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OPERATING AND ENVIRONMENTAL ,AW,ARENEESS • Sound Control As suggested in the aforementioned Technical Report, it may also be advisable to specify a design wet -bulb Sound produced by a NC Series tower operating in an temperature 1 °F higher than normal to compensate for unobstructed environment will meet all but the most restric- potential recirculation initiated by the enclosure. You'll tive noise limitations —and will react favorably to natural benefit from discussing your project with your Marley sales attenuation. Where the tower has been sized to operate representative. within an enclosure, the enclosure itself will have a damp- ing effect on sound. Sound also declines with distance —by System Cleanliness about 5 dBA each time the distance doubles. Where noise at a critical point is likely to exceed an acceptable limit, Cooling towers are very effective air washers. Atmo several options are available — listed below in ascending spheric dust able to pass through the relatively small louver order of cost impact: openings will enter the circulating water system. Increased concentrations can intensify system maintenance by clog- • In many cases, noise concerns are limited to night- ging screens and strainers —and smaller particulates can time, when ambient noise levels are lower and coat system heat transfer surfaces. In areas of low flow neighbors are trying to sleep. You can usually resolve velocity —such as the cold water basin — sedimentary de- these situations by using two -speed motors in either posits can provide a breeding ground for bacteria. 1800/900 or 1800/1200 RPM configuration— operat In areas prone to dust and sedimentation, you should ing the fans at reduced speed without cycling after consider installing some means for keeping the cold water hours ". The natural nighttime reduction in wet -bulb basin clean. Typical devices' include side stream filters and temperature makes this a very feasible solution in most areas of the world, but the need to avoid cycling a variety of filtration media. may cause the cold water temperature to vary signif- Water Treatment icantly. o The Marley Variable Speed Drive automatically min- In order to control the inevitable buildup of dissolved imize the tower's noise level during periods of reduced solids as water evaporates from the cooling tower, you load and /or reduced ambient temperature without should plan to develop a consistent, effective program of sacrificing the system's ability to maintain a constant water treatment. The program must control corrosion, cold water temperature. This is a relatively inexpen- scale buildup and accumulation of biological contaminants. sive solution, and can pay for itself quickly in reduced An acceptable water treatment program must be com- energy costs. patible with the variety of materials incorporated in a o Where noise is a concern at all times —for example, cooling tower, ideally the pHlof the circulating water should near a hospital —the best solution is to oversize the fall between 6.5 and 8.0. ! Batch feeding of chemicals tower so it can operate continuously at reduced (1200 directly into the cooling tower is not a good practice, since or 900 RPM) motor speed. Typical sound reductions localized damage to the tower is possible. Additional water are 7 dBA at 2/3 fan speed or 10 dBA at 1/2 fan speed. quality requirements appear in the NC User Manual which o Extreme cases may require inlet and discharge sound accompanies the tower. attenuator sections— however, the static pressure loss imposed by attenuators may necessitate an For complete water treatment recommendations, con - increase in tower size. This is the least desirable sult a competent, qualified water treatment supplier. approach because of the significant cost impact— Most systems can be successfully treated with a and because of the obstruction to normal maintenance MARLEYOZONE System. This usually removes the procedures. requirement for other chemical feed systems. In many Your Marley sales representative will help you meet your installations there is the potential for significant water sound requirements. savings. For complete information, contact your local Marley sales representative. Enclosures Occasionally, cooling towers are located inside archi N „ tectural enclosures for aesthetic reasons. Although NC Ylik ii4r to yr G .e o cated at. uch ,. Series towers adapt well to enclosures, the designer must s a� � � fl , 'W:r e: po SSxbtfJt P.of realize the potential impact of a poorly arranged enclosure cc a is . drawn on the tower's performance and operation. The designer tzfoOidfnga r ® a c �r tGi aser must take care to provide generous air inlet paths, and the a _% :ed tower's fan cylinder discharge height should not be lower 'P ,.otesfor , s o e rlter�ta than the elevation of the top of the enclosure. Obtain a copy iP,�r�£Welr " •* �=3* eaay of Marley Technical Report #H -004 "External Influences CDn]04yjt]4:c.gbJer.ollnfiota ,rte; and on Cooling Tower Performance" from your Marley sales c/e t air cod,rs , representative.