Impact of shortwave multiple reflections in an urban street canyon on building thermal energy demands

The urban fabric plays a fundamental role in convective and radiative heat exchanges between buildings. The main parameters which influence these heat exchange mechanisms are due to climate conditions such as air temperatures/humidity, wind speed/direction and solar irradiance. These weather data are related on where our cities are located rather than on how they are built. In this work, a building energy simulation tool is exploited to study the impact of multiple shortwave inter-reflections exchanges in an urban environment with the aim of evaluating their influence on the thermal energy demand of a building. These multiple radiative exchanges modify the buildings envelope energy budget influencing space cooling and heating demand. A street canyon model validated in a previous work was used to investigate the effects of the urban radiative trapping. Due to multiple shortwave reflections, the effective solar radiation absorbed by the buildings envelope surfaces is higher than in a street canyon building where only shadowing phenomena due to canyon geometry are considered. A comparison has been performed between these two configurations as a function of several driving parameters such as street canyon aspect ratio, orientation, transparent/opaque surfaces ratio and solar absorption. The goal is to characterize how these parameters influences the inter reflections inside an urban canyon and thus the buildings energy demands. Increases in cooling demand up to 35% and decreases in heating demand up to 7.5% are found