Full of Hot Air?
The University of Pittsburgh, in the educational and cultural enclave of Oakland, just outside the Steel City, is surrounded by forested hills—a much different vista from the acres of farm fields that typically surround many colleges and universities in more rural and open locations. At the same time, existing in a well-developed urban environment presents a number of challenges to the school, particularly when it comes to expanding the campus. Thus, it's not a surprise that the university's main chemistry building—the Chevron Science Center—is a 14-floor high-rise.
That said, when it came time to re-evaluate the fume hood venting scheme of the '70s-era building, a number of challenges other than energy efficiency—the main impetus of the upgrade—arose. One of the first issues was taking into consideration the residents who live on those scenic surrounding hills—and specifically, exhaust noise abatement.
“At the very top of the building we have a custom-designed, heavy-duty ventilation air-handling unit and exhaust stack discharge dampers that throw [at a discharge velocity of 3,000 fpm] the exhaust [and sound] straight up for effective exhaust dispersal,” says Doug Vogel, an HVAC designer with Moon Township Pa.-based CJL Engineering, the project's M/E/P engineer.
The unit, custom-fabricated by Greenheck, features a clamshell variable-volume exhaust damper rather than an iris design, he explains. The clamshell damper allows for variable-volume exhaust airflow control while maintaining constant discharge velocity with no negative static pressure effect on the fans. Additionally, the unit includes a pressure sensor that opens or shuts the clamshell if the exit velocity is not at its designated criteria. Its use enables effective exhaust, energy efficiency and quiet operation in keeping with being a good neighbor in a residential community.
“It's a most unusual installation,” says Vogel. “The only other installation of its kind that we are aware of is in Berkeley [at the University of California].”
On the subject of air movement, in the course of operation, 14 to 15 air changes per hour is the norm for the facility. Collectively, the new supply and exhaust systems can deliver around 300,000 cfm at maximum operation. Frankly, that's a lot of already conditioned air going to waste, which takes us to the heart of this retrofit: better energy efficiency through improved equipment. In fact the new systems also employ energy recovery, saving 400 tons of cooling. Indeed, prior to the retrofit, the Chevron Science Center was the largest energy consumer on campus, second only to the school's 42-story landmark, Cathedral of Learning building.
But before getting to the new, let's talk about the old. As is notably visible by the giant brown plenums that run the length of the building, the old venting system drew fume hood exhaust out of the labs and up the ducts to “doghouses” at the roof level. The housings contained some 150 fans that released the fume hood air at the roof. The idea of the retrofit, according to CJL's lead engineer Jim Vizzini, P.E., was to get rid of the individual fans collecting/supplying air from 11 ducts on the north side of the building and seven on the south, in favor of a pair of major supply air-handling units and exhaust fans.
“The old doghouses held as many as nine in-line fans,” says Vizzini. “So we essentially cut them all off and manifolded them into one exhaust plenum, then tied this to the exhaust collectors on the penthouse.”
And while this job was dubbed a “lab renovation,” it's the top of the building, not the individual labs, where the action takes place. And it was a good thing too for students and researchers in the facility, because there was no plan to shut down operations while the work was being done. “We tried not to touch anything in the building; almost everything we did was outside,” says Vizzini.
But we're not talking about a simple equipment enclosure. In reality—at least as the local authorities saw it—this was a two-story penthouse addition that required full code compliance, including sprinklering. In fact, the size of the enclosure and the weight of the roughly 420,000-lb. custom air-handling units also required significant structural support. “We had to place a spider web of structural steel to catch all the building's existing columns,” says Vogel.
Cutting to the chase, one of the big differences between old and new is the glycol coil loop run-around energy-recovery system that is also combined with indirect evaporative cooling in the summer to maximize efficiency. In winter mode, Vizzini says, the system uses the warm exhaust air to preheat supply air and vice versa in the summer. Furthermore, in summer mode, evaporative cooling is employed to further pre-cool incoming air before it hits the run-around cooling coils. And for an extra sustainable measure, CJL's system captures condensate from the cooling coils in summer and pumps it back up to supply the water for evaporative cooling.
In order to operate effectively, Vogel adds, the evaporative cooling system needs at least 12 gpm of water, so if the system can't generate enough condensate from the coils, an alternative supply of water must be used. However, the condensate is usually able to deliver about 80% of the demand. One cautionary note about the evaporative process: Vogel says that the water lines must be bled periodically and that the water must be disposed of properly.
