, due to its high thermal capacity and long warm-up times. The intention seems to be to use the CH return to supply reduced flow temperature for the UFH. I'd suggest a TMV or a motorized mixing valve.

Similarly does the ASHP only run when the rads are on? What happens when there's no demand for heat and the TRVs have shut? A separate circuit would be better.

There will be no circulation between the thermal store and DHW cylinder without a pump, unless the solar pump is supposed to do that; circulating hot water through the solar panels on dark winter nights is not a good idea.

 

[julybravo]

Many thanks for all the responses received, I've made a few changes accordingly.

[Norcon: The connection between the stove and uv cylinder is a no no]

OK, I can provide a separate pumped circuit from the heat store. This will mean the WBS will dissipate heat only by convection, will this be OK?

[Norcon: I would strongly recommend cad design for plumbing and electrics]

What I've done is to simulate all the conditions with the actual valves and thermostats on my kitchen table. I connected them according to the Honeywell sundial wiring diagrams which I found on the net, they are very informative. I powered everything up (very carefully) to make sure the valves were opening and closing at the right settings.

[Onetap: Strange; have you employed someone to design this for you?]

No, onetap, can't afford that. I did it myself, I've learned a bit of AutoCad in my employment.

[Onetap: The UFH will only work when the radiators are on. You'd usually want the UFH to be able to run when the rads are off]

Good point, I've made a change and will fit a three-way valve before the rads. This can bypass them and direct water around the heat pump and uf heating when the storage cylinder water is less than say 60C. Above that the valve will direct hot water as originally piped. I'll have two of the bathroom rads with no TRVs just to be safe

[Onetap: There will be no circulation between the thermal store and DHW cylinder without a pump, unless the solar pump is supposed to do that; circulating hot water through the solar panels on dark winter nights is not a good idea.]

I hadn't planned for circulation between the thermal store and DHW cylinder. The solar circuit is intended to pump as priority (with its own pump) to the DHW cylinder, at which time the loop into the thermal store will be effectively a dead leg. When the DHW temp reaches 60C, the solar flow will change over to the thermal store and there will be no flow through the DHW coil. There is a cut out on the solar unit to prevent it pumping when it is not developing heat.

[Gayton Tonner: He is better off using a thermal store in this application]

I'm a little confused by this. I thought that my vented 213L storage cylinder with all my input and output connections would actually be a thermal store (sort of).

 

[Onetap]

Many thanks for all the responses received, I've made a few changes accordingly.

There's an article here that may give you some ideas;

http://www.pmmag.com/Articles/Column/7df8232b040d7010VgnVCM100000f932a8c0____

Part 2 of the article is here;
http://www.pmmag.com/Articles/Column/c6f0232b040d7010VgnVCM100000f932a8c0____

The system described is solar, with a thermal store and an unvented water heater; there was a wood burner but it was later removed. The system is in the US so some of the design is unusual for the UK and the space allocation is larger.

You need a device to maintain the pumped return temperature to the wood burner above about 56 degC, otherwise the pumped circuit will cause rapid back-end corrosion. The gravity circuit is self-regulating to some extent.

If this is not a gasification boiler (expensive) that is designed for pumped circulation, I'd forget it. A cheaper one-stage wood burner will suffer from tar deposits on the heat exchanger surfaces; a gasification boiler burns the tars and volatile compounds emitted by the hot fuel in the secondary combustion stage.