Compact compressor-based dehumidifier for custom built dry cabinet?

[pipe2null]

I'm finally getting around to building a dry box/cabinet to store my 3d printer filament.  In the past I've used a gasketted sterilite storage container(s) with EvaDry renewable desiccant and wireless Accurite temp/humidity sensor(s) for monitoring, but I have yet to find an off-the-shelf container that has mounted-and-in-use-spool-friendly dimensions that also does not waste a lot of space, and using desiccant can take a full week or two in order to reduce humidity to the lowest it is able to go even for a small confined space, which I measured at around 40% in my previous setup.

Now that I have my Prusa MMU2S installed, I have 5 filament spools in active use at any given time and my old storage container is no longer good enough.  So, time to build a new dry box/cabinet that keeps my spools as dry as possible while in use or waiting to be used: just mount them all and run PTFE tube through the cabinet wall, and swap the PTFE tubes connected to my printer as needed.  My intention is to use plastic sheeting, the same stuff you use to winterize windows or maybe use clear plastic shower curtain material for dry cabinet walls, and standard lumber for the frame and support for several "shelves" of mounted spools.  If this is a bad idea in terms of humidity control, please comment.

But I've had a helluva time trying to find an appropriately sized dehumidifier.  I want to go with a compressor-based unit since they dry the air much faster than peltier junction (same thing as water coolers or small refrigerators) and I have the impression that compressors can reduce humidity lower than peltiers and desiccant are able to go.  Please correct me if my impression is incorrect.  Normal floor standing compressor units are much too large and I have only found peltier versions in the form factor I'm looking for.

If some manufacturer makes one, I'm looking for a compressor dehumidifier with dimensions that are 1/2 cubic foot or less in volume so it doesn't use much space inside the dry cabinet, is reasonably easy to mount or sit on a small shelf near the top of the cabinet so the gravity fed drain hose (duct-taped is acceptable) can get snaked through the cabinet wall and out the window: I don't want to empty a bucket every day, and the window sill is a few feet off the floor.

Anyone know of a product or a manufacturer that might make something like this?  Also, DIY dry cabinet construction comments are welcome as well.

[twospoons]

You'd do better to just use a dessicant, and plenty of it. Molecular sieves work better than the silica gel you've been using. 3A, 4A or 5A can be used for drying.
With a compressor based dehumidifier the minimum humidity is going to be driven by the minimum temperature achieved by the evaporator. You'd want it as close to ice-point as possible. Not sure if a domestic dehumidifier is going to do that.

[David Hess]

As twospoons points out, it just depends on temperature so peltiers can work just as well as compressors but their power efficiency tends to be worse which becomes less of a problem in lower power applications.

http://www.amstechnologies.com/products/thermal-management/thermoelectric-technologies/thermoelectric-cabinet-coolers-and-dehumidifier/view/thermoelectric-dehumidifier-device/

Before investing money in that type of solution, I would scale up using more rechargeable desiccant and and maybe install a small fan to circulate the air within the cabinet.

[Kleinstein]

Not all Plastics are really absolute tight to humidity. So the preferred material for the container is more like metal. A glass jar is also OK. Using glass plates is Ok, but needs care with the glue: most (if not all) types of silicone sealant let water through quite easy.

For just storage and also to get very low humidity molecular sieve or similar desiccant is the better choice. The thermal systems work well at high power and relatively high humidity levels only.

[NiHaoMike]

Probably the most efficient route would be to use calcium chloride desiccant and regenerate it with a solar thermal collector.

[pipe2null]

At the end of the day, I'm attempting to find a "happy medium" dehumidified storage solution between ElCheapo high maintenance/poor space efficiency and an industrial/commercial zero maintenance but expensive pre-made cabinet for an actively used dry box/cabinet.  Using cheap materials with a lower end commercial dehumidifier or vice versa is within range.  The 2 biggest reasons I'm trying to DIY a custom build is that my previous solution worked well enough for long term storage, but every time I opened the box to add a new roll or get one out for use, it would start from scratch and take a couple weeks to reduce humidity again (plus have to swap out the desiccant each time).  As pointed out, a fan would help speed up the process, but the dehumidifying problem is the same.  The second big reason I'm doing a custom build is because my office/workshop/lab/printshop/and general storage room is cramped for space, especially space useful for something other than storage.  For instance, I can't mount spools underneath my printer because I have a pile of lumber there.     Rebuilding my previous containers to be able to mount spools for active use (spools can spin and filament is tubed out the side to printer with PTFE) waste a significant amount of space due to off-the-shelf container dimensions.  The dry box I'm attempting to build will mount on the wall between my workspace and the above up-to-the-ceiling shelves, and has enough room for 40+ filament spools, each mounted and ready to use with a shared dehumidifying solution.  Compared to a max of about 10 spools with a minor upgrade to my previous solution with 2 separate dehumidifiers and using up valuable workspace since there is no good way to mount the containers on the wall.

