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re: solar pool heating
10 oct 1996
marc o'brien  wrote:

>	andrew my impression is that nick is a free minded creator with the
>characteristic light hearted attitude.

i do tend to minimize the actual work of building things, but it seems to me
that there are a lot of people in the world who are better at building things
than i am, things that don't leak or fall down, even. perhaps my niche is
suggesting different ways of building things, from a thermal point of view.
i prefer low-cost materials, at least at first, especially for experimental
systems like bubblewalls, but i think it's important to bear in mind that
solar structures can have many different architectural forms, with equivalent
engineering principles and performance, and that cost/performance ratio is
often more important than performance itself.

so, on to further crackpot schemes:

valerie sends a little picture, and a clarification:

>can you send me a simple ascii picture of this?

i try it, but it will be better in .bmp or another graphic format. if you
can to uudecode and unzip it i can send you picture in these formats.
see ascii:
                      /---   ---\
                    /             \
                  /                 \
                /                     \
            --/                         \
  output   _               fan            \
           /  __________   __   __________  \
         /   /__________\ i__i /__________\   \

...will send some equations later.

>>quantity of heat (q) = 1009 j/kg*grad * difference of temp * mass
>>or for my case  q = 1009 * 0.0063 * 7 = 44.1 watts
>>and cop = 44.1/2.4 = 18
>hey, that's great. what was the airflow rate in that case?

i wrote it for example. i never get it on my device. it was just about 7.

valerie i. kotelnikov                   tuvinian complex institute,
academic secretary                      667007, russia, republic of
phone 7 394 2236355                     tuva, kyzyl, international st.,117a,
fax   7 394 2236555                     e-mail

well, 7 is pretty good, and i think val has good reasons to expect higher.

meanwhile, back at the unfunny free energy farm, i spoke to an engineer friend
who went to dennis lee's free energy show in phila a couple of weeks ago. lee
is just out of jail, for failing to make good on a number of contracts, as
i understand it. he says he couldn't make good on the contracts because they
threw him in jail. but he rented the phila convention center for $50k for the
night, the last stop on a us grand national money harvesting tour. he's now
selling "franchises" for $10k each, "a maximum of 2,000 of them." every one
of the 30 devices on stage was connected to some sort of power source, but
the audience didn't seem to notice that. the "brown's gas" (h2+o2) engine
was connected to some huge bright orange industrial-looking electrolysis
boxes, plugged into the wall with huge fat black electrical cables.

why do we waste our time talking about or believing or debunking this stuff?
why not just build a few more things that do work, eg above-ground swimming
pools or hot tubs with good thermal covers with solar air heaters on their
sunny sides, so they can heat themselves. or buy more cf light bulbs.

a friend writes: 

>solar energy and the trees on  our property are about the only sources
>of renewable energy that we have.

it's unwindy and un-hydro-y where i live too, and i have lots of space
as well, a 5 acre "yard," which is now taller than i am, with about 100
55 gallon "accent drums" sprinkled around the yard.
>we have an oil burner which heats water for baseboard heat, and a  150
>amp service box where the utility power comes  in.   we  have electric
>central air conditioner and water heater.

do you have a damp basement too? perhaps with a dirt floor like mine? i have
an oil burner too, but i don't use it much. i'm thinking of air conditioning
the basement this winter, and heating the house with the warm side of the
air conditioner, to eliminate the 25 gallons of oil i used to heat the house
last winter. i didn't burn any wood last winter, either.

why not add a plastic film greenhouse onto the south side of your house,
or build yourself a plastic film greenhouse in the sun near your house,
with a strawbale tank lined with epdm rubber for space and water heating?
if the greenhouse were very near the house, some of the solar "waste heat"
from heating the water tank could heat the house with warm air. a greenhouse
might be a fine place to put your central air outdoor unit, if it can
work as a heat pump in the winter. 

stuppy (800) 877-5025 sells 20' wide x 10' tall greenhouses for 64 cents
per square foot, up to 48' long, 57 cents if longer, plus about $200 for
shipping from kansas city, and a 30' wide x 100' long x 15' tall 3,000 ft^2 
greenhouse can be put up by 3 people in one day, from scratch, including
the ground stake "foundation." the standard way to keep the plastic film
from fatiguing in the wind in the winter is to use two layers and inflate
it to 1/4" water column pressure with a $50, 50 watt blower. you might only
turn on the blower when it is windy, or just use 1 layer of plastic and some
sort of ridge venturi to make a slight vacuum inside when the wind blows.

as an alternative to those standard quonset hut or gothic arch-shaped
greenhouses made with curved galvanized pipes, you might spend another
day making the 18 curved beams you'd need for a 16' wide 8' tall x 32'
long greenhouse out of 36 12' 1x3s costing $2 each, bending two of each
to an 8' radius, with some 1x3 spacers and purlins and ridgepole every 2',
held together with deck screws, for a $200 512 ft^2 structure to collect
and store about 200k btu of sun per day, about 2 gallons of oil's worth,
on an average december day.

it might look something like this:

     ---                  .
                   .      c      .            the 10' x 32' r10 insulating 
               .               c     .        and reflective cover is shown  
      8'     .                      c  .      in the raised position.
           .                            c.
          . plants,       b "solar" pool  b   ---
         .  picnic table, a    cover      a.
        .   etc.          l  106 f water? l .  4'
        |                16'                |

