1、BRITISH STANDARD BS 4954-2: 1978 Methods for Testing and rating induction units for air distribution systems Part 2: Acoustic testing and rating UDC 628.8:697.953:620.111.3BS4954-2:1978 This British Standard, having been prepared under the directionof the Refrigeration,Heating and AirConditioning St
2、andards Committee, was published underthe authority ofthe Executive Board on 30November1978 BSI 12-1999 The following BSI references relate to the work on this standard: Committee reference RHE/6 Draft for comment 76/71261 DC ISBN 0 580 10332 3 Cooperating organizations The Refrigeration, Heating an
3、d Air Conditioning Standards Committee, under whose direction this British Standard was prepared, consists of representatives from the following Government departments and scientific and industrial organizations: Association of Consulting Engineers Association of Manufacturers of Domestic Electrical
4、 Appliances Boiler and Radiator Manufacturers Association Limited* British Combustion Equipment Manufacturers Association British Gas Corporation British Refrigeration and Air Conditioning Association* British Services Research and Information Association* Chartered Institution of Building Services*
5、 Department of the Environment (PSA) Department of Health and Social Security* Electricity Supply Industry in England and Wales Engineering Equipment Users Association Heating and Ventilating Contractors Association* Hevac Association* Institute of Fuel Institute of Refrigeration* Institution of Gas
6、 Engineers Lloyds Register of Shipping Manufacturers Association of Radiators and Convectors Ltd.* Ministry of Defence* National Coal Board Society of British Gas Industries Water-tube Boilermakers Association The organizations marked with an asterisk in the above list, together with the following,
7、were directly represented on the committee entrusted with the preparation of this British Standard: Department of the Environment Building Research Establishment Institute of Domestic Heating Engineers Portsmouth Polytechnic Amendments issued since publication Amd. No. Date of issue CommentsBS4954-2
8、:1978 BSI 12-1999 i Contents Page Cooperating organizations Inside front cover Foreword ii Section 1. General 1 Scope 1 2 References 1 3 Definitions 1 4 Nomenclature 2 5 General test requirements 2 6 Test conditions 2 7 Instrumentation 2 8 Test methods 2 9 Rating tests 4 10 Correlation and extrapola
9、tion of test data 4 11 Reporting of test results 5 Section 2. Test methods 12 General 5 13 Application 6 14 Precision 7 15 Instrumentation 7 16 Installation 7 17 Quantities to be measured 7 18 Discrete frequency components 8 19 Method of measurement 8 20 Determination of sound power level 10 21 Back
10、ground noise 11 Appendix A Example of analysis of single point data 12 Appendix B Method of testing and rating quiet equipment 13 Appendix C Quiet air supply for acoustic testing and rating 14 Figure 1 End reflection correction 1 Figure 2 Arrangement of equipment for insertion loss test 3 Figure 3 A
11、rrangement of equipment for generated noise test 4 Figure 4 Correlation example 5 Figure 5 Example of typical reference and source 11 Figure 6 Extrapolation of L Wdata on octave bands4, 5, 6 and7 below minimum measurable value of30dB 14 Figure 7 Equipment for quiet air supply 15 Table 1 Correction c
12、onditions for background noise 3 Table 2 Range of accuracy in determining sound power levels of broad band sources in reverberation rooms 7 Table 3 Bandwidths 8 Table 4 Significant discrete frequencies 8 Table 5 Number of microphone stations 9 Table 6 Standard deviations 10 Table 7 Minimum requireme
13、nts for traverse path 10 Table 8 Test octave band mean sound pressure levels 12 Table 9 Test results for generated noise 12 Publications referred to Inside back coverBS4954-2:1978 ii BSI 12-1999 Foreword This Part of this British Standard has been prepared under the direction of the Refrigeration, H
14、eating and Air Conditioning Standards Committee in response to requests from industry. The committee acknowledge their debt to the Building Services Research and Information Associations work in formulating the methods of testing that appear in this standard. It is intended to review this standard w
15、hen a series of ISO standards dealing with acoustic testing has been completed and published as British Standards. Where reference is made to British Standards for which no metric version is available, the appropriate British Standard in imperial units should be used in conjunction with BS350. Atten
16、tion is also drawn to BS3763 and PD 5686. A British Standard does not purport to include 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.
