Managing noise from your CHP
How decisions at the planning stage can help you comply with noise regulations
Cogeneration can have a key role to play in an energy strategy that focuses on the increasingly important areas of improved energy efficiency, lower cost and reduced emissions. It is also a leading technology when looking at a decentralised distributed energy plan. When considering a CHP system there are a number of factors to consider, one of these is noise. Understanding the noise associated with a generating system is a key, especially as there are regulatory and environmental requirements.
Combined Heat and Power (CHP) is covered by two different sets of requirements from and environmental and regulatory perspective. First there is The European Noise Directive from the EU that was passed in 2002.
The second is the control of noise at work regulations (2005) the aim of the Noise regulations is to safeguard workers' hearing, to ensure it is not subject to excessive noise in the workplace. The aim of these regulations is to prevent loss of hearing or the development of tinnitus.
It is important to secure compliance by choosing a CHP supplier that is aware of the different elements within the system that can impact on the noise outputs and that can offer different options to help you.
When looking at the location of the proposed CHP it is important to consider the following:
- Positioning – where is it going to be situated (internally in a plant room or external to a building? Are there any noise considerations to manage?
- Local restrictions – if it is new location it is important to check with the local planning and environmental authorities if there are any specific noise restrictions
- Nearby housing – if there is a residential area nearby there may noise standards that are more restrictive than those advised in national legislation.
Current noise standards are based on a daily or weekly exposure and is sound pressure measured in decibels and is A weighted. The level where businesses must assess the risk is 80 decibels at 1m and at 85 decibels at 1m a business most provide hearing protection. There is also an exposure limit value of 87 decibels at 1m, taking account of any reduction in exposure provided by hearing protection, works should not be exposed to anything above this.
Noise should be taken into consideration for every type application, whether you are looking at a CHP for a leisure centre, a hotel, a factory or hospital it is important to ensure you choose a supplier that actively limits noise exposure from its equipment.
Where does the noise come from?
There are various component within and connected to CHP system that can cause noise:
- The ventilation system
- The engine itself
- The exhaust system
- Auxiliary equipment (such as fans or radiators)
- Vibration from equipment
How can this noise be managed?
A responsible supplier will look at all the different element within the system to look to reduce noise. Confirm that your supplier has options for noise attenuation across the system that can adapt to specific site needs. Health and safety compliancy is paramount as workers need to be in a safe environment that operates to the correct noise levels.
CHP systems should always come in some form of acoustic enclosure whether this is to be sited internally within a plant room or as an external freestanding piece of equipment. A variety of noise options should be available, but systems that operate between 65dBA@1m and 75dBA@1m will meet all noise requirements. It is important to be aware that the enclosure needs to allow for access and maintenance of the CHP unit, ensure this access will not compromise any noise abatement.
Air intake & Ventilation
The air intake for generator cooling should be fitted with an attenuator. The attenuator reduces the generator breakout noise and should be designed specifically for the generator noise frequency spectrum. Where the ventilation air is extracted via fans, these should have a noise attenuator added also.
It is important to confirm with your supplier that their noise reduction systems are designed to adapt to the type of engine they are supporting. Different engines have different noise profiles across the frequency range so noise reduction must be balanced to that.
The Exhaust system
For the exhaust system a separate silencer should located within the flue.
Auxiliary equipment (such as fans or radiators)
For ancillary equipment such as fans or radiators, these are often located near the CHP and as such be selected appropriately for the target noise rating you require.
The installation design should ensure that the CHP unit operation does not create problems of noise and vibration. Check the position of the CHP unit. Units above the ground floor of the building may require additional measures to prevent transmission of noise and vibration, such as anti-vibration mounts or additional insulation within the CHP bed frame.
When planning for a CHP system, don’t forget to consider noise:
- Check local and national noise constraints
- Look for a supplier that can adapt to varying noise constraints
- Ensure that all elements of the system minimise noise where they can
- Count on experience, use experts that are noise conscious