Stack driven ventilative cooling for schools in mild climates: analysis of two case studies

This paper presents two case studies of stack driven ventilative cooling systems implemented in kindergarten schools located in the mild Subtropical-Mediterranean climate of Lisbon, Portugal. Both systems rely on stack driven natural ventilation supplemented by a larger, single-sided ventilation opening to be used in the warmer months. In both systems air enters the rooms at a low level, directly in front of the heating passive convector systems, and is exhausted in the back of the room, through a chimney. In addition to the smaller opening configuration, that is sized for the heating and mild seasons (1-3% of room floor area) both designs have larger openings to be used during the cooling season. This larger opening is fundamental to meet the minimum code requirement for total ventilation opening area (5% of floor area). The designs were developed and fine-tuned using dynamic thermal simulation (EnergyPlus). This approach allowed for straightforward statistical analysis of expected system performance, assessed in terms of thermal comfort and indoor air quality. Measurements in steady state mode show a good agreement between simulated and measured airflow rate. During the warmer months the smaller and protected heating season openings are opened for night cooling effect. The chimney exhausts were optimized to avoid opposing stack and wind effects. Both systems are user controlled. The importance of effective commissioning of passive systems is discussed and an example of a simple user manual is provided. The performance of these systems shows that a well-designed natural ventilation system can insure adequate levels of indoor air quality in kindergartens.