Natural ventilation strategy potential analysis in an existing school building

Natural ventilation is increasingly considered a promising solution to improve thermal comfort in buildings, including schools. However in order to support its planning and implementation, quantitative analysis on airflow paths and heat-airflow building interactions are needed. This requires an adequate accounting of both internal effects, from building layout and structure, and external forcings from atmospheric factors. The paper analyses the performances of natural ventilation strategies as retrofit solutions to improve thermal comfort in an existing school building in Lavis (Trento, Italy). A climatic analysis is performed to define the potential of wind driven natural ventilation. Meteorological data collected on site are analysed to identify typical wind conditions during the cooling season. The resulting daily cycle of wind speed and direction in sunny days reflects the typical dynamics of a regular valley wind, but also displays the peculiar characteristic of being strongly affected by the outbreak of a lake breeze flowing from a nearby valley and originated from Lake Garda. Based on these findings, three natural ventilation strategies are proposed (night cooling, wind driven cross ventilation and stack and wind driven cross ventilation), and their effectiveness on thermal comfort are compared by means of dynamic simulation tools. The thermal comfort in classrooms is evaluated according to the standard UNI EN 15251. For a standard occupant behaviour, discomfort situations from overheating occur in 34% of occupational period hours in the spring-summer season. The proposed ventilation strategies allow to reduce this value by up to 4%. Natural ventilation turns out to be an interesting low cost solution to control indoor temperatures without mechanical cooling systems.