Acoustic calculations

Among the problems of health improvement environment the fight against noise is one of the most pressing. IN major cities noise is one of the main physical factors shaping environmental conditions.

Growth of industrial and housing construction, rapid development various types transport, increasingly used in residential and public buildings plumbing and engineering equipment, household appliances led to the fact that noise levels in residential areas of the city became comparable to noise levels in production.

The noise regime of large cities is formed mainly by automobile and rail transport, accounting for 60-70% of all noise.

A noticeable impact on the noise level is exerted by the increase in the intensity of air traffic, the emergence of new powerful airplanes and helicopters, as well as railway transport, open metro lines and shallow metro.

At the same time, in some large cities where measures are being taken to improve the noise environment, a decrease in noise levels is observed.

There are acoustic and non-acoustic noises, what is their difference?

Acoustic noise is defined as a set of sounds of varying strength and frequency that arise as a result of 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 electric vacuum devices (shot noise, flicker noise), uneven processes of generation and recombination of charge carriers (conduction electrons and holes) in semiconductor devices, thermal movement of current carriers in conductors (thermal noise), thermal radiation of the Earth and earth's atmosphere, as well as planets, the Sun, stars, the interstellar medium, etc. (space noise).

Acoustic calculation, noise level calculation.

During the construction and operation of various facilities, noise control problems are an integral part of occupational safety and public health protection. Machines can act as sources vehicles, mechanisms and other equipment. Noise, its impact and vibration on a person depend on the sound pressure level and frequency characteristics.

Standardization 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 current regulations. sanitary standards and rules.

The objectives of the acoustic calculation are:

Identifying noise sources;

Determination of their noise characteristics;

Determination of the degree of influence of noise sources on standardized objects;

Calculation and construction of individual zones of acoustic discomfort of noise sources;

Development of special noise protection measures to ensure the required acoustic comfort.

Installation of ventilation and air conditioning systems is already considered a natural need in any building (be it residential or administrative); acoustic calculations must also be performed for premises of this type. So, if the noise level is not calculated, it may turn out that the room is very low level sound absorption, and this greatly complicates the process of communication between people in it.

Therefore, before installing ventilation systems in a room, it is necessary to carry out an acoustic calculation. If it turns out that a room has poor acoustic properties, it is necessary to propose a number of measures to improve the acoustic environment in the room. That's why acoustic calculations are also carried out for the installation of household air conditioners.

Acoustic calculations are most often carried out for objects that have complex acoustics or have increased 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 travels in air at a speed of 344 m/s in 3 seconds. 1 km.

The threshold of hearing depends on the frequency of the sounds felt and is equal to 10-12 W/m2 at frequencies close to 1000 Hz. The upper limit is the pain threshold, which is less dependent on frequency and lies in the range of 130 - 140 dB (at a frequency of 1000 Hz, intensity 10 W/m2, sound pressure).

The ratio of intensity level and frequency determines the sensation of sound volume, i.e. sounds of different frequencies and intensities can be assessed by a person as equally loud.

When perceiving sound signals against a certain acoustic background, a signal masking effect may be observed.

The masking effect can have a negative impact on 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 tone, which is less harmful to humans.

The procedure for performing acoustic calculations.

To perform an acoustic calculation, the following data will be required:

Dimensions of the room for which the noise level will be calculated;

Main characteristics of the premises and its properties;

Noise spectrum from the source;

Characteristics of the obstacle;

Data on the distance from the center of the noise source to the acoustic calculation point.

When calculating, first the noise sources and their characteristic properties are determined. Next, points on the object under study 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 made to reduce noise to the required standards. Having received all the necessary data, a project is carried out to develop measures that will reduce noise levels.

Correctly performed acoustic calculations are 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 noise levels:

* installation of soundproofing structures;

* use of seals in windows, doors, gates;

* use of structures and screens that absorb sound;

*planning and construction residential area in accordance with SNiP;

* use of noise suppressors in ventilation systems and air conditioning systems.

Carrying out acoustic calculations.

Work on calculating noise levels, assessing acoustic (noise) impact, as well as designing specialized noise protection measures must be carried out by a specialized organization with the relevant field.

noise acoustic calculation measurement

In the simplest definition, the main task of acoustic calculation is to estimate the noise level created by a noise source at a given design point with an established quality of acoustic impact.

The acoustic calculation process consists of the following main stages:

1. Collection of 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 weakened elements of enclosing structures through which noise will penetrate into the environment;

Geometric and soundproofing parameters weakened elements of enclosing structures;

Analysis of nearby objects with established quality of acoustic impact, determination of permissible sound levels for each object;

Analysis of distances from external sources noise to standardized objects;

Analysis of possible shielding elements along the path of sound wave propagation (buildings, green spaces, etc.);

Analysis of weakened elements of enclosing structures (window openings, doors, etc.) through which noise will penetrate into regulated premises, identifying their soundproofing ability.

2. Acoustic calculations are made based on current methodological instructions and recommendations. Basically these are “Calculation methods, standards”.

At each calculation point, it is necessary to sum up all available noise sources.

The result of the acoustic calculation is 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 calculation results.

Analysis of the results obtained is carried out by comparing the values ​​​​obtained at the design point with the established Sanitary Standards.

If necessary, the next stage of the acoustic calculation may be the design of the necessary noise protection measures that will reduce the acoustic impact at the design 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:

Noise Exposure Measurement existing systems ventilation and air conditioning for office buildings, private apartments, etc.;

Carrying out measurements of noise levels for certification of workplaces;

Carrying out work on instrumental measurement of noise levels within the project;

Carrying out work on instrumental measurement of noise levels as part of technical reports when approving the boundaries of the sanitary protection zone;

Carrying out any instrumental measurements of noise exposure.

Instrumental measurements of noise levels are carried out by a specialized mobile laboratory using modern equipment.

Acoustic calculation deadlines. The timing of the work depends on the volume of calculations and measurements. If it is necessary to carry out acoustic calculations for residential development projects or administrative facilities, then they are completed on average 1 - 3 weeks. Acoustic calculations for large or unique objects (theatres, organ halls) take longer, based on the data provided raw materials. In addition, the operating life is largely influenced by the number of noise sources studied, as well as external factors.

Ventilation calculation

Depending on the method of air movement, ventilation can be natural or forced.

Parameters of air entering the intake openings and openings of local suctions of technological and other devices that are located in work area, should be taken in accordance with GOST 12.1.005-76. With a room size of 3 by 5 meters and a height of 3 meters, its volume is 45 cubic meters. Therefore, ventilation should provide an air flow of 90 cubic meters per hour. IN summer time it is necessary to provide for the installation of an air conditioner in order to avoid exceeding the temperature in the room for stable operation equipment. It is necessary to pay due attention to the amount of dust in the air, as this directly affects the reliability and service life of the computer.

The power (more precisely, the cooling power) of an air conditioner is its main characteristic; it determines the volume of the room it is designed for. For approximate calculations 1 kW is taken per 10 m 2 with a ceiling height of 2.8 - 3 m (in accordance with SNiP 2.04.05-86 "Heating, ventilation and air conditioning").

