Subject: heating a pool?

From: [email-masked] (James A Bullard)
Date: 3 Sep 1996 17:36:28 GMT

I have an inground 14 X 28 foot swimming pool that refuses to stay above 
70 except in the hot August months.  Is there a way to run the water 
through black pipes on the roof and down to the pool?  How many feet of 
pipe?  How big a pump?
Any ideas?
James

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From: [email-masked]
Date: Fri, 06 Sep 1996 07:03:19 GMT

>through black pipes on the roof and down to the pool?  How many feet of 

Stay tuned.
I'm playing with the same idea right now.  I have a 11X23 foot pool
that is hovering at 83F with a cheap bubble pool cover and 400 feet of
black 1/2" hose laid flat on top of a patio cover. (Don't try this
with one big long 400 foot length!  Cut it in 50 ft sections and use
connectors for that sort of hose.)  I am tapping the high pressure
side of the pool pump that runs a pressure operated pool sweeper, and
returning to the low pressure side returning to the pool.  I have a
in-line screen filter (like you find for drip irrigation) and a pvc
ball valve set so about 1 gpm runs through the hose system.

Result?  With the nights dropping into the 50s and days around 85, I
think that the 83F I am sustaining now is pretty good.  But I suspect
that the pool cover is doing a lot more than the black hose.  This
weekend I will take temperatures exiting the hose and report back.  I
probably need about 8 times more hose to do any real good.

Steve

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From: john <[email-masked]>
Date: Fri, 06 Sep 96 08:07:56 GMT

> through black pipes on the roof and down to the pool?  How many feet of 
The cooling is mainly through evaperation, if you buy a whole lot of foating 
toys this will reduce the surface area of evaperation and reduce the wind speed 
across the pool.
Hose pipe in larg quantity is cheap and a pump meant for a pond fountain would 
drive the water through as long as air doesn't get in the syphon. -- 

Yours sincerely....John G.*?*?*?*?*? Us Neuron's don't KNOW that much, period.
*What is existance without socialising?*?*?*?*?*?*?*?*?*?*?*?*?
(Everybody wants to be certifiably nice on this tide of awesome tech' power.)c?
(Posts mispelt or not should be written with content to be worth saving
so as apathy doesn't drown lurkers)c?

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From: [email-masked] (Catherine Woodgold)
Date: 10 Sep 1996 20:45:54 GMT

I wonder whether painting the sides and bottom of the pool black
would make more difference than some black hose etc.

A pool cover to stop evaporation is very important.  Note safety
concerns re children getting trapped under the cover.

A simple idea:  Just put some little plastic pools on the deck
and fill them with water.  They get hot when the sun shines.
Dump them into the pool just before you go swimming.

An expensive idea:  Build the pool with three parts.
The middle part is a regular pool.  The other two parts are
the same area, but only 4 inches deep, painted black.  When
the sun is not shining, drain some water from the pool so the
shallow parts are empty.  (How to get the warm water to mix
into the rest of the pool, though?)  The shallow parts
could be covered with bubble cover all the time, or never
covered.

Sure, you can put black hoses on your roof.  Why not?
Depending on how you do it it may help cool your house.
Might make it hotter.  Probably won't make much difference.

Cathy
(just my opinion)
TISSATAAFL
Pessimists are more often right, but optimists accomplish more.

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From: [email-masked] (Sylvan Butler)
Date: 12 Sep 1996 19:06:16 GMT

[email-masked] wrote:
>lightweight coil of hose that is durable and lightweight.  I just
>threw it up on my patio cover and hooked it in line.  I now have 900
>feet of hose in the system.  Water entering at 82 degrees came out at
>96 degrees at 2 gpm flow.  The days and nights have been warmer the
>last few days; about 92 and 60.  The pool is now 88F, warmer than when
>the days were 104 and nights 75.  As I add coils I hope to maintain

Are you preventing water flow thru the coil when coil temp is
less than pool temp?  That can make a huge difference...

sdb

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From: [email-masked] (Hardison)
Date: Fri, 13 Sep 1996 01:25:00 GMT

>sdb

Good point.  Does anyone know of any homebrew plans for making your
own Radio Shackish differential temperature switch circuit for
controlling the bypass valve?

