# Thermal and Acoustic Design of a Shelter for High-Voltage Electrical Equipment
## 4 Thermal Aspects
### Validation of the Model  
#### 4.3.1 Experimental Setup  
The described full-scale model was reduced in dimensions and the materials were conveniently changed to experiment outdoors, in the presence of sun and with a heat source in the shelter. This model was replicated in COMSOL Multiphysics(r) to verify if the physics, boundary conditions and mesh were chosen adequately to describe the heat  
Figure 4: Plots of temperature (**left**), and velocity (**right**) of the full-scale model. Figure 3: A meshed portion of the model, boundary layers in blue. transfer phenomenon. The shelter used for the validation is a 1 m\({}^{3}\) cube made of 20 mm thick polystyrene panels. The aesthetic panels were built using 12 mm thick cardboard sheets. In such a way, this mock-up can be considered very similar to a 1:8 scale model of the full-scale geometry. This scaling affects the dimensions and positions of the inlets, outlet and aesthetic panels, as outlined in Figure 5.  
1. Inlets: the position was scaled down to (25.6 cm, 30.6 cm) and (78 cm, 30.6 cm) and their dimensions to 6.25 cm \(\times\) 48.08 cm. 2. Outlet: its centre was placed at (50 cm, 76.92) cm from the bottom left corner. Additionally, its dimensions were scaled down to 87.5 cm \(\times\) 10.38 cm. 3. Aesthetic Panels: each aesthetic panel was downscaled to 112.5 m \(\times\) 92.31 m.  
The assembled mock-up of the shelter is shown in Figure 6. As the principal objective of the project is to ensure that the temperature inside the shelter does not exceed a certain limit, temperature was measured inside and outside the downscaled model. Since it is impractical to obtain an accurate average temperature of the air inside the shelter, only the temperature at a centre point inside the shelter was measured. To compare the rise in temperature inside the shelter, the ambient temperature needs to be measured and monitored throughout the experiment. For this purpose, another temperature datalogger was placed outside the scaled model of the shelter, in between the shelter and the aesthetic panel. Figure 5: Downscaled model used for experimental validation. Figure 6: Picture of the experimental setup. An 8 cm gap is maintained between the main volume and the external panels. The power of the heat source should be, in proportion, downscaled to 8.68 W. The actual heat source is a disc obtained from the hot plate of a 3D printer, programmed to generate a heat power of 44 W and placed on two plastic beams to raise it from the floor. A heat power higher than 8.68 W was chosen for the experiment to obtain a rise in temperature higher than the margin of uncertainty of the dataloggers. The experiment was also replicated in COMSOL Multiphysics(r) to compare the simulation to the real case. Note that no box on top of the shelter is considered in this experimental validation. The scale model used for the validation was simulated in COMSOL Multiphysics(r) with the same setting as the full-scale model. The properties of the materials used in the scale model are given in Table 1. The physics and the corresponding boundary conditions used are the same as the ones used in the full-scale model and will be recalled hereafter. The physics used for heat transfer is 'Heat Transfer in Solids and Fluids' (ht), in which the ambient temperature assigned is 29.5 \({}^{\circ}\)C, obtained from the measurements of the external air temperature during the experiments performed outdoors. A wide and thin platform is constructed below the shelter to simulate the exchange of heat with the ground. The ground was assigned to the same temperature as the ambient temperature. Shelter walls and aesthetic panels are assigned as 'Thin Layers' with non-layered shells and a thermally thin approximation. The physics used for heat radiation is 'Surface-to-Surface Radiation' (rad) in which the irradiating surfaces chosen are all the ones receiving direct sun radiation.