17、 Summary of pages This document comprises a front cover, an inside front cover, pagesi andii, pages1 to16, 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
18、front cover.BS4954-2:1978 BSI 12-1999 1 Section 1. General 1 Scope This Part of this British Standard deals with methods of acoustic testing and rating of induction units, defined in Part1 of the standard, for: a) sound power emission; b) terminal attenuation. 2 References The titles of the publicat
19、ions referred to in this standard are listed on the inside back cover. 3 Definitions For the purposes of this British Standard the definitions of acoustic terms given in BS661 apply; other definitions given in BS4954-1, together with the following, also apply. 3.1 dummy load a flow restrictor or sim
20、ilar device having the same pressure/flow characteristic as the unit under test 3.2 insertion loss the insertion loss of an induction unit is the attenuation it gives to noise propagated from the system through the supply duct. It is defined here as the difference between the sound power radiated fr
21、om the open end of the supply duct and that radiated when the induction unit is connected to the supply duct. The test is conducted without air flow to determine the static insertion loss NOTENot all the sound power will radiate from the open end of the supply duct, some will be reflected back into
22、the system. In practice the total terminal attenuation can be taken as the insertion loss plus the end reflection (seeFigure 1) for the open end of the supply duct. this is achieved by determining the insertion loss of the induction unit and adding the end reflection of the open end of the supply du
23、ct Figure 1 End reflection correctionBS4954-2:1978 2 BSI 12-1999 3.3 terminal attenuation terminal attenuation is equal to insertion loss plus end reflection. It is defined here as the difference between the sound power level in the supply duct and that sound power level radiated from the induction
24、unit in the test location 4 Nomenclature NOTEIn the text, mean values are indicated by a bar over the symbol. 5 General test requirements The test shall be carried out in accordance with the conditions and methods described in section2 unless otherwise specified in section1. 6 Test conditions 6.1 Lo
25、cation of equipment. The unit shall be placed in the test room in a position relative to the room surfaces similar to its normal location in use. The unit shall be mounted for test in a manner which simulates, as closely as possible, the method normally used in practice. Water connecting pipes shoul
26、d be omitted from test rigs. 6.2 Operating conditions. The test shall be carried out under the steady state conditions described for the air flow tests in BS4954-1. 7 Instrumentation Instrumentation shall comply with the provisions of section2 and of BS4954-1. 8 Test methods 8.1 Static insertion los
27、s 8.1.1 Insertion loss need only be specified in frequency bands of one octave width. 8.1.2 The unit shall be connected as shown in Figure 2. The chamber cross-sectional area shall be at least100 times the air supply duct area. 8.1.3 A noise source shall be positioned inside the chamber. This source
28、 shall take the form of either: a) a loud-speaker connected to a random noise generator, b) the reference sound source described in section2. Where a tape recording is used for the noise source, precautions shall be taken to ensure that the output remains constant throughout the duration of the test
29、. A closed loop tape is recommended to minimize the effects of tape sensitivity variations and the loop should pass the play-back head at least three times during each frequency band measurement. The tape should be of the type recommended for closed loop working, i.e.with a permanently lubricated su
30、rface. 8.1.4 Background noise levels shall be measured with the sound source operating during both unit-in and unit-out tests. These levels should be more than6dB below the measured mean sound pressure levels (seealsoclause21). Symbol Quantity Unit P Sound pressure Pa P o Reference sound pressure (=
31、 2 10 5Pa) Pa L P Sound pressure level dB W Sound power W W o Reference sound power (= 10 12W) W L W Sound power level dB L P Mean band sound pressure level ofequipment dB L Pr Mean band sound pressure level ofreference source dB L Wr Band sound power level of referencesound source dB L W Equipment
32、band sound power level dB L W1 Sound power level in L W2 three adjacent one-third dB L W3 octave bands Arithmetic mean sound power levelin one-third octave band, sidebands dB I Insertion loss dB Q Air volume flow rate m 3 /s l Length of unit m l t Length of test unit m f c Centre frequency Hz T Reve
33、rberation time of the test room s Random incident absorption coefficient V Volume of the test room m 3 S Surface area of the test room m 2 Wavelength of sound m L sBS4954-2:1978 BSI 12-1999 3 If the background noise level is less than6dB below the mean sound pressure level measured during the unit-i
