"Pete C" wrote in message
...
On Mon, 20 Sep 2004 19:24:45 +0100, "IMM" wrote:

Another option is to save on an expensive pump is to put a microbore
pipe alongside the heavily lagged DHW pipe or even inside an oversized
DHW pipe.

This would have it's own pump and pipe stat and be connected across
the DHW coil of the heatbank.

Heat bank has a plate heat exchanger, no coil.

OK, is it a thermal store that's heated by a coil?

Yep. The termninolgy, which has not settled, is that a thermal store has a
coil and a heat bank a plate heat exchnager. Range call their Flowmax a
thermal store yet it has a plate heat exchanger. They are about the only one
who does, and as they started with coils and went to plates I think they
just kept the names up.

In that case you'd connect a DHW 'preheat' circuit across the
heatbank's primary water connections.

Possible. You could have a second plate heat exchanger on the flow fromthe
boiler with the cold mains running though it. It is better to have a
blending valve on the flow/return which ensures only 75-80C water enters the
store at the top and stays there. The store heats up "top down" being
direct. As the DHW plate takes its heat from the top of the store you gain
nothing by having a pre-heat plate on the flow.

There are hybrid stores that have a coil as a DHW pre-heat and a plate.
Mains into the coil, out of coil and into the plate. The flow switch is
adjusted so that the DHW plate pump only energised on high water flows as
the coil can easily do low flows. So no pump hunting.

I wonder if 4 10mm pipes in a 22mm pipe would make a good counterflow
heat exchanger...

Sounds like it would restrict flow.