## 5 Conclusions  
This study utilizes simulation software, EnergyPlus, to simulate the annual energy consumption of models with different passive cooling techniques applied to a public rental building in Hong Kong so as to comparatively analyze the impact of these technologies on building energy performance. In general, the most effective passive cooling techniques are the reduction in infiltration rate and addition of insulation. The alternation in building orientation, PCM, and a simple increase in ventilation rate are not effective for Hong Kong residential buildings. Combining the findings in the review of the literature and analyses of both annual energy consumption and the hour-based percentage of saving, the following is a summary of the findings in our analysis of the characteristics of the tested passive cooling techniques:  
1. PCM is not suitable for the Hong Kong climate and residential sectors due to the night-heating effect. 2. In terms of energy-saving, reducing the infiltration rate is highly effective in reducing annual electricity use for cooling purposes. In a small amount of days when the outdoor temperature is lower than indoor temperature, the low infiltration rate reduced effectiveness of free cooling, subsequently increasing cooling energy. Noticeably, over-reducing infiltration rates in residential units is not favorable in Hong Kong. In the cooling period, people may not intentionally open windows for fresh air, because this action is generally considered to be waste of cooling energy. In such cases, acceptable indoor air quality is maintained by infiltration. Further studies could aim to find a balanced infiltration rate of energy-saving and indoor air quality. 3. Insulation is effective in saving annual energy. However, insulation layers can reduce heat loss through external walls during the cool seasons, i.e., spring and autumn. A critical thickness exists. 4. The percentage of energy-saving is not linearly proportional to the thickness of insulation. Doubling the thickness of insulation cannot double the percentage of energy-saving. 5. The improvement of glazing effectively reduces the cooling load during both the day and night throughout the year. Reducing the window to wall ratio is not effective in annual energy-saving. 6. The combination of an overhang and side fin provides the highest saving. When used separately, the vertical shading devices are not as effective and horizontal shading devices under the same value of OPF or SPF. 7. Alternatives in building orientation are not effective for the concord-type public rental house. 8. Tested passive cooling techniques present no bias on different floor boundary conditions in terms of time characteristics, but some achieve higher saving on the ground floor or top floor in regard to saving potential. The study also has some limitations. While the validation of each type of passive cooling design would further improve the accuracy of the data, they could not all be included in this study due to financial, time, and knowledge constraints. Validation for all simulations will be considered in an early stage in further research. A detailed analysis of the time difference, parametric energy reduction model of each technology, and the impact on human comfort is yet to be performed due to time constraints and computer calculation limitations. Moreover, the analysis focused on annual consumption, and the improvement in the thermal performance of the building has not yet been fully tested. The box-and-whisker charts and median values only show the range of distribution and cannot analyze the time profile in detail. In short, more detailed and sophisticated studies including comprehensive affecting factors and full validations are required to show a more comprehensive examination of the characteristics and impact of these passive cooling techniques on the building's energy demand. Conceptualization, C.-R.Y., H.-S.G. and Q.-C.W. ; methodology, C.-R.Y. and Q.-C.W. ; case study, H.-S.G. and R.-D.C.; original draft preparation, H.-S.G., and Q.-C.W.