This paper presents a practical method for characterizing the static nonlinearity or gain variation in HVAC plants. The proposed method involves calculating the plant gain at different points of its input range and using the gain information to characterize the nonlinearities. Characterization of the static nonlinearity helps identify problems such as equipment oversizing, which can help in commissioning the system. A methodology is presented for cancelling the nonlinearity in software without replacing the device. This approach reduces the occurrence of oscillations caused by poor equipment sizing and provides consistent control performance across the range of the controlled device. Simulation and field results are presented to demonstrate the effectiveness of the proposed method.

Units: SI