MIMO Robust Control for Heating, Ventilating and Air Conditioning (HVAC) Systems

Potential improvements in heating, ventilating, and air conditioning (HVAC) system performance are investigated through the application of multiple-input, multiple-output (MIMO) robust controllers. This approach differs dramatically from today’s prevalent method of building HVAC controllers using multiple single-input, single-output (SISO) control loops. A simulation model of an experimental HVAC system is used in the design and simulation testing of controllers. While simulation can be insightful, the only way to truly verify the performance provided by different HVAC controller designs is by actually using them to control an HVAC system. Thus, an experimental system for testing advanced HVAC controllers is built. The construction and modeling of this system is the focus of a separate article [2]. While this system is only a portion of an overall HVAC system, it is representative of a typical hot water-to-air heating system. The performance of controllers in regulating the discharge air temperature and flow rate is verified using the experimental system. While simple optimal and SISO robust HVAC controllers have been designed and their performance experimentally verified, this project does so using MIMO robust controllers. The design and testing of these controllers provides valuable insight into potential improvements in performance, as well as constraints, associated with applying this control methodology to HVAC systems. Test results demonstrated that performance gains (reductions in discharge air temperature settle time) in excess of 300% may be achieved. Furthermore, it may be possible for such performance gains to be achieved without significant impact to current HVAC system architecture (interconnection).