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re: looking for info on pool solar heating in nj
1 oct 1996
andrew mckegney  wrote:
 
>>>...it seems you have been given a couple of real neat suggestions
>>>(plastic sheets on the roof, floating styrafoam balls !<)-
>>>impractical and inefficient, but neat.
>
>>care to explain why plastic sheets on the roof are impractical? there are
>>about 15,000 acres of greenhouses in the united states, and about 65% of them
>>have polyethylene film roofs, 15 square miles of such roofs with no solid
>>material underneath, sprinkled all over the country. professor bill roberts
>>at rutgers works with one new jersey greenhouse that measures 1320 x 250',
>>ie 7.5 acres. the one next door measures 1000 x 290', 6.7 acres. many growers
>>use inexpensive aluminum extrusion clamps to hold the film, making it easy
>>to change and recycle it every 3 years or so. 

i wonder why most solar heating professionals completely ignore the greenhouse
industry, who have been working with inexpensive and practical outdoor
transparent structures for years. and vice versa...

>i didn't say it wouldn't work!

well, good...

>it is very impractical for the average pool / home owner!

so you said... what you tell us three times is true?

>the maintenance on such a system would be horrendous compared to a
>conventional solar pool heater. 

i disagree. it might be less, with less plumbing and valves and so on.

have you ever worked for western union? many executives there had their very
own telegraph keys and sounders on their desks, in 1975. some of the sounders
were attached to tobacco tins with slots cut in the tins to vary the sound,
so they could more easily follow their sounders in rooms full of sounders.
really quite clever. the company's technically more advanced chief engineer 
was building 110 volt flip-flops out of discrete transistors, with load
resistors made from hundreds of feet of nichrome strips, in 1975. everyone
had high blood pressure. nobody liked to talk about fax machines. sometimes
it pays to take a fresh look at things, even when heating swimming pools...

>what about the roof itself?

perhaps it would last longer, with the shingles all covered with plastic. 

>fastening clamps to a standard asphalt shingle roof
>and then two layers of poly and then supply piping.

horrible thought, eh? i suppose the clamps might go on the sides of the house,
not screwed right flat on the roof. the upper layer of plastic would have to
be changed and recycled every 3 years or so, perhaps less often if it had
shadecloth over it in the summer (another useful greenhouse product, seldom
seen elsewhere, at 15 cents/ft^2, with an outdoor lifetime of 10 years (?))
changing the poly film should take less than an hour, on a calm day, at a
cost of 5 cents/ft^2. perhaps this thing should have one 2" pvc supply pipe.
should the plastic be draped over the ridge pipe? 

>what about water under the plastic rotting the roof...

that's a helpful thought. there is work to be done, to make this practical.
richard komp says that the large polyethylene sheets for sale 20 years ago
in hardware stores had pinholes. have things improved since then? should the
lower layer be epdm rubber, which lasts forever, with standing seams on the
roof that serve to help space the poly film over it, with a few plastic ropes
or boards or old tires over the film to keep it from billowing in the wind? 
perhaps a few leaks won't matter. roofs do get wet, and they don't have vapor
barriers underneath. 

>there are just so many drawbacks to this concept for 99% of the potential
>sites that the concept is impratical. 

so you said, twice before. does it have to be spelled right this time, to
make it true? how can a man who displays such attention to detail presume
to lecture us on roof practicalities?

>>and why is efficiency is so important, vs cost-effectiveness?

well?
 
>this approach would be significantly more expensive than conventional
>solar panels if you put any value to your time to maintain it.

you mean, 1 hour every 3 years? :-)

>>and why do you seem to be in love with "hi-tech" systems?
 
>i love only systems that work and have proven track records.

like cruise missiles?

>>swimming in styrofoam balls may not be everyone's cup of tea, nor was it my
>>suggestion. perhaps a layer of tiny foam bubbles would work better, with some
>>way to kill them quickly, c02 or dust, or hot air? make bubbles inside a
>>floating pool cover sandwich? roll it all up automatically, in a minute?
>>tiny cold bubbles have about the same r-value as fiberglass...
>>one might deflate 'em to let the sun shine in during the day.
 
>>so, speaking for the established greedy ignorant unimaginative shortsighted
>>solar pool industry collection of criminals slavering after government
>>subsidies, andrew, where are _your_ r10 pool covers?
 
