The basis for the design of noise suppression of ventilation and air conditioning systems is the acoustic calculation - a mandatory attachment to the ventilation project of any object. The main tasks of such a calculation are: determination of the octave spectrum of air, structural ventilation noise at design 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 calculated points is carried out, taking into account the effectiveness of these measures.

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 approximate calculations, the corrected sound power levels of noise sources in dBA can be used.

Design 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 are in transit; in the area of ​​the intake or exhaust device, or just intake air for recirculation.

The calculated point is in the room where the fan is installed

In general, the sound pressure levels in a room depend on the sound power of the source and the directivity of the noise emission, the number of noise sources, on the location of the design point relative to the source and enclosing building structures, on the size and acoustic qualities of the room.

The octave sound pressure levels generated by the fan (s) at the installation site (in the ventilation chamber) are:

where Фi is the directivity factor of the noise source (dimensionless);

S is the area of ​​an imaginary sphere or its part surrounding the source and passing through the calculated point, m 2;

B is the acoustic constant of the room, m 2.

Design points are located in the area adjacent to the building

Fan noise propagates through the duct and is radiated into the surrounding space through a grill or shaft, directly through the walls of the fan casing or an open branch pipe when the fan is installed outside the building.

When the distance from the fan to the design point is much larger than its size, the noise source can be considered a point source.

In this case, the octave sound pressure levels at the calculated points are determined by the formula

where L Pokti - octave sound power level of the noise source, dB;

∆L Pnetworki is the total decrease in the sound power level along the path of sound propagation in the duct in the considered octave band, dB;

∆L ni - directivity index of sound radiation, dB;

r is the distance from the noise source to the design point, m;

W is the spatial angle of sound radiation;

b a - attenuation of sound in the atmosphere, dB / km.

Acoustic calculation produced for each of the eight octave bands of the auditory range (for which noise levels are standardized) with geometric mean frequencies of 63, 125, 250, 500, 1000, 2000, 4000, 8000 Hz.

For central systems for ventilation and air conditioning with branched air duct networks, it is allowed to carry out acoustic calculations only for frequencies of 125 and 250 Hz. All calculations are performed with an accuracy of 0.5 Hz and rounding the final result to an integer number of decibels.

When the fan is operating in efficiency modes greater than or equal to 0.9, the maximum efficiency is 6 = 0. If the fan operating mode deviates by no more than 20% of the maximum, the efficiency is assumed to be 6 = 2 dB, and if the deviation is more than 20% - 4 dB.

It is recommended to take the following maximum air velocities to reduce the sound power level generated in the air ducts: in the main air ducts public buildings and auxiliary premises of industrial buildings 5-6 m / s, and in the branches - 2-4 m / s. For industrial buildings, these speeds can be doubled.

For ventilation systems with a branched network of air ducts, the acoustic calculation is done only for the branch to the nearest room (at the same permissible noise levels), with different levels noise - for the branch with the lowest permissible level. The acoustic calculation for air intake and exhaust shafts is done separately.

For centralized ventilation and air conditioning systems with a branched network of air ducts, the calculation can only be made for frequencies of 125 and 250 Hz.

When noise enters the room from several sources (from supply and exhaust grilles, from units, local air conditioners, etc.), several design points are selected at workplaces closest to the noise sources. For these points, the octave sound pressure levels from each noise source are determined separately.

With different during the day regulatory requirements to sound pressure levels, the acoustic calculation is performed at the lowest permissible levels.

In the total number of noise sources m, sources that create at the design point octave levels 10 and 15 dB lower than the normative ones are not taken into account, when their number is not more than 3 and 10, respectively.

Several evenly distributed supply or exhaust grilles from one fan can be considered as one noise source when noise from one fan penetrates through them.

