Biological Systems Engineering


Date of this Version



Applied Engineering in Agriculture Vol. 32(6): 751-757. DOI 10.13031/aea.32.11450


© 2016 American Society of Agricultural and Biological Engineers. Used by permission.


The Affinity Laws for fans (and pumps) provide a way of determining new fan or pump speed given fan or pump performance curve data and a desired operating point (combination of flow rate and pressure) that does not fall on the curve. However, the affinity law calculations require using a point on the curve (hereafter referred to as the “basic point”) to determine the new speed. Most references regarding the Affinity Laws do not give a clear description of the method for determining the “basic point”, and improper selection of this point can affect the results considerably. This article describes the requirements for the “basic point,” and presents an analytical solution to determine the “basic point” and the desired operating speed for the fan or pump to operate at the desired operating point conditions.