Feature
© RACA Journal FabricAir
Basement extract systems mean that ductwork is essential .
Fabric ducting at a gymnasium .
• Long “ meandering ” sections of ductwork can lead to trouble , such as ducts collapsing over time or becoming twisted and blocked .
• Air wants to go straight and will lose energy if you make it bend but from a cost perspective , straight runs costs less than “ fittings ” or connector pieces . Try to reduce the number of bends and turns .
• Ducts should be the correct size - too small and you won ’ t be able to carry enough air to heat or cool - too large ducting can lose both air and waste energy .
• Make sure you include enough return ducts – every system also requires enough return ducts to bring expended air back to the HVAC unit to be conditioned again . Each room that receives conditioning should have at least one return duct or provision .
• You may want to consider thermal zoning , a practice of dividing a building into distinct thermal zones which have similar heating and / or cooling requirements
• Balancing air is important in ductwork design layout . Actual air flow can exceed design flow if the fan pressure is higher than any pressure loss . Therefore the function of adjusting the volume control dampers equalises potential friction losses . Balancing may be required in both supply and return ducting .
• Operating pressure in the duct is also a significant consideration . If the pressure is minimal , materials with a great deal of strength are not needed . The thickness of the duct material thus depends on pressure as well as the dimensions , the length of the individual sections , and branch requirements .
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RACA Journal I October 2022 www . refrigerationandaircon . co . za