Wind-driven air infiltration has been recognized among the major reasons for energy loss in buildings, and the impact to energy efficiency under steady conditions has been reported and issued as part of many building codes. The nearly zero-energy building demand makes uncontrolled leakage paths even more undesired and creates the need for further investigation of their behavior under unsteady wind conditions. The present numerical study examines the role of wind gustiness on instantaneous infiltration rates of a low-rise building. For this purpose, two levels of gust frequency Ω have been simulated, expressed as a sinusoidal factor in the wind profile formula. In parallel, a ratio α is employed to represent seven different cases of external leakages distribution, while five scenarios of compartmentalization and internal leakages shows the impact of the latter on the dynamics of building air exchange rates. The results indicate that higher wind gustiness results in higher ACH, marking out gusts as a potential critical factor under unsteady climate conditions. The infiltration rates shown in relation to the leakage distribution ratio α provide arguments for the importance of the detailed detection of external leakages while the comparison of the different internal-volume-scenario highlights the key-role of internal leakages control towards a drastic reduction of infiltration rates.
Wind pressure coefficients (Cp) are important values for building engineering applications, such as calculation of wind loads or wind-induced air infiltration and especially for tall buildings that are more susceptible to wind forces. Wind pressure coefficients are influenced by a plethora of parameters, such as building geometry, position on the façade, exposure or sheltering degree, and wind direction. On-site measurements have been performed on a twin medium-rise building complex. Differential pressure measurements have been employed in order to determine the wind pressure coefficients at various positions along the windward façades of the twin buildings. The measurements show that one building provides substantial wind shelter to its twin and the microclimatic effect is captured by the measured wind pressure coefficients. They also showed that the wind pressure coefficients vary significantly spatially along the windward façades of the medium-rise buildings. Furthermore, the pressure measurements showed that the wind pressure coefficients fluctuate significantly during the measuring period. The use of the fluctuating Cp values by means of probability distribution function (pdf) for the calculation of air infiltration has been evaluated. The results indicate that the air flows deriving using fluctuating Cp values are more accurate than the ones calculated by the conventional method of using mean Cp values.
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