Extreme but effective condensation prevention in a bivy or single wall shelter?

[John Nestler]

David – Thanks for the insight. The mask will significantly reduce condensation inside the bivy as well as it fits well. I like the idea about inserting one tube inside the other. That would certainly warm the air as it enters the mask while cutting down on bulk – could be a good project for someone to continue on. Good idea on the vapor barrier tape too.

James – Glad you like it!

Jim – Of course you could position the intake tubing inside the bag to pull in heated air and exhale it outside of the bag provided that the input air source doesn't run out!

I'll post it somewhere else, but I use the Marmot Alpinist Bivy and it doesn't have any tabs to hang it from tree branches. Is there an easy way to make a little apex by hanging the fabric ontop so that it doesn't com into contact with the sleeping bag. Perhaps a washer and a line?

– John
http://fluidglass.com

[David Olsen]

The heat from breath should somehow be trapped in the sleeping system, not just released
to the outside. Same with moisture from breath. Think "DUNE".

[Larry De La Briandais]

For a lighter weight mask you could look into using the masks they use for CPAP machines. They only cover your nose so you have to train yourself to sleep with your mouth closed. I wouldn't think one could, but CPAP users everywhere do. It wasn't hard for my wife and she has slept for "many" years with her mouth open. Basically the have a big band that holds you mouth closed. You wear that for a week or so and you are magically trained.

[Thomas Rayl]

Greetings all… I just stumbled across this thread and — though it's a year old at the latest post — I had some thoughts if anyone's still interested. Here's my thoughts:

The basic function of the apparatus seems to be to (1) reduce condensation by getting exhalation air "out of the arena", (2) ensure an adequate supply of breathable (ie, non-rebreathing) air when "zipped in" to a bivy, sleeping bag, or whatever, and (3) pre-warm inhalation air.

Tube-within-tube systems sound great at the start, but become much more complex when you consider the issue of keeping the inner tube CENTERED within the outer tube. Otherwise, you get more kinky airflow and lose some of your head exchange. I propose a different approach:

I would consider a two-separate-tube system, one for intake and one for exhaust, each with the appropriate one-way valve, of course. Obviously, the exhaust tube ends up "outside" the tent/bivy/bag, or whatever to ensure the exhaust moisture is effectively removed from the anti-condensation area.

It would seem viable to have the intake end of the input tube tucked toward the bottom of the sleeping bag. (I conceptually envision it rubber-banded to an ankle.) This would draw in warmed air from inside the sleeping bag. Yes, that air would have to be replaced by unheated air from "outside" somewhere, but I would think there would be a pretty even trade of heat "lost" due to the influx of outside air into the bag (to replace the inhaled air) and head "gained" due to breathing in already-warmed air. The added benefit: you are automatically pumping moisture evaporated from the body which would otherwise collect in the bag insulation or go through it and condense in the bivy/tent out via the lungs and exhaust tube. Hopefully, that would keep things significantly dryer.

(Yes, one would have to exercise due diligence regarding issues of flatulence. 32 nudge-nudge-wink-wink comments elided here…)

I had originally thought that the exhaust tube (but not the intake tube) could be a super-light-weight tube of fabric (silnylon or some such), but the outside end may tend to freeze shut for those who like to camp with showflies instead of mosquitoes.

So, anyone have any thoughts?

[icefest From Australia]

If you are considering using lightweight materials, consider trying to get in touch with an anaesthetist and getting some used anaesthetic machine air lines. Or you can buy them here: http://www.myrespiratorysupply.com
They also can be extended to several feet in length.

Anyway, they'd be the lightest around and in combination with a nose clip and a lightweight snorkel mouthpiece you be looking at less than 1/2 a pound for the entire setup.

[Hikin’ Jim]

Interesting idea with tubes and such. Seems a little hard to get used to, but I guess CPAP users do it all the time.

On a slightly different note, I've tried a Polar Wrap hood that I bought at Sierra Trading Post. Kinda heavy, but I really wanted to reduce condensation inside my shelter.

My results weren't all that encouraging. The inside of my Gatewood Cape still had condensation on it in the morning. I didn't have any way to compare to how it would have been without the Polar Wrap, but the Polar Wrap certainly didn't entirely eliminate the condensation. Note: It was very damp then night I camped out, having rained the day before.

I also noticed that the Polar Wrap itself got a little damp which seemed a little unpleasant although not horrible. I haven't experimented with it more since last winter. Maybe I'll take it out again now that it's cooling down here.

HJ
Adventures In Stoving

[icefest From Australia]

Where were you expecting the condensation to go with the polar wrap?

