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Old 02-25-13, 09:34 AM   #1
NiHaoMike
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Default DIY solar dehumidifier

Calcium chloride is a desiccant that can absorb so much moisture that it forms a solution. It is often sold cheaply as Damprid and Dri-Z-Air (and probably other brands as well).

So here's a simple way to make a solar dehumidifier:
* Get a black container (vented at the top) and put some calcium chloride in it. The amount should be such that it will not overflow even when fully saturated.
* On a sunny day, move the container outdoors so the sun can heat it up and evaporate the collected moisture, making it reusable.

That has the obvious disadvantage of requiring manual intervention. So let's add some plumbing to automate the process.
* One pump draws off some solution into a chamber where it is heated by solar power (possibly with a glycol loop and solar thermal collectors), venting the moisture outside.
* Another pump (or just gravity) directs the more concentrated solution through a heat exchanger cooled by a small evaporative cooler and returns it to the indoor container.

Has that been done before? How well does it work?

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Old 02-25-13, 11:01 AM   #2
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Instead of pumping liquid calcium chloride, as it may not turn to that state, Use a solar powered fan to pump outside air threw a filtration box, shaped like a painting packing crate.

Use the same fan to circulate the moist inside air threw the Calcium Chloride filter box
until you want to vent it outside.
It could all be automated, but it may end up looking like the Mad Professor's house..
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Old 02-27-13, 01:33 AM   #3
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Quote:
Originally Posted by NiHaoMike View Post
Calcium chloride is a desiccant that can absorb so much moisture that it forms a solution. It is often sold cheaply as Damprid and Dri-Z-Air (and probably other brands as well).

Have you experienced doing it on your home? Will it really dries up the moist? How long does it take to totally dry up the moist by using the solution? I just wanted to clarify these things for I find a great interest about it. Thanks!
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Old 02-27-13, 02:51 PM   #4
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I haven't tried it yet, I'm looking for more information about how well it works in practice.
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Old 02-27-13, 09:36 PM   #5
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Interesting idea. My only thought would be you might have a surface area issue after the first cycle. My recollection is the calcium chloride comes in granular form from the sources you mentioned. It turns to a liquid upon absorbing lots of water, and I'd guess will form a solid cake on the container it is in when it dries. Having less surface area will slow the expulsion and absorption of water I'd guess. Not sure if it'd be an issue or not.

I do remember from one of the places I worked that had a very large air compressor that it ran through a large air dryer. It was comprised of two cylinders that were cycled (absorbing, then heated and vented to dry the desiccant). I tend to recall that they were filled with the silica gel desiccant. While I don't think this absorbs as much water, it also doesn't change shape/surface area.
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Old 10-03-13, 10:26 AM   #6
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Default Similar thought but...

Would it be safe to keep the container on top of a wood stove and to fire up the stove to heat the salt to dry it?
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Old 10-04-13, 05:01 PM   #7
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A bed of silica gel or zeolite are better choices. Solar heated air can be sent through the bed during the day for drying. I recall the results of testing that showed air heated to 160F will regenerate silica gel efficiently. A combination of a timer and a thermostat can be used here to control a fan that sends air through a solar heater. A second fan can be used to send outside air into the home at a low rate via the silica gel bed while drying the incoming air - or air from within the home can be circulated through the silica gel bed at a higher rate. I suppose an alternative heat source might be used in the form of a small furnace with air mixed with the hot combustion gases to take the temperature down. A batch system makes sense here where a furnace could operate for several hours at a low rate, then the system realigned for air drying. Blow air through it for a few minutes at a high rate to cool and flush the bed before sending air to the home.
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Old 11-07-13, 07:17 AM   #8
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Default old farmers trick

My grandparents used to us a trick in the musty basement of their old farmhouse that utilized rock salt. Place one 5 gallon plastic pail inside of another, drill a couple 1/8 inch holes around the perimeter of the bottom of the inner pail, and fill the inside pail with rock salt.

They would fill 2-4 of these each spring and fall and they would last for months pulling gallons of water out of the air. No power or circulation, just check and empty the bottom outside bucket every other day or so. In the spring and fall at the worst times, I recall my grandfather emptying the couple quarts of water out of the bottom bucket 2 maybe 3 times a day. They also had a way of saving the salt and drying it by pouring the liquid into a large black tarp hung like a basket between some fence posts on a bit sunny day. When it dried to a crust all it took was a simple shake of the tarp to break then salt up into small pieces again. Maybe some automation to this system would make for a very efficient drier?
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Old 11-07-13, 07:59 AM   #9
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I've never heard of that... how does it work?
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Old 11-07-13, 08:33 AM   #10
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I would have to do some research to find out the exact specifics of the science behind it, but I know that the inception of the idea revolved around the old time method of preserving meat by dehydrating it with salt alone. My grandparents "jerky" was made my placing meat strips in a sealed container filled with kosher salt. The minimum was somewhere around 1 cup salt to 10 pounds meat. A small screen was used as a false bottom in the container to allow the moisture to collect.

Now the basic idea is that one part of salt is can hold on to many parts of water. And will only give the water up to other parts of salt, unless it is forced too completely release the water by evaporating with heat or whatever. So the air moves over the top of the bucket full of rock salt "aka cheap salt" and the moisture is very highly attracted to and captured by the top layer in the bucket. When enough moisture builds up gravity and probably capillary action help move the moisture lower in the bucket freeing up the top layer to absorb more moisture. As you go lower in the bucket the salt becomes more saturated and the very bottom is at a maximum concentration of water to salt. A liquid forms and gravity pulls that into the bottom bucket through the 1/8 inch holes you drilled. Eventually the salt in the top settles down and put and needs to be replenished but very slowly.


This is just a generalised assumption, but if one cup of salt dehydrated 10 pounds of meat. And that 10 pounds is probably half water, I think one could assume that one cup of salt could absorb half a gallon of water, by weight of course. Just assumptions....

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