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Hi,<br>
This is all true, but fins as implemented on most flat plate
collectors have high efficiencies -- its easy to get up to 95% fin
efficiency, as this calculator shows: <a
href="http://www.builditsolar.com/References/Calculators/FinEficCalc/FinEficCalc.htm">http://www.builditsolar.com/References/Calculators/FinEficCalc/FinEficCalc.htm</a><br>
<br>
In a flat plate collector with a 95% efficient fin, the average
collector temperature is about 5F hotter than it would be with a
100% efficient fin. Under typical collection conditions, that 5F
difference costs about 1.5% in collector efficiency. There are so
many differences in the two collector designs that I'm not sure the
1.5% due to fin efficiency is going to be the biggest player --
there may be other things that matter more? I think the side by
side test will tell the story.<br>
<br>
It seems to me that once you have an efficient design (which I think
both are), things like life and maintenance become the important
deciding factors. The environment inside a collector is a tough
one, and you want a good internal design that will hold up over the
years.<br>
<br>
Gary<br>
<br>
<br>
<br>
<br>
On 12:59 PM, Clarke Olsen wrote:
<blockquote
cite="mid:%3C275E030E-03BB-4940-AFAD-E4B4E6EB55E8@fairpoint.net%3E"
type="cite">The expected efficiency would be from (a) having all
of the target surface in contact with the fluid, and,
<div>(b) eliminating the need to conduct heat through the
absorber. <br>
<div>
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style="border-collapse: separate; color: rgb(0, 0, 0);
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<div>Clarke </div>
<div><br>
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</span><br>
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<br>
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<div>On Oct 12, 2011, at 1:01 PM, Joe Killian wrote:</div>
<br class="Apple-interchange-newline">
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<div bgcolor="#ffffff" text="#000000"> <font size="+1">MTD
= Modified Trickle Down - After Thomason's early
designs as in the Vermont customs building which were
named Trickle Down.<br>
<br>
Thomason's design trickled water down the troughs in
metal roofing, with a glazing a few inches above. Many
thought condensing on the glazing would render the
approach useless, but it turned out to work quite well,
albeit with temperatures lower than we are accustomed to
in flat plate collectors. The lower temperatures
contribute to increasing the collecting efficiency.<br>
<br>
There have been several designs under the MTD label, all
of which capture the water between two sheets, both of
which are usually behind glazing. The object being to
eliminate the issue of condensing water on your glazing
surface and the accompanying losses. I believe all
these approaches have used some material between the two
sheets to help distribute the water flow to better
collect the heat - as Gary's piece in Build It Solar
amply shows is needed. <br>
<br>
These sheets are usually (always?) plastic, not much of
a heat conductor. But it's thin, with water immediately
on the back side, so we're conducting heat through a few
mils of plastic, not along several inches of the
material as in copper fins in a flat plat collector.<br>
<br>
Joe<br>
</font><br>
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