Engineering and construction magazine, N 5, 2010
Category: Technology
Doctor of Technical Sciences, Professor I.I. Bogolepov
GOU St. Petersburg State Polytechnic University
and GOU St. Petersburg State Marine Technical University;
master A.A. Gladkikh,
GOU St. Petersburg State Polytechnic University
Ventilation and air conditioning system (VVKV) - critical system for modern buildings and structures. However, in addition to the necessary quality air, the system transports noise into the premises. It comes from the fan and other sources, spreads through the duct and radiates into the ventilated room. Noise is incompatible with normal sleep, learning process, creative work, highly productive work, good rest, treatment, obtaining quality information. AT building codes and the rules of Russia, such a situation has developed. The method of acoustic calculation of the SVKV of buildings, used in the old SNiP II-12-77 "Protection from noise", is outdated and therefore was not included in the new SNiP 23-03-2003 "Protection from noise". So, old method outdated, and there is no new generally recognized yet. Below we propose a simple approximate method for the acoustic calculation of SSWR in modern buildings, developed using the best production experience, in particular, on marine vessels.
The proposed acoustic calculation is based on the theory of long sound propagation lines in an acoustically narrow pipe and on the theory of sound in rooms with an almost diffuse sound field. It is performed in order to assess the levels sound pressure(hereinafter - ultrasound) and the correspondence of their values current regulations acceptable noise. It provides for the determination of SPL from SVKV due to the operation of the fan (hereinafter referred to as the "machine") for the following typical groups of premises:
1) in the room where the machine is located;
2) in rooms through which air ducts pass in transit;
3) in the premises serviced by the system.
Initial data and requirements
Calculation, design and control of protection of people from noise is proposed to be performed for the most important octave frequency bands for human perception, namely: 125 Hz, 500 Hz and 2000 Hz. An octave frequency band of 500 Hz is a geometric mean value in the range of noise-normalized octave frequency bands of 31.5 Hz - 8000 Hz. For constant noise, the calculation involves determining the SPL in octave frequency bands from the sound power levels (SPL) in the system. The SPL and SPL values are related by the general relationship = - 10, where SPL is relative to the threshold value of 2·10 N/m; - USM relative to the threshold value of 10 W; - area of propagation of the front of sound waves, m.
SPL must be determined at the design points of noise-rated rooms using the formula = + , where is the SPL of the noise source. The value that takes into account the influence of the room on the noise in it is calculated by the formula:
where is the coefficient taking into account the influence of the near field; - spatial angle of emission of the noise source, rad.; - radiation directivity coefficient, taken according to experimental data (in the first approximation it is equal to one); - distance from the center of the noise emitter to the calculated point in m; = - acoustic constant of the room, m; - the average coefficient of sound absorption of the internal surfaces of the room; - total area of these surfaces, m; - coefficient that takes into account the violation of the diffuse sound field in the room.
The indicated values, design points and norms of permissible noise are regulated for premises various buildings SNiPOM 23-03-2003 "Protection from noise". If the calculated SPL values exceed the permissible noise level in at least one of the three frequency bands indicated, then it is necessary to design measures and means to reduce noise.
The initial data for acoustic calculation and design of UHCS are:
- layout schemes used in the construction of the structure; dimensions of machines, air ducts, control valves, elbows, tees and air distributors;
- speed of air movement in the mains and branches - according to the terms of reference and aerodynamic calculation;
- drawings of the general arrangement of the premises serviced by the SVKV - according to construction project structures;
- noise characteristics of machines, control valves and air distributors SVKV - according to technical documentation for these products.
The noise characteristics of the machine are the following levels of USM airborne noise in octave frequency bands in dB: - SPL of noise propagating from the machine to the suction duct; - USM noise propagating from the machine to the discharge duct; - USM noise emitted by the machine body into the surrounding space. All machine noise characteristics are currently determined based on acoustic measurements to relevant national or international standards and others. regulatory documents.
Noise characteristics of silencers, air ducts, adjustable fittings and air diffusers are represented by the SLM of airborne noise in octave frequency bands in dB:
- USM noise generated by the elements of the system when the air flow passes through them (noise generation); - USM of noise dissipated or absorbed in the elements of the system when the flow of sound energy passes through them (noise reduction).
Efficiency of noise generation and noise reduction by UHCS elements is determined on the basis of acoustic measurements. We emphasize that the values of and must be specified in the relevant technical documentation.
At the same time, due attention is paid to the accuracy and reliability of the acoustic calculation, which are included in the error of the result by the values and .
Calculation for the premises where the machine is installed
Let there be a fan in room 1 where the machine is installed, the sound power level of which, radiated into the suction, discharge pipeline and through the machine body, is the values in dB , and . Let the fan on the side of the discharge pipeline have a silencer with a silencer efficiency in dB (). Workplace located at a distance from the car. The wall separating room 1 and room 2 is at a distance from the machine. Room sound absorption constant 1: = .
For room 1, the calculation provides for the solution of three problems.
1st task. Compliance with the norm of permissible noise.
If the suction and discharge pipes are removed from the machine room, then the SPL calculation in the room where it is located is made according to the following formulas.
Octave SPL at the design point of the room are determined in dB by the formula:
where - USM noise emitted by the machine body, taking into account accuracy and reliability using . The value indicated above is determined by the formula:
If the premises are placed n noise sources, SPL from each of which at the calculated point are equal, then the total SPL from all of them is determined by the formula:
As a result of the acoustic calculation and design of the SVKV for room 1, where the machine is installed, it must be ensured that the permissible noise standards are met at the design points.
2nd task. Calculation of the SPL value in the discharge air duct from room 1 to room 2 (the room through which the air duct passes in transit), namely, the value in dB is made according to the formula
3rd task. Calculation of the SPL value radiated by the wall with the soundproofed area of room 1 to room 2, namely the value in dB, is performed by the formula
Thus, the result of the calculation in room 1 is the fulfillment of the noise standards in this room and the receipt of the initial data for the calculation in room 2.
Calculation for rooms through which the duct passes in transit
For room 2 (for rooms through which the air duct passes), the calculation provides for the solution of the following five problems.
1st task. Calculation of the sound power radiated by the walls of the air duct into room 2, namely, the determination of the value in dB according to the formula:
In this formula: - see above the 2nd task for room 1;
\u003d 1.12 - equivalent diameter of the duct section with a cross-sectional area ;
- room length 2.
