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and vapours ,” says Siphiwithemba Dube , mechanical and fire engineer at VMG Consultants .
Dube continues , “ The air movement in a space , also refers to as the required air changes per hour , is dependent on the space occupancy-classification – and is a mandatory inclusion . In South Africa , the ventilation requirements for different building / space classifications are outlined in SANS 10400 Part O – Lighting and ventilation – and includes the table that shows the minimum requirements of air per person using the room .”
Where spaces or rooms are , for example , open to smoking , a considerably higher supply of healthy air is required .
Fans , as an integral part of a building ’ s ventilation system also require several design considerations which include :
• The air flow rate to be extracted or supplied
• The system resistance or pressure drop
• The flow rate and the system resistance then determine the selection of the fan , that is , mixed air flow fan , centrifugal fan or axial flow fan
• The efficiency of the fan
• Fan speed ( number of poles )
• The noise levels or sound pressure
• Power consumption
• Operating latitude and temperature ( depending on the operating environment )
• Physical size of the fan – where or if there is a space limitation
• The occupancy classifications of the ventilated space , for example the use of non-ferrous fans for flammable stores
“ Some errors in design or installation in ventilation that I have observed , stem from not conducting a noise analysis resulting in noisy fan installations . The other common error is installation of normal canvas collars on kitchen canopy extractors that get damaged by heat over time and result in air leakage leading to inefficient extract systems . Further , inadequate ventilation systems result in build-up of carbon dioxide to above 1 000ppm – which is the accepted concentration in an indoor occupied space . High concentration of carbon dioxide and lower oxygen levels will result in drowsiness , shortness of breath , headaches , and fatigue of occupants . In ‘ wet ’ areas like bathrooms , incorrect ventilation designs will result in high levels of moisture causing , amongst other effects , wrinkling and peeling of the paint and formation of moulds on the walls and ceilings ,” Dube adds .
Other than the makeup air supplied to a building or space , air extraction as part of a building ’ s ventilation system in many
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RACA Journal I June 2021 www . hvacronline . co . za