A coordinated VAV control with integration of heat transfer coefficients for improving energy efficiency and thermal comfort

Abstract

The indoor temperature in traditional Variable Air Volume (VAV) systems is controlled synchronously by increasing or decreasing the damper of the valve based on the return air temperature. However, the thermal comfort cannot be guaranteed since the load inside may not be evenly distributed, energy is wasted due to continuing cool down space even though no occupants inside. Thus, this paper introduced a coordinated control strategy aiming to improve energy efficiency and thermal comfort of large-scale rooms. A case study was presented on a summer day to show the benefits of the proposed method. The selected chamber is divided into two subzones with each controlled by a separated VAV box. Typically, each zone can be controlled independently by regulating its corresponding VAV box to track the temperature set point. Since occupants may move randomly, the worst scenario is that one subzone was fully packed. In this case, the corresponding representative temperature cannot be cooled down to its set point, and an extra airflow rate may be needed using its neighbor VAV box to cool down the air inside. To achieve this function, the thermal coupling effect between zones is considered with the Heat Transfer Coefficient (HTC) integrated into the control platform established in TRNSYS. The simulation results show the proposed control can deal with the dynamic variation of load distributions inside. The introduction of heat exchange between adjacent zones can improve the accuracy of the temperature controls. The energy consumption of the variable speed supply fans was compared with conventional control, approximately 10% of energy saving was achieved.