Document 8RLKkVBeQvZ9ww8EpZqkL20yy

220 CHAPTER 14 a. Make sure there ia no solid connection between the machine and the structure (hold-down bolts, brackets, pipes, ducts and conduit connections). b. Make sure the flexible mounts are free and have not failed. e. Make sure there is an acoustical pad or grommet between spring mounts and the base, and that the material has not hardened or become brittle. d. Make sure the mounts provide horizontal as well as vertical flexibility. e. Make sure that pipes and ducts are isolated from the struc ture. f. Make sure drives are properly aligned and shafts are oot bent. g. Make sure there are no loose and rattling parts (gage lines, covers, bearings). b. If possible^ change the speed by about 10 percent. If resonance is involved, such a small change can make a big difference. 5. Sometimes fans are found to be poorly matched for the sys tem. If a belt-driven'fan delivers air at a higher static pressure that is needed to move the design air quantity through the sys tem, the fan speed should be reduced by changing sheaves. If the fan does not deliver enough air, an increase in fan speed should be considered only after checking the duct system fer avoidable loosen. Turbulence in the air approach to the fan inlet will not only increase the fan sound generation, but also decrease its air capacity. Other parts that may cause excessive turbulence are duct bends, sudden enlargements or contractions of the duct,and dampers. When investigating fan noise, assistance can usually be ob tained from the supplier or manufacturer of the fan 6. If the conclusion is reached that additional acoustical treat ment is to be installed in the ductwork, a frequency breakdown must be obtained so that the design procedure described in Step 4 can be carried out. This involves the use of an octave band analyzer and should generally be left to a trained acoustician.. Use and Care of Sound Measuring Instruments For practical reasons, instrumentation that can be carried on a field trip has to be limited to the bare essentials, usually a sound level meter, or a sound survey meter. To get the most out of this limited equipment, its capabilities must be understood.** A sound level meter4* gives only a single number reading^ which cannot fully describe a sound. However, when used with the A-weighting network, which simulates ear re sponse, this single number reading can be very useful.** The B-network of the sound level meter is normally not used in air-conditioning work. The flat response C-network is U9ed only when making an analysis by frequency. Instruments for measuring and analyzing sound are rather complex as compared to other instruments commonly used in air-conditioning work. Errors in the instruments and in their use are, therefore, more likely and harder to detect.*1 The, instructions coming with the instruments should be followed carefully and readings should be repeated as a doublecheck. The calibration of the instrument should be checked at least once a day. For this purpose, an acoustical calibrator is pre ferred, because it will alar check out the microphone. This, is important, because most microphones are very easily dam aged without giving any external indication of such damage. In .particular, temperatures above 110 F will ruin the more common types of microphones. The 110 F limit can easily be exceeded when the instrument is left in a car on a hot summer day. The basic sound. measuring system, therefore, should consist of a sound level or sound survey meter, together with' an acoustical calibrator. The latter consists of a pocket size oscillator and a small- loudspeaker fitting over the micro phone. REFERENCES 1 Measurement of Sound Power Radiated from