Posted by Jeff on March 21, 2007, 2:25 am
I'm thinking about a trickle type collector. The fluid would be a
calcium chloride brine. Brine enters at a low calcium chloride
concentration and at temperatures over 85F (100F - 120F operating)
"regenerates" driving off water. The enthalpy of change (from a mostly
exhausted brine to mostly reconcentrated) is about 200 BTU/lb of brine.
This leads to a collector with a slow flow and made out of non metalic
materials like plastic to keep it from corroding.
This would be mounted on a sloped roof.
I think there are a few ways to approach this:
1) Terraced collector. Sort of a series of solar troughs a few inches
deep. Could be made out of a roofing material like tyvex.
2) A big sponge. Perhaps something like the pads they use in swamp coolers.
3) A mesh like fiberglass window screen that the fluid percolates over
Something else? I'm thinking a terraced collector might have the
fewest side effects. I have some memory of Nick discussing something
I'm thinking that the cost of such a collector would not be great and
concentrated in the cost of the glazing (SunTuf ?).
This would give me about 200 ft2 of air collector (in test mode). 140
ft2 of solar water (still in the construction phase) and about the same
amount of brine collector that would mostly be used for AC.
Posted by Anthony Matonak on March 21, 2007, 4:18 am
Where do you expect the water to go once it's been removed
from the solution? Maybe what you need isn't so much a water
heater as a water still.
Posted by Jeff on March 21, 2007, 4:13 am
Anthony Matonak wrote:
Vented off to the atmosphere. The temperature rise is not great and this
could almost be done unglazed, but for keeping out rainwater.
If you look up a few threads for "desiccant AC", you'll see a couple
of links; one application where the brine was regenerated by sitting in
pools and another where it sprayed through heated air. Think of that
pot of almost boiling water, add a teaspoon of salt and it starts
boiling. This "regenerator" is at much higher concentrations and with
calcium chloride instead of sodium chloride.
I'm not convinced that it wouldn't be better to use solar hot air (or
solar hot water heating the brine) in a sprayer where the surface air
contact is so great. The plus to the trickle collector is it's very low
Maybe what you need isn't so much a water
Posted by nicksanspam on March 21, 2007, 12:12 pm
This sounds good. The brine will lower the vapor pressure and heat loss
from condensation under the glazing, and we can store more heat in a brine
solution than the same volume of warm water, with no heat loss over time.
Condensing water during regeneration can be more efficient than evaporating
it into the atmosphere.
Adding water to a brine solution will release heat, but the solution can
provide more heat if it absorbs water vapor, which can provide summer
dehumidification and winter house heating from a damp basement floor.
Some people have used a low-cost 2:1 CaCl/LiCl vs a CaCl solution.
Polycarbonate doesn't last long with warm water vapor...
Posted by Jeff on March 21, 2007, 2:35 pm
I don't understand this "Condensing water during regeneration",it
looks to me that this is lost to the atmosphere. The whole regeneration
issue for liquid desiccants is a little vague to me.
Aren't there some toxicity issues with the Lithium Chloride? I
suppose an updraft dehumidifier would keep the brine out of the exhaust.
How low in humidity can you go with the 2:1 CaCl/LiCl before it
crystalizes? I'm sure this must be much lower than just the CACl.
Seems right. Angled wooden slats holding the liner into V shaped
pools. Perhaps a 1/2" to 1" pond depth at the back of the trough? A 24
ft2 collector would hold about .5 to 1 ft3 of brine.
Perhaps acrylic? The collector would be well vented and the temps
would be lower. Or perhaps no glazing but a shutoff during rain, you'd
have to drain the return line though.