In 2003, a series of decrees and a circular were published updating acoustic regulations for commercial buildings.
At that time, ceiling fans were virtually non-existent throughout mainland France.
Nearly two decades later, the RE2020 has been published, and it clearly gives ceiling fans a higher profile in terms of summer comfort.
Taking account of the 2003 regulations, which are still in force, has become an important issue for designers. That’s why this article covers both the fundamentals of acoustics and the practical aspects of implementing the official texts.
We are focusing here on subjects relating to educational establishments, although we also provide links to texts relating to health establishments and hotels.
Decibels and decibels A – dB and dB(A)
What is a decibel (dB)?
A decibel represents the ratio between two power values expressed in W[i]. The decibel uses a logarithmic scale, which makes it possible to reduce a very wide range of physical powers to a smaller numerical range. For example, at a 2,000-strong rock concert, 10,000 W of power may be mobilised. However, the maximum dB measured [ii]is of the order of 115 to 120 dB. The scale is therefore smaller and easier to use. With the logarithmic scale, an increase of 10 dB corresponds to a 10-fold increase in sound intensity. So a 20 dB sound is 10 times more intense than a 10 dB sound. The name of the unit of sound measurement, the bel, comes from the name of the inventor Alexander Graham Bell, known for his patent on the telephone[iii]. One decibel is one tenth of a bel.
What is the difference between dB and dB(A)?
The dB establishes a simple ratio between two power values in W.
The dB(A) takes into account the sensitivity of the human ear to different frequencies (from bass to treble).
The ear can perceive a range of frequencies from 20 Hz to 20 kHz, but is generally most sensitive to frequencies between 2 and 5 kHz.
dB(A) weights the different sound frequency ranges to better represent human hearing perception. The calculation based on the so-called ‘A-weighting’ system is defined by standard NF EN 61672-1.
dB(A) is measured with a sound level meter.
What is the difference between sound power and sound pressure?
The sound power Lw of the air curtain itself corresponds to the total sound energy emitted by a sound source. It is measured in the laboratory. L’ stands for “level” and “W” for “Watt”. Equipment manufacturers generally give LwA values translated into db(A).
The sound pressure Lp measured in the room takes into account the sound power of the sound source and the environment around this source. It corresponds to the noise we hear.
It will depend on a number of parameters: the number of air baffles, the acoustic characteristics of the walls, the distance between the ceiling fans and the measuring device, the air flow rate (and therefore the shape of the ceiling fans). It is called Lp; as above, the terms come from the English, ‘L’ for ‘level’ and ‘p’ for ‘pressure’.
Sound pressure is generally expressed in dB(A) and is referred to as LpA. Standard NF EN ISO 3744 is used to calculate this value.
Sound power can therefore be equated with the cause, and sound pressure with the effect.
The illustration below, taken from the BRASSE [iv] project, shows the relationship between sound power and sound pressure:
Figure 1: Relationship between sound power and sound pressure
The upper red stripe above symbolises the absorbent ceiling, while the lower double orange stripe represents a carpet laid on the floor.
It appears that an absorbent ceiling is much more effective than a carpet.
How do you define reverberation time?
The reverberation time of a room is the time required for the sound pressure to return to its initial level.
In an enclosed space, sound bounces off surfaces such as the floor, walls, ceiling, windows or tables several times.
Reverberation decreases when echoes encounter surfaces capable of absorbing sound, such as curtains, chairs or people. So when sound in a room takes 10 seconds to go from 90 dB to 30 dB, the reverberation time is 10 seconds.
Ceiling-mounted fans and educational establishments: what do the regulations say?
Two additional texts apply to these premises:
What noise levels are expected?
Article 4 of the Order mentions two cases:
- the usual quiet rooms: libraries, CDI, medical rooms, infirmaries, rest rooms and music rooms.
- The other premises, classrooms, administrative offices and teachers’ rooms.
The circular specifies the measurement tolerance, which is 3 dB(A).
What does the sound pressure value LnAT correspond to?
Sound pressure is generally denoted Lp or LpA.
LnAT is a pressure level calculated within the regulatory framework. It is standardised, taking into account both the sound pressure level Lp and the reverberation time. [v]
Calculating LnAT requires a great deal of information about the room in question (reverberation time, equivalent absorption area of the room, etc.) during the use phase, including when the test is carried out during the construction phase.
How do you assess the concept of continuous or intermittent operation?
Equipment that is permanently in place, as in the case of ceiling fans (as opposed to floor-standing fans), falls into the category of continuous operation.
We need to think in terms of design. For example, the reference air speed is not necessarily the maximum speed, but the speed used.
For example, for a ceiling fan with 6 speeds, operating permanently at speed 3, the noise emitted at this speed will be taken into account. If there are one or two days in the year when it will be used on speed 6 in design, this period can be considered as intermittent.
How should the 3 dB(A) tolerance be interpreted?
