Environmental Noise Control

PDA Acoustics has been involved with noise control on various Greencore Group sites since 1988, mainly from the point of view of environmental noise, rather than occupational noise. The latter is governed by the Noise at Work Regulations lending itself to control by traditional enclosures and silencers, or more creative at-source-techniques. Environmental noise usually results from action by the local authority because of complaints from the public. The other angle on environment noise is associated with planning applications for new houses close to the factory.

Two case histories follow.

louvres.jpg (23993 bytes)

A Severe Noise Problem
with a Large Comprehensive Solution

By the end of 1995 HCF Warrington had been in receipt of complaints about noise for some time and had been dealing with problems on a fairly ad hoc basis. The local authority, and local residents had been putting pressure on management to reduce noise until they eventually served an abatement notice.

There is little point in denying the severity of the noise problem with a series of loud whines and broadband noise, 24 hours a day. A detailed computer model of around 100 sources of noise was built, all modelled to two key residential locations. From this a comprehensive series of noise control solutions was established and designed. Numerous potential conflicts between noise control requirements and the site’s extreme sensitivity to any reductions in cooling capacity had to be resolved before PDA was instructed to proceed with the project management of the noise control implementation.

Meanwhile, business was booming and the factory was making even greater demands on its cooling capacity and, two extremely hot summers later, more chillers had been added, all of them significant noise sources. A solution to this had to be found which allowed adequate air circulation for equipment, and which was up-gradable. Often, a solution for a given noise problem needs to be scrapped if it later needs to be upgraded because more of the same equipment is added. The solution was a set of huge acoustic louvres fitted to a tracking system which allows for more to be fitted if more noisy equipment is installed and designed to allow negligible resistance to warm air escape.

Our latest commissioning survey involved no measurement at all as the factory was completely inaudible in the presence of the background noise, except that is, for the sound of a water tank filling which is no more intrusive at the houses than, say, a garden water feature.

silencer.jpg (17658 bytes)

A Severe Noise Problem with No Solution at All

PDA was asked by HCF Plymouth to investigate vigorous complaints about noise and action by the local authority, and to design and implement noise control solutions as required.

In the cold early hours of a January morning we were on site to carry out the basic assessment of the factory noise and the background noise (i.e. the noise climate with the factory shut down). Communicating by walkie-talkie, we asked engineers to shut down the equipment most likely to be the main culprit. The idea was rather like weighing a bowl of sugar: we weigh the empty bowl, then the bowl with the sugar in it - the difference is the weight of sugar alone. So here, we measure the noise with all items running, then without the "noisiest" item, and we know how much noise the "noisiest" item makes on its own.

Here, however, no change in noise, either subjectively or by measurement, could be detected. Clearly this item was far from being the noisiest. By the time that engineers had shut down the six most likely noisiest items, we asked them to shut down the factory completely. They appeared unable to do this, with me insisting that the noise climate at the houses had not changed, despite engineers, and then my colleagues, assuring me that the whole site was indeed shut down.

"Is this the noise you can hear?" said an engineer to me over this walkie-talkie. He then held the walkie-talkie up against the offending equipment and sure enough, the source was found. It was a compressor from an entirely different factory and not the HCF factory at all.

HCF Plymouth
Graph showing the factory Noise Level at the Nearest House Against the Ambient Noise

OCTAVE BAND CENTRE FREQ

dB(A)

31.5

63

125

250

500

1k

2k

4k

8k

16k

Leq Level without Factory Running

39.3

50.0

45.0

41.0

38.0

38.0

35.0

28.0

22.0

17.0

13.0

Leq Level of Factory Running Alone

38.1

57.3

48.3

47.0

38.0

35.7

29.1

29.8

23.8

11.1

7.1

noise123.gif (4650 bytes)

For further details, contact:

Andrew Raymond, PDA Ltd., Vincent House, 212 Manchester Road, Warrington WA1 3BD

Tel: 01925 418188
Fax: 01925 417201
email: PDA_Ltd@compuserve.com


	Revised: December 01, 2004. Copyright © 1999/2005 Greencore Group plc. All rights reserved
	Design by drakesvision