Niederländische Vorschrift, 2011 (Englisch)

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The Dutch calculation method[1] is based on the Lden principle and uses 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.

DE UMWELT DEC (12).png


Wind speed

The Dutch 2011 code operates 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 are 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. In WindPRO is possible to choose the currently valid database from 2018 or the pre 2018 version. The 2018 version is documented here and provides wind distribution data in a dense (2.5km) grid across The Netherlands with data at 14 height levels from 10 m to 260 m. For hub heights in between the provided elevation levels an interpolation is made. 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.

DE UMWELT DEC (12.1).png

Note that because the Dutch method is linked to this database the Dutch method can only be used within the coverage of the database, meaning The Netherlands.

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.

DE UMWELT DEC (13).png


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.

DE UMWELT DEC (14).png DE UMWELT DEC (15).png


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Calculation Background

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

The Lden value has the formula

DE DEC Dutch1.png

The Leq noise value is calculated independently for the three situations: day, evening and night (Ldag, Lavond, Lnacht). In each case the formula is:

DE DEC Dutch2.png

"I" is the 8 octave bands,

"n" is the number of turbines.

The noise at each octave band is calculated as:

DE DEC Dutch3.png

Dref, Dscherm, Dveg and Dterrein can all be ignored.


LE

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

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

DE DEC Dutch4.png

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

Uj 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.


Dgeo

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

DE DEC Dutch5.png

"r" is distance from turbine to receptor.


Dlucht

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

DE DEC Dutch6.png

DE DEC Dutch7.png


Dbodem

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:

DE DEC Dutch8.png

Remote area:

DE DEC Dutch9.png

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:

DE DEC Dutch10.png

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

DE DEC Dutch11.png

h is hub height.

The Dmid is calculated as

DE DEC Dutch12.png

Cmeteo

Cmet is defined as

DE DEC Dutch13.png

hb is hub height, ho is receptor height.

Beta is the angle from downwind from turbine to receptor.


References:

  1. Reken- en meetvoorschrift windturbines, 2/2-2010


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