Natural ventilation energy saving potential by CFD

Abstract eng:
Natural ventilation in buildings, an ancient well-known technique, has been widely applied to residential and commercial buildings for its energy saving potential compared to modern mechanical HVAC systems. Since the use of natural (or hybrid) ventilation is closely related to the wind regime, building site, orientation, shape, window/wall ratio etc., a decision regarding its utilization often needs to be made during the early stage of building design, i.e. the conceptual design stage. Therefore, the analysis of natural ventilation potential for energy saving demands a quicker and relatively accurate method, such as using empirical equations, to determine natural ventilation rates and compare ventilation strategies. The paper applies a few empirical equations established by previous specific studies and investigates their applicability for more general use to determine natural ventilation rates for both cross ventilation and single-sided ventilation. By using computational fluid dynamics (CFD) with results validated for both natural ventilation strategies, this study conducted a series of simulations to determine critical ventilation variables as functions of wind direction, speed and building height (i.e. number of floors). The CFD simulations carried out use both steady state Reynolds-averaged Navier-Stokes (RANS) two-equation standard k-ε model and Large Eddy Simulation (LES) model. Natural ventilation rates were determined and energy saving potentials for cross and single-side ventilations were compared. The paper shows that the empirical equations with newly developed parameters can be used for natural ventilation analysis during the building conceptual design stage.

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