How much R-value would a human need to stay outside indefinitely at -25°C?
AlanB4
| Posted in Green Products and Materials on
I’m assuming those heavy winter coats have an R-value of less then 10, considering they are not many inches thick. Also air tightness is also probably a concern, though ability to breathe would be required.
What is the R-value of the different materials in winter coats?
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Alan,
The answer depends on whether the person is active or at rest. If the person is at rest, the usual method of staying alive is with a sleeping bag rated for -25°C (-13.0°F). I'm guessing that R-10 to R-15 would do it. Individuals vary, so the answer won't be the same for every person.
If a person is lying down, conduction to the cold snow/ice layer becomes a problem. When I've slept in igloos, I usually use a layer of hay, but winter campers often use closed-cell foam pads. You need a substantial barrier under you to be comfortable.
If you are assessing the R-value of a jacket with fluffy insulation, I'd use no more than R-3.5 or R-4 per inch for fibers like polypropylene or a natural insulation like down.
Alan, having spent many weeks out winter camping in Ontario, right down to 40 below (which, by the way is the same in Fahrenheit or Celsius...bloody cold), it is entirely possible to be indefinitely comfortable. A proper vapor barrier is required for both sleeping bag and Jacket. The vapor fabric allows about 5% breath-ability and this will still allow your insulation to remain dry. The jackets and bags are not rated by R values but by comfort to a certain temperature. A Good bag or parka can easily be rated to be "t shirt comfortable" at 40 below. As Martin says, I like a triple layer of closed cell foam under the bag since most heat loss will be downwards.
Interesting, i have heard of rated down to X temp but i like numbers.
I remember reading in a few places that a human generated about 100W of heat while wake but idle, and most coats are less then 1 inch thick, but vapour would be a constant concern and the necessity for breathing.
So at R3-4 per inch one can do well with R5-10 it would seem.
The point about conduction to the ground is very well taken, the ground would be much more conductive to heat then air, however wind will conduct cold relatively well.
Alan, wind chill is only about exposed skin. The tight nylon outer layer neutralizes the wind effect. That is one reason that wind shell pants are also a good idea. Bags, by the way can also be rated in "loft". If the insulation is high fill fine goose down (800 cu. in per ounce) then a 6 inch loft can suffice at 40 below.
The vapor condensation in the sleeping bag can be a big deal. See https://arapahoeprepfair.files.wordpress.com/2011/08/frost-in-arctic-sleeping-bags-edited.pdf
This is a case where the vapor condenses and freezes in the bulk of the fluffy insulation rather than at the sheathing!
Bill,
Winter campers are well aware of the condensation problem -- in clothing, sleeping bags, and tents.
For a vivid story of winter suffering, read Apsley Cherrry-Garrard's The Worst Journey in the World, about a midwinter man-sledging journey a hundred years ago in total darkness to an Emperor penguin rookery in Antarctica. The explorers' sleeping bags were made of reindeer fur, and the accumulated condensation turned the sleeping bags into rigid cylinders of ice that had to be thawed every night by the explorers' body heat before sleep could begin.
Bill,
After I wrote my last comment, I began reading the article you linked to -- and I now see that Cherry-Garrard is quoted. His book is a classic, so the coincidence isn't too surprising.
The paper cites the date of publication as 1965, which is wrong. Cherry-Garrard's book was first published in 1922.
When we were small children our parents used to tell us never to fall asleep in the snow because you wouldn't wake up. On a beautiful spring day, clad in a snowsuit, we would lie down in the park fighting what we thought was a life and death struggle not to doze off in the sun.