Heating, Re frigerating and Air Conditioning Equipment (ASHRAE Standard 36-62). * Method of Determining Sound Power Leads ofRoom Air Condi- 1965 Guide And Data Boole tionert and Other Ductless, Through-the-Wall Equipment (ASHRAE Standard 36A-63). * Method of Testing for Rating the Acoustic Performance of Air Control and Terminal Devices and Similar Equipment (ASHRAE Standard 3GB-63). * H. C. Hardy: Sources of machine noise (Product Engineering, March 1948, p. 87, and April 1948, p. 137). * G. J. Sanders and W. E. Lawrie: Low frequency combustion noise in oil-burning equipment (ASHAJ5 Journal Section, Heating, Piping A Air Conditioning, October 1958, p. 127). * G. J. Sanders: Identification and diagnosis of noise problems with reference to product noise quieting (Noise Control, March 1958, p. 15). ': 7 R. O. Fehr and R. J. Wells: Noise reduction of machinery and vehicles (Noise Control, January 1955, p. 30). 1 L. L. Beranek: Noise Reduction (McGraw-Hill Book Co., New York, 1960). I C. M. Harris: Handbook of Noise Control (McGraw-Hill Book Co., New York, 1958). `* 14 L. L. Beranek: Acoustics (McGraw-Hill Book Co., New York, 1954). u E. G. Richardson: The Technical Aspects of Sound (Elsevier' Publishing Co., New York, 1953). " Journal of the Acoustical Society of America (a publication of The Acoustical Society of America, New York, monthly). u C. M. Harris and C. E. Crede, eds: Shock and Vibration Hand book (McGraw-Hill Book Co., New York, 1961). 14 H. Bums-Meyer and L. Goodfriend: Acoustic* for the Archi tect (Reinhoid Publishing Co., New York, 1958). u American Standard Preferred Frequenciesfar Acoustical Meat-, vremenls (American Standards Association, Sl.6-1960). u Text of Coral Gables ordinance limiting night use of home air conditioning equipment (Atr Conditioning and Refrigeration News, June 11, 1962, p. 18). 17 J. L. Hunter ana E. F. C&rome: Anti-noise ordinance for a residential community (paper presented at the 60th Meeting of. the Acoustical Society of America, October 1960). I( The noise performance standards of the Chicago Zoning Ordinance (Noise Control, November 1957, p. 51). - 14 How to avoid noise control failures (Heating, Piping A Air ' Conditioning, August 1960, p. 141). ** C. H. Allen: Control air conditioning noise in the advanced planning stage (Heating, Piping A Air Conditioning, October 1959, p. 103). . u J. W. Little: Human response to jet engine noises (Noise Control, May/June 1961, p. 11). R. J. Wells and W. E. Biazier, Jr.: A procedure for computing, the subjective reaction to complex noise from sound power data' (ASHRAE Journal, June 1963, p. 82). ** W. R. Farrell: Acoustical privacy: what it is and bow it can be achieved economically (Architectural Record, June 1959, p. 226).; ** W. J. Cavanaugh, W. R. Farrell, P. W..Hirtle, ana B. G. Watters: Speech privacy in buildings (Journal of the Acoustical. Society of America, April 1962, p. 475). tt L. L. Beranek: Revised criteria for noise in buildings (Noise Control, January 1957, p. 19). * Proposed American Standard Procedure for the Computation of Loudness of Noise (American Standards Association, S3.4). II S. S. Stevens: Procedure for calculating loudness: Mark VT (Journal of the Acoustical Society of America, Vol. 33, No. 11, November 1961, p. 1577). " S. S. Stevens: Calculating loudness (Noise Control, Septem ber 1957, p. 11). ** C. M. Ashley: Criteria for room noise from air conditioning (ASHAE Journal Section, Heating, Piping A Air Conditioning, July 1957, p. 145). " C. M. Ashley: Simplifying room sound power calculations (ASHRAE Journal July 1963, p. 51). n National Residential Room Air Conditioner Survey, E. L duPont, 1955. J. Bf. Chaddock: Ceilina Air Diffuser Noise (Bolt, Beranek and Newman, Inc., Technical