Fixing an old problem typically brings a measure of satisfaction. Fixing one that’s not “old,” and has expensively festered from the beginning while also making a nuisance of itself adds new facets to the challenge.
Ultimately, the solution to a university’s vexing HVAC problem has won accolades from school administrators, students, faculty, bean counters and maintenance staff alike.
Inside Armstrong Atlantic State University’s (AASU) two-story, 126,000-square-foot (gross) Science Center in Savannah, GA, is a network of 36 state-of-the-art laboratory rooms, classrooms and offices. Immediately after construction wrapped-up in 2001, the building’s (supposedly) VAV exhaust and HVAC equipment showed its true colors. The ambient noise level in the laboratories was 72 dBa and, sadly, the system was anything but VAV (variable air volume).
Stringent codes and standards intended to protect an individual’s health and safety inside science and research laboratories require frequent air changes and constant negative pressure. These standards apply 24 hours a day including holidays, nights and weekends. The Science Center’s 78 fume hoods and non-functioning controls with individual exhaust fans ran constantly, moving 800 CFM each – whether the laboratory fume hoods were in use or not.
A functional and controlled exhaust system can modulate to a lower volume when the room is unoccupied, while still providing a level of safety. But the system at the Science Center ran full-tilt ‘round the clock. The building quickly became the school’s loudest and most expensive energy burden.
“Holding classes with high ambient noise levels became a very big problem,” said David Faircloth, director of plant operation at the 6,000-student university. “And we quickly felt the fiscal strain of maintaining 10 ACH (air changes per hour) in the building at all times. In terms of installed tonnage, the building represents 25 percent of the campus’ entire capacity. But in terms of energy, it accounted for 40 percent of use.”
Operating costs aside, school managers struggled for five years in their attempts to quiet the steady thrum of complaints about noise within the building. That is, until an experimental retrofit was born in an attempt to scale back noise in the rooms.
Piloting a project
With repair and renovation funds from the Board of Regents Facilities Office, the university embarked on a test project to see if retrofitting the entire building was financially feasible. A single-laboratory pilot project began in 2006.
Faircloth assembled the ideal team for a prototype project. Chuck Hanning, P.E., was chosen to design the system. Hanning is senior mechanical engineer at Rosser International, an Atlanta-based architecture and engineering firm with an office in Savannah.
Atlanta-based Thermal Recovery Systems (TRS) contributed to the design and supplied many of the system components. TRS is a commercial and industrial manufacturer’s rep firm that has served Georgia for over 30 years.
Mock Plumbing and Mechanical was the contractor of choice, based on their prior work for the University. Located in Savannah, the commercial and industrial company covers much of the Southeast US.
The test project would be General Chemistry Lab 2102. One of the larger labs in the building, the 1,450 square-foot room was equipped with a dozen constant volume fume hoods, cantankerous controls, and a terminal unit that was capable of supplying only one-third of the needed make-up air.
There were three key objectives for the pilot project: reduce noise level, correct the non-functional VAV operation of the fume hood exhaust system, and manifold the exhaust system to reduce energy consumption. The plan on the table was to use large VFD-driven fans, high-speed venturi valves and smart new controls to create a system capable of a vastly wider range of air volume.
Incredibly loud and extremely inefficient
“While searching for the root of the problem, we learned – among other things – that the fume hoods would not modulate, the hoods lacked blank-off plates, and the fan bypass dampers were never powered.” said Tim Crawford, of Thermal Recovery Systems.
The original design for each fume hood in the building included application-specific controllers, blade dampers and fume hood thermal anemometers, paired with individual fume hood exhaust fans.
To comply with laboratory codes, the system needed to run 24 hours a day, seven days a week. But at the Science Center, the faulty system couldn’t be turned down when the room was vacant. The Science Center’s exhaust system evacuated more than enough air to fill the Empire State Building twice a day. That’s right: 37,000,000 cubic feet x 2.
“Each lab room requires eight ACH when occupied, and four ACH when vacant.” said Hanning. “But the laboratories at the Science Center were getting 10 ACH ‘round the clock.”
Combined, the fume hoods in Lab 2102 pulled 9600 CFM out of the room, while the air handling unit could only supply 3,000 CFM of conditioned air. The rest of the make-up air was drawn through transfer ducts connecting the room with the adjacent corridor.
