Outdoor thermal comfort is associated with the usage pattern of urban open spaces. Thermally uncomfortable outdoor environments could discourage participation in outdoor activities and increase buildings' cooling energy consumption. This article evaluated the effects of various urban design strategies on summertime outdoor thermal conditions, focusing on applications of high-albedo pavement and vegetation. Field measurement was carried out in two high-rise residential quarters in Shanghai. The result of the measurement was used to interpret the numerical simulation. Numerical simulation using ENVI-met was then applied to examine a series of urban design strategies, using the physiological equivalent temperature (PET) as the thermal comfort index. The result shows that an increase of 0.4 in the ground surface albedo overall reduces the thermal comfort, as indicated by an increase of 5–7°C in PET during the day with a marginal decrease of less than 1°C at night. Increasing greenery cover, especially tree cover, improves thermal comfort during the whole period under evaluation. A reduction of up to 15°C in daytime PET is achieved by adding a dense tree cover (LAI = 6.4) over a grass lawn and up to 20°C by adding the tree cover over the hard pavement with an albedo of 0.2.

In order to reduce the contribution of the building sector to global greenhouse gas emissions and climate change, it is important to improve the building performance through retrofits from the perspective of carbon emission reductions. Data-driven methods are now widely used in building retrofit research. To better apply data-driven techniques in low-carbon building retrofits, a better understanding is needed of the connections and interactions in optimization objectives and parameters, as well as optimization methods and tools. This paper provides a bibliometric analysis of selected 45 studies, summarizes current research hotspots in the field, discusses gaps to be filled, and proposes potential directions for future work. The results show that (1) the building-performance optimization (BPO) process established through physical simulation methods combines the site, retrofit variables, and carbon-related objectives, and the generated datasets are either directly processed using multi-objective optimization (MOO) algorithms or trained as a surrogate model and iteratively optimized using MOO methods. When a sufficient amount of data is available, data-driven methods can be used to develop mathematical models and use MOO methods for performance optimization from the perspective of building carbon emission reductions. (2) The benefits of retrofits are maximized by holistically taking environmental, economic, and social factors into account; from the perspectives of carbon emissions, costs, thermal comfort, and more, widely adopted strategies include improving the thermal performance of building envelopes, regulating HVAC systems, and utilizing renewable energy. (3) The optimization process based on data-driven methods, such as optimization algorithms and machine learning, apply mathematical models and methods for automatic iterative calculations and screen out the optimal solutions with computer assistance with high efficiency while ensuring accuracy. (4) Only 2.2% and 6.7% of the literature focus on the impacts of human behavior and climate change on building retrofits, respectively. In the future, it is necessary to give further consideration to user behaviors and long-term climate change in the retrofit process, in addition to improving the accuracy of optimization models and exploring the generalization and migration capabilities of surrogate models.

Open residential neighbourhood (ORN) and vertical greening system (VGS) are two emerging urban design strategies in Southern Chinese cities. This paper numerically analysed the potential in thermal comfort improvement of these strategies. The strength and limitations of the ENVI-met model is understood through a validation against field-measured data. Then we conducted parameterized numerical simulation on the combined impacts of four types of building layout and six types of vertical greening on outdoor microclimate in a traditional urban block under renovation in Shanghai. Results indicate that the semi-enclosed layout with small building height difference and the enclosed layout are relatively beneficial; For different combinations of layout and greenery, the south-oriented vertical greening scenario yields the best thermal benefit per unit installed area, followed by the east-orientated scenario; overall, south-facing green facade allocated in semi-enclosed building layout with small height difference and enclosed building layout are recommended for optimizing pedestrian thermal comfort.

Elevated walkways can bring pedestrian-friendly urban space back to high-density urban centers that are planned largely for vehicle traffic—for instance, the Lujiazui CBD in Shanghai. Most studies on elevated walkways have focused on transportation planning, structural safety as well as urban form and design. Few have paid attention to thermal conditions and pedestrian comfort issues on elevated levels. Considering all of the environmental factors that influence human thermal comfort, one could claim that there will be more breezes on elevated levels compared to sidewalks at the ground levels, but they can be exposed to increased solar radiation and thus higher radiant temperatures, if not properly shaded. The overall effect of the change in elevation on human thermal comfort is thus unknown. This study attempts to investigate the microclimate and human thermal comfort of a recently completed Lujiazui Elevated Walkway (LEW) system in the Lujiazui CBD, Shanghai, under a hot-humid sub-tropical climate. Micrometeorological measurements and a guided questionnaire survey were carried out on peak summer days. The data analysis indicates that the LEW is thermally more uncomfortable than its ground level counterpart. Air temperature was higher, whereas wind velocity is lower on the skywalk level than on the ground level, which is counter-intuitive. The resultant physiological equivalent temperature (PET) indicates warm conditions on the ground level (with good shading) while there are hot conditions on the skywalk. Based on the empirical findings, design strategies are proposed to improve the thermal comfort conditions on the LEW, and to better support pedestrian activities in this typical high-rise high-density urban area.