Civil Engineering Reference
In-Depth Information
(3.12)
The Thermal Comfort Equation
yields the so-called
thermal comfort equation
This equation describes the heat balance of the human body, with the added
variables (air temperature, mean radiant temperature, velocity and
humidity of ambient air) and on two personal variables (metabolic activity
and clothing insulation). This equation permits, under the stated
hypothesis, the calculation of the operative temperature, which will provide
thermal comfort. Fanger (1970) assumes that “the thermal sensation at a
given activity level is a function of the thermal load L of the body, defined
as the difference between the internal heat production and the heat loss to
the actual environment for an occupant hypothetically kept at the comfort
values of the mean skin temperature and the sweat secretion…”. He further
assumes that “in the comfort conditions the thermal load will be equal
to zero” (Fanger, 1970). Operative temperature is defined as
“
the uniform
temperature of an imaginary black enclosure in which an occupant would
exchange the same amount of heat by radiation plus convection as in the
actual nonuniform environment” (ANSI/ASHRAE, 2010). From the above
definition, it can be shown that:
(3.14)
where
T
op
is the operative temperature,
h
rad
is the radiative heat transfer
coefficient, and
T
mrt
is the mean radiant temperature of the surroundings
of the occupant(s). These heat transfer coefficients are often assumed to
be equal in magnitude, which may be a reasonable assumption for typical
conditions and slow-moving air.
Eq. (3.13)
allows calculating the value of
operative temperature for which the energy balance
Eq. (3.2)
is fulfilled.
According to the rational approach, this value is the theoretical comfort
temperature given a specific metabolic activity, clothing, air humidity and
Search WWH ::
Custom Search