Instead of using one constant-volume bypass fan at each fume hood, the new design for Lab 2102 called for a common fan system. On the roof, a 10-horsepower Danfoss VLT HVAC Series VFD was used to control a Hartzell centrifugal exhaust fan, and ductwork was installed on the roof to consolidate the exhaust air from all of the fume hoods.
Replacing numerous fume hood fans with one central fan on the roof immediately lowered the sound level in the room. To further cut back on noise, a two-fold approach was taken. A Kinetics Noise Control sound attenuator was used on the exhaust fan, and sound baffles were placed on the ceiling of the lab.
During the pilot project, the existing blade dampers, flow rings, and space controllers were removed. Mock’s technicians replaced the airflow devices and controls with Phoenix Controls 12-inch high-speed venturi valves, which further helped with noise reduction.
Thermal sensors on the fume hoods were replaced with cable sash sensors and digital fume hood monitors equipped with emergency purge buttons. Maximum airflow with the sash open at 18 inches is approx 800 CFM, and turn down to an established minimum flow when the sashes are closed.
Zone Presence Sensors were installed, so each fume hood can be individually and automatically set back. Because some airflow is always required, each VAV fume hood now maintains a minimum airflow with the sash closed.
With the exhaust volume properly in check, focus turned to supply air. Replacing the existing supply terminal unit with dual high-speed 12-inch venturi valves offered the exact make-up air needed; no more, no less.
“When the VAV fume hood pilot project was completed, the noise complaints dropped off,” said Faircloth. “Room occupants now manage the sash, and we can use the project as an applied example of energy conservation in class. Even with one lab renovation, we could see the savings on the supply side of the campus. The pilot project gave us a near shovel-ready design for the rest of the building.”
Investing in America
Based on the success of the pilot project, AASU sought ARRA (American Recovery and Reinvestment Act) funding to retrofit the rest of the Science Center. Funds totaling 1.5 million dollars were granted, and the project began immediately. The sweeping renovation followed the same recipe for success used in Laboratory 2102. And the final product would show a 36% reduction in energy consumption at the Science Center.
Mock Plumbing and Mechanical’s superb work on the pilot project won their approval for work on the full-blown overhaul. “We started on the main project in May of ’11 and wrapped up in late November,” said Jack Cooey, project manager at Mock.
“Over the seven months on the job, the biggest challenge we came up against was making the modifications in an occupied building,” said Hanning. School was in session for much of the project.
One by one, the lab rooms were transformed. Small fans were removed, and decade-old airflow devices and lab controls were replaced with high-speed venturi valves. Big fans and sound attenuators started to populate the flat roof, and sound baffles were hung from the ceilings.
Leveraging the state of what works, not the art of technology
“The venturi valve approach isn’t new,” said Crawford. “The technology has been around for 30 years. In that time, much has changed, but the concept remains the same. A venturi valve is a good fit for new construction labs, but it takes the yellow jersey on renovation projects.”
According to Crawford, the retrofit market benefits from the pressure independence provided by venturi valves. There are no required straight runs, a necessity when using an invasive flow device or orifice plate.
“I spec Phoenix Controls on every laboratory job I’m involved with,” said Hanning. “The speed of response and overall performance are hard to beat.” The valves can turn down as much as 15:1, while maintaining accuracy at five percent on both ends. There’s no invasive flow measurement device, so an annual service isn’t required.
“We’ve been in the critical environment market for over 25 years,” said Rich Stakutis, VP of marketing at Phoenix Controls. “Our valve technology is purpose built for critical airflow control and we’ve continuously innovated the technology to improve the performance of the product.”
“The labs now have a manifold exhaust system with Hartzell Series 03 centrifugal fans,” said Hanning. “Hartzell’s acid-proof epoxy coating and industrial construction make their equipment a good choice for longevity in a harsh installation like a chemistry lab exhaust system.”
Instead of 78 constant volume fans on the roof, there are now 12, with 10-horsepower variable frequency drives controlling the fan motors. Six fans maintain a VAV duct system at 1.6 inches negative pressure, and the other six stand as backup.
Another essential part of the Science Center’s energy saving system can be found inside a small mechanical room atop the Science Center’s mansard roof. Like the single fan used in the Lab 2102 pilot project, the 11 fans serving the rest of the building are controlled by Danfoss VLT- HVAC Series variable frequency drives.
