Niederländische Vorschrift, 2011 (Englisch)

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The Dutch calculation method from 2011 is described in “Reken- en meetvoorschrift windturbines” from 2/2-2010. It is based on the Lden principle and use an adapted version of ISO 9613-2 as propagation model.

Calculation setup

The calculation model is selected by choosing Dutch 2011 as Noise calculation model.

Wind speed

The Dutch 2011 code operate with average noise received day, evening and night. In order to calculate how much noise on average is emitted in each time period, an average octave band distribution is calculated. This is based on the octave band distribution at each wind speed bin from cut in to cut out weighted with the frequency of that bin.

The octave band distributions for each wind speed bin must be found in the wind turbine catalogue. It goes without saying that it requires a fairly complete set of data, something which will rarely if ever be present among the default values in the catalogue. If only a limited amount of wind speeds will be available windPRO will interpolate between them, set noise below cut-in to 3 m/s and set the noise constant when extrapolating from the highest wind speed to cut-out. If no octave band distribution exist for a specific wind speed windPRO will scale the octave band distribution of the closest wind speed. If no octave band distribution exists at all windPRO will fit a generic octave band distribution to the total noise level. This is of course insufficient for a correct calculation.

The frequency of each wind speed is found from a database provided by KNMI and found on the web site www.windenergie.nl . Based on the location of the site center of the project windPRO looks up this location in the database and extract the frequency table for day, evening and night. This database describe wind speed between 80 and 120 m hub height. Outside this range windPRO applies a logarithmic fitted profile to find the Weibull distributions. It is important to note that while the code allows for this procedure, the procedure is not defined.

The formula for calculating the average noise for each time period is described in more detail in appendix.

Ground attenuation

The ground attenuation factor is defined for values of 0 and 1, but it is allowed to use any value in between. As default a terrain map can be used to calculate ground factor values, but alternatively a uniform value can be used.

Meteorological coefficient, C₀

For distances less than 10 times hub height (actually 10 times difference in z coordinate of hub and receptor) the meteorological coefficient, C₀ is 0. Beyond that distance C₀ is a function of distance and direction from turbine to receptor in the way that maximum C₀ is achieved downwind from the turbine.

The function for calculating C₀ is described in appendix.

Type of demand in calculation Only noise from WTG’s is taken into account.

Noise values in calculation windPRO will on its own present all values as Lden values although sub-results present Lday, Levening and Lnight specifically.

Pure tones Pure tone penalty are subtracted from demand.

Height of immission point above ground level There is no mention in the code of receptor height. For the calculations it is set to 5 m.

Deviation from official noise demand This field is open to the user.

Edit period The Dutch codes operate with noise values as Lden, where den is an abbreviation of day-evening-night. It represents a weighted average of noise, where noise during evening and night is penalized. The parameters can be seen or modified by pressing the Edit period button as seen below.

The period definition of day, evening and night can be set here, as well as the penalty due for each period.

Noise receptors

The general noise limit in The Netherland is 47 dB Lden and 41 dB Lnight. The default setting for a Dutch receptor is 47 dB and this is also the noise value used on the noise ISO line report, but both Lden and Lnight can be found in the noise report.

Noise data for WTG

As described in a separate section below an individual noise mode can be selected for the three periods as part of advanced settings of the turbine.

Source noise data for the turbine is based on wind speed at hub height. If data for the turbine is only given at 10 m height they may need to be converted to hub height (section 2.6). Since a calculation is made for each integer wind speed at hub height it may be preferable to convert 10 m height wind speeds to hub height integer wind speed even though that means an interpolation of data points.

Calculation Background

The Dutch codes require the calculation of an L_den value for each receptor.

The L_den value has the formula

The L_eq noise value is calculated independently for the three situations: day, evening and night (L_dag, L_avond, L_nacht). In each case the formula is:

"I" is the 8 octave bands,

"n" is the number of turbines.

The noise at each octave band is calculated as:

D_ref, D_scherm, D_veg and D_terrein can all be ignored.

L_E

L_E is the source noise emission. This is different from most other codes.

The L_E is the average noise emission from the turbine. The formula is the below:

The summation is done for each wind speed bin from V_ci (cut-in) to V_co (cut-out). At rated power it is assumed that the noise level does not change.

U_j is the frequency of the particular wind speed.

∆L is a direction component, which is usually not available and is therefore set to 0.

From this it is clear that a Weibull distribution is required at hub height for each turbine. This is done automatically with reference to http://www.mp.nl/rekentool/ . The codes recommend to use this resource however it only defines wind climate for height between 80 and 120 m. For heights outside this range windPRO fits the defined wind profile to a logarithmic function to extrapolate the Weibull distributions to higher and lower heights.

D_geo

This is the geometric damping. It is identical to the ISO 9613-2 standard.

"r" is distance from turbine to receptor.

D_lucht

This is the air absorption. The formula is the same as in ISO 9613-2 but the damping’s are different.

D_bodem

This is the ground absorption. This is similar to the general ground attenuation of the ISO standard.

The regions are defined in the same way:

Near area:

Remote area:

Middle area:

Everything in between.

B is the ground porosity: B=1 absorbing, B=0 hard.

In windPRO it is possible to use a universal ground porosity is selected by the user to cover all three regions for all turbine receptor couples or link to an area object defining areas with ground porosity 0 assuming everything else is 1.

The three components are added:

Unfortunately the damping in each frequency is different from ISO 9613-2.

h is hub height.

The D_mid is calculated as

C_meteo

C_met is defined as

h_b is hub height, h_o is receptor height.

Beta is the angle from downwind from turbine to receptor.