Ian Stirling wrote:
wrote:
Ian Stirling wrote:
Mary Fisher wrote:
Concentration improves this a lot, and is easy to do with all metal
radiators, eg with greased silvered mylar film. Even ali foil works for
a while. Concentration improves heat availability in poor weather,
financial efficiency or ROI, and system reliability (less plumbing
failure points).
But of course, concentration works best with direct sun.
well, it does improve capture with diffuse light, but not by anywhere
near as much as with direct sun. Poor real world performance of
concentrator systems in winter is down to their typically small
collector areas.
There are times a concentrator will deliver heat when flat panels wont.
I was actually wondering about a scheme which was an air heater alone,
for that one.
You have a stack of n (where n is a large number of panes, which absorbs
say 80% of incoming light before it hits the bottom.
The air is drawn past these from the outside in, in a serpentine
fashion, so that the inner panels are hottest, and hopefully essentially
all IR radiation is trapped.
I wouldn't be surprised if 2-300C was possible.
But, it'd use a hell of a lot of glass, and probably take a long time to
start up, due to thermal inertia.
ok theres a proven system a bit like this using shade cloth. 2 or more
layers of shade cloth, just one of glass. The air flow is from near the
outer glass towards the inside, through the cloth, and efficiency is
very high, far above any black or selective absorber system. And the
cloth is cheap, unlike glass.
If you have a lot of glass, how about a hot air collector with one
sheet of glass and one poly?
Possibly - there is an obvious tradeoff (for non evacuated panels)
between power output, and maximum temperature.
Obviously, adding another layer of glazing will always increase the
maximum steady-state temperature, but due to absorbing some light, will
decrease the power output.
only above a point. Double glazing will give more power out than
single, as conduction losses are less. Triple may not. Extending the dg
layer below the first glazing layer also provides reduced heat loss.
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in order from left to right:
dots for text formatting
roof/base of panel
single glazing layer
double glazing layer
The area below the panel captures heat that flows over the single
glazing layer, reducing panel heat loss further.
I suspect a 'low temperature' panel, and a high temperature one may be
worthwhile.
this is what I've been thinking about for some time now. Each panel
type performs best in different parts of the system. Eg vac tubes for
the top of the tank, as theyre the only thing that performs sensibly at
high temp, rads as a simple minimum cost inlet prewarmer, and flat
panel for the bulk of tank heating.
Also wondering what the possible ratio of a fan assisted panels
radiator/panel size is.
I still cant see what you mean there
2m^2 panel, 1m^2 radiator and a fan.
Or 0.5m^2 radiator, ...
Helps with the thermal inertia thing as well as to some extent the cost.
still just as puzzled
NT