The Performance of the Passive Ventilation of Vertical Chimney in Taiwan Considering Global Warming

Transcription

1 The Performance of the Passive Ventilation of Vertical Chimney in Taiwan Considering Global Warming Wei-Ying Chang 1, Po-Cheng Chou 1, Che-Ming Chiang 2 1 Graduate Institute of Architecture and Environment Design, Shu-Te University, Yenchao 82445, Taiwan. paul@mail.stu.edu.tw 2 Dept. of Architecture, National Cheng-Kung University, Tainan 70147, Taiwan. cmchiang@mail.ncku.edu.tw ABSTRACT: Its purpose was to update policy makers everywhere on climate change science, which is rapidly moving. General appraisals of it are carried out by the IPCC (Intergovernmental Panel on Climate Change), which has produced three assessment reports, in 1990, 1995 and The third assessment report (known as TAR) is chapter and verse on what the international community of climate scientists think is happening now, and likely to happen in the future, with global warming. The most important conclusion of TAR was that the earth's average surface temperature was likely to warm by between 1.4 and 5.8 degrees centigrade between now and 2100, depending on how human societies controlled their emissions of carbon dioxide, the waste gas from industry and transport which is retaining more and more of the sun's heat in the atmosphere. That swhy we should pay more efforts on turning face to the development of passive design instead of the active design on the building ventilation.in the high temperature environment as summer need to put the Exhaust Vent Shaft up on the Ventilation Shaft to exhust hot air out of indoor. KEYWORDS: Numerical Simulation, Stack Effect, Natural Ventilation 1. INTRODUCTION Before the human being began using petrochemical fuels, people used to adapt to the environment naturally and make good use of the natural factors in architectural design, and the endemic buildings all over the world reflected the natural environment of the places where they were situated. During the process of industrialization in Taiwan, the architectural practitioners usually employed active mechanical equipment to improve the indoor environment quality for satisfying the needs of high quality and comfortableness of the indoor living environment. The roles and functions of building structures in the natural environment system were neglected and it seemed that environmental control had become the concern of experts in air conditioning, water and power engineering, but not a way of the buildings themselves adapting to the nature. The purpose of this research is to advocate a new way for coexisting with the earth's ecology and find the architecture style that is the fittest for Taiwan in the hot and damp climate under the global warming. This paper probes into the effect of applying buoyancy force in the vertical ventilation of buildings, and the research is conducted with the concept of passive ventilation, so as to induce the application of solar energy and wind energy actively, provide architectural designers with a new perspective, and build a healthy environment in which human coexists with the nature harmoniously. A05-1

2 2. METHODS 2.1. Architecture model The space of bestrooms is used as the object of this research and discussion is made on the relation between the space and badgirs. Badgirs are set between two rooms. Induced draft pipe is laid on the first floor, and there are two bestrooms on each of the second and third floors, four bedrooms in total. In this research, numerial analysis is applied in the indoor environment impact assessment and the structure of air flow field is analyzed to discuss the relations between ventilation path, air flow rate and temperature. The CFD numerical analysis software used in this research is the PHOENICS package. Based on the SIMPLE (Semi Implicit Pressure Linked Equations) developed by Patankar and Spalding, the characteristics of broad-sense flow field diferential equations are utilized to analyze the continuity of flow field, i.e., the trends of the energy, mass and momentum of fluid changing with time in different spaces and different positions. This research employs the CFD technology and uses the k-ε turbulent flow model as the calculation basis of indoor flow field. The domain size of this research is 680.0(X) (Y) (Z)cm, the window size is (X) (Y) cm, and the badgir size is 210.0(X) (Y) (Z) cm. See Fig.1 and Table Experiment settings The variables of the experiment model are set as follows: badgir height, 300cm and 1200cm; temperature, 20.0and 40.0; and wind, southwest monsoon with a velocity of 0.1m/s. The badgirs are equipped with upper and lower fenestras, and the experiment is made with or without heat plates installed on badgirs, so as to analyze the indoor ventilation environment. See Table 1 and Table 2. Figure 1. The Size of Experiment Model A05-2

