Specifications

Specifications
Specification Value
MH Fluid Cooler — Specifications: Options
26
Sound Control:
1.2 Add the following paragraph in the Base
section: The closed circuit fluid cooler
shall be designed for quiet operation, and
shall produce an overall level of sound
not higher than the overall dB(A) values
shown in the following table when mea-
sured at a distance of ____ ft. Sound
levels shall be measured with a Type 1
(precision) system and in full confor-
mance with ATC-128 test code published
by the Cooling Technology Institute (CTI).
The measurement system shall have a
real-time frequency analyzer and separate
microphones with an overall tolerance +/-
3 dB. All low sound options shall be CTI
Certified for thermal performance
Inlet Sound Attenuation:
1.3 Add the following paragraph in the
Base section: The fluid cooler shall be
equipped with inlet sound attenuation baf-
fles positioned and spaced vertically. The
baffles will be spaced across the entire
length and extend the full height of the air
inlet. The baffles shall be constructed of
perforated sheet metal filled with sound
absorbing material, and contained within a
steel box that is self-supporting. The inlet
attenuation shall not impact the thermal
performance efficiency of the basic fluid
cooler configuration.
Quiet Fan: MHF7103, MHF7105 and
MHF7107 only.
7. 1 Replace paragraph 7.1 with the follow-
ing: Fan(s) shall be propeller-type, incor-
porating a minimum of seven aluminum
alloy blades attached to galvanized hubs
with U-bolts. Blades shall be individually
adjustable. Maximum fan tip speed shall
be 11,000 ft/min. Fan(s) shall be driven
through a right angle, industrial duty, oil
lubricated, geared speed reducer that
Location 63 125 250 500
1000
Air Inlet SPL
Cased Face SPL
Fan Discharge SPL
Location 2000 4000 8000 Overall dB(A)
Air Inlet SPL
Cased Face SPL
Fan Discharge SPL
■ Sound produced by a standard MH Fluid Cooler operating in an unobstructed
environment will meet all but the most restrictive sound limitations, and will
react favorably to natural attenuation. Where the fluid cooler 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
distance doubles. Where sound at a critical point is likely to exceed an accept-
able limit, you have several options listed below in ascending order of cost
impact:
• Where only a slight reduction in sound will satisfy—and the source of concern
is in a particular direction—merely turning the fluid cooler may be the answer.
Less sound emanates from the cased face of the fluid cooler than does from
the air intake face.
• In many cases, sound concerns are limited to nighttime, when ambient sound
levels are lower and neighbors are trying to sleep. You can usually resolve
these situations by variable speed drives, and operating the fans at reduced
speed “after hours”. The natural nighttime reduction in wet-bulb tempera-
ture makes this a very feasible solution in most areas of the world. Variable
speed drives automatically minimizes the tower’s sound level during periods of
reduced load and/or reduced ambient temperature without sacrificing the sys-
tem’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 sound is a concern at all times (for example, near a hospital), one pos-
sible solution is to oversize the tower so it can operate continuously at reduced
motor speed even at the highest design wet-bulb temperature. Typical sound
reductions are about 7 dB(A) at
2
⁄3 fan speed or 10 dB(A) at ½ fan speed, but
larger reductions may be possible.
Marley Ultra Quiet Fan