The sound insulation of the walls of a cylindrical duct in dB is calculated by the formula:
where is the dynamic modulus of elasticity of the duct wall material, N/m;
- internal diameter of the duct in m;
- duct wall thickness in m;
Soundproofing of duct walls rectangular section calculated using the following formula in DB:
where = is the mass of a unit surface of the duct wall (the product of the density of the material in kg/m and the wall thickness in m);
- geometric mean frequency of octave bands in Hz.
2nd task. Calculation of SPL at the design point of room 2, located at a distance from the first noise source (air duct) is performed according to the formula, dB:
3rd task. Calculation of SPL at the design point of room 2 from the second noise source (the SPL radiated by the wall of room 1 to room 2 - the value in dB) is performed according to the formula, dB:
4th task. Compliance with the norm of permissible noise.
The calculation is carried out according to the formula in dB:
As a result of the acoustic calculation and design of the SVKV for room 2, through which the air duct passes in transit, it must be ensured that the permissible noise standards are met at the design points. This is the first result.
5th task. Calculation of the SPL value in the discharge duct from room 2 to room 3 (the room serviced by the system), namely the value in dB according to the formula:
The value of losses due to the emission of noise sound power by the walls of air ducts on straight sections of air ducts of a unit length in dB/m is presented in Table 2. The second result of the calculation in room 2 is to obtain the initial data for the acoustic calculation of the ventilation system in room 3.
Calculation for rooms served by the system
In rooms 3 serviced by SVKV (for which the system is ultimately intended), the design points and norms of permissible noise are adopted in accordance with SNiP 23-03-2003 "Protection from noise" and the terms of reference.
For room 3, the calculation involves solving two problems.
1st task. The calculation of the sound power emitted by the air duct through the outlet air distribution opening into room 3, namely the determination of the value in dB, is proposed to be performed as follows.
Private problem
1
for low speed system with air speed v<< 10 м/с и = 0 и трех типовых помещений (см. ниже
пример акустического расчета) решается с помощью формулы в дБ:
Here
() - losses in the silencer in room 3;
() - losses in the tee in room 3 (see the formula below);
- loss due to reflection from the end of the duct (see table 1).
General task 1 consists of solving for many of the three typical rooms using the following formula in dB:
Here - SLM of noise propagating from the machine into the discharge duct in dB, taking into account the accuracy and reliability of the value (accepted according to the technical documentation for the machines);
- SLM of the noise generated by the air flow in all elements of the system in dB (accepted according to the technical documentation for these elements);
- USM of noise absorbed and dissipated during the passage of the flow of sound energy through all elements of the system in dB (accepted according to the technical documentation for these elements);
- the value that takes into account the reflection of sound energy from the end outlet of the air duct in dB, is taken from Table 1 (this value is zero if it already includes );
- a value equal to 5 dB for low-speed UACS (air speed in the mains is less than 15 m/s), equal to 10 dB for medium-speed UACS (air speed in the mains is less than 20 m/s) and equal to 15 dB for high-speed UACS (velocity in the mains is less than 25 m/s).
Table 1. Value in dB. Octave bands
Acoustic calculations
Among the problems of improving the environment, the fight against noise is one of the most urgent. In large cities, noise is one of the main physical factors that shape the conditions of the environment.
The growth of industrial and housing construction, the rapid development of various types of transport, the increasing use of sanitary and engineering equipment in residential and public buildings, household appliances have led to the fact that noise levels in residential areas of the city have become comparable to noise levels in production.
The noise regime of large cities is formed mainly by road and rail transport, which makes up 60-70% of all noise.
The increase in air traffic, the emergence of new powerful aircraft and helicopters, as well as railway transport, open metro lines and shallow metro have a noticeable impact on the noise level.
At the same time, in some large cities, where measures are being taken to improve the noise situation, noise levels are decreasing.
There are acoustic and non-acoustic noises, what is the difference between them?
Acoustic noise is defined as a combination of sounds of different strength and frequency, resulting from the oscillatory motion of particles in elastic media (solid, liquid, gaseous).
Non-acoustic noise - Radio-electronic noise - random fluctuations of currents and voltages in radio-electronic devices, arise as a result of uneven emission of electrons in electrovacuum devices (shot noise, flicker noise), uneven processes of generation and recombination of charge carriers (conduction electrons and holes) in semiconductor devices, thermal motion of current carriers in conductors (thermal noise), thermal radiation of the Earth and the earth's atmosphere, as well as planets, the Sun, stars, the interstellar medium, etc. (cosmic noise).
Acoustic calculation, noise level calculation.
In the process of construction and operation of various facilities, noise control problems are an integral part of labor protection and public health protection. Machines, vehicles, mechanisms and other equipment can act as sources. Noise, its magnitude of impact and vibration on a person depends on the level of sound pressure, frequency characteristics.
Normalization of noise characteristics is understood as the establishment of restrictions on the values of these characteristics, under which the noise affecting people should not exceed the permissible levels regulated by the current sanitary norms and rules.
The objectives of the acoustic calculation are:
Identification of noise sources;
Determination of their noise characteristics;
Determination of the degree of influence of noise sources on normalized objects;
Calculation and construction of individual zones of acoustic discomfort of noise sources;
Development of special noise protection measures that provide the required acoustic comfort.
The installation of ventilation and air conditioning systems is already considered a natural need in any building (whether residential or administrative), acoustic calculation should be carried out for rooms of this type. So, if the noise level is not calculated, it may turn out that the room has a very low level of sound absorption, and this greatly complicates the process of communication between people in it.
Therefore, before installing a ventilation system in a room, it is necessary to carry out an acoustic calculation. If it turns out that the room is characterized by poor acoustic properties, it is necessary to propose a series of measures to improve the acoustic situation in the room. Therefore, acoustic calculations are also performed for the installation of household air conditioners.
Acoustic calculation is most often carried out for objects that have complex acoustics or have high requirements for sound quality.
Sound sensations arise in the hearing organs when they are exposed to sound waves in the range from 16 Hz to 22 thousand Hz. Sound propagates in air at a speed of 344 m/s in 3 seconds. 1 km.
The value of the hearing threshold depends on the frequency of perceived sounds and is equal to 10-12 W/m 2 at frequencies close to 1000 Hz. The upper limit is the pain threshold, which is less dependent on frequency and lies within 130 - 140 dB (at a frequency of 1000 Hz, intensity 10 W / m 2, sound pressure).
The ratio of intensity level and frequency determines the sensation of sound volume, i.e. sounds that have different frequencies and intensities can be assessed by a person as equally loud.
When perceiving sound signals against a certain acoustic background, the effect of signal masking can be observed.
The masking effect can be detrimental to acoustic indicators and can be used to improve the acoustic environment, i.e. in the case of masking a high-frequency tone with a low-frequency one, which is less harmful to humans.