When several sources of the same sound power are located in the room, the sound pressure levels at the selected design point are determined by the formula

Engineering and construction journal, N 5, 2010
Category: Technology

Doctor of Technical Sciences, Professor I.I.Bogolepov

GOU Saint Petersburg State Polytechnic University
and GOU St. Petersburg State Marine Technical University;
Master A.A. Gladkikh,
GOU Saint Petersburg State Polytechnic University

Ventilation and air conditioning system (SVKV) - essential system for modern buildings and structures. However, in addition to the necessary high-quality air, the system transports noise to the premises. It comes from the fan and other sources, spreads through the duct and is radiated into the ventilated room. Noise is incompatible with normal sleep, educational process, creative work, highly productive work, good rest, treatment, obtaining high-quality information. V building codes and the rules of Russia have such a situation. The method of acoustic calculation of UHCW of buildings used in the old SNiP II-12-77 "Protection against noise" is outdated and therefore did not enter the new SNiP 23-03-2003 "Protection against noise". So, old method is outdated, and there is no new generally accepted one yet. Below is a simple approximate method for the acoustic calculation of the UHCW in modern buildings developed using the best manufacturing practices, 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 a practically diffuse sound field. It is performed in order to assess the sound pressure levels (hereinafter referred to as SPL) and their compliance with the current standards of permissible noise. It provides for the determination of the SPL from the SVKV due to the operation of the fan (hereinafter referred to as the "machine") for the following typical groups of rooms:

1) in the room where the machine is located;

2) in rooms through which air ducts pass in transit;

3) in rooms served by the system.

Initial data and requirements

It is proposed to perform calculation, design and control of protection of people from noise for the most important for human perception octave frequency bands, namely: 125 Hz, 500 Hz and 2000 Hz. The octave frequency band of 500 Hz is a geometric mean in the range of noise-normalized octave frequency bands of 31.5 Hz - 8000 Hz. For constant noise, the calculation provides for the determination of SPL in octave frequency bands from the sound power levels (SPL) in the system. The values ​​of SPL and SPL are related by the general ratio = - 10, where - SPL relative to the threshold value 2 · 10 N / m; - UZM relative to the threshold value of 10 W; - the area of ​​propagation of the front of sound waves, m.

The SPL should be determined at the design points of the premises normalized for noise by the formula = +, where is the SPL of the noise source. The value that takes into account the effect 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 radiation of the noise source, rad .; - radiation directivity factor, taken according to experimental data (in the first approximation it is equal to one); - distance from the center of the noise emitter to the design point in m; = - acoustic constant of the room, m; - the average coefficient of sound absorption of the internal surfaces of the room; - the total area of ​​these surfaces, m; - coefficient that takes into account the violation of the diffuse sound field in the room.

The indicated values, calculated points and norms of permissible noise are regulated for premises of various buildings by SNiPom 23-03-2003 "Protection against noise". If the calculated SPL values ​​exceed the permissible noise norm in at least one of the three frequency bands, then it is necessary to design measures and means of noise reduction.

The initial data for acoustic calculation and design of UHCW are:

- layout diagrams used in the structure of the structure; dimensions of machines, air ducts, control valves, elbows, tees and air distributors;

- the speed of air movement in the mains and branches - according to the technical specifications and aerodynamic calculation;

- drawings of the general arrangement of the premises served by the SVKV - according to construction project structures;

- noise characteristics of machines, control valves and air distributors SVKV - according to the technical documentation for these products.

The noise characteristics of the machine are the following levels of UZM of airborne noise in octave frequency bands in dB: - UZM of noise propagating from the machine into the suction duct; - USM of noise propagating from the machine into the discharge air duct; - USM of noise emitted by the body of the machine into the surrounding space. All machine noise characteristics are currently determined based on acoustic measurements in accordance with applicable national or international standards and others. regulatory documents.

The noise characteristics of mufflers, air ducts, adjustable fittings and air distributors are presented by the UZM of airborne noise in octave frequency bands in dB:

- USM of noise generated by the elements of the system when the air flow passes through them (noise generation); - UZM noise, scattered or absorbed in the elements of the system when passing through them a stream of sound energy (noise reduction).

The efficiency of generation and noise reduction by UHCW elements is determined on the basis of acoustic measurements. We emphasize that the values ​​of and must be indicated in the corresponding 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 in room 1, where the machine is installed, there is a fan, the sound power level of which radiated into the suction, discharge pipe and through the machine body are values ​​in dB, and. Suppose that a noise muffler with a muffling efficiency in dB () is installed on the discharge side of the fan. Workplace located at a distance from the car. The wall separating room 1 and room 2 is located at a distance from the car. Sound absorption constant of the room 1: =.

For room 1, the calculation involves the solution of three problems.

1st task... Compliance with the norm of permissible noise.

If the suction and discharge nozzles are removed from the machine room, then the SPL calculation in the room where it is located is made according to the following formulas.

