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• Once you have determined the thickness of material required , the next step is deciding on what flange connections will be suitable and the type of duct section joining techniques will be used . Here various industry standards may be applicable such as S / Drive , TDC , mezz flanges & angle flanges .
• Consideration of other services on a site as well as potential conflicts when installation is done could affect the overall system performance . For example if wet services are installed because of an easier route , this may affect duct installation and thus airflow delivery .
• Design needs to take into account if duct sweating will be a problem for site – this happens particularly when conditioned air inside the duct reacts with any outside air or particular conditions . An example here would be if ducting runs through a plant room area that is hot while conditioning is cold . This may require the addition of insulation , fibreglass or cloth materials at the manufacturing level .
• The amount of angles and guiding vanes in the dispersion system needs careful consideration . For example , 45 degree bends rather than 90 degree bends eliminate several challenges in airflow .
• Air leakage rate or potential leakage rates need to be accommodated in design . Air leakage typically occurs at joints and is the one component where several different connection types and ranges have been developed through the manufacturing process . These joining techniques are mentioned above .
COMMON SYSTEMS IN SOUTH AFRICA In South Africa , the most widely used systems include the traditional galvanised sheet metal and fabric duct systems that have gained ground in the region over the past couple of years while a little known fact about fabric material ducting is that is has been around commercially for around 35 years already . The following information is intended to give designers some points to consider when completing their project evaluations .
One would always need to consider total lifetime ownership cost of each solution and the aforementioned points around customisability , as well as provision for future expansion . One particular solution may well have clear and considerable advantages over another .
• Metal systems use duct , dampers and localised diffusers that are spaced out over the length of a run . This approach results in air drafts near the outlets and possibly hot and cold spots in the occupied space . Fabric ductwork is designed to provide uniform air dispersion through a combination of air-porous fabrics , linear vents , nozzles and orifices . This method has a positive impact on energy costs as these systems heat or cool
FabricAir FabricAir
Large fabric ducting installed in a warehouse .
Fabric ducting installation in a processing facility .
spaces faster and more uniformly to satisfy temperature set points . The result is reduced mechanical equipment runtime .
• Fabric dispersion systems are engineered to distribute and disperse air in open and finished ceiling architecture , critical environments and underfloor applications . They are an innovative , and an aesthetically pleasing alternative for indoor spaces .
• Technology advancements in fabric have created an opportunity for this solution to be used in applications where there are specific performance requirements . Anti-static fabrics are ideal for data centres and anti-microbial treated fabrics for laboratories , food processing and growing facilities .
• The difference in weight of a fabric system versus a metal system can be significant . This difference can impact logistics , installation time and cost , as well as the overall load on the structure .
• A properly designed fabric system will deliver air quietly without the resonation found in metal . Fabric can also absorb noise in certain applications . When there is mechanical noise coming from the air handling unit , a fabric sound attenuator can be installed for additional noise reduction .
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www . refrigerationandaircon . co . za RACA Journal I October 2022 33