From the looks of it, it just warns up the site you breathe in, there is no condensation removal.

[Roger Caffin]

Yeah, well, a snorkel might carry your breath out, but your body will still be evaporating. Your bivy bag will not stay dry in bad conditions.

Cheers

[Roger Caffin]

"A classic problem with sleeping in your tent in brutally cold conditions is waking up to find the inside of the tent lined with frost. Highly breathable fabrics will only go so far towards solving this problem. Even a tent made entirely out of mesh would still be lined with frost in the morning! To deal with this issue, NEMO created the Condensation Curtain™ to partition the area in which you breathe. The curtain attaches to the walls and ceiling of the tent and lightly drapes over your body around the chest area, trapping most of the vapor from your breathing in a small portion of the tent. In the morning, you simply pull the curtain aside and get dressed in the dry area of the tent! The Condensation Curtain™ is easily removed, shaken out and replaced."

Hysterical. Maybe the designer has never slept in the snow?

Reality: 'trapping most of the vapor from your breathing in a small portion of the tent' so you wake up with either condensation from the Curtain, or frost crystals, dripping all over you and your quilt/SB. Frankly, I suspect you would end up wetter with this thing than without.

Cheers

[Hikin’ Jim]

> Where were you expecting the condensation to go with the polar wrap?

Several people on several different forums mentioned the idea that a heat exchanger type mask might help alleviate condensation. Sierra Trading Post is cheap. I thought it might be worth a try. Didn't seem to help much. I certainly can't articulate a mechanism by which it would work.

> From the looks of it, it just warns up the site you breathe in, there is no condensation removal.

Yep, pretty much. Maybe it helps prevent bitingly cold air from going into the lungs. Again, it didn't prevent condensation.

HJ
Adventures In Stoving

[Patrick McFarlane]

It’s been a while since anyone has posted on this thread but I have become more interested in this idea after a few nights of testing my eVent bivy on snowy nights and cold temperatures.

I have concluded that the optimal setup needs a few things:

1. Two hoses.  Breathing air from inside the bivy doesn’t sound like a good idea.  If you’re zipped up tight, I wonder whether you would eventually end up with too much C02 accumulation.  A coaxial setup could work and these do exist for use by anesthetists (e.g., here)  but I wonder whether having the outlet from your inhalation hose right beside your exhalation hose is a good idea.   I think I’d prefer having the inhalation hose exit one side of the bivy and the exhalation the other.  Less chance of clogging up with ice and less chance of reducing oxygen content.  The coaxial setup might help you to sleep warmer though on account of heat exchange between incoming and outgoing air.

2.  The correct valve.  Needs two flappers and has to be high flow and connect near the mask to reduce dead air space.  The ideal setup would also have some swivel capabilities so that you can toss and turn a bit.

3.  A comfortable mask with a head strap.

All of the components seem to be available here:

http://www.vacumed.com/268.html

I’m going to get in touch with them and see what they recommend for the type of thing we are trying to do here.

 

[Michael B]

I lol’d at the fart comment.

[Patrick McFarlane]

So I’ve been doing quite a bit more research into making this work and my preferred option is to convert a 3M cartridge respirator for this purpose, given the wide availability of replacement parts (e.g., silicone flapper valves, etc.)…along the lines of John Nestler’s idea.  I would also use CPAP hoses for this purpose, again given low cost and wide availability.

Fortunately, the 3d printing community has designed many adapters for 3M respirators that would work directly or need only minor modifications.

For the inhalation hose, there’s a 3d printed swivel port that would allow you to roll around a bit without getting hung up in your hoses:

 https://www.thingiverse.com/thing:4605251

For the exhalation hose there’s a 3d printed adapter that clicks into the exhalation port on 3m 7000 series masks (there are designs available for other 3M models as well).  Just need to modify the outlet by adding a 22 mm o.d. tube that would slide into the CPAP hose cuff:

https://www.thingiverse.com/thing:4444335

…now just have to learn how to use a CAD program to make the modifications and how to 3d print.

 

[dirtbag]

I dunno.. sleeping with masks and hoses all over me would make me feel like im on a ventilator or something.  I think I would rather just embrace the condensation and learn to prevent it and deal with it as it happens.  Unless I was on some crazy arctic expedited.. I think a few nights/ week or so, out in the mountains during winter.. i would deal with the inevitable condensation that is expected.

[Jerry Adams]

“sleeping with masks and hoses all over me would make me…”

wait, I use a cpap machine, I do that every night : )

I don’t breath into my bivy which mostly eliminates condensation.