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From: [email-masked] (Nick Pine)
Date: 13 Sep 1996 08:44:05 -0400

Hardison <[email-masked]> wrote:

>Does anyone know of any homebrew plans for making your own Radio Shackish
>differential temperature switch circuit for controlling the bypass valve?

You might try a Grainger snap-disc thermostat (eg the $6.46 2E247 10 amp
thermostat, which turns on at 130 F and off at 115 F) in a little black box
with a transparent sun-facing cover.

Or a $75 (wholesale) DTT '94 differential thermostat, including power supply,
line cord, box, fuse, switched 110V receptacle and thermistors from Heliotrope
General at (800) 460-3930. Their design uses MSI ICs, and doesn't look like
it's changed much in the last 15 years.

Or a $199 Blue Earth BASIC programmable microcontroller from (800) DIGI-KEY,
http://www.digikey.com, which might do more, eg turn on a whole house fan at
night, during the summer, with a lower temp limit, or blow down some warm air
>from  the peak of an attic through a duct into the house on a sunny winter day,
after opening a return air damper with a $50 2-watt 24 VAC 45 in-oz Honeywell
6161MLB1000 direct-coupled damper actuator motor, or leave that attic floor
damper open, under a transparent south attic roof, for daylighting, with the
peak fan off, during the day, when the house is already warm enough. 

Or you might design and sell a new differential thermostat, starting with
Digi-Key's $7.05 22 microamp PIC16LC72A-04I/SP-ND microchip controller with
on-board 8 bit ADC. 

Nick

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From: [email-masked] (Nick Pine)
Date: 11 Sep 1996 09:32:03 -0400

>would make more difference than some black hose etc.

We could just dye the water black... :-)

But most of the sun would be absorbed anyway, no?
Here's a quote from Duffie and Beckman (1991), page 652:

  As radiation is transmitted through water, the longer wavelengths are
  absorbed near the surface. Measurements by Nielson (1988) indicate that
  little radiation at lambda > 0.7 micrometers is transmitted through a
  meter of clean water, but over 95% of the radiation in the wavelength
  range 0.3 to 0.6 micrometers is transmitted through this much water.

They also say solar ponds are of the order of 1 to 3 m deep.

Table 2.6.1 of the book shows that about 40% of the energy in the terrestrial
solar spectrum has wavelengths < 0.7 micrometers. And an ordinary pool paint
might reflect half of the sun, and that reflection has to go back out of the
water again, giving the water a second chance to absorb it on the way out, so
maybe only 0.4x0.95x0.5x0.95 = 18% of the incoming solar energy escapes from
the pool, ignoring the 5% water-air reflections... 

>An expensive idea:  Build the pool with three parts.

Hmmm.

>The middle part is a regular pool. The other two parts are the same area,

Why the same area? Vot is the goal here?

>but only 4 inches deep, painted black.

Why 4 inches deep? Why not dark green, which can look very dark to the sun,
but bright to the eye, which is most sensitive to yellowish green? Why does
the Lord permit such Suffering on Earth, if He is Omnipotent? What is Truth?

>When the sun is not shining, drain some water from the pool so the
>shallow parts are empty.

To avoid losing heat at night...

>(How to get the warm water to mix into the rest of the pool, though?)

The filter pump?

>The shallow parts could be covered with bubble cover all the time, or never
>covered.

Never seems simpler. If the shallow parts have some thermal mass (how much?),
and they are only covered with water once in a while (how often?) to remove
most of the collected and stored solar heat, evaporation loss won't be a lot.
How often should we spray a roof?
 
A square foot of 4" thick concrete weighing 48 pounds with a specific heat of
0.16 Btu/F and a thermal capacity of 8 Btu/F-ft^2 absorbing 300 Btu/hr of sun
might heat up 40 F in an hour, if it lost no heat to the to the air or the
ground. Suppose we covered it with 8 pounds (one gallon) of water per hour,
raising the water temp by something like 30 F. How long would the water have
to sit on the concrete, each hour? Suppose the main thermal resistance is
the concrete, at about 0.2/inch, ie about 0.4 for half the slab thickness.
We want to transfer about 300 Btu through a US R-value of 0.4 in t hours, with
an average temperature difference of 10 F? So, Ohm's law for heatflow says
U = t delta T A/R, ie 300 = t (10) 1/0.4, so t = 12 hours. Too long. What
to do? Add lots of steel to the concrete to raise the thermal conductivity?

