David Frimpong, Head of Specification – New Build at EnviroVent, looks at how housebuilders can better meet acoustic requirements with modern ventilation systems.
“Mechanical ventilation is extremely important in modern, well insulated homes in order to maintain energy efficiency and a healthy indoor environment. However, these systems need to achieve acoustic requirements so that they operate without disturbing occupants. Latest updates to Building Regulations’ Approved Document F sets out guidelines to minimise noise levels from both continuous and intermittent mechanical ventilation systems.
The legislation states that fans need to be correctly sized to ensure that they do not operate near maximum capacity in normal background ventilation mode, as this could cause excessive noise. The Approved Document offers guidelines relating to maximum sound levels, recommending a level of 30 dB LAeq,T* for noise sensitive rooms, like living rooms and bedrooms, and 45Db laEQ,T* for other rooms, such as kitchens and bathrooms. To ensure good acoustics with ventilation systems, sizing and jointing ducts must be correct and developers should ensure that equipment is securely fixed, according to manufacturer’s instructions.
While Approved Document F does not state either specific noise levels nor any requirement for the testing of noise emissions from mechanical ventilation systems, the Government has issued a ‘Domestic Ventilation Commissioning Sheet’ in Appendix C of Volume 1: Dwellings. The document must be signed and submitted by the person responsible for commissioning, within five days to ensure that manufacturers’ guidance has been followed. They must also ensure there are no abnormal sounds or vibrations upon start-up of the system.
So what causes excess noise levels with ventilation?
An article published in the International Journal of Ventilation entitled ‘How loud is too loud?’ identifies a list of potential causes of excessive noise in ventilation systems. These include problems with design, procurement, installation and commissioning of mechanical ventilation systems.
It is important to identify and address these issues which could potentially cause excessive noise from the installation of mechanical ventilation units. Issues are often caused by air flow rates and pressures within the ventilation ducting. It is therefore vitally important that a ventilation system is correctly dimensioned to suit the size of the building, and has an appropriate number of vents.
Correct sizing is essential
Ensuring the correct sizing of the ventilation unit is essential to its long-term efficiency, performance and acoustics.
Sizing the unit is calculated based on a minimum high rate for the wet areas and a minimum low rate, over the number of bedrooms or with a minimum trickle ventilation rate which should not be less than 0.3l/s per m2 of internal floor area. All floors within a building must be taken into account. Correct sizing is based on Approved Document F calculations and system ductwork resistance, with the resistance calculated using our BIM software.
Housebuilders and developers should refer to Approved Document F of Building Regulations for more details. If the airflow rate calculations are incorrect, the fan will not be optimized to push and pull air through the property, resulting in inefficient ventilation.
If the unit is undersized, it could lead to the under performance of the system, with an air flow rate that is too low, which can result in high humidity levels in dwellings. It can also mean a unit has to work extra hard in an attempt to achieve airflow rates, resulting in excessive noise and increased energy usage. When ventilation manufacturers work closely with specifiers from the design stage this can ensure that new homes can meet the requirements for both ventilation and air tightness.
Often the reason for the under sizing of ventilation units is due to space restrictions in the utility cupboard or lofts of new properties, but this can cause serious problems over the long term. Careful consideration should be given to the location of an MEV or MVHR unit as it should be accessible for maintenance.
As well as balancing the air flow rates from one room to the next, it is also important to consider the flow of air entering and leaving a building via external vents.
A study conducted by multidisciplinary building performance experts BPE Specialists states that “where systems are out of balance, either large amounts of colder air are delivered to the dwelling leading to additional heat loads and discomfort, or else larger amounts of warm air are lost to the outside. A large imbalance can also lead to excess system condensation.”
The routing of ducts and positioning of ventilation openings must be carefully planned to ensure adequate air flow, particularly in wet rooms, such as the kitchen or bathrooms, while avoiding noise disturbance in living spaces and bedrooms.
it is essential that commissioning is performed correctly, to ensure long term trouble-free operation of the unit. To correctly balance a system it is important to first ensure that the extract flow rate is the same as the supply flow rate, to avoid the build-up of positive or negative pressure. It is important then to ensure that the air flow rates in the individual rooms is carefully balanced. Both outlet and inlet vents must be adjusted to ensure an adequate supply of fresh air and the removal of stale air.
Care must be taken during all stages of installation to ensure the system is fully compliant with regulations on ventilation acoustics ‘The Noise Policy Statement for England’ refers to a ‘Significant Oerved Adverse Effect Level’ – this is the level above which noise exposure can have a significant negative effect on health and quality of life.
Acoustic measurement
As the effectiveness of a mechanical ventilation unit depends largely on correct installation, it is important that installers are fully trained. In addition, they should be aware that they can consult acoustic specialists, who can perform acoustic measurement and also provide advice on sound attenuation measures and relevant noise reduction products. Correct installation will ensure that there is minimal noise and vibration from a unit. For example, anti-vibrational mounts may be required to help reduce noise transfer from wall or floor mounted units, often in multi-occupancy dwellings.
To ensure acoustics are minimised, it is possible to choose ventilation products that are renowned for being quieter, for example, EnviroVent’s Silent range of kitchen and bathroom extractor fans, as well as the MEV 160/300 continuous mechanical extract unit and the energiSava 300/400 MVHR units, which operate with minimal noise levels.
There are a number of factors to take into account when designing, sizing and commissioning an MEV or MVHR system and it is essential to follow manufacturer guidelines. Ultimately, this will mean better acoustics and enhanced long term performance of the ventilation system, for the benefit of occupants.”