1、BRITISH STANDARD BS 4857-2: 1978 Methods for Testing and rating terminal reheat units for air distribution systems Part 2: Acoustic testing and rating UDC 628.8:697.978:697.356:620.111.3BS4857-2:1978 This British Standard, having been prepared under the directionof the Refrigeration, Heating and Air
2、 Conditioning Standards Committee, was published under the authorityofthe Executive Boardon 31August1978 BSI 01-2000 The following BSI references relate to the work on this standard: Committee reference RHE/6 Draft for comment 76/71260DC ISBN 0 580 10277 7 Cooperating organizations The Refrigeration
3、, Heating and 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 Domesti
4、c Electrical Appliances Boiler and Radiator Manufacturers Association Limited* British Combustion Equipment Manufacturers Association British Gas Corporation British Refrigeration and Air Conditioning Association* Building Services Research and Information Association* Chartered Institution of Build
5、ing Services* 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* Insti
6、tution of Gas 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
7、 following, were directly represented on the committee entrusted with the preparation of this British Standard: Department of the EnvironmentBuilding Research Establishment Institute of Domestic Heating Engineers Portsmouth Polytechnic Amendments issued since publication Amd. No. Date of issue Comme
8、ntsBS4857-2:1978 BSI 01-2000 i Contents Page Cooperating organizations Inside front cover Foreword ii Section 1. General 1 Scope 1 2 References 1 3 Definitions 1 4 Nomenclature 1 5 General test requirements 2 6 Instrumentation 2 7 Test methods 2 8 Rating tests 7 9 Reporting of test results 9 Section
9、 2. Test methods 10 General 9 11 Application 10 12 Precision 10 13 Instrumentation 11 14 Installation 11 15 Quantities to be measured 11 16 Discrete frequency components 12 17 Method of measurement 13 18 Determination of sound power level 15 19 Background noise 17 Appendix A Method of testing and ra
10、ting quiet equipment 18 Appendix B Quiet air supply for acoustic testing and rating 19 Figure 1 Arrangement of equipment for insertion loss test 3 Figure 2 Typical arrangement for unit-out test 5 Figure 3 End reflection correction 5 Figure 4 Arrangement of equipment for generated noise test; noise r
11、adiated, in direction of outlet 6 Figure 5 Arrangement of equipment for generated noise test; noise radiated, in direction of inlet 7 Figure 6 Arrangement of equipment for casing radiation test 8 Figure 7 Example of typical reference sound source 17 Figure 8 Extrapolation of L Wdata on octave bands
12、4, 5, 6 and 7 below minimum measurable value of30dB 18 Figure 9 Equipment for quiet air supply 19 Table 1 Correction conditions for background noise 4 Table 2 Range of accuracy in determining sound power levels of broadbandsources in reverberation rooms 11 Table 3 Bandwidths 12 Table 4 Significant d
13、iscrete frequencies 12 Table 5 Number of microphone stations 13 Table 6 Standard deviations 15 Table 7 Minimum requirements for traverse path 15 Publications referred to Inside back coverBS4857-2:1978 ii BSI 01-2000 Foreword This Part of this British Standard has been prepared under the direction of
14、 the Refrigeration, Heating and Air Conditioning Standards Committee in response to requests from industry. The committee acknowledge their debt to the Building Services Research and Information Association for the Associations work in formulating the methods of testing that appear in this standard.
15、 It is intended to review this standard when 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
16、 be used in conjunction with BS350. Attention is also drawn to BS3763 and PD5686. 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
17、 confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cover, pages i and ii, pages1 to20, 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 indic
18、ated in the amendment table on the inside front cover.BS4857-2:1978 BSI 01-2000 1 Section 1. General 1 Scope This Part of this British Standard deals with methods of acoustic testing and rating of terminal reheat units, defined in Part1 of the standard, for: a) static terminal attenuation; b) sound
19、generation, upstream and downstream of the unit; c) radiation of sound from the casing. 2 References The titles of the publications 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 BS6
20、61 apply; other definitions given in BS 4857-1, together with the following, also apply. 3.1 dummy load a flow restrictor or similar device having the same pressure/flow characteristic as the unit under test 3.2 insertion loss the insertion loss of a terminal reheat unit is the attenuation it gives
21、to noise propagated from the system through the supply duct. It is defined here as the difference between the sound power radiated from, the open end of the supply duct, and that radiated when the unit is connected to this supply duct. The test is conducted without air flow to determine the static i
22、nsertion loss 3.3 noise radiated in direction of inlet the rate at which sound energy enters a uniform airway connected to the unit inlet 3.4 noise radiated in direction of outlet the rate at which sound energy enters a uniform airway connected to the unit outlet 3.5 steady state conditions steady s
23、tate conditions are considered to exist for test purposes if the air volume flow rate does not vary by more than2% from a mean value during the test 3.6 terminal attenuation terminal attenuation is the difference between the sound power level in the supply inlet duct and the sound power level in the
24、 outlet duct. Terminal attenuation can be calculated from the insertion loss by adding the outlet duct and reflection and subtracting the inlet duct end reflection 4 Nomenclature Symbol Quantity Unit P Sound pressure Pa P O Reference sound pressure (=2 10 5 Pa) Pa L p Sound pressure level dB W Sound
25、 power W20 log 10 P P O - =BS4857-2:1978 2 BSI 01-2000 5 General test requirements 5.1 The tests shall be carried out in accordance with the conditions and methods specified in section2, unless otherwise specified in section1. 5.2 Multiple outlet boxes shall be tested with a single outlet duct fitte
26、d. This single duct shall have an outlet area equal to the sum of the areas of the multiple outlets. 5.3 Units designed for use in a specific situation shall be tested under conditions simulating this situation. 6 Instrumentation Instrumentation shall comply with the provisions of section2 and of BS
