Transient hygrothermal CFD model of Trombe wall system

In the context of the current worldwide energy situation, the building sector stands as a substantial contributor to worldwide energy consumption and the emission of greenhouse gases. To improve the building’s energy performance and hygrothermal comfort, it is crucial to adopt renewable energy resources and eco-friendly engineering solutions. Among various technologies, Trombe walls, are recognized as a cost-effective solution to reduce energy consumption. However, the performance of this type of system is highly sensitive to external weather conditions and depends on its configuration and management. Drawbacks such as overheating, reverse thermo-circulation, and low thermal resistance occur mainly in severe weather conditions where the temperature differential and the amount of water vapor in the air may be considerably high. Consequently, a careful selection and evaluation of Trombe wall design parameters is required for each climatic zone. Several theoretical and experimental studies have been carried out to investigate the thermal behavior of Trombe walls under various weather conditions and evaluate the impact of its geometrical parameters on its overall thermal efficiency. However, to date, very few developed CFD models take into account the dynamic behavior of such a system, and most of the available models in the literature did not consider the effect of moisture on Trombe walls as the focus is often on the determination of its thermal efficiency. The objective of this study is to develop a transient CFD model representing the dynamic behavior of Trombe walls. The CFD model is based on the geometric specifications of an existing Trombe wall test bench located at FEMTO-ST, which has dimensions of 1.5 meters in width and 1.95 meters in height. Since there is no a priori method for establishing optimal numerical parameters, mesh grid, and time step sensitivity analysis are first performed. Then, several user-defined functions and sources are programmed to take into consideration variable solar radiation as well as the presence of occupants and their activities. Finally, a methodology for investigating the impact of moisture on the hygrothermal comfort and the thermal performance of the Trombe wall is proposed.