single vs double wall in frigid conditions

[Garrett]

In conditions below 0F/-17C, does utilizing a double wall tent still hold its value in regards to condensation management? If the inner isn’t warm enough to transfer moisture to the outer wall, then wouldn’t the condensation level be the same as a single wall tent?

[Edward John M]

Double better, it’s about the wind and air infiltration and ventilation. Triple skin better again if you can do it.

[Jerry Adams]

another thing is, if you have double wall with breathable inside layer, condensation will occur on the inside of the outer layer.  The inner layer will remind you that you’re about to touch that condensation layer

in frigid conditions the condensation is frozen so it doesn’t matter that much

a third thing is that if you took the weight of that inner layer, and added that much down to your insulation, you’d probably be much warmer.  This being backpacking light

 

[Tipi Walter]

If it’s cold enough ice crystals will form on the wall of the inner tent in a double wall tent.  I agree with Edward John—double wall is better in winter due to the fact that many winter storms are cold rainstorms at 35F—the inner canopy then keeps significant condensation water coming off the inside of the fly off you and your gear.

One time I was in a 75 hour cold rainstorm in December (TN mountains) and my inner tent protected me from a lot of fly condensate—see pic.  All this would’ve fallen on me and my gear.

As far as ice condensation forming on the inner tent canopy when it’s very cold—most of it can be dislodged upon pack-up and when you reach the next day’s camp you can set up and thoroughly shake the inner tent and sweep out the ice—in certain conditions it can be a liter or more.

[Garrett]

Great feedback. Sorry this is the one subject in winter backpacking that I just can’t seem to shake. It has just been really bugging me for a while.

”in frigid conditions the condensation is frozen so it doesn’t matter that much. if you took the weight of that inner layer, and added that much down to your insulation, you’d probably be much warmer. ”

Jerry, this is exactly what has been confusing me. Basically, Im wanting the Hilly Soulo tent, however the inner just isn’t optimal without my bag touching the entire side wall (entrance side-not head/feet).  However, replacing the inner with an Argon90 bivy (head open via bungee), I would have plenty of distance between me and any point of contact. I believe an Argon 90 bivy has a high enough HH to handle the any contact.

”most of it can be dislodged upon pack-up and when you reach the next day’s camp you can set up and thoroughly shake the inner tent and sweep out the ice”

My primary objective is not having to upgrade to a 2P tent for my bag not to touch the inner wall. The 2P set ups carry a significant weight increase in comparison to the Soulo. I’ve been looking at the Jannu, however if I can make the Soulo work that would be optimal.

You think having a synthetic topquilt over a down bag would make any inner contact concern that I have minor or irrelevant? Temperatures hover around -15F low and 30F high, so rain is highly unlikely.

 

[Roger Caffin]

Double skin is better, but you must allow some through-flow under the fly to sweep the moisture away. Less flow inside the inner tent.

As for ice on the inside … it’s a 6 hour drive home from the snow, in a car with heating. I unrolled my tent when we got home to dry it out, and lots of ice fell out. That must have been a cold morning :)

Cheers

[Erica R]

I did spring ski  mountaineering a long time ago.

FWIW, I had a double wall Sierra Designs flashlight tent. It never let me down; though I never tried to camp on a ridge with it.

It helped lots to have a candle lantern inside the tent, though I never slept with it going.

Also, take a warm water bottle to bed with you, and even more important, hold onto it while sitting around the fire which slowly sinks deeper into the snow. One of the main problems with winter/spring camping is the nights are so long.

The problem with single wall tents is they are all designed to maximize ventilation. This is maybe what you don’t want. However, yes, adding down to your sleep gear and more importantly pad insulation will keep you warmer than raising the interior temperature ten degrees. But, you may well sleep better in a warmer enclosed space.

[Garrett]

”you must allow some through-flow under the fly to sweep the moisture away. Less flow inside the inner tent.”

Absolutely and generally overlooked by many. One of the main reasons I purchased the Nammatj2 actually. The ability for cross flow while utilizing the vestibule for flow underneath. BPL should really make a Sticky forum surrounding the basics on general & winter camping.

