A comfort zone set-based approach for coupled temperature and humidity control in buildings

This paper presents a modeling and control strategy for comfort zone set-based control of temperature and humidity in buildings. We first propose a coupled model for humidity and temperature dynamics based on lumped parameter analysis. The interconnection of rooms/zones is captured through an undirected graph, with rooms represented as capacitances and walls and doors/windows as resistances. Unlike traditional RC-models, however, this model captures both mass and heat transfer between zones as well as the bilinearity in the input mass flow-rate. Key parameters are identified by the model, such as mass (and thermal) conductance between zones as well as mass (and thermal) capacitance and this model structure is then validated using physics-based Computational Fluid Dynamics (CFD) simulations. The control inputs to the system are the mass flow rates into each zone and the control objective is to drive the system state into a comfort zone set (a humidity and temperature region defined on the psychometric chart). The dynamic system is shown to be passive, hence any passive controller is stabilizing and able to drive both temperature and humidity to steady states within the thermal comfort region for given ambient conditions. We then propose a set-based (passive) controller to regulate the system outputs within the comfort region. Simulation results from implementing the controller on the lumped model are then compared with CFD simulations, for a design model of an existing experimental 6-room test bed. The proposed controller design methodology is also shown to be model-independent with results of the CFD simulations verifying this feature.