This study presents a computational fluid dynamics (CFD) simulation of an earth tube heat exchanger (ETHX) integrated into a building heating, ventilation, and air-conditioning system. The objective is to investigate the impact of varying materials and airflow rates on the performance of the ETHX. The ETHX is a passive cooling and heating technology that utilizes the stable ground temperature to pre-condition the air entering the building. A three-dimensional (3D) model of the building and the ETHX system is developed using CAD software. The geometry includes the earth tubes, heat exchangers, and other relevant components. A fine mesh is generated to accurately capture the flow features and thermal gradients within the system. The fluid properties of the airflow through the ETHX and the surrounding soil are defined, considering factors such as density, specific heat capacity, and thermal conductivity. Boundary conditions are applied to simulate real-world scenarios, including inlet and outlet conditions for airflow, as well as wall conditions for the earth tubes. A suitable CFD solver is selected, and the simulation parameters are set up, including turbulence models, discretization schemes, and convergence criteria. The simulations are executed, and the results are analysed to assess the performance of the ETHX under different conditions. The fluid thermal variations are monitored and controlled by Internet of things. This study contributes to understanding the design and optimization of earth tube heat exchangers in building HVAC systems.