From the solar-ac archive:

Is anyone else on the list interested in trying some of this out?
Please speak up or send personal email.

I imagine that the basic first experiment would involve some
gallon metal cans, an oven, and a 50lb bag of calcium chloride
(which should cost $20 or so and be fairly easily available).
After heating the cans and capping them, I wonder what's the right
way to try to get some cooling and heating effects?  

The basic idea would be, sit the cans of dry-ish CaCl2 over *here*
and a pan of water over *there*, and enclose them in a bigger
container to exclude humidity and perhaps air.  Open the lids on
the CaCl2 containers, seal it up, and wait.

My unknowns are: do we really need a vacuum-tight
enclosure in order to produce decent cooling effect ...
Is there a role for brine or antifreeze solution to get reduced
temperature, or would that kill the H2O partial pressure ...
What's the ratio of heating to cooling effect and can we control that ...
Do we need to go to special lengths to increase water surface area
via spraying, splashing, or evaporative-cooler-style fins ...

--Marc  (ringuette@solarmirror.com)

Go for it, Marc!  I, too, am the type that likes to TRY THINGS.

There are too many people waiting, and waiting, and waiting for an "off the
shelf" solar cooler that just isn't going to come.

While lithium bromide adsorption coolers are nice to talk about, let's face
it: there are none small enough to buy for "the little guy".  Ammonia
adsorption coolers are, again, fine to talk about, but not really available.

In principle, an "open cycle" solar desiccant dehumidification system would
consist of:
    1) a "contactor" where the air from a building is exposed to the
concentrated salt
    2) a pump
    3) a "regenerator", where heat (from solar, hopefully) is used to drive
off water from the solution

Get a bit fancy, and you add
    4) a heat exchanger, which recovers some of the heat from your
"regenerator" and uses the warm outgoing concentrated solution to pre-heat
the incoming solution.

There are all kinds of ways we/you could build the components of the system.
The contactor could basically be one of those common humidifier pads
available in your hardware store.

The regenerator could be an open pond, a covered pond, or a fancy solar
heater.  The solution, once it is heated by the solar collector, could
"flash" into the air and lose its water vapor.

There are really endless possibilities.

The heat exchanger could be copper (which does corrode some in calcium
chloride, but only at the air/water contact zone) or plastic.

There are a huge number of ways to make the heat exchanger, and I think some
smart people out there will look at a wide range of existing products like
"corplas", a double-layer polypropylene sheet that could be made into a heat
exchanger plate, or greenhouse covers with corrugated form.

The contactor, which takes the building air and exposes it to the calcium
chloride, will tend to warm up, and this heat needs to be dissipated.  Why
not use the "sky cooler" concepts for this?

Get going, and try something, y'all!

-David Wells

I think it would be really great to use desiccants to draw water
from humid air, then heat off and condense the distilled water for
domestic use, using solar heat.  I'm not sure if this is feasible, or
how it would compare economically to other watermaking methods.

Desiccants are great ways to store heat: a block of dry desiccant
with a waterproof covering is like a block of stored heat with
a heatproof covering.   A basement full of dry desiccant could
heat a home through a cold winter.  Too bulky for most purposes, though.

Indirect evaporative coolers, in multiple stages, can theoretically
obtain any temperature down to freezing.  It's possible, but probably
not a useful idea, to combine dehumidification, cooling back down to
ambient temperature via a heat exchanger, and subsequent
re-humidification.

--Marc