## 4 Results and Analysis  
### Annual Electricity Consumption  
A number of simulations were conducted to generate results for each passive cooling techniques under the same building condition. Table 5 summarize annual building electricity consumption of all simulations. The energy-saving potential for passive cooling is not substantial but still provides a considerable amount of energy-saving. The equation to calculate the percentage difference is calculated as in Equation (3) for each timestep (hourly). The reference building consumes 3,162,523 kWh/annum. The electricity consumed per gross floor area is 127.97 kWh/m\({}^{2}\)/annum. Due to the invalidity of the raw building use data, the energy simulation data were validated by comparing them to others finding and the average electricity use data for public residential buildings in Hong Kong [32; 33]. The electricity intensity figure of the simulated baseline prototype building is 13% less electricity than the average of a public rental house (147 kWh/m\({}^{2}\)), which corresponds to the study of [PERSON] et al. [33] that the concord-type layout is more energy efficient than average. This suggested that the modelled prototype building is in line with the general building energy performance in Hong Kong. The analysis results are suitable as indicators for public residential buildings in Hong Kong. \[\%diff=\frac{N-N,ref}{N,ref} \tag{3}\]  
where, _%diff_--percentage difference; \(N\)--the inputted value or result value of the tested parameter; \(N\),_ref_--the baseline value of the tested parameter inputted in or resulted from the baseline simulation model. The most effective passive cooling design is that which has a reduction in infiltration and additional envelope insulation. The reduction in the infiltration rate substantially mitigates the heat gain from the hot outdoor air. When the outdoor air infiltration rate is reduced from 2 ach to 0.6 ach, 237,580 kWh of electricity per annum is saved. If the infiltration rate can be further reduced to 0.3 ach, the annual energy consumption saving can be 9.63% and 304,693 kWh in total. The insulation has a great saving potential by limiting the heat flux penetrating the external wall. By adding a 10-mm mineral wool insulation layer at the inner surface of the external layer, the annual energy consumption is reduced by 2.09% and 65,958 kWh. By increasing the thickness to 50 mm, the energy-saving in annual building energy consumption is only doubled to 4%. An increase in the thickness of the insulation layer is linearly related to energy-saving, which indicates that a critical thickness exists for balancing cost and saving potential. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline  & & \multicolumn{6}{c}{**Total Electricity Use**} & \multicolumn{6}{c}{**Annual Cooling Electricity**} \\ \cline{3-10}
**Variables** & **Inputs** & \multicolumn{1}{c}{**Total (MW)**} & **Difference (MW)** & **Difference (\%)** & **Per Total Building** & **Benchmark** & **Benchmark** & **Proposition in** & **Total (MW)** & **Proposition in** \\  & & & & & & & & & \\  & & & & & & & & & \\  & & & &  
Only a marginal saving of 0.66% is achieved by halving of the window size (WWR from 17.88% to 14.31%). However, improving window properties from clear glass to low-e glazing shows a higher energy-saving potential. Low-e glazing is more effective in blocking the solar heat gain in the conditioned areas than reducing the window size. When glazing is further improved to the low-e Spec Sel type, around 50,000 kWh of energy can be saved annually. Adding solar shading devices is another feasible way to reduce the cooling load. Extending the overhang to 0.5 OPF from 0.3 OPF reduces the annual energy consumption by 0.37%. However, if the overhang is further extended to 1.0 OPF, the annual energy-saving is 1.25%. Vertical shading devices are not as effective as the overhangs. When side fins are added at both sides of the windows to match original overhang with OPF 0.3, the annual saving percentage is only 0.24%.