| Fabric air dispersion system (FADS) is a flexible ventilation terminal made of one polymer. It can not only tranmit airflow, but also distribute airflow into the designed zone. It can also avoid many problems occured for conventional ventilation system such as condensation on HVACs'surface and deposition of micro-oganisms, and can create a comfort, health and clean indoor air with high quality. Airflow characteristics may be fluenced by physical properties of fibre and design method of openings.Airflow characteristics generated by FADS in penetration mode and in slot mode are conducted numerically and experimentally. A porous media model is used to describe the FADS, and the distribution of air velocity and internal pressure was analyzed, followed by the effect of physical properties of fibre and openings'design. Furemore, the properties of indoor air velocity and temperature in room generated by FADS are predicted, and the effect of the system layout, heat load and supply air velocity is discussed. The present work was fully supported by a grant from the Key Projects of the National Science & Technology Pillar Program during the 11th Five-Year Plan Period of China named the key technology in optimimal controlling and saving energy in the course of building (group) energy coupling and transfer in all climates (project No.2008BAJ12B03). The main contents and conclusions of present work are shown as follows:(1) A porou media model is brought out for modeling FADS based on physical properties of porous fibre, and the Carman-kozeny equation fitted for porous fibre is modified. Corresponding mathematic equations for airflow is developed and their feasibility is successfully proved by the comparison of simulation and experimental results for a specific case.(2) When air is supplied by FADS in penetration mode, supply air discharges out through micro-pores inside porous fibre in the direction perpendicular to fibre wall, the velocity is very low. The indoor air is distributed with low velocity and small temperature difference. The strength of heat resources has great impact on the distribution of indoor air velocity. The porosity should be less than one value in order to obtain the uniform distribution of air velocity, but it should also be large enough to reduce the pressure inside FADS. What's more, in order to fufill the design demand of air velocity and temperature in comfort air-conditioning, the supply air velocity must be controlled within one span, and the design load would not be less than 70 percent of real heat load. In addition, the layout of FADS in centre- supply-sides-exhaust can creat better air quality than others under the same condition.(3) When air is supplied by FADS in slot mode, part of supply air discharges out from porous fibre wall in very low velocity, and the rest jets through openings in high velocity, and then merges into one line-shape airflow with a proper velocity at one certain distance. The indoor air velocity reduces gradually from the upper zone to lower zone, and the air velocity around occupant's head can be treated as one design indictor for the design of FADS in slot mode. The effect of physical properties of porous fibre and design method of openings should be considered thoughtfully in order to obtain a reasonable and comfortable indoor air velocity and less pressure inside FADS.(4) The simplified description can avoid the difficulties in generating grids due to the large ratio of length to thickness. Furthermore, it also can reduce grids number and computing steps. As a result, it can be used in real project to predict the distribution of air velocity, temperature, and contaminant cencontration for the case of FADS in penetration mode.Results from present work would provide a theoretical reference for research on optimimal design for FADS'physical structure, air flow mechanisms and relative projects. |
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