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

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1 A STUDY ON THE INFLUENCE OF HORIZONTAL LOUVERS ON NATURAL VENTILATION IN A DWELLING UNIT CM Chiang 1, NT Chen 1, PC Chou, YY Li, IC Lien 1 1 Dept. of Architecture, National Cheng Kung University, Chinese Taipei Dept. of Interior Design, ShuTe University, Chinese Taipei ABSTRACT 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.. 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, 5 %. 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 1 st 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 3 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. 314

2 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.m.85m, and inner diameter being 5.5m.9m.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 Position Boundary condition & object size Velocity.1,.3,.5,1,m/s Outdoor 1 Temp. 3 C (Inlet) Pressure In cell Opening Size 78cm * 144cm ( Horizontal 3 Angle Fixed angle θ = 1 louvers) Depth 144,7,48,36,18,9,4cm Indoor 4 Heat flux 6W Inlet 1 Rest region Work region D model illustration According to the past research, the angle (θ) between the central horizontal pivot window and the external wall is 1~135 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 1 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) Central horizontal pivot window Horizontal air ducting louver θ Louver depth Louver depth Louver depth Outdoor Indoor θ = 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 (Q normalize ) is as equation (1): 3143

3 Q Q Q L L normalize = (1) QL Where Q L is the amount of air change with L cm-louvers, Q L is the amount of air change without louvers.. The evaluation of the effect of temperature and heat removal Evaluate the effect of temperature and heat removal through the situation of indoor temperature accumulation and distribution. 3. The evaluation of wind striking draft rate: According to the related specification of ASHRAE Standard 55P, the formula of wind striking draft rate is shown in the following (Equation ): DR = [( 34.6 t ) ( v.5 ) ] (.37 v T ) () a u Where t a is local temperature ( C), v is local average wind velocity (m/s), and T u is the percentage of local turbulence strength (%). The evaluation standard of DR in the specification is classified into three classes according to the draft rate: Class A (DR=15); Class B (DR = ); Class C (DR = 5). The research uses this standard for the evaluation of indoor comfort. RESEARCH RESULTS Based on the results from numerical simulations, the respective analyses of indoor air change, temperature distribution and wind striking are conducted so as to assess the overall ventilation efficiency from the view of indoor health and comfort. 1. The effect of horizontal air-ducting louvers on indoor air exchange Figure 5 shows the increased percentages of air change in all cases. In general, after the installation of louvers at the opening position, the amount of air change is larger than that of the control group has not been installed with louvers. Louvers with in depth can even increase 3% air change. Only the 4cm-louver results in insignificant increased percentage of air change, which indicates that louvers within 4cm in depth cannot significantly help increase indoor air change. Besides the 4cm-louver, the increased percentage of air change by louvers with different depths under the condition of.3 m/s wind velocity is much larger than that under the conditions of other wind velocities. This phenomenon indicates that louvers are capable of a significant efficiency of air change under the condition of low wind velocity. 5% % 百葉深度與換氣增加百分率關係圖.3 m/s.5 m/s 1. m.s. m/s Q normalize (%) 15% 1% 5% % % Louver depth (cm) Figure. The correlation between the increased percentage of air change and louver depths As from the display of aforementioned data after conversion (Figure 3,4), the amount of air change per unit area of floor increases along with the depths of louvers, and demonstrates an increasing linear trend along with the increase in the square of wind velocity (V ). After the further correlation analysis of variables, we obtain the regression model of equation (3) by adopting the multiple regression method. The P values of all variables in the equation are all less than.1, which reaches the significant level. The coefficient of determination (R ) reaches.9, and it indicates that the prediction equation is capable of good explanation. 3144

4 Q/FA (m 3 /h/m ) 1.3m/s 1.m/s.5m/s.m/s L (cm) V (m/s) Figure 3. The correlation between air change and louver depths Figure 4. The correlation between air change and wind velocity Q/FA (m 3 /h/m ) 1 4cm 9cm 18cm 36cm 48cm 7cm 144cm Table. The correlation analysis of each variable Q/FA V V V 3 L L L 3 Q/FA 1 V V V L E E E-17 1 L E E E L E-17 -E E *Q/FA: Amount of air change per unit area and per hour (m 3 /h/m ); V: Wind velocity of inlet (Range:.3~.m/s); L: Louver depths (Range:.4~1.44m); Opening sizes (.78m * 1.44m) Q/FA= V L (3). The effect of horizontal air-ducting louvers on the distribution of indoor temperatures Figure 8 is the cumulative distribution diagram of temperatures in the rest region, wherein the height section from.6 to.9 meters corresponds to the location where the human body rests. When the wind velocity is less than.5 m/s, if the opening is without installing louvers, the warm air indoor cannot be effectively removed, the temperature around the resting site for the human body thus accumulates quickly. The same phenomenon is also occurred when using 4cm-louvers. As the depth of horizontal air-ducting louvers increases, outdoor cool air can then be ducted into lower indoor place effectively, and the warm air can then be pushed to top space and moved out, so as to keep the comfort of human active region. When the outdoor wind velocity goes above 1. m/s, the 4cm-louver not only is unable to effectively slow up the temperature accumulation, but even worse than when the louver is not installed. It is supposed that this is caused by the fact that the depth of the louver blades is over small, resulting in the limited air ducting performance, and the over-dense blades disturb the exterior airflow into inside. It is noted that when the wind velocity is.3 m/s, the -louver begins to have the accumulation of temperature and heat in the place close to breathing belt. Thus, the buildings with the conditions of much low outdoor wind velocity are suggested to choose louvers with depth above to ensure the indoor comfort. 3145

