AL-2506 (RP 139) -- The Effects of System Connections on Fan Performance

In recent years there has been increased emphasis placed upon the rating, cataloging, and testing of fans and systems to assure their proper operation and to minimize the consumption of energy. As a result, safety factors in system design have been reduced so that there is very little allowance for error either in the calculated system resistance or the fan performance. It is, therefore, essential that those items which can affect fan performance and the magnitude of that effect become an important part of our general knowledge.

It has been known for many years that a fan tested in the laboratory may not perform the same once it is installed in the field. Several articles have been written which describe these phenomena. This project was initiated to address the problem, in much greater detail, of variations between laboratory fan ratings and the actual performance obtained under field conditions. Field installation conditions, including the specific location and design of ductwork components, can affect a fans performance. These elements influence not only the flow rate and fan static pressure, but also the fan brake horsepower. A-laboratory test program was initiated between ASHRAE and the Air Movement and Control Association (AMCA) utilizing the facilities of the AMCA testing laboratory and staff. A test schedule was prepared and the program was divided into phases, in order to focus on the various testing parameters, as outlined in the Scope. Emphasis was placed on achieving realistic goals. This report describes the results of Phase I. Phase I represents the results of over 400 individual tests on two fan types of identical size operated at selected fan speeds with various inlet and/or outlet duct configurations. This report provides basic information and develops a basis for future projects in this field. There remains a need to develop accurate installed fan rating information for designers. The concept of system effect and system effect factors is offered as a viable approach to resolving this problem. System effect is defined as the change in performance of a fan due to various flow conditions at the fan inlet or outlet. System effect factors are intended to be used in conjunction wi th th e system resistance characteristics in the selection of fans, and also applied in the calculations of the results of field tests. This concept helps to correlate results offield tests and laboratory fan rating tests.

Citation: ASHRAE Transactions, Volume 84, Part 2, Albuquerque, NM



Product Code(s): D-AL-2506