34、n test, then this will reduce the measured insertion loss. Where this occurs the results shall be reported with a note to this effect. A correction for the intrusion of background noise affecting the measurements of sound pressure level with the equipment operating shall be applied for the condition
35、 indicated inTable 1. NOTEFor measurement of noise of quiet equipment seeAppendix B. Table 1 Correction conditions for background noise 8.1.5 The test shall be carried out as follows: a) with the unit installed as shown inFigure 2 start the noise source and measure the mean sound pressure level in t
36、he test room; b) remove the unit and with the same input to the noise source as in a) measure the mean sound pressure level in the test room. 8.1.6 The static insertion loss is the difference in sound pressure levels between the unit out and the unit in. Noise from the source which reaches the micro
37、phone measuring stations without passing through the unit under test (flanking transmission) will appear to reduce the insertion loss. The following procedure shall be carried out to determine whether this is occurring. a) Measure the octave band sound pressure level in the same way as for the unit
38、in test with the sound source operating. b) Block the duct upstream of the unit with a high transmission loss barrier immediately upstream of the unit and repeat the test a). If the octave band sound pressure level measured under b) is at least10dB below that measured under a) in each band of concer
39、n, the insertion loss measurements made on the unit will not be affected by such flanking transmission. Figure 2 Arrangement of equipment for insertion loss test Increase in room sound pressure level produced by equipment operation Correction dB 0 to 5 No correction permitted but results may be repo
40、rted as affected by background noise 6 to 8 Subtract 1 dB from measured Above 8 No correction L PBS4954-2:1978 4 BSI 12-1999 8.2 Generated noise 8.2.1 The unit shall be connected to an air supply system similar to that shown inFigure 3. 8.2.2 The test shall be carried out as follows. a) Set the requ
41、ired air flow rate which shall be held constant (to2%) for a minimum period of5min before commencing the test and shall not vary by more than2% during the test. b) Measure the mean room sound pressure levels in one-third octave bands. c) If a reference sound source is employed, measure the sound pre
42、ssure levels in the room with the sound source operating. d) Measure the background noise level with the unit removed and with a dummy load equivalent to that imposed by the unit connected to the fan inlet. The air flow rate employed for this test shall be within2% of that used in the main test. The
43、 background level should be at least6dB below the test sound pressure levels; if it is less than6dB below these levels then test results may be reported as affected by background noise. No correction shall be made for background noise. e) Compute the one-third octave band sound power levels using on
44、e of the methods described in section2 and check for discrete frequencies (seeexample inAppendix A). The test results may then be converted to octave band data provided that bands containing discrete frequencies are identified. 9 Rating tests 9.1 Generated noise test. This test shall be carried out
45、on the unit at a minimum of three air flow rates covering a range in which the highest rate shall be three times the lowest rate. Where integral dampers are fitted the unit shall be tested at three damper positions (fully open,# open,“ open) for each air flow rate. The test shall be repeated for eac
46、h nozzle arrangement offered. 9.2 Static insertion loss test. This test shall be carried out on the unit with any dampers set fully open. The test shall be repeated for each nozzle arrangement offered. 10 Correlation and extrapolation of test data It is not possible to lay down rules to cover every
47、eventuality but the following equations will generally be found satisfactory for correlating test data. Figure 3 Arrangement of equipment for generated noise testBS4954-2:1978 BSI 12-1999 5 10.1 At a given damper setting, calculate L Woin a given octave band from the following equation: L Wo= L W 57
48、 log 10 Q where Q is the air volume flow rate (in m 3 /s) Plot L Woagainst centre frequency divided by volume flow rate as shown inFigure 4. If90% of the test results lie within 2dB of a mean line, then this line may be used to predict the unit sound power output within the test flow range and at an
49、y air volume flow rate lower than the minimum test flow rate. 10.2 Data on modular units may be extrapolated for lengths of unit other than that of the test unit provided that the correlation described in10.1 is satisfactory by means of the equation: where The required L Wmay be found fromFigure 4 at f c /Q = (f c l)/(vl t ), where v is the related air volume flow rate (in m 3 /s). 11 Reporting of test results The test results shall include at least the following items. a) A description of the unit being tested, its
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