To calculate the heat inflows of a given room, a simplified method was used:

where:Q - Heat inflow

S - Room area

h - Room height

q - Coefficient equal to 30-40 W/m 3 (in this case 35 W/m 3)

For a room of 15 m2 and a height of 3 m, the heat gain will be:

Q=15·3·35=1575 W

In addition, the heat emission from office equipment and people should be taken into account; it is believed (in accordance with SNiP 2.04.05-86 “Heating, ventilation and air conditioning”) that in a calm state a person emits 0.1 kW of heat, a computer or copy machine 0.3 kW, By adding these values ​​to the total heat inflows, you can obtain the required cooling capacity.

Q additional =(H·S opera)+(С·S comp)+(P·S print) (4.9)

where: Q additional - Sum of additional heat inflows

C - Computer heat dissipation

H - Operator Heat Dissipation

D - Printer Heat Dissipation

S comp - Number of workstations

S print - Number of printers

S operators - Number of operators

Additional heat inflows in the room will be:

Q additional1 =(0.1 2)+(0.3 2)+(0.3 1)=1.1(kW)

The total sum of heat inflows is equal to:

Q total1 =1575+1100=2675 (W)

In accordance with these calculations, it is necessary to select the appropriate power and number of air conditioners.

For the room for which the calculation is being carried out, air conditioners with a rated power of 3.0 kW should be used.

Noise level calculation

One of the unfavorable factors of the production environment in the ICC is high level noise generated by printing devices, air conditioning equipment, fans of cooling systems in the computers themselves.

To address questions about the need and feasibility of noise reduction, it is necessary to know the noise levels at the operator’s workplace.

The noise level arising from several incoherent sources operating simultaneously is calculated based on the principle of energy summation of emissions from individual sources:

L = 10 lg (Li n), (4.10)

where Li is the sound pressure level of the i-th noise source;

n is the number of noise sources.

The obtained calculation results are compared with the permissible noise level for a given workplace. If the calculation results are higher than the permissible noise level, then special noise reduction measures are required. These include: covering the walls and ceiling of the hall with sound-absorbing materials, reducing noise at the source, proper layout of equipment and rational organization of the operator’s workplace.

The sound pressure levels of noise sources affecting the operator at his workplace are presented in table. 4.6.

Table 4.6 - Sound pressure levels of various sources

Usually workplace operator is equipped with the following equipment: hard drive in system unit, PC cooling fan(s), monitor, keyboard, printer and scanner.

Substituting the sound pressure level values ​​for each type of equipment into formula (4.4), we obtain:

L=10 lg(104+104.5+101.7+101+104.5+104.2)=49.5 dB

The resulting value does not exceed permissible level noise for the operator's workplace, equal to 65 dB (GOST 12.1.003-83). And if we take into account that it is unlikely that peripheral devices such as a scanner and printer will be used at the same time, then this figure will be even lower. In addition, when the printer is operating, the direct presence of the operator is not necessary, because The printer is equipped with an automatic sheet feed mechanism.

2008-04-14

The ventilation and air conditioning system (HVAC) is one of the main sources of noise in modern residential, public and industrial buildings, on ships, in sleeping cars of trains, in all kinds of salons and control cabins.

The noise in the HVAC comes from the fan (the main source of noise with its own tasks) and other sources, spreads through the air duct along with the air flow and is radiated into the ventilated room. Noise and its reduction are affected by: air conditioners, heating units, control and air distribution devices, design, turns and branching of air ducts.

Acoustic calculation of the UVAV is carried out with the aim of optimal choice all necessary means of noise reduction and determination of the expected noise level at design points in the room. Traditionally, the main means of reducing system noise are active and reactive noise suppressors. Sound insulation and sound absorption of the system and room is required to ensure compliance with the norms of noise levels permissible for humans - important environmental standards.

Now in building codes and Russian rules (SNiP), mandatory in the design, construction and operation of buildings in order to protect people from noise, has developed emergency. In the old SNiP II-12-77 “Noise Protection”, the method of acoustic calculation of HVAC buildings was outdated and therefore was not included in the new SNiP 03/23/2003 “Noise Protection” (instead of SNiP II-12-77), where it is not yet included absent.

Thus, the old method is outdated, but the new one is not. It's time to create modern method acoustic calculation of UVA in buildings, as is already the case with its own specifics in other, previously more advanced in acoustics, areas of technology, for example, on sea vessels. Let's consider three possible ways acoustic calculation, in relation to UHCR.

The first method of acoustic calculation. This method, based purely on analytical dependencies, uses the theory of long lines, known in electrical engineering and here referred to the propagation of sound in a gas filling a narrow pipe with rigid walls. The calculation is made under the condition that the diameter of the pipe is much less than the length of the sound wave.

For pipe rectangular section side must be less than half the wavelength, and for round pipe— radius. It is these pipes that are called narrow in acoustics. Thus, for air at a frequency of 100 Hz, a rectangular pipe will be considered narrow if the cross-section side is less than 1.65 m. In a narrow curved pipe sound propagation will remain the same as in a straight pipe.

This is known from the practice of using speaking pipes, for example, on ships for a long time. Typical scheme long line ventilation system has two defining quantities: L wH is the sound power entering the discharge pipeline from the fan at the beginning of the long line, and L wK is the sound power emanating from the discharge pipeline at the end of the long line and entering the ventilated room.

The long line contains the following characteristic elements. We list them: inlet with sound insulation R 1, active silencer with sound insulation R 2, tee with sound insulation R 3, reactive silencer with sound insulation R 4, throttle valve with sound insulation R 5 and exhaust outlet with sound insulation R 6. Sound insulation here refers to the difference in dB between the sound power in the waves incident on a given element and the sound power emitted by this element after the waves pass through it further.

If the sound insulation of each of these elements does not depend on all the others, then the sound insulation of the entire system can be estimated by calculation as follows. The wave equation for a narrow pipe has the following form of the equation for plane sound waves in an unbounded medium:

where c is the speed of sound in air, and p is the sound pressure in the pipe, related to the vibrational speed in the pipe according to Newton’s second law by the relation

where ρ is the air density. Sound power for plane harmonic waves is equal to the integral over the cross-sectional area S of the air duct over a period sound vibrations T to W:

where T = 1/f is the period of sound vibrations, s; f—oscillation frequency, Hz. Sound power in dB: L w = 10lg(N/N 0), where N 0 = 10 -12 W. Within the specified assumptions, the sound insulation of a long line of the ventilation system is calculated using the following formula:

The number of elements n for a specific HVAC can, of course, be greater than the above n = 6. To calculate the values ​​of R i, let us apply the theory of long lines to the above characteristic elements of the air ventilation system.

Inlet and outlet openings of the ventilation system with R 1 and R 6. The junction of two narrow pipes with different areas cross sections S 1 and S 2 according to the theory of long lines are an analogue of the interface between two media with normal incidence of sound waves on the interface. The boundary conditions at the junction of two pipes are determined by the equality of sound pressures and vibrational velocities on both sides of the junction boundary, multiplied by the cross-sectional area of ​​the pipes.

