Plus:Dialog Orientation

Driving Rain

The driving rain coefficients (3) are used to estimate the driving rain load on the building component. The rain load on a wall is determined by the driving rain rather than the normal rain. Two different methods are offered by WUFI:

The driving rain coefficients R1 and R2 serve to estimate the driving rain load on a surface of arbitrary orientation and inclination from data on normal rain, wind velocity and mean wind direction, using the relation

 Driving rain load = rain · (R1 + R2 · wind velocity),

where 'rain' is the normal rain and 'wind velocity' is that component of the mean wind velocity (measured at a height of 10 m, in open area), which is orthogonal to the building surface. This component is determined from the mean wind velocity and the mean wind direction. The data on normal rain, wind velocity and wind direction are read from the selected weather file.

R1 and R2 are strongly dependent on the specific location on the building facade. For vertical surfaces, R1 is zero. R2 is about 0.2 s/m for free-standing locations without influence from surrounding buildings etc.; it is markedly less in the center of a facade (e.g. 0.07 s/m); it may even be greater at exposed locations of a building (near edges and corners).

If you have selected an inclination of 90° for your component, WUFI offers you a few predefined rain coefficients: one for a low building and three for different heights on a tall building. Advanced 3-D computational fluid dynamics simulations of droplet flow have been used by [Karagiozis and Hadjisophocleous, 1997] to determine these coefficients. Select the coefficients by clicking on the graphical building symbols or by choosing them from the drop-down list.

Of course, you can also enter arbitrary rain coefficients in the text boxes. In particular, you can use experimental values that have been measured for a specific location.

If you have selected another inclination than 90°, the situation becomes too complex to be cast into a simple multiple-choice option list. In this case WUFI defaults to the rain coefficients R1=1 and R2=0 (i.e. rain load = normal rain). It is then up to you to determine and enter appropriate rain coefficients.