UKH

Low temps, stormy weather and deep snow make camping in winter a challenge. But with the right gear and a few key tricks and tactics, nights out in winter can be a whole lot more comfortable. Here's how

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In reply to UKH Articles:

"But meanwhile, your body has been wasting valuable heat keeing a bladder full of urine warm."

Someone was asleep when they were taught basic thermodynamics!

In reply to davidbeynon:

Hah, I was just about to post something about that sentence too! I agree; I'm pretty sure that's not quite how it works.

There's some story in an Andy McNab book if I recall correctly (totally scientific reference, eh?) about the main character needing to pee but being near-hypothermic, and consciously not relieving himself, as he didn't want to relinquish the warmth held in the liquid in his full bladder to the outside world.

In reply to UKH Articles:

Sunset in northern Scotland is about 5pm at this time of year, Sunrise about 8am. So if you're going to pitch a tent in daylight hours I'd bring something to relieve the tedium. Kindle, video game, inflatable partner etc.

In reply to PM:

The stuff in your bladder should be in thermal equilibrium with the tissue around it, so no net heat flow.

If you are losing enough heat to the environment for the tissue to be cooling down then it will act as a heat reservoir that may help slightly, but you are probably screwed if it gets to the point where it would make a difference.

In reply to UKH Articles:

On a more positive note I agree 1000% with the point about keeping boots from freezing. I found that out the hard way once when it took me 20 mins to melt my way back into a pair and another hour of walking before feeling recovered enough for the hot aches to kick in.

In reply to davidbeynon:


a heat reservoir only works if you can abstract that heat, transfer it to somewhere you want, thereby cooling the reservoir. surely not something that the human body is capable of.
fluid in the body is at body temperature, and body temp won't change if you expel some of it. Given energy use to maintain a higher temperature than the surroundings is proportional to mass, less mass would save energy over time.

what's your understanding of basic thermodynamics?

In reply to daWalt:
I mean a heat reservoir in the sense that it increases the bodies thermal mass, and in the event that you were losing all your body heat to the environment it would take slightly longer to freeze solid if you haven't taken a leak.

I didn't mean to imply it would be useful or that humans had a system to make use of it.

I would say my understanding of thermodynamics is about exactly what you might expect from someone with an undergraduate physics degree who specialised in statistical physics when the relevant exams came around, but hasn't really used it much since.

If you like I can model it for you. I was writing a pde solver that can cope with diffusion equations fairly recently, the person would have to be 2D though.

In reply to davidbeynon:

just an explanation would be fine.

In reply to daWalt:
For the purposes of this article the GCSE level observation that heat flows from hot to cold bodies and not the other way around is sufficient. The rest is mere detail.

Basically if your bladder is full of warm wee then it doesn't take any extra energy to keep it warm. Any heat you are losing is going through your skin, and is a function of the temperature difference, surface area and thermal conductivity.

Taking a leak in this case may make you more comfortable but you are actually dumping heat into the environment.

In reply to davidbeynon:


none at all?.....

In reply to daWalt:
My understanding of thermodynamics is virtually nil. I'm not totally getting the 'more mass == more energy usage' thing. Here's my thinking:

If you have the following layers:
Skin: 33° in a toasty sleeping bag?
Inner tissues: 37°
Bag full of fluid inside body: 37°

The cooler skin is 'trying to make' the the inner tissues colder. Those tissues are actively expending energy to stay 37°. The bag of 37° fluid is contained within the tissues which are actively maintained at 37°, so there's no net loss/gain between the liquid and the container, irrespective of the mass of the liquid.

If the body temperature were to drop to 36°, then the tissues would actually be heated slightly by the warmer liquid, until they reached equilibrium (tissues now slightly warmer, liquid cooler). In this case, a larger mass of liquid would heat the surrounding tissue more (and itself, cool less) before reaching equilibrium. (This equilibrium may never occur if the skin were cooling the tissues faster than the liquid - and tissues themselves - were heating the tissues.)

There is no direct gain or loss of heat from the liquid to the skin, without first heating or cooling the intervening tissues.

Assumption here is that your bag of liquid is already 37°. If you're drinking Ice Cream Smoothies, then it's going to need heated. Here, I can see that more smoothie mass = more energy needed to heat it up. In terms of keeping something at a given temperature, as long as you're putting in heat as fast as it's being lost, I don't see how mass is a primary factor. I don't see how greater mass would cool quicker. Given similar insulation, surface areas etc. I'd expect a greater mass to retain heat better/longer.

(I suspect there are large parts of my thinking here which are totally incorrect, but I'd be interested to know which bits, and why, thus possibly gaining some understanding of thermodynamics.)

In reply to davidbeynon:

Thank you for the explanation David. My 'figure it out from logically thinking about it' seems to match what I missed by not taking GCSE.

