Noise and vibration control
Guide B provides guidance on the practical design of heating, ventilation and air conditioning systems. It represents a consensus on what constitutes relevant good practice guidance. This has developed over more than 70 years, with the Steering Groups for each edition of the Guide expanding and pruning the content to reflect the evolution of technology and priorities.
Since the last edition of Guide B in 2005, the European Energy Performance of Buildings Directive has been introduced. This requires national building energy regulations to be based on calculations that integrate the impact of the building envelope and the building services systems, formalising what was already recognised as good design practice. In addition, the use of voluntary energy efficiency and sustainability indicators has increased.
Guide B deals with systems to provide heating, ventilation and air conditioning services, and is divided into several chapters which are published separately. It will usually be necessary to refer to several — perhaps all — chapters since decisions based on one service will commonly affect the provision of others.
Forms chapter 4 of CIBSE Guide B, provides guidance to building services engineers and others involved in the design of building services on the generation, prediction, assessment and control of noise and vibration from building services, so that designers may produce systems which meet acceptable noise limits. Noise reduction procedures are always much more effective and economic when introduced at the design stage than when applied retrospectively. Therefore it is important that the issue of noise is taken into account at an early stage of the design process, involving advice from an acoustics expert in particularly noise sensitive situations.
The noise level prediction process involves tracking the flow of sound energy from the fan in the plant room through each component of the system, taking account of the sound attenuation and additional flow generated noise provided at each stage. In the final stage of the process the total sound power entering the ventilated room via the grille or diffuser is converted into a sound pressure level at the position occupied by the occupant. This process is indicated schematically in Figure 4.1 and a more representational diagram, illustrating the flow of sound energy through a heating, ventilation and air conditioning (HVAC) system in a building is shown in Figure 4.3 below and discussed in more detail in section 4.2.
Different types of mechanical equipment produce noise over different frequency ranges. This is illustrated in Figure 4.2, which shows the frequencies most likely to be produced by equipment and gives a typical subjective terminology by which listeners might describe the noises. Figure 4.2 indicates that central plant (fans and pumps) is likely to cause noise up to about 500 Hz, while the very lowest frequencies are a result of defective installation. VAV units lead to noise from about 125–3000 Hz, fan powered units being responsible for the lower end of this range. Chillers lead to noise in the 250–1000 Hz range while higher frequencies are due to diffuser noise. These system components are considered in more detail in section 4.3 and other sections.
The building services engineer should be aware of all these various noise related issues which can affect the comfort of those inside and outside the building and if not responsible for all of them (e.g. if only responsible for the HVAC system) should inform and liaise with those (e.g. architects) who have this responsibility.
Figure 4.3 Noise from rooftop and ground level plant; transmission paths
- noise radiates to atmosphere from the air inlet or outlet (path 1)
- vibration from the fan transmits to the structure (path 5)
- noise from the plant breaks out of the plant room (path 3)
- noise may break out of the supply duct to adjacent spaces (path 2)
- incorrect duct or pipe anchoring may put vibration into the structure (path 5)
- duct borne noise is emitted from the room units (path 4)
- vibration from ground level plant gets into the structure (path 5)
- noise from plant transmits through walls or windows to adjacent spaces (path 2).
Ref.: CIBSE Guide B4: 2016 – Noise and vibration control for building services systems