Thermal Energy Created Metabolic Rate by the Human Body

Related Resources: heat transfer

Thermal Energy Created Metabolic Rate by the Human Body

Heat Transfer Design and Engineering
Thermodynamics

Metabolic Rate Thermal Energy Created by the Human Body

Metabolic Heat Generation People for Various Activities - Typical

Metabolic rate varies over a wide range, depending on the activity, person, and conditions under which the activity is performed. The Table below lists typical metabolic rates for an average adult (AD = 19.6 ft2) for activities performed continuously. The highest power a person can maintain for any continuous period is approximately 50% of the maximal capacity to use oxygen (maximum energy capacity).

Estimating metabolic rates is difficult -the values given below indicate metabolic rates only for the specific activities listed. Some entries have a range and some a single value, depending on the data source.

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 A_sk

where:

Q = heat production rate
W = rate of work
M = metabolic rate
A_sk = 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 A_sk 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	met^a
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)

Source

2016 ASHRAE Handbook - HVAC Systems and Equipment, ASHRAE: 2016.