hughpinder
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| posted on 22/10/10 at 07:12 AM |
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Central heating problem
This problem is a bit different to your usual CH problem:
I heat my house using a straw burner in the winter. I have an oil fired boiler too thats usually just used for hot water in the summer. Both these
circulate water through the coil in the hot water tank to heat the tank. The tank has a second coil to do instant mains pressure hot water. The
central heating circuit circulates the water in the body of the tank round the radiators.
Here is the problem - the heating coil that the oil/straw burner use is leaking into the main part of the tank. Since the central heating header is
in the loft at about 10m, and the straw/oil boilers have an open vent at 3m water is being pushed through and out of the vent.
The options are:
1. replace the tank - the new model of this tank has all the ports in different places and this would be a bit(lot) of a pain to install(plus the tank
costs about £1200!!!).
2. I could pretty easily fit a swimming pool type heat exchanger plus an extra pump into the straw/oil boiler loop with the other side connected to
the tank coil and vented to the loft overflow This would isolate the two sides from each other again. This would be much cheaper, but would involve an
extra pump+some pipe work, and I'm not sure that the 230,000 btu rating is really that (the heat exchanger just looks too small). Anyone had any
experience of these?
What do people reccomend - any other ideas or other CH tanks - the one in at the moment is an 'albion mainsflow indirect MF30/210'?
Regards
Hugh
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cliftyhanger
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| posted on 22/10/10 at 07:48 AM |
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my thoughts are that a swimming pool heat exchanger may be designed to hest to mid 30's max, so may not be ideal for what you require? combi
boilers obviously use heat exchangers, which are very effective but can block easily (ask me how I know).
I suspect you need to bite the bullet and get a proper job done. What about some of the stainless tanks that are available. should be a very permanent
solution?
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tegwin
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| posted on 22/10/10 at 07:54 AM |
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I think you may find that a suitably sized plate heat exchange/pump/controller etc is the same price as a new tank!
Shop about online and you might be able to get it for less....
Unless there is anway of repairing the split coil, I would put a new tank in.
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markt0121
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| posted on 22/10/10 at 11:10 AM |
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I think you only need a tank with one coil if the water in the tank is never supplied to the taps. I think this is what you have at the moment as you
are circulating the water in the tank through the radiators. You could modify the plumbing to circulate the water of the tank to your boiler.
Either:-
1. Tee off the radiator feed from the tank to your boiler feed, then connect the boiler return to the radiator return.
2. Take the radiator feed from the tank to your boiler feed, then connect the boiler return to the radiator feed.
3. Change the system to a Y plan or S plan type.
Which one you choose depends how the boiler is controled. If it has it's own circulating pump then it's probably easiest to use option
1.
But I think the best option is 3. Advantage is that the feed from the boilers would be direct to the radiators and you would not need to heat all the
water in the tank before you get any heat to the radiators.
You could probably re-use the circulating pump from the radiator or boiler circuits, but might need to add a valve or two depending on what you have
at the moment.
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markt0121
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| posted on 22/10/10 at 11:20 AM |
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Just to try and clarify on option 3 above.
You keep the existing tank and keep using the coil to provide mains pressure hot water. Connect up the S-plan or Y-plan heating system controls to
heat the water in the tank.
If you can post a diagram of how your boiler and radiators are controlled, any pumps or controled valves, timer controls etc. then I might be able to
suggest a layout to re-use what you have.
I'm not a proffessional plumber or heating engineer, but I have done quite a lot of DIY.
Not sure if you would need to get a professional to do any work on the system, but if you are not doing anything to the boilers themselves then I
think you would be OK.
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hughpinder
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| posted on 22/10/10 at 11:27 AM |
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Thanks for the replies.
markt0121, I don't think that I can connect the boiler feed to the radiator circuit, as the boiler circuit is open vented and below first floor
level - they must be physically separated.
Unfortunately I think replaceing the tank is the only option, its just quite a lot of cost and work (I have found some suitable tanks that are a bit
cheaper)
Thanks again
Hugh
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markt0121
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| posted on 22/10/10 at 11:36 AM |
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Do you have two header tanks, one for boilers and one for the water in the tank?
If you try what I suggested you would need to remove/disconnect one of them.
I think you should keep the one in the boiler circuit, so you don't change the water pressure in the boilers. But this would only work if the
boiler header is higher than the water tank.
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markt0121
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| posted on 22/10/10 at 11:43 AM |
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Just saw your message about the boiler header below the first floor. You could only do the modification if your boilers can take 10m head of water and
you'd need to be carefull that the vent for the boiler system was correct. I think you'd need a heating engineer to check it out, then it
probably costs more than getting a new tank.
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hughpinder
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| posted on 22/10/10 at 12:46 PM |
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The boilers can both take the static head from the loft expansion tank, I know this because I've just re-plumbed it to separate the two
circuits. I did this because of a problem with the 'straw burner' - if you over fuel it, or get a very strong wind that sucks the air
through too fast, it is possible to boil the water in the system. With the expansion tank in the loft, this tends to cause an overflow into the
loft/upstairs bedrooms.
My solution was to try and separate the radiator system from the heating system. Unfortunately with the old setup the problem with the coil was not
apparent (it may have been a boiling session that burst/split/caused leak in the coil), but since it was all linked, no problem.
To make the problem worse, I have added a 3m3 thermal store, with built in expansion volume, to the straw burner, so that it should be much more
difficult to boil. This does mean the thermal expansion volume is now bigger than the loft tank (4% of the whole system is about 150l), so I couldnt
even make a temporary change (until spring) to restore the old vent and blank the thermal stores open vent.
Thanks for your ideas though
Hugh
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