Model Predictive Control of thermal comfort as a benchmark for controller performance Ion Hazyuk a* , Christian Ghiaus b , David Penhouet c a INSA-Toulouse, Université de Toulouse, Institut Clément Ader, Toulouse, France b INSA-Lyon, CETHIL, UMR5008, F-69621, Villeurbanne, France c CSTB (Centre Scientifique et Technique du Bâtiment), 84 avenue Jean Jaurès, 77421 Marne-la-Vallée, France Abstract Assessing controller performance in normal operation needs reproducible conditions and comparison with the best possible result. Tests in emulation are reproducible. Model Predictive Control (MPC) gives the best possible performance when the future inputs and the model of the process are known. When the benchmark is used for building energy management, the cost function of MPC becomes a linear programming problem with constraints given by the comfort. In emulation, the model of the building used in MPC may be obtained by gray-box parameter identification, using signals which excite all the modes of the complete model. The proposed benchmark was used to test a PID and a scheduled start PID-based energy management system. During the test periods, MPC benchmark always outperformed the PID controllers. It reduced the occupants discomfort by up to 97%, the energy consumption by up to 18%, and the number of on-off cycles of heat pump by up to 78%. Keywords: thermal control; nonlinear Model Predictive Control (NMPC); energy efficiency; intermittently occupied buildings; optimal heating restart time; multi-source multi- consumer system. 1 Introduction Building thermal behavior is characterized by, generally, great inertia and it is strongly influenced by the weather and occupation type. Most often, the occupation is intermittent, which implies variable indoor temperature set-point. Since space heating is responsible for over 50% of the total energy consumption in residential and tertiary sectors [1], thermal control has an important impact on energy consumption. Nevertheless, energy savings must not affect the comfort during the occupied periods because the cost of people discomfort is much higher than the operational cost of the building [2]. Several surveys on the current building thermal control strategies have shown that these are, generally, room thermostats or thermostatic valves on radiators [3-5]. In the best case, radiator valves are driven by PID controllers to cope with room overheating. Although these controllers are omnipresent in the field, they are not specifically designed or adjusted to minimize the energy consumption. Furthermore, their feedback loop introduces a lag between the indoor temperature and the set-point, which affects negatively the comfort. * Corresponding author: mechanical department, 135 avenue de Rangueil, F-31077 Toulouse, France. Tel.: +33 (0) 5 67 04 88 23. E-mail address: ion.hazyuk@insa-toulouse.fr (I. Hazyuk)