Fan discharge pressure may be maintained at a constant value over a wide range of flow rates by varying the fan speed using a proportional-integral (PI) control method. Values of the PI coefficients required to implement the control method are related to the pressure and volumetric flow rate characteristics of the fan and of the air distribution system. The PI coefficients and the sampling interval must be carefully selected to avoid system instabilities. A numerical model of a system consisting of an air distribution system, a fan, a fan motor, an inverter, and a PI controller is developed. The numerical model may be used to verify the suitability of the selected PI constants and sampling interval.

KEYWORDS: year 1995, controls, fans, speed, variable speed motors, constant, pressure, air distribution, testing, performance, calculating