In urban areas, meteorological conditions such as temperature and humidity are closely associated with “heat island” effects and at a smaller scale with the airflow in street canyons. This airflow is dominated by aerodynamic and thermal influences. The aerodynamic effects, including building geometry and architecture as well as street canyon dimensions, have been extensively studied (e.g., Oke, 1987; Hunter et al., 1992; Louka et al., 2000). The impact of solar radiation on the surrounding building facades and the street surfaces during the day is dependent on the street axis orientation, the shading caused by the buildings and the materials used. It greatly influences the thermal accumulation in buildings, the thermal fluxes in their close vicinity and consequently the mean airflow and turbulence within the street canyon. Furthermore, these conditions have an important impact on the heating and cooling loads of buildings (Papadopoulos, 2000). It is expected that these thermal effects are greatest under low wind conditions and wind direction perpendicular to the street canyon, i.e., for meteorology unfavourable to the pollutant dispersion from the street. This is particularly the case in densely built areas, with high buildings and relatively narrow streets, that form typical street canyons in many European city centers. The phenomenon can be enforced by the building heat transfers and HVAC systems generating disturbances in the temperature and flux distribution with additional ‘hot–spots’ at the surfaces within the air flow boundary layers.

Two-dimensional numerical investigation of the thermal effects (Sini et al.,1996) within a street canyon model demonstrated that wall temperatures could largely influence the in-street flow and its vertical transport capabilities. A recent experimental campaign in Nantes, France (Vachon et al., 2000) indicated that these effects influence the airflow locally within 2m from the walls. This paper investigates the influence of the heating accumulated on the west side in a north-to-south oriented street canyon on the airflow within the canyon and its impact on the buildings’ energy behaviour.

Results from a three-dimensional simulation of the airflow in the street “Rue de Strasbourg” in Nantes will be presented. The simulated case is based on the measurements of Nantes ’99 experiment obtained in low wind conditions and high solar radiation intensity; during the early afternoon a maximum temperature difference of 18°C between wall and air was observed.

The determination of the energy load of the buildings is performed by means of a dynamic simulation algorithm, used to approach similar problems under Greek climatic conditions.