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Author Topic: Two stoves, Dunsley Neutraliser, Thermosyphoning  (Read 10447 times)
Greenbeast
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« on: February 03, 2010, 09:18:22 AM »

Further to my thread in the solar thermal area, my step-father is possibly wanting to connect two wood burning boilers to one cylinder coil.
The stoves are at either end of an 11m house and the cylinder is two floors up in the middle.
Can he get these stoves to thermosyphon, i guess he has to given that they are uncontrolled heat sources?

Can someone explain why two stoves can't be piped together, if gravity fed, surely the hot water isn't going back down the pipe to the wrong stove in that situation?

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dhaslam
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« Reply #1 on: February 03, 2010, 10:34:00 AM »

If one stove is hot  it will increase the pressure in  its flow  to the cylinder.   If the feed from the other stove is connected the pressure would drive the  heat the wrong way down to the other stove and  the other stove's return would also  be in reverse.    If you then light the second stove the flow might continue reversed or it might  not.    Either way it could be quite spectacular. 

Is it necessary to connect both stoves to the cylinder?   If one is used less often it will heat up easier and need less fuel if it doesn't have a boiler.   
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Greenbeast
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« Reply #2 on: February 03, 2010, 12:08:35 PM »

fair enough thanks for that.

Will they thermosyphon over 5m horizontal (or perhaps at a slight incline) and 8m vertical?
if he wanted to pump in addition, would we need a laddomat for each stove?
is it worth pumping?

i'll enquire about not using a boiler in the one of the stove
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dhaslam
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« Reply #3 on: February 03, 2010, 12:23:26 PM »

It should work OK.  My last house had  about two metres vertical rise and eight metres horizontal.     For a small cylinder there shouldn't be any need for  thermostatically  controlled  return  to the boilers  but this assumes that there will be surplus heat which is circulated to radiators once the cylinder is hot.   The Laddomat is a bit of an overkill  but this type of  control is needed when heating a large volume to avoid cold water return and  to aid stratification. 
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Richard Owen
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« Reply #4 on: February 03, 2010, 03:37:27 PM »

I think the answer is, at least partly, in the title.

Connect the stoves to a neutraliser and the neutraliser to the coil and you won't have to worry about reverse thermo-syphoning.

If you think the laddomat is overkill, I'd still put a loading valve on the return to the stoves so that they run as hot (and therefore as efficient) as possible.
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« Reply #5 on: February 03, 2010, 06:25:42 PM »

Richard,

When you say 'put a loading valve on the return' any chance you can explain how you would do that without using the likes of the laddomat?

I have an oil boiler and WBS with back boiler hooked up via a Dunsley so of course, you have my interest.......

Thanks,

Ian.
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Richard Owen
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« Reply #6 on: February 03, 2010, 10:42:38 PM »

A loading valve is just a passive version of a laddomat.

They come in a variety of temperature settings and when in operation they short circulate the water around the boiler until it's up to temperature and then let the hot enough out to the tank.

I don't have details to hand, but it's been discussed a few times in this section of the forum.

Try searching on loading valve and see what happens.
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44 Yingli 230Wp panels feeding into 2x Solar Edge SE5000 inverters.
20x 58mm SE, 20x 58mm SW, Solar Thermal feeding 320l thermal store.
10kW heat pump.
300W of Hydro Power.
dhaslam
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« Reply #7 on: February 04, 2010, 10:26:48 AM »

This is a link  to previous  discussion on loading valves.   The 4043B valve in 28mm costs about 40 and you need pipe and fittings for the bypass  and a pipestat. 

www.navitron.org.uk/forum/index.php/topic,8886.msg95516.html#msg95516
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Tigger
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« Reply #8 on: February 04, 2010, 10:34:59 AM »

Cheers guys, I think I can just about afford 40.  It's a job that will have to wait until the warmer weather though, I don't want to be without heating right now.

Ian.
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SN15 (Wiltshire) 30 tubes, south facing gable wall (Navitron Fornax Trial System).  Hunter Herald 8, integrated boiler hooked up with Oil Boiler via H2 control panel.  Scrounging fire wood wherever possible Smiley
Brandon
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« Reply #9 on: February 04, 2010, 05:58:56 PM »

A loading valve will not however work on a gravity circuit, it requires a pump, and there for a gravity safe route for power outages.

This thread may help, as this has already been thought through.
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changing the world, one roof at a time.

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« Reply #10 on: February 04, 2010, 08:49:30 PM »

That only applies to the EBSE  valve.  The electrically operated valve  opens  in a power out.      I haven't had any problems  with mine.   
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DHW 250 litre cylinder  60 X 47mm tubes
Heating  180,000 litre straw insulated seasonal store, 90X58mm tubes + 7 sqm flat collectors, 1 kW VAWT, 3 kW heatpump plus Walltherm gasifying stove
Greenbeast
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« Reply #11 on: February 05, 2010, 10:46:10 AM »

Regarding loading the stoves would this work:

The Normally open MV would be controlled by a pipe stat at the boiler flow, so so with power available and fire lit, the valve closes and the pump runs.
The TMV opens up as the temp increases
In the event of a power failure, the pump stops ovbiously and the valve opens allowing standard thermosyphon flow

Or have i missed something?



obviously i've excluded feed/expansion pipework and tank.
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Brandon
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« Reply #12 on: February 05, 2010, 09:02:53 PM »

I would put the pump on the return, and you need to isolate the valve from the thermo siphon.

Reply #9 on the thread that I linked to is the easiest way to do what you want without a complete loading unit, you can ignore the flow and return coming in from the right, and just use the ones going vertically, as the drawing was done for a layout with pumped heating as well as back end protection on the Rayburn.

I would also encourage the use of a flue stat over a pipe stat, as the pipe stat may well be above the set temperature even when the fire is out due to the heat from the cylinder/store being pumped through it.


DH, I was, as you correctly pointed out talking about a thermostatic valve, given that the question was for a loading valve.

Hope that helps

Brandon.
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changing the world, one roof at a time.

Quality is never an accident; It is always the result of
high intention, sincere effort, intelligent direction, and
skilful execution; It represents the wise choice of many
alternatives.
Greenbeast
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« Reply #13 on: February 05, 2010, 09:37:40 PM »

thanks, i must have missed that drawing otherwise i would have realised sooner
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