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?

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..

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! :)

I haven't tried it yet, I'm looking for more information about how well it works in practice.

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.

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?

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.

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?

I've never heard of that... how does it work?

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....

Some manufacturers are incorporating this method of dehumidification into their heat recovery ventilators and air handlers.

They call it a dessicant wheel or an enthalpy wheel or a thermal wheel.

These guys have made a Rube Goldberg-esque machine that claims to do what you are after:

http://www.advantixsystems.com/pdf/H...s_Brochure.pdf

It looks almost like an ammonia refrigeration system to me!

They got a patent I looked at before, but here's the general article on U of MD's project.

Oops, just found out I'm still too new to post links, but if you'll search google news for
'university of maryland solar dehumidifier' it's the only link that pops up.

They did exactly what you're talking about.

http://2007.solarteam.org/page.php?id=641

I googled it and added the link for you.

I just did a little googling myself. Here is an interesting solar dehumidifier. I think they call it "solar" but in order to make it solar you'd have to have solar hot water. The hot water is used to regenerate the descicant. Their PDF manual has a lot of info on the unit.

Solar Dehumidifier

http://ecorenovator.org/forum/attach...1&d=1383847416

Now, the question remains....
How do I build it myself and how am I going to fit it in my little farm house....?

It would probably be easier to build outside and duct into the house.

Sorry I wasn't being serious with that statement. Most certainly would fit better outside, one thing I am honestly curious about is the cost effectiveness of such a unit. I could build one, I have access to all the equipment that I don't have at home to do so. But what would the pay off be in what amount of time. My goal is to be independent of the grid, so I tend to lean more towards the simpler ideas that can be constructed from easily accessible parts and uses the least amount of energy possible.

Peacmar,

It really depends on your dehumidification needs and available resources. It should be fairly simple to run a liquid loop like the university did. Rig up a swamp cooler indoors and fill it with salt. When the salt hydrates, run the fluid outdoors to a solar regenerator. Some sort of concentrator would work well with this type of setup, i.e. evacuated tube collector or parabolic trough. It would generate the high temperatures one would need to evaporate or boil the water out of the salt.

The funny thing is that I joined this thread for curiosity sake, but am now seriously considering such a contraption. Part of my foundation is over 100 years old and has a small stream that runs through my basement every spring so moisture is a large issue. Granted, I plan to replace the field stones one day but not any time soon. I also have an abundance of hot water at my disposal. I run an outdoor gasification burner year round to supply my family's hot water needs. We receive large amount of kiln dried scrap wood from local industry so I have an endless supply therefore it was an economical choice for us. That being said, I think I can utilise this heat source to regenerate the dessicant. Even if I have to manually switch out the media every so often it would be worth not running a 2500 watt dehumidifier 3-4 months a year. Last night while pondering this, I envisioned a resemblance to a swamp cooler also. Forced air to speed things up, a water overflow draining into the basement sump. I'm thinking about either interchangeable or refillable cartridges for ease. And material choice will be important also, especially if I use salt.



Now you guys have gone and done it..... yet one more project i have that was conceived on this wonderful website....


:D

Peacmar,

Here's an idea for you. Since you have a high-grade heat source, you could run a regenerator basically for free. Just run the dehumidifier as a traditional evap-pad cooler, which would dry the air with the brine solution. Either tap the pump outlet so that a percentage of the brine went through the regenerator and back into the sump, or gravity feed an overflow tube to the heat source where the hot brine could evaporate. As long as the heat source was active, the unit would move lots of water out of the airstream. If the air needs to be drier, just add more Damp-rid to the sump. At a certain point, you would never need to add more salt!

U CAN DU IT!

Well that's the basic idea, first order of business will be to design an air handler that will move the damp air around and second is to find the parts to do so. I think it will be a batch load system at first until I can work out some sort of idea of the capabilities of such a system. Quarts per hour or whatever it happens to be. I can easily tap into the boiler lines at any point in the basement to put the regeneration unit wherever works best. Now, I have all winter to scheme this up and put it into motion. Unfortunately I won't be able to truly test it out till spring arrives. Thinking about it now, I already have created an air exchange loop for my clothes drier and could use a damper system to circulate outside air into the drier and moist air outside. I wonder if convection currents would suffice or if I would need to force air. I guess that depends on the amount of moisture absorbed and the humidity of the outside air. Many things to prepare and test before I can call it a working system. Then, eventually, when I am able to construct a solar heater for my mass storage tank, I will hopefully be able to run the system without burning wood. As the future plan is to use solar as a primary heat source and wood fired heat as backup.

I wonder how the U of MD group kept the calcium chloride liquid? Keep it heated above it's melting point?

Boz,

Please google the term: Hygroscopy

Nature is awesome!

I found another decent website:

Scavenging-Air Regen

Follow the links scattered on the page for all the info.

A retail, residential, affordable dessicant wheel dehumidifier:

http://www.sunpentown.com/sddede.html

Which lead me to this: "Calcium chloride is so hygroscopic that it eventually dissolves in the water it absorbs: this property is called deliquescence."

OK, more thinking to do. And I need to find the patent and read it again.

Hi just joined the forum, I found this thread whilst looking up solar air heating for my outside office/workshop/equipment store. The store is cold and damp and I was investigating making and using a beer can solar air heater to provide warm ducted air to the building. These are really cheap to make and when done properly actually look quite good.

However, I also want to dry the air entering the building to stop damp in the equipment stored in there. Hence researching solar dehumidifiers.

The beer can/soda can air heater (check it out on instructables) provides a free solar powered warm air flow, I was wondering if this could be fed through a silica gel bed to dry out the air entering the building?

