Engineering Tools Fan Law Calculations To use the fan law calculator, enter the initial conditions and one of the final conditions. All of the final conditions will then be calculated based on the premise, that given an initial set of conditions, small changes in one parameter affect the fan's performance by the following fan speed relationships:                 Airflowinitial / Airflowfinal                   =   RPMinitial / RPMfinal Static Pressureinitial / Static Pressurefinal   =  (RPMinitial / RPMfinal)2                 Powerinitial / Powerfinal                    =  (RPMinitial / RPMfinal)3

Operating Changes Enter all the initial conditions in the left hand column and the one operating value to change in the final conditions column, then clicking the button to its right. The effects of environmental and mechanical changes entered below can be included by checking the appropriate boxes. Units need not be specified, since all calculations are based on ratios of initial to final conditions. Parameter Initial Conditions Final Conditions Include Environmental Changes Include Mechanical Changes Airflow (CFM, m3/s) Static Pressure (Pascals, PSI, in H2O) Fan Speed (RPM) Power (W, HP) Environmental Changes Air density effects can be viewed by entering the initial conditions above and the initial and final temperatures and/or altitudes. Clicking the Change Environment button will show only the effects of changing temperature and altitude. Temperature °C °F  K Altitude feet meter Mechanical Changes View the effects of small changes to the fan diameter by entering the initial conditions above and the initial and final fan diameters. Clicking the Change Fan Diameter button will show only the effects of changing the fan diameter. Units need not be specified, since all calculations are based on ratios of initial to final conditions. Fan Diameter (in, cm, mm, ft, m)

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