1、48.1CHAPTER 48NOISE AND VIBRATION CONTROLDATA RELIABILITY 48.1ACOUSTICAL DESIGN OF HVAC SYSTEMS 48.1Receiver Considerations 48.2Basic Acoustical Design Techniques 48.8Source Sound Levels 48.8Path Noise Estimation and Control 48.18Receiver Room Sound Correction 48.30Sound Control for Outdoor Equipmen
2、t 48.33Fume Hood Duct Design . 48.34Mechanical Equipment Room Sound Isolation 48.35HVAC Noise-Reduction Design Procedures 48.38Vibration Isolation and Control . 48.41Vibration Measurement 48.42Equipment Vibration 48.43Vibration Criteria . 48.43Specification of Vibration Isolators 48.45Vibration- and
3、 Noise-Sensitive Facilities. 48.49Internal Versus External Isolation 48.49Isolating Vibration and Noise in Piping Systems 48.50Seismic Protection 48.52Vibration Investigations 48.52COMMISSIONING 48.52TROUBLESHOOTING. 48.52Determining Problem Source. 48.53Determining Problem Type. 48.53VAC equipment
4、for a building is one of the major sources ofH interior noise, and its effect on the acoustical environment isimportant. Also, noise from equipment located outdoors often prop-agates to the community. Therefore, mechanical equipment must beselected, and equipment spaces designed, with an emphasis on
5、 boththe intended uses of the equipment and the goal of providing accept-able sound levels in occupied spaces of the building and in the sur-rounding community. Operation of HVAC equipment can alsoinduce mechanical vibration that propagates into occupied spacesthrough structureborne paths such as pi
6、ping, ductwork, and mounts.Vibration can cause direct discomfort and also create secondaryradiation of noise from vibrating walls, floors, piping, etc.In this chapter, sound and noise are used interchangeably, al-though only unwanted sound is considered to be noise.System analysis for noise control
7、uses the source-path-receiverconcept. The source of the sound is the noise-generating mechanism.The sound travels from the source via a path, which can be throughthe air (airborne) or through the structure (structureborne), or a com-bination of both paths, until it reaches the receiver (building occ
8、u-pant or outdoor neighbor).Components of the mechanical system (e.g., fans, dampers, dif-fusers, duct junctions) all may produce sound by the nature of theairflow through and around them. As a result, almost all HVAC com-ponents must be considered. Because sound travels effectively in thesame or op
9、posite direction of airflow, downstream and upstreampaths are often equally important.This chapter provides basic sound and vibration principles anddata needed by HVAC system designers. Many of the equationsassociated with sound and vibration control for HVAC may be foundin Chapter 8 of the 2013 ASH
10、RAE HandbookFundamentals.Additional technical discussions along with detailed HVAC compo-nent and system design examples can be found in the references.1. DATA RELIABILITYData in this chapter come from both consulting experience andresearch studies. Use caution when applying the data, especially for
11、situations that extrapolate from the framework of the originalresearch. Test data tolerances and cumulative system effects lead to atypical uncertainty of 2 dB. However, significantly greater variationsmay occur, especially in low frequency ranges and particularly in the63 Hz octave band, where expe
12、rience suggests that even correctly per-formed estimates may disagree with actual measured levels by 5 dB,so conservative design practices should be followed.2. ACOUSTICAL DESIGN OF HVAC SYSTEMSFor most HVAC systems, sound sources are associated with thebuildings mechanical and electrical equipment.