The procedure for performing acoustic calculation.
To perform an acoustic calculation, the following data will be required:
Dimensions of the room for which the calculation of the noise level will be carried out;
The main characteristics of the premises and its properties;
Noise spectrum from the source;
Characteristics of the barrier;
Distance data from the center of the noise source to the acoustic calculation point.
In the calculation, the sources of noise and their characteristic properties are first determined. Next, on the object under study, points are selected at which calculations will be carried out. At selected points of the object, a preliminary sound pressure level is calculated. Based on the results obtained, a calculation is performed to reduce noise to the required standards. Having received all the necessary data, a project is carried out to develop measures that will reduce the noise level.
Properly performed acoustic calculation is the key to excellent acoustics and comfort in a room of any size and design.
Based on the performed acoustic calculation, the following measures can be proposed to reduce the noise level:
* installation of soundproof structures;
* the use of seals in windows, doors, gates;
* the use of structures and screens that absorb sound;
*implementation of planning and development of the residential area in accordance with SNiP;
* the use of noise suppressors in ventilation and air conditioning systems.
Carrying out acoustic calculation.
Work on the calculation of noise levels, assessment of acoustic (noise) impact, as well as the design of specialized noise protection measures, should be carried out by a specialized organization with a relevant area.
noise acoustic calculation measurement
In the simplest definition, the main task of acoustic calculation is the assessment of the noise level generated by the noise source at a given design point with the established quality of the acoustic impact.
The acoustic calculation process consists of the following main steps:
1. Collection of the necessary initial data:
The nature of noise sources, their mode of operation;
Acoustic characteristics of noise sources (in the range of geometric mean frequencies 63-8000 Hz);
Geometric parameters of the room in which the noise sources are located;
Analysis of the weakened elements of the enclosing structures, through which the noise will penetrate into the environment;
Geometric and soundproof parameters of weakened elements of enclosing structures;
Analysis of nearby objects with the established quality of acoustic impact, determination of permissible sound levels for each object;
Analysis of distances from external noise sources to normalized objects;
Analysis of possible shielding elements on the path of sound wave propagation (buildings, green spaces, etc.);
Analysis of weakened elements of enclosing structures (windows, doors, etc.), through which noise will penetrate into normalized premises, identification of their soundproofing ability.
2. Acoustic calculation is carried out on the basis of current guidelines and recommendations. Basically, these are “Methods of calculation, standards”.
At each calculated point, it is necessary to sum up all available noise sources.
The result of the acoustic calculation are certain values (dB) in octave bands with geometric mean frequencies of 63-8000 Hz and the equivalent value of the sound level (dBA) at the calculated point.
3. Analysis of the calculation results.
The analysis of the results obtained is carried out by comparing the values obtained at the calculated point with the established Sanitary Standards.
If necessary, the next step in the acoustic calculation can be the design of the necessary noise protection measures that will reduce the acoustic impact at the calculated points to an acceptable level.
Carrying out instrumental measurements.
In addition to acoustic calculations, it is possible to calculate instrumental measurements of noise levels of any complexity, including:
Measurement of noise impact of existing ventilation and air conditioning systems for office buildings, private apartments, etc.;
Carrying out measurements of noise levels for attestation of workplaces;
Carrying out work on instrumental measurement of noise levels within the framework of the project;
Carrying out work on instrumental measurement of noise levels as part of technical reports when approving the boundaries of the SPZ;
Implementation of any instrumental measurements of noise exposure.
Conducting instrumental measurements of noise levels is carried out by a specialized mobile laboratory using modern equipment.
Timing of acoustic calculation. Terms of performance of work depend on volume of calculations and measurements. If it is necessary to make an acoustic calculation for projects of residential buildings or administrative facilities, then they are performed on average 1 - 3 weeks. Acoustic calculation for large or unique objects (theaters, organ halls) takes more time, based on the provided source materials. In addition, the number of studied noise sources, as well as external factors, largely affect the period of operation.
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(Gosstroy USSR)
instructions CH 399-69
CH 399-69
MOSCOW - 1970
Official edition
STATE COMMITTEE OF THE USSR COUNCIL OF MINISTERS FOR CONSTRUCTION
(Gosstroy USSR)
INSTRUCTIONS
ACCORDING TO ACOUSTIC CALCULATION OF VENTILATION INSTALLATIONS
Approved by the State Committee of the Council of Ministers of the USSR for Construction
PUBLISHING HOUSE OF LITERATURE ON CONSTRUCTION Moscow - 1970
gates, gratings, shades, etc.), should be determined by the formula
L p = 601go + 301gC+101g/? + fi, (5)
where v is the average air velocity at the inlet to the device under consideration (installation element), calculated by the area of the inlet air duct (pipe) for throttling devices and ceiling lamps and by the overall dimensions for grilles in m/s;
£ - coefficient of aerodynamic resistance of the element of the ventilation network, related to the air velocity at its inlet; for VNIIGS disk ceilings (separated jet) £ = 4; for anemostats and plafonds of VNIIGS (flat jet) £ = 2; for supply and exhaust grilles, the resistance coefficients are taken according to the graph in fig. 2;
supply grille
exhaust grille
Rice. 2. Dependence of the drag coefficient of the grating on its open section
F - cross-sectional area of the inlet air duct in m 2;
B - correction depending on the type of element, in db; for throttling devices, anemostats and disc ceilings D = 6 dB; for plafonds designed by VNIIGS B =13 dB; for gratings D=0.
2.10. Octave sound power levels of noise emitted into the duct by throttling devices should be determined by formula (3).
In this case, it is calculated according to the formula (5), the amendment AL 2 is determined from the table. 3 (the cross-sectional area of the duct in which the considered element or device is installed should be taken into account), and the corrections AL \ - according to Table_5, depending on the value of the frequency parameter f, which is determined by the equation
! = < 6 >
where f is the frequency in Hz;
D is the average transverse dimension of the duct (equivalent diameter) in m; v - average speed at the entrance to the considered element in m/sec.
Table 5
Amendments AL) for determining the octave sound power levels of the noise of throttling devices in dB
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Note Intermediate values in Table 5 should be taken by interpolation |
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2.11. The octave sound power levels of the noise generated in the shades and grilles should be calculated using formula (2), taking the corrections ALi according to the data in Table. 6.
