re: concrete solar collector feasibility in pnw? SOLAR.KnowledgePublications.com

re: concrete solar collector feasibility in pnw?
26 may 1998
solar heating a swimming pool from march through october seems like a
piece of cake in seattle, with mild temperatures and at least 700 btu/ft^2
of sun that falls on a horizontal surface on an average day...

still thinking about that 4' tall x 24' diameter $1099.99 above-grounder
from water warehouse (1-800-574-pool), with 10 4'x8'x 2" thick vertical
perimeter pieces of foam tucked under the liner, kerfed outside so they 
can bend, 14 more 4'x8' sheets for the top, a layer of poly film over them,
then 1" of sand or concrete for ballast and solar absorption, and a $59.95
"solar pool cover" over that to reduce evaporation, all tied to a few pvc
pipes to float it. about $500 for materials, plus a small air pump and
a couple of thermostats to make it work. 

this could lower the pool's thermal conductance and allow collecting an
average of about 700(450ft^2)0.9 = 284k btu of sun over a 6 hour day in
october in seattle. if the average solar energy that flows into the pool
during the day equals the average heat energy that flows out,

284k = 6h(t-53f)450ft^2/r1       for the cover during the day
    + 18h(t-53f)450ft^2/r11      for the cover at night
    + 24h(t-53f)300ft^2/r11      for the sides, 

so t = 53 + 284k/(2700+736+655) = 122 f. 

kept at 104 f, this 24' hot tub would lose about 24h(104-53)75 = 92k btu
on a cloudy day, cooling by 92k/(15k gal x 8 lb/gal) = 0.8 f.

nick