Building energy saving by active simplified CFD-based model predictive control and passive earth-sheltering technique

• Main Author: Zhou, Xiaoli
• Other Authors: Li Hua
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: Engineering::Materials
• Online Access: https://hdl.handle.net/10356/84524; http://hdl.handle.net/10220/50107
• Institution: Nanyang Technological University

Due to the increasing energy consumption and environmental impact caused by the building sector, the present research work mainly focuses on the improvement of overall energy efficiency in buildings by both active and passive strategies, for example, the model predictive control (MPC) and earth-sheltering respectively. As an advanced active technique, the MPC requires an accurate internal model to predict the system behavior and computes the control inputs by minimizing the cost function, while Computational Fluid Dynamics (CFD) describes well the internal dynamics of imperfectly mixed fluids. Therefore, it is a promising way to achieve energy saving by integrating CFD into real-time MPC. However, the literature review reveals that no study has been conducted on directly coupling the CFD model with the control system, due to the CFD high nonlinearity and enormous computational cost. In this thesis, a novel strategy is developed, called Simplified CFD based MPC (SCFDbMPC), for the real-time optimization of thermal performance in the indoor environment. A CFD model is simplified firstly to capture the thermal behavior of indoor environment with desirable computational cost. The simplified CFD model is then verified using the commercial CFD code FLUENT, and finally integrated into the MPC algorithm to form SCFDbMPC system via successive linearization technique. Finally, the effects of key parameters are investigated on the control performance of the SCFDbMPC system, including the inlet and outlet locations, multiple outlets, and occupant movement. It is found that the SCFDbMPC system is an efficient workable platform for optimal control and dynamic prediction of thermal distributions in indoor environment, which adapts well to the time-varying set points, various boundary conditions, and occupant movement. Apart from the active design strategy of MPC, the earth-sheltered building, as one of passive cooling techniques, could also be an efficient solution for sustainable development of building, characterized by solar heat reduction, stable soil temperature, and natural thermal insulation. However, few studies have paid attention to its CFD and energy modellings with consideration of the heat stored in soil, as well as to develop the optimal control system adapted with the time-varying temperature of the surrounding soil for the earth-sheltered building. Therefore, the second achievement in this thesis is made through the CFD and CFD-coupled energy modelling as well as full-CFD-coupled MPC design for earth-sheltered buildings. A transient CFD model is proposed firstly to analyze the heat flux transferred from soil to earth-sheltered building. Subsequently, the CFD model is coupled with energy simulation for prediction of the energy demand in earth-sheltered buildings. Furthermore, a predictive model is developed to properly represent the dynamic thermal behavior of the earth-sheltered building. According to the present predictive model and CFD simulation, a novel co-simulation optimal strategy is proposed for the thermal control of earth-sheltered buildings, which adapts well to the time-varying soil temperature. The proposed CFD model is then validated by published works. In addition, the influence of critical parameters is evaluated on the thermal and energy performance of earth-sheltered building, such as the depth, soil thermal property, temperature set point, envelope material, and climatic condition. Finally, the co-simulation optimal strategy is performed for case studies of earth-sheltered buildings, and it is thus concluded that the co-simulation optimal strategy is an efficient platform for the thermal control and energy efficiency of earth-sheltered building.