Solving the equations obtained in this way, we obtain the energy transmission coefficient and sound insulation of the junction of two pipes with the sections indicated above:

Analysis of this formula shows that at S 2 >> S 1 the properties of the second pipe approach the properties of the free boundary. For example, a narrow pipe open to a semi-infinite space can be considered, from the point of view of soundproofing effect, as bordering on a vacuum. When S 1<< S 2 свойства второй трубы приближаются к свойствам жесткой границы. В обоих случаях звукоизоляция максимальна. При равенстве площадей сечений первой и второй трубы отражение от границы отсутствует и звукоизоляция равна нулю независимо от вида сечения границы.

Active silencer R2. Sound insulation in this case can be approximately and quickly estimated in dB, for example, using the well-known formula of engineer A.I. Belova:

where P is the perimeter of the flow section, m; l — muffler length, m; S is the cross-sectional area of ​​the muffler channel, m2; α eq is the equivalent sound absorption coefficient of the cladding, depending on the actual absorption coefficient α, for example, as follows:

α 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

α eq 0.1 0.2 0.4 0.5 0.6 0.9 1.2 1.6 2.0 4.0

It follows from the formula that the sound insulation of the active muffler channel R 2 is greater, the greater the absorption capacity of the walls α eq, the length of the muffler l and the ratio of the channel perimeter to its cross-sectional area P/S. For the best sound-absorbing materials, for example, PPU-ET, BZM and ATM-1 brands, as well as other widely used sound absorbers, the actual sound absorption coefficient α is presented in.

Tee R3. In ventilation systems, most often the first pipe with cross-sectional area S 3 then branches into two pipes with cross-sectional areas S 3.1 and S 3.2. This branching is called a tee: sound enters through the first branch, and passes further through the other two. In general, the first and second pipe may consist of a plurality of pipes. Then we have

The sound insulation of the tee from section S 3 to section S 3.i is determined by the formula

Note that, due to aerohydrodynamic considerations, tees strive to ensure that the cross-sectional area of ​​the first pipe is equal to the sum of the cross-sectional areas in the branches.

Reactive (chamber) noise suppressor R4. The chamber noise suppressor is an acoustically narrow pipe with a cross-section S 4 , which turns into another acoustically narrow pipe with a large cross-section S 4.1 of length l, called a chamber, and then again turns into an acoustically narrow pipe with a cross-section S 4 . Let us also use the long line theory here. By replacing the characteristic impedance in the known formula for sound insulation of a layer of arbitrary thickness at normal incidence of sound waves with the corresponding reciprocal values ​​of the pipe area, we obtain the formula for sound insulation of a chamber noise muffler

where k is the wave number. The sound insulation of a chamber noise suppressor reaches its greatest value when sin(kl) = 1, i.e. at

where n = 1, 2, 3, … Frequency of maximum sound insulation

where c is the speed of sound in air. If several chambers are used in such a muffler, then the sound insulation formula must be applied sequentially from chamber to chamber, and the total effect is calculated using, for example, the boundary conditions method. Effective chamber silencers sometimes require large overall dimensions. But their advantage is that they can be effective at any frequency, including low ones, where active jammers are practically useless.

The zone of high sound insulation of chamber noise suppressors covers repeating fairly wide frequency bands, but they also have periodic zones of sound transmission, very narrow in frequency. To increase efficiency and equalize the frequency response, a chamber muffler is often lined on the inside with a sound absorber.

Damper R5. The valve is structurally a thin plate with an area S 5 and a thickness δ 5, clamped between the flanges of the pipeline, the hole in which with an area S 5.1 is less than the internal diameter of the pipe (or other characteristic size). Soundproofing of such a throttle valve

where c is the speed of sound in air. In the first method, the main issue for us when developing a new method is assessing the accuracy and reliability of the result of the acoustic calculation of the system. Let us determine the accuracy and reliability of the result of calculating the sound power entering the ventilated room - in this case, the value

Let us rewrite this expression in the following notation for an algebraic sum, namely

Note that the absolute maximum error of an approximate value is the maximum difference between its exact value y 0 and the approximate value y, that is ± ε = y 0 - y. The absolute maximum error of the algebraic sum of several approximate quantities y i is equal to the sum of the absolute values ​​of the absolute errors of the terms:

The least favorable case is adopted here, when the absolute errors of all terms have the same sign. In reality, partial errors can have different signs and be distributed according to different laws. Most often in practice, the errors of an algebraic sum are distributed according to the normal law (Gaussian distribution). Let us consider these errors and compare them with the corresponding value of the absolute maximum error. Let us determine this quantity under the assumption that each algebraic term y 0i of the sum is distributed according to the normal law with center M(y 0i) and standard

Then the sum also follows the normal distribution law with mathematical expectation

The error of the algebraic sum is determined as:

Then we can say that with a reliability equal to the probability 2Φ(t), the error of the sum will not exceed the value

With 2Φ(t), = 0.9973 we have t = 3 = α and the statistical estimate with almost maximum reliability is the error of the sum (formula) The absolute maximum error in this case

Thus ε 2Φ(t)<< ε. Проиллюстрируем это на примере результатов расчета по первому способу. Если для всех элементов имеем ε i = ε= ±3 дБ (удовлетворительная точность исходных данных) и n = 7, то получим ε= ε n = ±21 дБ, а (формула). Результат имеет совершенно неудовлетворительную точность, он неприемлем. Если для всех характерных элементов системы вентиляции воздуха имеем ε i = ε= ±1 дБ (очень высокая точность расчета каждого из элементов n) и тоже n = 7, то получим ε= ε n = ±7 дБ, а (формула).

Here, the result of a probabilistic error estimate in a first approximation can be more or less acceptable. So, a probabilistic assessment of errors is preferable and it is this that should be used to select the “margin for ignorance”, which is proposed to be necessarily used in the acoustic calculation of UAHV to guarantee compliance with permissible noise standards in a ventilated room (this has not been done previously).

But the probabilistic assessment of the errors of the result in this case indicates that it is difficult to achieve high accuracy of calculation results using the first method even for very simple schemes and a low-speed ventilation system. For simple, complex, low- and high-speed UHF circuits, satisfactory accuracy and reliability of such calculations can be achieved in many cases only using the second method.

The second method of acoustic calculation. On sea vessels, a calculation method has long been used, based partly on analytical dependencies, but decisively on experimental data. We use the experience of such calculations on ships for modern buildings. Then, in a ventilated room served by one j-th air distributor, noise levels L j, dB, at the design point should be determined by the following formula:

where L wi is the sound power, dB, generated in the i-th element of the UAHV, R i is the sound insulation in the i-th element of the UHVAC, dB (see the first method),

a value that takes into account the influence of a room on the noise in it (in construction literature, B is sometimes used instead of Q). Here r j is the distance from the j-th air distributor to the design point of the room, Q is the sound absorption constant of the room, and the values ​​χ, Φ, Ω, κ are empirical coefficients (χ is the near-field influence coefficient, Ω is the spatial angle of the source radiation, Φ is the factor directivity of the source, κ is the coefficient of disturbance of the diffuseness of the sound field).

