Noisy generators cost more as they require sound-proofing, so where you locate it and which model you choose can result in major savings. Here we’ll take you through some of the jargon that manufacturers use and explain what you need to know to secure the most cost effective installation.
Or if you prefer, feel free to call us and we’ll talk you through it.
What is meant by dB(A)?
Sound meters measure vibrations of the air at all different frequencies. Of course the human ear can’t achieve this level of sophistication, and therefore the meter’s responses have to be modified to simulate the human hearing response. This is what is known as a ‘weighting’. Whenever generators are specified or generator noise levels are discussed, 99% of the time it will be in dB(A).
The effect of distance on generator noise levels
The other major factor when discussing noise is distance. The further you are from a noise source the quieter the reading will be. The actual calculation is 20log(r) where r is the distance from the source. However as a quick guide, the noise level will reduce by 6dB for every doubling of distance.
You will see that most of the major generator manufacturers always quote the levels from their canopies sets at 3m. This is because 71dB(A) at 3m looks an awful lot better than 80dB(A) at 1m.
As you can see from the effect that distance has on the measured levels, it becomes very important from a cost point of view to carefully consider the siting of new diesel generating equipment. There can be major cost savings in attenuation equipment and exhaust systems if you can site the set away from possible problem neighbours.
Planning conditions that affect diesel generators
If the new equipment is subject to planning conditions, these will be written around the background conditions in the area.
If it’s an emergency standby set, you may be given some leeway above background (usually about 5dB). However the usual condition is that the noise from the new equipment shall not raise the background at the boundary, or in some cases the windows of a nearby property.
Unfortunately, what the man in the street considers a background is not necessarily shared by the authorities. They use what is known as an (L90). This is where the loudest 90% of the levels read are discounted, leaving the quietest 10% as the benchmark. This means that cars, trains, planes, etc, are removed from the readings just leaving the basic background volume. Again it is very important to site the generator as far away from sensitive properties or designated boundaries if at all possible as this could be a major cost saving.
Cost of noise control
Above a certain level of reduction, the cost of noise control becomes exponential to the levels required. It is relatively easy and cost effective to achieve a reduction of 25dB for a generator. However, the cost could be quadruples for a reduction of 50dB, not to mention the massive increase in space required for the extra attenuation.
5 ways to save money and aggravation:
1) Secure independent advice – dealing with planning authorities can be difficult and tedious
2) Don’t be fooled by plush catalogues which don’t specify noise levels in a way you can understand. Manufacturers want to sell you a generator and walk away. Once the sale is made the problems are yours.
3) Always look to site your generator as far away from potential problems as possible. This may involve slightly larger cables and longer cable runs, but remember, an environmental officer has the power to stop you running your generator.
4) Once an environmental noise problem with a generator has arisen the authorities will keep coming back to check it – make sure you have it installed correctly the first time.
5) Don’t site your new generator in a position to suit the electrical contractor. He is interested in making things easier for his installation.
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