Evaluating the effectiveness of current standards for designing Natural ventilation systems in hot climates and potential enhancements
Mourad Aziz, Mourad Magdy
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Over the past decade, the ventilation of domestic buildings in hot climates has been dominated by the mechanical systems with its centralized and standalone forms. The domination was initially sparked by the global warming thread, but it was later promoted by a financial incentive to the landlords which is the increased leasable areas due to reduced floor-to-floor height and absence of vertical stacks, shafts or Atriums. Other triggers for the mechanical domination were the elevated standard of living, absence of firm regulations in the hot countries that enforces the consideration of natural ventilation and lack of Architects who understand the fluid dynamics and can design an effective naturally ventilated building in hot climate, which is much more complicated in design than mechanically ventilated buildings, from the architectural point of view. However, the Natural ventilation strategies have recently been brought back to the scene by various local and international sustainability rating systems as potential tool for energy saving and clean indoor air quality. Due to the absence of local regulations and NV design guidelines, the sustainability ratings systems had to reference other codes and standards that were initially developed for cold and warm climates to set out their rules and targets. In this study, four common design standards were explored and applied on a case study in hot climate to stand upon the level of effectiveness of such scheme. According to ASHRAE (2016), the hot climate has an annual cooling degree day between 3500 °C to 5000 °C for a base temperature of 10°C. The study also tested some additional strategies on the case study to understand the potential enhancements. The study found that one standard only was able to achieve the targeted air flow rate, however, this air flow was achieved only at the window location and it was insufficient to achieve thermal comfort inside the room. The single sided enhancement strategies have indicated a potential improvement of 250% while the cross-ventilation strategies have indicated a potential improvement over the 1000%. These findings suggest the need for a climate specific design standard that provides full guidance on all system parameters, including the internal clear heights, facades treatments, design of system components such as stack, atrium and air ducts.