>there is no such cover that i know of, which is too bad. 

how pro-active. you know where to buy the uv poly. start with a hot tub, and
an $80 200 in^3/min 7 psi peak, 2 psi continuous duty danner dynamaster (800)
893-4220 piston air pump, 110vac at 0.66 amps, or their 120 in^3/min 12vac
version, or the $169 1.8 cfm 4-10 psi wp120 12vdc 7 amp diaphram air pump
from jade mountain at (800) 442-1972, jade-mtn@indra.com, feeding a large
airstone or screened well point filter? a 7x7' pool cover filled with 6" of
bubbles has a volume of about 25 ft^3, and 1 cfm will fill that in less than
a half-hour. if the bubbles last 2 hours, the pump would have to run about 
20% of the time. tiny bubbles have an expansion ratio of 200:1, which means
the soapy water container needs to hold about 0.125 ft^3 or 1 gallon of a
2% green dawn solution (?)

there's a hot tub air blower in the grainger catalog, $193 for their 2p681
35 cfm at 115 vac, 6.6 amps. yes, this is a bad habit, but maybe that blower
can also be used to inflate the bubble foam cover, somehow...

a 24x32' pool cover filled with 6" of bubbles would have a volume of 384 ft^3,
requiring a 16 gallon soapy water container and a larger air pump, eg the $58
grainger 4c442 140 cfm 0.95" blower, which uses 1 amp at 110vac. (this blower
is used to inflate 2 layers of plastic film on commercial greenhouses, 24
hours a day, to prevent wind fatigue. ct film's rule of thumb is that 1/30
blower horsepower protects 10,000 ft^2 of poly pillow area, so this blower
should work for a greenhouse up to about 1 acre. would it protect a rooftop
film pool heater, with a wind switch? probably so.) a bubble foam pool cover
might be inflated by bubbles that come out of a 30 gallon plastic drum full
of soapy water buried in the ground, with a 2" hose from the blower, mounted
on top of the drum, disappearing down into the center of a 14" diameter
floating platform in the drum, supported by a floating ring, with a piece
of plastic window screen around the hose. the foam needs recycling somehow,
perhaps through a filter to separate it into water and air. 

>insulation value of a cover is of little value if the cover is opaque.

what preposterous rubbish. are your house walls transparent? 

>pools heat up naturally by virtue of the sun shining on them.

about 500 btu/ft^2 per day in the winter, where i live. but they lose about
24 hours(76-36)r1 = 960 btu/day through an r1 cover, and solar pool covers
are r1 at best. an r10 opaque cover is far more efficient. and we are much
better off than that, with a film to prevent evaporation at all times, and
an insulating cover that retracts during the day. or a deflated bubble foam
cover to let in the sun during the day that is pumped back up with bubbles
at night. and a $500 commercial plastic film greenhouse over it all, with
white poly film on the north half, with the pool running east and west, to
reflect closer to 1000 btu/ft^2/day down into the pool in the winter.

>if you have an opaque cover the pool does not get warm - unless you use a
>pool heater.

duh. it actually stays fairly warm, perhaps warmer than with a cover,
because of heat from the ground. a little jet engine under the pool
might help here too, to extract ground heat at a higher temperature.
and fer chrissake some insulation around the sides of the pool.

>if you have an opaque cover or a shaded pool you are
>going to need a more powerfull heater (larger solar system).

duh^2. and perhaps a spellchecker.

>what a solar blanket really does is prevent water from evapourating
>from the pool. most heat loss in a pool is from evapouration. putting
>a blanket on the pool can reduce its' heat loss by 70%. (this make
>pools much easier to keep warm).

let's try that again.

>what a solar blanket really does is prevent water from evaporating
>from the pool. most heat loss in a pool is from evaporation. putting
>a blanket on the pool can reduce its heat loss by 70%. (this makes
>pools much easier to keep warm). 

duh^3. most third-graders could figure that out. 

>>a friend of mine invented one, also not everyone's cup of tea: a tracked
>>tennis court over a pool, with motors that slid the court back at the touch
>>of a button. he enjoyed inventing that horse.
 
>this concept sounds really cost-effective !<) ,  but if it works, great.

it was cheaper than filling his sloping lot for a separate tennis court.

>what about the other 6,000,000 (conservative estimate) pools in the us?

not my job. what are you doing about that, andy? just selling the same
old stuff, i guess. high-priced buckets for bottomless boats.

>>now where can i buy that foam blanket system? uv-poly comes in big pieces,
>>eg rolls 32' wide by 100' long that cost $160 and weigh 75 pounds, eg from
>>geiger at (800) 4geiger or ecgsales@hortnet.com or http://www.hortnet.com.
>>it's easy to heat seal. do you own an iron?  

well?

>blue sheild makes a foam blanket. you just shouldn't use it of the
>pool during the day (because it's opaque). (1/8" of foam)

an r-value of 1/2, if perfectly dry?

>it's easily rolled onto a conventional roller, but the foam does soak up water
>after a while and gets rather heavy.

do you think that might somehow affect its insulation value?

nick

  "just the place for a snark! i have said it twice.
    that alone should encourage the crew.
   just the place for a snark! i have said it thrice:
    what i tell you three times is true."

   the crew was complete: it included a boots--
    a maker of bonnets and hoods--
   a barrister, brought to arrange their disputes--
    and a broker, to value their goods.

   a solar pool heating professional, who
    might perhaps have won more than his share--
   but a banker, engaged at enormous expense,
    had the whole of their cash in his care...



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