The octave SPL at the design point of the room is determined in dB by the formula:

where is the USM of the noise emitted by the machine body, taking into account the accuracy and reliability using. The value indicated above is determined by the formula:

If the premises are located n noise sources, the SPL from each of which are equal at the design point, then the total SPL from all of them is determined by the formula:

As a result of the acoustic calculation and design of the UHCS 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. The calculation of the UZM value in the discharge duct from room 1 to room 2 (the room through which the air duct passes through), namely the value in dB, is made according to the formula

3rd task. The calculation of the UZM value emitted by the wall with soundproofing area from room 1 to room 2, namely the value in dB, is performed according to 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 in transit), the calculation provides for the solution of the following five problems.

1st task. Calculation of the sound power emitted by the walls of the duct into room 2, namely the determination of the value in dB by the formula:

In this formula: - see above the 2nd problem for room 1;

= 1.12 - equivalent cross-sectional diameter of the duct with a cross-sectional area;

- room length 2.

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;

- inner diameter of the duct in m;

- duct wall thickness in m;


Sound insulation of air duct walls rectangular section calculated by the following formula in DB:

where = is the mass per unit surface of the duct wall (product of the material density in kg / m and the wall thickness in m);

- geometric mean frequency of octave bands in Hz.

2nd task. The 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 (SPL emitted by the wall of room 1 to room 2, - 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 UHCW 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 UZM value in the discharge duct from room 2 to room 3 (room served by the system), namely, the value in dB by the formula:

The amount of losses due to radiation of sound power of noise by the walls of air ducts on straight sections of air ducts of 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), design points and norms of permissible noise are adopted in accordance with SNiP 23-03-2003 "Noise protection" and technical specifications.

For room 3, the calculation involves the solution of two problems.

1st task. The calculation of the sound power emitted by the air duct through the air outlet into room 3, namely the determination of the value in dB, is proposed to be performed as follows.

Particular task 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 noise muffler in room 3;

() - losses in the tee in room 3 (see the formula below);

- losses due to reflection from the end of the duct (see table 1).

General task 1 consists of solving for many of three typical rooms using the following dB formula:



Here - UZM of noise propagating from the machine into the discharge air duct in dB, taking into account the accuracy and reliability of the value (taken according to the technical documentation for the machine);

- USM of noise generated by the air flow in all elements of the system in dB (taken according to the data of the technical documentation for these elements);

- USM of noise absorbed and dissipated when the sound energy flow passes through all elements of the system in dB (taken according to the data of 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 equal to zero, if it already includes);

- a value equal to 5 dB for low-speed UHCW (air speed in mains is less than 15 m / s), equal to 10 dB for medium-speed UHCW (air speed in mains is less than 20 m / s) and equal to 15 dB for high-speed UHCW (speed in highways is less 25 m / s).

Table 1. Value in dB. Octave stripes

Ventilation calculation

Depending on the method of air movement, ventilation is natural and forced.

The parameters of the air entering the intake openings and openings of local suction of technological and other devices that are located in the working 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. Consequently, the ventilation must provide an air flow rate of 90 cubic meters / hour. In the summer, it is necessary to provide for the installation of an air conditioner in order to avoid excess temperature in the room for the stable operation of the 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 the air conditioner is its main characteristic, it depends on what volume of the room it is designed for. For approximate calculations, 1 kW per 10 m 2 is taken with a ceiling height of 2.8 - 3 m (in accordance with SNiP 2.04.05-86 "Heating, ventilation and air conditioning").

A simplified technique was used to calculate the heat flow in a given room:

where: Q - Heat flows

S - Room area

h - Room height

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

For a room of 15 m 2 and a height of 3 m, the heat fluxes will be:

Q = 15 3 35 = 1575 W

In addition, heat generation from office equipment and people should be taken into account, it is considered (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 a copier of 0.3 kW, by adding these values ​​to the total heat gains, the required cooling power can be obtained.

