wrote:

John Rumm wrote:

Dave Plowman (News) wrote:


relatively "slow" cylinder (reducing the cycling *does* reduce the fuel
used a little).


I've always wondered by how much though. The only difference I can see
is the boiler water output temp will be hgher during a brief full power
burst than it will be in modulation. Modulation will improve
efficiency, but not by much afaics. A difference of perhaps 30C out of
a flame temp of 10s of times that doesnt look like it would amount to
much, a few percent maybe.

The other big loss is that each time you cycle the boiler off, you can
end up blowing most of the primary heat exchanger's stored heat out of
the flue. With the next on cycle this will need to be reheated.
Obviously this is more of an issue with an old cast iron lump with high
thermal inertia, than a modern light weight design. How the pump control
is configured also has a bearing. Worst case being one that simply stops
at the end of the burn leaving the HE "hot".

A 40% saving in time to reheat could be feasable... (in fact a decent
fast recovery cylinder should be able to swallow at least 20kW, some of
the older standard ones may not be able to use more than 5kW).


Would 1960s be about the right guess for a cylinder that manages all of
2kW throughput?

Could be, sounds a bit low even so. Many convection circulation systems
can do better than that.

--
Cheers,

John.

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