"Andy Hall" wrote in message
...
On Wed, 22 Sep 2004 09:57:06 +0100, Malcolm Reeves
wrote:


"FrancisJK" wrote in message
...

Has anyone any opinions (silly me, of course you have) about alpha
pumps?

With an alpha, as TRVs close the flow falls but the head does not rise
as in normal pumps.

Not exactly.

Between a certain range of flow/pressure, the Alpha behaves
conventionally. When the flow falls below a certain point, that is
detected and the power is reduced to reduce the head.


With a normal pump you need a bypass. So normal
pump+bypass gives constant-ish flow rate and return temperature rises
as TRVs close. Alpha gives reducing flow and a lower return
temperature.

Only close to the point of total closure.


Hence Alpha's are a good idea if you have a condensing boiler since
those are more efficient with lower return temperature. But normal +
bypass is probably better for a standard boiler since they do NOT want
a lower return temperature due to the risk of condensing causing
boiler corrosion.

it's suitable for a normal boiler as well, since if the bypass opens,
the flow increases anyway.




.andy

To email, substitute .nospam with .gl

Andy,

I'm now puzzled.

Is it a choice between

Standard pump AND automativ by-pass

against

Alpha Pump AND no by-pass


Francis