5 3 風速 室內溫度垂直分佈 V=.3m/s 3 風速 1.m/s, 室內溫度垂直分佈 V=1.m/s.5.5 cm cm Height (m) 4 cm cm Temperature ( C) Human body Bed Height (m) 4 cm cm Temperature ( C) Figure 5. The vertical distribution of indoor temperature when V is.3 and 1. (m/s) 3. The effect of horizontal air ducting louver on the wind striking in sleeping zone Figure 9 is the analytic diagram of the wind striking draft rate for the human in the indoor sleeping zone. The louver with depth in 4~ can meet Class A of ASHRAE standard (DR 15 %), and the depth of 48, 7, 144 cm will cause over strong air flow and then raise wind striking draft rate. Among them, the pattern, under situations of any wind velocity of inlet, keeps the DR value far above 5 %, Class C of ASHRAE standard, and causes significant impact on the comfort of the people. To sum up, the indoor wind striking draft rate will rise with the increase of the louver depth, and after statistics and regression analysis, there is linear correlation between these two, with coefficient of determination (R ).89~.98 and the P value meeting significant level. The research suggests the designer to choose the louver with depth within 36m, so as to consider the comfort of the indoor user and at the same time to lessen the influence of the opening design on the indoor space usage. DR (%) 不滿意度 % 風速.3m/s, 睡眠區風擊分析 4 cm 5 Sleeping zone 4 V=.3m/s 3 7 cm Class A 1 位置 (m) Location (m) DR (%) 不滿意度 % 風速 1. m/s, 睡眠區風擊分析 4 cm 7 Sleeping zone 6 5 V=1.m/s 4 7 cm 3 1 Class A 位置 (m) Location (m) Figure 6. The wind striking draft rate in sleeping zone when V is.3and 1. (m/s) DISCUSSION The research has not been compared with the result of experiment yet. It can be considered in following studies. Moreover, there are still many complex factors in the application of louvers at present, so more and wide-ranging applications for designer are another significant issue, which is necessary to proceed with studies. ACKNOWLEDGEMENTS Support from the National Science Council through grant (NSC93-11-E-6-63-) in the study is gratefully acknowledged. Also, thanks Archilife Research Foundation for their computational facilities. CONCLUSION In general, horizontal air ducting louvers help raise the amount of indoor air change, and only the louver with depth less 4cm has limitation to raise the amount or even negative influence. As to the benefit of heat removal: when the base wind velocity.3m/s, louver depth should be above 9m. The louver with depth within 36cm can meet the wind striking draft rate Class A of ASHRAE standard, hereby it is suggested to usage. To sum up the 3146

6 above analysis, the research suggests the designer to choose louvers with depth 9~36m. The regression model (equation ) established by this research is able to assist the designer in designing proper louver depth, under the situations of different wind velocity, according to the required indoor air change rate, and to increase the indoor ventilation, together with indoor health and comfort. Proper design of the opening with horizontal air ducting louver can strengthen indoor ventilation and heat removal, and even help solve the problem of over high humidity in hot and humid region. REFERENCES Chiang CM., Li YY., Chou PC. Lai CM. 1999, CFD Simulation to Predict Natural Ventilation Efficiency in a Dwelling Bedroom with the Central Horizontal Pivot Window, INDOOR AIR 99, Edinburgh, UK. Athanassios A. Argiriou et al.,, Single-sided ventilation of building through shaded large openings, Energy 7, pp ASHRAE,, BSR/ASHRAE Standard 55P, pp.33. Prianto E., Depecker P., 3, Optimization of architectural design elements in tropical humid region with thermal comfort approach, Energy and Buildings 35, pp Gan GH.,, Effective depth of fresh air distribution in rooms with single-sided natural ventilation, Energy and Building 31, pp