RACA Journal August 2020 | Page 45

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