2.12. If the speed of air movement in front of the air distribution or air intake device (plafond, grille, etc.) does not exceed the allowable value of add, then the noise created in them is calculated
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Table 6 Amendments ALi, taking into account the distribution of the sound power of the noise of ceiling lamps and gratings in octave bands, in dB |
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necessary reduction in sound pressure levels (see Section 5) can be ignored
2.13. The allowable air velocity in front of the air distribution or air intake device of the installations should be determined by the formula
y D op \u003d 0.7 10 * m / s;
^ext + 101e ~ -301ge-MIi-
where b add - octave sound pressure level allowed by the standards in dB; n - the number of shades or gratings in the room under consideration;
B - room constant in the considered octave band in m 2, taken in accordance with paragraphs. 3.4 or 3.5;
AZ-i - an amendment that takes into account the distribution of sound power levels of ceiling lamps and gratings in octave bands, taken according to Table. 6, in dB;
D - correction for the location of the noise source; when the source is located in the working area (not higher than 2 m from the floor), A = 3 dB; if the source is above this zone, A *■ 0;
0.7 - safety factor;
F, B - the designations are the same as in paragraph 2.9, formula (5).
Note. The determination of the allowable air speed is carried out only for one frequency, which is equal to VNIIGS 250 Shch for ceiling lamps, 500 Hz for disk ceiling lamps, and 2000 Hz for anemostats and gratings.
2.14. In order to reduce the sound power level of the noise generated by bends and tees of air ducts, areas of a sharp change in the cross-sectional area, etc., it is necessary to limit the speed of air movement in the main air ducts of public buildings and auxiliary buildings of industrial enterprises to 5-6 m / s, and on branches up to 2-4 m/sec. For industrial buildings, these speeds can be respectively doubled, if this is permissible according to technological and other requirements.
3. CALCULATION OF OCTAVE SOUND PRESSURE LEVELS AT CALCULATED POINTS
3.1. Octave levels of sound pressure at permanent workplaces or in rooms (at design points) should not exceed the established norms.
(Notes: 1. If the regulatory requirements for sound pressure levels are different during the day, then the acoustic calculation of the installations should be made for the lowest permissible sound pressure levels.
2. Sound pressure levels at permanent workplaces or in rooms (at design points) depend on the sound power and the location of noise sources and the sound-absorbing qualities of the room in question.
3.2. When determining the octave levels of sound pressure, the calculation should be made for permanent workplaces or settlement points in rooms closest to noise sources (heating and ventilation units, air distribution or air intake devices, air or air curtains, etc.). In the adjacent territory, the design points should be taken as the points closest to noise sources (fans located openly on the territory, exhaust or air intake shafts, exhaust devices of ventilation installations, etc.), for which sound pressure levels are normalized.
a - noise sources (autonomous air conditioner and ceiling) and the calculated point are in the same room; b - noise sources (fan and installation elements) and the calculated point are located in different rooms; c - source of noise - the fan is located in the room, the calculated point is on the arrival side of the territory; 1 - autonomous air conditioner; 2 - calculated point; 3 - noise-generating ceiling; 4 - vibration-isolated fan; 5 - flexible insert; in - the central muffler; 7 - sudden narrowing of the duct section; 8 - branching of the duct; 9 - rectangular turn with guide vanes; 10 - smooth turn of the air duct; 11 - rectangular turn of the duct; 12 - lattice; /
3.3. Octave/Sound pressure levels at design points should be determined as follows.
Case 1. The noise source (noise-generating grille, ceiling lamp, autonomous air conditioner, etc.) is located in the considered room (Fig. 3). Octave sound pressure levels generated at the calculated point by one noise source should be determined by the formula
L-L, + I0! g (-£-+--i-l (8)
Oct \ 4 I g g W t )
N o t e. For ordinary rooms that do not have special requirements for acoustics, according to the formula
L \u003d Lp - 10 lg H w -4- D - (- 6, (9)
where Lp okt is the octave sound power level of the noise source (determined according to Section 2) in dB\
B w - room constant with a noise source in the considered octave band (determined according to paragraphs 3.4 or 3.5) in g 2;
D - correction for the location of the noise source If the noise source is located in the working area, then for all frequencies D \u003d 3 dB; if above the working area, - D=0;
Ф - radiation directivity factor of the noise source (determined from the curves in Fig. 4), dimensionless; d - distance from the geometric center of the noise source to the calculated point in g.
The graphical solution of equation (8) is shown in fig. 5.
Case 2. The calculated points are located in a room isolated from noise. Noise from a fan or an installation element propagates through the air ducts and is radiated into the room through an air distribution or air intake device (grille). Octave sound pressure levels generated at design points should be determined by the formula
L \u003d L P -DL p + 101g (-% + -V (10)
Note. For ordinary rooms, for which there are no special requirements for acoustics, - according to the formula
L - L p -A Lp -10 lgiJ H ~b A -f- 6, (11)
where L p in is the octave level of the sound power of the fan or installation element radiated into the duct in the considered octave band in dB (determined in accordance with paragraphs 2.5 or 2.10);
AL r in - the total reduction in the level (loss) of the sound power of the noise of the fan or electric
installation time in the octave band under consideration along the sound propagation path in dB (determined in accordance with clause 4.1); D - correction for the location of the noise source; if the air distribution or air intake device is located in the working area, A \u003d 3 dB, if it is higher, - D \u003d 0; Ф and - the directivity factor of the installation element (hole, grate, etc.) emitting noise into the isolated room, dimensionless (determined from the graphs in Fig. 4); rn is the distance from the installation element emitting noise into the isolated room to the calculated point in m
B and - the constant of the room isolated from noise in the considered octave band in m 2 (determined according to paragraphs 3.4 or 3.5).
Case 3. The calculated points are located on the territory adjacent to the building. Fan noise propagates through the duct and is radiated to the atmosphere through the grate or shaft (Fig. 6). Octave levels of sound pressure generated at design points should be determined by the formula
I = L p -AL p -201gr a -i^- + A-8, (12)
where g a is the distance from the installation element (grid, hole) emitting noise into the atmosphere to the design point in m \ p a - sound attenuation in the atmosphere, taken according to Table. 7 in dB/km
A is the correction in dB, taking into account the location of the calculated point relative to the axis of the installation element emitting noise (for all frequencies, it is taken according to Fig. 6).
1 - ventilation shaft; 2 - louvre
The remaining quantities are the same as in formulas (10)
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Table 7 Sound attenuation in the atmosphere in dB/km |
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3.4. The room constant B should be determined from the graphs in fig. 7 or according to table. 9, using the table. 8 to determine the characteristics of the room.
3.5. For rooms with special requirements for acoustics (unique
halls, etc.), the constant of the room should be determined in accordance with the instructions for acoustic calculation for these rooms.