”It helped lots to have a candle lantern inside the tent”

Never crossed my mind, but I have to admit I’m intrigued. Definitely useful for those longer nights.

 

[Eric Blumensaadt]

Garrett,

A sticky on winter camping basics is a good idea and it should have GEAR LISTS for various temperature ranges.

Further a good READING LIST (ex. “Allen & Mike’s Really Cool BACKCOUNTRY SKI BOOK”  which I consider the “Bible” of winter camping despite it being a thin paperback.

A “TIP LIST’ of, for example, “What to store in the foot of your sleeping bag” or “when and how to use VBL clothing”.

 

[Garrett]

Already read the book per your recommendation awhile back in another thread. Good book for sure.

[David Gardner]

This thread got me thinking about the Stevenson Warmlite tents, and making something similar with DCF. He used non-breathable inner and outer with a sealed space in between to act as an insulator, with very low cold air intake and very high warm & wet air vent. By keeping the inner warm moisture didn’t condense on it and the warm air acted as a convective heat pump or chimney to circulate cold dry air in at the bottom and warm, moist air out at the top. It worked best in cold weather. Some might say in only worked in warm weather.

[Roger Caffin]

Ah yes, the Warmlite. I have had one.

A very snug-fitting coffin for two, with no room for gear and no room for cooking, and only two poles to hold it up.

Cheers

[David Gardner]

I didn’t mean to endorse the Warmlite.
I was thinking about the concept of two impermeable walls and body heat to maintain a temperature differential inside vs. outside, combined with optimized vent size and location, to drive convection air flow sufficient to eliminate condensation.

My hunch is that tunnel or dome seem like the best starting points for designs to optimize that concept.

Total nerd question: are there formulas or methods to relate minimum heat input, shape, volume, and vertical distance between in and out vents, to volume and speed of convective airflow?

[Roger Caffin]

are there formulas or methods
Oh yes, I am sure there could be.
But they have more unknown (and unknowable) parameters than you could dream of. :)
Sorry about that :)

Cheers

[Martin D]

I go floorless, so single layer, in the winter all the time. The advantages of floorless are much greater in the winter. It’s lighter when you really need it, cleaner and just more practical for me.
I don’t have to worry about snow in the tent, which is something that has always bothered me with double tents. I take off / put on my boots inside. I can melt snow sitting in my sleeping bag in the morning, and put two hot 500ml hdpe bottles inside my boots while having coffee, and porridge without worrying about spills. I can just dig right there inside the tent to get my snow. I don’t have to worry about burning floor fabric. I use a canister stove, but thermal management of the canister is very easy when you’re sitting all toasty next to it. It makes the whole morning process much more confortable to me because I am ready to go right when I get out of my sleeping bag.
So then condensation is something I am very familiar with. It’s been at worst only a mild annoyance when some flyflakes fall on me at night. I sleep in a light bivy anyways, so when it’s cold enough flyflakes stay frozen on the outside and inside condensation just freezes inside of the bivy bag, which I just shake off outside in the morning. The colder it gets the less condensation becomes a problem for me. The worst is just a few degrees below freezing.

[Ben H.]

Total nerd question: are there formulas or methods to relate minimum heat input, shape, volume, and vertical distance between in and out vents, to volume and speed of convective airflow?

David, I might be able to help you out. Can you help flush out a little bit what you are looking for?

[David Gardner]

Hey Ben, thanks. I had two configurations in mind for the overall shape, regardless of specific pole numbers or configurations.

1. 2P Half Dome like the Black Diamond FirstLight, with intake vents no more than 4″ above the floor and exhaust vent at the peak

2. 3P Full Dome like Kelty Towpath 3 Tent or North Face Stormbreak 3 (with flies) and same vent parameters.

[Ben H.]

Hey David, sorry I forgot to check back in on this thread. I mean what do you want the analysis to tell you? The size of the vents?

It is not completely clear to me what Warmlite vents are doing. I can set-up equations for natural convection driven flow. I have to think about the vent area a bit because the pressure differential is very small. I’m still trying to digest how the air flow prevents condensation. What is your intuitive understanding of that part?