                          |       11'       |
        .                 . ............... . ---
        .                 . .      8'     . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . . 30'         . . 32'
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . .             . .
        .                 . . . . . . . . . .
        ..................................... ---

the tank might be 8' wide x 4' deep inside, made with about 80 strawbales
and a few 2x4s and dacron rope and ground stakes, and a single piece of epdm
rubber, 20' wide x 44' long. mouldy old $1 strawbales might have this piece
of epdm rubber draped over the top surface, with the sides uncovered, all
natural-like, with a plastic film vapor barrier underneath. (yuppies and
architects might use $2 bright yellow strawbales, with accent pumpkins.)

the cover might be

1. rigid as shown, weighing about 300 pounds at 1 lb/ft^2?, made with $160's
worth of 4x8 sheets of 2" styrofoam and a few 2x4s, painted white underneath 
and dark on top, with a counterweight and a small reversible motor and
photocontrol, or

2. a $24 flat polyethylene pillow, filled with tiny cold bubbles at night and
air during the day, using a $50 wet/dry shop vac with a bubble sensor in the
return line (i wonder how to make that?) to make bubbles out of a soapy water
puddle at the bottom of the plastic film and collect them at the top, for a
few seconds every few hours. this cover might be on the bottom if people were
sitting in this large hot tub, and they would want to be careful to neither
slip nor puncture the plastic film, nor crawl underneath, as one solar pool 
heating professional suggests. the north half of the poly film overhead might
be painted white, to reflect more sun down into the water on a winter day.

3. another way to make a cover is to assemble $30 worth of 4" solid thinwall
pvc drainage pipe on the floor of the tank, into a 30x8' picture frame, place
$120 worth of 2" styrofoam on top, lay plastic mesh on top for reinforcement,
and place 2" of concrete or pebbles over that. if all goes well, when you fill
the pvc pipe with 2 cubic feet of air at 2 psi from a 340 cfm, 150 mph $49
sears leaf blower, to make a bouyant force of about 120 pounds, the cover
might magically rise up to the top in 0.35 seconds, and people could sleep
on it at night. a guest room. with a klaxon and automated "dive! dive! dive!"
announcement a few seconds before the cover sinks at dawn the next morning
to absorb sun in the water through a single layer of plastic film on top?

4. or, you might lift the neutrally-bouyant slab with a polyethylene film
cover on top, by inflating that. more at night than during the day, when
the floor would be awash. or you could haul the cover up out of the water
with a rope harness and a $149 sears garage door opener, which some people
use to haul boats out of the water.

this could become a serious hobby. or even a business.

what would the average water temperature be in december? where i live,
the south wall might receive about 1000 btu/ft^2/day of sun, of which 90%
might make it through the outer layer of plastic film and 80% be reflected
from the white surface overhead, and 90% of that might fall into the water,
so the average daily solar gain into the water might be 1000x256x0.9x0.8x0.9
= 166 k btu. the greenhouse might be 70 f on an average december day in the
philadelphia area, with some sun, or warmer if there's a reflecting surface
to the south. 

the pool would mainly lose heat through the "solar pool cover," over a 6 hour
solar collection day, so if there were no useful heat output from the pool,
it might have an average steady-state stagnation water temp t such that
166k btu = 6(t-70)240 ft^2/r1 ==> t = 70 + 166k/(6x240) = 185 f. warm enough
to cook lobsters?

the thermal conductance of the pool with the cover in place would be about

    320 ft^2/r10 = 32 for the cover,
  + 320 ft^2/r50 =  6 for the walls,
  + 320 ft^2/r10 = 32 for the bottom,
    for a total of 70 btu/hr-f,

and the average temp inside the greenhouse might be 50 f in december, so if
the pool temp were 130 f, say, the top and sides of the pool might lose
24(130-50)70 = 134 k btu/day, and the 4x8x32x64 = 65,536 pounds of water
might lose 134k/66k = 2 f on a cloudy day, and another 2 f if it supplied
a modern house with the heat equivalent of a gallon of oil per day.

and another 1 f if it were supplying hot water for the house, via some hot
water plastic pipe running around the top edge... how much plastic pipe area
do we need to heat 3 gpm of water from 55 f to 110 f in 130 f water? we need
to transfer 3x8x(110-55) = 1320 btu of heat in a minute, or about 80 k btu/hr
(23 kw), which we might do across a liquid-liquid interface with an r0.1 thin
pvc pipe wall between (copper pipe might make this r0.03, and tend to inhibit
algae growth in the pool), with an average temperature difference of something
like 50 f, so we'd need a pipe surface area a such that 80k = 50 a /r0.1, so 
a = 0.1x80k/50 = 160 ft^2. a $10 10'x4" schedule 80 pvc pipe has an area of 
pix4/12x10 = 10.5 ft^2 and a volume of 3.14x(1/6)^2x10 = 0.87 ft^3 (which
would displace $1.77 worth of concrete at $55/yd^3.) so, do we need 16 of
these 10' pipes? i don't think so, since we do not or should not use 3 gpm
of hot water for more than about 20 minutes at a time, ie 60 gallons or
7.5 cubic feet, or about 8 pipefuls of water, or 80 linear feet of pipe,
once around the top edge, just under the water surface. 

now how can we keep this pipe half full of air, to float the pool cover?


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