Methodology for the Evaluation of Natural Ventilation in ... - Cham
Methodology for the Evaluation of Natural Ventilation in ... - Cham
Methodology for the Evaluation of Natural Ventilation in ... - Cham
Create successful ePaper yourself
Turn your PDF publications into a flip-book with our unique Google optimized e-Paper software.
w<strong>in</strong>dows <strong>of</strong> naturally ventilated build<strong>in</strong>g. Though designed specifically <strong>for</strong> <strong>the</strong> prototype ma<strong>in</strong>w<strong>in</strong>dows, <strong>the</strong> design could be adapted <strong>for</strong> application <strong>for</strong> o<strong>the</strong>r w<strong>in</strong>dow geometries and o<strong>the</strong>rbuild<strong>in</strong>gs.There were additional factors that <strong>in</strong>fluenced <strong>the</strong> model<strong>in</strong>g methods along with <strong>the</strong> challengesaddressed <strong>in</strong> monitor<strong>in</strong>g and evaluat<strong>in</strong>g <strong>the</strong> full-scale prototype build<strong>in</strong>g. The range <strong>of</strong> model<strong>in</strong>gmethods available, at scales rang<strong>in</strong>g from full-sized to 1/250 th scale, and <strong>the</strong>ir characteristicswere presented. Two <strong>of</strong> <strong>the</strong> more common techniques <strong>for</strong> model<strong>in</strong>g, us<strong>in</strong>g ei<strong>the</strong>r water or air,and <strong>the</strong>ir respective flow visualization techniques, were described. Flow visualization has beenshown to be a powerful technique to determ<strong>in</strong>e flow patterns with<strong>in</strong> a model but <strong>the</strong>re have beenconcerns raised regard<strong>in</strong>g <strong>the</strong> neutral buoyancy <strong>of</strong> <strong>the</strong> material selected to <strong>in</strong>troduce <strong>in</strong>to <strong>the</strong> fluidstream. The use <strong>of</strong> fog, at <strong>the</strong> same temperature as <strong>the</strong> enter<strong>in</strong>g air, proved useful <strong>for</strong> use <strong>in</strong> <strong>the</strong>reduced-scale model airflow pattern visualization. Model<strong>in</strong>g techniques were described <strong>for</strong> arange <strong>of</strong> applications, <strong>in</strong>clud<strong>in</strong>g how each method <strong>in</strong>corporated flow visualization <strong>in</strong>to <strong>the</strong>evaluation <strong>of</strong> fluid flow <strong>for</strong> <strong>the</strong> model. The requirements <strong>for</strong> trac<strong>in</strong>g flow patterns <strong>in</strong>cluded notonly neutral buoyancy, but also effective visualization and low diffusion rate. The benefits andproblems were identified <strong>for</strong> both water and air as <strong>the</strong> work<strong>in</strong>g fluids <strong>in</strong> model<strong>in</strong>g. F<strong>in</strong>ally, <strong>the</strong>methods <strong>of</strong> flow visualization used <strong>for</strong> <strong>the</strong> reduced-scale model were presented, <strong>in</strong>clud<strong>in</strong>gimag<strong>in</strong>g techniques. Based on <strong>the</strong> above requirements, a fogg<strong>in</strong>g mach<strong>in</strong>e as <strong>the</strong> neutrallybuoyant tracer, a digital video camera to capture <strong>the</strong> flow visualization and fluorescent lamps toprovide illum<strong>in</strong>ation proved a useful comb<strong>in</strong>ation.Critical to <strong>the</strong> use <strong>of</strong> scale model<strong>in</strong>g as a method <strong>for</strong> predict<strong>in</strong>g fluid flow <strong>in</strong> full-scale build<strong>in</strong>gshas been <strong>the</strong> similarity <strong>of</strong> calculated or monitored parameters. Dimensional analysis andsimilitude were presented as means to ensure similarity between <strong>the</strong> prototype and scale model.The govern<strong>in</strong>g equations, <strong>in</strong> <strong>the</strong>ir full and dimensionless <strong>for</strong>ms, were presented <strong>in</strong> chapter five.The result<strong>in</strong>g dimensionless parameters, <strong>the</strong> Reynolds, <strong>the</strong> Archimedes or <strong>the</strong> Grash<strong>of</strong>, and <strong>the</strong>Prandtl numbers, were identified, and determ<strong>in</strong>ation <strong>of</strong> characteristic length was discussed. Theselection <strong>of</strong> characteristic length affected <strong>the</strong> regime used to describe <strong>the</strong> flow, and results <strong>in</strong> <strong>the</strong>use <strong>of</strong> several characteristic lengths, depend<strong>in</strong>g on <strong>the</strong> field under evaluation. Comparisonsbetween <strong>the</strong> full-scale prototype, reduced-scale air, and reduced-scale water <strong>for</strong> <strong>the</strong> keyparameters <strong>in</strong>clud<strong>in</strong>g <strong>the</strong> Reynolds number, <strong>the</strong> Prandtl number, and <strong>the</strong> Grash<strong>of</strong> number werepresented. All <strong>of</strong> <strong>the</strong> models and <strong>the</strong> prototype were found to fall <strong>in</strong> <strong>the</strong> turbulent regime whenus<strong>in</strong>g <strong>the</strong> hydraulic diameter <strong>of</strong> a s<strong>in</strong>gle zone as <strong>the</strong> characteristic length.The reduced-scale air model constructed to meet <strong>the</strong> geometric similarity requirement waspresented <strong>in</strong> chapter six. Descriptions <strong>of</strong> <strong>the</strong> test chamber, control system and equipment used <strong>in</strong>carry<strong>in</strong>g out <strong>the</strong> experiments were discussed, along with descriptions <strong>of</strong> <strong>the</strong> experiments. Each<strong>of</strong> <strong>the</strong> experiments <strong>for</strong> buoyancy, w<strong>in</strong>d, and comb<strong>in</strong>ed w<strong>in</strong>d-buoyancy cases was described <strong>in</strong>detail. The <strong>in</strong>fluence <strong>of</strong> w<strong>in</strong>dow location on <strong>the</strong> flow pattern <strong>in</strong> <strong>the</strong> occupied space wasidentified us<strong>in</strong>g <strong>the</strong> s<strong>in</strong>gle zone model. Though <strong>the</strong>re was little change <strong>in</strong> <strong>the</strong> overall airflow ratethrough <strong>the</strong> build<strong>in</strong>g, <strong>the</strong> temperature distribution with<strong>in</strong> <strong>the</strong> heated zone was affected by <strong>the</strong>location <strong>of</strong> <strong>the</strong> w<strong>in</strong>dows. The two-zone model demonstrated <strong>the</strong> effect <strong>of</strong> <strong>the</strong> stack vents on <strong>the</strong>airflow and result<strong>in</strong>g temperature distribution with<strong>in</strong> <strong>the</strong> two zones. In poorly designed naturallyventilated build<strong>in</strong>gs, <strong>the</strong> upper floor can become <strong>the</strong> only location <strong>for</strong> outflow from <strong>the</strong> build<strong>in</strong>g,caus<strong>in</strong>g warm, stale air to traverse <strong>the</strong> occupied space be<strong>for</strong>e exit<strong>in</strong>g <strong>the</strong> build<strong>in</strong>g. The full-162