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Graham Laws, Business Development Officer at Siderise Group, provides some sound advice on HVAC acoustic design and offers up proven ways to deal with a potentially noisy issue.

Noise is an all pervasive facet in our lives, from the early morning alarm clock right the way through our working day. But does it need to be that way? When you consider that the estimated cost of noise pollution runs into billions of pounds according to DEFRA, architects and engineers have had to think long and hard on how to build out noise from buildings. With building services a well-known source of undesirable noise and vibration, what is the most cost effective way to reduce undesirable sound, whilst delivering noise control, air flow and thermal performance? Graham Laws, Business Development Officer at Siderise Group, provides some sound advice on HVAC acoustic design and offers up proven ways to deal with a potentially noisy issue.

Noise and vibration in building services come from a wide range of mechanical and electrical systems, everything from fans to variable air volume systems, grilles and diffusers to roof-top units, fan coil units to chillers, compressors and condensers, pumps and stand-by generators, boilers and cooling towers. All this unwanted noise can make a workplace environment uncomfortable and less productive.

Through the increased requirements for energy efficiency, buildings are better insulated and isolated, both thermally and acoustically. However, this further drives the need for ventilation and thermal management, and this required airflow can then introduce noise issues of its own, both break-out and in-line noise.

Sound matters

Break-out noise is where sound transmits through the wall of ducting and into the room through which the ductwork is travelling. In-line (duct-borne) noise or noise traveling through ductwork, can create unwelcome high levels of background noise if not properly managed. This noise can raise stress levels in the workplace, harming communication and concentration and increasing fatigue. A poorly designed acoustic solution can potentially exacerbate issues by causing regenerative noise, and negatively affecting airflow.

An additional issue to mechanically generated noise via the HVAC system is cross- talk, whereby speech privacy is compromised by room-to-room transmission via the ventilation system. A good example is in an office building where employees on one floor might hear conversations via the return grille. Even when intelligibility is not an issue, concentration and therefore productivity can be affected by those in adjoining rooms.

The essence of optimal practise comes down to:

  1. Understanding the legislative requirements of the building
  2. Understanding the design requirements of the building
  3. Optimising noise control treatments at source
  4. Optimising system design for airflow and regenerative noise
  5. Minimising breakout from ducts and air handling units
  6. Minimising structure borne noise

Meeting requirements

All buildings represent unique challenges, whether they are offices, schools, hospitals or commercial structures. In the education sector, noise and poor acoustics are an increasingly important issue. For example, in a school, there will be both separation requirements and background noise level requirements for the project.

These can be provided as a single figure rating or noise rating (NR) value, or as octave band values. When it comes to the design of a building, it’s vital to know the function of each room, and both the desired speech privacy and NR level. NR values are a way of describing, as a single figure, a measured noise level that takes into account the frequency content of the noise.

They are often used in the measurement of noise from mechanical sources such as air conditioning systems in environments such as hotels, cinemas and schools. Most buildings will have an ‘in-room’ NR level requirement based on function. For example, typical noise rating values for a concert hall or church would be NR25 while a school or hotel would be NR35, significantly less than say a factory or a noisier engineering environment which would have an NR70 rating. To ensure these levels are achieved, a given Sound Power Level (LwA) for the HVAC unit is required.

Noise Control Treatments

In terms of the system design, air velocity within a duct system influences the noise levels significantly. Regenerated noise can be created by transition pieces, bends, dampers, grilles and diffusers. Regenerated noise can be reduced by limiting the air velocities within the duct system, by easing transitions in the system design and by ensuring that internal acoustic treatments contain chamfers where appropriate to reduce the turbulent effect of sudden changes in opening or direction.

When two adjacent or closely positioned rooms are sharing the same ductwork, sound travels within ducts and will decrease the room-to-room sound insulation dramatically. This will of course impact speech privacy and negatively affect the working environment through disturbance.

Vibration and sound energy from HVAC operation will transmit to a structure and be redistributed around a building. By isolating your systems from the structure before it has a chance to vibrate, through isolation mounts or decoupled through flexible linkages from the structure via the noise source and the duct runs, another path of noise has been reduced through physical materials.

Solutions provider to manufacturers

With more than 40 years’ experience providing noise control treatments to manufacturers in the HVAC sector, SIDERISE offers a range of noise control solutions which can be tailored to meet project specific design and performance requirements. SIDERISE HV-NC noise control solutions, for example, are tailored to the octave band requirements of your HVAC unit, thereby delivering the optimum acoustic performance at the minimum cost. Manufactured from high performance open cell acoustic foam, parts are designed to ease airflow and lower regenerative noise, and the lining treatment is engineered to deliver the lowest possible Sound Power (LwA). These acoustic solutions give exceptional noise absorption, yielding reduced airborne noise at inlets and outlets, and lowering case radiated noise.

Lining kits are Class 0 fire rated to EN 13501-1 to comply with Building Regulations Approved Document B.

Offering ease of installation, SIDERISE noise control solutions are supplied as a pre-cut kit, backed with high performance modified acrylic adhesive for rapid installation on a manufacturer’s assembly-line; and offer exceptional performance for fan coil units, air handling units and heat exchangers.

Remedial treatment – building services

For an existing building with a ductwork ‘in-line’ noise problem, SoundPAC is an easy and cost-efficient way to introduce noise control. At the terminal ends, where air is being delivered to the occupied spaces, you can remove the grille and simply install the SoundPAC inserts. Inherently flexible, the inserts are ideally suited to retro-fit installation, particularly in situations where there is minimal access and/or where less disruption is a consideration. For ‘duct noise breakout’ another solution, which contributes well to quiet air-handling, are the DWX and DPF-RL external acoustic treatments, which are externally applied. Easy to install without disturbing the HVAC system, this solution reduces break-out noise by providing a combination of acoustic absorption and sound reduction via inherently damped flexible mass membrane.

We live in a very noisy world but by proactively considering potential acoustic problems at the design stage of an HVAC system and adding sound control measures to minimise unwanted noise, building owners will have a far quieter system, which in the end, can go a long way towards promoting comfort and productivity.

SIDERISE through a broad range of products and solutions are able to provide a holistic treatment to all areas of HVAC noise, ensure that a peaceful, stress-free and productive environment is experienced by all.

For further information about SIDERISE HVAC solutions or for specific technical advice contact our .

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