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Decentralized and partially decentralized control of a multizone variable air volume (VAV) system is studied. The VAV system consists of two environmental zones and an air distribution system. By assuming that the temperature of supply air is perfectly controlled and therefore remains constant, an eighth-order nonlinear model of the VAV system is developed. The control problem is to regulate the zone temperatures and air flow rates in response to step changes in cooling loads acting on the system. Decentralized controllers are designed by minimizing a quadratic performance index subject to constraints on the input energy and the eigenvalues of the slow and fast modes of the linearized model to preserve the two time scale property of the system. The designed controllers are implemented on the nonlinear system. The resulting closed-loop system responses show that good regulation of the zone temperatures can be achieved while maintaining sufficient air flow rates in the system with the designed decentralized controllers.