This standard applies to the determination of the sound power level of noise from heating, ventilation and air conditioning equipment (hereinafter referred to as the unit). This standard specifies the engineering determination method for the sound power level of noise under reverberant sound field conditions under free sound field conditions on the reflecting plane, and recommends the sound pressure level measurement method suitable for on-site determination in Appendix C (reference). GB/T 9068-1988 Engineering method for determination of sound power level of noise from heating, ventilation and air conditioning equipment GB/T9068-1988 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Noise emitted by heating-ventilating and air conditioning equipment
Determination of sound power levels for noise emitted by heating-ventilating and air conditioning equipment-Engineering method
1 Scope of application
UDC 621. 561- 57
：697.31.9-534.6
GB9068-88
This standard applies to the determination of sound power levels of noise emitted by heating-ventilating and air conditioning equipment (hereinafter referred to as units). This standard specifies the engineering determination method for the sound power level of noise emitted by reverberant sound field under free sound field conditions on the reflecting plane, and recommends the sound pressure level measurement method suitable for on-site determination in Appendix C (reference). 2 Reference standards
GB3102.7 Acoustic quantities and units
GB3241 1/1 and 1/3 octave band filters for sound and vibration analysis GB3785 Electrical and acoustic properties and test methods of sound level meters GB3947 Vocabulary of acoustic terms
JJG176
Trial verification procedure for sound pressure level calibrators
JJG I88
JJG 277
Trial verification procedure for sound level meters
Verification procedure for standard sound sources
3 Acoustic terms, acoustic quantities and units
The names and symbols of the terms, quantities and units used in this standard conform to the provisions of GB3947 and GB3102.7. 4 Test instruments
4.1 Overview
The test instruments shall be sound level meters of type 1 or above specified in GB3785, and other test instruments with equivalent accuracy. An extension rod or extension cable shall be used between the sound level meter or other test instruments and the microphone. The double-range filter shall comply with the relevant provisions of GB3241. 4.2 Calibration
Before and after each measurement, a sound level calibrator with an accuracy higher than ±0.5dB shall be used to calibrate the entire test instrument system at one or more frequencies. If the difference between the two calibration values ​​before and after the measurement exceeds 1dB, the measurement is invalid. The sound level calibrator shall be checked regularly in accordance with JG176, and the sound level meter and other test instruments shall be checked regularly in accordance with JG188 to ensure the accuracy of the test instruments. 5 Quantities to be measured and measurement error
5-1 Quantities to be measured
A sound power level and the sound power level of seven octave bands with center frequencies between 125 and 8000 Hz Approved by the State Machinery Industry Commission on April 5, 1988 and implemented on January 1, 1989
GE 9068-88
5.2 Measurement error
Measured in accordance with this standard, the standard deviation of the A-weighted sound power level is 2 dB The standard deviation of the octave band sound power level shall not exceed the value specified in Table 1.
Center frequency of octave band, Hz
500--4 000
Standard deviation + dB
Note: Measurement error refers to the standard deviation of the result caused by various factors, but does not include the change of the sound power of the machine itself caused by changes in the installation and operating status of the machine in each measurement.
6 Installation and operation of the unit
6.1 Installation
6.1.1 The unit should be installed in accordance with the requirements of relevant technical conditions. All parts should be installed completely, but no additional sound insulation and noise reduction parts should be added.
6.1.2 The unit should usually be installed on a reflecting plane (i.e. the ground). Ceiling-mounted and wall-mounted units should also be installed in a position with similar conditions to the wall increase or large ceiling when installed on the floor of the test room. 6.1.3 The unit usually installed against the wall should be installed against the wall during measurement. The wall should be a reflecting plane, that is, installed on two reflecting planes. 6.1.4 When measuring under reverberant sound field conditions, if the unit is neither against the wall nor installed on the wall, other installations should avoid symmetrical positions, and the main surface of the sound source should not be parallel to the adjacent wall of the reverberation room, and the distance between the unit surface and its wall should not be less than 1m. 6.2 Operation
The unit with fixed speed shall operate stably and continuously at the rated speed. The unit with stepped speed shall be measured at the highest speed or at each speed.
