The effects of orientation and dimensions of outdoor shading devices on thermal comfort

In recent years, climate change and the urban heat island effect have caused extreme heat and thermal discomfort in the city. To adapt to this extreme condition, shading is one of the adaptation strategies. Effective shade can protect people from excessive solar radiation, improve outdoor thermal comfort and encourage people to engage in outdoor activities. Therefore, several countries have developed shading policies including constructing shading devices such as shaded walkways and increasing tree shades. For shading facilities, the orientation and dimensions are key factors affecting thermal comfort beneath them. However, it is rarely discussed in past studies and isn’t particularly specified in the government policies. Therefore, the objective of this research is to understand the relationship between the orientation and dimensions of outdoor shading devices and thermal comfort to provide references for policy-making and design.

This research applies the Ladybug tool to calculate the physical equivalent temperature (PET) under various dimensions and orientations of two basic types of outdoor shading devices, the independent and the attached, during summer days. The effect of the dimensions on thermal comfort is evaluated with the effective aspect ratio.

The results show that the lower the effective aspect ratio, the higher the average PET and the discomfort rate (the percentage of time with PET over 34℃) during summer days. The discomfort rate can be reduced to less than 5% when the effective ratio of shading devices is above 1.8. The orientation of shading devices also affects PET. For independent shading devices, the average PET and discomfort ratio in the N-S orientation is the highest and the E-W orientation is the lowest, while the attached type is the highest in the west and the lowest in the north. In addition, this study finds regression equations for the average PET of shading devices in summer with the effective aspect ratio as a parameter. Moreover, this study organizes the results into a reference table so users can easily understand the PET discomfort rate of shading devices in different dimensions and orientations.

This research provides valuable information for the government to develop shading policies, assist designers to design comfort shading devices, and predicts thermal comfort levels under shading devices in various dimensions and orientation.