Next years paper round-2-it design project for me is going to be installing a thermal store/heatbank with a solar collector on the roof and mains pressure hot water for the house.
I would very much like to be able to swap notes and generally get experience from anyone who has gone down this path already. Of particular interest are the makers/suppliers of components for DIY installs and the choice of control systems. Most of my web searches seem to lead to Gledhill products as a market leader but they don't seem to offer systems with plate heat exchangers which I read are preferred in hard water areas like mine.
I spoke to the heatweb folks about their Pandora system a couple of years back. That would do all the things that you want. A bit pricey at about £1,600 at the time for a 250L store, PHE, blending valve etc.
There is a design for a DIY one here:
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of the difficulties is finding a large enough cylinder to use it with, without having to buy a unvented one!
Looking at the DIY system, it would appear that the flow temperature for the rads could be 80 odd degrees which seems a bit too hot really. I've been looking at TMVs to regulate this but it seems that they don't go above 60 degrees. Do you know of TMV suitable for radiator use?
In these days of modulating boilers, with load balancing, pump overrun and all the other efficiency measures built into then, there is nothing like the same incentive to use the heatbank for the heating, unless you have ample additional sources of heat to aggregate into the system (dribble will disagree of course and propose spending thousands in the quest for a further 1%).
It shows the rads being fed form a lower tapping on the cylinder - that should mitigate a bit. You don't have to heat the store to 80 either... (you will just lose some energy density)
You really do not know what you are writing about. Your understanding of heating, thermal storage and all is minimal at best.
The DIY instructions are limited at that wiki site. They assume all has to run at 80C. They have little idea of stratification or condensing boiler operation.
Interesting article here about the evolution of a solar system;
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2 here;
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'll have to sift out the bits that are relevant to you and make allowances for its being written for the USA market. Siegenthaler writes some good stuff.
PS He used a galvanized tank. Something I have discovered unwillingly was that conventional anti-freeze does not work with galvanized tube; probably why he used a drainback system with no anti-freeze.
I don't think solar thermal will provide any worthwhile space heating in the UK climate.
Thanks for your links in your other post. I'm not looking (or expecting) anything useful from the solar thermal collector in the months that I need space heating. My aim is that the output from my solar PV plus the Solar Thermal yield will men that the boiler can stay shut down completely other than when space heating is needed.
I wonder if evacuated solar tubes are OK with a drainback system or whether there is a risk of them overheating on rare sunny days in winter or other times when the water is not being circulated?
Our solar tubes have a glycol-type fluid (I would go and read the label if I didn't have a cat on my knee) and happily went down to -15C last winter and have been at 120C whhen the pump is switched off because the tank was at 70C.
Agreed. It seems the norm to use a glycol based transfer fluid in the UK systems. Sounds like you could recover more energy by raising the temperature setting of your store and provided you have a thermostatic mixing valve on the output of the DHW The drainback system in the article had air in the circuit which could lead to corrosion problems hence his custom built galvanised tank. It was also 350 gallons!! even allowing for smaller US gallons it was huge
I guess from your position, minimal must seem like a a long way up.
You will have to forgive dribble, but his reading and comprehension level are not very advanced.
Stratification is explained here:
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the diagram here:
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showing a store configured for DHW production specifically rather than also running the radiators. Needless to say, its easy enough to adapt the same concept to allow the rads to run from a lower tapping on the store if required.
Again..."You really do not know what you are writing about. Your understanding of heating, thermal storage and all is minimal at best."
directly from a boiler when a store of water is available. Having CH off the store using a Smart pump and TRVs on all rads means no central room thermostat is needed adding to comfort condition and simpler control. A boiler heating only a DHW/CH store operates at it maximum efficiency enhancing condensing efficiency. The boiler's longevity is greatly promoted.
That arrangement will destroy stratification, unless the pumps speed or volume is controlled in pumping water back into the cylinder.
The OP is using solar panel where the stratification levels have to be maintained, especially in winter,to get the most out of the panels. Otherwise he may end up with low grade heat inside the cylinder.
In this setup the OP is best having a coil for CH take off to separate the CH rads from the cylinder water to avoid sludge build up.
He is "probably" better off having a solar coil in the store heated by the panels - although done right heating he water directly is possible and more efficient. He is also "probably" better off having DHW take off via a coil as this will not destroy stratification. Or a control mechanism to only allow the correct volume of water enter the cylinder complete with anti stratification baffles.
It is best to use a stainless steel cylinder and coils (SS coils last longer). It is best the amateurs stay out of advising on such matters otherwise it will end in tears.
No shit sherlock. I see you did actually manage to understand when I said "Is showing a store configured for DHW production specifically rather than also running the radiators", well done the tablets must be working.
Well no, it give you mains pressure potable hot water for all the house with the flow rate not limited to what the boiler can heat on the fly. Does not require G3 certification, has an external PHE for improved serviceability in hard water areas. It also allows easy integration of other heat sources into DHW production.
That makes no sense really.
Simpler control huh? You need to drag yourself out of the '70s dribble. Modern boilers can reach seasonally adjusted efficiency figures well in excess of 90% without any type of store, without weather compensation, and often without even condensing while producing DHW with controls no more sophisticated than a room stat, and some TRVs. If all you seek are efficiency gains, then the hard reality is that there are very few remaining to be had. Adding external temperature sensors to boilers that support them, and can do weather compensation, remains about the only cost effective one.
Now if you have a store and another large source of heat available such as a wood burner, then using the store to run the rads as well will be worthwhile. As might be the case if you can make use of large quantities of warm rather than hot water for space heating - such as with UFH. However its unlikely to be worth the effort if your only other heat source is solar thermal - since its contribution to space heating requirements in our climate are likely to be negligible.
Pretty much the case these days with just the rads as well - certainly on medium and larger systems anyway.
Who by, a salesman such as yourself?
See your comment about baffles below...
Agreed.
Not much in it. It also means you need a vented primary which is less desirable in many cases.
It is 70C at the bottom of the store, so it will be higher at the top. I didn't fit the system and the manualks are in German, so I have never considered changing the setting (which I don't know how to. I assumed it is at that temperature for safety reasons. Boiling the water might be pretty catastrophic!
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