Environmental Engineering Reference
In-Depth Information
(Figure 8.12). We then have the daily total of short-wave radiation based on intensity
values every ten minutes. The contribution from diffuse radiation is assumed to be
constant throughout the day and so does not add to the spatial variability of solar receipt
at the surface. None the less it is vitally important for slopes with a northerly aspect or
very shaded locations, which would otherwise receive very little short-wave radiation.
Moon explorers were able to see this, for with no atmosphere there is no diffuse radiation
and any surface that is not directly in sunlight appears dark.
These effects of slopes upon radiation inputs mean that the radiation balance varies
locally with topography. In the northern hemisphere, slopes with a southerly aspect
receive a greater input of radiation than northerly ones, resulting in larger exchanges in
sensible heat and higher temperatures (Table 8.5). In high latitudes this additional energy
may be an advantage, but in more arid countries the increased radiation will evaporate
moisture more quickly and may produce even greater moisture stresses in plants.
HUMAN COMFORT AND BIOCLIMATOLOGY
applications
Climatology can be viewed as an abstract concept based on the synthesis of day-to-day
values of meteorological elements that affect that location. We can also examine the
factors that influence this climate, as we do in this topic, in order to explain the patterns
of climate that Earth experiences. However, we can also look at the relationship between
climate and humans in an area known as
bioclimatology
. In this instance we consider the
impact of climate directly on the human body so that we can comment on the sensations
that may be experienced by the average individual from extremes of heat stroke and
hypothermia.
The human body normally operates with a core temperature of 37° C. It tries to
maintain this value through a balance between heat gain and heat loss. We can think of
these energy exchanges as a human energy budget in which inputs and outputs to the
body are evaluated. For an individual, there is a metabolic heat input, dependent on level
of energy exertion, created chemically within the body. We can add to this any solar
radiational inputs, which are especially noticeable when the sun is shining. There will
also be a net radiational exchange of long-wave radiation, though this is usually negative
from a warm body. Convection may give either a gain or a loss of energy to the body,
depending on external conditions, whilst evaporation normally leads to cooling through
perspiration or loss of moisture through breathing. For the core body temperature to
remain stable there must be a balance between the gain and loss of heat. In practice this is
achieved most easily by the use of clothes which can modify many of the heat exchange
processes mentioned.
There are two individual and four atmospheric factors which are most important in
determining the balance of heat for the body:
1 Level of activity of the individual (the metabolic rate), which can vary from less than
50 W m
−2
during sleep to over about 1000 W m
−2
for hard running.
2 Thickness and nature of clothing. This is often indicated by the clo unit or a measure of
the insulational value of the clothing.
3 Air temperature.
4 Radiant temperature of the surroundings.
