Essentials
SELELE MASHILO
Selele Mashilo has a mechanical engineering diploma from Tshwane University of Technology and
a refrigeration and air-conditioning diploma from Unisa. His experience includes over a decade in
government as deputy-director building services before rejoining the private sector in 1998 as HVAC&R
project engineer. He is the former chairperson of the Refrigeration and Air Conditioning Empowerment
Forum of SA (RAEFSA), the Air Conditioning and Refrigeration Industrial Council of SA (ACRICSA), and
Black Energy Services Companies (BESCO).
AIR CONTAMINANTS
AND AIR CONDITIONING
By Selele Mashilo
Atmospheric air is composed of various gases. The composition of the air we
breathe may vary due to levels of contaminants found in the air.
The contaminants are added or reduced in the air due to a
number of activities and may change the air quality for human
consumption.
We know that the gaseous components of clean air near sea
level are comprised of oxygen 21%, nitrogen 78%, argon 1%, and
carbon dioxide 0.03%. There are traces of other gases at lower
percentages. When breathing, one thinks mostly of oxygen and
carbon dioxide, but the acceptable oxygen level may be different
due to air contaminants.
The designer of an air conditioning system must first assess the
environment under which the system is going to operate. This includes
the usage of the facility under consideration and kind of filtration that
will be required based on contaminated air as well as the amount of
fresh air to be supplied to the building so that the design does not only
look at human comfort. Comfort for human metabolic systems can
be achieved by regulating temperature. In addition, air conditioning
systems may consider other requirements to maintain good indoor
quality. When an environment reaches intolerable conditions, it may be
caused by high carbon dioxide concentration, low oxygen content and
excessive temperatures.
AIR CONTAMINANTS
Normal air contains permanent atmospheric impurities and manmade
contaminants. Natural contaminates originate from wind
erosion, sea evaporations and volcanic eruptions while man-made
contaminants come from power generation plants, transportation,
industrial processes, construction, mining and agriculture. Indoor air
quality is widely affected by tobacco smoke, radon and formaldehyde.
Contaminants may be in solid, liquid and gaseous forms.
DUST, FUMES AND SMOKE IN SOLID
PARTICULATE MATTER
Dust particles are solids which are smaller than 100µm (micron).
Dust can be naturally created by wind and earthquakes or by
demolition, sweeping and blasting. Fumes are solid particles formed
by condensation of vapours of solid material. They occur as oxides
due to the highly reactive nature of finely divided matter. They can
be formed by sublimation, distillation or chemical reaction. The
processes create airborne particles smaller than 1µm.
Smoke is formed by small solid and/or liquid particles produced by
incomplete combustion of organic substances such as tobacco, wood,
coal, oil and other carbonaceous materials. Average sizes of particles
vary from 0.1µm to 0.3µm.
Organic contaminants can include virus particles ranging in size
from 0.003µm to 0.06µm, fungus spores, usually from 10µm to 30µm
and pollen grains between 10µm to 100µm
Ignorance of the above air contaminants may cause the following
symptoms in the building occupants:
• Dryness and irritation of the eyes, nose, throat and skin
• Headaches
• Fatigue
• Shortness of breath
• Sinus congestion
• Dizziness
AIR CONDITIONING APPLICATIONS
Selection of proper air conditioning is very important, particularly the
method of filtration and ventilation. Filters may have arrestance of up
to 99.9% and are selected based on the kind and sizes of contaminants.
The type is referred to either chemical filtration, dust, fumes or viruses.
Outdoor air for air dilution must be carefully considered.
MAINTENANCE
Proper operation of air conditioning depends much on maintenance,
which is the responsibility of building owner. Poorly maintained
equipment may increase running costs, increase poor indoor air quality
and create what is known as Sick Building Syndrome diseases. RACA
REFERENCES:
1. ASHRAE
www.hvacronline.co.za RACA Journal I August 2020 43