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Author Topic: How to connect hot water cylinder as thermal store to wood stove & heating  (Read 4345 times)
TangentTwin
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« on: February 10, 2008, 09:27:31 PM »

List,

It is my intention to move my existing hot water cylinder and replace with a twin coil solar cylinder, the old cylinder will be then placed in the upstairs space above the new wood burner with a back bolier.
I then intend to connect the cylinder in reverse and have the main body of water as the storage, fed by a small feed and expansion tank.
The indirect coil I then intend to connect to the heating circuit of my system via a motorised two port valve and pump controlled by a pipestat.
The idea is for the cylinder to heat up and only pump water into the heating circuit when the cylinder is hot.

Any ideas orcomments would be welcome,

Rich

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Ivan
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« Reply #1 on: February 10, 2008, 09:33:02 PM »

Hmm. The main problem is that your heat output from the standard cylinder coil will be lousy - not enough to impact much on the central heating, but then again, it may be able to go as fast as the woodstove inputs heat, so it might not be a problem.

Have you considered using a heat exchanger of some kind? Or  a couple of dedicated radiators connected to the woodstove (this is what I've got). Also, consider getting a triple coil hot water cylinder, so that you can input heat from solar, boiler or stove. In practice, we find that we can be virtually 100% dependant on renewables (solar or woodstove) for hot water throughout the entire year, without having to put the woodstove on specially to heat water.


Ivan
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TangentTwin
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« Reply #2 on: February 10, 2008, 09:47:44 PM »

Ivan,

I have thought about linking the indirect coil to a retrocoil which will be also fitted to the old cylinder to give a larger heat transfer area.
I originally thought about trying to use a triple coil cylinder but the existing cylinder is on the ground floor so the problem is trying to link the gravity circuit with the cylinder.

Rich
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Ivan
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« Reply #3 on: February 10, 2008, 10:08:08 PM »

No, you wouldn't get enough surface area even with the additional coil...and the cost is increasing. For our custom cylinders,Navitron offers a 'underfloor heating coil' - off the top of my head, this is around 4m2 (though I'd need to check). Even this is insufficient to run a household radiator system, although it works ok on an underfloor heating system, as it has a much slower demand for heat.
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TangentTwin
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« Reply #4 on: February 10, 2008, 10:32:13 PM »

Hi Ivan,

The store doesn't have to run the heating it's really just to disappate the heat load from the stove as it's rather overkill for the room ( secondhand bargain couldn't refuse ) but I take on board what you are saying.
It will be one experiment! we will see what happens.

Cheers,

Rich
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Bargeman
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« Reply #5 on: February 10, 2008, 11:36:27 PM »

Hello Rich,

Another alternative configuration would be to create a direct connection from your 'thermal store' to a neutraliser creating a link up system with the boiler and CH circuit. Put in a couple of Essex flanges (28mm) on the old tank and forget about the coil. Wood stove heats the primary water and pumps from the heat store to a neutraliser under control of the cylinder stat. Pretty much a solution I'm implementing at the moment where there is no obvious route to link a wood stove directly to the main heat store.

 regards
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Ivan
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« Reply #6 on: February 13, 2008, 01:31:05 AM »

Oh, ok. So you probably want to strip off the insulation then? And use the tank itself as a radiator. Having said that, you could consider not using a tank at all. I have gravity feed on my woodstove to two radiators and the cylinder. When the cylinder gets hot, all the heat ends up going to the two radiators. You could just have the radiator(s). I find it makes a huge difference in that it helps distribute the heat upstairs, without having to leave the living room door open and associated draughts.
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Cliff top
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« Reply #7 on: February 21, 2008, 11:34:47 PM »

FWIW

I got a thermal store tank from Navitron just before xmas.  Luckily it came with 28mm connections direct to the tank as we found that the flow from the boiler up & through the 22mm unions and into the boiler coil wasn't sufficient- not blocked, just very difficult to push water through. Anyway glad the 28mms are there. We now use the boiler to gravity up HW to the tank water itself- works spot on to stop the boiler 'boiling' and having fitted a pump in that circuit we can later pump the hot water back down into the boiler and then off to the rads-  great for a quick start on a cold morning, but you only get 1hr at good temperature and another at mediocre heat before the reservoir is all cold.
Mind you its only 260L and we have 11 rads in use with lots of long microbore runs too Sad
It would work as Tangent twin wants. Wouldn't give you hot water for the taps though unless you have the high recovery extra coil fitted-  we specced that on ours and although a bit pricy for a few turns of finned copper pipe and a mixer valve- it works well- 

System doesn't use a neutraliser

Plus we have very soft water up here- I gather hard water areas will clog up the recovery coil piping in a few years

Looking forward to when I've saved up for the solar coils to add to it...not sure if it would be likely ,say with 30 tubes, to provide any radiator heat besides hot tap water though.
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Glass half full...half empty....As an engineer it's obvious the glass is twice as big as it needs to be
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