Comfort Considerations in Net ZEBs: Theory and Design - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 110

one particular part of the body (local discomfort) (Djongyang, Tchinda, and
Njomo, 2010). Specifically, the steady-state heat transfer model proposed
by Fanger to describe thermal comfort requires that no local discomfort
exist and that the human body be in heat balance with the environment.
This last condition is necessary, but not sufficient because the human
thermoregulatory system acts to restore “heat balance within wide limits of
the environmental variables, even if comfort does not exist” (Fanger, 1970).
It also assumes that mean skin temperature and skin wetness may fluctuate
as a consequence of the action of the thermoregulatory system of the human
body.Butsuchfluctuationsshouldremainwithinspecifiedlimitsdepending
on the activity level, in order for a person to feel within the condition
of thermal comfort. Fanger derived the relationships between the activity
level (metabolic rate per body surface area) and both skin temperature
and sweat secretion (evaporative heat loss per body surface area) using a
linear regression model - Eqs. ( (3.4) , (3.5) ). However, the source data are
very scattered and correlation coefficients are not reported for either of the
regression models.
Heat Balance of the Human Body
SummarizingtheworkofFanger(1970)andOlesen(1982),theheatbalance
between an individual and his/her environment can be expressed, per unit
of body surface area, by the equation
(3.1)
where S is the rate of change of internal energy stored in the body, M is
its metabolic rate, W is its external work, L cond is the sensible heat loss by
conduction due to contact of skin with solid objects, L conv is the sensible
heat loss by convection from the outer surfaces of the clothed body to air,
L rad is the sensible heat loss by radiation from the outer surfaces of the
clothed body to all surfaces of the environment viewed by the body, E evap is
the latent heat loss by evaporation (sweating and moisture diffusion) from
the skin, and E res is the total (sensible plus latent) heat loss by respiration.
E evap and E res , if present, act to reduce the internal energy of the human
body and both take negative values; the remaining heat fluxes on the
right-hand side of Eq. (3.1) can be added or removed from a person (where
addition is positive).