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re: plans to make pool solar heater
15 apr 1998
andy mckegney  wrote:

>nicksanspam@ece.vill.edu wrote:

>>where i live, in december, a 70 f 24x36x8' deep pool with us r20 sides 
>>and bottom would lose about 24h(70f-54f)1824ft^2/r20 = 35k btu/day to
>>the soil, and another 18h(70f-23f)24'x36'/rc = 731k/rc btu/day through
>>a us rc cover at night, and 6h(70f-38f)24x36/r1 = 166k btu/day through
>>the "solar pool cover" during the day, and gain about 620x0.9x24x36
>>= 482k btu/day of solar heat through the cover, so if the solar energy
>>that flows into the pool equals the heat energy that flows out during
>>an average december day, 482k = 35k + 731k/rc + 166k, so rc = 2.6.  
 
>>an inch of beadboard (r4) or styrofoam (r5) insulation might be enough,
>>or more, if the cover is in 4x8' modular rafts tied together with
>>uninsulated gaps between them.

isn't it surprising how little cover insulation it would take
to solar heat a pool in december, with no "solar pool heaters"?
how could so-called "solar pool heating specialists" have failed
to notice this? maybe they all have their heads in the sand. or
maybe they are just short-sighted crooks.

a pool with r20 cover insulation (like a house wall) might lose 
2189t-118k btu to the soil, 778t-18k through the cover at night, and
5184t - 197k through the cover during the day, so t = 815k/8150 = 100 f. 

>>let's see... the aforesaid pool with an r10 cover would lose about
>>24h(70f-30f)24x36/r10 + 35k = 118k btu on a cloudy december day. with
>>c = 442k btu/f of water and an equal thermal soil capacitance, the
>>temperature would decrease 118k/884k = 0.13 degrees f on a cloudy day. 

it looks like the temperature wouldn't change much over a cloudy week. 

>>>pool covers made of semi-transparent plastic, with bubbles moulded in, are
>>>made specifically for the pool industry and are very inexpensive.

a few years ago i told the local chinese restaurant that their food
was very bad, compared to the restaurant down the road. they said
"yes, but our food is less expensive." it's nice to have choices.

>>those pool covers are miserable insulators, us r1 at best,
>>vs. a common r20 house wall. very poor thermal band-aids.
>
>pool covers are really designed to prevent evapouration (where at
>least 80% of a pool's heat is actually lost).

perhaps they should be designed to prevent conductive heatflow
as well, in pools that are heated. a radical thought, eh?

>>>forget trying to float rigid foam boards, they are much too cumbersome...
>
>>these would automatically sink to the bottom for swimming or solar
>>collection. swimming under the concrete/foam covers is inadvisable,
>>in the sunken position.
>
>if you keep recommending this idea, you had better be responsible for
>any drownings associated with it !!!!!!!!!

don't swim under the cover. we could make graphic signs for canadians,
with a pool cover, and a swimmer underneath, and a big circle and
red line through it all...

>>>your best bet for solar pool heating is to purchase pre-manufactured
>>>plastic solar panels from a company like fafco, or solar industries,
>>>and install them yourself.
>
>>bailing buckets for bottomless boats... 
>
>well if someone wants to use solar to heat their pool, better a solar
>bailer than a gas powered one !<)

right. makes you feel ecological all over,
like owning a "passive solar house."

>nick,  as you have already confessed (long ago) to never having owned
>a swimming pool, i would suggest you are ill-advised to recommend
>solutions for solar pool heating.

or maybe it's like politicians in washington. an insular luxury industry.
a technological backwater. where's the imagination, vs making the same
old same old products over and over and over again?

>the primary purpose for heating a pool is to extend the swimming season,

like, 365 days a year? :-)

>not the "keep the pool above air temperature - even if the air temperature
>is so cold you wouldn't want to swim anyway" season.

i swam comfortably (well, it was too warm) in the conventional-sized
outdoor 98 f banff springs hotel pool one night, when it was -12 f
and snowing. the handrails were covered with ice.

>to that end, going to the extreme lengths of building an ugly,
>difficult to manage and dangerous concrete pool cover, is not
>a practical idea for 99.999% of the pool owning population.

de gustibus... 

nick




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