Subject: Re: Looking for Info on Pool Solar Heating in NJ

From: [email-masked] (Nick Pine)
Date: 9 Sep 1996 12:11:44 -0400

John W. Moffett <[email-masked]> wrote:

>Hello all,

Hello John,

>I live in New Jersey with a well shaded pool.  Have nice sunny roof and 
>would like to use solar to warm up the pool by 10 degrees.

How about floating two dozen $16 2' x 8' x 2" thick pieces of Styrofoam on the
pool, and putting a layer of 5 cent/ft^2 black polyethylene film on your sunny
roof, and putting another layer of clear film over that, attached with some
75 cent/linear foot aluminum extrusion clamps, and drilling a 1/8" hole every
6" in a 1 1/2" PVC pipe along the ridgeline, to spray some pump filter water
between the two plastic films, which runs down into the gutter and back into
the pool, whenever the sun is shining and the pool is not warm enough?

The weak point in solar pool heating is usually the cover, which is a poor
insulator, compared to a house wall. A 24' x 32' 80 F pool with an outdoor 
temp T might lose 24(80-T)768ft^2/R10 Btu/day through a 2" Styrofoam cover,
and a rooftop with a south-facing area of 20' x 32' might gain 640K Btu/day
of winter sun, and lose (6 hr)(80-T)640ft^2/R1, so if Ein = Eout,

   24(80-T)76.8 = 6(80-T)640, or equivalently,
    4(80-T)76.8 = (80-T)640,  or equivalently,
     (80-T)76.8 = (80-T)160,  or equivalently,
	   76.8 = 160.

Hmmm. What is wrong with this solar arithmetic? Is it true that solar heating
does not work, as many people say?

Aha, I forgot the sun...

   24(80-T)76.8       = 640K - 6(80-T)640,  or equivalently,
     (80-T)76.8       = 26.7K -6(80-T)26.7, or equivalently,
     (80-T)(76.8+160) = 26.7K,              or equivalently,
     (80-T)236.8      = 26.7K,              or equivalently,
      80-T            = 26.7K/236.8,        or equivalently,
      80-T            = 112.8,              or equivalently,
                    T = 80 - 112.8 = - 32.8. 

So, could this pool stay 80 F when the outdoor temp is minus 33 F? Probably
not, since there would be some evaporation of water and heat losses between
the floating panels, and losses to the cool ground around the sides, and 55 F
R10 ground under the bottom, but still... Not bad.

How hot could we make the pool, with this arithmetic? In Philadelphia,
in December, with an average outdoor temperature of 36 F? Tp-36 = 112.8,
so Tp = 112.8 + 36 = 148.8 F. Could we make it a 104 F hot tub?

How much would it cool over a cloudy week? If it were 4' deep, and most of
the heat loss were through its R10 cover, it would hold C = (24x32)x4x64,
about 200,000 pounds of water, with a thermal resistance R = R10/(24x32), so
RC = R10/(24x32)x(24x32)x4x64 = 10x4x64 = 2560 hours or 106 days or 15 weeks.

Over one week, it might cool to 36 + (104-36)exp(-1/15) = 99.7 F.

Nick

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From: [email-masked] (Andy Burgess)
Date: 12 Sep 1996 12:37:34 -0700

>pool, 

<actual heater idea deleted, good one Nick!>

An idea for insulating pools is to float styrofoam spheres (1-2 inches
in diameter or so, a couple of spheres deep). That way you insulate and can 
still swim without messing with the insulation. I don't know if styrofoam 
popcorn used for packing would work -- might saturate and sink but worth 
experimenting with outside the pool perhaps.

Even air filled plastic balls would help insulate and allow pool use.

Good luck.
-- 
Best regards,
Andy Burgess
[email-masked]

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From: [email-masked] (Nick Pine)
Date: 12 Sep 1996 22:12:48 -0400

Andy Burgess <[email-masked]> wrote:
>Nick Pine wrotes about:
 
>>...floating 2 dozen $16 2' x 8' x 2" thick pieces of Styrofoam on the pool, 

Oops. That shoulda been 2 dozen $8 2' x 8' x 2" thick pieces of Styrofoam.
Still a lot of stuff to get out of the way when you want to go for a swim.

><actual heater idea deleted, good one Nick!>

Thank you :-)

>still swim without messing with the insulation.

You can? Hmmm. Underwater, maybe.

>I don't know if styrofoam popcorn used for packing would work -- might
>saturate and sink but worth experimenting with outside the pool perhaps.

I think that popcorn is more like beadboard than Styrofoam, 
ie, white, not blue or pink. Oh wait, I've seen pink...
Would a lot of kids probably swallow the popcorn and drown?

>Even air filled plastic balls would help insulate and allow pool use.

One place I worked used ping-pong balls to cover their IC boiling bath.

How about putting the popcorn in a heat-sealed polyethylene film pillow? 

Or filling the pillow with soap bubbles, and squeezing them out through
a filter to break them down into 200 times less liquid by volume when
the pillow is rolled up?

Nick

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From: [email-masked] (Seamus)
Date: Sun, 15 Sep 1996 15:59:37 GMT

>Even air filled plastic balls would help insulate and allow pool use.
	Yes, I found that it sinks or becomes sticky, saturated, heavy
and obnoxious to handle.(In the pool.)
	Floating bubble plastic from an elevating counterpoised
roller, with balancers to auto spread the sheet on the surface, works
and stops heat loss by evaporation dead. The bubble plastic can be
recycled from commercial sources and NOT joined by sticky tape as it
degrades, but coarsely sewn with a manmade yarn such as agricultural
bale binder twine. This works. Bear in mind that if the pool is not
shaded or indoor, then these materials are UV degradable.
	This cover is manually workable by one ordinary unfit person
in under a minute.

Best regards, Jim