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1、BRITISH STANDARD BS 848-2: 1985 Incorporating Amendment No. 1 Fans for general purposes Part 2: Methods of noise testing Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:44:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 848-2:1985 This British Standard, havi
2、ng been prepared under the direction of the Machinery and Components Standards Committee, was published under the authority of the Board of BSI and comes into effect on 31 December 1985 BSI 04-1999 First published November 1966 First revision December 1985 ISBN 0 580 14855 6 Committees responsible f
3、or this British Standard The preparation of this British Standard was entrusted by the Machinery and Components Standards Committee (MCE/-) to Technical Committee MCE/17, upon which the following bodies were represented: Chartered Institution of Building Services Department of Trade and Industry (Na
4、tional Engineering Laboratory) Electricity Supply Industry in England and Wales Engineering Equipment and Materials Users Association Hevac Association Institution of Mechanical Engineers National Coal Board Amendments issued since publication Amd. No.Date of issueComments 9374March 1997Indicated by
5、 a sideline in the margin Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:44:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 848-2:1985 BSI 04-1999i Contents Page Committees responsibleInside front cover Forewordiii 1Scope1 2Definitions1 3Symbols and units3
6、4Test methods, general4 5Instrumentation6 6In-duct test methods11 7Reverberant field test method19 8Free field and semi-reverberant test method26 9Conversion rules for sound power levels35 10Information to be recorded35 11Information to be reported36 Appendix A Precision of the in-duct method of mea
7、surement37 Appendix B Determination of the signal-to-noise ratio of sound to turbulence noise in the test duct37 Appendix C Examples of suitable instrumentation systems38 Appendix D Anechoic termination40 Appendix E Reverberation time qualification test and evaluation of environmental correction fac
8、tor K45 Appendix F Absolute comparison qualification test for evaluation of environmental correction K46 Appendix G Generalized guide for sound power level prediction47 Appendix H Characteristics and calibration of reference sound source49 Figure 1 Example of frequency response of microphone fitted
9、with protection grid as supplied by a manufacturer39 Figure 2 Schematic drawing of a typical sampling tube9 Figure 3 Limiting dimensions of test ducts, intermediate ducts and transitions for type B installation13 Figure 4 Limiting dimensions of test ducts, intermediate ducts and transitions for type
10、 C installations14 Figure 5 Limiting dimensions of test ducts, intermediate ducts and transitions for type D installations15 Figure 6 Test room with whole air circuit within walls21 Figure 7 Test room with type A installation21 Figure 8 Test room with types B and C installations22 Figure 9 End refle
11、ction correction23 Figure 10 Microphone positions for a hemispherical measurement surface for type A installation39 Figure 11 Microphone positions for a hemispherical measurement surface for types B and C installations33 Figure 12 Microphone positions for spherical measurement surface34 Figure 13 Ex
12、amples of anechoic termination41 Figure 14 Examples of three catenoidal designs of anechoic termination42 Figure 15 Examples of inlet anechoic termination (catenoidal)43 Figure 16 Example of stepped inlet anechoic termination44 Figure 17 Environmental correction K, in dB46 Figure 18 Example of deter
13、mination of a and b for typical fan series50 Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:44:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 848-2:1985 ii BSI 04-1999 Page Table 1 Uncertainty in determination of the broad band sound power levels5 Table 2
14、Example of instrument response correction to measured sound pressure levels7 Table 3(a) Flow velocity correction C3 for sampling tube in outlet side duct7 Table 3(b) Flow velocity correction C3 for sampling tube in inlet side duct7 Table 4(a) Modal correction C4 for a sampling tube7 Table 4(b) Modal
15、 correction C4 for omnidirectional microphones7 Table 5(a) Maximum standard deviation7 Table 5(b) Corresponding maximum range of sound pressure levels7 Table 6 Coordinates of microphone locations for hemispherical measurement surface for type A installations and corresponding representative surface
16、areas29 Table 7 Coordinates of microphone locations for hemispherical measurement surface for type B and C installations and corresponding representative surface areas30 Table 8 Coordinates of microphone locations for spherical measurement surface and corresponding representative surface areas31 Tab