information Report No. 45, 1957). ** B. H. Marvet: Experimental study of grille noise character istics (ASHP^AE Journal, July 1959, p. 63). u W. L. Batchelor and W. J. Waeldner:-How air diffusing, equipment is sound rated under ADC's Test Code (Heating, Piping, A Atr Conditioning, Vol. 35, No. 11, November 1963, p. 143). '. * H. C. Hardy: Standard mechanical noise sources (Noise Con trol, May 1959, p. 22). M R. W. Young: Sabine reverberation equation and. sound (Continued on p. ttt) Soundj Control 221 Name _ ASHRAE SOUND CONTROL WORK SHffiT (Based on ASHRAE Guide And Data Book, 1965; Chapter 14) ' Architect:. Mechanical Engineer: Floor. No. - ,r6ooo RHP 3. , StAt Eff. - 1.67 X CFM/10,000 X SP/BHP X 100 - 70 : ROOM TERMINALS (Diffusers, Grilles, Induction Units, etc.) .. . ' (Make, Type):------------------ ------------ li--------------------------------------------------------------No. ------------ : CFM, Each Terminal , _________ .____ 4 Terminal cfm/Fan elm X 100 -- --:----- ----------- - % ' 10 li;:: 12 STyTpHe>o#f1A: rXeDaE(TSeMe T!NaEbleD4E)S:IGN: G1_O__A_-LrO*aet**$o*/M\/Ct+fc'*. . . --. -1-1-- NC-TLpeiv--e1l f(tfpr.onmt AArchitect or Table 4):._3S-- * STff'ii:. CALOJLATE PKMISS1BLE SOUND POWtt LEVH. AND SaECT ROOM TERMINALS Terminals:-Number _^_;-Ihstalled Height: 16 ft; Min. Distance from -listener (Kg. 4), r V--3-- + -L&- " ; RrmmirKmenrinna:ft X "ft = JPojj.'Bx\ ft Floor Area, lY ft Ceiling Height - Room Construction.-fHeavyyMcdium/Ligbt Panda. Room Surfaces': Hard^veragsySoft (Table 7) _ tin* ` . ' Item : Octave Band Center, qu 106 212 425 650 1700 3400 6900 125 250 .500 1000 2000 4000 8000 24,.. Room Effect, Lr -- L*, db. ' * (Based on Floor Area (line 22) or Distance (Line 21), whichever gives lower value). , Figure 6 - .- . 25 Sound Pressure Level for. NC - :.26 .Total Permisible Sound Power Level , \'. ` 27 ' Allowance for M-- Terminals J' ,.. - t, 28 * Permissible Sound Power Level per Terminal. : Ratings of-Terminal(s) selected Figure 2 Line 24 +line 25; Table 8 line 28 -- Tine 27. Manufacturer :. . 710 / // K (* 7# is- ,1? So 17 t/ 61 n IS 19 1o Ho_ b (, (? i 6 6 65 is 19 37 31 $1 31 .NOTE: This shortcut method equal and'evenly distributed-terminals and gives values of permissible sound power levelwhicb'are generally on the safe side. In critical cases,'the actual sound pressure level at any point due to each-source can be found by using Kgs. 5 and 8 and totalled by using Table 2. s? 7 * ' . 30 'STEP #3; CALCULATE DUCT, ATTENUATION. REQUIRED TO REDUCE FAN AND HTT1NG NOISE Sound Power Output of From ^x~r Power Divisions to Terminal, % Aria 1, Table !1:or 12 ' 7 Natural Attenuation,^#'xSjf ini I)uct,4 ft'long Table 13`X Length Attenuation of-2/in. Elbow, with/without Vanes ~ Elbow Attenuation of/Jt iri. Take-Off, t with/without Vanes Tables 14 and 15. Tables 14 and 15 Natural Attenuation,X^?in.Duct,2Cft long Table 13 X Length Attenuation of__in. Elbow with/without Vanes - Odm.lond Center, c 6900106 212 425 850 1700 3400 125 250 500 1000 2000 4000; 6000 i? 77 n 6? 1 fi IS 73 73 13 73 73 y 9 V /:. 7 7 /, %1 1J 3 3 $ 0 9 .5 3 3 3 3 1 3 9 ? 5 9- 9 Attenuation of: Table 13 X Length End Reflection for Sixe^2 X & in. Total Natural Attenuation in Branch Sound Power Level per Terminal without Sound Treatment Permissible Sound Power Level per Terminal, Allowing 3 db for Return.Duet Min. Attenuation of Sound Treatment to be designed for13. X Zfin. Duct Figure 13 Sum of lines 32 to 39 line 31 Minus-line 40 line 28 of Step 2, Minus 3 db line 41 Minus Line 42 sJ 0 O 00 95 99 99 99 99 (>! SI 59 17 19 37 59 IS 37 33 31 ? n IS /S 11 7J 6 * NOTE: Calculated attenuation required (line 43) for each significant sound source (Fan, fittings, etc.) separately, and add r Table 2.