But "why" build a custom dry box is probably obvious to you, so I'll stop my rampagy digression.   

@ Everyone who's posted: Thanks for the pointers and links!  I've attempted to condense the info below.
@ Kleinstein: Thanks for pointing out the issue of choosing materials for cabinet walls and sealants.  I guess that means this topic is really 2 questions: dehumidifying and appropriate material options.  Generally speaking, I have no idea what specific materials are good for humidity isolation, and what is more of a "screen door" for water vapor.

Materials Choice for Walls:
Best but potentially more difficult to work with:  Metal, glass (acrylic?)
Cheaper and potentially easier to work with: Plastic sheeting (but which type is ideal for $/humidity isolation?).  I've considered the following so far:
- Plastic sheeting intended for weather proofing windows, for example: $30/roll https://www.amazon.com/Warp-Bros-NFG-36P-Flex-O-Glass/dp/B001457JBS/
- 12 Gauge clear PVC sheet, similar material as heavy duty shower curtain (or literally cut up an $11 shower curtain): https://www.amazon.com/gp/product/B07YFPPH4Q/

Materials Choice for Door Seals (and/or gaps in walls for filament/PTFE):
It's probably best to seal individual PTFE tubes where they go through the wall with caulking/sealant, but using a long narrow gap in the wall to snake out PTFE tubes between weather stripping (if it'll maintain a good enough seal) is a much more flexible solution and allows variable "where and how many" filaments are externally accessible without opening the dry cabinet.  I've considered the following so far:
- self adhesive magnetic tape (door or "plastic flap door" only): https://www.amazon.com/Magnetic-Adhesive-Backing-whiteboards-Organization/dp/B07QKNZZ3J/
- open cell foam weather stripping similar to neoprene, no idea how much the material "breathes": https://www.amazon.com/gp/product/B0814KHG9T/
- closed cell vinyl foam weather stripping, no idea much about it, but it was $2 for about 3 meters of material: https://www.amazon.com/gp/product/B01NAH18WF/

Materials Choice for Sealing wall material seams, edges, small gaps, etc:
- Silicone Caulking, but some varieties are in the "screen door for humidity" category of materials
- ?  I want to say some type of epoxy, but that seems overkill, and a bit of a PIA for a larger project.  I would think something suitable would be available for a caulking gun, but no idea what to look for since "water seal" and "humidity seal" are 2 different things.

Dehumidifier, Condensing Compressor Type:  Minimum RH% achievable at room temperature = *?*
Pro's:  Removes moisture significantly faster than other methods and can be more power efficient
Con's:  Much noisier than other solutions and typical consumer-grade units are large and bulky, too big for small to medium sized dry cabinets.
Options: I'm not sure if smaller or more compact units are even manufactured... ?  I have a floor standing unit in the other room that can drop humidity from 65% to less than 40% in a few hours for several decent sized rooms.  In a sealed area (without an external door opening/closing throughout the day), it should be able to hit 35% without too much additional time.  If it were smaller with lower volume/minute fans, I'd just duct tape a hose to it, throw it into my cabinet and call it a day, but waaaay too big for that.
Options:
- To-Be-Discovered compact commercial/industrial compressor type unit, if such a product exists
- (I THINK this is a compressor type...): https://www.aliexpress.com/item/33008690071.html?spm=a2g0o.productlist.0.0.3a031c1bdFxSqs&algo_pvid=5aad1fb7-1a86-46f1-8ede-2e7bd6013eb8&algo_expid=5aad1fb7-1a86-46f1-8ede-2e7bd6013eb8-2&btsid=0ab6f82c15818565280654285eceb7&ws_ab_test=searchweb0_0,searchweb201602_,searchweb201603_

