Pressure loss testing of saddle tap tees and a fabric air duct

Pressure loss tests were conducted on diverging and converging flow saddle tap tees per ASHRAE Standard 120 (2008). A power law curve-fit was used for diverging flow tees to correlate branch loss coefficients as a function of branch-to-common flow rate and area ratios. Likewise a logarithmic curve-fit model was used to correlate branch loss coefficients for converging flow tees as a function of branch-to-common flow rate ratio. The argument of the logarithmic function was corrected to account for the area ratio of the fitting. For both diverging and converging flows, main loss coefficients were correlated in terms of an inverse linear relationship with the straight-to-common flow rate ratio. Main loss coefficient data were largely independent of branch-to-common area ratio. The resulting coefficient of determination values ranged from 0.543 to 0.927, indicating a suitable degree of correlation.;Friction factors for a round non-porous fabric duct were measured per ASHRAE Standard 120 (2008). Two configurations were tested. In one instance an internal frame to maintain a round cross section when no air was flowing through the system was absent. For other tests a tubular steel frame was inserted through the entire length of the duct so as to maintain the duct shape in the absence of air flow. It is recommended that round fabric ducts lacking an internal support frame be categorized as “MEDIUM ROUGH" in the Duct Design chapter of the ASHRAE Handbook of Fundamentals. It is further recommended that round fabric ducts possessing a tubular steel internal support frame be categorized as "ROUGH" in the Handbook.