Flood it more often, using less water each time, to remove the heat from
the surface, before it has a chance to propagate into the concrete? This
means more evaporation loss... A less porous surface like tile would help.

Some people say thin-walled 4" PVC sewer pipe costs less than the volume of
concrete it displaces (but doesn't the slab have to be thicker, if it has
4" pipes inside?) Maybe the water should flow through pipes in the slab.
Maybe smaller pipes, eg polyethylene tubing, just inside a masonry wall
to the north of the pool, if we want to use the pool in the winter.

Most pools have a shallow part already, a skirt, about 6' wide, with almost
the same area as a 24' x 32' pool surface. Make it thinner, of reinforced
concrete? Hard to do for existing pools. Paint the skirt darker, and put some
PVC pipe with some holes in it around the outer perimeter, and add a solenoid
valve and controls to the filter pump to divert the flow to intermittently
wash the skirt with some pool water, if the pool were too cool and the skirt
were warm, washing dried Cool-Aid, cookie crumbs, etc., into the pool along
with the warm water. 

We might wash the skirt during the day to keep it cooler for feet, and
wash it at night sometimes, if the pool got too warm, automatically.

Nick

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From: [email-masked] (Nick Pine)
Date: 11 Sep 1996 09:58:44 -0400

Steve <[email-masked]> wrote:
 
>I found a way to handle the hose better.  Just use a hot melt glue gun
>and 500 feet of hose to glue a 6 foot diameter flat coil.

28 ft^2? How much does the hose cost? What next? Lay a piece of plywood on
the ground with some 1" beadboard impaled on a few headless nails to guide
the hose, and make a spaced rectangular coil with a 3" gap between tubes, and
some sort of thin concrete fill, with chicken wire on both sides, to cast
sections of a freestanding north wall, with polyethylene film glazing?

>I now have 900 feet of hose in the system.

51 ft^2 of solar collector?

>Water entering at 82 degrees came out at 96 degrees at 2 gpm flow.

Sounds like (96 F - 82 F)(8 lb/g)(2 g/m)(60 m/hr) = 13,440 Btu/hr 
out of 300 Btu/ft^2/hr x 51 ft^2 = 15,300 Btu/hr in full sun.
88% efficient, as a solar collector! :-)

>As I add coils I hope to maintain the temperature thorugh October.

This might work very well with a good pool cover.

Nick

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From: [email-masked]
Date: Wed, 11 Sep 1996 08:01:06 GMT

I found a way to handle the hose better.  Just use a hot melt glue gun
and 500 feet of hose to glue a 6 foot diameter flat coil.  Use about
an inch of hot melt glue every 4 or 5 inches.  The result is a
lightweight coil of hose that is durable and lightweight.  I just
threw it up on my patio cover and hooked it in line.  I now have 900
feet of hose in the system.  Water entering at 82 degrees came out at
96 degrees at 2 gpm flow.  The days and nights have been warmer the
last few days; about 92 and 60.  The pool is now 88F, warmer than when
the days were 104 and nights 75.  As I add coils I hope to maintain
the temperature thorugh October.

STeve

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From: [email-masked]
Date: Thu, 12 Sep 1996 07:12:34 GMT

>Steve <[email-masked]> wrote:
...... 500 feet of hose to glue a 6 foot diameter flat coil.

>28 ft^2? How much does the hose cost?
$30 per 6ft diameter coil plus $10 worth of hot melt;  and 4 hours of
my time.   Dang, how cheap do you want?

>. . .freestanding north wall, with polyethylene film glazing?
This assumes you have the funds and space for a north wall, of course.
I don't have ground level sun exposure that I can use.   How about a
comment on pulling heat from a hot attic?  How big a radiator?  Any
ideas?

>88% efficient, as a solar collector! :-)
I guess I should have re-measured the flow rate after the last 500
feet add-on.  And isn't 8lbs/gal for water a bit high?  Anyway, what
efficiency can a simple open air collector hope to get on a windless
day in full sun?

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From: [email-masked] (Nick Pine)
Date: 12 Sep 1996 10:19:32 -0400

>$30 per 6ft diameter coil

6 cents/foot...?

