## 2 Methods
### Data Acquisition
Figure 3: Layout of the residential building. Prandtl number \(Pr\) = 0.715 u-c\({}_{\rm p}\)/k, thermal conductivity \(k\) = 0.0243 W/m\(\cdot\)K, dynamic viscosity \(\mu\) = 1.720 \(\times\) 10\({}^{-5}\) N\(\cdot\)s/m\({}^{2}\), specific heat \(c_{p}\)=1005 J/kg\(\cdot\)K, and density \(\rho\) = 1.293 kg/m\({}^{3}\). For the vertical walls of this house, the characteristic length was 3.0 m, which was the height of the room. Thus, the Grashof number \(Gr\) was  
\[Gr=\frac{\rho^{2}L^{3}}{\mu^{2}}g\beta(T-T_{\infty})=1.07\times 10^{10} \tag{1}\]  
\[\text{Rayleigh number }Ra\text{ is }Ra\ =\ Gr\times Pr=7.63\times 10^{9}\textgreater 10^{9} \tag{2}\]  
From Equation (2), the \(Ra\) is greater than 10\({}^{9}\); therefore, the flow of the air inside the room was turbulent. The average Nusselt number \(Nu_{avg}\) was  
\[Nu_{avg}=0.677(0.952+Pr)^{-\frac{1}{2}}Pr^{\frac{1}{2}}Gr_{L}^{\frac{1}{2}}=148.9 \tag{3}\]  
The average heat transfer coefficient \(h_{\text{avg}}\) was  
\[h_{avg}=\frac{Nu_{avg}k}{L}=1.21\text{ W/m${}^{2}$\cdot$K} \tag{4}\]  
The calculated convective heat transfer coefficient was 1.21 W/m\({}^{2}\cdot\)K, which was in the range of data reported by [PERSON] and [PERSON] [25]. Based on the building layout and dimensions in Figure 3, a 2D model was created in ANSYS software to analyze the heat flux through the building. The model is shown in Figure 4a. Because of the thin glass panel in the windows, a mesh size of 0.006 m was used, and the ANSYS 2D plane thermal element type 55 was used for meshing the walls, windows, and doors. The calculated convective heat transfer coefficient of 1.21 W/m\({}^{2}\cdot\)K was applied to the wall, window, and door surfaces. The mesh of the internal partition wall with different material layers are shown in Figure 4b, for which there was one layer of mortar plasters on each side of the clay brick internal wall. The external surface of the front wall had a layer of ceramic tiles. To analyze heat transfer by convection and minimize heat loss via the convection mode, the relationships between the external convective heat transfer coefficient and wind velocity were studied. [PERSON] and [PERSON] [26] measured the convective heat transfer coefficient for building envelopes, which is influenced by wind speed. [PERSON] et al. [27] reviewed prediction models of external convective heat transfer coefficients in building energy simulation programs and pointed out that different models can result in 30% deviations in the yearly energy demand. It is recommended by [PERSON] and [PERSON] [28] that the model should be used for one-story buildings; hence, it was adopted in this paper. External convective heat transfer coefficient \(h_{c,\text{ext}}\) for total wind velocity at 0.5 m away from the wall is shown in Equations (5) and (6) [28]. \[h_{c,ext}=2.08\text{V}+2.97\text{ }(\text{Windward}) \tag{5}\]  
\[h_{c,ext}=1.57\text{V}+2.64\text{ }(\text{Leeward}) \tag{6}\]  
Figure 4: (**a**) Finite element model of the building (plan view) and (**b**) finite element mesh of the internal partition wall. In order to analyze the effect of wind on the heat transfer coefficient and understand the effect of the building layout on the wind velocities, a numerical model was created using ANSYS CFX software to obtain wind velocities near the buildings. Fine meshes were used in the modelling; an element size of 0.2 m was used for meshing the surfaces of the building. To simulate the mean flow characteristics for turbulent flow conditions, the most common k-\(\varepsilon\) model was used as it is suitable for a wide range of simulations. A no-slip wall boundary condition was applied to all surfaces, and the standard wall function in ANSYS CFX was used with zero roughness height, as used by [PERSON] and [PERSON] [29]. The model and a part of the numerical mesh are shown in Figure 5a,b, respectively. When the north and west winds were simulated separately, a typical wind velocity of 10 m/s was applied to the model to show the variations of wind velocities near the building envelopes.