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Solomed, Sofia. The site’s cooling plant – two chillers – stands outdoors, close to a residential building.
An official measurement by an accredited inspection body showed 61.2 dB(A) at the dwellings (point IT1) against a limit of 55 dB(A) – an exceedance of 6 dB. Right next to the chillers the level was 72.4 dB(A).
The client came to us with the report in hand. The task was clear: a solution that brings the noise below the limit and is proven by a new official measurement.
The chillers stay where they are and must run without restrictions. They are surrounded by walls that reflect the noise. A ramp runs above them – point IT4 is on it, at a height of 4 m. The barrier had to leave access for servicing the machines.
We measured the noise at the same points as the inspection body and made a calculated prediction for a noise barrier around the chillers.
We agreed the prediction for each point in advance with the inspection body that carries out the official measurement: 52 dB(A) at the dwellings, 57 dB(A) at IT2, 63 dB(A) next to the chillers and 50 dB(A) on the ramp.
The barrier was built to the design. At the client’s explicit request, a drainage gap was left at its base for the yard.
After installation, the inspection body carried out a control measurement at the same points. Results in dB(A):
| Point | Before | Prediction | After |
|---|---|---|---|
| IT1 – at the dwellings (limit 55) | 61,2 | 52 | 55,0 |
| IT2 | 66,7 | 57 | 60,5 |
| IT3 – next to the chillers | 72,4 | 63 | 63,3 |
| IT4 – on the ramp | 54,0 | 50 | 50,0 |
At the dwellings the noise dropped by 6 dB – from 61.2 to 55,0 dB(A), i.e. to the limit value. Next to the chillers and on the ramp the prediction was met.
Honestly about the difference: at the dwellings the prediction was 52 dB(A) and we achieved 55.0. The reason is the drainage gap the client asked to keep – noise passes around the barrier through it. We show the result as measured.
Background noise during the measurement: 44.1 dB(A).
A walk around the noise barrier and the chillers behind it, with the sound on site. The sound was recorded on a phone: it gives an idea of what the noise is like, but not how loud it is – the phone evens out the recording level by itself. The measured levels are in the table above.
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