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• Non-insulated metal ductwork has the tendency to drip condensation and potentially rust in humid applications or climates . Based on the nature of the material , a porous fabric system is not prone to condensation or rust issues . However , steel ducting systems are designed or specified to have specific insulation be this internally or externally .
• Fabric ducts are available in a variety of standard colours , patterns and custom branding .
• Metal systems require minimal upkeep , such as repainting over time , periodic tightening of louvers / registers / grills and resealing of transitions . This remains true even when they are scratched or dented . The durability of the metal makes it that steel ductwork can last for many , many years before replacement is required .
• Fabric systems on the other hand can be commercially laundered multiple times , which is important in applications that have hygiene standards .
• Metal ductwork systems can be exposed to damage over time that will not necessarily affect function , while fabric has the risk for tearing affecting function and has a lower pressure tolerance than steel .
• The price of metal , particularly over the last few years , has been unstable and has become very high over the years along with several supply chain availability problems . The price of fabric on the other hand , has been relatively stable and has therefore not changed substantially over the years .
• In the current economic environment , transportation has escalated to a major cost component for projects . Metal ducts historically have “ taken up a lot of space during transportation ” while fabric systems can be rolled up and transported by courier or a freight company . To increase efficiency of delivery on metal ducts , they can now be transported in panel-forms to significantly reduce space on transport vehicles .
• Labour costs are another major increase and one needs to consider the time consuming elements that pertain to each solution .
• In an ever-advancing environment of health and hygiene , this factor must be taken into account as well as the function of cleaning and maintenance requirements . RACA
ARTICLE SOURCES :
• ASHRAE Handbook / guidelines
• Continuing Education and Development
• DuctShop
• DuctSox
• FabricAir
• Sheet Metal and Air Conditioning Contractors ' National Association ( SMACNA )
• South African National Standards ( SANS ): SANS 1238:2005 - Air-conditioning ductwork
© RACA Journal
An example of the PVC-type material sandwiched between two aluminium skins .
© RACA Journal
A rooftop installation .
www . refrigerationandaircon . co . za RACA Journal I October 2022 35