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Posted by Curbie on November 28, 2010, 4:55 pm

Could you explain your thinking here, I don't understand how there
could be different outputs for a solar, or gas, or wood furnaces given
a particular house, doesn't the house's R (or UA) value plus
infiltration determines its heat loss? How would the outside
temperature and wind speed effect the same house differently based
solely on furnace type?


I'm using TMY data to estimate worst-case conditions, but am not
comfortable with the notion of depending solely on a DIY solar heating
system, I think the sun is dependable, but my DIY skills…

Do you have an opinion on solar efficiency, I'm estimating using
general efficiencies from BIS and yahoo's solar-thermal group which
seems to suggest that both passive and active panels are about 50%
efficient, although active systems can loose up to another 25% through
heat fluid transmission. I'm looking at an active system due to a use
for "summer heat".


Posted by Morris Dovey on November 28, 2010, 8:06 pm
On 11/28/2010 10:55 AM, Curbie wrote:

Sort of. :)

From personal experience, solar intensity is anything but constant. Even
on a clear day the input (and therefore the output) varies noticeably
from minute to minute. I heated a home in Minnesota for over a decade
with a Jøtul fireplace/stove) and the heat varied from tree to tree of
the same species.

I could be mistaken, but it seemed to me that as the temperature dropped
and/or the wind picked up, the rate of heat loss went up in a non-linear

The invitation to visit the shop (just 150 mi east of Omaha) is still
open. DIY skills are easily acquired, and I might be able to offer a few
suggestions and bit of useful show-and-tell to bolster confidence. If
it's any comfort to you, I started building panels without much
experience - but there seems to be only one way to get it...

Hmm - yes. I chose not to join the Yahoo! solar-thermal group because of
Yahoo's Terms of Service, and pretty well lost interest in the group
when, after suggesting venetian blind slats for absorber construction to
one of its members, he quoted the private e-mail to the group and
reported that /I/ was building absorbers with venetian blinds. I decided
that I couldn't afford to be associated with such folk. If you happen to
run across this dufus, you might point him at

   http://www.iedu.com/DeSoto/Misc/Coil (320x240).jpg

so he and the group can see the last 400m or so of one of /my/ venetian
blind slats. (There are some folks who just plain aren't worth trying to
help.) Although I would tend to trust anything Gary Reysa told me, I'd
still want to check it out carefully. At this point, I'm inclined to be
suspicious of anything/everything appearing in Yahoo! Groups.


I think there may be a lot of difference between space heating and water
heating. My not-very-refined measurements indicated a final efficiency
in the 85% ballpark for a fairly well-refined passive solar panel
incorporated into the structure wall. My largest loss came from
non-ideal transmissivity of the UV-protected twin-wall polycarbonate
glazing - a loss that I was willing to accept in trade for longevity,
improved safety, and significant reduction of other losses.

I carefully stayed away from fluid-heating systems and anything that
required non-solar power for operation. One of my quirks is that I like
machines without moving parts - another is that I like systems that do
their job reliably, silently, and efficiently without supervision.

Heh - did you know that purely passive systems aren't eligible for an
Energy-Star rating? There's gotta be a joke in there somewhere... :-/

Drove across Nebraska (W to E) Friday. Very much warmer than what I'd
experienced at 11,000' in Colorado. Sunny - a great solar day all across
the Cornhusker State. :-)

Morris Dovey

Posted by Curbie on November 28, 2010, 10:06 pm

Ok, I'm following your thinking there.

That would have to be a summer trip; I'm in the very west part of the
state and am still trying to get by with only my motorcycle. I don't
think I've ever been accused of having a lack confidence, but I am
looking at an active system for "summer heat" use reasons and it seems
to me that it may not be my skills as much as anything with moving
parts can break or wear out.

I agree that there are lots of people who don't want to see anyone
helped and will trash any idea that isn't theirs, the solar-thermal
group has its share of pin-heads as does any group, but there are some
helpful ideas out there and like here, I read there every morning.

I don't post much there because any help I could offer would be on
concentration and what I know about collection comes from that group
and BIS to begin with, and that group is mostly focused on collection,
as am I now.


There seems to be an on-going spiting match between the passive and
active advocates on that yahoo solar-thermal group where both side
think they have the right plan in all circumstances, and in all
circumstances the other plan is wrong. They seem to believe that the
square pegs and round holes are not an issue as much as the size on
the hammer you're using is.

In my view, the Energy-Star rating is more about helping consumers
consume than helping consumers conserve.

So far the whether has been nice, I don't expect that to last much



Posted by Morris Dovey on November 29, 2010, 1:53 am
 On 11/28/2010 4:06 PM, Curbie wrote:

That's a long ride, but I'm not trying to be pushy - just want you to
know that you'll be welcome. I promise that if you do come you'll return
home with a whole new perspective on at least solar heating technology. :-]

Suggested reading (in the unlikely event you haven't already): "Zen and
the Art of Motorcycle Maintenance". I don't know anything about
motorcycles, but Persig makes some brilliant observations about how the
analytical methods we use influence how we approach problem-solving and
have a significant effect on the solutions we adopt (thus square pegs
and round pegs as below).

AFAICT there's an epidemic of that kind of contentiousness - and,
regrettably, it's not limited to discussions of solar energy. <sigh>

Morris Dovey

Posted by Gordon on November 28, 2010, 12:19 am

Well, actually it does.  There is some heating of the motor
and the moving air will eventually turn to heat from friction.
But, air moving over objects and persons will have a cooling
effect as well.  In any case, the standard method of measuring
efficency does not take the movement of air into account.

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