The influence of green roof pot designs, openings, and spacing on the heat flow in the growth medium by CFD simulations

• This study explores pot design, openings, and spacing effects on airflow and thermal performance. • Optimal pot opening of 40% enhances airflow, lowering root zone temperature for better cooling. • Smaller pots improve thermal performance, distributing heat more effectively than larger pots. • Wider spacing (25–50 cm) boosts airflow and cooling efficiency while ensuring practical usability. • Pot openings enhance ventilation and plant growth, balancing cooling and solar radiation effects. This study employed computational fluid dynamics (CFD) simulations to investigate the effect of green roof pot opening design on the internal heat flow field of the growing medium, aiming to address the issue of elevated root zone temperature (RZT) that may impact plant growth. To isolate convective heat transfer mechanisms, this study focused exclusively on thermal convection, temporarily excluding the effects of solar radiation and evapotranspiration. The model was validated using experimental data, with an error rate of less than 7.6%, confirming its accuracy. Firstly, for a 25 cm × 25 cm × 20 cm (L × W × H) pot, increasing the opening ratio on the pot walls effectively enhances internal air circulation, thereby lowering RZT. An opening ratio of 40% was found to be optimal; compared to closed pots, it achieved a temperature reduction of approximately 10.7 °C at a depth of 2.5 cm (YZ cross-section), with cooling benefits saturating beyond this point. Secondly, by comparing the convective heat exchange efficiency of a small pot (25 cm × 25 cm × 20 cm) and a large pot (50 cm × 50 cm × 40 cm), the study found that the small pot exhibited higher convective heat exchange efficiency due to its smaller media mass and volume. Lastly, regarding pot spacing, a 12.5 cm gap was found to enhance media ventilation and significantly improve convective cooling through the Venturi effect and vortices, resulting in the strongest airflow at the windward and leeward sides. Compared to no spacing, the temperature difference between spaced and non-spaced configurations reached up to 6 °C on the windward and leeward sides (at 2.5 cm and 22.5 cm depths on the YZ cross-section). In conclusion, optimizing container openings and layout can significantly increase airflow within the medium, thereby providing a suitable RZT for plant growth.