Dehumidifier, Condensing Thermoelectric/Peltier Type: Minimum RH% achievable at room temperature = *?*
Pros:  Quiet, very compact units are commonly available.
Cons: Removes moisture much slower that compressors, at least for common consumer grade products.  Not sure about commercial/industrial units.
Options:
- Commercial grade unit: http://www.amstechnologies.com/products/thermal-management/thermoelectric-technologies/thermoelectric-cabinet-coolers-and-dehumidifier/view/thermoelectric-dehumidifier-device/

Dehumidifier, "Humidity Trapping" Type:  Minimum RH% achievable at room temperature = *?*
Pros:  Cheap, renewable, commonly available, likely the optimal and ideal solution for long term storage when the container remains constantly sealed.  No idea if silica gel/molecular sieves can achieve better (or worse) RH% than condensation type dehumidifiers.
Cons:  Very very slow to absorb humidity (can be sped up a little with fan), so not ideal for a dry box that gets opened up at any regular interval or has even a small flaw/gap in construction.  Renewing desiccant usually requires opening the dry box, compared to compressor/thermoelectric that you just flip a switch from outside the cabinet.
Options:
Cheap silica gel, but per good advice, molecular sieves of grade 3A, 4A or 5A are a better choice.

Dehumidifier, "Other?"
As I was digging around, I found some type of "mechanical" molecular sieve that is apparently used in refrigeration units...  I have no idea what it does or if something similar might be usable for dry cabinet purposes, so thought I would temporarily include it on the list until someone corrects my ignorance:  https://www.amazon.com/Danfoss-Liquid-Drier-Sweat-Connection/dp/B06XXTCRQ7/


Other thoughts or suggestions?  If I have something wrong, please correct me.  If you've had similar issues when building your own dry box, I'd love to hear how you dealt with them.

[wraper]

AFAIK with condensation dehumidifier it will be nearly impossible to achieve really low humidity. They simply stop condensing anything once humidity drops to around 40%. Also they are quick to remove moisture only at high humidity levels, once it drops, they become really slow.

[amyk]

I'm looking for a compressor dehumidifier with dimensions that are 1/2 cubic foot or less in volume

The compressor itself will be around that volume already...

[NiHaoMike]

Explanation of how calcium chloride can be used as a dehumidifier:

Basically, a scaled down version will just be a container of calcium chloride solution with some tubing that allows the solution to be exchanged with a container on the outside for regeneration, both containers designed to allow air circulation. Apart from heating the outside container with a solar collector as mentioned before, it could be possible to make use of a Peltier to cool the inside container while heating the outside container, getting better efficiency than a standard Peltier dehumidifier.

Another possibility is a desiccant wheel which works on a similar principle.

[twospoons]

https://www.sorbentsystems.com/desiccants_charts.html

The first chart shows you molecular sieves are better than silica gel at low RH, and only beaten by CaO.

[vk6zgo]

I'm finally getting around to building a dry box/cabinet to store my 3d printer filament.  In the past I've used a gasketted sterilite storage container(s) with EvaDry renewable desiccant and wireless Accurite temp/humidity sensor(s) for monitoring, but I have yet to find an off-the-shelf container that has mounted-and-in-use-spool-friendly dimensions that also does not waste a lot of space, and using desiccant can take a full week or two in order to reduce humidity to the lowest it is able to go even for a small confined space, which I measured at around 40% in my previous setup.

Now that I have my Prusa MMU2S installed, I have 5 filament spools in active use at any given time and my old storage container is no longer good enough.  So, time to build a new dry box/cabinet that keeps my spools as dry as possible while in use or waiting to be used: just mount them all and run PTFE tube through the cabinet wall, and swap the PTFE tubes connected to my printer as needed.  My intention is to use plastic sheeting, the same stuff you use to winterize windows or maybe use clear plastic shower curtain material for dry cabinet walls, and standard lumber for the frame and support for several "shelves" of mounted spools.  If this is a bad idea in terms of humidity control, please comment.

But I've had a helluva time trying to find an appropriately sized dehumidifier.  I want to go with a compressor-based unit since they dry the air much faster than peltier junction (same thing as water coolers or small refrigerators) and I have the impression that compressors can reduce humidity lower than peltiers and desiccant are able to go.  Please correct me if my impression is incorrect.  Normal floor standing compressor units are much too large and I have only found peltier versions in the form factor I'm looking for.

If some manufacturer makes one, I'm looking for a compressor dehumidifier with dimensions that are 1/2 cubic foot or less in volume so it doesn't use much space inside the dry cabinet, is reasonably easy to mount or sit on a small shelf near the top of the cabinet so the gravity fed drain hose (duct-taped is acceptable) can get snaked through the cabinet wall and out the window: I don't want to empty a bucket every day, and the window sill is a few feet off the floor.

