Measurements of Semi-urban Gust Factors for Wind Load Determination
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Wind turbine and building codes used to design photovoltaic installations among other structures, typically use a gust factor to convert wind speeds averaged over 10 min (IEC standards for wind turbines) or 1 h (many building codes) into 3 s averages for determining the extreme wind loads. The IEC standard for small wind turbines assumes the gust factor has a universal value of 1.4, which is close to that used in many international wind loading standards. Ultrasonic wind speed measurements at a height of 50 m in a semi-urban location in north Calgary were sampled at 100 Hz and analyzed to determine the gust factor in a novel manner. 692 h of measurements were obtained and fitted to the generalized extreme value probability distribution function. We find gust factors as low as 1.26 at the 99% confidence interval, corresponding to 3 standard deviations from the mean value. Since the square of the gust factor is used in estimating extreme loads, this represents a 19% reduction in these loads compared to the values mandated by the IEC standard.
KeywordsGust factor Urban wind flow Wind energy Anemometry Wind loads
This work was supported by the Schulich endowment to the University of Calgary. The anemometer mast was provided by WSP, as part of their involvement with an Industrial Research Chair in Renewable Energy funded by NSERC and the ENMAX Corporation.
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