>plus $10 worth of hot melt;  and 4 hours of my time.

Another $14 :-) Hmmm. $44/28 ft^2 = 1.57/ft^2. Not bad, but...

>Dang, how cheap do you want?

I still like the south roof idea. 10 cents/ft^2 for the two layers of poly
film, another 75 cents/linear foot for the extrusion clamps to hold it (or
maybe some cheaper 1x3s or aluminum strips with screws), and another $1/ft
for the 1 1/2" PVC pipe along the top edge? $60 + $75 + $30 = $165 for a
30' long x 20' slant height 600 ft^2 roof, ie 28 cents/ft^2?

>This assumes you have the funds and space for a north wall, of course.

Funds may be easy, vs. space. That wall might cost 10 cents/ft^2 for the
beadboard back, another 10 cents/ft^2 for the concrete, another 10 cents
for the chicken wire, 18 cents for the tubing on 4" centers and 5 cents
or so for the poly film cover, ie 43 cents/ft^2, not counting labor. More
than the roof, but swimming pools often need walls around them anyway.
 
>How about a comment on pulling heat from a hot attic?

Good idea. Especially if you make the south roof transparent, like mine. Ed
Palmer of Solar Attic in Minnesota (612) 441-3440 sells something like this
for use with an ordinary attic. You might start with a used auto radiator
with its attached 12 V fan, like the $35 1984 Dodge Omni radiator in my
living room floor. Ed charges more than that for his version, $1500 or so 
in the tax credit era, $500 or so now :-)

Or you might use a duct heat exchanger like the $139 all-copper 2' x 2'
SHW 2347 unit made by Magic Aire, which transfers 45K Btu/hour between
125 F water and 68 F air, ie about 800 Btu/hr-F at 1400 cfm, with a 0.1"
H20 air pressure drop. The $12 Chinese-made Holmes (800)-5-HOLMES 20" 
box fan moves about 1000 cfm, whilst consuming about 100 W. 

>How big a radiator? 

How big an attic? How big a pool? Where I live, a 24'x32'x6' deep pool at
72 F might lose 24(72-36)768ft^2/R10 = 66K Btu/day of heat through its
floating 2" Styrofoam cover, another 24(72-45)672ft^2/R10 = 44K Btu from its
R10 sides, if any, to the warmer ground, and another 24(72-55)768/R10 = 31K
through its uninsulated bottom, ie 141K Btu/day in December. A 150 ft^2 $50
solar collector could keep it heated in December, if it were mostly covered.

>...isn't 8lbs/gal for water a bit high?

Heavy water.

8 is a nice binary number, no? As is 64 pounds for a cubic foot.

>Anyway, what efficiency can a simple open air collector hope
>to get on a windless day in full sun?

It can hope for 100%, or more, if the air is warmer :-)

Nick

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From: [email-masked] (Nick Pine)
Date: 19 Sep 1996 12:19:41 -0400

Solardc <[email-masked]> wrote:

>Use a u/v resistant cover on a roller or connected to hula hoops.

How do you connect a cover to hula hoops? Most covers seem to have
very poor R-values, 1 vs 10 or 20... 

>...you won't need the cover except in the coolest ends of the season.

I keep thinking about year-round use. Swimming in January,
with the cover off, but not more than an hour a day or so. 

>Designs from worst (1) to best(higher numbers)
>
>Starting with the poorest design (sorry, Nick I only speak from 22 years
>experience) 

Aha, an old hand, like the folks in Wash, DC :-) 

>1."Trickle" (evaporation, corrosion, low flow)

I think we've been through this before: trickle between two layers of plastic
film on a roof, a black one over the shingles to keep them from rotting, and
a clear one over that to eliminate evaporation. Use al extrusion clamps to
make the 5 cent/ft^2 film replacement and recycling every 3 years very easy.

Low flow? Seems like we'd want 1 gpm/10 ft^2 or so, which might easily
emergy from a 2" PVC ridge pipe with 1/8" holes every 6" or so on the
south side, that trickle water between the plastic films.

>6. EPDM (Solaroll, Sunmat)

And EZ-Heat? $4/ft^2 seems expensive, vs 30 cents/ft^2...

Nick