Anyone know of a product or a manufacturer that might make something like this?  Also, DIY dry cabinet construction comments are welcome as well.

Dehydrators were used in their thousands with long line cables back in the day, & are still in use for coaxial feeders in TV & FM broadcast sites.
The main problem is that there was  never a great incentive to miniaturise them, so the efficient ones are fairly large.

I have seen them where the air drying elements,are housed separately from the compressor, etc, so they could be "shoehorned" into smaller sized equipment, but still not as small as you require.

[Someone]

Have you considered a fairly tight enclosure and purge gas (even bottled?). How dry is "dry" ?

Dental compressors have options for dehumidifiers to produce continuous "dry" air. With a large enough receiver you can leave a small bleed to keep the enclosure under positive pressure.

[Ground_Loop]

Is your concern relative humidity or absolute water vapor content.  Relative humidity can be decreased by simply heating the air.  Warm air, a circulating fan, and desiccant bed will drop drop both humidity and water vapor content.  I used this technique for storing VOC sample tubes in a Lab I worked for.  Compressor type de-humidifiers use a LOT of energy for what they do.

[pipe2null]

Thanks for all the input!  Here are my conclusions so far:
Note: By "absolute optimum solution", I mean the best possible solution available outside of a high end commercial lab.  Basically, it's intended as the ideal target to work backwards from to find the right $/performance solution for a persons individual needs.

For long term storage in a container that is rarely opened, the best humidity protection is also one of the cheapest: Copious amounts of desiccant.  Molecular sieves are best for absorption speed, CaO/Calcium Oxide/"Quick Lime" is slow but best for absorption amount and is effective at very low RH% (RH < 10%).  So the absolute optimum solution would probably be including some proportion of both molecular sieves and CaO in the container with a small fan.  Or keep it simple and pick one or the other.

For dry boxes/cabinets that are opened more often than "rarely", the over-the-top, absolute optimum solution (ignoring pressure, vacuum,etc.) is to perform a purge cycle every time the enclosure door is closed: Refrigerate the enclosure down close to freezing in order to increase RH% and maximize how much water vapor a condenser-type dehumidifier can physically remove from the enclosure, and the higher RH% also helps the desiccant be more effective in trapping any remaining water vapor.  Then follow the initial humidity purge by heating the enclosure back up to ambient or higher temperature to minimize the resulting RH% after the maximum water vapor has either been physically removed from the enclosure by a Compressor/Thermoelectric dehumidifier or trapped by the desiccant.  If you want to be extra fancy with it, you can use different desiccant materials at different stages/temperature ranges for more optimum results.  It would not be cheap, but I suspect it is likely you could build something like this that has enough volume to easily store 40+ rolls of filament (or camera lenses, or precision tools, etc), with spools mounted and actively-usable through the wall, for cheaper than a commercial filament dryer that only holds 1 - 5 spools like https://massportal.com/home/filament-dryers/filament-dryer-fd1/ .  I am quite curious how well this solution would compare to the commercial one.

But, as stated, that is a bit over-the-top for my purposes.  I was hoping for a "build it and forget it, electric only, zero maintenance" solution, but apparently there is no way to avoid using desiccant if I want to try to go below 40% RH.  Well, I'm not going to build a fancy fridge (I'd like to though, just to compare to $$$ commercial solutions), so desiccant is necessary, but I do want to build in an electric dehumidifier to help with the initial purge and hopefully stretch the desiccant a bit.

The type of cheap and flexible plastic sheeting (as opposed to solid and more effective material like glass) to use for cabinet build that seal humidity well is still an open question.  Would any plastic referred to as a "vapor barrier" be ideal?

@David Hess:  The form factor of the thermoelectric unit you linked is spot on perfect for what I was looking for (since no one makes a similarly sized compressor...  heh).  And running on 24V DC is a big unexpected bonus.  I'm building my dry cabinet onto the wall of my workbench, and since all my workbench lighting is all 24V LED, it's easy to connect up and do all the climate control from the same arduino that controls the lighting.  The unit is a bit pricey and I would go with something else if I had more room, but...  Well, I'm seriously looking at it.  Do you have any experience with it, as far as performance compared to...?  I can read just fine, but I don't understand the $/tradeoff between the PSE 30 and PSE 30L if you have any insight.

