Why Is Your Tent Wet in the Morning?

[pivoxa15]

If you camp outside, you often find that in the morning, it’s wet on the outside. Other solids also seem wet. Why?

FIrst of all, is water vapour always around us at night and day? At around midnight, the air and tent is at their coldest. When the sun slowly rises, it heats up the tent and air but the tent raises its temperature more slowly than air hence there is disequilibrium.

Solids generally heat more slowly due to the fact that air can receive a smaller amount of energy per degree rise in temperature than solid because the intermolecular forces between water is much lower than that between solids. At the higher temperature, it’s now more thermodynamically favourable for the water vapour to condense into liquid and give off heat to the tent, which is at a lower temperature. So the main reason is that water vapour can raise its temperture more easily than solids.

 

[D H]

First, a correction. The low temperature of the day often occurs a bit after sunrise. This is particularly so on a calm, clear night. The temperature drops at night because of radiative cooling. The meager solar heating at first dawn is weaker than the heat loss due to radiative cooling. It is only after the sun rises above the horizon a bit that the solar radiation overwhelms the radiative cooling.

One of the primary reasons you get condensation on your tent is because you are inside your tent. You lose about a pint of water overnight just from breathing. Your breathing creates a lot of humidity inside your tent if the tent is not well-ventilated. The tent walls are just a bit warmer than the air outside your tent. On a clear night, the tent walls can get quite cool. Most of the condensation on your tent occurs when the humidity from your breath hits the cool tent walls.

 

[pivoxa15]

But that would mean the inside of the tent gets wet. I seem to only recall the outside being wet. Or it could have been the case that the outside was wetter than the inside hence i mostly noticed the wetness of the outside material.

 

[DaveC426913]

I'm afraid he's got you there D_H. The dew is on the outside.

Moisture on the inside of a tent would pretty much be a tent that's not doing its job.



BTW, tents are made of a material that is designed to pass moisture. This ensures the vapour inside the tent doesn't stay inside the tent. But a tent needs a waterpoof "fly" to keep the moisture off the outside.

That is not the full picture, it is just one peice.

 

[Gokul43201]

If you camp outside, you often find that in the morning, it’s wet on the outside. Other solids also seem wet. Why?

FIrst of all, is water vapour always around us at night and day?

Yes, look up humidity.

At around midnight, the air and tent is at their coldest. When the sun slowly rises, it heats up the tent and air but the tent raises its temperature more slowly than air hence there is disequilibrium.

Solids generally heat more slowly due to the fact that air can receive a smaller amount of energy per degree rise in temperature than solid because the intermolecular forces between water is much lower than that between solids. At the higher temperature, it’s now more thermodynamically favourable for the water vapour to condense into liquid and give off heat to the tent, which is at a lower temperature. So the main reason is that water vapour can raise its temperture more easily than solids.

No, this is not the reason. In fact, there are no intermolecular forces between the water molecules in air. The reason that moisture forms on the tent is that the air temperature falls below the dew point (the temperature at which air is saturated with water vapor). The solid surface of the tent simply provides nucleation sites for conddensation.

This is very similar to the precipitation of a solute (whose solubility in the solvent increases with temperature) from a saturated solution, upon cooling the solution.

 

[Integral]

Sounds like a Bunch of non campers. It is not at all uncommon, in this very wet region, to find the inside walls of the tent wet.

2 reasons. When it is raining and wet out if you touch the inside of the tent wall you can cause water to wick through the tent wall essentially creating a leak.

In cool (2 - 10 C), high humidity cliamate your warm moist breath can and will cause condensation on the interior of tent walls.

I have observed this in both ancient canvas tents from the '50s to more modern fabrics of the '90s.

I was camping with regularity though the mid '90s, including '96 the year of the 500 yr flood here in the Pac Northwest. I just so happens that I was also camping in '64 the worst previous flood to '96. I have camped in the rain.

 

[DaveC426913]

It is not at all uncommon, in this very wet region, to find the inside walls of the tent wet.

Well, that's not ideal. You are using a fly, right?

(noncamper, my ***)

 

[D H]

Sounds like a Bunch of non campers.

Sure does. Try googling 'tent condensation'. I got about 520,000 hits, mostly about condensation inside the tent. Try winter camping. The temptation to zip up the tent good and snug is hard to overcome. The result might well be a cold, wet night due to the little rainstorm the campers are creating inside the tent. The problem is aggravated if the campers bring wet gear into the tent.

Some condensation on the outside of the tent will occur because the humidity in the outside air finds nice nucleation sites on the tent. This is not nearly as big a problem as condensation inside the tent.

 

[Integral]

Well, that's not ideal. You are using a fly, right?

(noncamper, my ***)

Yep, that is with a fly on the modern fabric tents, weren't no such thing on the old canvas pyrmid tents I started out in.

Maybe you ought to plan a November or December camping trip into the Pacific Northwest Rainforests.

 

[pivoxa15]

Yes, look up humidity.

No, this is not the reason. In fact, there are no intermolecular forces between the water molecules in air. The reason that moisture forms on the tent is that the air temperature falls below the dew point (the temperature at which air is saturated with water vapor). The solid surface of the tent simply provides nucleation sites for conddensation.

This is very similar to the precipitation of a solute (whose solubility in the solvent increases with temperature) from a saturated solution, upon cooling the solution.

Interesting, so it dosen't depend on the temperture of the solid tent. If there were no tent, water (which transisted from gas to liquid) would fall onto the ground. I seem to recall on cold mornings in winter, the grass gets very wet. And the concrete ground also? But water vapour can evaporate from concrete more easily than from cellulose like grass due to stronger intermolecular bonding (i.e. electronegative carbon, oxygen, hydrogen).

 

[pivoxa15]

Sure does. Try googling 'tent condensation'. I got about 520,000 hits, mostly about condensation inside the tent. Try winter camping. The temptation to zip up the tent good and snug is hard to overcome. The result might well be a cold, wet night due to the little rainstorm the campers are creating inside the tent. The problem is aggravated if the campers bring wet gear into the tent.

Some condensation on the outside of the tent will occur because the humidity in the outside air finds nice nucleation sites on the tent. This is not nearly as big a problem as condensation inside the tent.

True, the last time I went camping was 7 years ago so my memory has faded somewhat. It was during winter so the condensation on the outside was quite high so the inside wasn't as notecible. Google had many articles about reducing water condensation on the inside but none on the ouside partly due to the fact that the outside condensation is uncontrollable - unless you heat your tent? Which would mean the water liquid will evaporate on the outside and not condense on the inside either. But probably not practical, economically.

 

[planish]

The majority of modern summer tents that come with a fly also have screened roof vents that would reduce condensation on the inside, because much of the air that the camper breathe out is replaced throughout the night.

There's also the "Dew Point" to consider - http://en.wikipedia.org/wiki/Dew_point .

 

[Ouabache]

One variation I did not see mentioned is frost on your tent. I have a vivid recollection of this occurring while camping near Mount Rainier (WA). There were feathery patterns of frost on the fly. So instead of the vapour condensing to liquid phase as with dew, it crystalized directly to solid phase.

For those who are timid about camping in the rain, the easiest way to cope is to string up a tarpaulin over your tent pitched preferably downhill (easiest to do when you are camping near trees, without trees you can afix the tarp to tall stakes or telescopic poles and guy them).

 

[russ_watters]

Old thread, but yes, I've seen frost on the fly before. The northeast is pretty humid, so you can see all the different variations (Integral mentioned, plus frost) here.