A modification of the power-law equation to account for large scale wind turbulence.

Existing infiltration and exfiltration calculation methods are mainly based on the stationaryapproach, where long term mean values are used for wind input data. The real wind speed is,however, varying continuously with time. Because the process of the crack flow is non-linear,using mean wind speed values will give erroneous results for the air flows. The goal of theresearch has been to develop a simple method to account for the effect of large scale windturbulence on the calculated air flows.A modification of the power-law equation has been derived based on the assumption ofsinusoidal wind speed fluctuation. The equation is integrated over time to form a newturbulent power-law equation. The integration is carried out numerically using the simpletrapezoidal rule approximation. This equation can be used in flow computation in the place ofthe ordinary power-law equation. The additional input data needed for such a computation isthe wind turbulence intensity.The performance of the turbulent power-law equation is tested computationally by comparingits results against the results of a theoretically far more detailed calculation method, whichtakes into account the dynamics of the air in the cracks and the capacity of the building space.The computations are carried out using Simon, a program specially designed for simulationof non-linear systems. Real, with one second time interval measured wind speed has beenused as input data. A simple building model with two floors and eight cracks in the walls hasbeen used as a test case. The results show, that the error in the flow rates caused by thestationary approach is mainly dependent on the flow exponent and the turbulence intensity andvaries roughly between 0 - 20 %. The higher the turbulence intensity and the more laminar thecrack flow, the higher is the error. The turbulent power-law equation performs well and iscapable to reduce this error by roughly one decade.