Volume 22 Issue 7 - July 6, 2012 PDF
Natural ventilation design mixes in elementary school classrooms
Che-ming Chiang1,*, Chi-ming Lai2
1 Department of Architecture, College of Planning & Design, National Cheng Kung University
2 Department of Civil Engineering, College of Engineering, National Cheng-Kung University
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In Taiwan, electricity usage by buildings accounts for 27% of the total national electricity consumption, second only to industrial use. The electricity consumption of various buildings can be classified into three sectors: lighting, air conditioning, and dynamic power.  Therefore, more emphasis should be placed on saving electricity by reducing the electricity consumption of air conditioning.

As most elementary schools are not equipped with air conditioners, the classrooms, particularly those located on the upper floors, are always overheated.  This problem is compounded as external air is blocked from entering most conventional classrooms because windows and doors are kept closed to reduce noise levels.

The objective of the present study is to provide insights into how six combinations of natural ventilation designs (double roofs, CRSOs (Covered Ridge with Sidewall Openings), roof ridge openings, and window openings) influence indoor thermal environments during the summer season with low outdoor wind speed. CFD (Computational Fluid Dynamics) numerical simulations via a finite volume method have been performed for the steady-state three-dimensional turbulent flow phenomena induced by outdoor wind and indoor heat sources.  To complement the numerical simulations, reduced-scale experiments were also conducted to determine some of the physical parameters under consideration.

Due to the wind force and the effects of thermal buoyancy, a good indoor flow field is achievable.  The indoor air can discharge simultaneously through the ridge openings and the windows, as shown in the figure.  It is obvious that outdoor air can enter the room through the windows, directly discharging airflow from the windows on the other side, thus creating a shortcut phenomenon. 

Among the designs tested, the Basic Mode (a single roof without a CRSO) results in the worst natural ventilation and thermal environment.  Designs that incorporate a double roof, a CRSO, roof ridge openings, or open windows provide natural ventilation and improve the indoor stuffiness.  The results show that when a double roof, roof ridge openings, and a CRSO are implemented, both the ventilation performance and the thermal environment of the classrooms are improved, regardless of whether the windows are laid out in a staggered formation (high-low) or in a conventional window layout.
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