The Identification of Pressure-Independent Variable Air Terminal with Hydronic Reheat

Z. Zhao and W. Liu (PRC)


: single duct pressure-independent VAV Box, hydronic reheat, open loop identification, closed-loop identification.


This paper presents modeling on single duct, pressure-independent variable air terminal with hydronic reheat. Cascade control strategy is commonly used for them to maintain zone temperature at setpoint value. It consists of temperature control loop and airflow control loop. An open loop identification method is used for the process plant of airflow loop while closed loop one for the temperature loop plant according to the technical conditions. Analysis of these processes verifies the reheat supply water temperatures and zone temperature reference signal are the significant inputs and zone temperature is the output. So multivariable identification method is employed. While the transfer function of airflow loop plant is being estimated, the hysteresis for the box is studied. Wavelet analysis is used to preprocess the acquired experimental data. When temperature loop plant is identified, the closed-loop identifiability is judged first. Box-Jenkins model is normally capable of giving a correct description of the dynamics of the system. A set of candidate model structures is tried out for comparison of their properties. The calculation of residuals between process and model outputs shows their validation. The modeling results for several intelligent buildings have proven their correct, efficient and robust features.

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