13、 As shown in Figure1, there are many possible paths for airborne and structurebornesound and vibration transmission between a sound source and re-ceiver. Noise control involves (1) selecting a quiet source, (2) opti-mizing room sound absorption, and (3) designing propagation pathsfor minimal noise t
14、ransmission. Different sources produce sounds that have different frequencydistributions, called spectral characteristics. For example, asshown in Figure 2, fan noise generally contributes to sound levels inthe 16 to 250 Hz octave bands (curve A). Frequencies that designateThe preparation of this ch
15、apter is assigned to TC 2.6, Sound and VibrationControl.Fig. 1 Typical Paths of Noise and Vibration Propagation in HVAC Systems48.2 2015 ASHRAE HandbookHVAC Applications (SI)the octave bands are often called octave midband (or center) fre-quencies. Variable-air-volume (VAV) valve noise usually contr
16、ib-utes to sound levels in the 63 to 1000 Hz octave bands (curve B).Diffuser noise usually contributes to the overall HVAC noise in the250 to 8000 Hz octave bands (curve C). The overall sound pressurelevel associated with all of these sound sources combined is shownas curve D.Figure 3 (Schaffer 2005
17、) shows the frequency ranges and de-scriptive terminology of the most likely sources of HVAC sound-related complaints. Figure 4 (Schaffer 2005) shows the frequenciesat which different types of mechanical equipment generally controlthe sound spectra in a room. Occupant complaints may occur, how-ever,
18、 despite a well-designed sound spectrum in the room. Criteriaspecified in this chapter do not necessarily correspond with all indi-viduals acceptability criteria.2.1 RECEIVER CONSIDERATIONSIndoor Sound CriteriaWhether an occupant considers the background noise acceptablegenerally depends on two fact
19、ors. First is the perceived loudness ofthe noise relative to that of normal activities; if it is clearly notice-able, it is likely to be distracting and cause complaint. Second is thesound quality of the background noise; if the noise is perceived asa rumble, throb, roar, hiss, or tone, this may res
20、ult in complaints ofannoyance and stress. The frequency spectrum is then said to beunbalanced.The acoustical design must ensure that HVAC noise is of suffi-ciently low level and unobtrusive quality so as not to interfere withoccupancy use requirements. If background noise reduces speechintelligibili
21、ty, for example, complaints of lost productivity can result.Accordingly, methods of rating HVAC-related noise ideally assessboth perceived loudness and sound quality (Wang et al. 2013).Design Guidelines for HVAC-Related Background Sound inRooms. Table 1 presents recommended goals for indoor back-gro
22、und noise levels in various types of unoccupied rooms served byHVAC systems. Perceived loudness and task interference are fac-tored into the numerical part of the rating. The sound quality designtarget is assumed to be a neutral-sounding spectrum, although somespectral imbalance is probably tolerabl
23、e within limits for most users.The criteria used are described in the next section.An acceptable noise level depends on the specific use of thespace, so each number rating typically represents a range of 5 dBfor the design target. For example, private offices and conferencerooms are listed as NC/RC
24、30. This means that unless there areextenuating circumstances, the background noise level should beless than NC/RC 35, but in some locations (e.g., executive offices orspecialty conference rooms), a noise criterion of as low as NC/RC25 might be warranted. On the other hand, there is not necessarily
25、abenefit to achieving the lower number in regular offices, as somebackground noise maintains a minimum level of acoustic privacybetween adjacent offices.The NC/RC designations relate to reference curves with octaveband sound pressure levels that are (1) selected based on appropri-ate loudness in the
26、 speech interference range (500 to 2000 Hz) and(2) show contours for high and low frequencies that are balanced atthe same loudness level. Acoustical evaluation based on octavebands and target balanced contours is recommended, because over-all dBA ratings do not reflect undesirable contributions of
27、excessivelow-frequency noise. The dBA and dBC levels are listed only asapproximate references in the case of simplistic measurements,where dBA indicates relative loudness and dBC indicates preva-lence of low-frequency noise. Exact specifications should be estab-lished by acoustical experts consideri
28、ng occupant sensitivity.Criteria Descriptions. This section presents ways to rate ormeasure the sound to determine acceptability. The informationFig. 2 HVAC Sound Spectrum Components for Occupied SpacesFig. 3 Frequency Ranges of Likely Sources of Sound-Related Complaints(Schaffer 2005)Fig. 4 Frequen
29、cies at Which Different Types of Mechanical Equipment Generally Control Sound Spectra(Schaffer 2005)Noise and Vibration Control 48.3should help the design engineer select the most appropriate back-ground noise rating method for a specific project. Current methodsdescribed here and in other reference
30、s include the traditional A-weighted sound pressure level (dBA) and tangent Noise Criteria(NC), the Room Criterion (RC) and more recent RC Mark II, theBalanced Noise Criterion (NCB), and the Room Noise Criteria(RNC). Each method was developed based on data for specificapplications; hence, not all ar
31、e equally suitable for rating HVAC-related noise in the variety of applications encountered. The pre-ferred sound rating methods generally comprise two distinct parts:a family of criterion curves (specifying sound levels by octavebands), and a procedure for rating the calculated or measured sounddat