If m air distributors are located in the premises of a modern building, the noise level from each of them at the design point is equal to L j, then the total noise from all of them should be below the noise levels permissible for humans, namely:

where L H is the sanitary noise standard. According to the second method of acoustic calculation, the sound power L wi generated in all elements of the UHCR and the sound insulation Ri occurring in all these elements are determined experimentally for each of them in advance. The fact is that over the past one and a half to two decades, electronic technology for acoustic measurements, combined with a computer, has progressed greatly.

As a result, enterprises producing UHCR elements must indicate in their passports and catalogs the characteristics of L wi and Ri, measured in accordance with national and international standards. Thus, in the second method, noise generation is taken into account not only in the fan (as in the first method), but also in all other elements of the UHCR, which can be significant for medium- and high-speed systems.

In addition, since it is impossible to calculate the sound insulation R i of such system elements as air conditioners, heating units, control and air distribution devices, therefore they are not included in the first method. But it can be determined with the necessary accuracy by standard measurements, which is now being done for the second method. As a result, the second method, unlike the first, covers almost all UVA schemes.

And finally, the second method takes into account the influence of the properties of the room on the noise in it, as well as the values ​​of noise acceptable for humans according to the current building codes and regulations in this case. The main disadvantage of the second method is that it does not take into account the acoustic interaction between the elements of the system - interference phenomena in pipelines.

The summation of the sound powers of noise sources in watts, and the sound insulation of elements in decibels, according to the specified formula for the acoustic calculation of UHFV, is valid only, at least, when there is no interference of sound waves in the system. And when there is interference in pipelines, it can be a source of powerful sound, which is what, for example, the sound of some wind musical instruments is based on.

The second method has already been included in the textbook and in the guidelines for course projects in building acoustics for senior students of the St. Petersburg State Polytechnic University. Failure to take into account interference phenomena in pipelines increases the “margin for ignorance” or requires, in critical cases, experimental refinement of the result to the required degree of accuracy and reliability.

To select the “margin for ignorance”, it is preferable, as shown above for the first method, to use a probabilistic error assessment, which is proposed to be used in the acoustic calculation of UHVAC buildings to guarantee compliance with permissible noise standards in premises when designing modern buildings.

The third method of acoustic calculation. This method takes into account interference processes in a narrow pipeline of a long line. Such accounting can radically increase the accuracy and reliability of the result. For this purpose, it is proposed to apply for narrow pipes the “impedance method” of Academician of the USSR Academy of Sciences and the Russian Academy of Sciences L.M. Brekhovskikh, which he used when calculating the sound insulation of an arbitrary number of plane-parallel layers.

So, let us first determine the input impedance of a plane-parallel layer with thickness δ 2, the sound propagation constant of which is γ 2 = β 2 + ik 2 and the acoustic resistance Z 2 = ρ 2 c 2. Let us denote the acoustic resistance in the medium in front of the layer from which the waves fall, Z 1 = ρ 1 c 1 , and in the medium behind the layer we have Z 3 = ρ 3 c 3 . Then the sound field in the layer, with the factor i ωt omitted, will be a superposition of waves traveling in the forward and reverse directions with sound pressure

The input impedance of the entire layer system (formula) can be obtained by simply applying (n - 1) times the previous formula, then we have

Let us now apply, as in the first method, the theory of long lines to a cylindrical pipe. And thus, with interference in narrow pipes, we have the formula for sound insulation in dB of a long line of a ventilation system:

Input impedances here can be obtained both, in simple cases, by calculation, and, in all cases, by measurement on a special installation with modern acoustic equipment. According to the third method, similar to the first method, we have sound power emanating from the discharge duct at the end of a long UHVAC line and entering the ventilated room according to the following scheme:

Next comes the assessment of the result, as in the first method with a “margin for ignorance,” and the sound pressure level of the room L, as in the second method. We finally obtain the following basic formula for the acoustic calculation of the ventilation and air conditioning system of buildings:

With the reliability of the calculation 2Φ(t) = 0.9973 (practically the highest degree of reliability), we have t = 3 and the error values ​​are equal to 3σ Li and 3σ Ri. With reliability 2Φ(t)= 0.95 (high degree of reliability), we have t = 1.96 and the error values ​​are approximately 2σ Li and 2σ Ri. With reliability 2Φ(t)= 0.6827 (engineering reliability assessment), we have t = 1.0 and the error values ​​are equal to σ Li and σ Ri The third method, aimed at the future, is more accurate and reliable, but also more complex - it requires high qualifications in the fields of building acoustics, probability theory and mathematical statistics, and modern measuring technology.

It is convenient to use in engineering calculations using computer technology. According to the author, it can be proposed as a new method for acoustic calculation of ventilation and air conditioning systems in buildings.

Summing up

The solution to pressing issues of developing a new acoustic calculation method should take into account the best of the existing methods. A new method for acoustic calculation of UVA buildings is proposed, which has a minimum “margin for ignorance” BB, thanks to taking into account errors using the methods of probability theory and mathematical statistics and taking into account interference phenomena by the impedance method.

The information about the new calculation method presented in the article does not contain some necessary details obtained through additional research and work practice, and which constitute the author’s “know-how”. The ultimate goal of the new method is to provide the choice of a set of means for reducing the noise of the ventilation and air conditioning system of buildings, which increases, compared to the existing one, efficiency, reducing the weight and cost of the HVAC.

There are no technical regulations in the field of industrial and civil construction yet, so developments in the field, in particular, of reducing the noise of UVA buildings are relevant and should be continued, at least until such regulations are adopted.

