Specifications
Marley
/
MD Cooling Tower
/
Specifications: Options
39
Specification Value
■ Sound produced by a standard MD tower operating in an unob-
structed environment will meet all but the most restrictive noise
limitations—and will react favorably to natural attenuation. 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 or 6 dB(A) each time the dis-
tance doubles. Where noise at a critical point is likely to exceed an
acceptable limit, you have several options—listed below in ascend-
ing order of cost impact:
• In many cases, noise concerns are limited to night time, when
ambient noise levels are lower and neighbors are trying to sleep.
You can usually resolve these situations by using two speed
motors in either full / half speed or full / 2/3 speed configuration,
and operating the fans at reduced speed without cycling “after
hours”. (The natural night time 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.)
• Variable speed drives automatically minimize the tower's noise
level during periods of reduced load and/or reduced ambient
without sacrificing the system's ability to maintain a constant cold
water temperature. This is a relatively inexpensive solution, and can
pay for itself quickly in reduced energy costs.
• Where noise is a concern at all times (for example, near a hos-
pital), the best solution is to oversize the tower so it can operate
continuously at reduced (2/3 or ½) motor speed even at the highest
design wet-bulb temperature. Typical sound reductions are 7 dB(A)
at 2/3 fan speed or 10 dB(A) at ½ fan speed, but larger reductions
are often possible.
• The most extreme cases may require discharge sound attenuator
sections—however, the static pressure loss imposed by discharge
attenuators may necessitate an increase in tower size. Your Marley
sales representative will be able to help you meet you sound
requirements.
Sound Control
1.2 Add the following paragraph under
Base: The cooling tower shall be quiet
operating, and shall produce an overall
level of sound no higher than ____
dBA, measured at the critical location
indicated on the plans.
