Building control systems: Fuzzy rule-based approach to performance assessment

A simple case study (the water temperature control loop of a fan-coil unit) is used to demonstrate a semi-qualitative approach to assessing the performance of building control systems. The reasons for the diversity of opinion are considered, and possible methods of evaluating the performance are discussed. Five performance criteria are defined, including one that can be used as a simple indicator of reliability and maintenance costs. Sets of linguistic rules, that are based on expert opinion, are then used to relate the behaviour of the control system to the opinions of the various interest groups. Results are presented that demonstrate the way in which the tuning of the controller affects the different aspects of its overall performance. The paper provides a simple introduction to the use of fuzzy sets in a building services application and illustrates both the highly subjective nature of the evaluation process and the difficulties of assessing the overall performance of a building control system in a realistic manner. It is concluded that any practical method of evaluation must be capable of incorporating qualitative opinion and resolving conflicting points of view.