## 4 Discussion  
### Research Implications  
This study proposed to optimize the urban layout design in the aim of achieving better outdoor comfort at both block and street levels. Genetic algorithm was used for optimization and two parameters were applied: building form and street width. To assess the performance, this study made use of four factors: MRT, UTCI, average wind speed, and unacceptable wind percentage. Further, the study investigated the characteristics of urban layout under different optimization results. Final optimization indicated that the acceptable comfort percentage of the whole optimization was 87.7%, and the street space optimization could reach 90.6%. Regarding urban morphology indices, at the block level, the predictive indices did not show obvious correlation with comfort ratio. However, at the street level, except for plot ratio, other predictive indices demonstrated high correlation with comfort ratio. Specifically, the percentages of influence of the variation of building heights, SVF, building enclosure, and density were 47%, 30%, 18%, and 5%, respectively. Therein, SVF and variation of building heights were negatively correlated with comfort ratio, and density and building enclosure were positively correlated with comfort ratio.  
The main results of this study were as follows: (1) The layout of high-rise buildings had an important influence on the micro-climate performance of the whole block and the microclimate performance of the street space for small and medium-sized blocks in cold cities; (2) while at block level and street level, their optimal layout tended to choose the smallest possible street width. A certain number of high-rise blocks were in the windward direction, and the remaining high-rise buildings were arranged in the shadow area. The difference was that the whole block optimization included the interior of the small block, so we avoided placing it in the northeast corner, which was vulnerable to the lateral wind and instead placed it in the middle of the north side. There was no such problem in street space optimization, so high-rise blocks were usually placed in the northwest corner of the wind to protect the rear blocks; (3) the results a of high-rise building suggest that the higher the upwind density, the greater the maximum wind speed ratio and the larger the uncomfortable range of the  
Figure 20: Correlation results of unacceptable wind percentage, avg. wind speed, and acceptable UTCI percentage at street level.  
block. When the distribution location of the high-rise blocks was the same, the buildings tended to face the wind direction with their long sides, blocking the invading airflow to the maximum extent; (4) as for open space, it is inappropriate to arrange large area open spaces in cold-area cities. If necessary, open spaces should be placed in the middle of blocks surrounded by buildings, and the upwind location should avoid high-rise buildings to prevent high-rise-accelerated airflow from affecting the square's wind environment.  
Not only can this study support urban layout design, especially providing strategies for cold-region cities, it can also provide significant insights to support sustainable development for cities where microclimate and sustainability highly correspond. Further, this study can help analyze the urban block energy use since the microclimate in block area can influence the heat gains from outside for buildings. By optimizing urban layout design, it can further benefit the urban block energy study, as well as benefit sustainability of a city.