@Someone and NiHaoMike: I hadn't considered air replacement or calcium chloride.  I'll check those out before I purchase anything.

... How dry is "dry" ?

Very good question.  Simple answer is, I don't know.  For my purposes, it's about storing actively-used 3d printer filament spools as long as possible before they inevitably have to be baked in an oven to restore print quality.  I read somewhere that after producing the filament, (good) manufacturers will cook spools in a vacuum oven to fully dry them, and then immediately vacuum package the spools with a desiccant pack.  The moment the seal is broken, the filament starts absorbing water vapor and the print quality degrades.  Many types of filament material can be left in open air for many weeks before quality noticeably degrades, other materials can barely make it through a few overnight prints before needing to be baked again.  I haven't used nylon yet, but apparently it is pretty bad in this regard.  AFAIK there isn't a "good enough" amount of dry outside of a vacuum oven to preserve quality indefinitely, but reducing humidity as much as you reasonably can will make it last a lot longer.  Someone building a dry cabinet to store camera lenses, test tubes, precision tools, or whatever else people store in these things would probably have a different answer to what is good enough humidity levels...

[benryanau]

Out of the box.. why not just an atmo purge? Bottled inerts like Argoshield or beer gas/CO2 are common and wouldn't be hard to source and rig a pressure-capable small bottle you could fill from someone with a big tank.
Either do a volume replacement *N to be sure or pre-evac the chamber.
Check the TDS's but IIRC industrials mentioned contain very little H2O.
For adsorbed H2O a light vacuum and subzero cold plate (peltier) should draw and immobilise and gaseous or adsorbed liquid H2O.
Just a thought.
Oh and keep silicones away unless tested.. Fluorinated siloxanes may be ok but be wary otherwise. They're swear words in some industries
Few polymers are gas-tight, you'll see foil-coated mylar used often and that layer of Al one of its purposes is to make the polymer gas-tight.

[coppercone2]

has this been mentioned? This is not peltier. It uses a special membrane.


This has no moving parts.

If you want it fast, you need something like a vacuum dessicator with phosphorus pentoxide (fuming sulfuric acid is out).

As for not dealing with crazy shit, consider getting a bottle of something called Clean Dry Air (sold on lease) to purge the container. What it is, is just clean dry air fed through alot of filters. Alot of the options here are asphixiants and potentially dangerous. (I personally don't keep any gases other then like a lighter in my house, all that is in well vented semi outdoor area. Clean dry air comes with a specification of purity depending on your needs (i.e. huge industrial application standard sits behind clean dry air).


Also, for business reasons, you might want to consider moving to arizona if its big.

[pipe2null]

That...  Is...  Freakin...  Cool...

Yea, that's a new one for the list.  The unit in the video was tested drying out a tiny enclosure, but the dehumidifier unit is small enough to mount in a 12mm hole.  Also very cool: it appears to work by breaking water molecules inside the enclosure into oxygen and pumping hydrogen atoms through the membrane and out of the enclosure.  Reducing humidity by destroying the water molecules themselves!  No drain hose, no drip tray!

Looks like the performance/speed of dehumidification is kinda on par with peltier, maybe better?  But this electrified membrane unit keeps working under 40% relative humidity.  Video notes show 67% to 33% in 6 hours and down to 22% in about a day, power consumption DE-creasing at lower RH...  Very cool.  I'm curious about the cost of the slightly larger units. 

If it's not too pricey, this might be my new front runner once the insane world calms down and I get back to building my dry box instead of playing with germicidal UVC light bulbs and 3d printing a bioreactor to fry little tiny buggers...   

Links from video:
www.micro-dehumidifier.com
westside-int.com

[coppercone2]

its better then a peltier because it wont drip and its power efficient. Peltier can grow mold or something possibly and it probably requires a fan unless its big/heatpiped/engineered well. You can probobly put a few of those units to increase surface area too. It's very elegant.

Those peltier things are 50W. The membrane ones are like <0.1 W, 98% less power use. And they look more solid (peltiers can short out and a fan can go bad and make very annoying noises)

That is like 25-50$ per year to run the peltier, vs like 50 cents for the other one

[pipe2null]

Good point on the cost of electricity part.  Main drawback seems to be kinda tight power requirements at 3.0 +/- 0.1V with max 0.2V ripple.  Seems pretty picky for a part that is just 2 electrified mesh screens sandwiching a membrane?!?  Why is voltage tolerance so tight?

