CFD analysis of temperature-driven flow for passive HVAC applications in Irish homes

Buoyancy-driven ventilation is a sustainable alternative to conventional HVAC systems, leveraging temperature differences to induce airflow. This study analyzes buoyancy-driven flow using Computational Fluid Dynamics (CFD) in ANSYS Fluent to evaluate its feasibility for natural ventilation. The simulation models a contracting pipe with internal heating fins, made of copper, which gets heated by sunlight up to 60°C, inducing airflow through natural convection. A pressure inlet at 0 gauge pressure and a pressure outlet at -20 Pa were applied. The steady-time simulation used the realizable k-ε turbulence model with buoyancy effects enabled and the energy equation enabled. Results show flow from the inlet to the outlet domain, which was confirmed by evaluating volumetric flow rate at the outlet and observing velocity streamlines, confirming that the design effectively enhances natural ventilation. A grid independence study was conducted by evaluating the Grashof number (Gr) on one of the heated walls. Grid independence was achieved with 693635 elements with a Grashof number value of 3*e 10 . A parametric study was conducted for varying wall temperatures (30°C, 40°C, 50°C, and 60°C), and the Volumetric flow rate at the outlet was monitored. Results indicate a linear trend between temperature and volumetric flow at the outlet, proving that more air can be expelled with higher blade temperatures.