Radio stations' rooftop systems dial down noise and vibration
Entercom Communications, based in Pittsburgh, is one of the largest owners of AM and FM radio stations in the United States. The Kansas City stations appeal to a variety of audiences - formats include news, sports, talk, rock, classical, and country - but none of the stations’ listeners would appreciate hearing HVAC noise along with their favorite tunes.
Reducing Noise And VibrationEntercom completed a $12 million renovation of the 60,000-sq-ft building in October 2006. Tenants are housed on the first floor, studio personnel on the second, and broadcasting studios for its eight radio stations on the third. Located on the corner of a busy intersection, the all-steel, prefabricated building required significant renovation to overcome outside noise from traffic and inside noise from reverberation.
“Our acoustical requirement was between NC 20 and NC 25,” said Dave Dawson, principal of W.L. Cassell, the mechanical and engineering firm in Kansas City that completed the mechanical renovation. “It was all about making sure any equipment we put in didn’t carry into the studio through ductwork or radiate through the walls. We needed a solid, rigid HVAC system as well as a quiet one to prevent vibration and radiated sound.”
Meeting an NC (noise criteria) requirement of 20 to 25 is challenging. Rooms in this range are considered “very quiet” and include concert and recital halls and broadcast and recording studios. HVAC systems can be a significant contributor to background noise, so Dawson also had to factor in air velocities for supply and return air. Recommended airflow for a room this quiet is 250 to 300 fpm for supply air and 300 to 360 fpm for return air.
Rooftop Location Adds To Low-Noise ChallengeIsolating the broadcast studios on the third floor from noise was relatively straightforward. “The studios are essentially a room within a room,” said Dawson. “One room is built inside the other and separated by the sound insulation. Duct silencers in the insulation help kill any air noise generated by air moving through the ductwork or any noise generated by the control damper or VAV box.”
The bigger challenge was finding a place for the new HVAC equipment. Dawson would have recommended a separate mechanical room, but Enter-com needed as much space as possible for tenants, offices, and studios. That left the roof as the only choice for the new HVAC installation. Working with Thermal Components, an HVAC supplier in Kansas City, Dawson was able to design a system with the flexibility to meet his low-noise requirements.
Two McQuay rooftop units were selected to serve the year-round cooling load of up to 175 tons for the top two floors. A 100-ton unit provides year-round cooling to the top floor and a 75-ton unit serves the second floor. Both units are controlled by MicroTech® II controls with McQuay’s Open Choices™ feature, which simplified integration into the Andover BAS. Titus VAV boxes with Fulton hot water boilers provide zone control and heat the building. A McQuay Vision™ AHU, an exterior 60-ton condensing unit, and two 50-ton rooftop units serve the first-floor spaces. Aerosonics provided the duct silencers.
“The McQuay units give us the performance we need for acoustic reverberation and radiated sound,” said Dawson. “Discharge sound is mainly attributed to the fan of a unit, so we chose plenum fans and wheels because they’re much quieter than other fan configurations.
“The flexibility to choose the fans and wheels we required helped us meet the NC requirements. And we were able to cut down on vibration and radiated sound because these units are built so solidly.” To provide further soundproofing, the ceiling of each of the top-floor studios is resiliently suspended from the roof to avoid any vibration transmission from the rooftop equipment.
“Not only did we need a quiet system, we also needed a reliable one,” said Dawson. “HVAC systems in studios are important not just for the people who work there, but also for the broadcast equipment, which must operate 24 hours a day.” Kansas City listeners would be reassured to know that even the HVAC system has a role in keeping news, music, and sports coming through loud and clear without a hint of background distraction. ES