Performance Evaluation of Passive Cooling in a Multi-Zone Apartment Building Based on Natural Ventilation

In moderate climates, using natural ventilation systems could allow to save up to 60 % of the end energy for ventilation and air conditioning. Natural ventilation systems depend on pressure differences to move fresh air into buildings by wind effect and pressure effect. Night cooling can be achieved either by an increased air change rate. The higher air change rate can be realized by ventilators/ mechanical ventilation systems or by free convection. The main objective of this paper is to reduce the internal summer cooling load by increasing the natural cross ventilation between different zones in apartment buildings. The performance of natural ventilation is highly dependent on the external outdoor temperature. Over the last years, an increase in the outdoor temperature has been noticed and predicted to rise by the end of this century according to IPCC which puts into consideration the uncertainty of the climate. This paper investigates the performance of natural ventilation using building energy simulation tool ‘DesignBuilder” to simulate a multi-zone apartment building in Belgium. The indoor thermal comfort is enhanced by determining an optimum set of input parameters such as the setpoint temperatures, the discharge coefficient of the night ventilation, and the opening areas in the building. Those parameters are optimized using current and future weather data to evaluate the evolution of natural ventilation system performance and indoor thermal comfort. The results show that proper use of natural ventilation can significantly reduce the overheating risk during a typical year and that the benefits of natural ventilation are not expected to vanish with global warming. It can be seen that, without natural ventilation, thermal comfort could be reached on average 53.7% of the time, while it could reach 66.2% of the time using single-sided ventilation and 78.8% with cross ventilation. However, during heatwaves, natural ventilation becomes inefficient and cannot guarantee the thermal comfort of the occupants all the time as the thermal comfort of occupants can only be achieved 51% of the time during heatwaves.