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Re: Ohio sunny enough for domestic solar?

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Posted by nicksanspam on April 30, 2006, 12:00 pm
 


Glass blocks IR longer than 3 microns, which is good...


We had tight space limits. Thomason published a lot of design material,
lots of patents and plans and pamphlets, mostly through Edmund Scientific.


He patented it, which is evidence that he was. Maybe TVA had a license.
He wrote "Solar Space Heating and Air Conditioning in the Thomason Home"
in Solar Energy Journal, Vol 4, No. 4, Oct. 1960, pp 11-19, describing
the trickle collector on his Washington DC house.


Polar bear hair works that way, and black chrome selective surfaces, on
a lightwave scale, but I don't think the roof metal geometry helps much.
 

Thomason worried that water drops would act as solar reflectors (ice does),
but he discovered they only acted as lenses. Condensation adds heat loss,
but these collectors still seem to work well in cold weather, esp with
low temp water, eg at 23 F with 250 Btu/h-ft^2 of sun and a single layer
of R1 glazing with 90% solar transmission:

10 TAF#'outdoor temp (F)
20 TA=TAF+460'outdoor temp (R)
30 TG=TA+22.5'glazing temp (R)
40 PG=EXP(17.863-9621/TG)'vapor pressure near glazing ("Hg)
50 PW=PG+2.25'vapor pressure near water ("Hg)
60 TWB21/(17.863-LOG(PW))'breakeven water temp (R)
70 FOR TWFp TO INT(TWB)-460 STEP 5'water temp (F)
80 TW=TWF+460'water temp (R)
90 PW=EXP(17.863-9621/TW)'vapor pressure near water ("Hg)
100 TGE=(TA+TW)/2'glazing temp est (R)
110 TG=TA+10*PW-10*EXP(17.863-9621/TGE)'glazing temp calc (R)
120 IF ABS(TG-TGE)>.01 THEN TGE=TG:GOTO 110'iterate to find glazing temp
130 Q*(TG-TA)'glazing loss (Btu/h-ft^2)
140 I"5-Q'useful heat output (Btu/h-ft^2)
150 E=I/250'efficiency (fraction)
160 PRINT TWF,TG-460,E
170 NEXT TWF

water         glazing       efficiency
temp (F)      temp (F)      (fraction)

70            28.86005      .6655981   |
75            30.15708      .613717    | water freezes to glazing?
80            31.65738      .5537049   |
85            33.38818      .4844727
90            35.37683      .4049268
95            37.65308      .313877
100           40.24829      .2100684
105           43.19483      .0922070

Frank de Winter points out in the story that the glazing conductance
in line 130 might be 4X less with large pieces of low-temp glazing
in slow moving air.

Nick


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