2.1.2. Building and Construction

The simulation is based on a typical office building with 20 floors. The plan of a standard floor is illustrated in Figure 3a. The external window area accounts for 50% of the wall, and the exterior blinds work when the incident solar intensity exceeds 50 W/m2. The external wall is mainly composed of extrusion polystyrene insulation (XPS) and concrete (Figure 3b), and the thermal properties of the structures meet the national building efficiency standard [3]. The internal heat gains and their scheduling are illustrated in Figure 3c.

**Figure 3.** Building information. (**a**) The plan of a standard floor, (**b**) external wall construction (from outside to inside), (**c**) scheduling of internal heat gains in the building (heat gain from occupants: 12 W/m2; heat gain from lighting: 13 W/m2; heat gain from equipment: 20 W/m2).

The insulation and concrete in the external wall are sandwiched by two thin cement mortar layers, and the concrete layer is placed inside (Figure 3b). Thermal mass can be defined as the specific capacity multiplied by the mass of construction. For the 1D structure, the thermal mass per square meter of the external wall can be written as follows:

$$\text{Thermal mass} = \mathcal{C}\_{\text{pi}} \times \rho \times D \tag{9}$$

where *Cpi* is the specific capacity, J/kg·K; <sup>ρ</sup> is the density, kg/m3; and *<sup>D</sup>* is the layer thickness, m.

Given that specific capacity and material density are fixed, the layer thickness is the only function of the thermal mass of the construction. The normal thermal resistance of the external wall remains constant to distinguish the effects of thermal mass on the indoor environment, transmission load, and room sensible cooling load in a perimeter zone. Thus, the thermal mass increases as the thickness of the concrete layer increases, whereas the thickness of the insulation layer decreases. Table 1 shows

that the thermal mass in external walls without concrete layer (lightweight structure) only accounts for 10% of the total in a perimeter zone on one standard floor in the office building, and the percentage increases to 43% as the thickness of the concrete layer extends to 200 mm.


**Table 1.** Concrete thickness of external opaque wall and the thermal mass in a perimeter zone on one standard floor in the office building.