“We install VFD’s on almost every project” said Cooey. “Since the construction of the Science Center, they’ve become the standard in higher efficiency systems.”
Through the use of VFDs, the fans are accurately ramped up and down to maintain the static pressure set-point. At the Science Center, a slight deviation from the set-point could result in hazardous conditions and code violations – defining the importance of total fan redundancy.
“Since the drives are pre-programmed for HVAC application, there’s almost no commissioning time,” said Terry Davies, Southeast regional manager for Danfoss North America. The VFDs – which feature a bypass and built-in USB port for ease of programming – are capable of meeting any HVAC panel requirement.
“I’ve spoken with engineers who’ve told me that programming VFDs is the bane of their existence,” continued Davies. “Their tune changes quickly when they see how easy it is to plug their laptop into the unit, punch in a dozen parameters, and call it a wrap. Simple inputs, such as voltage, maximum and minimum speeds, ramp-up and down times and horsepower are all that’s needed.”
Robert Stephens, lead HVAC technician at Mock Plumbing and Mechanical, sets up the parameters of the a variable frequency drive connected to an exhaust fan at the Science Center.
Sound of silence
In the event of a pop quiz, students who attend class in the Science Center will need to find a new alibi for not absorbing information. Excessive fume hood noise drowning out the instructor is no longer a viable excuse for undergrads. Gone is the end-of-semester curve for HVAC system interruption.
To help reduce noise from the rooftop fans, Mock employees installed Kinetics Noise Control stainless steel, packless-type sound attenuators at the inlet to each fan. Stainless steel construction offers annual wash-down ability by the AASU maintenance staff so that any collected chemicals can be eliminated on a regular basis. The units are 42-inch by 24-inch and 10 feet long. Unlike space inside, rooftop realty wasn’t at a premium.
“After the installation of the venturi valve system and sound attenuators, the ambient noise in the rooms measured 62 dBa,” said Crawford. “With the addition of the sound baffles, that number dropped to 51 dBa with all the fume hoods operating at full capacity.”
Suspended from the ceiling in each lab room, Kinetics Noise Control KB-803 noise control baffles further diminish the already-improved sound level. “We picked those baffles specifically because of the Mylar coating option,” said Hanning. “The non-absorbent covering makes them ideal for hospitals, clean rooms and in this case, chemistry labs.”
“The noise problem was the starting point for the entire project,” said Faircloth. Our educators and students can now speak using a normal voice.” A total noise reduction of 21 dBa made the sound reduction goal of the project a home run.
Giving energy loss the run around
Another interesting facet of the systems design is the reworking of the existing hydronic heating system to form a run-around loop between the air handler preheat coil and the air terminal reheat coils.
“Air handlers 1 and 2 serve the second floor and air handler 4 serves the first floor,” said Hanning. “In the summer, the run-around loop transfers heat from the outside air to the preheat coil, and a Taco inline pump circulates warm water to the reheat coils.”
Shawn Norman, of Mock Plumbing and Mechanical, inspects the wiring on a pump used for the Science Center’s run-around loop.
The control system installed by Facility Automation Solutions will monitor the systems and print out a monthly report on energy transferred. Additional savings are achieved by reducing the outside air temperature entering the cooling coils.
The run-around loop is connected to the hydronic system through a control valve. The control system monitors space conditions and opens the control valve to increase the loop water temperature as needed.
According to Hanning, water flow is bypassed through the preheat coil when the loop temperature is warmer than the outside air temperature. As outside air temperatures drop below 55°F, the control system modulates the preheat control valve to maintain 55°F air temperatures leaving the air handlers.
“All we’re doing is reclaiming some energy from unused parts,” explained Hanning.
The M&V report conducted in early 2012 showed an energy savings of $192,000 per year, at current electric and natural gas rates. However, that number isn’t indicative of all the savings the project is capable of.
Because the data period didn’t include weather conditions over a hot, humid Savannah summer, it’s estimated that an additional $45,000 savings is likely. That would bring the total to $237,000, or a 36% reduction in energy cost for the building; 11% reduction campus-wide.
“In 2001, the emphasis was on laboratory safety, not energy efficiency,” said Faircloth. “I think it’s safe to say that both are of the utmost importance now.”