Theoretical and physical modelling of the thermal performance of water wall systems

摘要

Water wall is an excellent passive solar strategy which can maintain thermal comfort in buildings while reducing energy consumption. Existing water wall studies are mainly based on simple heat balance models, in which convective heat transfer coefficients are assumed constant and radiation exchange is commonly neglected. Further, the application of the CFD approach to water wall research is very rare. These research gaps are addressed in this study through the development of a comprehensive transient heat balance model and unsteady CFD modelling. udThe thesis covers three major topics. Firstly, the turbulent natural convection with and without radiation transfer in two-dimensional and three-dimensional air-filled differentially heated cavities is numerically investigated using various RANS (Reynolds Averaged Navier-Stokes) turbulence models and the Discrete Ordinates radiation model. It is found that the shear-stress transport k-ω model has the best overall performance in terms of capturing the main features of the flow and predicting the time-averaged quantities. Secondly, a comprehensive conjugate conduction-convection-radiation model for transient analysis of a semi-transparent water wall system is developed. It is found that reducing the transmissivity of the Perspex or glass walls is the most effective, practical and economical way to improve the thermal performance of the semi-transparent water wall system. Finally, the thermal performance of an opaque water wall system is numerically investigated and compared against a conventional concrete wall system for the typical climate conditions in Sydney, Australia. The results indicate that less supplementary energy is required in winter than that in summer to maintain a comfortable interior temperature. Further, the water wall system performs significantly better than the concrete wall system of the same thickness in the winter climate of Sydney, whereas both systems have a similar performance in summer.