Wed, 17 Jun 2026 14:12:14 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57036#Comment_57036 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57036#Comment_57036 Wed, 01 Jul 2009 10:47:50 +0100 jezza22
It struck me that with stratification being so important the tank-in-tank solution will not get the primary water as mixed up as a heat bank as it does not have the heat plate X circuit running through it.

Does anyone know if the tank inside the outer tank is vented or unvented? Chelmer do them and I think they are un-vented and AVC do them but not sure if the inner tank is vented or not?

Thanks]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57054#Comment_57054 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57054#Comment_57054 Wed, 01 Jul 2009 12:29:52 +0100 Mike (Up North) The T in T is just an expansion of the latter as would be S/S as would contain the potable water. It is normal that this is un-vented i.e. at mains pressure particularly if the primary store side is sealed. It’s then just a UV cylinder inside another cylinder which could be sealed or unsealed.
A ribbed cross section is important not just for extra heat transfer surface but also for additional buckling strength.
There is a comment on a thread here which questions the strength of some of the internal welds within the T in T. Worth searching here for all info on thermal stores / buffer stores
Size wise smallest would be about 600-700 lit then upwards. Remember that the DHW will be about 200 lit so the remaining volume is the buffer volume. As the T in T will be in the upper section the buffer volume will be that below it, so perhaps only 2-300 buffer volume at the smallest size.
Cheers
Mike up North]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57064#Comment_57064 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57064#Comment_57064 Wed, 01 Jul 2009 13:36:21 +0100 Johan
An internal coil is better then a PHE as it doesn't require any pumps. However, if your accumulator tank is on sealed system it does require compliance with section G3 in part G of the Buildings regs. I would imagine the T-in-T solution probably should comply to G3 as well.

Mike,

Most larger mild steel stores (having one myself) from Europe normally have internal coils made from extruded/corrugated copper pipe and not S/S. It's easier to get a good seal around the entry.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57073#Comment_57073 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57073#Comment_57073 Wed, 01 Jul 2009 14:22:38 +0100 Tuna https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57083#Comment_57083 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57083#Comment_57083 Wed, 01 Jul 2009 16:24:21 +0100 Johan
Akvaterm is the easiest one to get hold off in UK, but there others if you are prepared to talk directly to the supplier. Stroma imports a tank from TiSun in Austria (very, very nice tank but quite expensive). I bought one directly from Sweden, 750l tank just over £1700 inc. shipping, ex. VAT.

The UK ones are smaller and fairly expensive as they tend to be made from copper (steel is cheap!). As most systems (not to say all) on the continet are sealed there isn't really an issue with the steel rusting, but with the open vented systems used in UK I can see tha appeal of using copper for the tank. That said most modern CH installations are sealed anyway so using a mild steal accumulator isn't a problem.]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57164#Comment_57164 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57164#Comment_57164 Thu, 02 Jul 2009 10:49:44 +0100 Mike (Up North) Actually, I think you are thinking of the other variant I omitted.
The Akvatherm (me) and Capito tanks use a wrapped up copper coil on a flange at the top. One advantage is that a lower flange can be used instead of solar for a DHW pre heat.
The stainless corrugated coils come in at the very bottom do some tight loops at the lower party, then a wider spiral up to the upper part where they then do tight spirals again. These might hold 30 – 40 or in some cases 60 lit of water so, themselves provide some stored capacity.
Typically, the stainless coils are found from
TiSun
Wagner
Windhager
Viessmann
Kloben
Solar Bayer
Solar Focus
Rotex (also do a PEX variant)
Other suppliers such as Hoval or Boiler Nova and any of the ” PS” range of buffer tanks supplier by say Kotly etc etc with the F designation have a blinded flange this can be used for solar or pre heats of lower and DGHW if upper. Most of mild steel tanks are fabricated in Italy where an awful lot of traditional fabrication is still done.
By the way, many of the T in T are actually mild steel enamelled sometimes called glass lined. You get this in the UK for UV cheaper UV cylinders in place of S/S

Cheers
Mike up North]]> https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57234#Comment_57234 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=4221&Focus=57234#Comment_57234 Fri, 03 Jul 2009 02:55:07 +0100 wookey http://www.navitron.org.uk/pmwiki/pmwiki.php?n=SolarThermal.Tanks

Some of those do tank-in-tank variants.

There are quite a few that need adding to that list but Navitron put a password on wiki editing which I've forgotten.

Thanks for above info Mike - very interesting.]]>