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solar thermal payback? - Page 6

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Posted by Solar Flare on October 3, 2006, 11:45 pm
Paint them dark flat paint or as somebody has menytioned there is a
special paint for highr absorption. As far as how nuch higher
absorption nobody seems to know. I used rust coloured primer because
it matches my metal roofing and was cheap, flat finish, fairly dark
and I was painting a galv. iron sheet metal as the heat absorber plate
that may need primer anyway.

My double wall polycarb panels have a special side to block UV for the
greenhouses????? This should preserve the paint also.

Posted by Jeff on September 27, 2006, 5:10 pm
Darrylv wrote:


   Collectors lose heat to the ambient. For something that cold you'll
want to take a few more steps than in a warmer climate. Look into some
kind of double or triple glazing and look into selective surfaces (they
radiate less), there's a thread on DIY Cansolar a week or two back that
has some information on Solkote selective paint. If you are building a
water collector you can buy just the guts ready to drop in your box.

  Do look through http://builditsolar.com  and search the groups archives
as there has been some designs hashed out. Gary is out in Montana so he
knows a few things about cold weather solar!

I've got the "Passive Solar Handbook" here and can give you clear day
solar totals if you have a latitude and if you can give a Canadian City
you are near I have degree day heating totals as well as typical solar
insolation by month. It's a cool book with lots of tables that is out of
print, I've borrowed mine!


Posted by Darrylv on September 27, 2006, 5:22 pm

This is where we're at:

Latitude:     49 53'    North
Longitude:     97 10'    West

The city in question in winnipeg.

Where can you buy the guts to 'drop in' for a water collector?

I'd love to be able to find sources in canada for stuff like this...


Posted by Jeff on September 27, 2006, 7:21 pm
 Darrylv wrote:

Everything is South Facing!!!!

Horizontal Surface BTU/day-sq ft for Winnipeg

Jan 488
Feb 835
Mar 1354
Apr 1641
Sep 1190
Oct 767
Nov 446
Dec 345

The sun is lower in winter so horizontal surfaces collect much less,
multiply  by conversions below to get...

Hor to Vertical Conversion (double pane glass) for 48 lat, sorry chart
stops there! 50 will be somewhat higher.

Jan 1.54
Feb 1.26
Mar  .90
Apr .6
Sep .74
Oct 1.09
Nov 1.43
Dec 1.62

   There's a trig equation using tangents, I believe, that may be
helpfull to you, I don't remember it...

Avg Daily Temp for Winnipeg in F
Jan 3.2
Feb 7.1
Mar 21.3
Apr 40.9
Sep 58.6
Oct 45.6
Nov 25.2
Dec 10.1

Optimal angle clear day total for 48 lat BTU/sq ft day
Jan 21 3422
Feb 21 4560
Mar 21 5560
Apr 21 6150
Nov 21 3330
Dec 21 2888

Your efficiency is going to be roughly 50%, less on really cold days,
for most collectors.

   Gary, knows that. Or Google it up. There's quite a few...

   Hey Gary, how is your latest project going?


Posted by Darrylv on September 27, 2006, 8:07 pm

Thanks a lot for those numbers!

I figured I could google for suppliers but i was hoping someone had
some good experiences with someone in canada.


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