Influence of the urban environment on the effectiveness of natural night-ventilation of an office building

The effectiveness of natural night-ventilation in the urban environment depends on local climate char- acteristics, but also on solar shading and wind shielding effects of the surrounding buildings. However, the impact of the latter factors on the effectiveness of night-ventilation is often disregarded, altering the predicted building energy performance. Building Energy Simulation tools coupled with Airflow Net- work models allow estimating the effect of the urban environment on the cooling energy savings due to night-ventilation. Nevertheless, external sources of wind flow data are needed to account for the wind shielding effect of surrounding buildings. In this paper, the cooling effectiveness of night-ventilation for an office building placed in the center of urban areas of increased density is analyzed for three European locations. The energy demand of the unventilated building is first assessed, also considering the effect of environmental albedo and a simplified Urban Heat Island scenario. Then, night-ventilation rates and energy savings for the ventilated building are calculated to estimate the variation of the cooling effect of night-ventilation. Results show a strong reduction of the energy savings in high-density urban areas and point out that a detailed description of the surroundings is crucial to assess the suitability of passive cooling solutions.