Two nights I cowboy camped, clear night, 25 F – a lot of condensation inside and outside of bivy outer shell.  If I had slept in my tent it wouldn’t have been a problem

[Patrick McFarlane]

sleeping with masks and hoses all over me would make me feel like im on a ventilator

I agree there could be some discomfort but I’ve come to realize that some discomfort is part of backpacking.

Also, you can get a lot of condensation even in one night.  I slept outside in my backyard testing out my winter setup and I got a lot of condensation in the neck area of my quilt despite having the top of my bivy completely open.  The loft was visibly reduced.

I think the biggest advantage though is not needing to have overhead cover when using a bivy.  Setting up stakes in snow is one of my least favourite activities.  With this setup, if it’s howling outside, you could zip up your bivy and direct the hoses outside.  I use a vapor barrier suit, only the small exposed part of my face would emit vapor that could lead to condensation inside the bivy.

[Jerry Adams]

that makes sense, good experiment, results will be interesting

given that I use a cpap machine every night with hoses, I can see how your idea is viable

[Nick Gatel]

Insensible water loss is the water loss through our skin and airways. Years ago I read a study that claimed 48% of insensible water loss is from the skin and 52% from airways.

So the mask idea is only going to address 52% of the problem.

I’ve been using single wall shelters for over 50 years. Ventilation is the key and in some conditions you are just going to get condensation no matter what you do.

BTW, I’m not a scientist.

[Michael B]

Maybe one of those stillsuits from the Dune series would work.

 

[Patrick McFarlane]

Insensible water loss is the water loss through our skin and airways. Years ago I read a study that claimed 48% of insensible water loss is from the skin and 52% from airways.

My silnylon vapor barrier suit that I wear covers another 51% (my unscientific estimate) because it’s completely impermeable and I wear it with the hood up.  The only exposed skin would be the part of my face that the mask doesn’t cover, which isn’t very much.

[Patrick McFarlane]

Update… I’ve been working with a local 3d design company to design a 3d printable part for for the 3M 7500 series respirator to make this work.   Basically, the setup consists of the following:

1. A 3m 7500 series respirator

2. A 90 degree swivel connector that connects one of the inhalation ports for the respirator to a 22 mm CPAP hose, just like this one:  https://www.thingiverse.com/thing:4605251

3. A cap to block off the other inhalation port:  https://www.thingiverse.com/thing:4146711

4. An adapter for the outflow port that connects to a 22mm outflow hose.  This is the part that I’m working to get designed.  But it would look something like this only with a hose connector instead of a filter:  https://www.thingiverse.com/thing:4444335

Once the design is done, I’ll post it on thingiverse and provide a link here.  Then anyone that wants to try this out can just pick up a mask, some CPAP hoses, and get the parts printed.

Regarding Roger’s earlier comment about condensation, I think there’s probably an easy solution:

a) Create an insulated sleeve for the outflow hose (e.g., out of insultex, sew one out of climashield, etc.)…kind of like the sleeves used to keep drinking tubes from freezing.

b) Elevate the middle of the hose somehow (e.g., attach a loop to the insulated sleeve and tie that to a trekking pole, tree, etc.) or use an elbow so that the outlet of the exhalation hose points straight down to the ground.

That way, condensation would stay in liquid form until it gets to the end of the hose and from there it would drip down harmlessly without blocking the hose port.

[Roger Caffin]

I agree with the idea of insulating and tilting the outlet hose so it drips ‘elsewhere’.
But if you try to use this in the snow (ie reasonably <0 C), I predict that the drips will quickly turn into icicles – which may block the exit.

Cheers

[Patrick McFarlane]

Okay, with some help from a local company, I was able to complete a design for a 3d printable CPAP hose adapter for the outflow port of 3M 7500 series respirators:

https://www.thingiverse.com/thing:5732488

The one way valves in the respirator prevent rebreathing and allow you to direct (via a hose) your moist exhaled air out of your bivy.

This adapter can also be combined with a cap for one of the inflow ports and a 90-degree swivel adapter for the other so that fresh air can be drawn in from outside using another hose.  3d printable designs for those have already been created (links below).   Or you can simply breathe in the air from inside your bivy  …with care, depending on what you ate that night.  ;-)

     Swivel 90-degree hose adapter:  https://www.thingiverse.com/thing:4605251

     Cap:  https://www.thingiverse.com/thing:4146711

Pic of the whole setup below.   I hope to post back here soon with some testing results.  Not really cold enough here yet to give it a good shake-down.

[Author]

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