3 Table 1. Experiment Settings Module Type Lower fenestra Upper fenestra Lower fenestra Upper fenestra type1 type 2 type 3 type 4 Table 2. Space Dimensions (unit: cm) Facilities Bedroom Window Dimensions Window azimuth 90.0 (Z) badgir Badgir fenestra Human (seated) 680.0(X) 305.0(Y) 325.0(Z) (X) (Y) 210.0(X) (Y) (Z) 130.0(X) 30.0 (Z) 25.0(X) 20.0(Y) 90(Z) Facilities Temperature Wind velocity and direction Badgir height Temperature of heat plate Dimensions m/s, southwest 300(Z) 1200cm(Z) RESULTS AND DISCUSSION The CFD simulation is used in this research, and the experiment of ventilation environment is carried out under 2 sets of different badgir heights, 2 sets of different ambient temperatures, with or without heat plate on badgir. From the results of experiment it is found that the high temperature environment of 40.0is fit for opening the upper fenestra of badgir to discharge the indoor hot air; when the vertical badgir is installed with a heat plate, the air flow is drawn upward under the buoyancy force effect, reducing the turbulent and eddy flows between badgir and fenestras; The low temperature environment of 20.0is fit for opening the lower fenestra, the joint use of badgir and heat plate is helpful for retaining the hot air indoors, and the convection of cool air in the lower part through the fenestra provides a better effect of ventilation and better mixing of indoor air. The indoor pollutants are discharged through the fenestra, reducing the mixing of air flows in the spaces. For example, when the outdoor temperature is 40.0and the badgir is installed with a heat plate, the left room on the second floor has a better ventilation effect than when there is no heat plate. When the outdoor temperature is 20.0 the, badgir height is 1200cm and the temperature inside badgir is 40.1 the, pressure difference and the buoyancy force effect bring a better effect of natural ventilation, and the ventilation effect with heat plate is 5% of that without heat plate. A05-3

4 Figure 2. Air flow rate of fenestra under 20.0without heat plate on badgir Figure 3. Air flow rate of fenestra under 40.0without heat plate on badgir Figure 4. Air flow rate of fenestra under 20.0with heat plate on badgir Figure 5. Air flow rate of fenestra under 40.0with heat plate on badgir A05-4

5 When the temperature rises to 40.0, the vertical badgir of building sees a better buoyancy force effect and the natural ventilation effect is 15%~20% higher than when the outdoor temperature is When the vertical badgir is installed with a heat plate, the discharge efficiency of indoor hot air is 3.11~5.61 times higher than when there is no heat plate (see Fig.6). Facing the challenge of global warming and the coming of the high temperature environment of 40.0, the application of badgir in building facilitate the air exhaust with the aid of the stack effect, thus realizing the concept and idea of pasive ventilation. Figure 6. Air flow rate of upper fenestra Figure 7. Air flow rate of lower fenestra 4.CONCLUSIONS As shown in Fig. 8 and Fig. 9, the heat plate in badgir can effectively prevent air flowing from the left room to the right room and solve the turbulent flow in badgir. The heat plate will increase the gathering of heat, and the pressure difference will draw the air upward (see Fig. 10). When there is no heat plate, through flow will take place in badgir and the two rooms (see Fig. 11). The high temperature environment of 40.0 is fit for opening the upper fenestra to discharge the indoor hot air; while the low temperature environment of 20.0 is fit for opening the lower fenestra to retain the hot air indoors with the aid of heat plate, showing a 15%~20% increase in the Discharge efficiency of fenestra. Figure 8. Upward flow is generated to obstruct through flow when heat plate is installed Figure 9. The path of air flow when there is no heat plate A05-5

6 Figure 10. Upward flow is induced when heat plate is installed Figure 11. Through flow takes place when there is no heat plate ACKNOELEDGEMENT We are especially grateful to ARCHILIFE Research Foundation for their computational facilities, and this study is gratefully acknowledged. REFERENCES [1] IPPC. (2007). Climate Change 2007: The Physical Science Basis. [2] P. V. Nielsen (1976) Flow in air conditioned rooms, English translation of Ph.D. thesis, Technical University of Denmark, Danfoss A/S, Denmark. [3] M.N.Bahadori, (1978), Passive Cooling Systems in Iranian Architecture, Scientific American, Vol.238, No. 2, Feb. pp [4] T.G.M. Demmers (2000), Assessment of Techniques for Measuring the Ventilation Rate, using an Experimental Building Section, J. agric. Engng Res. 76, [5] Shuzo MURAKAMI,Dr. Eng, (2005), Evaluation of Indoor Environment in Vernacular Dwellings-Numerical Analysis of The Igloo by CFD, The 2005 World Sustainable Building Conference [6] Susanti LUSI,M.Eng.et al(2005), Experimental Study On Natural Ventilation Effect Of A Cavity In An Inclined Double RoofSB2005 Conference. [7] Tanaja H.et al(1997), Thermal characteristics of a hoop structure for swine productionamerican Society of Agricultural Engineers40(4) [8] Zhang Lin. et al, (2005), Comparison of performances of displacement and mixing ventilations.part1: thermal comfort, [9] Yi Jiang(2003), Natural ventilation in buildings: measurement in a wind tunnel and numerical simulation with large-eddy simulationjournal of Wind Engineering and Industrial Aerodynamics 91pp [10] Mistriotis, A. et al. (1997), Computational Analysis of Ventilation in Greenhouses at Zero- and Low-Wind-Speeds. Agricultural and Forest meteorology, 88(1-4): [11] P. Ole Fanger, (1987), A New Chart Identifies the Percentage of Subjects Cissatisfied due to Craft as a Function of the Mean Air and the Air TemperatureASHRAE JOURNAL January. [12] A. Sreshthaputra, (2004), Improving building design and operation of a Thai Buddhist temple, Energy and Buildings 36, pp A05-6