Environmental Engineering Reference
In-Depth Information
depending upon their nature. The classification of organic compounds
represents chemical compounds that contain carbon-hydrogen bonds in
their basic molecular structure. Their sources can be either natural products
or synthetics, especially those derived from oil, gas and coal. Organic con-
taminants may exist in the form of gas (vapour), liquid or as solid particles in
the atmosphere, food and/or water. Inorganic compounds are those that do
not contain carbon-hydrogen bonds in their molecular structure.
The danger of particulate matter is its ability to become contaminated by
other ambient sources, increasing health risks to individuals who are exposed
to respirable suspended particles. Particles in this category are, usually, less
than 10 mm in aerodynamic diameter. As mentioned previously, particles
smaller than 5 mm are capable of bypassing the respiratory defences.
Biological contaminants are generally referred to as microbes or microorgan-
isms. Biological contaminants are minute particles of living matter produced
from a variety of sources. The variety of biological compounds that may be
present in the ambient environment is immense. Sources of pollution exist
in the internal and external environment. The air quality is controlled by
removal of the contaminant or by dilution. American Society of Heating,
Refrigerating and Air conditioning Engineers (ASHRAE) [22] prescribes nec-
essary quantities of ventilation for various types of occupancies and methods
of determining the proportions of outside air and recirculated air. If the level of
contaminants in outdoor air exceeds that for minimum air quality standards,
extraordinary measures must be used. Although proper air-conditioning
designs are helpful in the prevention and treatment of diseases, the applica-
tion of air-conditioning to health facilities presents many specific problems.
Those are not encountered in the conventional comfort conditioning design.
7.3.3.2 Problem Identification
The contaminant concentration mainly depends on two factors: air pressure
relationship and air movement efficiency. So the optimum design of these
two factors leads to accepted concentration and safe distribution of the con-
taminant. Actually, most guidelines to date do not restrict any airside design
for each application. This gives a large tolerance and many design alterna-
tives that are not totally perfect.
7.3.3.3 Status Quo
Comfort and air quality are investigated with the aid of experimental
and numerical techniques to represent the relation between the ther-
mal conditions and the air quality [1]. Thermal conditions affect the air
quality; therefore, any recommended numerical models should account for
balanced thermal conditions. This would affect the discrepancies between
measured and simulated results and consequently create a more gener-
alised numerical formula for the air characteristics. The effect of thermal loads
