5. COOLING TOWERS AND FANS. Noise from cooling towers and fans is caused by air turbulence from the rotating blades. With water cooling towers there is the added noise level of splashing water over the external fill and collecting basins. (Always check manufacturer's rating when available).
Cooling towers and fans can be considered as a continuous source of noise. The following graph gives the noise level in dba at a distance of 3ft. for various horsepower (h.p.) ratings.
SOUND PRESSURE LEVEL IN DBA AT 3 FEET OR 1 METEL
110
10 20
50 100 500 500 1000 ́RATED HP OF FAN OR COOLING TOWER. GRAPH NO. 5
6. UNIT AIR-CONDITIONERS. Package compressor condenser units and window air conditioners produce high noise levels. The noise is primarily from the condenser air blower and the compressor. The following graph can be used as a guide for estimating dba against tonnage. (Always check manu- facturers' ratings where possible).
SOUND PRESSURE LEVEL IN DBA AT 3 FILT OR IM
1104
100
2
5 10 20
30 100 200 500 1050 RATED H.R OF AIR CONDITIONING COMPRESSORS.
GRAPH NO. 7
8. TRANSFORMERS. Transform- ers emit low frequency noise from within the magnetic steel core and coil windings. The noise level increases with increasing KVA rating. There is little increase in noise from loading. The maximum noise level expected is given in the following graph. Note: Check manufacturer's rating noise levels should be considered an impor- tant factor in choosing transformers.
SOUND PRESSURE LEVEL IN DBA AT 3 FEET OR I METER
60
·
10.TRANSMISSION PATHS. The transmission path is the link between noise source and the listener and is the component of the system most easily controllable. The principal sound transmission paths are:
i) Direct radiation of the sound in the air — airborne sound.
ii) Transmission through structure structure-borne sound.
iii)A combination of i) and ii) where the structure is vibrated by the noise source which in turn generates direct airborne noise.
Careful analysis of possible sound transmission paths form the basis of noise control.
LISTENER. The listener, the third component of the system, requires evaluation in determining the design factors on which to adjudge noise con- trol requirements.
SOUND PRESSURE LEVEL IN MBA AT 3 FEET OR IMETER
3 +
12 14 24
RATED COOLING CAPACITY OF UNIT AIR-CONDITIONER GRAPH NO. 6
(IN TONS)
7. REFRIGERATOR COMPRES- SORS. Refrigeration compressors in central air-conditioning systems are one of the major sources of internal noise. Proper location and installation are important factors, especially in lightweight structures. The following graph estimates dba at 3ft. against rated horsepower (h.p.)
14
40
Acceptable ambient sound levels vary with building or room use. As an example: Rural areas 25 dba, cities 40 dba, cafeterias 50 dba.
Method of noise control
By employing the following 'rules of thumb' reasonably successful noise control results can be expected and should the problem be of a sophisti- cated nature it should be possible to recognise it and know when to call in competent help. Noise control is
10. 20:30 50 100 2 3 5 7 103 2 3 57109 1 3 5 1000 normally achieved by two methods: i)
TRANSFORMER RATING IN KVA.
GRAPH No. 8
9. INTERNAL COMBUSTION ENGINES. Engines operating on vari- ous fuels drive electric generators, etc. They require acoustical mufflers on in- let and exhaust manifolds and vibra- tion isolating mountings. The follow- ing graph estimates dba against horsepower (h.p.)
SOUND PRESSURE LEVEL IN DBA AT 3 FELT OR | METER
1104
1001
25
INADEQUATÉ SILENCINÉ OF EXN. É/MLET
SILENCED EXHAUST È INLET/
30
100
200
400 OPERATING HIP OF INTERNAL COMBUSTION ENGINE GRAPH NO.9
control of the source and ii) control of the transmission paths.
Control of the noise source is obvi- ously the better form of protection, but architects, engineers and builders have only recourse to selection of equipment. This selection of equip- ment (hermetically sealed compres sors,, oil bound transformers, several smaller sized condensers instead of one large unit for air-conditioning etc.) is an important factor which should be taken into account during the design and tender period and noise ratings should be carefully analyzed.
Control of transmission paths is the most effective means by which noise control can be practised. The follow- ing methods apply to transmission path noise control.
1. REDUCTION OF NOISE LEVEL WITH DISTANCE. The fol- lowing graph demonstrates the reduc- tion in noise level with increasing distance from the source
Far East BUILDER, July 1970