| Author |
passive solar question
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| Robert Megee 2005-08-08, 10:21 pm |
| What material is used to cover passive solar collectors?
thanks,
Robert
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| Anthony Matonak 2005-08-08, 11:21 pm |
| Robert Megee wrote:
> What material is used to cover passive solar collectors?
> thanks,
I don't think you're question is clear enough for someone to
answer well. You'll need to define "cover" and "passive solar
collector".
For instance, do you mean "cover during the summer to keep
them from overheating" or "what is the cover (glass) made
of?"
Then there is the collector. What kind of solar collector
were you thinking of? Water? Air? What makes you think they
are covered?
Anthony
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| Robert Megee 2005-08-09, 12:21 am |
| On Mon, 08 Aug 2005 18:53:50 -0700, Anthony Matonak
<anthonym40@nothing.like.comcast.net> wrote:
>Robert Megee wrote:
>
>I don't think you're question is clear enough for someone to
>answer well. You'll need to define "cover" and "passive solar
>collector".
>
>For instance, do you mean "cover during the summer to keep
>them from overheating" or "what is the cover (glass) made
>of?"
>
>Then there is the collector. What kind of solar collector
>were you thinking of? Water? Air? What makes you think they
>are covered?
>
>Anthony
Let's see if I can do better. I was thinking of a cover that would be
use while the device was in operation. I was thinking in general
since ideally one would want to trap the heat. In heat and thermo
class the affect of a greenhouse was for it to have a layer of co2
which would transmit the shorter waves of sunlight but reflect the
longer heat waves. So it doesn't really matter what kind of
collecting system I would think. For the sake of discussion let's say
a water system. I have seen these system with some sort of cover over
them. I seem to recall that there is a minimum spacing required for
the greenhouse affect to work so this panel probably doesn't have
a co2 barrier. The affect of a cover would be to prevent convection
cooling then. I would think that glass would be fragile but I do
know that there is tempered glass. Also glass would be heavy.
If it's some sort of plastic what kind? If the cover blocked more
heat than it trapped, then it would be a bad thing too. So perhaps
it is better to live with it uncovered. At night radiation cooling
might be an issue to consider too.
this any better?
Robert
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Robert Megee wrote:
> For the sake of discussion let's say
> a water system. I have seen these system with some sort of cover over
> them. I seem to recall that there is a minimum spacing required for
> the greenhouse affect to work so this panel probably doesn't have
> a co2 barrier.
Correct sir. Putting in a CO2 barrier would require either a pressure
rated box to seal in the gas, or supplying gas constantly or
intermittently. The commercial units do neither. And CO2 is a corrosive
gas, to boot. Not something you want to have around thin copper tubing.
> The affect of a cover would be to prevent convection
> cooling then. I would think that glass would be fragile but I do
> know that there is tempered glass. Also glass would be heavy.
> If it's some sort of plastic what kind?
Nope, it's tempered glass. Dimpled on the inside, though, to aid in
reflecting the light back inside against the heat transfer fins in many
models.
> If the cover blocked more
> heat than it trapped, then it would be a bad thing too. So perhaps
> it is better to live with it uncovered.
But then you get the problem with convection cooling. You don't want
that. You want the trapped air in that box to just get hotter and
hotter as the sun beats down on it. Just keep that cover clear.
> At night radiation cooling
> might be an issue to consider too.
Yep. That's why they generally shut down at night. There are many ways
to do that. Some do it with temperature differential meters, that
measure the temperature inside the box against the temperature of the
medium they are supposed to be heating. If the box is cooler, they shut
down. Some use a more simplistic approach wereas the recirculating pump
is matched to a small photovoltaic panel, and if the sun isn't shining
enough to power the pump, then it isn't shining enough to heat the box
to any worthwhile degree.
These folks have alot of good engineering grade information on their
web page:
http://www.thermo-dynamics.com
DJ
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| Anthony Matonak 2005-08-09, 2:21 am |
| Robert Megee wrote:
....
> Let's see if I can do better. I was thinking of a cover that would be
> use while the device was in operation. I was thinking in general
> since ideally one would want to trap the heat.
....
Most solar heaters use glass for the covers. Glass works well at
transmitting most light while trapping infrared (like heat). Low
iron glass works best because it's more clear and most makers use
tempered glass to resist hail and baseballs.
Homemade heaters can be made with nearly anything transparent or
translucent. Something like translucent fiberglass corrugated
roofing panel isn't going to be as efficient as double pane low
iron glass but it's so cheap you can make up for it by just making
the collectors larger.
Glass also has the big advantage that it doesn't melt at the normal
stagnation temperatures a collector can reach (around 250-300 deg F).
It's usually a good idea to build a solar collector out of materials
that won't self destruct.
Not all solar heaters use the greenhouse effect. Simply placing a
dark object in the sun will heat it. Camp showers, pool heaters and
some building intake air pre-heaters work on this principle.
The following articles (and any of the thousands of similar things
out on the net) might help.
http://solarcooking.org/sbcdes.htm
http://www.motherearthnews.com/top_...ar_Water_Heater
http://www.txses.org/epsea/wtr.html
http://www.backwoodshome.com/articles/hackleman65.html
Anthony
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| nicksanspam@ece.villanova.edu 2005-08-09, 5:21 am |
| A single layer of polycarbonate.
Nick
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| Robert Megee 2005-08-09, 7:21 am |
| Thanks for all the information and links. very useful.
Robert
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| Robert Megee 2005-08-09, 7:21 am |
|
>These folks have alot of good engineering grade information on their
>web page:
>
>http://www.thermo-dynamics.com
>
>DJ
Excellent source of info! Many thanks.
Robert
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| Solar Flare 2005-08-09, 9:21 pm |
| What is the effectiveness of polycarbonate. It looks good for home projects.
Has anybody ever compared productivity of materials against low iron glass?
<nicksanspam@ece.villanova.edu> wrote in message
news:dd9mcn$l72@acadia.ece.villanova.edu...
> A single layer of polycarbonate.
>
> Nick
>
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