WUFI

The rain load on a surface is calculated in two locations. If the absorption is set to 0 there is no rain load no matter what the driving rain parameters are, However, if the absorption is 1 I seem to get the whole rain without the driving rain calculation. Can you confirm the relationship between the driving rain calculation and the absorption factor (availavle rain)?

Hello Ned,
in the driving rain section the amount of rain is calculated that can hit the surface of your building. The result depends on the inclination/orientation (because of the wind) of the surface and the given factors.

The rain water absorption factor takes into account that some of the rain water hitting the component surface splashes off on impact and is not available for capillary absorption. The calculated amount is reduced by the rain reduction factor (it is the absorption and not the reduction factor - bad translation). Zero is no rain. If you set it to 0.5 50 percent of the amount of the result from the driving rain is avaliable for suction of the surface, if it is 1, 100 percent of the water are avaliable for suction.

However, if the absorption is 1 I seem to get the whole rain without the driving rain calculation. Can you confirm the relationship between the driving rain calculation and the absorption factor (availavle rain)?

That only should happen in case of a flat roof. For a flat roof R1 is usually 1 while R2 is zero (no wind dependency, all water hits the surface). Then by using an absorption factor of 1 the total amount from the climate file should hit the surface. In all other cases, the amount of hitting water gets changed.

BTW: By using "Rain load calculation according to ASHRAE" the amount of rain always gets reduced by the rain factors and always depends on wind. So this can only be used for walls.

Please check also the WUFI Help file by pressing help, there is a description of the factors and coefficients.

Unfortunately there is no posibility to export the hourly rain in Wufi2D for analysis. This can only be done with WufiPro.

Regards,
Christian