Subject: Re: Passive solar heating for pool?

From: [email-masked] (Nick Pine)
Date: 16 May 1996 11:59:59 -0400

Shane Peterson <[email-masked]> wrote:
 
>I have a friend who is looking for information on passive solar
>heating designs for a kid's swimming pool.

Sounds interesting... Solar pool heating should be very easy,
with low water temps and all that built-in storage...

>Specifics:  Pool size is about 3700gal

eg 462 ft^3 of water in a circular pool, 3' deep, 14' diam, 154 ft^2 cover?

>            Location is western Washington near Olympia

          SP (sun power)    Daily air temperature   Pool temp

Hmmm. Jan 450 Btu/ft^2/day  38 F average  44 F max  83 F
      Feb 640 ( > of vert,  41 F          50 F      94 F
      Mar 880  horizontal)  44 F          54 F     105 F
      Oct 810               50 F          61 F     131 F 
      Nov 490               43 F          50 F      92 F
      Dec 390               38 F          44 F      77 F

>     Cost should be kept low, construction of
>     heating panel would be done by the owners.

The main thing is to have a good cover. Suppose it's R10 foil-faced foam,
2" thick, 16 x 16, hinged along the north edge, with a counterweight, and
you have R10 foamboard around the perimeter, and you use an R1 floating 
transparent cover and open and close the rigid reflective cover every day
when the sun is shining, except in October... 

Air temp Ta and water temp Tw make a daily heat loss Eout of roughly

      6 hr (Tw-Ta) 154/R1     cover open
   + 18 hr (Tw-Ta) 154/R10    cover closed
   + 24 hr (Tw-Ta) 132/R10    sides
   
= (924+277+317)(Tw-Ta) = =1518(Tw-Ta) = 154 SP = Ein ==>

Tw ~= Ta + SP/10 (see table above.)

Nick