Additionally whether a second air flow from the beer can air heater could be used to regenerate another silica gel bed. The silica gel beds could be periodically swapped over to regenerate one whilst the other is drying the inlet air.

Having read this thread I thought of possibly using a dessicant wheel such as the one posted by Daox so that the swapping over the dessicant could be automated/motorised.

Could a dessicant wheel be made to turn under gravity? The wetter side would be heavier and therefore, if the unit was angled correctly turn the wheel under its own weight, with the lighter drier side gradually moving up as it dried.

Ross

This would be very easy to test. You wouldn't even need a whole wheel, just a simple balance, and silica gel. Try it out and let us know what you have learned.


But back to the de-humidify question, I haven't been following this thread, but...

Whenever you heat air, the amount of moisture it contains remains the same, but at the same time, the relative humidity (AKA: "RH") gets smaller. This is because warm air can hold more moisture than cold air.

So, no matter what the relative humidity of the outside air is, when you heat it, the new RH will be lower, and thus capable of holding more moisture.

On sunny days, if you continuously brought in cold air from the outside, heated it, circulated it around your space, and then dumped it outside, you would de-humidify your space. If you got some cheapo PV panel (I think there actually is such a thing now) and used it to power your beer can heater fan, your system would only run on sunny days.

Personally, I doubt that the gel approach will be very useful useful... but I'm open to being show to be wrong.

-AC

AC,

I have been pondering this idea and following this thread for awhile. Both solid (silica gel cartridge) and liquid (brine solution) systems have been used in commercial applications since the energy crisis of the 70's happened. Apparently, either method is much more efficient than ammonia systems at transferring latent energy loads. Many supermarkets and factories use their inherent waste heat stream as a source of "free" energy to regenerate the dessicant.

Only lately has the residential segment caught on to this process. The big eye-opener to residential architects and energy experts was the University of MD 2007 solar decathlon "leaf" house, cited earlier in the thread. They won the silver medal. Since then, the university has (you guessed it) built another "watershed" house for the competition and won Gold with it in 2011. It is truly a mad science project that works exceptionally well.

http://2011.solarteam.org/design

The idea of dehumidifying the air before it is circulated through the building is to reduce the moisture content of the air.

If outside air is used as the building cools at night, it will eventually reach the dew point of the air and the building will become damp, condensing on the cooler surfaces and equipment stored in there.

By recirculating the internal air during the day, dehumidifying it and heating it, the overall moisture content within the building will reduce. Which will reduce any condensation overnight, it should also contribute to overall higher temperatures within the building.

Ross

OK, so we're talking about driveway salt dissolved in water, right?

Do we have a how-to yet?

Hmmm...

I just took a 50 lb bag to the dump, too.

So what is the critical % and how do you measure it?

Looks like the CO2 sensor project I did could be used, but you'd excise the CO2 part, and keep the humidity/temperature sensor, and use that as your input to modulate your PWM stream which could control your pump... Or use the set-point approach... on & off as required.

But getting rid of the water in the brine would be the real task.

-AC

Here is a regenerator that is said to have a thermal COP of 1.0 or better when used with gas:

http://ailr.com/our-technology/two-stage-regenerator/

The cool thing about this one is that it takes advantage of the natural stratification of the saltwater solution. Since the strong solution is denser, it naturally descends in the tank.

Dessicant Waterfall...
 

The waterfall idea looks pretty interesting to me.

Has anyone found info about the percentages of dissolved CaCl2 in water to make this thing work? Seems there should be some kind of chart that would indicate the range of CaCl2 per water that would be effective in a 'waterfall' setup.

This waterfall setup with solar drying, would be a good combo for areas with abundant sun AND excessive humidity... it would suit quite a few EcoRenovaters!


BTW, CaCl2 has also been used in some of the more successful Phase Change Material thermal energy storage studies... but that would be a topic for another thread.

-AC

kind of...
 

What happens to the woodwork and internal finishings?

Easy fix for that is to use a humidity sensor to either turn off the dehumidifying setup or turn on an evaporative cooler.

MN,

Just imagine something being left in the desert for a few weeks. Woodwork shrinks and warps. Plants drop their flowers or leaves. People develop dry skin and sinus infections.
When the indoor RH goes much below 40% for long, people and objects acclimated to high humidity take notice. Some of these systems, especially those that utilize temps above 190 degF, claim that their systems can lower RH down into the teens and twenties.

AC,

Now that you mention it, this solar dessicant dehumidification system could easily be bent to become a high-capacity thermal store. Say one were using an evacuated tube collector on the roof, with the batch tank filled with CaCl2 brine solution. With a temp diff controller and a few sensors here and there, one could direct the hot brine solution to a DHW tank or a hydronic loop or tank to cool the solution. It could then top off the fountain to dehumidify if necessary.

A good video describing operation:
http://www.advantixsystems.com/video1.php

And here it is on youtube:
http://www.youtube.com/watch?v=WNvxkXyKwGw

Another image I could just not resist to doubt:
https://ecorenovator.org/forum/attac...1&d=1591718926

That is weird, but really cool.

There was a guy named George Lane, that worked for Dow chemical doing extensive work on phase change material.

HERE'S HIS PATENT

...and then there is Carl Venner's Dissertation.

There's so much to be said about this stuff that it should be continued on another thread.

-AC

It is a shorter route to comfortville, but there remains the issue of easily & effectively removing the water.

With a de-humidifier, you dump the reservoir out, job done.

Here, we're only half way home.

-AC