Q add = (HS oper) + (C S comp) + (PS print) (4.9)

where: Q add - The sum of additional heat fluxes

C - Computer heat dissipation

H - Heat dissipation of the operator

D - Printer heat dissipation

S comp - Number of workstations

S print - Number of printers

S operas - Number of operators

Additional heat fluxes of the room will be:

Q add1 = (0.1 2) + (0.3 2) + (0.3 1) = 1.1 (kW)

The total amount of heat gains is equal to:

Q total1 = 1575 + 1100 = 2675 (W)

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

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

Calculation of the noise level

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

To decide whether it is necessary and advisable to reduce noise, 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 calculation results obtained are compared with the permissible noise level for a given workplace. If the calculation results are higher than the permissible noise level, then special measures are required to reduce the noise. These include: lining the walls and ceiling of the hall with sound-absorbing materials, reducing noise at the source, correct layout of equipment and rational organization of the operator's workplace.

Sound pressure levels of noise sources acting on the operator at his workplace are presented in table. 4.6.

Table 4.6 - Sound pressure levels of various sources

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

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

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

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

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(GOSSTROY USSR)

directions

SN 399-69

MOSCOW - 1970

Official edition

STATE COMMITTEE OF THE COUNCIL OF MINISTERS OF THE USSR FOR CONSTRUCTION

(GOSSTROY USSR)

INSTRUCTIONS

ACOUSTIC CALCULATION OF VENTILATION UNITS

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

BUILDING LITERATURE PUBLISHING Moscow - 1970

gates, grilles, shades, etc.), should be determined by the formula

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

where v - average speed air at the inlet to the considered device (installation element), calculated by the area of ​​the supply air duct (branch pipe) for throttling devices and shades and by the overall dimensions for grilles in m / s;

£ - coefficient of aerodynamic resistance of a ventilation network element, referred to the air speed at the entrance to it; for disk shades VNIIGS (separation jet) £ = 4; for anemostats and plafonds VNIIGS (flat stream) £ = 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 free cross-section

F is the cross-sectional area of ​​the supply air duct in m 2;

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

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

In this case, it is calculated according to the formula (5), the correction AL 2 is determined according to 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 amendments AL \ - according to the data in 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 - medium transverse dimension duct (equivalent diameter) in m; v is the average speed at the entrance to the element under consideration in m / s.

Table 5

Amendments AL) to determine the octave sound power levels of the noise of throttling devices in dB

Frequency parameter f

Note Intermediate values in table 5 should be taken by interpolation

2.11. The octave sound power levels of the noise generated in the shades and grilles should be calculated using the 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 (cover, grille, etc.) does not exceed the permissible value of additional, then the noise generated in them is prn calculation

Table 6 Corrections ALi, taking into account the distribution of the sound power of the noise of the plafonds and gratings by octave bands, in dB

Device type Anemostat .......... Plafond VNIIGS (tear-off jet)........... Plafond VNIIGS (flat jet)........... Disc cover ...... lattice...........

the required reduction of sound pressure levels (see section 5) can be disregarded

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

y D op = 0.7 10 * m / s;

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

where bop is the permissible octave sound pressure level in dB; n is the number of shades or grilles in the room under consideration;

B is the constant of the room in the considered octave band in m 2, taken in accordance with paragraphs. 3.4 or 3.5;

AZ-i is a correction that takes into account the distribution of the sound power levels of the plafonds and grilles by 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 (no higher than 2 m from the floor), A = 3 dB; if the source is higher than this zone, A * ■ 0;

0.7 - safety factor;

F, B - designations are the same as in section 2.9, formula (5).

Note. The determination of the permissible air speed is carried out only for one frequency, which is equal for VNIIGS shades 250 Shch, for disk shades 500 Hz, for anemostats and grilles 2000 Hz.

2.14. In order to reduce the sound power level of noise generated by bends and tees of air ducts, areas with a sharp change in the 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 / s, and on branches up to 2-4 m / s. For a production building, these speeds can be correspondingly doubled, if technological and other requirements make it possible.

3. CALCULATION OF OCTAVE SOUND PRESSURE LEVELS AT DESIGN POINTS

3.1. Octave sound pressure levels at permanent workplaces or in rooms (at design points) should not exceed the established standards.

(Notes: 1. If the regulatory requirements for the sound pressure levels are different during the day, then the acoustic design of the installations should be made at 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 the noise sources and the sound-absorbing qualities of the room in question.

