Commissioning of a Coupled Earth Tube and Natural Ventilation System at the Design Phase

Abstract

Natural ventilation airflow rate is generally calculated using indoor and outdoor temperature difference without consideration of thermal interaction between the ventilated air and the room in simple analytical method based on pressure balance. However, room air temperature is influenced by natural ventilation airflow rate, and airflow rate is influenced by room air temperature, so it is necessary to perform a coupled analysis taking into account both thermal interaction and ventilation to obtain the correct result. Moreover, when there is marked temperature stratification, as found in large enclosures, or when ventilation airflow rate is small, significant computation error will occur if the set value of room air temperature differs greatly from the actual value. To solve the problems mentioned above, the authors developed a natural ventilation tool that takes into account indoor vertical temperature distribution and proposed a coupled simulation method using this tool in conjunction with CFD (Computational Fluid Dynamics) to simultaneously calculate indoor air flow/temperature distribution and natural ventilation airflow rate. In this paper, at the design phase of an actual coupled earth tube and natural ventilation system in a gymnasium, natural ventilation airflow rate for four outdoor air conditions have been calculated to perform commissioning and several findings were obtained.