Building surface cool materials are novel materials that can reduce urban heat island intensity and decrease building energy consumption. This study investigated the impact of radiative properties of materials, façade orientation, and morphological parameters on energy consumption in six typical residential neighborhoods in Nanjing, China. The neighborhood energy consumption of 16 application schemes considering the façade orientation factor is compared to determine the best energy-saving scheme. Seasonal and annual energy-saving rates, savings in electricity costs, and the price ceiling for materials per unit area are analyzed. The results show that for low-rise buildings, using cool materials only on the roof can reduce the annual energy consumption by 1%. When cool or super cool materials are also used on the building façade, the annual energy saving rate can be up to 3.4% and 4.3%, respectively. Using cool materials on the south façade of buildings is not recommended due to significant heat loss in winter. Considering savings in electricity costs and the price ceiling for materials per unit area, the price of cool and super cool materials should be less than 3.0 and 3.7 RMB/m², respectively, assuming a lifespan of eight years in Nanjing.

Focusing on the effect of street morphology on the ventilation efficiency, this paper presents 3D computational fluid dynamics (CFD) simulations of airflow and pollutant dispersion within urban-like three-way intersections, four-way intersections and roundabouts. The steady-state Reynolds-averaged Navier-Stokes (RANS) k–ε turbulence model is adopted and eight directions of the approaching wind are considered. The ventilation efficiency is evaluated using the ventilation indices purging flow rate (PFR) and the net escape velocity (NEV). Results show the sensitivity of the ventilation efficiency to the type of intersection, to the wind direction and to the number of branches. Specifically, the ventilation efficiency of the investigated three-way intersections is found to be better than that of the other intersections, especially when the angle between the streets is large, while that of roundabouts is also considerable, even with a similar average wind velocity, among the cases evaluated in this paper. Further, the influence of the wind direction for the three-way and four-way intersections is greater than that on roundabouts. Studies on the ventilation efficiency at urban intersections are not common in the literature and this work may help urban planners to better design such hub nodes of urban traffic, where traffic-related pollutants are not easily dispersed, thus avoiding harm to the health of pedestrians and surrounding residents.

This study quantifies the influence of green spaces on microclimate and PM10 concentration in a typical residential district of Nanjing (China) by employing the CFD-based and microclimate model ENVI-met 4. Five green indices, related to quantity and structure of vegetation, are employed to investigate the impact of different types (grass, shrub and tree) and layouts of a green space located in the center of the residential district under an average Nanjing summer day. Results show that the thermal comfort (expressed by the mean radiant temperature MRT and the predicted mean vote PMV) is slightly enhanced with increasing green quantity, especially trees, even though more trees may increase the wind blocking effect with a consequent slight increase of pollutant concentration. In this regard, a single patch of trees located in the central part of the green space is preferable. The green indices are shown to be useful for studying the relationship between green space morphology, microclimate and air quality in cities.