SPX Cooling Technologies Marley Sigma Steel Sound Control, Enclosures, Keeping It Clean

Marley / Sigma Steel CoolingTower / Engineering Data: Environmental

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Sound Control

Sound produced by a Sigma Steel tower operating in an un- obstructed environment will meet all but the most restrictive noise limitations—and will react favorably to natural attenu- ation. Where the tower has been sized to operate within an enclosure, the enclosure itself will have a damping effect on sound. Sound also declines with distance—by about 5 dBA each time the distance doubles. Where noise at a critical point is likely to exceed an acceptable limit, several options are available—listed below in ascending order of cost impact:

•In many cases, noise concerns are limited to nighttime, when ambient noise levels are lower and neighbors are trying to sleep. You can usually resolve these situa- tions by using two-speed motors in either 1800/900 or 1800/1200 RPM configuration—operating the fans at reduced speed without cycling “after hours”.The natural nighttime reduction in wet-bulb temperature makes this a very feasible solution in most areas of the world, but the need to avoid cycling may cause the cold water temperature to vary significantly.

•The Marley Variable Frequency Drive automatically mini- mizes the tower’s noise level during periods of reduced load and/or reduced ambient temperature without sacrificing the system’s ability to maintain a constant cold water temperature. This is a relatively inexpen- sive solution, and can pay for itself quickly in reduced energy costs.

•Where noise is a concern at all times—for example, near a hospital—the best solution is to oversize the tower so it can operate continuously at reduced (1200 or 900 RPM) motor speed. Typical sound reductions are 7 dBA at 2/3 fan speed or 10 dBA at half fan speed.

•Extreme cases may require inlet and discharge sound attenuator sections—however, the static pressure loss imposed by attenuators may necessitate an increase in tower size. This is the least desirable approach because of the significant cost impact—and because of the obstruction to normal maintenance procedures.

Your Marley sales representative will help you meet your sound requirements.

Enclosures

Occasionally, cooling towers are located inside architec- tural enclosures for aesthetic reasons. Although Sigma tow- ers adapt well to enclosures, the designer must realize the potential impact of a poorly arranged enclosure on the tower’s performance and operation. The designer must take care to provide generous air inlet paths, and the tower’s fan cylinder discharge height should not be lower than the elevation of the top of the enclosure. Obtain a copy of Marley Technical Report #H-004, “External Influences on Cooling Tower Perfor- mance” from your Marley sales representative or on the web at spxcooling.com.

As suggested in the aforementioned Technical Report, it may also be advisable to specify a design wet-bulb tem- perature 1°F higher than normal to compensate for potential recirculation initiated by the enclosure. You’ll benefit from discussing your project with your Marley sales representative.

Keeping It Clean

Cooling towers are very effective air washers. Atmo- spheric dust able to pass through the relatively small louver openings will enter the circulating water system. Increased concentrations can intensify system maintenance by clogging screens and strainers—and smaller particulates can coat system heat transfer surfaces. In areas of low flow velocity— such as the cold water basin—sedimentary deposits can provide a breeding ground for bacteria.

In areas prone to dust and sedimentation, you should con- sider installing some means for keeping the cold water basin clean. Typical devices include side stream filters and a variety of filtration media.

Water Treatment

Contaminants including Legionella, an effective consistent water treatment program is required. Controlling blowdown may be adequate in mitigating the potential of corrosion and scale, but biological contamination can only be controlled with biocides.

An acceptable water treatment program must be compat- ible with the variety of materials incorporated in a cooling tower—ideally the pH of the circulating water should fall between 6.5 and 8.0. Batch feeding of chemicals directly into the cooling tower is not a good practice since localized dam- age to the tower is possible. Specific startup instructions and additional water quality recommendations can be found in the Sigma User Manual which accompanies the tower and also is available from your local Marley sales representative. For complete water treatment recommendations and services, contact your local Marley sales representative.

CAUTION

The cooling tower must be located at such distance and direction to avoid the possibility of contaminated discharge air being drawn into building fresh air intake ducts. The purchaser should obtain the services of a Licensed Professional Engineer or Registered Architect to certify that the location of the cooling tower is in compliance with applicable air pollution, fire and clean air codes.