# Re: Yet another solar heated swimming pool--a correction

```Seems like I have to go back and fix even the simplest things, even while they
are still on paper, which is a good time to do that. Perhaps this post should
have stewed for a couple of days before posting, but you know how it is when
you get excited about an idea, especially after a dozen espressos :-)

So here's the problem, in the following paragraph--not a large enough ratio of
thermal mass surface area to glazing surface area, in this solar closet. That
ratio should be 10:1 or so, to keep the temperature difference between the
air heater air and the thermal mass low, in this system with thermal mass
indirectly heated by warm air, and make the solar collection efficient, but
the glazing here is 80 is ft^2, and it's really equivalent to 120 ft^2 of
solar heat, with the reflecting pool, and the round pool sides are only 165
ft^2 and the pool bottom only has about 32 ft^2 of surface exposed to the sun-
warmed air, so that ratio is only 2.5:1, as posted. Nobody noticed this, altho
I did get some email from someone who said he "didn't do math," but we should
cover the top with PV and water heating panels and use antifreeze and pumps
and pipes buried in a radiant concrete floor slab under the pool :-)

The straw bales under the pool itself could be spread apart to make 8 air
ducts, each 6" wide x 16" deep, running from north to south along the ground,
to allow solar-warmed air from the south glazing to travel across the top
of the pool, under the cover, down the north back wall of the pool, between
the pool and the bales, and under the pool from north to south. This might
work with passive plastic film gravity backdraft air dampers in holes at the
top and bottom of the straw bales behind the glazing, but a PV-powered (-:)
fan would make it work better. The whole ground area should be covered with
some sort of vapor barrier, eg poly film, to keep moisture out of the straw,
and the tops of the ducts below the pool should have some bridging, eg 1/8"
of newspaper with 3 layers of chicken wire on top of that, and an inch of sand
mix cement over that. Let's ignore the heat loss from the ducts to the ground.

Here's a fix: forget the newspaper, make the ducts a foot wide, use 30 instead
of 40 straw bales under the pool and put in 100 concrete blocks with holes in
them, standing on end between the ground and the chicken wire ferrocement, to
act as fins to conduct heat up to the pool bottom. Each concrete block has a
surface area of about 6 ft^2 exposed to the warm air, so this way, we have 80
ft^2 of glazing and about 200 + 6*100 ft^2 of thermal mass surface area to
gather heat from the warm air, ie a nice 10:1 ratio.

Nick

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