32、a relative to the criterion curves with regard to sound quality.Ideally, HVAC-related background noise should have the follow-ing characteristics:Balanced contributions from all parts of the sound spectrum withno predominant frequency bands of noiseNo audible tones such as hum or whineNo fluctuation
33、s in level such as throbbing or pulsingdBA and dBC: A- and C-Weighted Sound Level. The A-weightedsound level (described in Chapter 8 of the 2013 ASHRAE Hand-bookFundamentals) has been used for more than 60 years as a sin-gle-number measure of the relative loudness of noise, especially foroutdoor env
34、ironmental noise standards. The rating is expressed as anumber followed by dBA (e.g., 40 dBA).Table 1 Design Guidelines for HVAC-Related Background Sound in RoomsRoom TypesOctave Band AnalysisaApproximate Overall Sound Pressure LevelaNC/RCbdBAcdBCcRooms with Intrusion from Outdoor Noise SourcesdTraf
35、fic noise N/A 45 70Aircraft flyovers N/A 45 70Residences, Apartments, CondominiumsLiving areas 30 35 60Bathrooms, kitchens, utility rooms 35 40 60Hotels/Motels Individual rooms or suites 30 35 60Meeting/banquet rooms 30 35 60Corridors and lobbies 40 45 65Service/support areas 40 45 65Office Building
36、s Executive and private offices 30 35 60Conference rooms 30 35 60Teleconference rooms 25 30 55Open-plan offices 40 45 65Corridors and lobbies 40 45 65Courtrooms Unamplified speech 30 35 60Amplified speech 35 40 60Performing Arts Spaces Drama theaters, concert and recital halls 20 25 50Music teaching
37、 studios 25 30 55Music practice rooms 30 35 60Hospitals and Clinics Patient rooms 30 35 60Wards 35 40 60Operating and procedure rooms 35 40 60Corridors and lobbies 40 45 65Laboratories Testing/research with minimal speech communication50 55 75Extensive phone use and speech communication 45 50 70Grou
38、p teaching 35 40 60Churches, Mosques, SynagoguesGeneral assembly with critical music programse25 30 55SchoolsfClassrooms 30 35 60Large lecture rooms with speech amplification 30 35 60Large lecture rooms without speech amplification 25 30 55Libraries 30 35 60Indoor Stadiums, GymnasiumsGymnasiums and
39、natatoriumsg45 50 70Large-seating-capacity spaces with speech amplificationg50 55 75N/A = Not applicableaValues and ranges are based on judgment and experience, and represent general limits ofacceptability for typical building occupancies.bNC: this metric plots octave band sound levels against a fam
40、ily of reference curves, with thenumber rating equal to the highest tangent line value.RC: when sound quality in the space is important, the RC metric provides a diagnostic toolto quantify both the speech interference level and spectral imbalance.cdBA and dBC: these are overall sound pressure level
41、measurements with A- and C-weight-ing, and serve as good references for a fast, single-number measurement. They are alsoappropriate for specification in cases where no octave band sound data are available fordesign.dIntrusive noise is addressed here for use in evaluating possible non-HVAC noise that
42、 islikely to contribute to background noise levels.eAn experienced acoustical consultant should be retained for guidance on acous-tically critical spaces (below RC 30) and for all performing arts spaces.fSome educators and others believe that HVAC-related sound criteria for schools,as listed in prev
43、ious editions of this table, are too high and impede learning foraffected groups of all ages. See ANSI/ASA Standard S12.60 for classroomacoustics and a justification for lower sound criteria in schools. The HVAC com-ponent of total noise meets the background noise requirement of that standard ifHVAC
44、-related background sound is approximately NC/RC 25. Within this cate-gory, designs for K-8 schools should be quieter than those for high schools andcolleges.gRC or NC criteria for these spaces need only be selected for the desired speechand hearing conditions.48.4 2015 ASHRAE HandbookHVAC Applicati
45、ons (SI)A-weighted sound levels can be measured with simple soundlevel meters. The ratings correlate fairly well with human judg-ments of relative loudness but take no account of spectral balance orsound quality. Thus, two different spectra can result in the samenumeric value, but have quite differe
46、nt subjective qualities.Along with dBA, there is also a C-weighted sound level,denoted as dBC, which is more sensitive to low-frequency soundcontributions to the overall sound level than is dBA. When thequantity dBC dBA is large (e.g., greater than 25 dB), significantlow-frequency sound is present.
47、It is recommended that whenspecifying background sound levels in dBA, the dBC is alsoincluded in the specification and does not exceed the dBA readingby more than 20 dB.NC: Noise Criteria Method. The NC method for rating noise(described in Chapter 8 of the 2013 ASHRAE HandbookFunda-mentals) has been
48、 used for more than 50 years. It is a single-numberrating that is somewhat sensitive to the relative loudness and speechinterference properties of a given noise spectrum. The method con-sists of a family of criterion curves, shown in Figure 5, extendingfrom 63 to 8000 Hz, and a tangency rating proce
49、dure. The crite-rion curves define the limits of octave band spectra that must not beexceeded to meet occupant acceptance in certain spaces. The ratingis expressed as NC followed by a number (e.g., NC 40). The octavemidband frequency of the point at which the spectrum is tangent tothe highest NC curve should also be reported e.g. NC 40 (125 Hz).The NC values are formally defined only in 5 dB increments, withintermediate values determined by discretionary interpolation.Widely used and understood, the NC method is sensitive to levelbut has the disadvantage that the tangency
