Enclosure with Underground Passive Cooling System for High Power Vehicle Charging Station

This paper presents the approach to designing the electrical casing with a passive cooling system for a high-power charging station. Fast-charging stations of 50 kW need to be installed in various locations in Germany. It is challenging to install such systems in congested areas as this system together with its components and cooling system requires large spaces. Thus, it is proposed to be installed under the ground of parking lots with dispensing units available over the ground. Passive cooling systems play a vital role in maintaining the efficiency. It saves the energy required for a fan or liquid circulation in active cooling. In this case, it is not possible to use natural convection for passive cooling therefore geothermal cooling is considered. The idea is that at a depth of 2 m to 4 m under the ground temperature remains constant at around $20^{\circ} \mathrm{C}$ throughout the year. Thus, the casing is designed to dissipate around 500 W of heat from the electrical components mounted on heatsinks in contact with soil. Soil plays a major role in heat dissipation underground. In general soil thermal conductivity is low therefore large surface area-to-heat ratio is required to dissipate the heat. For design basis, two experiments are performed to know, the behavior of local soil and thermal conductivity. In the former experiment, the temperature of the soil at 2 m depth is recorded, and later the thermal conductivity is evaluated for dry and moist soil resulting in 1.8 to $2.0 \mathrm{~W} / \mathrm{m}^{\circ} \mathrm{C}$. Other parameters such as heat from each component, even heat distribution and weather conditions are also considered. Transient thermal simulation is performed to analyse the design resulting in a temperature of $66^{\circ} \mathrm{C}$ in 16 hours of heat application. Based on simulation results casing is manufactured and tested in real conditions resulting in a maximum temperature of $56^{\circ} \mathrm{C}$ in 16 hours. Thus, it provides a suitable temperature for the working of electrical components.