This question is burning me, so I have to post.

I just reread two aricles:
http://www.backpackinglight.com/cgi-bin/backpackinglight/single_wall_shelters_condensation_factors_tips.html
http://www.backpackinglight.com/cgi-bin/backpackinglight/night_time_condensation_on_tarp_and_tent_fabrics.html

My idea is that by maximizing condensation we can produce distilled drinking water. This would work only in tents with very steep wall such as mids and twin sisters designs. Condensation will run down the wall instead of dripping and can be collected at the bottom. This is very similar to how solar stills work.

This idea could be useful in desert and in winter.

comments? :)

Edited by huzefa on 07/20/2009 06:55:12 MDT.

u mean sweat and condensation from breathing? probably safe to drink, but i would find other water lol.

It would work in theory, but you would end up soaked, your equipment soaked, and it would take a huge tent over a large amount of open ground to get any usuful amount of water out of it.

First your tent would have to be sealed to the ground, open floor (dirt so really a tarp), transparent would help and probably filled with vegitation besides a person to get anything out of it.

It would basically be a sauna tent in the desert and an ice cube in the winter.

It takes 2 large 6x6 or so solar stills to make enough water just to survive.

Order a sheet of 56" wide x 2 yds of cuben and some tubing and just carry that. Should only weigh a few ounces.

That said I always thought the desert suits in the movie Dune were way cool.

Edited by tammons on 07/20/2009 21:03:21 MDT.

Huzefa you must have been a mad scientist in a past life!

Considering the tent an isolated environment practically all condensation would originate from insensible body loss which is estimated to be about .8 liters per 24 hours. About half comes from breathing and half from sweat. That would be about .26 liters in 8 hours sleep. Of course this volume is highly variable. It would be higher, for example, in hot dry weather and multiplied by the number of individuals in the tent. This does not consider the moisture that is absorbed by clothing, sleeping bags, etc. I like the idea. I think the trick would be a tent with a design that could channel the water into only 1 or 2 points where cups may be placed.

Hennessey Hammocks has a device that is meant to clip water bottles to the corners of their overhead tarp, to catch rainwater. Perhaps something similar?

But, frankly, I doubt that you would be able to collect emough condensation to make this worthwhile. Good luck, though.

Troy has the right idea...
All you will be doing is making your tent a more uncomfortable environment ending up with half a glass of water in the morning.
Keep in mind that the "unbearable" amount of condensation reported by some is the "almost bone dry" reported by others...
(depending on how you like or hate your shelter)


Solar stills don't really work anyway, if they did arid countries would be filled with them..

( they are OK for "survival style TV shows")
Franco

Keep in mind that condensation will happen even if there in no human factor. If you read up the articles linked in my original post you will see that temperate differential is more important then humidity. That means you can theoretically produce much more water then your sweat. Actually I would recommend vapor barrier because insulation will have hard time drying once sweat get into it. I will post more thoughts on this later.

Basics: Warm air hold more water vapor and cool air hold less water vapor. When warm air contacts a cool surface condensation results. To maximize condensation we need to make the air inside the tent as warm as possible and fabric as cold as possible. Heat is transferred by conduction, convection, evaporation and radiation.

Shelter design: A single/two pole mid is most suited for this technique. Water will run down the steep wall instead of dripping. Single wall shelter will produce more condensation because fabric will readily lose heat by conduction and convection. A smaller shelter ie one with less volume will be warmer then a large shelter.

Shelter fabric: Silicone has one the least surface energy and therefore is hydrophobic ie. water beads instead of forming a film. Silnylon and spinnaker are most suited. The best fabric for this application is aluminized silicone fabric. An aluminized bottom fabric will reflect radiation back into the tent there by cooling the surface and heating the air inside the tent. If you want to produce water during day then double aluminized fabric will be needed. The outer will reflect radiation and so the fabric will stay cool.

Keeping the air inside the shelter warm: Groundsheet sewn to fly with no ventilation will prevent convective heatloss inside the tent. To minimize evaporative heat loss vapor barrier is the best solution. You need to make sure you and your insulation stays dry. Wet pack/clothing, rain water, open floor, sweat will all lead to evaporative heat loss INside the tent. You want the inside as warm as possible.

Collection condensation: One idea is to have a kind to sloping flap along the walls at the bottom. Water will collect in the flap and move downward to the lowest point where you can have a nozzle directing water straight into your bottle.

Winter: If you have strong pole, anchors and guylines it may be possible to cover the shelter with few feet of snow and have a igloo. Snow acts as insulation and keeps the inside warm. A well designed igloo will have above freezing temperature inside. This will prevent frost. Another technique is to use tent stove.

Since my idea is to prevent evaporative/convective/radiative heat loss inside the tent, once water vapor in the air condenses an interesting situation happens: inside will get drier and warmer. Infact such a tent will have the highest warmth to weight ratio.

If anyone thinks my analysis is wrong let me know.

Just a point of correction. What you are talking about is not distillation. Getting distilled water involves boiling it. Condensation is actually the opposite where water vapor contacts a surface with a temperature cool enough to turn it to a liquid state.

Well, yes it is, actually- sort of.

When you distill water you evaporate or boil it, yes, but then you have to condense it, too, or all you have is water vapor. Right? That's why stills have that corkscrew-shaped tubing at the end. :o)

If you are condensing water vapor then you're getting pretty pure water. The biggest issue is contaminants picked up from the air or from whatever you condense it upon. After all a 'solar still' just uses the sun to evaporate the water into vapor, instead of some sort of combustion, and condenses it on a membrane- not unlike a tent wall.

So boiling or evaporating is the opposite of condensing. But distillation involves BOTH processes. So saying that condensation is the opposite of distillation is not QUITE correct, either.

Edited by acrosome on 07/25/2009 04:19:10 MDT.

I'll agree that the two aren't opposites but condensation is only one part of the distillation process. Distillation purifies largely by boiling the water and then collects it in liquid form through condensation. The condensation you are talking about does not have the purifying effect of boiling.

only slightly off topic - the original point of this is to get drinking water by condensing the water vapor you give off in the night. why not try and perfect using a vapor barrier sleeping system. the one time i've tried this (at home) the thing i noticed was i *wasn't* thirsty in the morning. normally i drink a glass of water first thing but instead i felt "moisturized" (in a good way). if you can make it so you don't get overly damp then you'll accomplish the original goal by not losing the moisture in the first place.

>> The condensation you are talking about does not have the purifying effect of boiling.

Of course it does. What difference does it make where the water vapor comes from? (Other than crud it picks up off of the wall of the condenser, of course, but that is a problem in a still, too.) The water from a still isn't "clean" because it was boiled. It is "clean" because water vapor doesn't carry crud and bugs any more than oxygen does. It's a gas.

Distillation does not really require boiling in the way that you mean it. It just needs vapor. For instance, a solar still produces essentially pure water, and nothing gets boiled in a solar still. (Well, there ARE pretty intense commercial solar stills nowadays. I am instead referring to the old "clear plastic over a hole in the ground" kind of solar still.)

I suppose you could make a stretch and say that a lot of the condensate comes from microdroplets rather than vapor, but the microdroplets invariably are formed from water vapor as well. So, I don't think it matters.

>> why not try and perfect using a vapor barrier sleeping system.

I think that's a pretty profound point. It does, however, make the assumption that we're talking about condensing one's own perspiration, rather than condensing ambient moisture. I guess that condensing ambient moisture would be heavily dependent upon weather and other conditions, though. Probably not something to depend upon.

Edited by acrosome on 08/26/2009 13:53:10 MDT.