An environmental control system for a building is shown. The system includes a control device operable affect a static pressure in a conduit, a building device operable to affect a flow rate of a fluid through the conduit, and a controller including a processing circuit configured to perform a volumetric control process to generate a control signal for the drive device. The processing circuit is further configured to receive an operating position signal of the control device. The processing circuit is further configured to determine an estimated static pressure level within the duct using the operating position signal of the control device and update the control signal based on the estimated static pressure level determined using the operating position. The processing circuit is further configured to operate the drive device based on the updated control signal to affect the flow rate of the fluid.