Inlet Installation Effects on Different Types of Fans and Ductwork Designs

C2 - Performance Measurements

It is known that installing a ductwork fitting at the inlet of a fan can have a significant effect on the performance curve of the fan. Conversely, when the fitting is connected to the fan outlet the performance curve is not significantly modified but the pressure loss of the fitting itself may considerably increase due to the strong non-homogeneity of the flow velocity at the fitting entrance.

This paper presents an analysis of test results obtained by NEL and AMCA with the financial support of FETA and ASHRAE respectively in order to quantify the fan system effect due to various duct singularities or obstructions (bends of different shapes, duct contractions, bearings, plenum with lateral opening, wall close to the fan, …) at the inlet of axial or centrifugal fans of different types. Unlike the methodology described in AMCA Publication 201 the system effect is assessed here by calculating the drop in flow rate due to the presence of the inlet appurtenance on a system resistance curve. The pressure loss of the fitting itself is subtracted from the total fitting performance penalty in order to assess the actual system effect. An average of the relative flow drop on several system curves is then calculated, which quantifies the system effect of each inlet obstruction for a given fan.

The amount of system effect strongly depends on the fitting shape and type of fan with a relative flow reduction which may exceed 20 % in some extreme cases and is totally insignificant in other cases.
This approach has been extended to quantify the system effect on fan power and sound power levels due to inlet fittings. A few test data are presented to illustrate the analysis in this case.