SPX Cooling Technologies Marley Sigma Marley Sigma Steel, Engineering Data

Marley 

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Sigma Steel 

Cooling Tower 

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Engineering Data: Environmental

10

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.