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Re: Single-panel radiator as solar water heater... |
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| message from Ian Stirling on 11 May 2004 |
Maybe.
It'll probably catch more light (less bounce off) when the sun is at
a fairly steep angle to the panel (put the fins vertically).
However, the thermal resistance of the thin fins will mean that the
fins will be hotter than the radiator, so you'll lose a little bit
of temperature.
(if you post the fin thickness and lengths, this could be worked out).
You want to absorb all IR as well as visible rays.
There may be significant differences between visibly identical matt blacks.
Glass will greatly raise the temperature.
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| Ian Stirling replied to Ian Stirling on 11 May 2004 |
When I looked at this a bit back, I concluded that a reasonable idea
might be to use clear twinwall glazing.
Take a couple of sheets of it.
Place the first with an air gap in front of the second.
Now, feed dyed black water through the second.
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| Abdullah Eyles replied to Ian Stirling on 12 May 2004 |
Huh... And I spent so long searching for the radiators... :-(
How would you ensure the dye stayed "in suspense" in the water?
AND How could you seal the gap between the thinwall glazing and
whatever pipe you use? Sounds worse the more I think of it..
As far as I can tell, the radiators have already been used with black
water, due to the build-up inside them!!!
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| Ian Stirling replied to Abdullah Eyles on 12 May 2004 |
Well, it's nice and easy, and involves no challenging plumbing.
Dye is a small molecule that stays in suspension, like sugar.
Pigment is a larger lump of stuff that is suspended in a liquid, and
will settle out over time, like cocoa powder.
I haven't completely worked out how to fit pipes.
Other than this, it's almost ideal.
Cheap, no problems with freezing, low heat capacity, so that it can
get hot with a short time of sun, ...
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| N. Thornton replied to Ian Stirling on 13 May 2004 |
Convection isnt really an option. Convection circulation only works
when the heat source is near the bottom of the loop, with most solar
installs its at the top.
2nd, convection is so slow it requires very large pipes: so large it
would take hours for the HW to even warm up with solar.
While its not entirely impossible to use convection, its not a
practical move.
Regards, NT
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| Pete C replied to Abdullah Eyles on 12 May 2004 |
Hi,
Maybe a layer or two of twinwall in front of the radiator would trap
the suns heat well. Some insulation on the back wouldn't go amiss
either.
cheers,
Pete.
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| nick smith replied to Abdullah Eyles on 12 May 2004 |
What a complete and utter load of old rubbish ! Troll alert !!
By FAR the most efficient way of collecting solar heat to heat water is
using the Evacuated tubes with hi-tech interiors (heat pipes) but this
is expensive in capital outlay.
Next is to DIY a solar collector - perhaps out of an old flat panel radiator
housed in a well insulated glass-fronted box with its output going to a storage tank
(insulation is very important on "high grade" heat)
When using solar collectors in a "low grade" heat application such as heating a swimming
pool where the water temp is only a few degrees above ambient, most don't even bother
with any insulation - the heat differential is only a few degrees and the heat loss is
minimal.
Efficiencies of the above will be in the order of 50 to 90 % of incident energy
collected.
The LEAST efficient will be to collect radiation, convert it to electricity (solar panel)
store it (convert it to chemical energy, then back to electrical energy - battery) to
run a heating element(s) - maybe a few percent efficient and costing a fortune !
The worrying thing is that you think you are correct because solar panels for producing
electricity ARE getting more efficient (which is good) but they are way off direct
collection
of energy in efficiency for heating purposes.
The only applications for solar panels for making electricity is where electricity is
needed
because there is no mains or unviable to lay mains, use a genny, use batteries, ie
remote outposts for telemetry and control (space stations) and cellular phone boxes in
Scandinavia.
Or for keeping you car or boat battery topped up when you are away for a few weeks, or
charging you satellite phone when you are walking across the Sahara... you get the
picture.
Still I knew it was a troll..............