3.2. When determining octave sound pressure levels, the calculation 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.). On the adjacent territory, the calculated points should be taken as the points closest to the sources of noise (fans openly located 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 plafond) and the design point are 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 in the room, the calculated point - on arrival in the middle of the territory; 1 - autonomous air conditioner; 2 - calculated point; 3 - noise-generating plafond; 4 - vibration-insulated fan; 5 - flexible insert; в - central muffler; 7 - sudden narrowing of the duct section; 8 - branching of the air duct; 9 - rectangular turn with guide vanes; 10 - smooth turn of the air duct; 11 - rectangular turn of the air duct; 12 - lattice; /

3.3. The octave / design point sound pressure levels are to be determined as follows.

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

L-L, + I0! g (- £ - + - i-l (8)

oct \ 4 I g g V t)

Note. For ordinary rooms, which do not have special requirements for acoustics, according to 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 - constant of a room with a noise source in the considered octave band (determined by clauses 3.4 or 3.5) in f 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 it is higher than the working area, - D = 0;

Ф is the directivity factor of the radiation source of the noise (determined from the curves in Fig. 4), dimensionless; d is the distance from the geometric center of the noise source to the design point in w.

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

Case 2. The calculated points are located in a noise-insulated room. Noise from a fan or a unit element spreads through the air ducts and is radiated into the room through the air distribution or air intake device (grille). The octave sound pressure levels generated at the design points should be determined by the formula

L = L P -ДL p + 101g (-% + - V (10)

Note. For ordinary premises, 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 - 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 clauses 2.5 or 2.10);

AL p in - the total decrease in the level (loss) of the sound power of the noise of the fan or

installation time 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 higher than it, - D = 0; Ф and is the directional factor of the installation element (hole, lattice, etc.), emitting noise into the insulated room, dimensionless (determined from the graphs in Fig. 4); g „-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 considered octave band in m 2 (determined by clauses 3.4 or 3.5).

Case 3. Design points are located in the area adjacent to the building. Fan noise propagates through the duct and is emitted to the atmosphere through a grate or shaft (Fig. 6). The octave sound pressure levels generated at the 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 (lattice, hole), emitting noise into the atmosphere, to the design point in m \ p a is the sound attenuation in the atmosphere, taken according to table. 7 in dB / km \

A - correction in dB, taking into account the location of the design 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 grill

The rest of the quantities are the same as in formulas (10)

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

Average geometric frequencies of octave bands in Hz

3.4. The 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 with special acoustical requirements (unique viewers

halls, etc.), the constant of the room should be determined in accordance with the instructions for acoustic design for these rooms.

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

The room constant at the calculated frequency is equal to the room constant at 1000 Hz multiplied by the frequency factor ^ £ = £ 1000

3.6. If noise comes to the design point from several noise sources (for example, supply and recirculation grilles, autonomous air conditioner, etc.), then for the considered design point, the octave sound pressure levels created by each of the noise sources separately should be determined using the corresponding formulas in clause 3.2. , and the total level in

These "Guidelines for the acoustic calculation of ventilation units" were developed by the Research Institute of Construction Physics of the USSR Gosstroy together with the institutes Santekhproekt of the USSR Gosstroy and Giproniiaviaprom 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 permissible sound pressure levels.

Editors: A. No. 1. Koshkin (Gosstroy USSR), Dr. Sciences, prof. E. Ya. Yudin and technical candidates. 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 mechanical ventilation, air conditioning and air heating installations. Methods of reducing the sound pressure levels at permanent workplaces and in rooms (at design points) to the values ​​established by the standards are considered.

at (Giproniiaviaprom) and Ing. | g. A. Katsnelson / (GPI Santekhproekt)

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

2. Noise sources of installations and their noise characteristics 5

3. Calculation of octave sound pressure levels in the calculated

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

4. Reduction of levels (loss) of sound power of noise 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 calculation of ventilation, air conditioning and air heating installations with mechanical induction ... 39

Plan I quarter. 1970, no. 3

Characteristics of the premises Table 8

Description and purpose of the premises Characteristics for using the graphs in Fig. 7 Rooms without furniture, with a small number of people (for example, metalworking shops, ventilation chambers, test benches, etc.) ............... Rooms 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 tiled ceilings (for example, office buildings, conference rooms, auditoriums, restaurants, department stores, design offices, airport lounges, etc.) ......... ... Rooms with sound-absorbing ceilings and walls (for example, radio and television studios, data 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 choke) from one system (supply or exhaust) penetrates 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" duct passes, and noise penetrates into 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 sound power level of the noise source radiated into the duct, in dB (determined in accordance with paragraphs 2 5 and 2.10);

ALp b - total decrease in sound power levels (losses) along the path of sound propagation from a noise source (fan, choke, 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 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 establish the need to reduce the noise of ventilation, air conditioning and air heating installations with mechanical induction to sound pressure levels permissible according to the standards.

