[Low-Tech] [High-Tech] Portable cooling: higher-TL replacement of water jugs?

[Bruno]

Originally Posted by Dustin

There are also metal canteens with a woolen covering, intended both to insulate the canteen and to cool it via evaporation when wetted.
Examples: http://www.ebay.com/sch/i.html?_kw=scout+canteen+wool

That's a far more controlled, if fiddly, method - it means you can stop the process if water conservation becomes an issue, but you have to take time out to wet it periodically. Under the "right" conditions, that could be every 20-30 minutes... but then under those conditions you'd need to be constantly refilling it.

[vicky_molokh]

Originally Posted by Bruno

That's a far more controlled, if fiddly, method - it means you can stop the process if water conservation becomes an issue, but you have to take time out to wet it periodically. Under the "right" conditions, that could be every 20-30 minutes... but then under those conditions you'd need to be constantly refilling it.

I think it probably doesn't make sense to keep all of the water in evaporative containers. Assuming the 5%/+1 figure is right, there doesn't seem to be a point of storing more than a day's supply in them. The rest should go into sealed storage. Wineskins seem like a cheap, light, high-volume storage.

[Agemegos]

With those covered canteens you can use non-potable water for cooling.

[vicky_molokh]

Regarding the '12°' claim from the video: found a mention elsewhere where it says the bags keep the water 12° cooler than the environment, which looks more realistic.

[johndallman]

That sounds a lot more plausible. I'm a bit surprised that cool water gives +1 to some specialisations of Survival (it would certainly be nice to have) but I presume the authors of Low-Tech had sources for that.

[Kale]

Originally Posted by johndallman

That sounds a lot more plausible. I'm a bit surprised that cool water gives +1 to some specialisations of Survival (it would certainly be nice to have) but I presume the authors of Low-Tech had sources for that.

I imagine it would help ward off heat stroke. Drinking fluids is a quick way to raise or lower your body temperature if said fluids are hot or cool respectively. The heat transfers quickly through your gut.

[vicky_molokh]

Originally Posted by johndallman

That sounds a lot more plausible. I'm a bit surprised that cool water gives +1 to some specialisations of Survival (it would certainly be nice to have) but I presume the authors of Low-Tech had sources for that.

With my current build, I half-wish that it gave +1 to HT rolls for resisting FP loss to heat (an effective 15 and an effective 16 are a big difference in terms of how long it becomes possible to go without trouble if the checks become more frequent than hourly).

[Anthony]

Originally Posted by vicky_molokh

I think it probably doesn't make sense to keep all of the water in evaporative containers.

Ideally, you want to keep water in evaporative containers for only long enough for it to cool, right before you drink it. This is generally not going to be possible, but certainly any water you aren't planning on using today should be kept sealed.

Note that, fundamentally, an evaporative container is just 'pre-sweating' -- if you evaporate a bit of water to cool the rest of the water and drink the cooled water, the effect on body temperature is the same as drinking the entire amount of water and sweating an extra amount equal to the amount you would evaporate. The advantage being that there's a limit to how much you can sweat, and the pre-cooling gets around that limit.

[Flyndaran]

Originally Posted by Kale

I imagine it would help ward off heat stroke. Drinking fluids is a quick way to raise or lower your body temperature if said fluids are hot or cool respectively. The heat transfers quickly through your gut.

Not by much really. A few ounces of cool-ish water isn't going to do much to the 60% of your body weight that is hot-ish water.
It feels wonderful, but that's purely psychological which is nothing to sneeze at of course. Often times, morale is what separates the haggard from the hopeless and soon dead.

Also, heat stroke is potentially lethal dehydration not overheating. Healthy humans are exceptionally resistant to heat stress assuming enough water.

[Agemegos]

Originally Posted by Flyndaran

Not by much really. A few ounces of cool-ish water isn't going to do much to the 60% of your body weight that is hot-ish water.

When the weather is hot my dog (whose mass is about 36 kg) begs for cold water from the fridge, which at 2 C is about 36 K cooler than the core temperature of an uncomfortable dog. If he were to drink 400 ml of it (which I reckon he often does) that would be 1/90 of his mass, and sufficient to cool him down by 0.4 K. That is certainly enough to be physiologically significant.

Suppose a 68 kg man drinking half a litre of water 12 K cooler than today's ambient temperature hereabouts, which is 28 C in the shade. That's 16 C compared to say 37 C core temperature of a heat-distressed bushman: 21 K times half a kilo over 68 kg = 0.15 K. Not a huge amount, but physiologically significant.