Heat Bank, Thermal store or unvented

[Ed Sirett]

It's like low level noise pollution you don't really notice it when it's there but it's a nice surprise when it goes.

[Ed Sirett]

With Alpha logo?

ROFL.

[Andy Hall]

Dunno.

Who's offering the best deals at the moment?

Mind you, with two combis and one of those magnetic sludge grabbing things per customer, it's pretty easy to be the sales star.

[robgraham]

Hi John - yes I thought it a little odd when you denied your own writings !!

What if the boiler is somewhat more modest - mine for instance is

17kW. Would the same principle apply if it is a direct feed on the basis that even with the smaller heat source, the ratio of boiler capacity to DHW allowance of say 3kW is such that the re-heat rate would be pretty fast, though not 'blindingly'. My mansion is a somewhat more modest than Peter's (the OP) and with only two of us, DHW demand is not great.

Rob

[John Stumbles]

With my own setup on the few occasions that we've run the bank cold (which is inevitably when you've got into a half-full bath and the hot's run cold) it takes just a few minutes to get a reasonable stream of hot water out again. With the non-rapid-recovery conventional cylinder we had before you could, if you were patient, get a trickle of hot water out after a quarter of an hour or so.

Apart from the equivalence of a directly-coupled arrangement to an infinitely rapid-recovery coil I think there's also the factor that even the fastest coil is heating the top half or so of the cylinder by convection whereas in the direct heat bank the hot flow from the boiler is probably getting sucked directly out of the top of the cylinder by the DHW pump. Connecting the boiler flow to the top, rather than side tapping of the cylinder, might help further but I haven't tried it. (If you saw the state of the attic^H^H^H^HSWMBO's junkyard you'd appreciate why :-)

[Peter]

Well - everybody has certaily been giving me food for thought.

It seems to me that a directly heated heat bank with "blindingly fast" recovery is the way to go.

So - I now have 3 further - and related questions:

1. With blindingly fast recovery .. how do I figure out how small the heat store can be? I mean normally, you'd use the calculator for #baths, singks, showers etc. But with my arrangement what I've got is more like a very large water content combi! [ Standard calculator on heatweb suggests 230ishlitres ]

1. I already have, existing, 4 pipe runs to the attic. It is difficult - though not impossible to add more.

If I go for a fully direct system (Rads off heat store as well), then I need a header and expanstion tank in attic. So that means I need pipes: Flow, returm, Cold feed, Vent, Mains Cold. Thats five! So - my quesiton is .... what are the dos and donts about the header tank feeding into the return line? [ If I did this, I get back to 4 pipes again ] I know normally you do it just after an air seperator and just before the pump - but I dont understand why.

1. Alternative to the idea in (2) is to run the rads off a seperate heat exchanges off the heatstore and pressurise just the rads. Anybody got any thoughts about the pros and cons. Ones I can think of are: Yet another pump (would not be up to 4) Not quite as fast heatup separate boiler/heatstore water from rad water (a good thing i think)

Again - very grateful for all the ideas and discussion.

Peter

PS Amazing how ones thoughts change - I realsie that none of the above options leaves me with my rads running off the clever modulating controller - something which earlier on in the disucssion I said was a must-have. Now it just doesn't seem so important.