On Sat, 08 Jan 2005 22:38:00 GMT, Phil Addison
wrote:



But it still shows 100% efficiency.

ISTR some discussion about an EU way of measuring that could result in
more than 100%. I didn't take much notice at the time, thinking that was
nonsense. Is there something I'm missing or should the ASA, or at least
the CA, look into this? (the CA have been having a go at the ASA in the
latest "Which?").

It's all kosher and has to do with how the calorific value of the fuel
is considered - i.e. whether it is on a net or gross basis, taking
account of the latent heat recovered from the water vapour in the
combustion products of the condensing boiler or not.

The UK uses the gross value (including the possible latent heat) which
is why efficiencies never exceed 100%.

The rest of Europe uses net calorific value and so if there is latent
heat contribution through condensing, efficiencies do go abover 100%.

There is a good technical note written by Viessmann on this and the
principles of condensing technology in general.

http://tinyurl.com/54aqs




They should have probably dotted the curve below about 25-30 degrees,
since that is generally about the minimum modulated down temperature
in steady state.

Hmmm... if you extrapolate their straight line it implies well over 100%
during warm up of an empty house on a cold day.

It's also possible that they have included the latent heat in the
figures...

I hope British Gas, et al, don't get wind of that or they'll be upping
the price of gas to include the value of the 'free' latent heat...
err... not!

Phil
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