Nick
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| BigWallop replied to nick smith on 12 May 2004 |
I stand corrected then. :-))
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| N. Thornton replied to BigWallop on 13 May 2004 |
The side receiving sun should have the sun directly hit the metal in
contact with the water.
Colour is not important there, but white is the ideal.
The quickest dirtiest way to get such panels working is to cover them
in polythene - might be ok if youve got easy access to the panels to
replace the poly. A proper cover is much better of course.
There are 2 issues with rad panels:
1. like most solar panels, feezing will break them, so you need to
either
a) use a drain down system, ensuring you empty the things before frost
turns up, or
b) use an indirect system with antifreeze.
2. The rads hold a lot of water, so will take longer to provide hot
water. I've never heard of anyone doing it, but I wonder if you can
pour hollow beads into it to get round that?
One rad also makes a useful first warming panel: it is cheap and
simple and adds a bit of warmth before your main solar panel, thus
improving heat out/cost in ratio.
Water can be raised to above boiling with simple home made
concentrating panels, to around 80C with well designed flat panels, or
to about 60C with simple diy hosespipe panels.
Flat plate solar panels can achieve upto 50% heat collection
efficiency with hot water: higher efficiencies should occur while the
water is still cool.
Finally one thing makes a big difference: arrange reflectors to add
extra sun to your panels. They will only add sun for part of the day,
but this makes a big difference to amount of heat collected, final
water temp, speed with which hot water is obtained, and extends the
useful heat capture season.
Regards, NT
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| Michael Mcneil replied to N. Thornton on 14 May 2004 |
"N. Thornton" <bigcat@meeow.co.uk> wrote in message
news:a7076635.0405130500.925f55e@posting.google.com
The fins will absorb heat convected from lower down on a roof if that is
where it is going.
The biggest problem is finding a device that will shut it off in the
evening and when it is cloudy and when it is raining and when the sun is
shining but it is still cold.
Have fun.
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| Abdullah Eyles replied to Michael Mcneil on 13 May 2004 |
Elektor Elektronics published a circuit having two LM334 sensors, one
on the panel outlet, the other on the storage vessel. This activates
the pump when the panel's temperature rises above the storage vessel.
The circuit was published in the book "305 Circuits", ISBN 0 905705 36
X, 1995.
I guess similar things can be found on the 'net...
Thanks! and you!
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| IMM replied to Abdullah Eyles on 14 May 2004 |
http://www.cat/org.uk
Sell a book on how to make the panels (also sell a kit too) and how to make
the differential controller with component parts, diagram, etc.
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| N. Thornton replied to Michael Mcneil on 14 May 2004 |
The ideal thing is a diffrential thermostat and a small pump. Such a
beast is fairly easy to make. The panels will work without that, but
not as well. Many solar setups dont use a diff stat.
Regards, NT
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| Mark replied to Michael Mcneil on 14 May 2004 |
I've got 3 double rads on the roof, they are pumped by a small 12v pump,
powered by a large-ish solar panel.
It works surprisingly well, the brighter the sun the faster the pump goes.
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| N. Thornton replied to Mark on 15 May 2004 |
This is a common approach and works fairly well, but is not the best
efficiency wise. With such a system sometimes the pump can run when
the panel is cooler than the tank. A proper diff stat woudl give you a
bit more heat output.
Regards, NT
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| Ian Stirling replied to Mark on 14 May 2004 |
Insulated/glazed?
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| Mark replied to Ian Stirling on 15 May 2004 |
They're glazed with acrylic sheet on a wooden frame.
This is no high tec installation though, it was basically thrown together
with bits I had to hand or had picked up at farm/boot sales, total cost was
not much more then the copper pipe and antifreeze used.
The hardest part to replace would be the pump, no idea what it came from
originally, but a very nice stainless casing/impeller with 3/4 ins
in/outlets driven by a small 12v motor, possibly something medical. its got
3M Sterivac on a lable.
