The two-story, 126,000-sq-ft Science Center at Armstrong Atlantic State University (AASU) in Savannah, Ga., is a network of 36 state-of-the-art laboratories, classrooms, and offices. Immediately after construction was completed in 2001, problems became apparent. The ambient-noise level in the laboratories was 72 dBA, and the building's variable-air-volume (VAV) exhaust system was anything but.
“Holding classes with high ambient-noise levels became a very big problem,” David Faircloth, director of plant operation for the 6,000-student university, said. “And we quickly felt the fiscal strain of maintaining 10 ACH 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.”
In 2006, AASU embarked on a test to determine whether retrofitting the entire Science Center was financially feasible. A 1,450-sq-ft general chemistry laboratory equipped with a dozen constant-volume fume hoods was chosen for the project.
Three key objectives were: reduce noise, correct fume-hood-exhaust-system VAV operation, and manifold the exhaust system to reduce energy consumption. The plan was to use large variable-frequency-drive- (VFD-) driven fans, high-speed venturi valves, and new smart controls to create a system capable of a vastly wider range of air volume.
Extremely Loud and Incredibly 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,” Tim Crawford of Thermal Recovery Systems, a commercial and industrial manufacturers’ representative that contributed to the design of the new system and supplied many of the components, said.
The original fume-hood design included application-specific controllers, blade dampers, and thermal anemometers paired with individual exhaust fans.
The exhaust system, which needed to run 24 hr a day, seven days a week to comply with laboratory codes, could not be turned down when the laboratory was vacant. It evacuated 74 million cu ft of air, more than enough to fill the Empire State Building twice a day.
“Each lab room requires eight ACH when occupied and four ACH when vacant,” Chuck Hanning, PE, senior mechanical engineer for Rosser International Inc., who designed the new system, said. “But the laboratories at the Science Center were getting 10 ACH around the clock.”
Combined, the fume hoods pulled 9,600 cfm of air out of the room, while the air-handling unit could supply only 3,000 cfm of conditioned air. The rest of the makeup air was drawn through transfer ducts connecting the room to the adjacent corridor.
Instead of one constant-volume bypass fan at each fume hood, the new design called for a common fan system. On the roof, a 10-hp Danfoss VLT HVAC Drive was used to control a Hartzell centrifugal exhaust fan, and ductwork was installed to consolidate exhaust air from all of the fume hoods. This lowered the sound level in the room immediately. To further reduce noise, a Kinetics Noise Control sound attenuator was used on the exhaust fan, and sound baffles were placed on the ceiling.
For the pilot project, blade dampers, flow rings, and space controllers were removed. Mock Plumbing and Mechanical technicians replaced the airflow devices and controls with Phoenix Controls 12-in., high-speed venturi valves, which aided 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 18 in. was approximately 800 cfm.
With zone presence sensors installed, fume hoods can be set back individually and automatically. Each fume hood maintains a minimum airflow with the sash closed.
With exhaust volume in check, focus shifted to supply air. Replacing the supply terminal unit with dual 12-in., high-speed venturi valves offered the exact makeup air needed.
“When the VAV-fume-hood pilot project was completed, the noise complaints dropped off,” Faircloth said. “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 American Recovery and Reinvestment Act funding to retrofit the rest of the Science Center. Funds totaling $1.5 million were granted, and the project began immediately.
“We started on the main project in May of ’11 and wrapped up in late November,” Jack Cooey, project manager for Mock Plumbing and Mechanical, said.
Said Hanning, “Over the seven months on the job, the biggest challenge we came up against was making the modifications in an occupied building.”
School was in session for much of the project.
One by one, the laboratory 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.
“The venturi-valve approach isn’t new,” Crawford said. “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.”
Crawford said retrofit projects benefit from the pressure independence provided by venturi valves. Straight runs are not required, a necessity when an invasive flow device or orifice plate is used.
The Phoenix Controls valves have a turndown ratio as high as 15:1 and maintain 5-percent accuracy at both ends. With no invasive flow-measurement device, annual service is not required.
“The labs now have a manifold exhaust system with Hartzell Series 03 centrifugal fans,” Hanning said. “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 the previous 78 constant-volume fans on the roof, there are now 12, controlled by 10-hp Danfoss VLT HVAC drives. Six of the fans maintain a VAV duct system at 1.6-in. negative pressure, while the other six stand as backup.
Through the use of the VFDs, the fans are ramped up and down accurately to maintain the static-pressure setpoint. At the Science Center, even a slight deviation from the setpoint could result in hazardous conditions and code violations.
“Since the drives are preprogrammed for HVAC application, there’s almost no commissioning time,” Terry Davies, Southeast regional manager for Danfoss North America, said.
The VFDs, which feature a bypass and built-in USB port for ease of programming, are capable of meeting any HVAC-panel requirement.
Page 2 of 2
“I’ve spoken with engineers who’ve told me that programming VFDs is the bane of their existence,” Davies said. “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.”
Sound of Silence
To reduce noise, Mock Plumbing and Mechanical installed Kinetics Noise Control stainless-steel, packless-type sound attenuators at the inlet to each rooftop fan. Stainless-steel construction enables annual washdown to eliminate any collected chemicals.
“After the installation of the venturi-valve system and sound attenuators, the ambient noise in the rooms measured 62 dBA,” Crawford said. “With the addition of the (Kinetics Noise Control KB-803) sound baffles (suspended from the ceiling in each laboratory), that number dropped to 51 dBA with all the fume hoods operating at full capacity.”
Said Hanning: “We picked those baffles specifically because of the Mylar-coating option. The non-absorbent covering makes them ideal for hospitals, cleanrooms, and, in this case, chemistry labs.”
Added Faircloth: “Our educators and students can now speak using a normal voice.”
Giving Energy Loss the Runaround
The hydronic heating system was reworked to form a runaround 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,” Hanning said. “In the summer, the runaround loop transfers heat from the outside air to the preheat coil, and a Taco inline pump circulates warm water to the reheat coils.”
The control system, installed by Facility Automation Solutions, monitors the systems and prints a monthly report on transferred energy.
Additional savings are achieved by reducing the temperature of outside air entering the cooling coils.
The runaround loop is connected to the hydronic system through a control valve. The control system monitors space conditions and opens the control valve to increase loop water temperature as needed.
According to Hanning, water is bypassed through the preheat coil when loop temperature is higher than outside-air temperature. As outside-air temperature drops below 55°F, the control system modulates the preheat control valve to maintain the temperature of air leaving the air handlers at 55°F.
“All we’re doing is reclaiming some energy from unused parts,” Hanning said.
Measurement and verification performed in early 2012 showed an energy savings of $192,000 per year at current electricity and natural-gas rates. Because the study did not include weather conditions over a hot, humid Savannah summer, it is estimated that an additional $45,000 in savings is likely. That would bring the total savings to $237,000 for a 36-percent reduction in energy cost for the building and an 11-percent reduction campuswide.
Dan Vastyan is an account manager for Common Ground, a trade-communications firm based in Manheim, Pa.
For Design Solutions author guidelines, call Scott Arnold, executive editor, at 216-931-9980, or write to him at [email protected].