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GRANT LAIDLAW
Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy ( ACRA ) in Edenvale . He holds a Bachelor of Business Administration and an associate degree in educational administration . He has a National Technical Diploma and completed an apprenticeship with Transnet . He has dual-trades status : refrigeration and electrical . He has been involved with SAIRAC for over two decades and served on the Johannesburg committee as chairman and was also president between 2015 and 2018 . Currently he is the SAIRAC national treasurer .
WELCOME TO THE SOLUTIONS PAGE
Contributed by Grant Laidlaw
Many people ask for assistance in the understanding of theoretical and practical aspects of the industry . I will endeavour to enlighten . We are going back to basics as I have questions coming in that indicate that the basic understanding necessary to work in industry is not in place .
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David asks : Hi Grant . I would like to ask a question about all the types of filters we can expect to find on a central airconditioning plant . We are expanding our maintenance into this area only to find quite a diverse range of filters , nothing like one would see on a mid-wall split unit .
Hi David , I would imagine moving from a split unit environment to a central plant situation could be somewhat eye opening . Let us consider the air itself as a starting point .
Air is a mixture of gases . Normal atmospheric air consists of 21 % oxygen , 78 % nitrogen , 1 % argon and 0.03 % carbon dioxide . There are also small quantities of other gases such as hydrogen , neon , helium , ozone and xenon and varying amounts of water vapour .
We depend on air to survive and any substantial differences in the percentage composition of normal air makes it unsuitable . Oxygen concentrations of less than 12 % and carbon dioxide concentrations of less than 5 % – even for short periods – are dangerous . Over long periods , even smaller variations in the composition of the air may be dangerous .
A human being uses approximately 30 litres of oxygen per hour . The air requirement is thus in itself quite small , 150 litres or about 0.15m ³ per hour . However , the carbon dioxide produced by humans means that the air required to keep the carbon dioxide concentration below the danger level rises to about 5m ³ per person per hour . Greater air flows may however be needed in order to control heat , cooling or contaminants .
In addition , air contains various foreign materials , both from natural processes such as wind erosion , evaporation from the sea , earthquakes and volcanic eruptions and from industrial activities , such as products of combustion from industrial processes .
Atmospheric dust consists of a mixture of mist , fumes , dry granular particles and fibres . An analysis of the air usually reveals soot and smoke , quartz , clay , traces of decomposed animals and
RACA Journal I January 2024 plants , organic material in the form of cotton and plant fibres and metallic fragments . It also contains organisms such as bacteria , spores and plant pollen . Such floating particles mixed in air or gas are often called ‘ aerosols ’.
Despite the fact that these impurities occur in small concentrations in ordinary air , they have a decisive effect on our environment . Electrical effects in the atmosphere , absorption of solar radiation and cloud formation are all affected to some degree by the impurities in the air . What is perhaps more evident is the effect of atmospheric air pollution on materials and living creatures .
The concerns of particulate matter and gases – which influence our health or comfort and contaminate the spaces we occupy , or which affect the products and components we manufacture – are very real and not unique to specific areas , but rather standard elements in the atmosphere irrespective of location . All that really changes are the concentration levels .
Although great strides have been made to identify the hazardous particulate matter in the atmosphere , the reality of it all is that the air we breathe is not very clean at all .
Contaminants originate from the outdoor air and from building contents such as furniture and furnishings and from processes and materials used within the building . Many of these are nuisances such as cooking odours , but others are identified as causing discomfort and even illness for some ( if not all ) of the building occupants .
David , let us move on to the contaminants . An aerosol is a suspension of solid or liquid particles in the air . The size of an aerosol is usually measured in microns . One micron is one millionth of a metre or one thousandth of a millimetre . Under the International System Units ( SI ) the term ‘ micron ’ is being replaced by ‘ micrometer ’. However , we will use the term micron due to it being the most popular term in industry . The abbreviation for micron is ‘µ’.
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