A STUDY ON THE INFLUENCE OF HORIZONTAL LOUVERS ON NATURAL VENTILATION IN A DWELLING UNIT

According to previous research, the central horizontal pivot window could contribute to the improvement of indoor air quality under single-sided ventilation. But for interior space using, it would be inconvenient. In the present study, the horizontal pivot window would be replaced by horizontal louvers and the work was focused on what is a proper opening design, which could be used to promote natural ventilation, and keep users be comfortable. We tried to use numerical method (CFD) to simulate ventilation performance of different louver’s depths as well as different wind speed. Air flow was considered, turbulent, steady, and the effects of buoyancy were taken into account. Our major findings were as below: 1. The proper horizontal louvers can be used to improve indoor air quality by means of increasing air change rate, especially the site under lower velocity. However when a louver depth is smaller than 4cm, it cannot be helpful to increase air flow rate. Furthermore, in this situation hot air would not be moved out effectively, that is to say, people would not feel thermal comfortable. 2. Generally speaking, the draft rate, DR, of a room with a longer depth of thirty-six centimeters louvers opening is over Class A, 15 %, established by ASHRAE. The DR of 144 centimeters louvers can’t get up to Class C, 25 %. 3. According to the results of the simulations, and the way of regression to analysis the correlation on ventilation performance, the depths of louvers, and outdoor velocity, we established the empirical model. And the finding may help designers to predict ventilation performance of a room before building it. INDEX TERMS Single-sided ventilation, CFD, Horizontal louvers, Natural ventilation INTRODUCTION After stepping into the 21 century, people demand the housing to be of higher and higher performance and quality and all governments pay more attention to the relevant policy. Take Japan and China Mainland for example, they both establish some relevant measures to protect people’s residence rights and interests, and to solve the dispute of housing trade. As for that in Taiwan, the Green Building Evaluation System (GBES) developed by Architectural Building Research Institute (ABRI) was also revised in 2003 and integrated into the indoor environmental index. At the same time, ABRI actively pushed forward the Housing Performance Evaluation System (HPES), and among the indices, indoor air environment and building ventilation are regarded very important. In narrow but densely-populated Taiwan, the buildings in cities are over-dense and most of the housing spaces just depend on an single-sided opening to ventilate, this results in poor indoor air quality (IAQ) and further influences health of residents. According to the past domestic research, a central horizontal pivot window can be installed on the opening of the external wall to enhance the indoor Air Exchange Efficiency (AEE) under the situation of single-sided ventilation. However, the usage mode to open the window will cause some limits to the space usage. The present research attempts to find suitable opening patterns for buildings in Taiwan, with the consideration of the climatic environment of high humidity and temperature, as well as the indoor space usage during ventilation and cooling. Thus, the central horizontal pivot window is changed to horizontal air ducting louver. The influence of different louver depths on the health and comfort of the indoor environment under natural ventilation is discussed to evaluate its essential application pattern and benefit. Proceedings: Indoor Air 2005 3143 RESEARCH METHODS This present research utilizes Computational Fluid Dynamic (CFD) method to simulate the distribution of the air flow field and the temperature field under various conditions of slat depth and outdoor wind velocity, and to further analyze the effects of different horizontal louvers on the factors such as air change rate, the cumulative distribution of temperatures at straight heights and wind striking draft rate in human inhabited place. The related settings are described as follows: The research investigates a dwelling unit, a unit space with outside diameter being 6.1m×3.2m×2.85m, and inner diameter being 5.5m×2.9m×2.55m; it is divided into rest region and working region according to its usage. The settings of boundary conditions and object sizes are presented in Table 1. Table 1. The description of boundary condition and object size According to the past research, the angle (θ) between the central horizontal pivot window and the external wall is 120~135° can effectively strength the effect of thermal buoyancy, obtain better Air Exchange Efficiency (AEE), and decrease the accumulation of indoor carbon dioxide. Hereby the research lays 120° as the setting value of the angle (θ) to further investigate the air change rate when using different louver depths. (As indicated in Figure 1) Figure 1. The illustration of horizontal air ducting louver in the study The software of CFD used in the research is “PHOENICS”, and the RNG k-ε turbulence model is adopted to simulate the air flow field and the temperature field under a steady condition, and the setting of thermal buoyancy is also considered at the same time. In the aspect of ventilation evaluation, the research selects the following evaluation factors of ventilation efficiency connected with health and comfort. 1. The evaluation principle of air change Study the effect of louvers on indoor air change through the calculation of the increased percentage of air change. The expression of increased percentage of air change (Qnormalize) is as equation (1): Position Boundary condition & object size Velocity 0.1,0.3,0.5,1,2m/s 1 Temp. 23 °C Outdoor (Inlet) 2 Pressure In cell Size 78cm * 144cm Angle Fixed angle θ = 120° Opening ( Horizontal louvers) 3 Depth 144,72,48,36,18,9,4cm Indoor 4 Heat flux 60W Inlet 1 2 3 4 2 2 2 Rest region Work region 3-D model illustration