"Andy Hall" wrote in message
...
On Wed, 16 Feb 2005 10:11:26 -0000, "Doctor Evil"
wrote:


"Andy Hall" wrote in message
.. .
On Wed, 16 Feb 2005 08:00:10 +0000, Tim S wrote:

On Wed, 16 Feb 2005 06:08:37 +0000, John Rumm wrote:

Doctor Evil wrote:

circulation. Each pump can have its speed set to the needs of the
zone.
There will be no parasitic circulation if each zone has its own
flow
and
return tapping off the store.

except you don't want to be running your heating off the store with
a
modern boiler....

Hi John,

Why not - I thought thermal stores assisted the boiler by ensure long
efficient burns?

Tim

This depends on the type of boiler in use.


If you are talking about a conventional one operating at 82 degree
flow and 70 return, then there *could* be a benefit in the approach of
running the heating circuit from the store on the long efficient burn
argument.

However, with a condensing boiler, the greatest efficiencies occur
when the burner is modulated down

Many heat banks run at 75C and many condensing boilers have a flow/return
22C temp differential. If two stats are used to ensure no boiler
cycling,
the stores water is quite cool when the boiler is called to re-heat.
Most
of the burn the boiler will be operating very efficiently. The overall
operation is very efficient. There is also the simplicity of having the
CH
zones off the store (a neutral point). One circuit does not interfer with
the other and are simple to balance. The CH flow & returns are taken off
the
bottom of the cylinder where it is cooler.


This implies that the boiler would be operating in its most efficient
range with 75 flow (and by your numbers) 53 return.

No. When the store calls for heat the bottom will be very cool. This is the
return temp, which is makes the boiler very effcient. Whhe the store warm
sup this will gradually rise. So, for most of the re-heat time the boiler is
operating effciently.

snip


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