17、le 9 Effect of end reflections37 Table 10 Effect of transitions37 Table 11 Computation of power from pressure measurements37 Table 12 Maximum difference between the sound pressure level readings of a microphone fitted with a nose cone and of a microphone fitted with a sampling tube as a function of
18、the turbulence noise suppression %Lt of the sampling tube, for a minimum signal-to-noise ratio of sound to turbulence noise of 5 dB38 Table 13 Turbulence noise suppression %Lt of typical sampling tube as compared with that of a 13 mm nose cone39 Table 14 Maximum pressure reflection coefficient40 Tab
19、le 15 Calibration accuracy for reference sound source49 Publications referred toInside back cover Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:44:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 848-2:1985 BSI 04-1999iii Foreword This Part of BS 848 has be
20、en prepared under the direction of the Machinery and Components Standards Committee and is a revision of BS 848-2:1966, which is withdrawn. This standard describes four methods for determination of the sound power radiated by fans in each of the standardized installation types described in BS 848-1.
21、 Installation type A: free inlet, free outlet. Installation type B: free inlet, ducted outlet. Installation type C: ducted inlet, free outlet. Installation type D: ducted inlet, ducted outlet. The terms used in this classification have the following meanings. Free inlet or outlet signifies that the
22、air enters or leaves the fan directly from or to the unobstructed free atmosphere, except that, in type A installations, a partition in which the fan is mounted may support a pressure difference between the inlet and outlet sides. Ducted inlet or outlet signifies that the air enters or leaves the fa
23、n through a long, straight duct directly connected to the fan inlet or outlet respectively. These standardized airways recognize that fan performance is influenced by the presence or otherwise of ducting connected to the fan. The four methods of fan noise testing described are the in-duct, the free
24、field, the reverberant field and the semi-reverberant field methods. It is not likely that these methods will permit determination of sound power in all on-site conditions, although the semi-reverberant field method will provide practical guidance for those few cases beyond the scope of the free fie
25、ld and semi-reverberant methods described in clause 8 of this standard. This standard is concerned with the testing of fans under laboratory conditions. Fans which are too large to be tested in an acoustic laboratory or fans whose noise output is measured in the presence of an appreciable amount of
26、background noise, as is often the case when testing on site, require the use of different techniques from those discussed herein (e.g. sound intensity measurements). Such tests, however, are outside the scope of this standard. The frequency range to be determined has been extended in this revision t
27、o include the 63 Hz octave band, whilst the band width for measurement has been reduced to one-third octave to allow assessment of the presence of narrow band noise sources such as blade passing frequencies. The band width used for reporting information remains as octave bands and the precision of m
28、easurement has been evaluated to include effects of duct end impedances, transitions, noise sampling, instrumentation calibration and computation of sound power from sound pressure levels. Information on scaling of fan sound power and frequency from one fan size and/or speed to another is also inclu
29、ded. The sampling tube has been included for noise measurements in in-duct test environments where wind shielded microphones are necessary. These tubes are directional and are used to suppress the turbulent pressure fluctuations at the microphone. Therefore only the sound pressure attributed to the
30、fan noise radiation is measured. These tubes are commercially available. In order that the fan noise should be representative of the fan in one of the standardized installation types, intermediate airways have been specified corresponding to those parts of the common airway sections included in clau
31、se 24 of BS 848-1:1980 adjacent to the inlet and outlet of ducted fans. In the case of B and D type installations the outlet side flow straightener has been removed, since it might interfere with the acoustical measurements; simultaneous determination of standardized air and noise performance is not
32、 then possible. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:44:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 848-2:1985 iv BSI 04-1999 Data obtained in accordance with this standard may be used for the following purposes amongst others: a) comparison o
