Okermühle Custom-made sound insulation for the source of the grain

Hedwigsburger Okermühle, located in the district of Wolfenbüttel in the middle of one of Germany’s wheat growing areas, is amongst the largest mills in the country. Seven hundred tonnes of wheat are ground there everyday. As a specialist for wheat milling products, the company produces different types of flour as well as special products for the food and pharmaceutical industries. In 2019, the company invested in the construction of new silos with fully automated control of the filling and emptying systems.

The Hum

For cooling and ventilation of the stored grain, four fans with a total air capacity of 160,000 m³/h are in operation outside the new silo facility.

Connected to pipelines on the pressure side, a hum – that is, low-frequency noise – is generated, which most people find extremely unpleasant. Due to their long wavelengths, these noises are generally difficult to locate and spread quickly throughout the entire environment.

In order to efficiently reduce sound propagation and noise pollution in the surrounding residential environment, individually adapted noise control coverings were designed for all fans used. The coverings surround and completely insulate the noisy fans and prevent the propagation of disturbing noise emissions by means of an sound-absorbing lining and a supply air silencer.

The guidelines for the design, construction, shape and size were taken from DIN EN ISO 3740, which stipulates a specified final sound level of 60 dB(A) at a distance of 10 m under “free field” conditions.

The noise control coverings were constructed in a robust design and consist of galvanised sheet steel in the appropriate material thickness and with the required insulation to ensure they will be resilient against outdoor conditions and weather. Maintenance doors allow easy access to the inside of the enclosure.

An additional requirement for the design and construction of the noise control coverings was the ventilation for the fans. The heat generated by the drive motors should be dissipated without additional ventilation components. This was solved by a free intake of the fan in the covering. Fresh air is drawn in via the roof surface by means of an additional supply air silencer with rain hood. The required process air is thus used to cool the drive motors.