John Beardmore wrote:
In message . com,
writes
Richard Bates wrote:
First, flat panels give much better ROI than vac tubes
Quick nurse - the tin opener !
heh, yes
Second, British winters are mostly overcast, and flat panels work ok on
indirect sun, whereas silvered evacuated tubes work a lot less
efficiently under these conditions.
What do you mean by "silvered" ?
outer envelope part silvered to concentrate sun onto the inner tube.
3rd, it is all more complex than that,
Quite so !
but suffice it to say that flat
panels are very much a going concern in Britain.
Yes.
An optimally designed system would have a mix of both flat panel and
vac tube, with each heating a separate part of the system.
Yes - been there, got the T-shirt.
Really they need to be on separate primary circuits.
Yes, thats what I mean. The FP makes warm water, then this goes to the
final high temp circuit with ETs.
Flat panel
is best for mid-temp water, as it gives much more output per £/$. Vac
tube is best for the final max temp water, as it gives high output
temps that flat panels cant consistently deliver. However, the ROI on
the flat tubes will be much poorer, so spending some of the money on
flat panels will much improve total annual output.
Hmmm... Have you seen the prices of the Chinese import ETs ?
To be honest, while what you say was true 10 years ago, the difference
in cost per area is now pretty small, and the prices we quote to end
users are much the same per area for FP and ET, because while ET is
slightly more expensive, installation is easier and safer in lifting and
handling terms, if not actually quicker.
Cheers, J/.
I suppose thats true of professional installs on rooftops, I'm thinking
more of diy installs, where the cost for a decent area of tubes is way
above that of flat panels, and makes a real difference to ROI figures.
Flat panels can give much better performance at ground level or on a
flat roof, as 1 or 2 reflectors are easily added to give anything from
1-2 suns. Equipment on a flat roof ditto, mounting the panel either at
an angle from roof to wall or else flat on the wall, reflector below.
I guess the ultimate is a 3 zone system, with a drain heat exchanger
providing the 1st stage of heat input, flat panels the 2nd (with
reflectors for best performance), and vac tubes the last. Perhaps one
day the equipment will be cheap enough for this to be the done thing.
NT