The heat-recovery equipment itself is housed in the second story of the penthouse. In this penthouse, besides the massive AHUs, are four 150-horsepower variable-frequency drives on the supply side. The VFDs are in place for the next phase of the project, which will be the implementation of variable-air-volume control units at each lab fume hood.
That said, the 45-and 60-in. fans in the penthouse are AMCA-rated with spark-proof motors to ensure safety in case fume exhausts contain any kind of explosive properties. Another big issue is keeping the big VFDs cool to avoid tripping. As a result, outside air is independently drawn through the penthouse.
But back to plans for VAV, CJL is rolling out implementation on a lab-by-lab basis due to the fact that the majority of labs are still in use. In the long run, this will produce significant energy savings. The firm is also phasing in replacements of the fume hoods, which will incorporate variable-flow control valves.
While it's hard to get a current handle on what these phased improvements will bring to bear, the fact that CJL managed to trim 400 tons off the cooling load has the university pointed in the right direction. The system even helped with heating loads this past winter.
“With the escalated cost of gas last year over the winter, the energy-recovery effort really proved a blessing, because it significantly reduced the Chevron Science Center's load on the campus steam system,” says Vogel.
So having survived three decades of safely exhausting a plethora of chemical fumes with only minor corrosion in the old fan bearings and control wiring, the Chevron Science Center is ready for continued action in a new century, but with an HVAC system girded to meet 21st century energy bills.
VAVs at Low Loads
Many large buildings use variable-air-volume (VAV) systems to deliver the appropriate amount of chilled air. The problem is that large buildings typically spend most of their time operating at part load. In such a mode, VAV systems often operate far less efficiently than they could because air distribution system components are typically not selected and controlled to work in an integrated fashion.
The California Energy Commission, through its “Advanced Variable Air Volume System Design Guide,” is hoping to rectify this issue by providing some best-practice recommendations, including:
Using a “dual maximum” control logic, which allows for a very low minimum airflow rate during no- and low-load periods.
Setting the minimum airflow set point to the larger of the lowest controllable airflow set points allowed by the box and the minimum ventilation requirement—often as low as 0.15 cfm/per sq. ft.
For all, except very noise-sensitive applications, select VAV boxes for a total pressure drop of 0.5 in.s H 2 O to optimize energy use over the course of a year.
Using supply-air temperature reset controls to avoid turning on the chiller whenever possible.
Using demand-based static pressure set point reset to reduce fan energy up to 50%, reduce fan operation in surge conditions, reduce noise and improve control stability.
Application of the guide's principles, according to the authors, can cut HVAC system electricity use by 24% or more and cut gas heating energy use by 41% compared to standard practice. Visit
New Tools for HVAC Commissioning
A big issue in achieving LEED certification can be verifying that the HVAC system is indeed meeting the requirements of ASHRAE 55 and 62. Hearing the cries of building commissioners everywhere, the folks from Fluke, who dropped by our offices recently, are demoing some new products geared specifically to such purposes. First is the 975 air meter, which simultaneously measures, logs and displays temperature, humidity, CO 2 and CO. With an optional probe, airflow and velocity can also be measured.
One of the best features of the device, according to Eric Hudson, a product manager with the Everett, Wash.-based company, is that it automatically does a lot of the required calculations. For example, let's say the commissioning consultant needs to calculate the percentage of outside air. By simply using the device to capture the return air temp, the supply air temp and the outdoor temp, the user can simply hit a button and the device delivers the complex calculations.
The company has also come out with a couple of portable thermal imaging cameras geared at checking building envelopes for leaks and similar problems. At the high end is the TIR Flexcam with fusion, which is a thermal and digital camera in one. In fact, one feature is that the camera can be programmed to look for certain variables, and when something is not in line with acceptable settings, the camera shows those areas in infrared. The IR Insight is the more economical, but fully functional, portable camera geared more for facility operators.
According to Fluke PR Manager Larry Wilson, the accuracy of a lot of existing air movement measurement devices has not been very good, thus the manufacturer saw an opportunity for more reputable precision-calibrated instruments. “And this is huge in this day and age of litigation in that it helps you better defend and document your case, if need be.” —By Jim Crockett