ASHRAE AB-10-002

Abstract

<strong>INTRODUCTION</strong> <br>Corrugated spiral ducts are increasingly being used in aboveground HVAC systems. The presence of corrugations increases the rigidity and structural strength of the duct, so that lighter gauges can be employed in many applications. Under those circumstances corrugated ducts may be less expensive and easier to install than conventional spiral seam ducts. Furthermore their enhanced resistance to permanent deformation allows them to be stacked higher for transportation and storage. <br>In the present research the roughness characteristics of corrugated galvanized spiral ducts having a somewhat different corrugation profile from that examined by Kulkarni et al. (2009). The objective of this research was to verify whether minor corrugation profile and seam pitch variations have a significant impact on the resulting absolute roughness and roughness category. The test procedure was validated by measuring pressure loss characteristics of a standard conventional spiral seam duct per ASHRAE Standard 120. Those results were then compared to data presented previously in the literature. <br>Pressure loss characteristics of conventional galvanized steel ducts with continuously rolled spiral seams have been described in Griggs et al. (1987). Similarly, roughness factors for galvanized steel spiral seam ducts with varying numbers of ribs have been reported in Griggs et al. (1987). In these instances the data were not obtained by tests conducted in accordance with ASHRAE Standard 120. Until recently there has been a lack of corrugated galvanized spiral round duct information available to the designers of duct systems. However Kulkarni et al. (2009) used ASHRAE Standard 120 to obtain pressure loss data for one particular corrugation configuration.