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The room constant at the calculated frequency is equal to the room constant at a frequency of 1000 Hz multiplied by the frequency multiplier ^ £ = £ 1000 |
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3.6. If the design point receives noise from several noise sources (for example, supply and recirculation grilles, an autonomous air conditioner, etc.), then for the considered design point, according to the corresponding formulas in clause 3.2, the octave sound pressure levels generated by each of the noise sources separately should be determined , and the total level in
These "Instructions on the acoustic calculation of ventilation units" were developed by the Research Institute of Building Physics of the USSR State Construction Committee together with the institutes Santekhproekt of the USSR State Construction Committee and Giproniiaviaprom of Minaviaprom.
The instructions were developed in development of the requirements of the chapter SNiP I-G.7-62 “Heating, ventilation and air conditioning. Design Standards” and “Sanitary Design Standards for Industrial Enterprises” (SN 245-63), which establish the need to reduce the noise of ventilation, air conditioning and air heating installations for buildings and structures for various purposes when it exceeds the sound pressure levels allowed by the standards.
Editors: A. No. 1. Koshkin (Gosstroy of the USSR), Doctor of Engineering. sciences, prof. E. Ya. Yudin and candidates of tech. Sciences E. A. Leskov and G. L. Osipov (Research Institute of Building Physics), Ph.D. tech. Sciences I. D. Rassadi
The Guidelines set out the general principles of acoustic calculations for mechanically driven ventilation, air conditioning and air heating installations. Methods for reducing sound pressure levels at permanent workplaces and in rooms (at design points) to the values established by the standards are considered.
at (Giproniiaviaprom) and eng. | g. A. Katsnelson / (GPI Santekhproekt)
1. General Provisions............ - . . , 3
2. Noise sources of installations and their noise characteristics 5
3. Calculation of octave levels of sound pressure in the calculated
points................. 13
4. Reducing the levels (losses) of the sound power of noise in
various elements of air ducts ........ 23
5. Determining the required reduction in sound pressure levels. . . *. ............... 28
6. Measures to reduce sound pressure levels. 31
Application. Examples of acoustic calculation of ventilation, air conditioning and air heating installations with mechanical stimulation...... 39
Plan I quarter. 1970, No. 3
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Room characteristics Table 8 |
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each octave band. The total sound pressure level should be determined in accordance with clause 2.7. Note. If the noise of a fan (or throttle) from one system (supply or exhaust) enters the room through several grilles, then the sound power distribution between them should be considered uniform. |
3.7. If the calculated points are located in a room through which a “noisy” duct passes, and noise enters the room through the walls of the duct, then the octave sound pressure levels should be determined by the formula
L - L p -AL p + 101g --R B - 101gB „-J-3, (13)
where Lp 9 is the octave level of the sound power of the noise source radiated into the duct, in dB (determined in accordance with paragraphs 2 5 and 2.10);
ALp b is the total reduction in sound power levels (losses) along the sound propagation path from the noise source (fan, throttle, etc.) to the beginning of the considered section of the duct that emits noise into the room, in dB (determined in accordance with Section 4);
State Committee of the Council of Ministers of the USSR for Construction Affairs (Gosstroy of the USSR)
1. GENERAL PROVISIONS
1.1. These Guidelines are developed in development of the requirements of the chapter SNiP I-G.7-62 “Heating, ventilation and air conditioning. Design Standards” and “Sanitary Design Standards for Industrial Enterprises” (SN 245-63), which established the need to reduce the noise of mechanically driven ventilation, air conditioning and air heating installations to sound pressure levels acceptable by the standards.
1.2. The requirements of these Guidelines apply to acoustic calculations of airborne (aerodynamic) noise generated during the operation of the installations listed in clause 1.1.
Note. These Guidelines do not consider calculations of vibration isolation of fans and electric motors (isolation of shocks and sound vibrations transmitted to building structures), as well as calculations of sound insulation of enclosing structures of ventilation chambers.
1.3. The method for calculating airborne (aerodynamic) noise is based on determining the sound pressure levels of noise generated during the operation of the installations specified in clause 1.1 at permanent workplaces or in rooms (at design points), determining the need to reduce these noise levels and measures to reduce sound levels pressure to the values allowed by the standards.
Notes: 1. Acoustic calculation should be included in the design of mechanically driven ventilation, air conditioning and air heating installations for buildings and structures for various purposes.
Acoustic calculation should be done only for rooms with normalized noise levels.
2. Airborne (aerodynamic) fan noise and noise generated by air flow in air ducts have broadband spectra.
3. In these Guidelines, under the noise should be understood any kind of sounds that interfere with the perception of useful sounds or break the silence, as well as sounds that have a harmful or irritating effect on the human body.
1.4. When acoustically calculating a central ventilation, air conditioning and hot air heating installation, the shortest duct run should be considered. If the central unit serves several rooms, for which the normative noise requirements are different, then an additional calculation should be made for the duct branch serving the room with the lowest noise level.
Separate calculations should be made for autonomous heating and ventilation units, autonomous air conditioners, units of air or air curtains, local exhausts, units of air shower installations, which are closest to the calculated points or have the highest performance and sound power.
Separately, it is necessary to make an acoustic calculation of the branches of the air ducts that go out into the atmosphere (suction and exhaust of air by installations).
If there are throttling devices (diaphragms, throttle valves, dampers), air distribution and air intake devices (grilles, shades, anemostats, etc.) between the fan and the serviced room, sharp changes in the cross section of air ducts, turns and tees, acoustic calculation of these devices should be made and plant elements.
1.5. Acoustic calculation should be made for each of the eight octave bands of the auditory range (for which noise levels are normalized) with the geometric mean frequencies of the octave bands 63, 125, 250, 500, 1000, 2000, 4000 and 8000 Hz.
Notes: 1. For central air heating, ventilation and air conditioning systems in the presence of an extensive network of air ducts, it is allowed to calculate only for frequencies of 125 and 250 Hz.
2. All intermediate acoustic calculations are performed with an accuracy of 0.5 dB. The final result is rounded to the nearest whole number of decibels.
1.6. Required measures to reduce noise generated by ventilation, air conditioning and air heating installations, if necessary, should be determined for each source separately.
2. SOURCES OF NOISE IN INSTALLATIONS AND THEIR NOISE CHARACTERISTICS
2.1. Acoustic calculations to determine the sound pressure level of air (aerodynamic) noise should be made taking into account the noise generated by:
a) a fan
b) when the air flow moves in the elements of the installations (diaphragms, chokes, dampers, turns of air ducts, tees, grilles, shades, etc.).
In addition, the noise transmitted through the ventilation ducts from one room to another should be taken into account.
