Heating, Ventilation and Air Conditioning Multivariable Control System with Least Energy Dissipation
The highest energy consumption in building sector is caused by building's services such as lighting units and thermal comfort systems. Heated Ventilated Air Conditioning (HVAC) system consumes approximately 50% of the total building energy bill. Many measures have been proposed to achieve energy efficient buildings. Accurate HVAC mathematical models, as well as suitable HVAC control system that leads to optimised energy consumption and improved system performance are part of the engineering efforts to achieve greater efficiency. This study is part of such engineering efforts. It concentrates on employing a ready developed reliable HVAC system mathematical model, namely hybrid distributed-lumped parameter model which handles HVAC as spatially and dimensional dispersed systems for specific HVAC components such as ventilated volume. Other components, such as fan motors, inlet and exit impedances, have physical properties that treated as concentrated lumped mass elements without compromising on the accuracy. Applying an appropriate automatic control strategy to achieve improved HVAC system performance associated with least control energy consumption is one of the major research objectives. This objective has been achieved by adopting and applying a multivariable Least Effort (LE) control technique to regulate a multivariable three inputs-three outputs HVAC system model that employs output feedback, passive compensators and proportional gains, avoiding employment of active integrators. Direct Nyquist Array (DNA), as an alternative multivariable control technique, was employed to compare with the LE performance in terms of system performance and proportional control energy cost. Contrasting the straightforward procedure used to decouple the interaction between the outputs in the LE controller, the identification of decoupling matrix in the DNA controller was based on a trial and error approach, which was very time consuming. After decoupling the plant transfer function matrix, the DNA controller was able to regulate and control the HVAC multivariable system based on using PID loop control, but on the price of consuming higher proportional control energy cost which contravenes with global efforts to minimize energy consumption inside buildings. The ratios of proportional control energy cost between LE and DNA at the time 900 seconds following disturbance unity changes on the system outputs are , and for three different disturbance scenarios. LE controller has shown also better system performance than DNA which at the end makes it superior to the DNA control solution based on the consideration of the simplicity of each controller, the system behaviour under closed loop control and the control energy dissipation.