Pressure Setpoint Control of Adjustable Speed Fans

Abstract

In a variable air volume (VAV) ventilation system equipped with an adjustable-speed supply fan, the fan speed typically is controlled based on the pressure measured at some location in the duct. The pressure setpoint can be fixed at a value chosen to meet maximum flow requirements, or, for greater energy efficiency, can be continuously minimized to provide for only the current flow rate. This paper describes one such pressure reset strategy, presenting energy consumption and pressure setpoint data measured in a pair of mixed-use university buildings. Fan power is modeled as a function of duct pressure, flow, and air temperature, and the model is fit to measured data. The results are used to estimate savings due to the pressure reset scheme. Savings estimates also are derived directly from measured performance of several fans under both pressure reset and fixed pressure mode control.