Can vapor pressure differential predict condensation in tents?

[@julien3949]

One of the best video on this subject, as always your videos are amazing, my only complaint as someone from "the rest of the world" is the units, it'd be nice to have the conversions. I'm converting myself but it's a pain as a viewer.

[@That_Guy_Outside]

This is why I love BPL and it’s community so much. This learning makes my trips faster, lighter, more comfortable => MORE FUN. That’s why I’ve supported the community by being a member for so many years.

[@BackpackingLightUSA]

Thank you! We're happy to be part of your journey!

[@frstesiste7670]

Some serious work went into that video. Impressive!

[@luciano.a]

This is great! I only missed one last step that would corelate temperature and RH, showing the threshold which condensation would occur (VPD=3)

[@PHYSIZIST]

you also breath out litres of water each night. being in scotland, camping near rivers and breathing with zero wind/venting are the worst offenders imo. since we cant really fully stop condensation through breathbility, another aspect that gets looked over is drainage away from the bathtub which is just as or more crucial. for this, i kinda like the x-mid 1 and pro. just done the west highland way, fly was soaked but inner was as far as i could see and feel, very dry. if im not mistaken, i love the look of the x-mid pro mesh, which is higher on the bathtube than it is where stitched to the fly, meaning it wont wick water down and into the bathtube. i was thinking of making a custom tarpless bivi that has vents for every angle of breath (side sleeping and back sleeping) whilst creating geometry that takes care of drainage from breath that touched the fly. i may also have had too much alcohol to drink. another youtube could see how much condensation i (we) had that morning - kzbin.info/www/bejne/r6KTeYGAfaaNjcU

[@rodoutdoors]

This is great. Thanks a lot. I might start bringing a pair of Govee bluetooth thermometers that have a relative humidity reading. I've been surprised how much condensation is from my own breath.

[@neemancallender9092]

excellent work Question How do we the camper predict and them mitigate this differential

[@tomnoyb8301]

Great topic. Couple issues: 1) Weather reports often give Dew-point forecasts, which may be more useful for hikers to make decisions? 2) Radiation discussion is incorrect and misleading. 3) Discussion of heat-transport mechanisms are fundamental and missing. Heat, and therefore cold, move by a) Conduction, b) Convection, c) Radiation. Most understand cold-ground 'conducting' heat from below and cold-air convecting heat away and even how a fire can provide 'radiant' heat. Radiation is key to understanding condensation. At night, the one thing outside man's direct awareness is that the clear sky shines cold. Very cold. (more...) In fact, a clear sky shines -450°F (-269°C), way colder than most realize. However, net temperature is a combination of all three (Conduction, Convection, Radiation), so one never really feels the full-effect of such cold temperatures and hence, why they are outside normal experience. One can see the sky-shine effect on a cold morning when grass has frost everywhere but under trees. Because trees are much warmer than the cold clear sky (for example, even if freezing themselves, 20°F is much warmer than -400°F). So while conduction and convection contribute the vast majority to surface-temperature, sky radiation lowers that surface-temperature just enough to dip below the dew-point and condensate. While infra-red, sky-shine is a lot like sunshine. For example, clouds block cold sky-shine. If clouds are at 30°F, then tent-wall's surface will be much warmer than an unblocked clear sky's -450°F (radiant-contribution) and condensation will be commensurately reduced. While helpful in understanding the mechanism for condensation, suspect video's charts and graphs might be less useful than the single dew-point number available to most hikers? Dew-point effectively rolls all those charts and graphs into a single, easy to understand data-point. A data-point provided in most weather reports. If one assumes clear-sky, West-Coast sky-shine radiation may lower the apparent surface temperature of a tent-wall by 1-3°, and hikers can plan tent sites accordingly.

[@daven.7685]

I think my head just exploded.

[@BackpackingLightUSA]

Thanks for your feedback. Agreed that you can't have a comprehensive discussion about condensation without acknowledging the use of dew point temp and the impacts of radiative heat exchange processes. You'll find this all tied together in the webinar linked at the end of the video, which summarizes best practices for hikers and rolls in the dew. point. That wasn't the purpose of this particular video, which just focuses on VPD and its impact on condensation.

[@daddancingmywaythroughit]

Simple man me just tries to pitch tent under tree, hope for best

[@simon7719]

"cold shine" Isn't that just lack of incoming thermal radiation?

[@tomnoyb8301]

@@simon7719 - Yes, however it's best thought-of as 'shine.' By thinking of the night sky shining coldness down, it better allows one to setup camp, for example. Upon looking up, one potential tent-site has 30% of the sky covered by trees and rocks, while another has 60%. Obviously, the 60% coverage site might be expected to yield less condensation, all other things being equal. Take another pair of potential sites, this time both are 30% covered, but one has a single tree directly overhead and the other has its 30% covered from the sides, with no coverage directly overhead. (more...) By thinking of it as sky-'shine,' one quickly realizes that shine from angles lower to the horizon has to go through more atmosphere and more atmosphere attenuates (warms) the cold-shine more than it does from directly overhead. Therefore, having a tree blocking directly overhead is better than trees blocking from the sides, even though the percentage of sky being blocked is equal.

[@pgreenx]

This was excellent. Thanks

[@PaulSchortemeyer]

Extremely unscientific analysis: why don't we all just use little fans (think low-voltage computer fans) near a tent vent - to encourage air exchange and less vapour pressure/temperature difference between inside and out? They are practically silent and I believe a 5V / .5A fan would run for about 80 hours with a 10,000 mah battery pack. The weight cost is about 45g. Would this help with condensation issues?

[@simon7719]

10Ah battery pack has about 35Wh of energy (?a bit more, but theres also conversion losses), the fan draws 2.5W, that's 35/2.5h=14h of runtime. It may also be hard to make sure it doesn't end up making things worse if the wind direction changes, by fighting the ambient draft or otherwise blocking airflow. Still, it could perhaps work. Depends on how much it helps the inside humidity ofc. I don't have an estimate for that.

[@wisenber]

Meanwhile in the Southeast.....

[@WilliamTheDestroyer.]

I look at thumb nails first, then titles. When I see a red line at the bottom of the thumbnail I assume I've watched the vid and don't bother reading the title. I'm pretty sure I'm not alone in this pattern of observation.