1. Brekhovskikh L.M. Waves in layered media // M.: Publishing House of the USSR Academy of Sciences. 1957.
2. Isakovich M.A. General acoustics // M.: Publishing house "Nauka", 1973.
3. Handbook of ship acoustics. Edited by I.I. Klyukin and I.I. Bogolepova. - Leningrad, “Shipbuilding”, 1978.
4. Khoroshev G.A., Petrov Yu.I., Egorov N.F. Fighting fan noise // M.: Energoizdat, 1981.
5. Kolesnikov A.E. Acoustic measurements. Approved by the Ministry of Higher and Secondary Specialized Education of the USSR as a textbook for university students studying in the specialty “Electroacoustics and Ultrasonic Technology” // Leningrad, “Shipbuilding”, 1983.
6. Bogolepov I.I. Industrial sound insulation. Preface by academician I.A. Glebova. Theory, research, design, manufacturing, control // Leningrad, “Shipbuilding”, 1986.
7. Aviation acoustics. Part 2. Ed. A.G. Munina. - M.: “Mechanical Engineering”, 1986.
8. Izak G.D., Gomzikov E.A. Noise on ships and methods for reducing it // M.: “Transport”, 1987.
9. Reducing noise in buildings and residential areas. Ed. G.L. Osipova and E.Ya. Yudina. - M.: Stroyizdat, 1987.
10. Building regulations. Noise protection. SNiP II-12-77. Approved by Resolution of the State Committee of the USSR Council of Ministers for Construction Affairs dated June 14, 1977 No. 72. - M.: Gosstroy of Russia, 1997.
11. Guidelines for the calculation and design of noise attenuation of ventilation units. Developed for SNiP II-12–77 by organizations of the Research Institute of Building Physics, GPI Santekhpoekt, NIISK. - M.: Stroyizdat, 1982.
12. Catalog of noise characteristics of process equipment (to SNiP II-12–77). Research Institute of Construction Physics of the USSR State Committee for Construction // M.: Stroyizdat, 1988.
13. Construction norms and rules of the Russian Federation. Sound protection. SNiP 23-03–2003. Adopted and put into effect by Decree of the State Construction Committee of Russia dated June 30, 2003 No. 136. Date of introduction 2004-04-01.
14. Sound insulation and sound absorption. Textbook for university students studying in the specialty “Industrial and Civil Engineering” and “Heat and Gas Supply and Ventilation”, ed. G.L. Osipova and V.N. Bobyleva. - M.: Publishing house AST-Astrel, 2004.
15. Bogolepov I.I. Acoustic calculation and design of ventilation and air conditioning systems. Guidelines for course projects. St. Petersburg State Polytechnic University // St. Petersburg. Publishing house SPbODZPP, 2004.
16. Bogolepov I.I. Construction acoustics. Preface by academician Yu.S. Vasilyeva // St. Petersburg. Polytechnic University Publishing House, 2006.
17. Sotnikov A.G. Processes, devices and systems of air conditioning and ventilation. Theory, technology and design at the turn of the century // St. Petersburg, AT-Publishing, 2007.
18. www.integral.ru. Firm "Integral". Calculation of the external noise level of ventilation systems according to: SNiP II-12–77 (Part II) - “Guide to the calculation and design of noise attenuation of ventilation units.” St. Petersburg, 2007.
19. www.iso.org is an Internet site that contains complete information about the International Organization for Standardization ISO, a catalog and an online standards store through which you can purchase any currently valid ISO standard in electronic or printed form.
20. www.iec.ch is an Internet site that contains complete information about the International Electrotechnical Commission IEC, a catalog and an online store of its standards, through which you can purchase the currently valid IEC standard in electronic or printed form.
21. www.nitskd.ru.tc358 is an Internet site that contains complete information about the work of the technical committee TK 358 “Acoustics” of the Federal Agency for Technical Regulation, a catalog and an online store of national standards, through which you can purchase the currently required Russian standard in electronic or printed form.
22. Federal Law of December 27, 2002 No. 184-FZ “On Technical Regulation” (as amended on May 9, 2005). Adopted by the State Duma on December 15, 2002. Approved by the Federation Council on December 18, 2002. On the implementation of this Federal Law, see Order of the State Mining and Technical Inspectorate of the Russian Federation dated March 27, 2003 No. 54.
23. Federal Law of May 1, 2007 No. 65-FZ “On Amendments to the Federal Law “On Technical Regulation”.

Ventilation systems are noisy and vibrate. The intensity and area of ​​sound propagation depends on the location of the main units, the length of the air ducts, overall performance, as well as the type of building and its functional purpose. The calculation of noise from ventilation is intended to select the operating mechanisms and materials used, in which it will not exceed the standard values, and is included in the design of ventilation systems as one of the points.

Ventilation systems consist of individual elements, each of which is a source of unpleasant sounds:

• For a fan, this may be a blade or a motor. The blade makes noise due to a sharp difference in pressure from one side to the other. Engine - due to breakdown or improper installation. Refrigeration units make noise for the same reasons, with the addition of improper compressor operation.
• Air ducts. There are two reasons: the first is vortex formations from the air hitting the walls. We talked about this in more detail in the article. The second is a hum in places where the cross-section of the air duct changes. Problems are solved by reducing the gas velocity.
• Building construction. Incidental noise from vibrations of fans and other installations transmitted to building elements. The solution is achieved by installing special supports or gaskets to dampen vibration. A good example is an air conditioner in an apartment: if the external unit is not fixed at all points, or the installers forgot to install protective gaskets, then its operation can cause acoustic discomfort to the owners of the installation or their neighbors.

Transfer methods

There are three ways sound travels, and in order to calculate the sound load, you need to know how exactly it is transmitted in all three ways:

• Airborne: noise from operating installations. Distributed both inside and outside the building. The main source of stress for people. For example, a large store whose air conditioners and refrigeration units are located at the rear of the building. Sound waves travel in all directions to nearby houses.
• Hydraulic: the source of noise is pipes with liquid. Sound waves are transmitted over long distances throughout the building. Caused by a change in the size of the pipeline cross-section and a malfunction of the compressor.
• Vibration: source - building structures. Caused by improper installation of fans or other system parts. It is transmitted throughout the building and beyond.

Some experts use scientific research from other countries in their calculations. For example, there is a formula published in a German magazine: it is used to calculate the generation of sound by the walls of the air duct, depending on the speed of the air flow.

Measuring method

It is often necessary to measure the permissible noise level or vibration intensity in already installed, operating ventilation systems. The classic measurement method involves the use of a special “sound level meter” device: it determines the strength of sound waves. Measurement is carried out using three filters that allow you to cut off unnecessary sounds outside the boundaries of the studied area. The first filter measures sound whose intensity does not exceed 50 dB. The second is from 50 to 85 dB. The third is over 80 dB.

Vibrations are measured in Hertz (Hz) for several points. For example, in the immediate vicinity of the noise source, then at a certain distance, after that - at the most distant point.

Rules and regulations

Rules for calculating noise from ventilation and algorithms for performing calculations are specified in SNiP 23-03-2003 “Protection from noise”; GOST 12.1.023-80 “System of occupational safety standards (SSBT). Noise. Methods for establishing the values ​​of noise characteristics of stationary machines.”

When determining the sound load near buildings, it must be remembered that the standard values ​​are given for intermittent mechanical ventilation and open windows. If closed windows and a forced air exchange system capable of providing the design multiplicity are taken into account, then other parameters are used as standards. The maximum noise level around the building increases to a limit that allows maintaining standard parameters indoors.

The sound load level requirements for residential and public buildings depend on their category:

1. A – the best conditions.
2. B - comfortable environment.
3. B – noise level at the limit limit.

Acoustic calculation

Used by designers to determine noise absorption. The main task of acoustic calculation is to calculate the active spectrum of sound loads at all points determined in advance, and compare the resulting value with the standard, maximum permissible. If necessary, reduce to established standards.

The calculation is carried out based on the noise characteristics of ventilation equipment; they must be indicated in the technical documentation.

Calculation points:

• direct installation location of the equipment;
• neighboring premises;
• all rooms where the ventilation system operates, including basements;
• air duct transit rooms;
• places of inlet inlet or exhaust outlet.

Acoustic calculations are performed using two basic formulas, the choice of which depends on the location of the point.

