## 5 Conclusions  
The relationship between urban features and microclimate is a hot topic in urban studies, since it has an enormous effect on the thermal comfort of urban blocks. This study investigates the method of solar radiation reduction that may be achieved by determining the favorable design factors of the urban block, Qilou street, and the non-linear regression model that was established.  
Sunshine-hours is a dominant indicator of the solar radiation on the received area. So, it is also an important meteorological parameter for architectural design, urban planning, and landscape layout. Based on the analysis of the sunshine hours in the street by conducting computational simulation, it is found that the sunshine hours and the street orientation have a significant influence on the height-to-width ratio. By fitting the power function of height-to-width ratio, sunshine hours and street orientation angle, the relationship between the three parameters was determined. Consequently, an exponential model which determines the height-to-width ratio of Qilou street was developed. Through the analysis of the sunshine simulation of Qilou streets in Nanning, the optimal height-to-width ratio of the street can be determined from the required sunshine hours and the street orientation. The analysis revealed that when the street orientation angle was less than 30\({}^{\circ}\), the effect of the height-to-width ratio on the sunshine hours decreased rapidly. At this moment, the street required a larger height-to-width ratio to reduce the sunshine hours to create an ideal thermal environment. However, this imposed a relatively strong sense of expression in people. When the street orientation angle exceeded 60\({}^{\circ}\), the effect of the height-to-width ratio on the sunshine hours increased sharply. Therefore, combined with the application requirements of Qilou commercial streets, the streets were classified into three categories: east-west, north-south, and northeast-southwest streets, based on their orientations. The design schemes were investigated based on the effect of the sunshine hours and street orientation angle on the height-to-width ratio. The results showed that:  
1. The north-south street is suitable for forming a large shadow area by using the high height-to-width ratio. When the ratio is 0.95-1.13, the street sunshine hours decrease to less than 4 h, thereby affording a more comfortable thermal environment.
2. The adoption of recessed spaces is suitable on the east-west street to create a cool resting space in summer. The recessed spaces should be reasonably designed by using Equation (7).
3. The northeast-southwest-oriented streets should organically combine height-to-width ratio and \" recessed area\" design methods to create a comfortable Qilou street environment based on actual urban morphology.  
The model for predicting the relationship among the height-to-width ratio, sunshine hours, and street orientation established in this study can serve as a basis for the thermal environment design of traditional commercial streets in hot and humid areas.  
Conceptualization, X.H.; methodology, X.H.; investigation, X.H., C.L. and Z.Z.; writing, X.H., C.L. and Z.Z.; visualization, X.H., C.L. and Z.Z.; supervision, X.H.; project administration, X.H.; funding acquisition, X.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by National Natural Science Foundation of China, grant number 51568003.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflict of interest.