Unfortunately I wasted so much time thinking about it and typing that I'd missed the fact that you'd posted the answer I was looking for before posting my thinking. : )

In reply to daWalt:


So what you propose is something of temperature X which (proportional to mass) draws heat from its surroundings, which are also temperature X? Why does this thing not heat up and then exchange heat in the opposite direction (from itself, now temperature X+, to the surroundings, which are now X-)?

In reply to davidbeynon:

Sorry David: GCSE physics was a long time ago. My reasoning was pretty basic: if you've, say, 1litre of pee in your bladder isn't that an extra 1kg of body mass that you're burning calories to keep warm unnecessarily? Surely the bigger you are, the more energy you need to burn to remain at x-degrees? Though I guess more mass also means slower heat loss...

Granted it's not going to make an enormous difference either way though.

Guess I'm wrong anyway..?

In reply to Dan Bailey - UKHillwalking.com:
'Top tips for Winter Camping, some of which don't make an enormous difference either way', doesn't have quite the same ring.

Pee bottle overall is very useful though, just not the timing advice, for the 'Clearly [...] more efficient' reasons stated. Think if we're talking efficiency, if you can sleep through it, hold off as long as you can, instead of potentially going twice, which is (as they say) clearly less efficient.

(I did enjoy the article, thanks!)

In reply to UKH Articles:

Moving away from the theory of thermodynamics....
The choice is between a snowhole (obviously in suitable snow) and using a tent. Having camped and snowholed on the Ben, Aonach Beag, Lochnagar and Cairngorms in full winter conditions, i have no hesitation in suggesting using a snowhole. No flapping, warmer than a tent, no problem if a storm hits, and it only costs a bit of effort. Condensation is really bad in a tent in winter and freezes to the inside roof of the tent when the stove is switched off. Start up the stove again and it all drips over you and you lovely warm dry down bag! A no-brainer if staying more than one night.

In reply to UKH Articles:

In defence of Dan I know that the Norwegian army's survival instructors advise their students that they should not hold onto a bladder full of liquid, that they'll be warmer if they get rid if it into a pee bottle. I guess these things are always marginal, but not being able to sleep because you want a piss is never conducive to the next days performance.

In reply to UKH Articles:

Another way to look at this is to think about what would happen if you do have a piss before going to sleep. Imagine the situation, you're freezing your knackers off, and you piss into some fresh white snow. The snow melts and you're literally pissing away heat doing this. The thermal energy in your piss (the piss will be in thermal equilibrium with your body when your nice and warm) is best kept inside.

If you're worried about having a sleepless night, piss into a bottle and cuddle it to keep yourself warm

4th yr engineering student

In reply to UKH Articles:
My top tip for winter camping is to build up some body heat before you retire to your pit. If safe, you can run about/on the spot when you go out for your last pee. Otherwise, press ups or sit ups in the tent. Learned this one 50 years ago and it really works.

In reply to UKH Articles:

Another reason to blow up any mattresses asap is that they 'sag' over time as they lose heat to the ground (because they were filled with warm, low-density air from your lungs which upon cooling becomes higher density, reducing the volume).

In reply to UKH Articles:
Another couple of top tips (you can work out the experiences they are based on!).
Ice crystals getting into zips, especially modern ones with small teeth, can cause the zip to fail. It is worth having a couple of biggish safety pins to at least control the door. Thread a sock through the gaps to cut down on wind flow.
When pitching on snow, be careful to tread down the snow to ensure that there isn't a large rock. or multiple pointy ones, which will emerge as body weight and heat compress the snow.
Collect snow for melting before you go to bed. squash it down into a pan, then make a "snow-pie" ready to melt in the morning.

In reply to andy kirkpatrick:


From a perspective of reduced thermal mass, voiding your bladder will reduce your thermal mass. Given the heat flux from your body is dependent on surface area, which won't change, that heat flux will reduce the temperature of a smaller mass more quickly than it would the larger thermal mass. Without an active heat source, your body temperature would drop quicker.

However, the body does have an active heat source, and other mechanisms that determine how our bodies react to cold, and how we sense cold.

I'd suggest the most significant of these mechanisms is that, in order to retain a full bladder, we constrict our lower body. This constriction impedes blood flow, and so our non-core body (legs, in this case) feels colder. I certainly know (as someone with Raynaud's) that hanging on to a full bladder makes my feet feel colder, and having a pee allows me to relax, and thus improve the circulation to my legs, making my feet feel warmer.

The ideal solution is to void your bladder, but hang on to the thermal mass; pee into a nalgene bottle and bring it into your sleeping bag...

In reply to captain paranoia:

Interesting - though personally I might give the pee bottle in sleeping bag trick a miss thanks!

I've amended the contentious line anyway. Back to school for me...