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On 3/25/09 7:40 AM, Peter Parrish wrote:
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<p class="MsoNormal"><font color="black" face="Times New Roman"
size="3"><span style="font-size: 12pt; color: black;">could we start a
thread?</span></font></p>
<p class="MsoNormal"><font color="black" face="Times New Roman"
size="3"><span style="font-size: 12pt; color: black;"> </span></font></p>
<p class="MsoNormal"><font color="black" face="Times New Roman"
size="3"><span style="font-size: 12pt; color: black;">My principal
reason for looking into this
technology is for space-limited applications. Right now we are looking
at
trying to find space on a crowded roof for about 100-120 sq-ft of
conventional
flat plate collectors (e.g. SunEarth Empire 4’x8’ or 4’x10’),
and skylights, parapet walls and a PV array are getting in the way.
Climate is
southern California coastal.</span></font><br>
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</blockquote>
<br>
I asked for evacuated tube experiences on this list and have
subsequently queried a number of installers and manufacturers over the
past 2-3 years. There were some facts, a lot of bad experiences early
on, and plenty of opinions. What I have distilled from all of this so
far is:<br>
<br>
ETs make sense when ∆T is high and when the location has a lot of
overcast days.<br>
ETs do not make sense when ∆T is low to moderate and when the location
has few overcast days.<br>
ETs cost more per square foot of aperture.<br>
ETs present much lower wind loads than flat plates (potentially
allowing installation using ballasted racking on low slope roofs.)<br>
Stagnation and scale present bigger risks with high fluid temps.<br>
<br>
<br>
<br>
<br>
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