How to reduce the noise of a heat pump

How to reduce the noise of a heat pump ? This is a question that may arise for an architect, an installer of Heating Ventilation Air Conditioning (HVAC), a homeowner concerned about his acoustic comfort or that of his neighborhood, or a neighbor being exasperated, when it is not a co-ownership trustee that one solicits to remedy a problem of noise nuisance.

Because a heat pump is an equipment that is by nature a source of noise (due to the operation of components such as compressors, fans) and is often close enough to homes or housing so that its sound emissions are very noticeable, even by people who do not especially have keen hearing.

It is not uncommon for emergence i.e. the difference between the A-weighted equivalent continuous pressure levels of the ambient noise - heat pump in operation - and the residual noise - in the absence of the noise generated by the heat pump, but measured at complainant’s place of residence over the period of operation of the heat pump - reaches 10 or even 15 decibels, which is then an exceeding of the regulatory limit.

For the period 7 am - 10 pm (except Sundays and public holidays), the permissible emergence is 6 dB (A) for an ambient noise level between 35 dB (A) and 45 dB (A) and 5 dB ( A) for an ambient noise level greater than 45 dB (A).

For the period 22h - 7h (and for Sundays & public holidays), the permissible emergence is 4 dB (A) for an ambient noise level between 35 dB (A) and 45 dB (A) and 3 dB (A) for an ambient noise level greater than 45 dB (A).

In relation to the noise of a heat pump, an aggravating circumstance related to the nuisance of local residents may be the presence of a stong tone when the difference in level between the band of third octave and the four nearest third octave bands (the two immediately lower bands and the two immediately higher bands) reach or exceed the following levels for the band: 10 dB 50 Hz to 315 Hz, 5 dB 400 Hz at 1250 Hz, 5 dB from 50 Hz to 315 Hz.

In addition, the normalized sound pressure level, LnAT, of the noise of a heat pump (heat pump) must not exceed certain limits that depend on the room in question: in a residential building e.g. 35 dB (A) in a main room, in an educational institution e.g. 33 dB (A) in a library, in a health facility e.g. 30 dB (A) in an accommodation, in a hotel e.g. 30 dB (A) in a room.

Such limits are sometimes exceeded.

In all these situations, it is necessary to reduce the noise of the heat pump causing these disturbances for neighborhood.

The principle is to install devices to separate the air flow related to the inlet - often: on the side parts of the heat pump, when it comes to large units, the air in front being guided to heat exchangers - from the one linked to the discharge - often: in the upper part, when fans are provided whose blades are then in a horizontal plane when it is a question of large units - while preventing the propagation of noise.

Absorption silencers consisting of a metallic duct (usually made of steel) and absorbent separators (a.k.a. baffles) with a metal frame (also: usually made of steel) and with a lining made of mineral wool lining (then covered with a anti-defibering veil) or made of polyester wool (then with a special surface treatment) ensure this functionality.

The sizing of such silencers (generally: with a rectangular section) intended to reduce the noise of a heat pump must be carefully performred because their acoustic performance should not be accompanied by a total pressure loss being too important (the pressure drop available for silencers is often almost zero in such cases) and the air velocity must be kept low enough not to generate too much self noise.

A simulation software such as SILDIS® is then a valuable tool because reliable and accurate to optimize the technological choices related to these soundproofing equipment since its Module 1 allows the prediction of acoustic and aeraulic performances of silencers.

In case of need, the continuity of the acoustic insulation (between the silencer at the inlet and the silencer at the discharge) is ensured by metallic soundproofing panels (usually made of steel) with a mineral wool lining (then covered with a anti-defibering cloth) or polyester wool (then with a special surface treatment) and with a perforated protective sheet. If necessary, easily removable parts for maintenance or acoustic door blocks allowing access must be envisaged.

In some contexts, to reduce the noise of a heat pump, the installation of silencers at the discharge (only) is sufficient (they can then have a circular section), the effectiveness of the soundproofing system being able to be completed by a screen built with metal acoustic insulation panels (absorbent on one side) as mentioned above.

How to reduce the noise of a heat pump?

How to reduce the noise of a heat pump
   

What is true for the soundproofing of a heat pump is also true in the case of air conditioning, air coolers, air condensers, refrigeration units and other Heating Ventilation Air Conditioning (HVAC) equipment for domestic or industrial use.

ITS can size and market soundproofing equipment to reduce the noise of a heat pump and also for many other noisy hardware.

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How to reduce machine noise

How to reduce machine noise ? This is a question in many contexts related to the application of Directive 2003/10/EC on the minimum safety and health requirements relating to the exposure of workers to the risks arising from physical agents (noise), transposed in French law by the Decree n ° 2006-892 of July 19, 2006 relating to the safety and health prescriptions applicable in the event of exposure of the workers to the risks due to the noise and modifying the Labor code.

Indeed, the exposure limit values ​​are set as follows: a daily noise exposure level of 87 dB (A) or a peak sound pressure level of 140 dB (C).