1. The calculation point is taken inside the building, in the immediate vicinity of the fan. Sound pressure depends on the power and number of fans, wave direction and other parameters. Formula 1 for determining octave sound pressure levels from one or more fans looks like this:

where L Pi is the sound power in each octave;
∆L pomi - reduction in the intensity of the noise load associated with multidirectional movement of sound waves and power losses from propagation in the air;

According to formula 2, ∆L is determined:

where Фi is the dimensionless factor of the wave propagation vector;
S is the area of ​​the sphere or hemisphere that covers the fan and the calculation point, m 2 ;
B is the constant value of the acoustic constant in the room, m2.

1. The calculation point is taken outside the building in the nearby area. The sound from operation spreads through the walls of the ventilation shafts, grilles and fan housing. It is conventionally assumed that the source of noise is a point source (the distance from the fan to the calculated position is an order of magnitude greater than the size of the device). Then the octave noise pressure level is calculated using formula 3:

where L Pocti is the octave power of the noise source, dB;
∆L Pneti - loss of sound power as it propagates through the air duct, dB;
∆L ni - sound radiation directivity indicator, dB;
r is the length of the segment from the fan to the calculation point, m;
W is the angle of sound radiation in space;
b a - reduction in noise intensity in the atmosphere, dB/km.

If one point is affected by several noise sources, for example, a fan and an air conditioner, then the calculation method changes slightly. You can’t just take and add up all the sources, so experienced designers take a different path, removing all unnecessary data. The difference between the largest and smallest source in intensity is calculated, and the resulting value is compared with the standard parameter and added to the level of the largest.

Reducing the sound load from fan operation

There is a set of measures that make it possible to level out noise factors from fan operation that are unpleasant to the human ear:

• Selection of equipment. A professional designer, unlike an amateur, always pays attention to the noise from the system and selects fans that provide standard microclimate parameters, but, at the same time, without a large power reserve. There is a wide range of fans with silencers on the market; they provide good protection against unpleasant sounds and vibrations.
• Selecting an installation location. Powerful ventilation equipment is installed only outside the serviced premises: this can be a roof or a special chamber. For example, if you put a fan in the attic of a panel house, the residents on the top floor will immediately feel discomfort. Therefore, in such cases only roof fans are used.
• Selection of air speed through channels. Designers proceed from acoustic calculations. For example, for a classic 300×900 mm air duct it is no more than 10 m/s.
• Vibration insulation, sound insulation and shielding. Vibration isolation involves installing special supports that dampen vibrations. Sound insulation is carried out by gluing the housings with a special material. Shielding involves cutting off the sound source from a building or room using a shield.

Calculating noise from ventilation systems involves finding such technical solutions when the operation of the equipment will not disturb people. This is a complex task that requires skills and experience in the field.

The Mega.ru company has long been involved in the issues of ventilation and creating optimal microclimate conditions. Our specialists solve problems of any complexity. We work in Moscow and its neighboring regions. The technical support service will answer all questions by phone numbers listed on the page. Remote collaboration is possible. Contact us!

page 1

page 2

page 3

page 4

page 5

page 6

page 7

page 8

page 9

page 10

page 11

page 12

page 13

page 14

page 15

page 16

page 17

page 18

page 19

page 20

page 21

page 22

page 23

page 24

page 25

page 26

page 27

page 28

page 29

page 30

(GOSSTROY USSR)

instructions

CH 399-69

MOSCOW - 1970

Official publication

STATE COMMITTEE OF THE USSR COUNCIL OF MINISTERS FOR CONSTRUCTION

(GOSSTROY USSR)

INSTRUCTIONS

ON ACOUSTIC CALCULATION OF VENTILATION UNITS

Approved by the State Committee of the USSR Council of Ministers for Construction Affairs

PUBLISHING HOUSE OF LITERATURE ON CONSTRUCTION Moscow - 1970

dampers, grilles, lampshades, etc.) should be determined by the formula

L p = 601go + 301gC+101g/? + fi, (5)

where v is the average air speed at the inlet to the device in question (installation element), calculated by the area of ​​the supply air duct (pipe) for throttling devices and lampshades and by the overall dimensions for grilles in m/sec;

£ is the aerodynamic drag coefficient of the ventilation network element, related to the air speed at its inlet; for VNIIGS disk lamps (separated jet) £ = 4; for VNIIGS anemostats and lampshades (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 grating resistance coefficient on its open cross-section

F is the cross-sectional area of ​​the supply air duct in m2;

B - correction depending on the type of element, in dB; for throttling devices, anemostats and disk lamps B = 6 dB; for lampshades designed by VNIIGS B =13 dB; for lattices B=0.

2.10. Octave levels of sound power of noise emitted into the air duct by throttling devices should be determined using formula (3).

In this case, it is calculated according to formula (5), the correction AL 2 is determined according to table. 3 (the cross-sectional area of ​​the air duct in which the element or device in question is installed should be taken into account), and 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 frequency in Hz;

D - average transverse size of the air duct (equivalent diameter) in m; v is the average speed at the entrance to the element in question in m/sec.

Table 5

AL corrections for determining octave sound power levels of throttling device noise in dB

Frequency parameter f

Note Intermediate values ​​in Table 5 should be taken by interpolation

2.11. The octave levels of sound power of noise created in lampshades and grilles should be calculated using formula (2), taking the ALi corrections 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 permissible value, then the noise created in them is calculated

Table 6 Corrections ALi, taking into account the distribution of sound power of the noise of lampshades and grilles across octave bands, in dB

Device type Anemostat......... VNIIGS lampshade (tear-off jet)........... VNIIGS lampshade (floor-mounted jet)........... Disc lamp...... lattice...........

the required reduction in sound pressure levels (see section 5) can be ignored

2.13. The permissible speed of air movement in front of the air distribution or air intake device of the installations should be determined by the formula

y D op = 0.7 10* m/sec;

^ext + 101e ~ -301ge-MIi-

where b add is the permissible octave sound pressure level in dB; n is the number of lampshades or grilles in the room in question;

B is the room constant in the octave band under consideration in m 2, adopted in accordance with paragraphs. 3.4 or 3.5;

AZ-i - correction taking into account the distribution of sound power levels of lampshades and grilles across octave bands, adopted according to table. 6, in dB;

D - correction for the location of the noise source; when the source is located in the working area (no 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 permissible air speed is carried out only for one frequency, which is equal to 250 Shch for VNIIGS lampshades, 500 Hz for disk lampshades, and 2000 Hz for anemostats and grilles.

2.14. In order to reduce the level of sound power of noise generated by turns and tees of air ducts, areas of sharp changes in cross-sectional area, etc., the speed of air movement in the main air ducts of public buildings and auxiliary buildings of industrial enterprises should be limited to 5-6 m/sec, and on branches up to 2-4 m/sec. For industrial buildings, these speeds can be doubled accordingly, if technological and other requirements allow this.

3. CALCULATION OF OCTAVE SOUND PRESSURE LEVELS AT CALCULATION POINTS

3.1. Octave sound pressure levels at permanent workplaces or premises (at design points) should not exceed those established by standards.

