On Sun, 09 Jan 2005 00:08:00 +0000, Andy Hall wrote:
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%.
OK, I'll just have to accept that is the way the specs are written, but
I don't like it - it seems the UK has got it right this time.
One can ask where the heat that converts the generated H2O into vapour
came from. Surely from the energy created by burning the gas? It's
rather like defining a coal fire as 100% efficient if burnt in an open
grate, and then claiming 110% in a system that extracts the tar from the
smoke and re-burns it. Or saying a jet engine is 110% when the
afterburner is on. It's not compatible with the physics I learnt to
claim over 100% just because at some point in history it was not thought
realistic to utilise energy that was known to be present. One might as
well say a light bulb is 100% efficient because all the light is
emitted.
There is a good technical note written by Viessmann on this and the
principles of condensing technology in general.
http://tinyurl.com/54aqs
Thanks for that - an interesting update on the technology - I didn't
realise so much thought had gone into it.
Phil
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