Humans and
their Environment
13
Human-environment interaction involves the same principles discussed
in Ch. 12. However, we need to look at three additional factors. They are
clothing, sweating, and comfort. These are examined by considering survival in cold environments, survival in hot environments, and the human
thermoneutral energy budget. The variables that need to be considered
are metabolic rate, surface area, latent heat exchange, body temperature,
and body (clothing and tissue) conductance.
13.1 Area, Metabolic Rate, and Evaporation
The total body area in square meters (often called the DuBois area in
honor of DuBois and DuBois (1915) who first proposed the formula) can
be calculated from:
where m is the body mass in kilograms and h is height in meters. As a
rough rule of thumb, body area of adults can be estimated from:
A = 0.026 m.
(13.2)
Metabolic rates can be calculated using Eq. (12.14), but a better guide
can be obtained from measurements. Table 13.1 gives values of M for
various activity levels. These activity levels conform quite well to our
rules of thumb of M b = 30 - 50 w/m2 and
The published values for caloric content of foods are normally in units
of kilocalories (called calories in the food literature) rather than joules.
Assuming a 2 m
2 surface area for a person, W m-2 in Table 13.1 can be
converted to kcal of food intake per hour. The conversion factor is:
kcal
-
J
1 cal
1 kcal
3600 s
hr
= x -
x 2 m x - x
x - = 1 . 7 ~ .
m 2 s
4.18J
1OOOcal
hr
Therefore, according to the numbers in Table 13.1, desk work would
consume 160 kcdhr and sleeping 85 kcdhr. For eight hours of sleep
their Environment
13
Human-environment interaction involves the same principles discussed
in Ch. 12. However, we need to look at three additional factors. They are
clothing, sweating, and comfort. These are examined by considering survival in cold environments, survival in hot environments, and the human
thermoneutral energy budget. The variables that need to be considered
are metabolic rate, surface area, latent heat exchange, body temperature,
and body (clothing and tissue) conductance.
13.1 Area, Metabolic Rate, and Evaporation
The total body area in square meters (often called the DuBois area in
honor of DuBois and DuBois (1915) who first proposed the formula) can
be calculated from:
where m is the body mass in kilograms and h is height in meters. As a
rough rule of thumb, body area of adults can be estimated from:
A = 0.026 m.
(13.2)
Metabolic rates can be calculated using Eq. (12.14), but a better guide
can be obtained from measurements. Table 13.1 gives values of M for
various activity levels. These activity levels conform quite well to our
rules of thumb of M b = 30 - 50 w/m2 and
The published values for caloric content of foods are normally in units
of kilocalories (called calories in the food literature) rather than joules.
Assuming a 2 m
2 surface area for a person, W m-2 in Table 13.1 can be
converted to kcal of food intake per hour. The conversion factor is:
kcal
-
J
1 cal
1 kcal
3600 s
hr
= x -
x 2 m x - x
x - = 1 . 7 ~ .
m 2 s
4.18J
1OOOcal
hr
Therefore, according to the numbers in Table 13.1, desk work would
consume 160 kcdhr and sleeping 85 kcdhr. For eight hours of sleep