2.2. Noise characteristics (octave sound power levels) of noise sources (fans, heating units, room air conditioners, throttling, air distribution and air intake devices, etc.) should be taken from the passports for this equipment or from catalog data
In the absence of noise characteristics, they should be determined experimentally on the instructions of the customer or by calculation, guided by the data given in these Guidelines.
2.3. The total sound power level of the fan noise should be determined by the formula
L p =Z+251g#+l01gQ-K (1)
where 1^P is the total sound power level of vein noise
tilator in dB re 10“ 12 W;
L-noise criterion, depending on the type and design of the fan, in dB; should be taken according to the table. one;
I is the total pressure created by the fan, in kg / m 2;
Q - fan performance in m^/sec;
5 - correction for the fan operation mode in dB.
Table 1
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Noise criterion L values for fans in dB |
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Notes: 1. The value of 6 when the deviation of the fan operation mode is not more than 20% of the maximum efficiency mode should be taken equal to 2 dB. In the fan operation mode with maximum efficiency 6=0.
2. To facilitate the calculations in fig. 1 shows a graph for determining the value of 251gtf+101gQ.
3. The value obtained by formula (1) characterizes the sound power radiated by an open inlet or outlet pipe of the fan in one direction into the free atmosphere or into the room in the presence of a smooth air supply to the inlet pipe.
4. When the air supply to the inlet pipe is not smooth or the throttle is installed in the inlet pipe to the values specified in
tab. 1, should be added for axial fans 8 dB, for centrifugal fans 4 dB
2.4. The octave sound power levels of fan noise emitted by an open inlet or outlet of the fan L p a, into the free atmosphere or into the room, should be determined by the formula
(2)
where is the total sound power level of the fan in dB;
ALi is a correction that takes into account the distribution of the sound power of the fan in octave bands in dB, taken depending on the type of fan and the number of revolutions according to table. 2.
table 2
Amendments ALu taking into account the distribution of the sound power of the fan in octave bands, in dB
|
Centrifugal fans | |||
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Geometric mean hour |
Axial veins |
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tots of octave bands in Hz |
with blades, |
with blades, zag |
tilators |
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bent forward |
kicked back | ||
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(16 000) (3 2 000) | |||
Notes: 1. Given in Table. 2 data without brackets are valid when the fan speed is in the range of 700-1400 rpm.
2. At a fan speed of 1410-2800 rpm, the entire spectrum should be shifted down an octave, and at a speed of 350-690 rpm, an octave up, taking for the extreme octaves the values indicated in brackets for frequencies of 32 and 16000 Hz.
3. When the fan speed is more than 2800 rpm, the entire spectrum should be shifted two octaves down.
2.5. Octave sound power levels of fan noise radiated into the ventilation network should be determined by the formula
Lp - L p ■- A L-± -|~ L i-2,
where AL 2 is the correction that takes into account the effect of connecting the fan to the duct network in dB, determined from the table. 3.
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Table 3 Amendment D £ 2 > taking into account the effect of connecting a fan or a throttling device to the duct network in dB |
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2.6. The total sound power level of the noise radiated by the fan through the walls of the casing (housing) into the ventilation chamber room should be determined by formula (1), provided that the value of the noise criterion L is taken from Table. 1 as its average value for the suction and discharge sides.
The octave levels of the sound power of the noise emitted by the fan into the room of the ventilation chamber should be determined by the formula (2) and Table. 2.
2.7. If several fans operate simultaneously in the ventilation chamber, then for each octave band it is necessary to determine the total level
sound power of the noise emitted by all fans.
The total noise sound power level L cyu during operation of n identical fans should be determined by the formula
£sum = Z.J + 10 Ign, (4)
where Li is the sound power level of the noise of one fan in dB-, n is the number of identical fans.
Table four.
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Table 4 Addition of sound power or sound pressure levels |
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Note. When the number of different noise levels is more than two, the addition is performed sequentially, starting from two large levels. |
2.8. Octave sound power levels of noise radiated into the room by autonomous air conditioners, heating and ventilation units, air shower units (without air duct networks) with axial fans should be determined by formula (2) and Table. 2 with a 3dB up-correction.
For autonomous units with centrifugal fans, the octave sound power levels of the noise emitted by the suction and discharge pipes of the fan should be determined by formula (2) and table. 2, and the total noise level - according to table. four.
Note. When air is taken in by installations outside, it is not necessary to take a higher correction.
2.9. The total sound power level of noise generated by throttling, air distribution and air intake devices (throttle valves.
Description:
The norms and regulations in force in the country stipulate that the projects must provide for measures to protect against noise of equipment used for human life support. Such equipment includes ventilation and air conditioning systems.
Acoustic calculation as a basis for designing a low-noise ventilation (air conditioning) system
V. P. Gusev, doctor of tech. sciences, head. noise protection laboratory for ventilation and engineering equipment (NIISF)
The norms and regulations in force in the country stipulate that the projects must provide for measures to protect against noise of equipment used for human life support. Such equipment includes ventilation and air conditioning systems.
The basis for the design of sound attenuation of ventilation and air conditioning systems is acoustic calculation - a mandatory application to the ventilation project of any object. The main tasks of such a calculation are: determination of the octave spectrum of airborne, structural ventilation noise at the calculated points and its required reduction by comparing this spectrum with the permissible spectrum according to hygienic standards. After the selection of construction and acoustic measures to ensure the required noise reduction, a verification calculation of the expected sound pressure levels at the same design points is carried out, taking into account the effectiveness of these measures.
The materials given below do not claim to be complete in the presentation of the method of acoustic calculation of ventilation systems (installations). They contain information that clarifies, supplements or reveals in a new way various aspects of this technique using the example of the acoustic calculation of a fan as the main source of noise in a ventilation system. The materials will be used in the preparation of a set of rules for the calculation and design of noise attenuation of ventilation installations for the new SNiP.
The initial data for the acoustic calculation are the noise characteristics of the equipment - sound power levels (SPL) in octave bands with geometric mean frequencies of 63, 125, 250, 500, 1,000, 2,000, 4,000, 8,000 Hz. For indicative calculations, corrected sound power levels of noise sources in dBA are sometimes used.
The calculated points are located in human habitats, in particular, at the place where the fan is installed (in the ventilation chamber); in rooms or in areas adjacent to the installation site of the fan; in rooms served by a ventilation system; in rooms where air ducts pass in transit; in the area of the air intake or exhaust device, or only the air intake for recirculation.