I couldn't find comprehensive/official? pricing, but the tiny membrane units appear to be about 20 Euro's, or something like that.  For my dry box, I'd need one of:
MDL-3 up to 0.5m3 at EUR 96
MDL-5 up to 1m3 at EUR 158
MDL-7 up to 2m3 at EUR 258
(Doesn't include power supply)

More expensive than a cheapo consumer dehumidifiers, but seems on par or a little cheaper than commercial dehumidifiers built for enclosures.

[coppercone2]

just use a LDO on that with a 5V adapter. it still costs nothing. You can plug a 317 into a phone charger and beat that specification to quarks. with 10 cent resistors you will have something like <1mV noise and very low drift. The biggest one is a bit more challanging but its only a 4 watt power supply.

Commercial peltier requires more expensive supply and is typically expensive too if its not built like garbage. They also age a bit with thermal contacts wearing out (decrease thermal transfer).

I would love to hear about someone actually using this thing, I had it on my mind for a while for Gauge blocks.

Not saying its the best option for you, but it would be a new for EEVBLOG as far as I know.


I.e. cheap peltier one (keep in mind, made in china. probobly not great quality, but thats going to be bottom dollar pretty much unless you put one of those cheap home units into a box)
https://sandaenvicool.en.made-in-china.com/product/IsoQmUqOaGWE/China-Thermoelectric-Dehumidifier-for-Electrical-Cabinets.html

Keep in mind, it drips. You need to manage the condensate, its potentially a slip hazard and water hazard in a lab (i don't know if you are out fitting a commerical lab/manufacturing place). I would make this a modest consideration. It's also advised you get a leakage sensor, because they will make a mess out of things if you forget to empty a bucket or a hose breaks. Also you probobly need to clean it once in a while, I have my indoor air conditioner, even with the filters eventually it gets filthy and I need to poke at a inaccessible fan with a rag to clean it.. the dust like glues itself in, so its much worse then cleaning a computer from dust. I took apart a few broken peltier refrigerators before, the power supplies they come with are horrible (it was a trend to own them in an area I frequented, and they broke ALOT. Usually a PTC on the power supply.

[pipe2null]

Well, I cannot 100% guarantee the membrane dehumidifier is the direction I'll go for my build, but I can 90% guarantee it's something I'll probably try.  Previously I was seriously looking at the commercial unit posted earlier in the thread:
http://www.amstechnologies.com/products/thermal-management/thermoelectric-technologies/thermoelectric-cabinet-coolers-and-dehumidifier/view/thermoelectric-dehumidifier-device/
But now the MDL-5 membrane is my front runner.  Or maybe target MDL-7 or multiple MDL-5's since those units are designed for rarely/never opened enclosures?

My build is for home-use, but my target is a scale-able, over-engineered-but-easily-duplicated design plus yet another filament spool mounting system.  I can put it up on thingiverse and people can pick and choose what features they want to add to their own dry cabinet.  The simplest and best solution is still mounting a single filament spool in an airtight Tupperware container with copious amounts of desiccant and running the filament through the wall.  But that solution doesn't always scale well, and there are more things in the world than 3d printer supplies.   

Tentatively at least, I'm mounting my dry box above the corner of my oversized workbench, less than 1 meter from a window that I can snake a tube out for drainage if needed.  It's the same window I'll use for exhaust when I finally get around to adding fume extraction to my workspace.  Rough dimensions of dry box are around 110 w x 80 h x 40 d (cm) = 0.352m3, but that's just for ballpark use and only for storing actively use-able 3d printer filament.  I've been thinking of adding another zone to the enclosure for storing things like lenses and such, so that brings the ballpark up to 0.5m3.  And because it will not be completely airtight and will be periodically opened/re-humidified, seems that >=1m3 is a decent number to target for sizing the dehumidifier.  I'm still prototyping a clean and mostly airtight way to run printer filament through the wall, for EVERY filament spool inside, but that's secondary to humidifier selection.  I have an MMU2S for my Prusa MK3S, so I always have 5 filaments in active use (they share a single extruder), but the retraction of filament makes things more complicated if you try and keep it all inside a dry box.


I'm curious what affect a fan directed at the membrane would have.  On one hand, it could cause a higher impact rate of water molecules on the membrane, but is there a minimum time for the membrane to capture the water molecule?  Hmm...