Related Resources: heat transfer

### Thermal Energy Created by the Human Body

Thermal Energy Created by the Human Body

The body is a heat engine. It converts chemical energy of the food consumed into both heat to sustain metabolism and work. The harder the body exercises or works, the greater the need to reject heat in order for the body to maintain thermal balance. The human body primarily rejects heat to the environment from the body surface by convection, radiation, or evaporation.

The total energy production rate of the body can be written as:

Q + W = M Ask

where:

Q = heat production rate
W = rate of work
M = metabolic rate
Ask = total surface area of skin.

The metabolic rate is customarily expressed in units of mets (or M) where:
1 M = 1 met = 18.4 Btu/h ft2 = 58.2 W/m2

Since the area Ask for adults is of the order of 16 to 22 ft2 (1.5 to 2 m2), heat production rates by adults are about 340 Btu/h (110W) for typical indoor activities. Metabolic rates in units of mets for various activities are shown below.

 Activity Btu/hr · ft2 W/m2 meta Resting Sleeping 13 40 0.7 Reclining 15 45 0.8 Seated, quiet 18 60 1.0 Standing, relaxed 22 70 1.2 Walking (on level surface) 2.9 ft/s (0.88 m/s) 37 115 2.0 4.4 ft/s (1.3 m/s) 48 150 2.6 5.9 ft/s (1.8 m/s) 70 220 3.8 Ofﬁce activities Reading, seated 18 55 1.0 Writing 18 60 1.0 Typing 20 65 1.1 Filing, seated 22 70 1.2 Filing, standing 26 80 1.4 Walking about 31 100 1.7 Lifting, packing 39 120 2.1 Driving/ﬂying Car driving 18 – 37 60 – 115 1.0 – 2.0 Aircraft, routine 22 70 1.2 Aircraft, instrument landing 33 105 1.8 Aircraft, combat 44 140 2.4 Heavy vehicle 59 185 3.2 Miscellaneous occupational activities Cooking 29 – 37 95 – 115 1.6 – 2.0 Housecleaning 37 – 63 115 – 200 2.0 – 3.4 Seated, heavy limb movement 41 130 2.2 Machine work sawing (table saw) 33 105 1.8 light (electrical industry) 37 – 44 115 – 140 2.0 – 2.4 heavy 74 235 4.0 Handling 110-lb (50-kg) bags 74 235 4.0 Pick-and-shovel work 74 – 88 235 – 280 4.0 – 4.8 Miscellaneous leisure activities Social dancing 44 – 81 140 – 255 2.4 – 4.4 Calisthenics/exercise 55 – 74 175 – 235 3.0 – 4.0 Tennis, singles 66 – 74 210 – 270 3.6 – 4.0 Basketball 90 – 140 290 – 440 5.0 – 7.6 Wrestling, competitive 130 – 160 410 – 505 7.0 – 8.7

a 1 met = 18.43 Btu/hr · ft2 (58.2 W/m2)