The calculated point is in the room where the fan is installed
In general, sound pressure levels in a room depend on the sound power of the source and the directivity factor of noise emission, the number of noise sources, the location of the design point relative to the source and the enclosing building structures, and the size and acoustic qualities of the room.
The octave sound pressure levels generated by the fan (fans) at the installation site (in the ventilation chamber) are equal to:
where Фi is the directivity factor of the noise source (dimensionless);
S is the area of an imaginary sphere or part thereof surrounding the source and passing through the calculated point, m 2 ;
B is the acoustic constant of the room, m 2 .
The calculated point is located in the room adjacent to the room where the fan is installed
The octave levels of airborne noise penetrating through the fence into the isolated room adjacent to the room where the fan is installed are determined by the soundproofing ability of the noisy room fences and the acoustic qualities of the protected room, which is expressed by the formula:
| (3) |
where L w - octave sound pressure level in the room with a noise source, dB;
R - isolation from airborne noise by the enclosing structure through which the noise penetrates, dB;
S - area of the building envelope, m 2 ;
B u - acoustic constant of the insulated room, m 2 ;
k - coefficient that takes into account the violation of the diffuseness of the sound field in the room.
The calculated point is located in the room served by the system
The noise from the fan propagates through the air duct (air duct), partially attenuates in its elements and penetrates into the serviced room through the air distribution and air intake grilles. Octave levels of sound pressure in a room depend on the amount of noise reduction in the air duct and the acoustic qualities of this room:
| (4) |
where L Pi is the sound power level in the i-th octave radiated by the fan into the air duct;
D L networki - attenuation in the air channel (in the network) between the noise source and the room;
D L remember - the same as in formula (1) - formula (2).
Attenuation in the network (in the air channel) D L R network - the sum of the attenuation in its elements, sequentially located along the sound waves. The energy theory of sound propagation through pipes assumes that these elements do not influence each other. In fact, a sequence of shaped elements and straight sections form a single wave system, in which the principle of attenuation independence in the general case cannot be justified on pure sinusoidal tones. At the same time, in octave (wide) frequency bands, standing waves created by individual sinusoidal components compensate each other, and therefore the energy approach, which does not take into account the wave pattern in air ducts and considers the flow of sound energy, can be considered justified.
Attenuation in straight sections of air ducts made of sheet material is due to losses due to wall deformation and sound emission to the outside. The decrease in the sound power level D L R per 1 m of the length of straight sections of metal air ducts, depending on the frequency, can be judged from the data in Fig. one.
As can be seen, in rectangular ducts, the attenuation (lowering SAM) decreases with increasing sound frequency, while that of a circular duct increases. In the presence of thermal insulation on metal air ducts, shown in fig. 1 values should be approximately doubled.
The concept of attenuation (reduction) of the sound energy flow level cannot be identified with the concept of a change in the sound pressure level in the air duct. As a sound wave travels through a channel, the total amount of energy it carries decreases, but this is not necessarily due to a decrease in the sound pressure level. In a narrowing channel, despite the attenuation of the total energy flow, the sound pressure level can increase due to an increase in the sound energy density. Conversely, in an expanding duct, the energy density (and sound pressure level) can decrease faster than the total sound power. The attenuation of sound in a section with a variable cross section is equal to:
 |
(5) |
where L 1 and L 2 are the average sound pressure levels in the initial and final sections of the channel section along the sound waves;
F 1 and F 2 - cross-sectional areas, respectively, at the beginning and end of the channel section.
Attenuation at bends (in elbows, bends) with smooth walls, the cross section of which is less than the wavelength, is determined by the reactance of the additional mass type and the appearance of higher order modes. The kinetic energy of the flow at the turn without changing the cross section of the channel increases due to the resulting non-uniformity of the velocity field. The square turn acts like a low pass filter. The amount of noise reduction at a turn in the plane wave range is given by an exact theoretical solution:
 |
(6) |
where K is the modulus of the sound transmission coefficient.
For a ≥ l /2, the value of K is equal to zero, and the incident plane sound wave is theoretically completely reflected by the channel rotation. The maximum noise reduction is observed when the turning depth is approximately half the wavelength. The value of the theoretical modulus of the coefficient of sound transmission through rectangular turns can be judged from Fig. 2.
In real designs, according to the data of the works, the maximum attenuation is 8-10 dB, when half the wavelength fits in the channel width. With increasing frequency, the attenuation decreases to 3-6 dB in the region of wavelengths close in magnitude to twice the channel width. Then it again smoothly increases at high frequencies, reaching 8-13 dB. On fig. Figure 3 shows the noise attenuation curves at channel turns for plane waves (curve 1) and for random, diffuse sound incidence (curve 2). These curves are obtained on the basis of theoretical and experimental data. The presence of a noise reduction maximum at a = l /2 can be used to reduce noise with low-frequency discrete components by adjusting the channel sizes at turns to the frequency of interest.
Noise reduction on turns less than 90° is approximately proportional to the angle of the turn. For example, the noise reduction on a 45° turn is equal to half the noise reduction on a 90° turn. On curves with an angle of less than 45°, noise reduction is not taken into account. For smooth bends and straight bends of air ducts with guide vanes, the noise reduction (sound power level) can be determined using the curves in Fig. four.
In branching channels, the transverse dimensions of which are less than half the wavelength of the sound wave, the physical causes of attenuation are similar to the causes of attenuation in elbows and bends. This attenuation is determined as follows (Fig. 5).
Based on the medium continuity equation:
From the pressure continuity condition (r p + r 0 = r pr) and equation (7), the transmitted sound power can be represented by the expression
and the reduction in the sound power level at the cross-sectional area of the branch
 |
(11) |
 |
(12) |
(13) |
With a sudden change in the cross section of a channel with transverse dimensions less than half-wavelengths (Fig. 6 a), the decrease in the sound power level can be determined in the same way as with branching.
The calculation formula for such a change in the channel cross section has the form
 |
(14) |
where m is the ratio of the larger cross-sectional area of the channel to the smaller one.
The reduction in sound power levels when the channel sizes are larger than the non-planar half-wavelengths due to a sudden narrowing of the channel is
If the channel expands or gradually narrows (Fig. 6 b and 6 d), then the decrease in the sound power level is equal to zero, since there is no reflection of waves with a length shorter than the channel dimensions.
In simple elements of ventilation systems, the following reduction values are taken at all frequencies: heaters and air coolers 1.5 dB, central air conditioners 10 dB, mesh filters 0 dB, the junction of the fan to the air duct network 2 dB.
Reflection of sound from the end of the duct occurs if the transverse dimension of the duct is less than the length of the sound wave (Fig. 7).
