Method and apparatus for controlling variable air volume supply fans in heating, ventilating, and air-conditioning systems

Abstract

A control strategy for supply fans in variable-air-volume heating, ventilating, and air-conditioning systems that reduces the static pressure at part-load conditions. The invention consists of a static pressure sensor, an airflow sensor, a supply fan, a fan modulating device, and a controller coupled to the static pressure sensor and the airflow sensor. The controller includes a calculator that calculates the static pressure setpoint as a function of the airflow rate. The static pressure setpoint is lower when the airflow rate is lower. The controller compares the static pressure setpoint with the static pressure, and it commands the fan modulating device so that the static pressure remains close to the static pressure setpoint. Alternatively, the controller includes a calculator that calculates a loss coefficient as a function of the static pressure and the supply rate. The controller compares the loss coefficient with a loss coefficient setpoint, and it commands the fan modulating device so that the loss coefficient remains close to the loss coefficient setpoint. When the airflow rate is sufficiently high, the alternative embodiment switches to a constant-pressure controller.

Dependencies are inferred from the claim text.