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Sustainable dehumidification for a "dry room"

Mike Haasl

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posted 8 years ago

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Hello permies! I've come to realize that I have many microclimates inside my house. Warm coat closet = fermentation area. Cool, dark, damp basement = root cellar. Airy, light basement area = seed drying.

The one microclimate I don't have but would really like is a cool, dark and DRY area for storing seeds, grains, canned goods, etc. It's humidish here for 6 months of the year (dew point 55-70). I can section off an area of my basement for the purpose and seal it up to prevent air exchange, but how do I dry it out sustainably?

I could put in a tiny dehumidifier. I could rig up some kind of a desiccant (suggestions?). Are there other ways?

Thanks!

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Genevieve Higgs

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posted 8 years ago

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Our smallish (2 bedroom 1 bath ) house is soggy and a single dehumidifier keeps it nice and dry through west-coast winters. It doesn't seem to use too much electricity and can even permit us to rack dry clothes indoors all winter. BUT it does heat things up to the point it is our primary heat source spring and fall.

Cody DeBaun

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posted 8 years ago

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I've wondered about the mechanics of this as well. My thought process on it so far has gone something like this:

- When air cools, it loses moisture due to condensation
- When it warms, it *can* take up moisture again
- A system that cools incoming air and drains off the condensation, then allows the air to warm back up again without any exposure to another moisture source would result in drier air
- Or doesn't let the air warm up?

I dunno, as you can tell from the complete lack of facts or figures this is purely conceptual on my end. I don't know that this would work, or if it would reduce the moisture level sufficient to create the conditions you're looking for. With some knowhow and experimentation though, I would bet you could dry air simply by passing it through a length of earth tube with a well placed water catchment/drain system. Maybe taking air from a warmer part of the house and putting it through that tube (ideally in a passive flow) might yield the greatest moisture change....

Of course the whole thing would probably work better if you crammed one of those H2out style silica gel canisters in one end of the tube

(edited to include silica gel cramming)

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Mike Haasl

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posted 8 years ago

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Cody, the process you're describing is basically how a dehumidifier works. I'm not sure how dry I need this room to be but 40% humidity at 60-65 degrees would probably work well. According to my little dew point chart, to condense water from that air, it would have to be cooled down to 35-40 degrees. I could do that in the winter by channeling the air outside. Or just swapping some inside air for dry outside air. But I wouldn't have a way to do it in the summer. Our earth is probably 50 degrees which would condense 60 degree air down to 70% humidity (still too wet).

I just checked Amazon for silica gel and they do sell big buckets of it. Some color changes when it's halfway filled with water. And you can put it in the oven to dry it back out and reuse. That could be a solution. I couldn't easily determine how dry the silica can make it in an enclosed space. And it looks like there is a pink indicating one that is safer and a blue one that has toxic gick in it.

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Cody DeBaun

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posted 8 years ago

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Might be worth a whirl.

Reading a little bit more about condensation, I'm wondering if you might get dryer air by tilting the pipe, such that the inlet is higher than the outlet? Moist air is lighter than dry air, so that air which touches the walls of the pipe and loses moisture first would first... is that right?

I don't know if that would lead to overall dryer air or just more time between bakes for the silica gel.

Mostly I think I'm just hoping that if I say 'I don't know' enough times someone with a better understanding of fluid dynamics, gasses and humidity will come along and drop some wisdom.

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Roberto pokachinni

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posted 8 years ago

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You could maybe have a well lit room full of succulents, like Aloe, that serves as the air intake for the space, and another for the air outlet, and all you would need is a fan to move the air between the rooms. The succulents would draw humidity from the air that they need for growth. Initially you would need to water them, but once established they would dehumidify the air in order to drink. Never tried this, but thought of it a while back.

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Mike Haasl

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Robert, that's an interesting thought. Using plants to consume the water in the air. It would be a challenge for this particular application since they'd need CO2 so some air would have to enter and leave the "system". And then it would accept humidity with that air. And I'd have to have two chambers, one that's dark for the storage and one that's light for the plants.

But I like the concept. For things like living areas where you already have plenty of CO2 and light they could potentially draw humidity out of the air. Neat thought!

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Dale Hodgins

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posted 8 years ago

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If the area has very little air coming in or out, you could simply hang a few flannel sheets. They would absorb moisture. Hang them in a sunny window first, to get their moisture level down to a bare minimum.

Wool, will also absorb moisture, as will sawdust. Cedar sawdust has the added benefit of deterring moths.

Mike Haasl

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Sawdust and planer shavings I have plenty of. Do you know how dry that would make it? I can seal up the closet/room pretty well to prevent air infiltration.

I've heard of using rice for this as well. Any other common materials that I could use? Does anyone know how low a humidity level any of these materials would provide?

If I was fancy I could put the sawdust in permeable bags and cook them in the solar oven to dry them out every once in a while. If I was really fancy I could weigh the bag when it's dry and figure out when it needs to be redried by how heavy it's become.