7 Test method under free sound field conditions on the reflection plane 7.1 Test environment
7.1.1 Reflection plane
The reflection plane shall be a flat surface made of concrete, asphalt or other similar solid materials, and its size shall be larger than the projection of the measurement surface on it.
7.1.2 Suitable test environment
The suitable test environment shall be specified as a half space on one reflection plane or a quarter space on two reflection planes. The ideal test environment is one with no other reflectors except the specified reflection plane. Appendix A (Supplement) gives the identification method of the test environment.
7.2 Reference body
The reference body is a minimum rectangular hexahedron that just envelops the unit under test and ends on the reflection plane. When determining the base body, small parts protruding from the unit (such as connecting pipes, handles, etc.) are not considered. 7.3 Measuring surface
The measuring surface is divided into a semi-circular measuring surface and a rectangular hexahedron measuring surface, see Appendix B (Supplementary Part) Figures B1 to B3. 7.3.1 Hemispherical measuring base surface
The hemispherical measuring surface is suitable for units with smaller dimensions installed on a reflection plane. 7.3.1.1 The center of the hemispherical measuring surface is the projection of the geometric center of the reference body on the reflection plane 1:. The radius of the hemispherical measuring surface should not be less than twice the characteristic distance d. GB 9068-88
Characteristic distance d. Calculated by formula (1), = [(0.5)+(0.5)+
Where: d. —Characteristic distance, m;
The length, width, height of the reference body + 1.
The radius r is preferably 1m or 2m. If d. > 1m, the rectangular hexahedral measurement surface described in 7.3.2 should be used. 7.3.1.2 The area of ​​the hemispherical measurement surface is calculated by formula (2): S, = 2 yuan
Where: S: —Hemispherical measurement surface area, m2; Hemispherical measurement surface radius, m.
7.3.2 Short hexahedral measurement surface
· (2)
The rectangular hexahedral measurement surface is a rectangular box surface located on the reflection plane, with each face parallel to the corresponding face of the reference body and the distance between the corresponding faces being 1m, see Appendix B (Supplement).
7.3.2.1 The area of ​​the measuring surface on one reflecting plane is calculated by formula (3): S′ = 4(ab + bc + ca)
Where: S′-
-area of ​​the measuring surface, m,
-half the length and width of the measuring surface,
height of the measuring surface, m.
7.3.2.2 The area of ​​the measuring surface on two reflecting planes is calculated by formula (4): S′ = 4(a'b +'B'c + 0.5c'a')Where: S′-
-half the length and width of the measuring surface,
c-height of the measuring surface, m.
7.4 Sound pressure level measurement
7.4.1 Background noise
7.4.1.1 If any of the following conditions occurs, the background noise shall be measured at only one measuring point: a. The background noise sound pressure level is at least 10 dB lower than the unit noise sound pressure level; b. The background noise source is removed from the test site.
Otherwise, the background noise shall be measured at each measuring point. ++++++++++(3)
7.4.1.2 The background noise shall be corrected according to Table 2. This standard requires that the difference between the measured unit noise sound pressure level and the background noise sound pressure level should not be less than 6dB.
The difference between the measured unit noise sound pressure level and the background noise sound pressure level is 6~-8
9, 10
7.4.2 Wind speed
The amount of correction removed from the measured sound pressure level
The measurement is invalid
GB 9068-88
7.4.2.1 When measuring outdoors, the wind speed near the measuring point should be less than 6m/s (equivalent to level 4 wind). When the wind speed is greater than 1m/s, the wind should be used.