In practice, the aim is not to systematically apply the tolerance to 100% of the rooms where measurements are taken; nevertheless, regulatory compliance is achieved, for example, if the level is less than 41 dB(A) in a classroom under steady-state conditions (38+3).
Intermediate summary table
The table below shows the maximum levels and the measurement tolerance.
Figure 2: Levels and tolerances in teaching premises
Examples for several configurations
For the Brasse project, a particularly useful summary table can be found on page 62 of the acoustic report.
Figure 3: Table taken from the BRASSE acoustic report
It appears that in the case taken as an example in the BRASSE programme, the Samarat appears compliant in classroom configurations, including in speed setting 6, whereas current use is more in speed setting 3.
For Exhale, acoustic data can be accessed in the pro area in connected mode (technical specifications).
You can now download an empirical calculation tool based on approaches proposed on the Energieplus BE. website. You can use it to carry out some rough simulations.
In addition, as soon as it is made public, we will put the acoustic pre-dimensioning tool developed as part of the BRASSE project online.
Naturally, a good acoustic design of the room is necessary, and only field measurements can confirm full compliance with the regulations.
STD, dimensioning and noise
Dynamic thermal simulation is extremely useful for anticipating the situation.
Take, for example, the result of an STD for a given classroom; the limit of the comfort zone at 0.5 m/s is shown in yellow below.
So, with 0.5 m/s air speed, occupants can cope with most discomfort situations.
For sizing purposes, if this air speed is reached in speed 3, for example, we can base our calculations on the Lw value of the Samarat in v3, i.e. 30 dB(A) for continuous operation.
It is also possible to consider use at maximum speed to cope with periods when the speed must be greater than 0.5 m/s. In this case, the base Lw value is 35 dB(A), but in an intermittent mode of operation, because it is very punctual.
Figure 4: Thermal comfort zones
From acoustic regulations to sound design?
To date, we have not encountered any blocking regulatory situation for ceiling fans in commercial premises. However, regulations can be a tool, both for designers themselves and for suppliers, to help raise the standards of products on the market.
Although ceiling fans can sometimes cause psychological acoustic discomfort, their sound level does not cause hearing pain, unlike the extreme sounds emitted by amplification systems at festivals.
Context is fundamental, which is why the notion of sound design is emerging more and more.
- In a classroom, the technical systems have to work in such a way that the whole audience can hear what the teacher is saying. In fact, we carry out field surveys to ascertain the level of hearing satisfaction in educational establishments.[vi].
- In an individual office, noise should not disturb the employee’s concentration.
- In a landscaped office, on the other hand, it can be pleasant to have a slight masking background noise, so that everyone can work without being disturbed by the slightest noise emitted by a colleague.
In these different situations, the designers will take into account the level and nature of the sound emitted by the ceiling fans (quality polished blades emit a more pleasant sound), the absorbent materials and their surface, as well as the reverberation time…
Acoustic design is now an integral part of every building project, helping thermal systems to fulfil their raison d’être: to provide the best possible service for the occupants of the premises.
What regulations apply in health establishments and hotels?
The original version of the decree of 25 April 2003 is available in pdf format at this link ; it covers all tertiary buildings, including health establishments and hotels.
The versions in force on Légifrance can be accessed below:
Acknowledgements
We would like to thank Pierre OSSAKOWSKY, head of the Mediterranean branch of LASA, a consultancy specialising in acoustic and vibration engineering, for his careful proofreading and corrections of this article. LASA was responsible for all the acoustic aspects of the BRASSE project (see below).
Simplified acoustic calculation tool
[i] XdB=10.log10(P1/P0) [ii] For sound, we talk about dB SPL (Sound Pressure Level) [iii] In all likelihood, the telephone was actually invented by an Italian, Antonio Meucci, whose commercial and financial talents were inferior to those of Bell… [iv] The main aim of this research project is to provide the building sector with more knowledge about ceiling-mounted ventilation systems, to develop methods and tools to help with integration, and to disseminate this knowledge. With the support of ADEME, it involves the following six bodies: Surya Consultants (R&D energy – environment consultancy), project leader; LASA : private acoustics laboratory ; ISEA (independent sociologist) ; PIMENT Laboratory (University of La Réunion) ; Eiffel Aerodynamics Laboratory (a subsidiary of the CSTB group); EnvirobatBDM (Mediterranean sustainable building approach and resource centre). This programme is the winner of the 2020 Responsible Buildings call for research projects. [v] LnAT = Lp + 10 Log (Tr/T0), with Lp : sound pressure level ; Tr : room reverberation time ; T0 : reference reverberation time = 0.5s. Dans LnAt :
- L represents « Level », the level ;
- n corresponds to the notion of « normalized – standard » ;
- A refers to Adjustment, and indicates that the sound pressure level is adjusted or normalised according to certain conditions, such as reverberation time;
- T is the reverberation Time required for the sound pressure level to drop by 60 dB after the sound source has stopped.
[vi] For general information on this type of premises, please refer to our dedicated publication: Summer comfort in educational establishments: fans to the rescue?