In an earlier contribution to this discussion,
dennis@home wrote:

"Roger Mills" wrote in message
...
I know that something similar was discussed recently, but I'm not
sure that there were any concrete conclusions.

I'm currently trying to fine tune my system, and am having great
difficulty in achieving a satisfactory set of settings. [See my
other post on non-contact flow meters.]

SNIP
Any comments?

I thought the idea was to maintain constant flow not pressure.

The idea of what?

The idea of a variable speed pump certainly *isn't* to maintain constant
flow - but to back off as more amd more TRVs close, maintaining flow just
through the rads which are still open. This implies keeping the pressure
constant (by reducing the speed) as the flow reduces.

The idea of an automatic by-pass valve is to maintain *some* flow through
the boiler - particularly during the pump over-run phase, when the zone
valves are closed. Arguably it also needs to open a bit when *most* of the
TRVs are closed in order to maintain the minimum required flow through the
boiler. But since it is operated by (differential) pressure, if it is to
open by different amounts under different circumstances - which it needs to
do - then surely the pressure (pump head) needs to change with these
circumstances. It can't do this if it's 'clever' control system is striving
to keep the pressure constant.

Any further comments?
--
Cheers,
Roger
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