7.4.2.2 When the wind speed at the measuring point at the unit outlet is greater than 5m/s, the measuring point should be offset in the 45\ direction to avoid the outlet. 7.4.3 Measurement point location
All measuring points should be on the measurement surface determined in 7.3. Figures B1 to B3 show the locations of the measuring points on the measuring surface, and Tables B1 to B3 give the coordinates of each measuring point. 7.4.3.1 There are 10 measuring points arranged on the hemispherical measuring surface (see Figure B1 and Table B1). 7.4.3.2 The measuring points on the rectangular hexahedron measuring surface are divided into basic measuring points and additional measuring points. The rectangular hexahedron measuring surface on one reflection plane has 9 basic measuring points and 8 additional measuring points (Figure B2 and Table B2); the rectangular hexahedron measuring surface on two reflection planes has 6 basic measuring points and 5 additional measuring points (see Figure B3 and Table B3). 7.4.3.3 Additional measuring points should be added in the following cases: a. The size of any side of the reference body is greater than 2Ⅲ; b. The difference between the maximum and minimum decibels of the sound pressure suffix measured at the basic measuring point exceeds the number of measuring points. 7.4.4 When measuring
, the microphone should face the direction of the unit under test. The sound level meter should adopt the "slow time weighting characteristic measurement. When the sound level meter pointer swings no more than ±3dB, read the average value by visual inspection. For the octave band with a center frequency of 125Hz, the observation time is at least 30s; for A-weighted and other octave bands, the observation time is at least 10. When the sound level meter pointer swings more than ±3dB, an analog instrument with a longer time constant or a digital integrating sound level meter should be used for measurement.
7.4:5 Correction of measurement environment
When there are unnecessary reflectors in the measurement environment, the measurement results should be corrected. The method for determining the environmental correction value K is shown in Appendix A (Supplement).
7.5 Calculation of surface sound pressure level
The average sound pressure level of the measurement surface is calculated by formula (5): L=10 lg2
: Where: L,——the average A-weighted or octave sound pressure level of the measurement surface, dB (the reference value is 20μPa, the same below), Lm—according to 7.4. 1 A-weighted or multiplied sound pressure level at point i after background noise correction, dB; N number of measuring points.
7.6 Calculation of sound power level
The sound power level is calculated by formula (6):
Lw=(LK)+10 Ig(S/S.)
Where: L--A-weighted or octave band sound power level, dB (reference value is lpW, the same below), average sound pressure level of the measuring surface, dBt
K-environmental correction value (see Appendix A), dB;
S measuring surface area, m,
S,-reference area is lm2.
Reverberation sound field measurement method
(6)
This chapter specifies the relative comparison method for determining the unit noise sound power level of the reverberation chamber. For reverberation chambers that have been identified as qualified, direct method measurements may be used in accordance with relevant standards.
8.1 Requirements for reverberation chambers
GB 9068—88
The test room can be a special reverberation case or an ordinary room with a hard reflective surface, but it should comply with the following regulations: 8.1.1 The mutual ratios of the length, width and height of the reverberation room should not be close to integers, and the ratio of the maximum size to the minimum size should be less than 3. 8.1.2 The volume of the reverberation room is 180~400m. 8.1.3 The sound absorption coefficient of the reflective surface should be less than 0.06, and the sound absorption coefficient of any surface should be between 0.5 and 1.5a, where 4 is the total average sound absorption coefficient of the room.
8.1.4 The unit volume should be less than 1% of the reverberation room volume. 8.1.5 In order to avoid excessive changes in air sound absorption in the test room during the measurement process, the temperature t(C) and relative condensation RH(%) should be controlled during the entire test process of the standard sound source and unit noise in the test room. When the product RH×( When the change of (5) exceeds ±10%, the measurement shall be stopped.
8.2 Measurement of sound pressure level
8.2.1 Sound pressure level measurement in reverberation room should use pressure type microphone, otherwise random incidence response correction shall be made. 8.2.2 The distance between the measuring point and the room surface shall be greater than 1m. The distance between any two measuring points shall be greater than 1m. The minimum distance between the measuring point and the unit surface shall be calculated by formula (7)
Daim 0. 3 V
Where: Dai——the minimum distance between the measuring point and the unit surface, m; - the volume of the reverberation room, m.
