5.4 Summary

In section 1.1, a general two-step approach was introduced for the translation of weather station data to driving rain data on a building envelope. Figure 1.1 depicts this approach. In the present chapter, parts of the steps were reported:

• weather station $\rightarrow$ site:
  • the correlation between the hourly wind speed at the weather station of Eindhoven Airport ( $U_{\text{h,EA}}$) and at the TUE site ( $U_{\text{h,\texttt{P1}}}$) seems to be quite independent of the wind direction in the range 180$^\circ$-360$^\circ$, namely $U_{\text{h,\texttt{P1}}} = 0.90 U_{\text{h,EA}}$,
  • the monthly horizontal rain amounts at the weather station and at the TUE site are in good agreement, see table 5.2 and figure 5.5,
• site:
  • the spatial variation of the wind speed and direction at the site was not investigated,
  • the spatial variation of the horizontal rain amounts was investigated with the two rain gauges on the roof of the Auditorium. The measured 5-min rain intensities of the two gauges differ less than 10% (30%) for approximately 52% (83%) of the total collected rain amount,
  • raindrop spectra were measured by our disdrometer during approximately three months. The measured spectra vary much over time. Generally, the measured median drop size is between the two median drop sizes calculated from the parameterisations of [Wessels 1972] with $A=0.88$ and $A=1.77$, respectively, which encompass 90% of his measurements in the Netherlands,
• site $\rightarrow$ building:
  • driving rain intensities vary much at a façade position and on a small time-scale (5 min), even for narrow ranges of reference wind speed, wind direction and horizontal rain intensity (see e.g. figure 5.14 and section 5.2.5). Moreover, the correlation between the two measurement positions P4/5 and P6 is very complex and depends to a great degree on wind direction (section 5.2.6),
  • two empirical models, yet to some extent similar, were formulated to describe the driving rain intensity as a function of wind speed, wind direction and horizontal rain intensity (section 5.3). The same measurement data set was used for parameterisation as well as for checking the driving rain estimates from the models with the driving rain measurements. Model 1, based on the simple empirical formula 5.3 according to [Lacy 1965], yields less realistic estimates of (especially maxima of) 5-min driving rain intensities than model 2, which is our improvement by taking wind direction and position on the façade more explicitly into account (eq. 5.4). However, the models overestimate the cumulative driving rain amounts after 24 months by up to 35-45%,
  • the influence of the raindrop spectrum on driving rain quantities was not investigated.