Body Heat Wattage

[Proteus]

How much power does the human body need to keep its temperature constant in different ambient temperatures ("ambient" meaning in the immediate environment, ie, under clothing)?

[swansont]

~90 Watts.

 

http://hyperphysics.phy-astr.gsu.edu/HBASE/thermo/coobod.html#c1

[Proteus]

"Even when still…" What if the person is shivering? That way, the body can produce more heat.

 

According to the diagram, at 23 C the body would have to produce at least an additional 70 watts to prevent hypothermia, excluding the unknown value of convection. So that's a total of more than 160 watts. What if it's freezing point? What's the highest number of watts the body can invest into heat while standing still, but shivering?

 

Note that the 90 watts figure is due to the basal metabolism of the body, that is, the basic mechanisms it needs to stay alive: heartbeat, breathing, brain function, muscle tone, etc. This does not include extra heat production due to cold.

Edited December 30, 2009 by Proteus

[swansont]

You have many variables to worry about. Your question does not have a simple answer — shivering is a way of doing mechanical work, which generates waste heat. Sweating allows for evaporation, which cools, and the efficiency of this depends on the ambient humidity. Clothing adds insulation, which affects the losses. The amount of radiative absorption and loss depends on the temperature. All of these, and other factors, would need to be quantified.

[Proteus]

That's why I wasn't searching for a formula that would cover every possibility, just for examples. What I'm most interested in is, how much energy does a traditional Inuit (clothed) need to keep warm outdoors in Arctic temperatures?

Edited December 30, 2009 by Proteus

[greenprogrammin]

Wouldn't you be concerned with calories using a calorimeter and the Basal Energy Expenditure, then build upon that?

 

I know Wattage as Voltage multiplied by Current. This is electrical.... Not metabolic. This is where we gain most of our thermal content... Right?

[John Cuthber]

2500 Calories a day is, according to Google, about 120W.

Most of the energy we consume gets converted to heat so, under typical conditions, we use about 120W keeping ourselves warm.

[Mokele]

2500 is too high. I'm a big guy, and my resting metabolic rate (seated) is ~2325 (I'd have to dig out the old spreadsheet - I was bored and had access to a respirometer).

 

Plus, while we burn most of it, about 10% or so is used in "productive" means (though about half the energy of the reaction probably winds up as heat).

 

A more reasonable 2200 calories/day and the above gives a bit more than 100W, which lines up nicely with swansont's post.