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Dale Hodgins

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I accidentally created a dehumidifier in my room when I was a teenager. I had a rabbit hide that I was trying to dry out, by putting salt on it. At first, the salt got wet, and I figured that it was drying out the hide. But it happened every day for a couple of weeks, and the hide seemed as thick as ever. I was gathering moisture from the room, and it was dripping into the pan under the hide. My room was in a damp basement.

I'm not sure how well this would work in a drier room, but it might be worth a try. Instead of using a rabbit hide, a towel could be soaked in salty water and then allowed to dry out, with the salt covering it. It could then be hung up, to allow any moisture gathered, to drip into a collection tray. The salt would never be lost, since it could be dehydrated and used again.

There's probably a special type of salt that would work better. A tray filled with rock salt, might be able to collect water. The salt could sit on some sort of screen, so that water drips down into a tray. Save this water and dry out the fluid in a separate area.

Mike Haasl

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posted 8 years ago

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Just found this info on a salt or silica base diy dehumidifier. I'm surprised the media can absorb water and then somehow release it to drop into the collection container.

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Roberto pokachinni

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Sawdust and planer shavings I have plenty of

If I was fancy I could put the sawdust in permeable bags and cook them in the solar oven to dry them out every once in a while.

I think this is your way to go, Mike. Wood is always seeking humidity equilibrium and shavings and sawdust have great surface area to make that energy transfer. If you could hang pillow cases (or burlap sacks might be better) from the corners of the ceiling and put one each in the corners by the floor, this would probably accomplish the task pretty easily. Rotating the 8 bags with another 8 that are in the solar drier (or something to that effect), throughout your humid season might likely be adequate to the task.

A good salt system might be a great addition to this, using the solar oven to dry the salt out as well.

Mike Haasl

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Thanks Roberto, a burlap sack of cedar planer shavings sounds like a perfect solution. I think I'll go with that and see how dry it makes the room. If I need it drier, I can try salt. If that doesn't work, I can get silica gel.

Thanks team

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Roberto pokachinni

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You could put a smaller cloth sack of salt in the center of a bag of chips/shavings. Or you could salt the shavings by soaking them in a saturated solution of salt water and then drying them out before adding the shavings to the sack. ...I just took a permaculture design course with Geoff Lawton this year and one of the earlier modules included making random assemblies of data.

It helps one come up with ideas that one might not have thought of.

Mike Haasl

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posted 7 years ago

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Here's a quick update. I tried a tub of DampRid and it didn't change the humidity at all. I tried a bowl of silica gel and it didn't do anything either. I bought a silica gel dehumidifier for gun cases (StackOn) and it also didn't do anything. These were put in quite decently sealed cabinets where they only had to dry less than 20 cubic feet of volume.

In all three cases the temp was about 55 and the relative humidity was around 45%. My suspicion is that a lack of air movement could limit their effectiveness. Or they can only get air to dry down to that level.

I haven't tried cedar shavings or salt. I found one plug-in mini dehumidifier with a collection tank on Amazon but based on reviews and Q&A I'm not convinced it will do the trick either.

I'll try the cedar next and see what happens.

My goal for seed saving is to have the temp plus the humidity be below 100 (per the experts). Right now I'm right at that limit and would like to be lower.

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William Bronson

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posted 7 years ago

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Have you considered a solar chimney as a way to move air and moisture?
Maybe try a galvanized dryer vent,painted black,running up the south side of your house.
Aluminum downspout might be better.
Place in a glazed box? Insulate? Add thermal mass to continue convection at night?
Worked for one of Paul's Poopers.

Flap to prevent reverse convection flow at night.
Route make up airflow through a container of desicant?
Intake right at basement floor,maybe pipe snaking across the floor?

Pass air through a water cooling jacket?
Gas water heaters have a chimney running through their centers.
Strip off the insulation and park it in a tray.
Run your cold water supply though the tank before sending it to your water heater.
Run air through the center chimney,blowing from low sito high .
The air will cool.
Collect the condensation that rolls down the chimney,into the tray.
This is kind of like a column still.
You could stuff the chimney with stainless steel scrub pads,for more surface area.
Enclose the entire tank in a plenum and run the air through that for still more surface area.

Maybe intake>desicant container> water cooling >dry room>flap>solar chimney...

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Tim Bermaw

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posted 7 years ago

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How about moving in a frost free fridge and using it as a free 24/7/365 dehumidifier?

Most folks don't know that their 'frost free fridge' can be easily hacked to act as a dehumidifier. As it runs continuously, it can be used to suck moisture out of a humid space all.. year.. long.

