Field Measurements of Wind-Driven Rain on Mid - and High - Rise Buildings in Two Canadian Regions

Wind-driven rain (WDR) is an important boundary condition for the study of the hygrothermal behaviour and durability of building envelopes. Understanding the WDR characteristics is important for establishing designs that minimize the moisture related issues. The objectives of this study are to generate a unique set of measurements to characterize the WDR distribution on mid- and high-rise buildings for different Canadian climatic regions, to provide data for validating CFD models and to evaluate the accuracy of existing semi-empirical methods used for quantifying WDR loads on building façades. Three buildings located in two Canadian cities (i.e., McLeod House in Fredericton; HB and FB Building in Montreal) have been instrumented with equipment to simultaneously record local weather data of wind speed, wind direction, temperature, relative humidity, horizontal rainfall, and WDR loads on building façades. Onsite data, collected for fourteen months from McLeod House, fifteen months from HB Building, and twelve months from FB Building, has been used for analysis. The historical and onsite wind and rain conditions, spatial distribution of wind-driven rain on façades in terms of catch ratios and wall factors, and comparisons between measured and predicted wind-driven rain using the semi-empirical models are reported for the monitoring periods.
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\nThe analysis of field measurements shows that catch ratios vary with rain events with higher values at the corners and edges of the façades. Typically catch ratios are higher at the top of the facades and decrease towards the bottom. The catch ratios are higher for the thirteen story high-rise building compared to the four and seven story mid-rise buildings at the same height below the roofline. Catch ratios are higher when approaching wind is normal to the façade and values increase with the increase of wind speed. Discrepancies between the ISO standard suggested wall factors and wall factors calculated based on measurements are observed for all three test buildings. It is found that the wall factors vary along both the building height and across the building width, while the ISO standard only suggests two values along the building height with no change across the building width. The ISO semi-empirical model overestimates the WDR at all monitored façade locations on McLeod House and HB Building, and 83% of the monitored façade locations on FB Building. The ASHRAE 160 model overestimates the WDR amount largely for most of the monitored façade locations of the test buildings. The discrepancies between measurements and predictions using semi-empirical models are due to the lack of variation of wall factors across building façade suggested in the standards and limited number of building geometries. The errors associated with WDR measurements vary with rain events with the maximum error contributed by adhesion-water-evaporation, however, the total amount of error is small as compared to WDR amount. To improve the semi-empirical models for estimating WDR on façade, wall factors based on field measurements on buildings with a wider range of building geometries and at more façade locations are needed.

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