Declining decibels – putting HVAC on mute

Dealing with excessive noise from heating, ventilation and air conditioning (HVAC) plant within commercial and residential buildings can require complex and extensive noise control solutions. Rob Lomax, Sales Director at Wakefield Acoustics, explores further.

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aced with a need to improve amenity while ensuring noise levels remain below strict environmental limits, contractors, architects and specifiers are increasingly turning to noise control technologies as a means to deliver practical and cost-effective solutions.

Large numbers of commercial and residential developments rely on HVAC systems to provide adequate ventilation, heating and cooling. While these systems obviously improve the conditions for people inside the building, specifiers and architects need to consider the environmental impact of the breakout noise they emit.

Such considerations are usually made at the start of the project and it is not uncommon for challenging targets to be set by planners. New plant installations are often required to attenuate noise levels to as low as 10dB below background when assessed in line with BS4142:2014 ‘Methods for rating and assessing industrial and commercial sound’. The aim of these targets is to prevent noise from developments adversely affecting the amenity of the neighbourhood.

Meeting these targets is particularly challenging in cases where HVAC systems are operating during the night as the lower background noise levels mean their noise emissions will be more pronounced.

Quiet HVAC solutions

Mitigating noise from HVAC plant can be a complicated undertaking. Differing noise paths pose an assortment of issues and require a variety of solutions. The most effective noise mitigation comes from the installation of full acoustic enclosures; however, these can impede the high airflow required by some HVAC systems and so are not feasible for all applications. To attenuate noise to levels which meet the acoustic criteria set for the development, each solution needs to be purposely designed.

Contractors, architects and specifiers have a varied collection of noise control solutions at their disposal. These include attenuators and acoustic enclosures, acoustic panel screens, absorbent linings and acoustic louvres. However, putting the best solution in place can require specialist knowledge. As no two plant installations are identical, there is no one-size-fits-all solution. Finding the most effective noise control solution necessitates detailed deliberation of many factors, including the system’s function, location and noise levels.

When considering local amenity, another issue is the unappealing appearance of HVAC systems. Here, noise control solutions can play a double role, with more visually appealing louvred screens and acoustic panel walls helping to conceal unsightly plant. This can also increase security for plant items.

To overcome these challenges effectively, specifiers and architects are increasingly turning to noise control specialists to implement the solutions that deal with excessive noise from HVAC plant items.

Low level noise

When a leading UK supermarket company faced planning issues concerning noise from external chillers and air conditioning plant, acoustic specialist, Wakefield Acoustics, was asked to provide an effective solution.

The supermarket required the plant to operate 24 hours a day to ensure the integrity of its stock and provide comfort for employees. The development included externally mounted condensing units for air conditioning systems, together with chillers for cooling of the refrigerators and freezers in the store.

A preliminary noise impact assessment, undertaken on site in line with BS4142:2014 procedures, indicated the plant items would have a negative impact on noise-sensitive receptors, including causing noise nuisances to nearby residents. As further plant items were then added to the project, it became clear that noise control solutions were required to safeguard local residents and remove the potential for local authority enforcement action.

Wakefield Acoustics was commissioned to carry out a full acoustic analysis of the site which assessed the final agreed plant layout and specifications. This ensured that any noise control measures would fit in with the project’s design intentions.

The analysis identified three significant challenges. Firstly, to operate efficiently in open conditions, high airflow was required by all the plant items and this meant there could be no obstructions or walls nearby. Secondly, to maintain goods in refrigerators and freezers, the plant needed to operate on a 24-hour basis. Finally, the low level of background noise at the supermarket’s rear meant a high degree of noise reduction was required.

Following consideration, the agreed noise control solution was a series of full acoustic enclosures and acoustic louvres. A large enclosure was built to house two chiller units and four condensing units situated at the store’s rear. This incorporated 300mm deep acoustic louvre elements at the sides and directly above the plant which enabled sufficient airflow for the chiller and condensing equipment.

In the areas of the acoustic enclosure which did not require airflow, solid metal acoustic panelling was used. This screened the plant from adjacent properties whose windows were in direct line of sight. All items were mounted into a structural steel framework and, for easy plant maintenance, this was constructed with hinged access doors.

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