Pump Head
On 2008-02-11, adder1969 wrote:
On Feb 11, 4:40*pm, John Phillips
wrote:
Indeed. By contrast to the pump, a CH system's radiators and pipework
(including the boiler) will have a head (pressure) versus flow curve
where friction causes the head to *increase* as the flow increases.
Head is approximately proportional to the square of flow in pipework.
I always fit the 5m head pumps rather than the 3m ones as I find they
can be run on a lower speed setting without stalling.
Having a pump that runs the CH system properly at its lowest setting is
probably a good idea to reduce pump noise.
However, for small systems a pump capable of 5m dynamic head, even on
its lowest (fixed) setting, may result in too fast a flow which means
noise from the pipes.
My small system only needs a 3m head pump on its lowest setting and still
the flow is fast enough to keep the drop across the radiators low-ish at
about 8 C. It is quiet enough almost everywhere in the house but flow
noise is just audible in places. Perhaps I will get a Grundfos Alpha
or some other adaptive pump some time to see if I can get both a quiet
pump and a quiet flow everywhere.
A fixed setting 5 m pump in my system, even on its lowest setting, might
well produce more flow and therefore more flow noise than a 3 m pump.
--
John Phillips
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