3.2.2. The Thermal Setup

The cabin enclosure is composed of body structure, door, floor and glass, exposed to outdoor climatic conditions with sun and wind directly; the mixed wall thermal boundary was uniformly applied to the shell. According to the local summer weather condition, the ambient temperature of 38 ◦C was set as free steam and external radiation temperature for the whole cabin body, except for the driver's foot space adjacent to the engine cooling water. The appropriate thermal resistance across the wall thickness was imposed according to the wall thickness and material properties. The details are presented in Table 4. Besides, the shell conduction approach was utilized to model conduction in the planar direction of steel body with good thermal conductivity. All solid surfaces were considered stationary walls with No-slip conditions. The convective heat transfer coefficient was calculated based on the empirical formula in Equation (12) [29]. The inlets and outlets of the HVAC system were treated as the wall when the vehicle kept ventilation off.

$$h = 1.163(4 + 12v^{0.5})\tag{12}$$

where *v* is the wind speed relative to the parked vehicle with 0.2 m/s, *h* = 10.89 W/m2K.


3.2.3. The Radiation Setup

The windshield, side window, and rear window were treated optically as semi-transparent walls; all other surfaces were considered opaque. All surfaces participated in radiation heat transfer. The emissivity of interior surfaces was assumed to be 0.95 [30], and 0.88 for the windows [57]. The optical properties of the cabin surfaces are listed in Table 5.

**Table 5.** The optical properties of the surface.

