KA-2148 -- Research Toward an In-Duct Fan Sound Power Mearing System

Sound measurements on both ducted and non-ducted fans today are made mainly in reverberant rooms. For both types of devices the standard of Air Moving and Conditioning Association (AMCA) (Bulletin 300, 1965), which is based partly on the generic ASHRAE Standard 36-62, is applicable. According to the Standard, ducted devices are to be placed entirely within the room at a minimum distance of 3 ft from any wall and coupling effects between the duct and the room are to be taken into account by correction factors. From an economical point of view and in order to eliminate the coupling problems, it would obviously be desirable to perform the measurements directly in the duct. It is not surprising therefore that in the last 15 years several investigators have devoted their efforts to the in-duct test method. Refs 1 through 13 describe some of the more recent investigations. As a result of mainly British efforts, the British Standards Institution in 1966 submitted a proposal to the International Standards Organization which includes an in-duct method of sound measurement. A number of problems still remain, however, and it is the purpose of our current research to provide additional knowledge for the writing of an improved in-duct standard.