"Pete C" wrote in message
...
On Thu, 23 Sep 2004 12:28:20 +0100, "IMM" wrote:

Gledhill do not have a flow switch. They use a temp senor on the DHW
draw-off that times the rate of temp change and modulates the pump to
suit
to maintain a DHW draw-off temp of 55C. If low flows a low pump speed.

Sounds like a DIY electronics project in there.

That is why it is best to have a
hybrid heat bank: a coil and a plate heat exchanger. The coil for low
flow
rates, where no pump operates and the plate with pump for high flowrate.
Only when high DHW flows will the pump and plate cut in. The coil also
acts
as a pre-heat to give higher flows in winter when the mains water may be
colder, although a correctly sized plate would make no difference.

Could an immersion cylinder be used as a heat bank?

A cheap plain direct cylinder can be used. One with a shower tapping on the
side for the flow from the boiler, and have two tapping at the bottom (Range
have these mostly as standard) One bottom tapping for the return to the
boiler and one for the return from the plate. the draw-off at the top is the
flow to the plate. Have two strap on cylinder stats to prevent boiler
cycling. The top stat set to approx 65C and the bottom to approx 70-75C. A
relay is required using these and latching is required. When starting from
cold the store heats up and the boiler is cut out when the bottom stat is
75C. The store cools as water is being drawn-off. Only when the water at
the top is below approx 65C does the boiler cut in. Then it heats the whole
store all in one long efficient burn. No boiler cycling on a few degrees as
with one stat.