(Notes: 1. If regulatory requirements for sound pressure levels are different during the day, then the acoustic calculation of installations should be carried out at the lowest permissible sound pressure levels.

2. Sound pressure levels at permanent workplaces or premises (at design points) depend on the sound power and location of noise sources and the sound-absorbing qualities of the room in question.

3.2. When determining octave sound pressure levels, calculations should be made for permanent workplaces or design points in rooms closest to noise sources (heating and ventilation units, air distribution or air intake devices, air or air-thermal curtains, etc.). In the adjacent territory, the design points should be taken to be the points closest to the noise sources (fans openly located on the territory, exhaust or air intake shafts, exhaust devices of ventilation units, etc.), for which sound pressure levels are standardized.

a - noise sources (autonomous air conditioner and ceiling lamp) and the design point are located in the same room; b - noise sources (fan and installation elements) and the design point are located in different rooms; c - noise source - the fan is located in the room, the design point is on the arrival territory; 1 - autonomous air conditioner; 2 - design point; 3 - noise-generating lamp; 4 - vibration-isolated fan; 5 - flexible insert; c -- central muffler; 7 - sudden narrowing of the air duct cross-section; 8 - branching of the air duct; 9 - rectangular turn with guide vanes; 10 - smooth rotation of the air duct; 11 - rectangular rotation of the air duct; 12 - grate; /

3.3. Octaves/Sound Pressure Levels at design points should be determined as follows.

Case 1. The noise source (noise-generating grille, lampshade, autonomous air conditioner, etc.) is located in the room under consideration (Fig. 3). Octave sound pressure levels created at a design point by one noise source should be determined using the formula

L-L, + I0! g (-£-+--i-l (8)

oct \ 4 I g g V t )

Note: For ordinary rooms that do not have special acoustic requirements, use the formula

L = 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\

V w is the constant of the room with a noise source in the octave band under consideration (determined according to paragraphs 3.4 or 3.5) in w 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 = 3 dB; if above the working area, - D=0;

F is the radiation directivity factor of the noise source (determined from the curves in Fig. 4), dimensionless; g - distance from the geometric center of the noise source to the calculated point in the railway.

The graphical solution of equation (8) is shown in Fig. 5.

Case 2. The design points are located in a room isolated from noise. The noise from a fan or installation element spreads through air ducts and is radiated into the room through an air distribution or air intake device (grill). Octave sound pressure levels created at design points should be determined using the formula

L = L P -ДL p + 101g(-%+-V (10)

Note: For ordinary rooms for which there are no special acoustic requirements, 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 noise of a fan or installation element emitted into the air duct in the octave band under consideration in dB (determined in accordance with clauses 2.5 or 2.10);

AL р в - total reduction in the level (loss) of sound power of fan or electrical noise

installation ment in the considered octave band 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 = 3 dB, if above it, D = 0; Фi is the directivity factor of the installation element (hole, grille, etc.) emitting noise into the insulated room, dimensionless (determined from the graphs in Fig. 4); r„-distance from the installation element emitting noise into the insulated room to the design point in m\

B and is the constant of the room insulated from noise in the octave band under consideration in m 2 (determined according to clauses 3.4 or 3.5).

Case 3. Calculation points are located in the area adjacent to the building. The fan noise travels through the duct and is emitted into the atmosphere through the grille or shaft (Fig. 6). Octave levels of sound pressure created at design points should be determined by the formula

I = L p -AL p -201gr a -i^- + A-8, (12)

where r a is the distance from the installation element (grid, hole) emitting noise into the atmosphere to the calculated point in m\ r a is the attenuation of sound in the atmosphere, taken according to the 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 noise-emitting element of the installation (for all frequencies it is taken according to Fig. 6).

1 - ventilation shaft; 2 - louvered grille

The remaining quantities are the same as in formulas (10)

Table 7 Attenuation of sound in the atmosphere in dB/km

Geometric mean frequencies of octave bands in Hz

3.4. Room constant B should be determined from the graphs in Fig. 7 or according to table. 9, using table. 8 to determine the characteristics of the room.

3.5. For rooms that have special acoustic requirements (unique audience

halls, etc.), the permanent premises should be determined in accordance with the instructions for acoustic calculations for these premises.

Room volume in m Geometric mean frequency in g]Hz Frequency multiplier (*. 200 < У <500

The room constant at the design frequency is equal to the room constant at a frequency of 1000 Hz multiplied by the frequency multiplier ^£=£1000

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 design point in question, using the appropriate formulas in clause 3.2, the octave sound pressure levels created by each of the noise sources separately should be determined , and the total level in

These “Instructions for the acoustic calculation of ventilation units” were developed by the Research Institute of Construction Physics of the USSR Gosstroy together with the Santekhproekt Institute of the USSR Gosstroy and Giproniiaviaprom of the Ministry of Aviation Industry.

The guidelines were developed to develop the requirements of the chapter of SNiP I-G.7-62 “Heating, ventilation and air conditioning. Design Standards" and "Sanitary Standards for the Design of Industrial Enterprises" (SN 245-63), which establish the need to reduce the noise of ventilation, air conditioning and air heating installations in buildings and structures for various purposes when it exceeds the permissible sound pressure levels according to the standards.

Editors: A. No. 1. Koshkin (Gosstroy USSR), Doctor of Engineering. sciences, prof. E. Ya. Yudin and candidates of technical sciences. Sciences E. A. Leskov and G. L. Osipov (Research Institute of Construction Physics), Ph.D. tech. Sciences I. D. Rassadi

The Guidelines set out the general principles of acoustic calculations of mechanically driven ventilation, air conditioning and air heating installations. Methods for reducing sound pressure levels at permanent workplaces and in premises (at design points) to the values ​​​​established by standards are considered.

at (Giproniaviaprom) and engineer. |g. A. Katsnelson/ (GPI Santekhproekt)

1. General Provisions............ - . . , 3

2. Sources of noise from installations and their noise characteristics 5

3. Calculation of octave sound pressure levels in the calculated

points......................... 13

4. Reducing the levels (losses) of sound noise power in

various elements of air ducts........ 23

5. Determination of the required reduction in sound pressure levels. . . *. ............... 28

6. Measures to reduce sound pressure levels. 31

Application. Examples of acoustic calculations of ventilation, air conditioning and air heating installations with mechanical stimulation...... 39

Plan I quarter 1970, No. 3

Characteristics of premises Table 8

Description and purpose of the premises Characteristics for using the graphs in Fig. 7 Premises without furniture, with a small number of people (for example, metalworking shops, ventilation chambers, test benches, etc.)......................... Premises with hard furniture and a small number of people (for example, offices, laboratories, weaving and woodworking shops, etc.) Rooms with a large number of people and upholstered furniture or with a tiled ceiling (for example, work areas of administrative buildings, meeting rooms, auditoriums, restaurants, department stores, design offices, airport waiting rooms, etc.)....... ... Premises with sound-absorbing ceiling and wall cladding (for example, radio and television studios, computer centers, etc.).......

