Stability analysis of reduced order building energy models for optimal energy control

Buildings account for 30% to 40% of the world's energy use and different control techniques together with intelligent building technology are used to improve the energy performance index of buildings. The most significant part in design of an effective energy control strategy for buildings is modelling. It is imperative to develop accurate energy models of the system under study before developing energy control strategies. In this paper, conventional stability checks are carried out on a reduced order building energy model. Single zone building energy model is developed taking into account the hygro-thermal interactions of the building energy systems under study with surroundings. Building energy system under study is modelled as a Linear Time-invariant (LTI) state space system. Subsystems of building energy system like windows, building space, construction elements and HVAC systems are modelled. Root locus plots of the sub-systems' coefficient matrix are developed and visually analyzed for stability checks. Post analysis, it was found that for temperature control of the building energy system model developed, a reset integral control action (PI controller) is necessary to achieve near zero error control. Building space air temperature value had no impact sue to variations in internal and external thermal mass of the building energy system.