[David Gardner]

I’m wondering, if the heat source is just one or two occupants, is that sufficient to drive convective airflow into and out of the tent sufficient to avoid condensation, with any reasonable combination of vent sizes?

As starting points we could assume impervious tent walls and 5* F temperature differential, and for 2P: 100 sq. in. intake and 50 sq. in exhaust, 3P: 150 sq. in. intake and 75 sq. in exhaust, if that seems reasonable.

[Roger Caffin]

if the heat source is just one or two occupants, is that sufficient to drive convective airflow into and out of the tent sufficient to avoid condensation, with any reasonable combination of vent sizes?
My own experience with a tunnel tent with two occupants is very definitely NO. Other design have been the same.

In fact, without good ventilation and at least an external breeze to drive air-flow, having two occupants just means you have two sources of moisture evaporating steadily. Under subzero conditions with no wind at all, that means a steady growth of frost on the inside of the tent.

If it is not too cold and its a genuine double-skin tent (ie not netting), the condensation might be on the inside of the fly rather than the inside of the inner tent. Fine, But at -10 C the condensation (ie frost) is usually on the inside of the inner tent.

Having a bit of a storm outside has never been a problem for us: I just adjust the windward ventilation and the inside of the tent stays mostly dry. The lee end is usually open a bit more, and the wind does a venturi-suck at that end too.

Cheers

[Ben H.]

I am still confused about how natural convection driven flow between the inner and outer tent could reduce condensation.

This is my understanding of condensation in a tent: people exhale hot humid air. The hot air is able to hold more moisture than the environment’s cold air. The hot humid air floats up (less dense than cold air) and comes in contact with the tent wall. The tent wall, in contact with the outside cold air is at a temperature below the dew point and therefore condensation occurs.

So what you need to do is make sure the tent wall is above the dew point to prevent condensation. You can do that by having good ventilation reducing the temperature and humidity of the air inside the tent. You can also do this by making the tent double walled  increasing the temperature of the inside wall of the tent above the dew point (you will still probably get condensation on the outside wall).

It sounds like the Warmlite is trying to induce flow between the inner and outer layer of the double wall tent… but why? Convection driven flow outside the inner tent will drop that inner tents temperature possibly enough to cause condensation (not prevent it). Is the flow to prevent condensation on the inside of the outer tent wall without causing condensation on the inner tent wall?

 

[David Gardner]

I was thinking that the less time that hot, moist air spends in the tent near the tent walls the less it will condense. I think it will also reduce the average humidity inside the tent by venting the moist air and drawing in dry, cold air, which will also reduce condensation.

My understanding of the Warmlite system is that the air between the impermeable inner and outer walls is sealed off so that it will act like insulation. I might be wrong about that but I like the concept. The warmer the inner walls the less condensation. Also, the bigger the temperature differential between inside and outside the better the convection.

[Roger Caffin]

@Ben

Sort of correct, but a bit more complex.

The incoming air will not be 100% saturated. If there is water (or ice) on the inside of the tent, there is a chance for the unsaturated incoming air to sweep up some moisture and carry it out. Not a lot, and not fast, but over the length of the night it helps.

But what if the incoming air IS at 100% – like in a thick fog?
Then you have bit of a problem! But note that a fog is necessarily above 0 C.

Cheers

[Ben H.]

ok, so the idea is: if you get condensation on the inner tent it gets sucked through the permeable fabric and evaporated by the flowing gas in the gap. It is a complex analysis. Let me think about it some more. The good news is that there is a heat and mass transfer analogy, so if you can quantify the natural convection (heat transfer) you know what the driving potential is for the mass transfer (evaporation). The natural convection driven flow I still have to think a bit about. Most correlations define it for external surfaces not internal surfaces we have here.

 

[Roger Caffin]

Hi Ben

If you want to do a heat&mass transfer analysis, you could start by treating the inside of the tent fly as an external surface. The radiant heat transfer will be different of course, but I am not sure that the difference will be very significant. After all, the very thin tent fly will be subject to the external radiation environment anyhow.

Cheers

[Author]

Posts