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 distribution of sound power between them should be considered uniform.

3.7. If the calculated points are located in a room through which a “noisy” air duct passes, and noise enters the room through the walls of the air duct, then the octave sound pressure levels should be determined using the formula

L - L p -AL p + 101g --R B - 101gB„-J-3, (13)

where Lp 9 is the octave level of sound power of the noise source emitted into the air duct, in dB (determined in accordance with paragraphs 2 5 and 2.10);

ALp b - 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 air duct emitting noise into the room, in dB (determined in accordance with section 4);

State Committee of the USSR Council of Ministers for Construction Affairs (Gosstroy USSR)

1. GENERAL PROVISIONS

1.1. These Guidelines have been developed to develop the requirements of the chapter of SNiP I-G.7-62 “Heating, ventilation and air conditioning. Design Standards" and "Sanitary Standards for the Design of Industrial Enterprises" (SN 245-63), which establish the need to reduce the noise of mechanically driven ventilation, air conditioning and air heating installations to sound pressure levels acceptable according to 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 cover calculations of vibration insulation of fans and electric motors (insulation of shocks and sound vibrations transmitted to building structures), as well as calculations of sound insulation of the 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 premises (at design points), determining the need to reduce these noise levels and measures to reduce sound levels pressure to values ​​allowed by standards.

Notes: 1. Acoustic calculations should be part of the design of ventilation, air conditioning and air heating installations with mechanical drive for buildings and structures for various purposes.

Acoustic calculations should be done only for rooms with standardized noise levels.

2. Airborne (aerodynamic) fan noise and noise created by air flow in air ducts have broadband spectra.

3. In these Instructions, noise should be understood as any kind of sounds that interfere with the perception of useful sounds or break 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 air heating installation, the shortest branch of air ducts should be considered. If the central installation serves several rooms for which regulatory noise requirements are different, then an additional calculation should be made for the branch of air ducts 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-thermal curtains, local suction units, units of air shower installations, which are closest to the design points or have the highest performance and sound power.

Separately, an acoustic calculation of air duct branches escaping into the atmosphere (air intake and exhaust by installations) should be carried out.

If there are throttling devices (diaphragms, throttle valves, dampers), air distribution and air intake devices (grills, shades, anemostats, etc.) between the fan and the room served, sudden changes in the cross-section of air ducts, turns and tees, an acoustic calculation of these devices should be carried out and installation elements.

1.5. Acoustic calculations should be made for each of the eight octave bands of the auditory range (for which noise levels are normalized) with geometric mean frequencies of octave bands of 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, calculations are allowed 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. The required measures to reduce noise generated by ventilation, air conditioning and air heating installations, if necessary, should be determined for each source separately.

2. NOISE SOURCES OF 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 created by:

a) fan;

b) when air flow moves in installation elements (diaphragms, throttles, dampers, air duct turns, tees, grilles, lampshades, etc.).

In addition, noise transmitted through 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 according to the passports for this equipment or according to catalog data

If there are no noise characteristics, they should be determined experimentally according to the customer’s instructions or by calculation, guided by the data given in these Guidelines.

2.3. The overall sound power level of the fan noise should be determined using the formula

L p =Z+251g#+l01gQ-K (1)

where 1^P is the overall sound power level of venous noise

Tilator in dB relative to 10“ 12 W;

L-noise criterion, depending on the type and design of the fan, in dB; should be taken according to the table. 1;

R is the total pressure created by the fan, in kg/m2;

Q - fan productivity in m^/sec;

5 - correction for fan operating mode in dB.

Table 1

Noise criterion values ​​L for fans in dB

Fan type and series Pumping. . . Suction. . .

Notes: 1. Value 6 when the fan operating mode deviates by no more than “and 20% of the maximum mode, efficiency should be taken equal to 2 dB. In the fan operating mode with maximum efficiency, 6=0.

2. To facilitate calculations in Fig. Figure 1 shows a graph for determining the value of 251gtf+101gQ.

3. The value obtained from formula (1) characterizes the sound power emitted by the 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. If the air supply to the inlet pipe is not smooth or a throttle is installed in the inlet pipe to the values ​​​​specified in

table 1, should be added for axial fans 8 dB, for centrifugal fans 4 dB

2.4. Octave sound power levels of fan noise emitted by the open inlet or outlet pipe of the fan L p a into the free atmosphere or into the room should be determined by the formula

(2)

where is the overall sound power level of the fan in dB;

ALi is a correction that takes into account the distribution of fan sound power across octave bands in dB, taken depending on the type of fan and the number of revolutions according to the table. 2.

table 2

ALu corrections taking into account the distribution of fan sound power across octave bands, in dB

	Centrifugal fans
Geometric mean hour			Axial veins
octave band totes in Hz	with shoulder blades	with shoulder blades, zag	tillers
	bent forward	pushed back
(16 000) (3 2 000)

Notes: 1. Given in table. 2 data without brackets is 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 up an octave, taking for the extreme octaves the values ​​indicated in brackets for frequencies of 32 and 16000 Hz.

3. When the fan speed exceeds 2800 rpm, the entire spectrum should be shifted down two octaves.

2.5. Octave sound power levels of fan noise emitted into the ventilation network should be determined using the formula

Lp - L p ■- A L-± -|~ L i-2,

where AL 2 is an amendment that takes into account the effect of connecting the fan to the air duct network in dB, determined from the table. 3.

Table 3 Amendment D £ 2 > taking into account the effect of connecting a fan or throttling device to the air duct network in dB

Square root of the cross-sectional area of ​​the fan pipe or air duct in mm Geometric mean frequencies of octave bands in Hz

2.6. The total level of sound power of noise emitted by the fan through the walls of the casing (casing) into the ventilation chamber should be determined using formula (1), provided that the value of the noise criterion L is taken according to table. 1 as its average value for the suction and discharge sides.

Octave levels of sound power of noise emitted by a fan into the ventilation chamber should be determined using 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 noise emitted by all fans.

The total sound power level L cyu when operating n identical fans should be determined by the formula

£sum = Z.J + 10 Ign, (4)

where Li is the sound power level of one fan in dB-, n is the number of identical fans.

To summarize the sound power levels of noise or sound pressure created by two noise sources of different levels, you should use the table. 4.

Table 4 Addition of sound power or sound pressure levels

Difference of two stackable levels in dB Addition to a higher level to determine the Total level in dB

Note. If the number of different noise levels is more than two, the addition is performed sequentially, starting with two large levels.

2.8. Octave levels of sound power of noise emitted into the room by autonomous air conditioners, heating and ventilation units, air shower units (without air duct networks) with axial fans should be determined using formula (2) and table. 2 with a boost correction of 3 dB.

For autonomous units with centrifugal fans, the octave levels of sound power of noise emitted by the suction and discharge pipes of the fan should be determined using formula (2) and table. 2, and the total noise level is according to table. 4.

Note. When air is taken from outside by installations, no higher correction is required.

2.9. The overall sound power level of noise generated by throttling, air distribution and air intake devices (throttle valves.