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Energy-guzzling fume hoods put on a diet

University chemistry labs are turning down airflow when teaching facilities are closed

by Cheryl Hogue
February 22, 2022 | A version of this story appeared in Volume 100, Issue 8

Two people in lab coats, goggles, and gloves stand next to a fume hood.
Credit: Justin Knight/MIT
Massachusetts Institute of Technology students work in a fume hood at the school's undergraduate chemistry lab. This 2019 photo was taken before the COVID-19 pandemic.

Walls lined with humming fume hoods are a defining feature of many chemistry laboratories. These safety devices, part of a lab’s overall ventilation system, suck hazardous airborne chemicals away from people running experiments and others in the lab.

Fume hoods are notorious energy hogs. But rapidly changing technologies are leading a number of US colleges and universities to shrink the energy and climate footprint of their spaces—particularly undergraduate chemistry laboratories that sport scads of hoods.

Beyond this, some lab ventilation specialists are raising questions about the need for large numbers of hoods in teaching labs. They are challenging instructors to consider changes in lab courses to allow for alternative, effective safety measures that are less energy intensive than standard fume hoods.

Ventilation consumes 60–70% of a chemistry laboratory’s energy, says Ralph Stuart, environmental safety manager at Keene State College. Electricity to run the fans that pull air through hoods and lab spaces contributes to this consumption. But the greatest portion of the energy goes to heating or cooling large volumes of air entering the ventilation system, says Stuart, who has worked on laboratory environment, health, and safety (EHS) issues for decades.

Key to control
Schematic drawing of a Venturi valve and a photo of a Venturi valve made by Phoenix Controls.
Credit: Yang H. Ku/C&EN (schematic); Phoenix Controls (photo)
The interior of a Venturi valve, left, has a cone that moves back and forth on a shaft in response to pressure changes. This maintains airflow in a fume hood when its sash is open. The Venturi valve on the right, which can range in length from about 60 to 76 cm, is manufactured by Phoenix Controls.

University engineers and lab managers who spoke with C&EN say the best time to consider optimizing fume hoods’ energy use is when plans are being drawn up for teaching labs, whether for a new building or renovated space.

“You can save more money doing it when you’re building a new lab rather than doing it after the fact,” says John J. Dolhun, director of the Undergraduate Teaching Laboratory for the Department of Chemistry at the Massachusetts Institute of Technology. The facility opened in 2018, replacing a century-old lab.

Even so, it’s also possible to implement new energy-saving practices with existing equipment. Whether working with new hoods or old, the general approach is to turn fume hoods’ airflow to a minimum when a teaching lab sits unused for part of a day, on weekends, and during semester breaks. Teaching labs with a lot of hoods that have a regular schedule of vacancy and occupancy generally offer a surer return on this type of conservation investment than do research labs, experts agree.

The ability to turn down airflow hinges on outfitting hoods with control valves that keep a constant volume of air flowing through a hood, regardless of the position of its sash. The generic shorthand for these variable air volume control devices is venturi valves. They are named for Italian physicist Giovanni Battista Venturi, who in 1797 described the increase in the velocity of a fluid flowing from a wider to a narrower section of a pipe.

A venturi valve for a fume hood has a constricted part that forms a funnel shape. Inside the narrowed section, a cone assembly can move back and forth on a shaft, says David Rausch, senior business development manager for Phoenix Controls, a leading manufacturer of venturi valves. The device alters airflow rates in response to air pressure changes, such as when a fume hood’s sash is opened.

Installing venturi valves in hoods isn’t always necessary or appropriate, Rausch notes. For instance, he says, safety concerns may require hoods in some labs to run at the same rate 24 h a day if they are used to store chemical waste or hold experiments in process. But equipping a set of hoods with venturi valves in a large lab allows for airflow to be adjusted to save energy and maintain safety, according to a number of colleges.

In 2016, for example, Yale University opened newly renovated teaching labs in its Sterling Chemistry Laboratory building. Shortly after, Julie Paquette, Yale’s director of engineering and energy management, began to explore the idea of turning down the airflow of the teaching labs when they aren’t in use. This puts the ventilation system into what she calls vacancy mode.

You can save more money doing it when you’re building a new lab rather than doing it after the fact.
John J. Dolhun, director, Undergraduate Teaching Laboratory, Department of Chemistry, Massachusetts Institute of Technology

“Unlike a research lab or graduate lab, where people could be in there any hour of the day, the schedule is very specific for undergraduate chemistry labs,” Paquette tells C&EN. “And there’s typically a lab manager who really takes ownership of the space and works closely with EHS.

“We knew that we could have a more advanced approach to controlling the airflow” when the lab is closed, Paquette says. “What that meant for us was bringing the fume hoods down below their minimum exhaust flows, such that we’re maintaining the air change rate in the lab” and keeping negative pressure in that space when it is vacant.

Negative pressure means more air is exhausted than supplied to the space, Rausch of Phoenix Controls explains. Fume hoods, along with the rest of a lab’s exhaust system, are designed to keep the facility under negative pressure to prevent airborne chemicals from reaching adjacent areas such as hallways or neighboring rooms, he says. Stuart and other experts say turning down airflow when labs are closed is not as easy as simply flipping a switch on fume hoods. It takes time and expertise to balance ventilation to maintain negative pressure when conditions change.

In the Yale teaching labs, fume hoods are banked together in the ventilation system, according to Paquette. Specifically, she says, each venturi valve controls the airflow for four fume hoods. If one hood in a bank is in use, all four stay on at the in-use setting and will not go into vacancy mode.

