Abstract

Good HVAC control schemes in buildings help reduce energy use and maintain occupant comfort. During the last 10 years, VAV-HVAC systems are widely used in commercial buildings because they can reduce energy use significantly and provide good temperature control of the conditioned spaces compared to CV-HVAC systems. However, the controls for VAV systems are somewhat difficult and further research in this area still needs to be carried out. This research will focus on local control loop interactions and operating strategies for VAV control systems. To reach this objective, experiments were conducted in a two-zone VAV test facility. The facility consists of six control loops (cooling valve, fan speed, two dampers, two electric heaters) activated by DDC PI controllers. Experiments were conducted in this facility and the results were processed, and analyzed in this thesis. The steady state and dynamic characteristics of a VAV-HVAC control system has been studied. The interaction between control loops of a VAV system operating under (i) open-loop, (ii) closed-loop control modes were evaluated. Also six local loops were tuned and optimal range of controller gains for single-loop and multi-loop VAV system operation were determined. Experiments were conducted to compare the operating performance of Pressure Independent Control (PIC) and Pressure Dependent Control (PDC) strategies. The results show that PIC strategy is more stable than PDC. However, a finely tuned PDC strategy gives good room temperature control compared to PIC. The results of this research will help building engineers identify operating problems and interactions between local loops in VAV systems. In addition, the optimal range of controller gains obtained in this research can offer guidelines in PID controller tuning. Moreover, the tests conducted provide experimental data to building engineers and researchers for model development and control design