1.2. The requirements of these Guidelines apply to the 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 methodology 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 a part of projects of ventilation, air conditioning and air heating installations with mechanical induction for buildings and structures for various purposes.

The acoustic calculation should be done only for rooms with normalized noise levels.

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

3. In these Instructions, under noise, one should understand all kinds of sounds that interfere with the perception of useful sounds or disturb the silence, as well as sounds that have a harmful or irritating effect on the human body.

1.4. When calculating the acoustic design of a central ventilation, air conditioning and air heating unit, the shortest branch of air ducts should be considered. If the central unit serves several rooms for which the regulatory requirements for noise are different, then an additional calculation should be made for the branch of air ducts serving the room with the lowest noise level.

Separately, a calculation 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 units that are closest to the design points or have the highest performance and sound power.

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

If there are throttling devices (diaphragms, throttle valves, dampers), air distribution and air intake devices (grilles, shades, diffusers, etc.) between the fan and the room being serviced, there are sharp changes in the cross-section of air ducts, bends and tees, an acoustic calculation of these devices should be performed and installation elements.

1.5. The acoustic calculation 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 the 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 a branched 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 decibel.

1.6. The required measures to reduce the noise generated by ventilation, air conditioning and air heating installations, if necessary, should be determined for each source separately.

2. SOURCES OF UNITS NOISE 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 installations (diaphragms, throttles, 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 according to the passports for this equipment or according to catalog data

In the absence of noise characteristics, they should be determined experimentally at the request of the customer or by calculation, guided by the data given in these Instructions.

2.3. The general 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 the 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;

I is the total pressure created by the fan, in kg / m 2;

Q is the fan performance in m ^ / sec;

5 - correction for the fan operating mode in dB.

Table 1

Values ​​of noise criterion L for fans in dB

Fan type and series Injection. ... ... Suction. ... ...

Notes: 1. A value of 6 with a deviation of the fan operating mode by no more than 20% of the maximum efficiency should be taken equal to 2 dB. At the fan operating 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 the formula (1) characterizes the sound power emitted by the open inlet or outlet of the fan in one direction into the free atmosphere or into the room in the presence of a smooth supply of air to the inlet.

4. In case of non-smooth air supply to the inlet pipe or installing a throttle 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 the fan noise radiated by the 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 by octave bands in dB, taken depending on the type of fan and the number of revolutions according to table. 2.

table 2

Corrections ALu taking into account the distribution of the sound power of the fan by octave bands, in dB

	Centrifugal fans
Geometric mean hour			Axial veins
Tota octave bands to Hz	with shoulder blades, behind	with shoulder blades, zag	tilators
	bent forward	chucked back
(16 000) (3 2 000)

Notes: 1. Given in table. 2, the data without brackets are valid when the fan speed is within the range of 700-1400 rpm.

2. At a fan speed of 1410-2800 rpm, the entire spectrum should be shifted one octave down, and at 350-690 rpm, an octave up, taking the values ​​in brackets for frequencies 32 and 16000 Hz for the extreme octaves.

3. At a fan speed of more than 2800 rpm, the entire spectrum should be shifted down two octaves.

2.5. The octave sound power levels of the fan noise radiated into the ventilation network should be determined by the formula

Lp - L p ■ - A L- ± - | ~ Л i-2,

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

Table 3 Correction 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 or duct in mm Average geometric frequencies of octave bands in Hz

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

The octave levels of the sound power of the noise emitted by the fan into the ventilation chamber should be determined by the formula (2) and table. 2.

2.7. If several fans are running simultaneously in the ventilation chamber, then for each octave band it is necessary to determine the total level

the sound power of the noise emitted by all fans.

The total sound power level of the noise 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.

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

Table 4 Adding Sound Power Levels or Sound Pressure Levels

Difference of two stacked levels in dB Add to a higher level to determine the Total level in dB

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

2.8. The octave sound power levels 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 by formula (2) and table. 2 with a 3 dB boost correction.

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

Note. When air is taken from outside units, the over correction is not required.

2.9. The total sound power level of the noise generated by throttling, air distribution and air intake devices (choke valves.