Wind turbine noise at neighbor dwellings, comparing calculations and measurements

Danish wind turbine noise regulation (currently BEK 1736) is based on calculated noise levels at residents from sound power level measurements at a wind speed of 6 and 8 m/s (10 m height). Doubt has been raised on whether the above-mentioned method gives the same results as actual measurements where residents live. The Danish Environmental Protection Agency (Danish EPA) has therefore initiated several projects with noise measurements at residents. DELTA has conducted one of the measurement campaigns where synchronized measurements were carried out both close to the turbines (IEC distance), at an intermediate position and at the residents - both indoor and outdoor. The project consists of two types of measurements, the first being highly surveyed short term measurements of 2-3 hours and the second being long term continuous measurements. The two different approaches ensure that different ranges of wind direction and wind speed were included in the measurements and hence describe the noise around the turbines and not necessarily only in downwind direction. The short-term measurements ensure that part of the measurements is conducted in a close to controlled environment. The results of the measurements are compared with the calculated values. The calculations are carried out using the prescribed method in BEK 1736 and a more advanced model, in this project the Nord2000 model. The goal of the comparison is to clarify the following: I) Are there systematic differences between calculation and measurements both indoors and outdoors? II) What is the uncertainty using measurements contra calculation? III) Does other wind speeds and directions than 6 and 8 m/s cause the wind turbines to emit more pronounced tones or low frequent noise than expected?