1.Introduction
Urban thermal environment is exacerbating due to the influence of climate change in recent years. Thermal environment could be improved by implementing green building design. The Taiwanese green building labeling system is launched in 1999, in which system, the greenery and water retention indices are related to the urban thermal environment. The objective of this study is to quantify the effect of implementing these indices on the alleviation of the urban thermal environment and the improvement of the outdoor thermal comfort. The research results could be provide as a reference for formulating urban heat island mitigation strategies. To this end, computational numerical simulation was adopted to construct the quantitative appraisal models between the green building design and its inducing effect.
2.Methodology
Literature reviews were firstly conducted to identify crucial factors that affects the urban thermal environment as well as outdoor thermal comfort. Furthermore, international green building labeling systems were also collected, the evaluating methods regarding the urban environment were compared. This study adopted computational fluid dynamic (CFD) technique to study the effects on the thermal environment of green building designs such as strategies of water retention, greenery, material of the pavement etc. Concerning the numerous environmental designing factors to be considered with and due to the fact that the process of CFD analysis is time-consuming, the design of experiment method was employed to facilitate the research efficiency by limiting the simulation runs to 27 cases. The ANOVA was adopted to analyze the relative contributions of each design factors and to construct the predicting models of the ambient temperature mitigation and the outdoor thermal comfort improvement.
3.Major findings
(1)This study accomplished the comparisons of the evaluation methods of urban heat island existing in green building labeling systems worldwide.
(2)A field measurement campaign was conducted for validation against the CFD simulation software.
(3)Identification of Taipei’s extreme meteorological data for simulation was performed to study the urban environmental thermal condition on the extremely hot date.
(4)Green building design factors that affected the thermal environment were identified:
i.The influential factors against the diurnal temperature mitigation are the average building height, tree’s canopy coverage ratio, albedo of the pavement material, and the building coverage ratio.
ii.The influential factors against the nocturnal temperature mitigation are the average building height, tree’s canopy coverage ratio, and the building coverage ratio.
iii.The influential factors against the severity of outdoor overheating are the average building height, tree’s canopy coverage ratio, and the greenery coverage ratio.
(5)The predicting models of both urban heat island mitigation potential and the outdoor thermal comfort improving effect were established.
(6)The application of the established models were demonstrated by 12 actual green building cases and the feasibility of the models were confirmed.
4.Recommendations
As the quantitative models for appraising the green building design against the urban thermal environment have been established, it is suggested that to gradually evaluate the urban heat mitigation and thermal comfort improving potentials of every green building labeled cases.