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re: self-insulating water wall
25 may 2002
jerry ellinghuysen  wrote:

>uh, anybody want to discuss the original post??

sure.

>self-insulating water wall
 
>a self-insulating water wall may have advantages when used with
>the direct gain system in some situations... for heating as well
>as cooling and has the advantage of in-built insulation.

underwater insulation that needs to be tightly-installed to keep
water from leaking around it... seems like a more difficult and
expensive job than insulating the outside of a tank or plywood box
with fiberglass. 

this is similar to "the buckley two-compartment, thermosyphon,
non-reversing, solar-energy-absorbing-and-storing, water-filled
tank" as described on pp 62-65 of william shurcliff's book new
inventions in low-cost solar heating (brick house, 1979.)

shurcliff says it was also described in "solar energy digest, jan,
1977, solar energy 20, 495 (1978), solar age p. 22 (april, 1978),
the proceedings of the 2nd national passive solar converence,
vol. 2. pp. 271 and 469 (1978), and in many special reports." 
buckley attempted to commercialize it.

shurcliff continues:

  one might ask this question: inasmuch as the tank includes two
  compartments and each must be inslated from the other, why not use
  two separate tanks? one of them (the thin one) could be mounted on
  the vertical south wall of the house and the other (the thick one)
  [which might have a smaller surface to volume ratio if it needn't be
  part of the first tank--nick] could be mounted somewhat higher up,
  close to the ceiling... [or in the attic, for gravity-fed hot water.]

  then, because the larger tank is higher up, no valve at all would be
  needed. gravity convection, via connecting pipes, would do the entire
  control job automatically. also, less prime space would be taken up
  and leakage of heat from the big compartment to the small one would 
  be entirely avoided. admittedly, there are impressive advantages
  in having the two tanks teamed together as one integral unit; but
  there are impressive advantages the other way also; if two separate
  tanks are used, installation and maintenance may in some situations
  be easier and there is much greater freedom of choice as to where
  to place the larger version of the equipment.

zomework's "big fins" are a "separate tank" design. steve baer is about 
to market another version that uses modified freeze-tolerant plastic
"pig mats" as thermosyphoning collectors.

buckley's version used a valve containing some oil and water.
shurcliff described his own water-only floating-valve version 
on pages 66-69 of his book. less-sensitive but more robust and 
suitable for heating potable water. steve baer tested it. 

> ...these modules are best used in conjunction with direct gain
>and/or solar greenhouse.

direct gain, as in behind a window, inside the house? they might work
against the north insulated wall of a greenhouse, with low plants.
on the south side, they would shade the plants.

>the absorbing efficiency is between 55 - 65% of available radiation,
>very little heat is lost at night.

shurcliff calculates the floating-valve version would circulate water
when the south compartment becomes 2.5 f warmer than the north one,
in a 4'-tall version. 

>if used with direct gain, then the south side of the house is made up of
>self-insulating water wall modules and windows. the inner surface of the
>modules radiate heat to the interior and the rate of radiation can be
>controlled by a curtain.

seems to me this would leak lots of heat when closed and require manual
room temp control. opaque insulation over an air gap with temperature-
controlled upper and lower ventilation holes seems like a better choice
for automatic room temp control in a well-insulated house. 

nick




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