27、 4857-1. 7 Test methods 7.1 Terminal attenuation 7.1.1 The unit shall be connected to a system similar to that shown inFigure 1. The minimum dimension of the chamber shown shall be three and a half times the air supply duct diameter (or mean of sides if rectangular). 7.1.2 A suitable random noise so
28、urce is 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. A closed loop
29、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 surface. 7.1.3 Back
30、ground 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 (seealso clause19). If the background noise level is less than6dB below the mean sound pressure level measur
31、ed during the unit-in 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 applie
32、d for the condition indicated inTable 1. NOTEFor measurement of noise of quiet equipments, seeAppendix A. W O Reference sound power (=10 12 W) W L W Sound power level dB A Octave band terminal attenuation dB T Reverberation time of the test room s Random incident absorption coefficient V Volume of t
33、he test room m 3 S Surface area of the test room m 2 Wavelength of sound m X r End reflection dB NOTEIn the text, mean values are indicated by a bar over the symbol.10 log 10 W W O - =BS 4857-2:1978 BSI 01-2000 3 Figure 1 Arrangement of equipment for insertion loss testBS4857-2:1978 4 BSI 01-2000 Ta
34、ble 1 Correction conditions for background noise 7.1.4 The test shall be carried out as follows. a) With the unit installed as shown inFigure 1 and the noise source operating, measure the mean sound pressure level, in octave bands, in the test room,. b) Remove the unit and substitute a length of str
35、aight duct as shown inFigure 2. a) Repeat test a) maintaining the output of the noise source constant. This gives . 7.1.5 The terminal attenuationA shall be calculated from the following equation. where 7.1.6 Noise from the source which may reach the microphone measuring stations without passing thr
36、ough the unit under test (flanking transmission) will appear to reduce the terminal attenuation of the unit. 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-in test with the sound sou
37、rce operating. b) Block the inlet duct with a high transmission loss barrier immediately upstream of the unit and repeat testa). If the octave band sound pressure level measured underb) is at least10dB below that measured undera) in each band of concern, the terminal attenuation measurements made on
38、 the unit will not be affected by such flanking transmission. 7.2 Generated noise 7.2.1 General. The tests described in this clause are for the determination of air flow generated noise radiated through both the inlet and outlet connections. Increase in room sound pressure level produced by equipmen
39、t operation Correction dB 0to5 a No correction permitted but results may be reported as affected by background noise 6to8 Subtract1dB from measured Above 8 No correction a The presence of a discrete frequency component in any one-third octave band means that any measurements in this band are of doub
40、tful value. Measurements may be made in either one-third or one octave bands not containing the discrete frequency, and these will have the usual accuracy. is the measured mean sound pressure level for the unit-in test (indB) is the measure of mean sound pressure level for the unit-out test (indB) X
41、 ri is the end reflection obtained fromFigure 3 for the terminal duct dimension for the unit-in test (indB) X ro is the end reflection obtained fromFigure 3 for the terminal duct dimension for the unit-out test (indB) L P L Pi L Po AL Po L Pi X ro X ri + = L Pi L PoBS4857-2:1978 BSI 01-2000 5 Figure
42、 2 Typical arrangement for unit-out test Figure 3 End reflection correctionBS4857-2:1978 6 BSI 01-2000 The noise radiated through the inlet connection is measured with the fan connected to the outlet duct. The unit shall be capable of withstanding the negative pressures resulting from this arrangeme
43、nt. The background noise level shall be measured with the unit removed and replaced by plain ductwork and a dummy load connected to the fan inlet (or outlet if the test is for noise radiated upstream of the unit). All air control dampers shall be in the position required for the test and the dummy l
44、oad adjusted such that the air flow rate is within5% of that required for the test. No correction shall be made for background noise. If the background level is less than6dB below the noise generated by the unit then the test results may be reported as affected by background noise. 7.2.2 Noise radia
45、ted in direction of outlet. The unit shall be connected to an air supply system similar to that shown inFigure 4. The outlet duct from the unit shall be not less than2m long and shall be positioned in the test room such that the discharge end is at least1m from the room surfaces. The test shall be c
46、arried out under steady state conditions, such conditions being satisfied if the air volume flow rate does not vary by more than2% of the mean value during the test. The outlet generated sound power level L wcof the unit shall be calculated from the following equation: 7.2.3 Noise radiated through i
47、nlet connection. The unit shall be connected to an air supply system similar to that shown inFigure 5. It is necessary to employ a flared entry to the inlet duct to prevent significant air flow noise being generated at this position. The end reflection correction (seeFigure 3) for such an entry is c
48、alculated as the arithmetic average of the values previously used for the duct itself and for the maximum opening of the flared entry. The inlet static pressure shall be the differential pressure indicated inFigure 5. The test shall be carried out and the results calculated as described in7.2.2. 7.3
49、 Casing noise radiation 7.3.1 For this test the unit shall be connected to an air supply system similar to that shown inFigure 6. All ductwork and connections shall be such that the radiation from them is at a much lower level than the radiation from the unit casing. This may be achieved by either: a) using very heavy duct materials, or b) using an efficient acoustic lagging for the ductwork, if it is similar in thickness to the unit casing. Figure 4 Arrangement of equipment for generated noise test; n