If a plane wave propagates, then there is no reflection in a large duct, and we can assume that there are no reflection losses. However, if an opening connects a large room and an open space, then only diffuse sound waves directed towards the opening, the energy of which is equal to a quarter of the energy of the diffuse field, enter the opening. Therefore, in this case, the sound intensity level is attenuated by 6 dB.
Characteristics of directivity of sound emission by air distribution grilles are shown in fig. eight.
When the noise source is located in space (for example, on a column in a large room) S = 4p r 2 (radiation in a full sphere); in the middle part of the wall, floors S = 2p r 2 (radiation into the hemisphere); in a dihedral angle (radiation in 1/4 sphere) S = p r 2 ; in the trihedral angle S = p r 2 /2.
The attenuation of the noise level in the room is determined by formula (2). The calculated point is selected at the place of permanent residence of people closest to the noise source, at a distance of 1.5 m from the floor. If the noise at the design point is created by several gratings, then the acoustic calculation is made taking into account their total impact.
When the source of noise is a section of a transit air duct passing through the room, the initial data for the calculation according to formula (1) are the octave sound power levels of the noise emitted by it, determined by the approximate formula:
(16) |
where L pi is the sound power level of the source in the i-th octave frequency band, dB;
D L' Рneti - attenuation in the network between the source and the transit section under consideration, dB;
R Ti - sound insulation of the structure of the transit section of the air duct, dB;
S T - surface area of the transit section, which goes into the room, m 2 ;
F T - cross-sectional area of the duct section, m 2 .
Formula (16) does not take into account the increase in the density of sound energy in the duct due to reflections; the conditions for the incidence and passage of sound through the duct structure are significantly different from the passage of diffuse sound through the enclosures of the room.
Settlement points are located on the territory adjacent to the building
Fan noise propagates through the air duct and is radiated into the surrounding space through a grill or shaft, directly through the walls of the fan housing or an open pipe when the fan is installed outside the building.
When the distance from the fan to the calculated point is much larger than its dimensions, the noise source can be considered as a point source.
In this case, the octave sound pressure levels at the calculated points are determined by the formula
(17) |
where L Pocti is the octave level of the sound power of the noise source, dB;
D L Pseti - total reduction of the sound power level along the path of sound propagation in the duct in the considered octave band, dB;
D L ni - sound radiation directivity indicator, dB;
r - distance from the noise source to the calculated point, m;
W - spatial angle of sound emission;
b a - sound attenuation in the atmosphere, dB/km.
If there is a row of several fans, grilles or other extended noise source of limited dimensions, then the third term in formula (17) is taken equal to 15 lgr .
Structural noise calculation
Structural noise in rooms adjacent to ventilation chambers occurs as a result of the transfer of dynamic forces from the fan to the ceiling. The octave sound pressure level in the adjacent isolated room is determined by the formula
For fans located in the technical room outside the ceiling above the isolated room:
 |
(20) |
where L Pi is the octave sound power level of airborne noise emitted by the fan into the ventilation chamber, dB;
Z c - total wave resistance of the elements of vibration isolators, on which the refrigeration machine is installed, N s / m;
Z lane - input impedance of the ceiling - the carrier plate, in the absence of a floor on an elastic base, the floor plate - if available, N s / m;
S - conditional floor area of the technical room above the isolated room, m 2;
S = S 1 for S 1 > S u /4; S = S u /4; with S 1 ≤ S u /4, or if the technical room is not located above the isolated room, but has one common wall with it;
S 1 - the area of the technical room above the isolated room, m 2;
S u - area of the isolated room, m 2;
S in - the total area of the technical room, m 2;
R - own insulation of airborne noise by overlapping, dB.
Determination of required noise reduction
The required reduction in octave sound pressure levels is calculated separately for each noise source (fan, fittings, fittings), but at the same time, the number of noise sources of the same type in terms of the sound power spectrum and the magnitude of the sound pressure levels created by each of them at the calculated point are taken into account. In general, the required noise reduction for each source should be such that the total levels in all octave frequency bands from all noise sources do not exceed the permissible sound pressure levels .
In the presence of one noise source, the required reduction in octave sound pressure levels is determined by the formula
where n is the total number of noise sources taken into account.
In the total number of noise sources n, when determining D L tri the required reduction in octave sound pressure levels in urban areas, all noise sources that create sound pressure levels at the design point that differ by less than 10 dB should be included.
When determining D L tri for design points in a room protected from ventilation system noise, the total number of noise sources should include:
When calculating the required fan noise reduction - the number of systems serving the room; noise generated by air distribution devices and fittings is not taken into account;
When calculating the required noise reduction generated by the air distribution devices of the considered ventilation system, - the number of ventilation systems serving the room; the noise of the fan, air distribution devices and fittings is not taken into account;
When calculating the required noise reduction generated by shaped elements and air distribution devices of the considered branch, the number of shaped elements and chokes, the noise levels of which differ from one another by less than 10 dB; the noise of the fan and grilles is not taken into account.
At the same time, the total number of noise sources taken into account does not take into account noise sources that create at the design point the sound pressure level 10 dB lower than the permissible one, if their number is not more than 3 and 15 dB less than the permissible one, if their number is not more than 10.
As you can see, acoustic calculation is not an easy task. The necessary accuracy of its solution is provided by acoustic specialists. The efficiency of noise suppression and the cost of its implementation depend on the accuracy of the performed acoustic calculation. If the value of the calculated required noise reduction is underestimated, then the measures will not be effective enough. In this case, it will be necessary to eliminate the shortcomings at the operating facility, which is inevitably associated with significant material costs. If the required noise reduction is overestimated, unjustified costs are laid directly into the project. So, only due to the installation of silencers, the length of which is 300-500 mm longer than required, additional costs for medium and large objects can amount to 100-400 thousand rubles or more.
Literature
1. SNiP II-12-77. Noise protection. Moscow: Stroyizdat, 1978.
2. SNiP 23-03-2003. Noise protection. Gosstroy of Russia, 2004.
3. Gusev V.P. Acoustic requirements and design rules for low-noise ventilation systems // ABOK. 2004. No. 4.
4. Guidance for the calculation and design of noise attenuation of ventilation installations. Moscow: Stroyizdat, 1982.
5. Yudin E. Ya., Terekhin AS Fighting the noise of mine ventilation installations. Moscow: Nedra, 1985.
6. Noise reduction in buildings and residential areas. Ed. G. L. Osipova, E. Ya. Yudina. Moscow: Stroyizdat, 1987.
7. Khoroshev S. A., Petrov Yu. I., Egorov P. F. Control of fan noise. Moscow: Energoizdat, 1981.
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