"Andy Hall" wrote in message
...
On Wed, 3 Dec 2003 00:06:05 +0000, Andrew
wrote:
In article .uk, Ed
Sirett writes
snip
I've yet to see the plume as the boiler is only on when someone's having
a
bath (reheating the cylinder) or for odd quater-hours here and there.
So what do you use for space heating ? - just curious. £800 for a Keston
is an expensive way of heating water.
This is fairly typical behaviour with a modulating boiler.
For example, this Keston model drops its power level down to 7kW - I
have a different make which will drop as low as 3-4kW.
During a large part of the year, spring and autumn, and during the day
through he winter, the amount of heat required is much less than the
full output of the boiler. With a conventional boiler, the burner
is turned on and off to reduce the average heat output. In the case
of most types of condensing boiler, the burner power is reduced which
reduces output and water temperature.
It is more efficient to reduce power than to start and stop the
burner.
Depends on the burner design. A highly efficient spot rated burner
(non-modulating) coupled to a heat bank can be very efficient overall.
Many top end developers are fitting Myson Kickspace heaters in kitchens.
These require a high temperature flow for efficient draught free operation.
The solution used to be an integrated thermal store as it provides 75-80C
temps and a spot rated burner boiler always set to max temp. The efficiency
was good as the burner was highly efficient with design maximised for a set
rate.
Condensing boilers have advanced recently so now some approach it.. A DHW
only heat bank with one high temp circuit taken off the heat bank for the
Myson(s) and the CH circuit left to modulate on a condensing boiler. When
the heat bank requires heat the boiler runs up to full temp. When back on
CH it is left to modulate.
Moreover, reducing the temperature increases the boiler
efficiency as it is pushed further into condensing operation.
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