I had originally posted this to an existing thread I started, but as
it apperas to be 'just off the end' of the standard 25 message
display .. perhaps people missed it.

Anyway - I'm reporting in the hope people can help me.

Situation in summary is that I have a 45kW boiler currently connected
to an aging unvented copper cylinder.
I'm looking to install a new heat bank which when directly connected
to the boiler should provide (as somebody put it) "blindingly fast"
recovery. I am looking to add rads to the attic at the same time.

The question is where to run the rads from and how large the store
should be:


1. With blindingly fast recovery .. how do I figure out how small
the
heat bank can be?
I mean normally, you'd use the heatweb calculator for #baths, #sinks,
showers etc. But with my arrangement what I've got is
more like a very large water content combi!
I'd want to run a bath and shower and a tap at the same time, and
would want to run 2 baths and two showers within an hour.

2. I already have, existing, 4 pipe runs to the attic. These will
become available for use with the
mains pressure DHW provided by the heat store.
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.


3. Alternative to the idea in (2) is to run the rads off a seperate
heat exchanger off the heatbank and pressurise just the rads.
Anybody got any thoughts about the pros and cons. Ones I can think
of
a
Yet another pump (would now 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.

On 27 Mar 2007 02:26:01 -0700
"Peter" wrote:

From: "Peter"
Subject: Heat bank - one or two plates and other detailed decisions
Date: 27 Mar 2007 02:26:01 -0700
User-Agent: G2/1.0
Newsgroups: uk.d-i-y
Organization: http://groups.google.com

I had originally posted this to an existing thread I started, but as
it apperas to be 'just off the end' of the standard 25 message
display .. perhaps people missed it.

Google groups isn't the usual way of looking at Usenet lists, so no,
very few of us missed it for that reason!

R.

On Tue, 27 Mar 2007 02:26:01 -0700, Peter wrote:

The question is where to run the rads from and how large the store
should be:


1. With blindingly fast recovery .. how do I figure out how small
the
heat bank can be?

I mean normally, you'd use the heatweb calculator for #baths, #sinks,
showers etc. But with my arrangement what I've got is
more like a very large water content combi!
I'd want to run a bath and shower and a tap at the same time, and
would want to run 2 baths and two showers within an hour.

If it weren't for the stratification factor it should be fairly
straightforward O-level physics (though it's so long since I did mine
it's now rocket science to me :-)). In practical and economic terms it
probably comes down to a standard cylinder from Screwfix etc being the
best bangs per buck.

3. Alternative to the idea in (2) is to run the rads off a seperate
heat exchanger off the heatbank and pressurise just the rads.
Anybody got any thoughts about the pros and cons. Ones I can think
of
a
Yet another pump (would now be up to 4)

Is that a problem? They're not expensive. The PHE would cost more (but
needn't be as big or as expensive as a DHW one).