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| Pete C replied to N. Thornton on 14 May 2004 |
Hi,
Good idea, if you fill the rads with pieces of polystyrene or closed
cell foam that would give the frozen water somewhere to expand when
the radiator freezes too. Braided hose would be fairly frost proof
too.
cheers,
Pete.
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| N. Thornton replied to Pete C on 15 May 2004 |
Yeah, I like that, though I foresee problems. You'd need to use marine
polystyrene, as most is not closed cell, and water logs. The other
thing is if youre going to rely on being able to freeze the rad, you
need to be sure the beads are in every section of the rad. And I would
expect they would jam here and there and not fill all areas of the
thing. Result: rad splits when it freezes.
I think I'd sooner go for either a drain down system, or one that
warms a cold water tank feeding the bath cold tap and shower, thus
enabling the existing HW to be used much less for a given amount of
warm bath or shower.
Dont forget to use a waste water heat exchanger on the bath too: the
payback figs for those are impressive.
Regards, NT
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| Steve Firth replied to N. Thornton on 15 May 2004 |
Glass beads. Commonly used in chemical plant, very cheap and would last
forever in this application.
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| nick smith replied to Steve Firth on 15 May 2004 |
EH ? I thought glass was not very compressible - so how does this work then or is it a
troll again,.,.,,.,
Nick
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| IMM replied to nick smith on 16 May 2004 |
You are right, it isn't.
Alas a Troll.
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| nick smith replied to IMM on 16 May 2004 |
Thought so (knew so!) - another one for the kill file - plonk !
Nick
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| N. Thornton replied to nick smith on 16 May 2004 |
Glass beads dont have substantially less thermal capacity than water,
nor are they compressible.
Regards, NT
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| Steve Firth replied to N. Thornton on 18 May 2004 |
Well duh, glass has a thermal capacity (SHC) 0.84 that of water, and
polystyrene has a thermal capacity (SHC) of 13. So errm, glass has a
thermal capacity significantly less than that of water and polystyrene
right at the other end of the scale. Somehow I don't think you meant
to type the above. At least I hope you didn't.
Only relevant if your suggestion had any merit.
And your suggestion isn't going to work. If one fills the radiator with
compressible polystyrene beads, they will, unsurprisingly migrate and
compress as the water is pumped. Again this effect is well known to
those who design various bits of chemical equipment because we often
need to immobilise reactants on a substrate. Sometimes you have no choice
but to use a compressible substrate and then one finds that the pumping
speeds that can be used are extremely limited. Pump too fast and the
compressible medium will compress and obstruct flow.
And of course since we intend to use this medium in a hot liquid,
hopefully well over 60C, polystyrene is a pretty poor choice since it
will soften.
And of course you can't get closed cell polystyrene balls, or ballotini.
I suggested glass beads because they are inert, rigid, available in a
wide range of sizes, and cheap. The specific heat capacity of the beads
is a red herring, since they won't be going anywhere, so the heat
absorbed by the beads is a constant. It gives a small amount of thermal
lag in the system, and that's it. However they do greatly reduce the
volume of water in the system and will lead to faster warm up times than
if larger volumes of water were to circulate through the channels.
The notion of frost protection by using compressible beads is IMO a
bloody non-starter because you won't be able to get beads with the
characteristics required.
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| Steve Firth replied to nick smith on 16 May 2004 |
It's not.
It takes up space in the radiator and reduces the volume of water.
FFS are you scared of your own shadow as well?
Hint: frost proofing wasn't the be all and end all of the suggestion.
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| IMM replied to Pete C on 14 May 2004 |
As would plastic pipe. Makes mainly don't want the pipes near high temps,
like boilers. So make not be the right pipe as summer solar temps make get
near boiling.
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| Grimly Curmudgeon replied to IMM on 15 May 2004 |
something like:
Syntax error. Auto fault self report feedback defective.
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