APPLICATIONS
ROOF TOP UNITS

Roof top units are used to service small to medium sized areas. They are available as relatively inexpensive, off the shelf, ready to use machines which can be installed and commissioned with ease. With real estate at a premium, designers are increasingly placing these units close to occupied spaces. They can be frequently placed above occupied spaces to save ceiling space. With multiple noise paths between the Roof top unit and the receiver, noise attenuation from these units becomes a challenge.

DUCTBORNE
NOISE

Problem

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The first thing that mechanical engineers consider is Duct-Borne noise. A common practice for engineers is to pick catalogue models. The catalogue models do not take the inlet and outlet conditions and system effects into consideration. The result is a silencer which has a higher installed pressure drop than what is indicated on the submittal sheets. Higher pressure drop means the fan has to work harder to push air through to the occupied space. The fan uses more energy than what was initially intended.

Solution

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Vibro-acoustics’ engineers always consider the system effects when designing a silencer. So along with the ideal pressure drop, the pressure drop with system effects is also taken into consideration and spelled out on the submittals. An optimized selection means that the silencer performs exactly as required while the installed pressure drop is kept to a minimum. The result is a system which performs exactly as expected, with no extra energy consumption due to unforeseen higher pressure drop.

ENVIRONMENTAL
NOISE

Problem

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Condenser fans, compressors, fresh air intake and exhaust air openings can be a source of environmental noise. If buildings are huddled close to each other or offices overlook the roof top units, environmental noise can become a nuisance.

Solution

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Vibro-acoustics includes environmental noise into consideration, if required. A combination of silencers, acoustic plenums and acoustic louvers can be used to make sure that environmental noise is contained.

RADIATED
NOISE

Problem

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Noise from the compressors, condenser fans and even the supply and return fans can radiate through the casing and seep into the building. Buildings that do not have concrete roofs can experience higher noise levels because of the radiated noise. The problem is compounded if the roof top unit is placed directly on top of occupied spaces.

Solution

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Radiated noise analysis is part of Vibro-Acoustics’ analysis. The noise control curb package includes acoustic treatment for radiated noise, if required, to prevent radiated noise from entering the occupied space.

BREAKOUT
NOISE

Problem

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Noise can break out of the duct and into the occupied space. This problem is critical when the duct is coming down directly from the roof top unit into a ceiling space right above noise critical space.

Solution

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Vibro-Acoustics includes breakout analysis as part of our design and High Transmission Loss “HTL” casings to make sure that breakout noise is not a concern,

SEISMIC AND
WIND

Problem

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Roof top equipment is subject to wind loads, especially in territories susceptible to high winds, tornadoes and hurricanes. Such applications require care in the curb and curb anchorage design to make sure that the units do not get uprooted during adverse conditions.

Solution

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Vibro-Acoustics provides Seismic and wind rated roof curbs that are designed to meet local wind and seismic criteria as required. Vibro-Acoustics can also provide wind and seismic anchorage calculations, stamped by a professional engineer licensed by the concerned State.

VIBRATION AND
STRUCTURE-BORNE
NOISE

Problem

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Vibration from the roof top unit can be transmitted to the building occupants through the structure. This is more common in cases where the roof is made of corrugated steel.

Solution

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Vibro-Acoustics noise control curbs have vibration isolators. These isolators can be selected with 1”, 2” or 3” deflection as they need be to contain structure borne vibration.