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dougal
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tawny owl
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Andy B
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giraffe
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Jonnyboy
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dougal
Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
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 Posted: Wed Nov 16, 05 2:52 pm Post subject: |
 
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| Judith wrote: |
| dougal wrote: |
| Note that solar and wood burner could also contribute, as and when, to the same thermal store... |
In our experience, the thermal store / solar water heating combo hasn't been a happy one. Our store was designed to keep the water at a constant 60� C temperature at all times of the day and night. As a result, the boiler would cut in constantly before the solar panels had a chance to do their stuff. This 60� value was fixed, so the only way to get any value from the solar panels was to turn the boiler off altogether - which is not a satisfactory situation. After around a year of arguing with the thermal store supplier, they finally produced a new chip for us - the minimum temperature in the store is now 50�. We would have preferred 40�, but they wouldn't come down that low. |
Judith - there seems to be a communication disconnect or a mistaken design here.
Ordinarily, the solar coil should be in the bottom of the tank, where it can heat the coldest, just arrived water.
The boiler would be controlled by the temperature of water near the top of the tank. Thus the boiler ensures that there is always water available at the appropriate temperature, while the solar system reduces the work that the boiler has to do.
Consolar diagram here.
Note that the boiler *cannot* heat the water at the bottom of the tank...
The basic idea is that the solar tries to heat the whole tankful, and the boiler just "tops up" the heat needed.
It sounds like your system has that back-to-front.
I can imagine that things would be more difficult if a "direct" thermal store were used (where the contents of the tank circulate through the boiler. But AFAIK that would be plain wrong to combine such a design with a solar coil in that store. (One might combine that type of store with a solar pre-heat in a second tank...)
The main reason that I would recommend evacuated tube solar collectors is that they will reach a useful temperature for more of the year. Flat plate collectors may struggle to deliver any heat for 4 or months of the year - but flat plate has traditionally had a big price advantage...
I'm a bit mystified as to what your system might actually be, not least because it would be normal to provide an adjustable thermostat rather than a "chip". There are lots of differences between the things that different people call "thermal stores"...
And it would be normal to have the boiler on a timeclock. There is no point whatsoever in having the boiler 'cycling' at 3am, rather than (if required) having a decent run at 7am... And it certainly should not be needed to have the boiler switched on 24/365.
I think you perhaps ought to call in an independent heating engineer to look at exactly what your system is, and how its being used.
Its quite mainstream, and effective, to combine solar with a boiler by the use of an appropriate thermal store.
And its the normal way in which multiple heat sources would be integrated.
EDIT: long link text tidied up.
Last edited by dougal on Wed Nov 16, 05 3:59 pm; edited 1 time in total |
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judith
Joined: 16 Dec 2004
Posts: 22789
Location: Montgomeryshire
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Northern_Lad
Joined: 13 Dec 2004
Posts: 14210
Location: Somewhere
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dougal
Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
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dougal
Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
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| Posted: Wed Nov 16, 05 3:53 pm Post subject: |
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| Judith wrote: |
| dougal wrote: |
| I'm a bit mystified as to what your system might actually be, not least because it would be normal to provide an adjustable thermostat rather than a "chip". There are lots of differences between the things that different people call "thermal stores"... |
We have a Gledhill Boilermate with the Solarpod attachment. |
Right. I've never heard of the Solarpod, and though there is a mention of it on Gledhill's website, there is no info about it at all.
Gledhill are well established as a high-quality tank manufacturer, though they have not been (themselves) particularly involved with solar systems. (They supply tanks to many systems integrators though).
The "Boilermate" is a basic direct thermal store.
This is a diagram of the Boilermate:
I can imagine that the "solarpod" might well be a secondary "pre-heat" tank as I mentioned in my previous post, above. Essentially, I'd expect it to pre-heat the cold water inlet to the Boilermate in the above diagram. Thus the solar only contributes to the hot water.
The arrangement isn't daft, and should work - but it is very far from an ideal design.
You *shouldn't try to reduce the thermal store temperature.
When solar heated water "passes through" the store it will be "topped up" to the requested hot water temperature by heat from the store.
It will only take out the heat required to 'top it up'.
In summer this should be zero. Which means the boiler doesn't need to fire up to replace that heat.
The disadvantage is just that the store must be hot (boiler heated) to avoid cooling the solar-heated water! (Because the store is super-insulated, this shouldn't be a massive disadvantage).
In winter, its likely very close to the same as without the solarpod - but it should never be more than without it.
Gledhill do offer a "proper" solar-integrating thermal store, the "Torrent"
https://www.gasapplianceguide.co.uk/gledhill_torrent_solar.htm
There's a (big) diagram here
https://www.gasapplianceguide.co.uk/Dia%20large.jpg
where you will note the solar coil working in the *coolest* part of the tank.
And contributing to the *store* - not directly to the hot water. And thereby (potentially) allowing the boiler to be turned off for the summer...
I don't know if Gledhill offer the option, but a coil fron the woodburner could take the place of the immersion element in this diagram. |
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Treacodactyl
Downsizer Moderator
Joined: 28 Oct 2004
Posts: 25795
Location: Jumping on the bandwagon of opportunism
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| Posted: Fri Nov 18, 05 7:46 pm Post subject: |
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| dougal wrote: |
| Treacodactyl wrote: |
| ...Gas may be a good option now but what about the price in 5 years, could it double? |
ALL energy prices are likely to rise.
And that will 'knock-on' into prices of any manufactured or transported item, according to its 'energy content'.
Most UK gas is used for industry and electricity generation, IIRC.
Electricity is likely to remain far the most expensive kwh for kwh, although the relationship between electricity/oil/gas/coal/wood will adjust with market conditions - based on demand, after all, and hence somewhat self-adjusting.
But it certainly makes sense to look to allowing oneself the potential for some diversity... |
While it would seem logical for energy prices to balance in the short term they may not. I remember my mum having an oil fired boiler installed and a year or so afterwards oil prices rising much faster than gas and now I notice whole-sale gas prices have doubled in the last week. 
As industry and power generators are not going to switch to wood fuels for a long, long time, and households are not going to suddenly replace their new gas boilers I would think wood and wood products as fuels to get cheaper. And, of course, you can buy a piece of woodland. |
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dougal
Joined: 15 Jan 2005
Posts: 7184
Location: South Kent
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gil
Downsizer Moderator
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dpack
Joined: 02 Jul 2005
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dougal
Joined: 15 Jan 2005
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Location: South Kent
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