On Sun, 26 Oct 2003 13:49:38 -0000, "mike.james"
wrote:


"Andy Hall" wrote in message
.. .
On Sun, 26 Oct 2003 12:01:28 -0000, "mike.james"
wrote:

The point is that the boiler heat exchanger is rated to give 20
degrees temperature lift at full burner output - that's it. At
lower outputs it may operate with lower temperature differentials.

Right - now I've got it.
Many thanks.

I'm focusing on the return temperature thinking that the boiler can take
care of the flow temperature and bring it up to the higher level needed by
the smaller rads.
You're saying that I have to have a higher return temp to ensure that the
smaller rads are kept as hot as they need to me. So if I do drop the return
temp I'm effectively opting for the lower flow temp.

I need to think about this.
(and read the technical stuff on the Keston)

mikej


Exactly. It is a kind of circular argument, I'm afraid.

It's easy to just focus on one aspect, when in reality it's all
inter-related.

A useful, although not totally applicable analogy is an electric
circuit.

Think of it like a circuit with a 6v battery and two 6 volt bulbs.
You can't increase the voltage of the battery.

If you connect both bulbs in parallel and measure the current, if the
battery were perfect, the current from it would double when compared
with just having one bulb across the battery. This is analogous to
doubling the flow rate and you would double the power output from the
battery in effect.

However, if you connected the bulbs in series, you would get half of
the voltage across each and reduced brightness. You could
compensate this by going for 3v bulbs - analogous to upping the
radiator size.

This is a gross simplification, of course - I am not sure what the
direct electrical equivalent of a condensing boiler would be :-); biut
it illustrates the point..



..andy

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