Inlet and outlet shape design of natural circulation building ventilation systems

Swiegers, Jacobus Johannes (2015-03)

Thesis (MEng)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: Increased awareness of environmental problems has awakened interest in renewable energy systems. Natural ventilation systems are especially of interest, as people spend most of their time indoors. Indoor air quality is an important consideration when human health and occupant comfort is to be maintained. This study focusses on determining the best inlet and outlet shape for a natural ventilation system from a chosen set of configurations. The inlet and outlet configurations were tested on a PDEC (Passive Downdraught Evaporative Cooling) shaft and solar chimney. The PDEC incorporated an evaporative cartridge made from cotton cloth. Independent models of the PDEC and solar chimney were built in a thermally controlled space where the configurations were tested at different wind speeds. The configurations were tested on a wet or dry PDEC shaft and on a hot or cold solar chimney. One-dimensional finite difference models, accounting for some two-dimensional effects in the evaporative cartridge, of the cartridge and solar chimney were developed. CFD (Computational Fluid Dynamics) models were further constructed in FLUENTr, simulating operating conditions for each inlet and outlet test. The CFD models were constructed to obtain numerical comparisons for the experimental data. The ability of the one-dimensional and CFD models to predict the performance of the PDEC and solar chimney were investigated. The results indicated that an inlet configuration called a TFI (Turbine Fan Inlet) performed the best at the tested wind speeds. The TFI was further able to significantly increase volumetric flow rate in the PDEC shaft for the dry evaporative cartridge tests. The outlet that performed best under the tests is a Windmaster Tornado Wind Turbine, or Whirlybird, which is a commercially available configuration. The one-dimensional models were not able to accurately predict conditions during start-up. The CFD models were highly accurate in predicting the experimental values. It is recommended that a two-dimensional theoretical model be developed to better predict start-up conditions.

AFRIKAANSE OPSOMMING: Verhoogde bewustheid van omgewings probleme het belangstelling in hernubare energie stelsels ontwaak. Natuurlike ventilasie stelsels is veral van belang, sedert mense die meeste van hul tyd binnenshuis spandeer. Binnenshuise lug kwaliteit is ’n belangrike oorweging wanneer menslike gesondheid en insittendes se gemak in stand gehou moet word. Hierdie studie fokus op die bepaling van die beste inlaat en uitlaat vorm van ’n gekose stel konfigurasies vir ’n natuurlike ventilasie-stelsel. Die inlaaten uitlaat-konfigurasies is op ’n PDEC (Passive Downdraught Evaporative Cooling) skag en sonkrag skoorsteen getoets. Die PDEC het ’n verdampings doek, gemaak van katoen, ingesluit. Onafhanklike modelle van die PDEC en sonkrag skoorsteen is in ’n termies-beheerde ruimte en die konfigurasies is by ’n onveranderende wind spoed getoets. Die konfigurasies is op ’n nat of droog PDEC skag en op ’n warm of koue son skoorsteen getoets. Een-dimensionele eindige verskil modelle, wat sommige twee-dimensionele effekte in ag neem in die verdampings doek, van die doek en sonkrag skoorsteen is ontwikkel. CFD (Computational Fluid Dynamics) modelle is verder gebou in FLUENTr, wat die werkstoestande vir elke inlaat en uitlaat toets simuleer. Die CFD modelle is ontwikkel om die eksperimentele data met numeriese waardes te vergelyk. Die vermoë van die een-dimensionele en CFD modelle om die verrigting van die PDEC en sonkrag skoorsteen te voorspel, is ondersoek. Die resultate dui daarop dat ’n inlaat opset genoem TFI (Turbine Fan Inlet) die beste vaar by die elke getoetsde wind spoed. Die TFI was verder in staat om die volumetriese vloeitempo in die PDEC skag aansienlik te verhoog vir die toetse met ’n droë verdamping doek. Die uitlaat wat die beste presteer het in die toetse is ’n Windmaster Tornado Wind Turbine, of Whirlybird, wat ’n kommersieel beskikbare konfigurasie is. Die een-dimensionele modelle was nie in staat om die toestande tydens die begin-fase akkuraat te voorspel nie. Die CFD modelle was hoogs akkuraat in die voorspelling van die eksperimentele waardes. Dit word aanbeveel dat ’n twee-dimensionele teoretiese model ontwikkel word om die toestande tydens begin-fase beter te voorspel.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/97110
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