If the selected measuring point is in a plane, the angle between the plane and the room surface is greater than 10°. 8-2.3 Select 6 measuring points according to the provisions of Article 8.2.2, measure the octave band sound pressure level at each measuring point, and calculate the standard deviation of each borrowed frequency band according to formula (8):
a=(N- 1)-1
Where: ... - standard deviation of measurement.dB
Im octave band sound pressure level at point i, dB
Z, —- average value calculated according to formula (9), dB; N - total number of measuring points.
The standard deviation should be less than 2.3dB, otherwise the measuring points should be increased to 12 and calculated according to formula (8). At this time, the standard deviation should not be greater than 4 dB, otherwise the test site should be changed. 8.3 Calculation of sound power level
8.3.1 Place the standard sound source that meets the provisions of relevant standards and is qualified according to JJG277 on the floor of the test room so that its distance from any microphone meets the provisions of Article 8.2.1. 8.3.2 According to the provisions of Article 8.2, measure and calculate the octave band sound pressure level of the standard sound source. 8.3.3 The octave band sound power level is calculated by formula (10): Lws = Lp + (Lur - L)
Wherein: Lgrt
Octave band sound power level of the unit, dB;
Z, the average octave band sound pressure level of the unit, dB; Lr. Octave band sound power level of the standard sound source. dB; Lpr—Octave band sound power level of the standard sound source measured according to 8.3.2., dB. (10)
8.3.4 The A-weighted sound power level is calculated by formula (11); GB 9068-88
Iawa =- 10 igl
101g+)
Where: LwA—·Calculated A-weighted sound power level, dB; L—-the octave band sound power level calculated by formula (10), dBC, —A-weighted attenuation determined according to Table 3. Table 3
Center frequency of octave band, Hz
Record content
The test record should include the following content, and the record form is shown in Appendix D (reference). 9.1 Test unit
a. Model, name, manufacturing and factory number and other relevant parameters of the unit; b. Test operating parameters of the unit.
9.2 Test environment
9.2.1 The test under free sound field conditions on the reflection plane should record: a.
The condition of the reflection plane;
The size of the test room and the sound absorption treatment; b.
The distance between the measuring point and the nearest reflector, etc. 9.2.2 The reverberation market test should record:
The volume of the test room;
The physical treatment of the walls, ceiling and floor; h.
Draw a diagram of the sound source location.
9.3 Test instrument
a. The model, name, manufacturer and factory number of the instrument; h. The date and department of the instrument inspection.
9.4 Acoustic data
The location of the measuring point, and draw a schematic diagram of the measuring point location; a.
b. A-weighted or octave band sound pressure level measured at each measuring point; c. Background noise sound pressure level and corresponding correction value; C. edBWww.bzxZ.net
d. Free sound field test on the reflecting plane should also record the size of the reference body, the size and surface area of ​​the measuring surface and the environmental correction value K determined in Appendix A:
9.5 Meteorological conditions
Temperature, relative turbulence and atmospheric pressure.
