The impact of microclimatic conditions in urban areas on the thermal loads of buildings has been appreciated fairly recently. The modulation of street canyons has led, inter alia, to temperature conditions that depart from the climatic data monitored at meteorological stations, affecting the heating balance of buildings, while the building operation affects the present conditions. The installation of air conditioning units leads to heat emission, which, at a microscale level, strengthens this phenomenon. The present paper outlines a computational approach to the street canyon phenomenon, with the determination of flow and temperature fields which are developed, and discusses their influence on the dynamic thermal balance of the building.