14 / 68
Thermal balance
Thermal comfort is achieved when the flows of ener-
gy to which the human body is exposed are balanced.
The heat generated inside the body, which depends
on our activity, must offset the energy flows with our
environment.
Thermal comfort is achieved when we reach a
state of thermal neutrality. We feel neither too
warm nor too cold. In physical terms, this state
of neutrality means that the thermal flows created
by metabolism and the exchanges with the
exterior are in equilibrium.
Humidity
Very humid ambient air (60% and above) is almost
saturated with water. Our skin can no longer release
all the perspiration and we start to feel hot again.
On the other hand, if the humidity of the air is 30%,
then 70% of its capacity to store water vapour
remains available. Perspiration evaporates more easily,
helping to keep the body cool.
g
The production of energy (metabolism),
part of which is dissipated as heat
g
Conduction between the inner body and
the surface of the skin
g
Heat exchanges through the lungs, by emitting
water vapour and a rise in the temperature of the
air we breathe out
g
Exchanges of mass, through the evaporation
of sweat
g
Convective exchanges between the skin and
the ambient air
g
Direct solar radiation or radiation reflected
by objects
These flows correspond to the following
mechanisms:
6. Thermal
comfort
12