A Little Forethought Can Save Money
- By Jeff Teel
- May 1st, 2010
Acoustical consultants are called upon to provide expertise in a wide variety of projects. The project size and duration varies quite widely. Some projects will go on for years, such as a large-scale, multi-building development that encompasses everything from an arena, to a bowling alley, to an office building, to residential condos. On the other hand, a project may require only a few hours of time. This often involves a site visit to a facility for purposes of trouble-shooting an acoustics or noise problem.
The level of difficulty in trouble shooting a noise problem varies greatly as well. Sometimes the problem is easy to solve in theory, but the solution is arduous to implement in the field. Other times the only item prohibiting a solution to the problem is cost. Like a lot of things in the architecture and construction industries, it can cost much less addressing potential problems in design rather than after construction.
One particular time, we got a phone call from a local high school complaining of a noisy gymnasium. The high school was newly constructed and had been open for only a short time. The noise in the gymnasium was said to be so severe that when the HVAC system was operating, not only was the gymnasium unusable for non-sporting events requiring some semblance of a quiet room — convocations, guest speakers, presentations — but it was also unusable for team practices and games, such as basketball and volleyball. Generally, a noisy building system does not conflict with athletic events and activities such as these, since these activities are noisy as well. However, while the HVAC system was operating, it was so noisy that players and coaches could not communicate during practices, the game announcer could not be heard over the roar of the HVAC system and public address announcements were unintelligible.
When we got to the school, it was actually quite simple to diagnose the problem — an outdoor air handling unit was situated on the roof top at exactly the center of the gymnasium. The ceiling of the room was exposed to the structural roof deck. The supply ductwork from the air handling unit penetrated through the roof deck and elbowed to the supply diffusers 10 feet later. The return air duct was short in length, open-ended and stubbed through the roof deck into the air handling unit. Simply put, the proximity of this giant air handling unit — made up of fans, compressors and other noisy components — was much too close and directly exposed to a space where verbal communication is important, even if half of the intended functions are noisy athletic events. The HVAC system was not designed with noise control in mind.
The diagnosis of what was causing the noisy environment, as explained, was fairly simple — it was the roof-mounted air handling unit. However, there were many items that needed to be addressed in order to properly piece together a solution. Radiated noise from the air handling unit penetrating through the roof deck. Fan noise screaming through the supply and return ducts. Turbulence noise from high-velocity airflow breaking out of the walls of the ductwork. Structure-borne vibration flanking through the roof deck and connecting walls.
Noise control is one of these instances where all pieces of the puzzle need to be in place in order for the problem to be solved. If one part of the solution is not implemented, then the noise cannot be sufficiently alleviated and the problems, in all likelihood, will continue. So, my thoughts went into a solution that, in theory, could be applied to alleviate the noise. Build a drywall noise control box around the complete supply duct penetration for radiated noise control. Apply fiberglass duct liner internally to the supply and return ducts to attenuate downstream fan noise. Lag the high velocity ducts with insulation and loaded vinyl to control duct break out noise. Ensure that the fans in the air handling unit are installed on vibration isolation springs and, if so, that the springs are not short-circuited or undersized.
In theory, implementing all of these items will sufficiently cut down the noise rumbling throughout the gymnasium if designed correctly. In practicality, it was difficult to conclude if all of these items could be done or not. Can the structure support the framing? Is there enough physical room within the structural beams and girders to accommodate all of these items? Consultation is needed with the structural engineer to ensure these items, and with the mechanical engineer to ascertain if any of the noise control solutions will detrimentally affect the performance of the system.
Then there’s the cost. The cost of the materials needed for all facets of the solution is one thing. The contractor’s labor cost of putting it all together is another. But don’t forget the cost that incurs to design the solution. Already, we were billing hours to conduct the site visit at the school and diagnose the problem. Some office time will also be needed to design conceptual sketches to give to the contractor so the contractor can draw shop drawings to give back to us for approval. The shop drawings would also have to have the blessing of the structural engineer, mechanical engineer and, if the school cares about how all of this stuff looks in the end, an architect.
All in all, this particular project was turning into a mess. I was the deliverer of bad news to the owner, and as I was going over each and every item that needed to be done to make the gymnasium usable again, I could see the anger in his face start to build as he was undoubtedly adding up the cost of everything. I’m sure he was also trying to figure out in his mind who was ultimately responsible for this situation — after all, the school was brand new — therefore who he would try to get to pay for it all. The ironic thing, I told him, was that even if all of these items were implemented, it would still not be nearly as good of a solution as if the roof mounted air handling unit was not located right over the middle of the gymnasium and, instead, was located somewhere else, such as over a storage room, restroom or mechanical room. Practically speaking, nothing could be done to the air handling unit in its current location that would make it seem like the air handler wasn’t there at all.
That was then when he asked me, “What if we just move the unit so that it is located over the storage room right next to the gymnasium?”
It was then that I was told that not only was there a storage room right next door to the gymnasium, but there was nothing on the roof structure over the storage preventing the air handling unit from being installed there in the first place. Had the HVAC system been designed so that the unit was placed over the storage room to begin with, I would not be out there because there would not be a noise problem.
Ultimately, the air handling unit was moved to the roof over the storage room, and the HVAC system for the gymnasium had to be redesigned. This was an even more expensive option than the complicated “piece together” solution that would have been required had the unit stayed located over the gymnasium. But, that solution was a band-aid approach and could only do so well. Relocating the air handling unit was the only solution that would solve the noise problem 100 percent. And, it was what should have been implemented during the school’s mechanical system design.
In the end, the price incurred for the gymnasium HVAC system was multiple times what it would have cost had the potential noise problem simply been noticed during design. Unfortunately, although sound is integral in our daily lives, acoustics and noise are often overlooked in today’s school projects.
Jeff Teel is a senior associate at Acoustical Design Group, Inc., an independent acoustical consulting firm located in Mission, Kan., a suburb of Kansas City. You can email him at JeffT@adgkc.com.