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Author Topic: Back boiler temperature  (Read 8374 times)
Amy
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« on: April 27, 2010, 08:23:32 AM »

Im going to install a multifuel stove with backboiler.

I anticipate using coal overnight to keep the fire in on tickover but wood the rest of the time

What sort of temperature can I expect the water to reach in the backboiler and how far do I have to run 22mm copper before I can change to HEP?


Should have mentioned its a 5kw Morso Squirrel
« Last Edit: April 27, 2010, 08:26:59 AM by Amy » Logged

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Billy
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« Reply #1 on: April 27, 2010, 09:27:48 AM »

Hi Ames,

I run a Squirrel with the 2kw stainless back boiler on a gravity system.  I have pipe thermometers on the flow and return.  The maximum flow temperature I have seen is 72C at 1metre.  You could get more I suspect from coal but only if you fire it well.  I also have big pipes (11/4") which moves the heat quite quickly.  Low fire temperature is around 40C.

It also depends on what sort of size your rads/tank are.  I can get rid of the heat without any problem but if the tank is hot and the rads are not that big then the heat can build up.  This is not too much of a problem if the stove is on tickover but can you guarantee that, I always panic when someone is barge sitting for me. facepalm

If memory serves me right the distance for a gas/oil boiler is 1m but not sure if this is ok for solid unregulated particularly without a pump (but they can always fail).

If you are going to be on inland waterways then I think there are new regs for fitting solid fuel stoves after all the recent problems.  When I fitted mine three years seven year ago they were in draft stage.  Just a thought and how time flies.

I will stop waffling now, sorry.

Billy.

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« Last Edit: April 27, 2010, 04:04:00 PM by Billy » Logged
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« Reply #2 on: April 27, 2010, 03:25:00 PM »

Amy - I don't know your whole feelings on coal burning - but friends of ours with an Esse wood fired range cooker use my wood briquettes to keep the fire in overnight. Cleaner burning and a LOT less garbage to clean out of the fire - which would be pretty much a daily chore using coal on a Squirrel. And of course carbon neutral, sustainable etc etc blah blah!!

Andy
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Amy
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« Reply #3 on: April 27, 2010, 07:18:23 PM »

Andy,  - what ever works best, I have no fixed agenda, coal or briquettes are fine.

Billy,  Youve made me wonder if its all such a good idea now. If it produces too much heat, which im sure it will after a couple of hours, then im gonna need more than 100 lts of hot water tank as a heat dump. I wasnt planning on adding rads as the squirrel will be in the middle of the boat, calorifier at the stern, and at least one rad needed at opposite end, all a potential problem for a no pump system. I was going to reply on warm air convection/circulation.

Maybe I could put a rad / towell rail in the bathroom, halfway tween fire and tank, but when happens when that hot too, then where does it all go?

I just thought it was wise to optimise the heat output and save running the engine for hot water.
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« Reply #4 on: April 27, 2010, 07:45:51 PM »

amy, a towel rail will keep chucking the heat out provided that there is no TRV involved, leave the door open and you'll be finr, but I would urge the use of copper all the way.
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« Reply #5 on: April 27, 2010, 07:50:10 PM »

I was hoping to get onto Hep as soon as possible to make the bends easier, but hey ho.

Still not convinced its going to circulate ok by convection as Im going to struggle to get any rise on the pipe from boiler to tank
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Billy
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« Reply #6 on: April 27, 2010, 10:04:29 PM »

Ames,

My rise is only 50mm/metre and that is double what was recommended.  I did that because we don't always settle level when the tide leaves us.  If your boiler is 2kw max then just make sure your system can get rid of it, then no problem and it is nice to have a warm bathroom.

Billy

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« Reply #7 on: April 27, 2010, 10:23:13 PM »

Im still stuffed Billy

The calorifier will lie on its side on a shelf in the engine room, 24'' above main floor level, same floor the stove is standing on. I anticipate the top outlet from backboiler will be 18 -22'' above the floor, and a run of 8 mts to calorifier, im out of luck on the rise ratio
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Billy
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« Reply #8 on: April 28, 2010, 07:26:48 AM »

Reckon you are then.

I am experimenting with taking the boiler out of the WBS for next season at it don't burn as well with the boiler.  The boiler temp never gets really hot so it cools the fire and I get lots of tar.  We'll see.

Hot water, I got 20x48mm tubes but the turntable for the wheelhouse roof has taken a back seat what with everything else going on.

Best think again and come up with another solution.  I put my calorifier on a plinth and it's vertical but it was still marginal.

Billy

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Amy
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« Reply #9 on: April 28, 2010, 07:43:48 AM »

I guess I just bite the bullet and get a 12v heating pump, and do it that way.

Its too much of a heat source not to make use of, and it gives me backup to the engine method of water heating
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Billy
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« Reply #10 on: April 28, 2010, 07:48:06 AM »

Have you seen the price of them 12v circulating pumps?

I thought it was cheaper to get a dedicated inverter and run a mains one but it uses more watts.  There are some that are very frugal 3-5w.

Don't forget the heat sink if it fails mind.

Billy

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Amy
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« Reply #11 on: April 28, 2010, 08:02:30 AM »

I havent looked into the cost of the 12v ones yet.

I guess 240 is better. How many watts do they draw?
I could wire it to a pipe stat near the backboiler
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Billy
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« Reply #12 on: April 28, 2010, 09:22:50 AM »

Depends on the speed setting but the normal  (Grungefos) CH pump draws about 40-65-105w +/- but you can get lower ones for a price.  I guess you could do something with a stat on the tank to call for heat and a pipe state for when there is heat.  Sounds good, but it would be nice to have all the heat going to hot water without dumping to the heat sink.  Motorised valve perhaps but is that fail safe for the heat sink?  That's the problem with unregulated heat source I guess.

Billy

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Amy
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« Reply #13 on: April 28, 2010, 09:42:14 AM »

I have thought about a 3 port valve to divert to a bathroom underfloor coil or towell rail.

A tank stat calls the 3 port to divert to tank when cold, then when up to temp, open to bathroom.

Normally open setting to bathroom, diverted to tank.
Nah that cant work, it would have to be  S plan not Y.
When the tank is cold, it would constantly call for heat and power the valve closed to bathroom and open to tank, and that would use un nesessary power
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Billy
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« Reply #14 on: April 28, 2010, 10:14:39 AM »

All this non standard stuff takes time to work out as I found out but there is normally a way round things somewhere.

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