BSEE


Rob Lomax, sales director at Wakefield Acouscs, explores the latest advancements in noise control technology and the potenal to reduce heang, venlaon and air condioning (HVAC) plant noise and meet regulatory requirements within commercial buildings


rowing awareness about the importance of Indoor Air Quality (IAQ), paired with tightening compliance and employment law restrictions to ensure working conditions are comfortable and safe, have seen air conditioning


HEATING & PLUMBING


The sound of silence G


systems become more prevalent in UK buildings, with around 65 per cent of UK office premises and 30 per cent of UK retail space now air-conditioned. And whilst a number of modern-day developments have turned towards natural ventilation solutions, a large proportion of buildings, principally in the public sector, continue to utilise commercial mechanical HVAC systems designed to provide adequate ventilation, heating and cooling for optimum comfort for users. Understandably, when it comes to installing and maintaining HVAC systems the primary focus of specifiers, installers and architects is on ensuring the correct conditions are provided for the building occupants. However, as restrictions on noise pollution from commercial premises, in particular, continue to become more stringent, environmental noise emissions from such equipment are increasingly important to consider.


In cases where HVAC systems are required to be in operation during the night, this is particularly crucial as noise emissions are likely to be more prominent against a backdrop of lower ambient noise levels.


A sound solution


When it comes to addressing excessive noise from heating, ventilation and air conditioning (HVAC) plant, environmental noise should be considered from the outset of development – especially given the often onerous targets imposed on plant noise levels on the back of renewed legislation. Such are the restrictions imposed on levels of noise, that it has become increasingly common for planners to insist upon new plant installations being attenuated to levels as low as 10dB below background noise levels, when assessed in line with BS4142:2014 ‘Methods for rating and assessing industrial and commercial sound’. This, in turn, reduces the possibility of noise from developments having an adverse impact upon the surrounding areas, and thus compromising the amenity of any nearby properties.


Addressing excessive noise from plant items can be a complex task for even the most experienced building professionals. This is particularly true of installations where high levels of noise reduction are required.


Indeed, different noise paths present diverse problems and, therefore, require distinctive solutions. While full acoustic enclosures offer the greatest level of noise mitigation, these can often be impractical in many applications as they inhibit the high air flows required for HVAC equipment including chillers, condensing units and compressors. Without due consideration of ventilation and airflow, plant items can easily overheat or have operational inefficiencies. Noise emissions from an external air conditioning unit, therefore, will likely require a combination of a full acoustic enclosure and acoustic louvres to allow adequate airflow, whilst at the same time ensuring adequate attenuation. However, each solution needs to be specifically designed to ensure acoustic criteria set for the project are achieved. A wide selection of noise control solutions are available for specifiers and installers, ranging from acoustic panel screens to absorbent linings, acoustic louvred screens, attenuators and acoustic enclosures. Establishing the most effective noise control solution, however, often requires expert knowledge.


Supermarket case study


When a major UK supermarket chain encountered planning issues relating to noise from externally located chillers and air conditioning plant, they turned to acoustic specialists Wakefield Acoustics for an effective solution. Much like many modern day buildings, the supermarket’s facilities required fixed mechanical plant to operate on a 24- hour basis. Whilst this ensured optimum comfort for all employees on site, and the integrity of food stored on site, the continuous nature of the equipment had the potential to present considerable issues when it came to noise. The retailer, therefore, understood that unless suitable measures were put in place from the outset of the project, noise from the chiller and air conditioning plant could not only lead to significant disturbances to nearby residents, but also enforcement actions being taken by local authorities. The supermarket development required a number of externally-mounted condensing units for air conditioning systems, along with chillers for cooling of the refrigerators and freezers in the store. Whilst on many sites such plant may not cause any noise issues, due to the equipment’s locality to the rear of the store and its close proximity to a number of residential properties, a degree of noise control was required. To safeguard local residents from potentially disruptive and harmful noise emissions, and to satisfy planning requirements, an initial noise impact assessment was conducted on site in line with BS4142:2014 procedures.


The assessment revealed that the supermarket’s plant items were likely to have adverse impacts on noise sensitive receptors, including causing noise nuisances to residents in the vicinity of the store. And with additional and revised plant items incorporated into the scheme as the project developed, changing the initial noise impact assessment undertaken at the planning stage, there became a clear requirement for noise reduction solutions on site. Following initial consultation, Wakefield Acoustics was commissioned to complete a full acoustic analysis of the site, taking into account the final agreed plant layout and specifications. This ensured that any proposed measures would meet the original design intentions for the project. Wakefield Acoustics identified three major challenges within the specific application. Firstly, all plant items required a high airflow in order to operate efficiently in open conditions, with no obstructions or walls placed nearby. Secondly, the plant needed to operate on a 24- hour basis to provide cooling to the fridges and freezers in the store. Finally, as background noise levels to the rear of the store were particularly low, a high degree of noise reduction was required.


A range of noise control solutions were considered, with the agreed outcome being a series of full acoustic enclosures and acoustic louvres. A large enclosure was constructed to house two chiller units and four condensing units located at the rear of the store. In order to permit sufficient airflow to the chiller and condensing apparatus, 300mm deep acoustic louvre elements were installed to the sides and directly above the plant equipment.


uA large enclosure was constructed to house two chiller units and four condensing units located at the rear of the store


18 BUILDING SERVICES & ENVIRONMENTAL ENGINEER AUGUST 2019


Solid metal acoustic panelling was positioned in other areas of the acoustic enclosure which did not require airflow, this provided direct line-of-sight screening to the windows of nearby properties. All items were mounted into a structural steel framework, with hinged access doors for plant maintenance purposes.


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uSolid metal acousc panelling was posioned in other areas of the acousc enclosure which did not require airfiow


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Addressing


excessive noise from plant items can be a complex task for even the most experienced building professionals


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