Frost free fridges actually have a heating element. This heating element comes on every-so-often to thaw out the cooling plate. Any frost/ice that has formed on the cooling plate melts, drips into a plastic trough, drains to the bottom-rear of your fridge via a small tube, and then ends up in a plastic bowl located on top of your compressor. The compressor, as it works to pump heat out of your fridge and into the surrounding air, heats up. Heat from the compressor warms the bowl and evaporates the water, returning the moisture back to the room where it originally came from. So, under normal circumstances, this operation is humidity-neutral.

Assuming your fridge is against an external wall, or above an accessible basement, or near a drain, you can get a short piece of scrap tubing, attach it onto the end of the drain tube (just above the bowl), and instead of the water ending up in the bowl, it can be redirected outside, to a container or drain. In any case, since it is no longer being heated and evaporated back into the air, it is effectively removed from the humidity equation and your internal air becomes drier.

Depending on how easy it is to access the back of your fridge, this hack takes mere minutes. I think it took me all of 5 minutes to do mine — and I chose to drill a hole into our back wall so that the water would go to plants outside.

It doesn't take any extra electricity, and doesn't harm your fridge in any way. It's just the free 24/7/365 dehumidifier that y'all have in your kitchen/shed but weren't aware of.

PS: I'm not suggesting buying a new fridge just for this purpose, or putting in an empty fridge. If you're anything like us you may have one or two fridges in the shed just for preserved food. Move those into the "dry room" and every time you go to get something from the fridge the room will get a little bit drier. The more often you access it the drier the room will become.

PPS: A frost free freezer can probably be hacked exactly the same way.

Mike Haasl

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posted 7 years ago

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Thanks William for the air movement ideas. I'm not sure I want to force air from outside the cabinet through a desiccant into the cabinet because the air in the basement is moderately humid so I'd be using a lot of desiccant to make that air dry and then sending it up the chimney after a little bit. But a tiny fan to blow air in the cabinet through a desiccant could do the trick. And in my particular situation it's hard to get a chimney into the sun from where this cabinet happens to be located.

Thanks Tim! How would I be able to identify a frost free refrigerator? Is there something obviously different about it? I don't have a spare one but if I find a free one I could be tempted to pick it up. If I understand your description, the water that is melted by the heating element goes to a bowl that is still within the insulated envelope of the refrigerator? That way when it evaporates it returns to the interior of the fridge (under "normal" operation)?

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Tim Bermaw

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Mike Jay wrote:How would I be able to identify a frost free refrigerator? Is there something obviously different about it? I don't have a spare one but if I find a free one I could be tempted to pick it up. If I understand your description, the water that is melted by the heating element goes to a bowl that is still within the insulated envelope of the refrigerator? That way when it evaporates it returns to the interior of the fridge (under "normal" operation)?

Frost-free fridges have been the dominant form of fridge for at least 20 years. You'd have to have a really, really old (or really, really cheap) one for it to be non-frost free.

The bowl is outside of the insulated envelope. Usually at the back and bottom in an open cavity:

Of course, with the public brainwashed by marketing/advertising to expect/demand "pretty" fridges with clean lines, the pipe is often embedded within the back wall, and the cavity/bowl is often hidden by a slotted panel, but they're still there. Have to be.

The moisture is normally returned to the room it came from. It only makes its way back into the fridge again when you open the door (again).

Mike Haasl

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posted 7 years ago

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Awesome, thanks Tim! I'll have to keep my eyes open to see if I can find one laying around. I have the seed cabinet already set up so I'm still going to try the cedar first.

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Peter VanDerWal

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posted 7 years ago

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You might do some research into "Desiccant wheels" and "Desiccant Waterfalls"

Desiccant wheels are a more mainstream method of dehumidifying air, desiccant waterfalls are just cool!

A desiccant waterfall uses a liquid desiccant, typically something like Calcium Chloride and water. You run the wide waterfall down a well, etc. and it absorbs moisture out of the air, you then pump it outside to a solar heater and boil off some of the extra water and then back to the waterfall. You can use storage tanks to hold surplus desiccant (in either state) until the sun comes out again.

My opinions are barely worth the paper they are written on here, but hopefully they can spark some new ideas, or at least a different train of thought

Rosie Carducci

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Mike Jay wrote:In all three cases the temp was about 55 and the relative humidity was around 45%.

At 55F and with a relative humidity of 45%, that is a dew point of 34F. That's pretty dry. How much drier do you want it?

Rosie

Mike Haasl

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Rosie Carducci wrote:

Mike Jay wrote:In all three cases the temp was about 55 and the relative humidity was around 45%.

At 55F and with a relative humidity of 45%, that is a dew point of 34F. That's pretty dry. How much drier do you want it?

I'd like it around 30% RH but that's just a random number based on where I'm starting at. I've seen in a number of seed saving presentations to have your temp (in degrees F) plus you RH percentage to be below 100 for good long term seed saving. Since these are winter conditions in my basement, I'm assuming the temp and humidity will rise in the summer bringing me above 100. I also have some salt and dry goods I'd also like to store in low humidity, cool, dark conditions.

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