33、f fans which are similar in size and type; b) comparison of fans which are different in size and type; c) rating of fans in terms of any constituent of its sound power level; d) scaling of fan noise from one size and speed to another size and speed; e) prediction of sound pressure levels in an insta
34、llation of which the fan forms a part. NOTEThe prediction of near field sound pressure levels is not practicable. For example, a sound pressure level at 1 m is only appropriate if this represents a far field condition. This may limit the size and type of fan for which direct measurements are appropr
35、iate. (See clause 8.) This standard describes a series of methods for the laboratory determination of fan sound power levels to form an integral part of the statement of complete fan performance, including noise for one of the installations of types A, B, C or D shown in BS 848-1. The sound power ra
36、diated by a fan in each of these installation types comprises: an inlet sound power; an outlet sound power; and a casing and/or drive sound power. These sound powers are determined individually, or in combinations as follows: type A free inlet and part1) of casing sound power; type A free outlet and
37、 part1) of casing sound power; type B free inlet and casing sound power; type B ducted outlet sound power; type C ducted inlet sound power; type C free outlet and casing sound power; type D ducted inlet sound power; type D ducted outlet sound power. The sound powers leaving a fan inlet into free spa
38、ce and into a duct are different, and each is also affected by what is connected to the outlet, and therefore the outlet acoustical impedance. Similarly, the sound powers leaving a fan outlet into free space and into a duct are different, and each is also affected by what is connected to the inlet,
39、and therefore the inlet acoustical impedance. Eight sound powers are therefore required for a complete statement of the standardized performance of a fan adaptable to all installation types. It is, however, permissible to group some sound powers together provided they are only slightly different, as
40、 found in many instances. The casing and, if required, the drive sound power may be determined in a type D installation test either by the reverberant field method (see 7.3.8) or by the free or semi-reverberant field methods (see 8.3.8). In this standard the computation of sound power from sound pre
41、ssure level measurements is based on the premise that the mean-square sound pressure averaged over the enveloping measuring surface and over time is: 1) directly proportional to the sound power output of the source; 2) inversely proportional to the area, Sm, of the measurement surface or to the equi
42、valent absorption area, Sa, of the room; 3) otherwise dependent only on the physical constants of air dentisy and sound velocity. NOTEIn view of the fact that sound transmitted along ducts is often modified prior to reaching the environment in which its effect is felt, the use of an A-weighted in-du
43、ct sound power level cannot be recommended. 1) This depends on the location of the partition. Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:44:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 848-2:1985 BSI 04-1999v A British Standard does not purport to in
44、clude all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pag
45、es i to vi, pages 1 to 50, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Licensed Copy: London South Bank University, London South Bank Univ
46、ersity, Fri Dec 08 01:44:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI vi blank Licensed Copy: London South Bank University, London South Bank University, Fri Dec 08 01:44:17 GMT+00:00 2006, Uncontrolled Copy, (c) BSI BS 848-2:1985 BSI 04-19991 1 Scope This Part of BS 848 deals with the determinatio
47、n of the acoustic performance of fans designed to be capable of operating against a difference of pressure and may be used to determine the sound power of a fan combined with an ancillary device such as a roof-cowl, damper or fan silencer. They may be of the axial, centrifugal, mixed flow or other t
48、ype. Fans designed solely for air circulation, such as ceiling fans or table fans, are excluded. The uncertainty of measurement applies primarily to the steady broad-band noise as defined in ISO 2204 as emitted by fans. Prominent narrow-band and discrete frequency noise is determined only insofar as
49、 it can be deduced from an analysis in third-octaves with increased uncertainty of measurement. Narrow-band or discrete frequency levels in a reverberant chamber can only be accurately determined by the method of BS 4196-2, or in an anechoic chamber by the method of BS 4196-5. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Part of BS 848 the definitions given in BS 661 apply together with the following. 2.1 free fie