How many watts does the human body put off

[vwhammer]

I have done some looking around and I did a little math on my own but does anyone have real info on how many watts the human body puts off at rest.

 

[hacksaw]

450 btu/hr (courtesy of google-130 watts) unless you are moving around

 

[SNORGY]

I would imagine ASHRAE Handbooks have data on this related to human occupancy, etc...

Regards,

SNORGY.

 

[DRWeig]

Hacksaw's answer matches ASHRAE Fundamentals handbook.

Good on ya,

Goober Dave

 

[SomptingGuy]

100W is what I've always understood. It equates (in old money) to about 2.5 kCal per day. Burger, fries and a beer. Any more and you put on weight, unless you do external work.

- Steve

 

[vwhammer]

All of these answers are in the range I have been finding.

I saw anything from 96 to 116.
130 is the highest number I have seen yet but I think that will give me a nice higher end to shoot for.

Incase anyone is wondering I am building a stirling powered cool jacket to wear when riding my mororcycle.

 

[IRstuff]

Then the values are too low. Based on a diet of 1800 kcal/day, the AVERAGE power is 87 W.

However, physical activity cranks up the caloric output quite a bit:

http://www.nutristrategy.com/activitylist2.htm

Based on 240 kcal/hr, that's 280 W.

TTFN

FAQ731-376

 

[racookpe1978]

Two problems then: For your own design, you know your own weight and metabolism, and so should use the best (conservative) value: At only 155 lbs, but eating more calories per day than the "average person", I'd have to account for more heat energy than "the generic average." You'll want (need!) to be comfortable under "worst case" riding conditions, but able to proceed without duress when temperatures rise (later in the afternoon for example) or fall - after a storm or shower or after dark.

Second: You're in the wind (very important!) and in outdoors conditions for specific periods of time directly exposed to the weather and cold, NOT the "average" generic TV-watching couch potatoe doing average "nothings" for an average 24 hour day indoors. Balancing that exposure to wind and temperature is the fact that you will be sitting/riding, not running the Boston Marathon.

Allow some testing. Some adjustment. A throttle valve. Or two. A zipper.

Be safe.

 

[hacksaw]

vw,

in the mean time you might put a cooler in the saddle bags,, fill it with ice and a bit of water, circulate the water through your jacket with small pump, you sort our the generic heat loads well enough without having to solve all of the design problems

good luck

 

[SNORGY]

I would be too concerned about the parasitic cooling load required to keep my beer cold. I would not want to encroach on that.

Regards,

SNORGY.

 

[hacksaw]

leave room for the beer, the most important part of the design effort

 

[electricpete]

I didn't follow the diet argument. Was the caloric content of excrement subtracted from the energy balance?

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[electricpete]

... silly comment. Disregard. The beer temperature however is worth further consideration.

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[SNORGY]

The caloric content of excrement in the energy balance is accounted for in the variable "P"; however, as the amount of beer increases, "P" tends to become constant.

Regards,

SNORGY.

 

[Zesti]

So far, nobody mentioned the fact that the heat coming from a person is divided in a sensible part and a latent part in the form of water vapour.

On the other hand, actually sweating will cool the person as well as the air in the room...

 

[IRstuff]

not much so, if one is wearing the proper protection gear, which tends to stop air flow to the skin.

Or are you suggesting riding bareback?

TTFN

FAQ731-376

 

[fea4mil]

Please find attached representative rates at which heat and moisture are given off by a human being in two different states of activity (from fundamentals AHRAE 2005)
- Seated at theater
Total heat : 95 W
Sensible heat : 65 W
Latent heat : 30 W
- Moderately active office work
Total heat : 130 W
Sensible heat : 75 W
Latent heat : 55 W
(Adjusted values are based on 24 °C room dry-bulb temperature and rounded to nearest 5 W)
Regards

 

[IRstuff]

That's interesting, but ASHRAE's focus is people inside a building, so unless they have numbers for gymnasiums and the like, the values are not necessarily applicable.

TTFN

FAQ731-376

 

[tkordyban]

Don't forget the solar load! Of course it is good to consider the body heat load. At best you can use an order of magnitude estimate for that, because it is highly variable with time. And the heat load from the environment, including the sun on your back and head, can be larger than the internal heat load.

 

[IRstuff]

Just for giggles; worst case solar load:

1120 W/m^2 * (3/8m)*(1m) = 420 W

But, that occurs for 2 hrs a day in a hot climate, and the above assumes 100% absorption.

TTFN

FAQ731-376