But the lower exposure values ​​triggering the preventive action provided for in Article R. 231-131 (1) (1), Article R. 231-133 and Article R. 231- 134, paragraph II, are lower, since they are fixed as follows: a daily noise exposure level of 80 dB (A) or a peak sound pressure level of 135 dB (C).

Therefore, it is important to know how to reduce machine noise, if its noise emissions are (as is often the case without soundproofing device) likely to impact the driving position or other nearby workstations in a workshop or in other work premises.

In particular, machines in the corrugated cardboard industry (e orrugators and processing machines), rotary presses in the printing industry, machine tools in the metalworking sector (presses, punching machines, milling machines), lathes) are noisy enough for the question to arise: how to reduce the noise?

Indeed, the list of machines being noisy by nature would be long to establish, covering very different realities in terms of sound emissions: concrete press (emitting low frequency sounds), woodworking machines (with high frequency noise), ultrasonic welders (to name a few) are some typical examples.

In many cases, the noise reduction of the mechanisms involved for the operation of the machine is a step being too delicate to be considered a posteriori (but it can usefully be considered at the design stage e.g. by favoring stop pieces in nylon rather than steel where possible).

Therefore, a usual way to reduce machine noise is to limit the propagation of its sound production by means of a protection (to which are associated several language elements e.g. enclosure, hood, carterization) able to oppose the transmission of sounds through it while avoiding the reflections of acoustic waves inside (the protection must be absorbent) and which must be sufficiently enveloping not to leave outside noise sources.

To reduce machine noise one must therefore use industrial soundproofing panels: some are modular and easily removable, what can be useful in case of modification of the arrangements envisaged at a certain time for sound insulation, and what is often imperative for maintenance (some panels are equipped with glazing, for the visual control of the production process by an operator).

In general, access must be managed (by means of doors or hatches e.g. pivoting, sliding in vertical translation).

The air renewal of such an enclosure must be taken into account, involving a soundproof air inlet and a soundproof air outlet, with a fan.

Sizing and generally technical choices in relation to the problematic of reducing machine noise requires multidisciplinary skills and the success of a project is promoted by the experience i.e. by the previous confrontation with the same problematic.

To reduce machine noise, one can solicit Isolation Technologie Services (ITS) which can perform acoustic measurements on site or base its worm on drawings, and offer solutions optimized for each context and subject to a guaranteed result .

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How to reduce noise in a canteen

How to reduce noise in a canteen? This is the question faced by many managers and operators of collective dining rooms, in a context of hosting of young children, or of schools, of university restaurants or of corporate restaurants.

Indeed, a canteen is often a noisy place, because of the manipulation by its users of the table art accessories (e.g. plates, glasses, cutlery), and furniture items (e.g. chairs) and also because of the conversations of guests, sometimes animated, a fortiori if they are eager to be noticed or simply to be understood, while they have difficulties for that because of the sound competition that is made by others.

In relation to this problem, the consideration of the effect of the reverberation of the local is primordial, in relation to the reflection of sounds on hard surfaces, which thus contribute to the increase of ambient sound levels.

In order to avoid noise increase in a canteen, it is necessary to install sound-absorbing materials, i.e.materials limiting such acoustic wave reflections, for a sufficient percentage of the surfaces delimiting the space considered (e.g. walls, ceiling) depending on its volume.

Of course the frequency range in which these materials are intrinsically effective in terms of acoustics must include the frequencies corresponding to the human voice: the materials with an absorption coefficient close to 100% in the frequency range with octave central frequencies 500 Hz and 2000 Hz generally meet this requirement.

Depending on the particular context of each project, one or more forms of implementation of such sound-absorbing materials may be preferred or sometimes combined to reduce noise in a canteen: in the form of suspended ceiling tiles or baffles, in the form of wall linings, in the form of screens movable (on legs or on wheels) or stationnary. 

071 restaurant reverberation reduction device
How to reduce noise
in a canteen
   

In any case, the choice of materials must meet the strict conditions for reaction to fire (with respect to blaze risks) and the requirements for decoration also occupy a prominent place among the selection criteria, just as the possibilities for supply and installation.

With a choice of a suitable acoustic treatment system, a canteen can be (or, in the case of a renovation project: can become) a space that is comfortable enough to allow its users to recover, what is obviously not the least of the promises associated with such a place of life.

Unless the noise from Heating Ventilation Air Conditioning (HVAC) installation terminals is a problem, because its level is too high and it then affects the tranquility of the occupants.

If this is the case, it is necessary to consider the insertion, in the aeraulic network, between the source of noise (often constituted by a fan) and the air diffusion openings, of devices referred to as "silencers" which must be carefully sized to allow the necessary compromise between acoustical and aerodynamic performance, sometimes antagonistic.

To reduce noise in a canteen, one can sollicit Isolation Technology Services (ITS), which can perform acoustic measurements on site or perform its work based on drawings, and suggest improvement opportunities with the selection or with the defintion of technical solutions being appropriate for each situation.

This also applies to other similar premises: collective dining rooms, company restaurants, cafeterias, refectories.