In 2018, Paquette shared what Yale had done with Nicole Imbergamo, MIT’s sustainability project manager. Paquette and Imbergamo worked together previously in heating, ventilation, and air-conditioning design at Vanderweil Engineers.

Imbergamo says she proposed a similar plan for MIT, to do what she calls hood hibernation. The school had installed venturi valves in each of the hoods in its new teaching labs but was not using them for that purpose. In April 2021, after Imbergamo’s plan was vetted and approved, the university had the lab’s computerized ventilation control system changed, she says. The program now turns down airflow to 58 of the lab’s 69 hoods—the other 11 store chemical waste—each weekday at 6:30 p.m. and ratchets it back up at noon Monday through Friday, Dolhun explains. The system remains in hibernation over weekends.

“It was really just a matter of us reprogramming it, and it was less than a week’s worth of effort for our controls contractor to do,” Imbergamo says. “It’s not rocket science.” And ventilation specialists can easily change a waste hood to a regular hood, or vice versa.

“We do have some safety features built into the system,” Dolhun says. If a sash on one of the fume hoods is opened while the equipment is hibernating, that hood immediately goes into active-use mode and stays there until the next hibernation cycle. “It’s a great safety feature, which alleviated a lot of concerns from EHS [officials] about students using the hoods during off hours,” Dolhun says.

He can check on the status of all the hoods remotely, after the lab is locked and students and staff are gone for the night. “If I see one section of the lab where the hoods are supposed to be hibernating and they’re all in normal mode, I immediately email the TA [teaching assistant] who was in that section” and instruct that person to go and close the sashes, he says.

The process to restore the hood to service is automatic. This is an important safety precaution to ensure a hibernated hood cannot be used accidentally.
Matthew Gudorf, director of energy, engineering, and inspection, University of California, Irvine

MIT spent about $40,000 installing the fume hood hibernation system, Imbergamo says. It is reaping an estimated $18,000 in utility cost savings per year accrued from MIT’s power plant. That utility provides heating and cooling of air as it’s drawn inside and also electricity to run fans, she says.

In 2018, the University of California, Irvine, also upgraded its fume hoods in several chemistry teaching labs to allow for hibernation mode, says Matthew Gudorf, director of energy, engineering, and inspection at UCI. Utility incentives and energy cost savings covered expenses for the upgrade, which was part of the university’s strategic energy program, according to Gudorf.

UCI’s system takes a slightly different approach from MIT’s. Putting a hood into hibernation “takes direct user input at the hood,” Gudorf says. “The process to restore the hood to service is automatic. This is an important safety precaution to ensure a hibernated hood cannot be used accidentally.”

Maintaining safety and energy savings takes vigilance, Gudorf says.

“It is the job of everyone to check, maintain, and repair, when needed, these exposure control devices to ensure that we not only reduce our climate impact but keep all lab users safe throughout their time in the lab,” Gudorf says.

Besides turning airflow down or off in large undergraduate labs at certain times, institutions can save energy by switching off hoods that are not used for months, says Ellen M. Sweet, laboratory ventilation specialist at Cornell University. Cornell has hibernated some hoods in its large labs for more than a decade.

A hood needs to be turned off for roughly 3 months for energy savings to exceed costs, according to Sweet. “There are costs for our controls technicians to do the hibernation process and then to reverse that to get it all back up and running when somebody needs the fume hood,” she says.

In addition, those who run labs need to be aware of the energy costs of running fume hoods used to store items that don’t need to be in such an intensely ventilated space, Sweet says. Keene State’s Stuart adds that he has found books stored in operating fume hoods at universities.

In addition, MIT’s Imbergamo emphasizes the importance of considering the future when universities plan lab renovations. “Even if right now it doesn’t make sense for the [airflow] systems to be turned off or turned down, having the infrastructure in place makes it so much easier to change in the future,” she says. “It could cost you a little bit more up front but gives you future flexibility for savings.”

Universities should also consider safety strategies for undergraduate teaching labs that cost less and use less energy than standard fume hoods, Sweet and Stuart say.

Stuart points to ductless fume hoods as one innovation. Instead of sending exhaust air outside, these hoods draw the air through a filter to remove chemical vapors. The air is then recirculated to the building, reducing the need for heating or cooling.

Some campuses have committed to ductless fume hoods in teaching labs, Stuart says. Besides saving energy and money, these hoods are much quieter than ducted ones. He points out that faculty and teaching assistants sometimes struggle to be heard over the roar of traditional hoods.

Using ductless fume hoods requires careful consideration of the type of experiments that will take place. Faculty members need to select teaching experiments for students that are within the limits of safety that ductless hoods provide, Stuart says. He talks to faculty members about which kinds of chemistry experiments they are planning each semester and then works with them to guarantee that they understand those limits.

Similarly, Sweet at Cornell challenges chemistry educators to look beyond optimizing the energy that fume hoods use and to think more broadly about sustainability.

“There are lots of things that can be done on the bench” instead of in a fume hood, Sweet says.

Many substances used in an academic lab are toxic but do not pose airborne hazards. They don’t have to be handled in a hood, though they require other safety measures, Sweet points out. Localized ventilation, such as drop-down exhaust snorkels that capture vapors or dusts, can provide appropriate and less energy-intensive safety than a bank of hoods for those working in a lab, she says.

Sweet encourages instructors and researchers to ask themselves, “What are you using in your chemistry that you actually need a fume hood?”.


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