Feature
Louvres are similar to grilles but are comprised of one-way or two-way adjustable air stream deflectors and dampers to restrict the amount of air flow required to be returned , supplied or exhausted .
Dampers An air damper is a mechanical device used to stop or regulate the flow of air within a duct , chimney , variable-air-volume ( VAV ) box , air-handling unit or other similar equipment . Dampers can also be used to stop airflow into unoccupied or unused rooms where air conditioning is not required . Dampers can further be operated manually or by means of electrical control .
Fire / smoke dampers A fire / smoke damper is a device installed in ducts and air transfer channels intended to interrupt the passage of flame or smoke , and therefore maintain the integrity of any fire rated break or separation sections of a facility . Fire dampers are different from regular air flow dampers as they are equipped with a “ fusible link ” ( rated for a particular temperature ) that holds the unit ’ s blades open until the rated temperature is reached . Upon the melting point , the blades then shut closed and stop any flame or smoke from moving into adjoining spaces . Fire dampers are generally installed in or near the wall or floor , at the point of duct penetration into a space or zone to retain integrity and fire rating of a wall or floor .
Attenuators and noise Noise criteria ( NC ) values are established in the HVAC sector for evaluating the acceptability of various sound levels . NC values for different types of buildings form part of a particular range measured in decibels . A decibel is a unit of comparative sound measurement . A whispered conversation , for example , has a sound level of 30 decibels . This is similar to the target range of most fans . However , fans can contribute upwards of 80 decibels onto a duct system . For comparison , the banging of a hammer equals approximately 130 decibels .
Various documents exist for designers and installers to understand the impact of noise on air dispersion systems . The major source of noise in a HVAC systems is due to air velocity as well as the noises originating from any fans or components that can generate vibrations . Sound attenuators , also known as silencers , sound traps , or mufflers , are generally standalone components fitted to duct sections as a noise control treatment that are designed to reduce the transmission of noises through the ductwork system . Attenuators can
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RACA Journal I October 2022 www . refrigerationandaircon . co . za