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.
Anyone been this way before?
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:
One 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)
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:
Note the diagram here:
Is 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."
That is for DHW only. It is pointless, and highly inefficient, running CH
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
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
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
It is best to use a stainless steel cylinder and coils (SS coils last
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
> It is pointless,
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.
> and highly inefficient,
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...
Not much in it. It also means you need a vented primary which is less
desirable in many cases.
Interesting article here about the evolution of a solar system;
Part 2 here;
You'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?
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