9.6 Others
GB906888
Test personnel, time, place and other conditions that should be explained. Test report
The test report should include the following contents. The form of the test report is shown in Appendix D (reference). Unit model, name, manufacturer and factory number, b. Test conditions;
c: A-weighted sound power level and octave band sound power level; The report should indicate that it is measured according to the free sound field or reverberation sound field method on the reflecting surface of this standard. d
A1 Overview
GB 9068-88
Appendix A
Test environment identification method
(Supplement)
This appendix specifies the determination of the environmental correction value K by the absolute comparison method. A1-1 Environmental correction may not be performed (i.e. K=0) in the following cases:. Outdoor venues with reflectors within 10 m from any measuring point. b. Semi-anechoic cases that have been identified as qualified according to relevant standards. Note: Sound reflectors mainly refer to buildings and some larger equipment. When the width of an obstacle close to the sound source (such as the diameter of a pile or column) is greater than one-tenth of its distance from the sound source, it is considered a reflector. A1.2 The environmental correction value K should not be greater than 2 dB. If the measured K value is greater than 2 dB,Measurement: Sound absorption measures can be adopted to reduce the value; h When the K value is greater than 2dBH and less than 7dB, the A-weighted sound power level is determined according to the test procedure given in this standard and used for comparison of the sound power levels of similar units in the same test environment. The standard deviation caused by the uncertainty of this comparison shall not exceed 3dB. A2 Absolute comparison method
A2.1 Method
A standard sound source that complies with relevant regulations and is regularly calibrated according to JJG 277 shall be placed in the test environment at the same location as the unit under test, and the sound power level of the standard sound source shall be measured and calculated according to the method in Chapter 7 (no environmental correction item is required). When the standard sound source is placed at multiple locations, the average sound pressure level Lr of the measured surface is calculated by formula (A1); L.- 10 gl NM
Wherein, L,——the average sound pressure level of the measured surface, dB; N——the total number of measuring points:
MThe number of standard sound source placement points:
The sound pressure level of the th standard sound source placement point at the th measuring point, dB. Lu
The sound power level is calculated according to formula (6) (where K=0), then the K value is calculated by formula (A2): K = Lw -- Lwo
Wherein, K —environmental correction value, dB t
IwThe sound power level of the standard sound source measured on site (no positive environmental term is required), dB; Loru——the calibrated sound power level of the standard sound source, dB. A2.2 Placement of standard sound source
According to different situations, the placement of standard sound sources is divided into two methods: substitution method and side placement method. H(Al)
42.2.1 When the unit under test can be removed from the test site, the substitution method is adopted. The standard sound source placement point is the projection of the geometric center of the reference body on the reflection plane.
A2.2.2 When the unit under test cannot be removed from the test site, the side placement method is adopted. The standard sound source is placed at the midpoints on both sides of the bottom of the reference body on the air inlet and exhaust surfaces, two positions. For units installed close to the base, it is only placed at the midpoint of the front side of the bottom of the base body on the exhaust surface, one position. GB 9068—88
Appendix B
Reference body, measurement attenuation surface and measurement point location
(Supplement)
B1 See Figure B1 and Table B1 for the measurement point locations on the hemispherical measurement surface. Reference body
Tidal plate surface
Measuring point number
0 Auxiliary point position query
GB 9068—8B
B2The positions of the reference body, measuring surface and measuring points on a reflecting plane are shown in Figure B2 and Table B2. Measuring surface
Basic measuring point
Measuring point number
Measuring point number
B3 The reference body, measuring surface and measuring point positions on the two reflecting planes are shown in Figure B3 and Table B3. 748
O Basic measuring point
X Additional point
Point number
Basic measuring point
GB 9068-88
Measuring surface
Measuring point number
Reflection surface
Friendly reflection
O Basic auxiliary point
× Additional measuring point
Reflection body
Additional measuring point
GB 9068—88
Appendix C
Method for measuring sound pressure level
(reference)
When the factory inspection and on-site test of the unit do not meet the conditions for sound power level testing, the sound pressure level testing method can be used. C1 Measurement environment
According to the provisions of Article 7.1 If the standard time cannot be met, the test situation should be recorded. C2 Measuring instruments
According to the provisions of Chapter 4.
C3 Installation and operation of the unit
According to the provisions of Chapter 6,
C4 Measurement point location
C4.1 The measurement point location of the unit installed on the ground or on the wall shall be in accordance with the provisions of Figure C1. C4.2 The measurement point location of the unit installed on the ceiling shall be in accordance with the provisions of Figure C2. Microphone position
C5 Measurement and calculation of sound pressure level
C5.1 Sound pressure level measurement shall be carried out in accordance with Article 7.4.4. Unit
Blowing port
Microphone position
C5.2 Background noise is corrected according to Table C1. This standard requires that the difference between the measured unit noise and the background noise sound pressure level should not be less than 5dB. Table C
The difference between the measured unit noise sound pressure level and the background noise sound pressure level is calculated according to formula (5). The correction amount subtracted from the measured sound pressure level is invalid.
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