Close Your Hood! | October 8, 2007 Issue - Vol. 85 Issue 41 | Chemical & Engineering News
Volume 85 Issue 41 | pp. 44-45
Issue Date: October 8, 2007

Close Your Hood!

Easy ways to save on energy costs include installing fewer fume hoods and vigilantly closing sashes
Department: Science & Technology | Collection: Green Chemistry, Sustainability
Safety Cost
Hoods consume energy as they draw away chemical fumes.
Credit: Bethany Halford/CEN
Safety Cost
Hoods consume energy as they draw away chemical fumes.
Credit: Bethany Halford/CEN

YOU MIGHT not realize it, but the fume hood whirring away in the corner of your lab is sucking up a lot more than chemical vapors. Fume hoods are serious energy hogs, and their operating costs take a big bite out of budgets.

The average fume hood consumes as much energy as three houses, according to Dale Sartor, an engineer and fume hood expert at Lawrence Berkeley National Laboratory. Operating a fume hood is like opening all the windows in your house and then turning the air-conditioning on full blast, he explains.

All the air the fume hood expels has to be replaced with air from outdoors. "No matter how hot or cold that air is, it has to be heated or air-conditioned, filtered, and then distributed," Sartor says. That's in addition to the energy consumed by the fan that drives the hood.

With energy costs on the rise, cost-conscious chemistry departments are looking for ways to make fume hoods more efficient. One of the simplest ways to do that, Sartor says, is by installing smaller hoods or not putting in fume hoods at all.

"Typically, if you walk around a laboratory building, a lot of the hoods aren't being utilized. They're being used for storage or they're not actively being used. The problem is that they keep on using energy," Sartor says. Taking unused hoods out of service, sharing hoods, and considering smaller hoods are all measures that can cut down on energy consumption. Of course, it's important to keep in mind that hoods serve a critical safety function, he adds. "Efficiency does not trump safety."

"There's no getting around the problem that the more fume hoods you have, the higher your energy costs will be," says Gary Spessard, a chemistry professor at St. Olaf College in Northfield, Minn.

When the time came to design a new chemistry building at St. Olaf, the original plan included 88 fume hoods. Spessard and his colleagues decided one of the best ways to cut their expenses was to revamp their curriculum so they could cut down on the number of hoods needed.

"Over the past few years, we have developed experiments that follow the tenets of green chemistry, and with green chemistry the necessity for hoods is greatly diminished," Spessard says. Most of the hazards in organic chemistry labs are associated with volatile organic chemicals, he points out. "If you eliminate those, then you don't really need to work in a hood."

St. Olaf was able to reduce the number of hoods in its new building from 88 to 53, saving the school $250,000 on the cost of the hoods and installation alone. "That's a big savings up front," Spessard notes. But beyond that, the reduction in the number of hoods will save money on heating and cooling costs in years to come.

A green approach also helped at the University of Oregon, where hood space was once so tight for the undergraduate organic chemistry program that instructors had to run labs late at night and on weekends to accommodate all the students.

To solve the problem, the university decided to adopt a greener approach to the traditional organic chemistry laboratory course. Now a class of 44 students uses just six hoods—a big difference from the usual ratio of two students per hood.

The laboratory experiments do not require the entire experiment to be done inside a hood, explains Kathryn Parent, a senior staff associate at the American Chemical Society Green Chemistry Institute who studied the University of Oregon's adoption of a greener curriculum as part of her master's thesis. She estimates that the University of Oregon saved roughly $250,000 on hoods and installation and nearly $87,000 annually in energy costs by adopting its greener curriculum.

The hood isn't eliminated entirely, Parent says, but it's used mostly for simple things such as transferring chemicals if they're hazardous or volatile. "Typically, what you're going to see is fewer volatile organic compounds, staying away from halogenated organic compounds like methylene chloride, using air or oxygen rather than a stronger oxidizing agent, doing experiments at ambient temperature or heating with microwave energy, as opposed to refluxing for hours and hours," Parent says.

The drive for fewer fume hoods and greener curricula has been catching the attention of architectural firms. "We're learning more about green chemistry so that when we have clients and they're looking to design a new facility, we can give them all the tools and information that we've acquired, and maybe they'll begin to make that switch," says Erika Morgan, an architect for the sustainable design firm Perkins & Will.

"The big thing that surprises people is that it costs less to build an energy-efficient building. People always assume it costs more," adds Gary C. McNay, who designs lab space for colleges and universities for Perkins & Will.

When it comes to designing a more energy-efficient lab, the first thing McNay recommends is reducing the number of hoods. A hood is one piece of the mechanical system, but the number and type of fume hood used impacts a number of systems down the line, he says. "If you could reduce the energy usage by 30% in a laboratory building, that means the mechanical system can be 30% smaller, which means the building costs are less and you're using less energy," McNay adds.

Of course, if you can't cut down on the number of hoods, a number of interesting technologies are still available to improve energy efficiency of those fewer hoods that do get installed. These include low-flow hoods, which restrict sash openings and improve airflow via the hood's aerodynamics, as well as variable-air-volume hoods, which alter their exhaust power on the basis of how far open the sash is.

"Every fume hood manufacturer has some sort of a redesigned product that came into the marketplace within the last three to six years that can operate at a lower flow rate," says Jon Zboralski, director of airflow products at Hamilton Laboratory Workstations, part of Thermo Fisher Scientific.

There are a number of things to consider when picking the best fume hood for your lab: number of hoods, new construction versus retrofit, and climate. But ultimately, Zboralski says, you have to do the math to see if energy savings offset the cost of the equipment.

For established laboratories that are not contemplating refurbishing any time soon, the easiest way to cut the energy costs of fume hoods is simply to make sure that sashes are closed when not in use. "A lot of times, we go into laboratories and people will not be at the hoods, but all the sashes will be open. That's an incredible waste of energy," McNay says.

That point was recently driven home to chemists at Massachusetts Institute of Technology by a mechanical engineering undergrad, Steven T. Amanti. His senior thesis, "Potential Energy Savings on the MIT Campus," spotlighted how hoods in the chemistry department were frequently left open when not in use. By Amanti's calculations, the department could save $350,000 annually in utility costs by simply making sure unused hoods were closed.

"I think that the chemistry department was always aware that fume hoods are a large consumer of energy," says Richard J. Wilk, administrative officer for MIT's chemistry department. But, he says, how much energy was lost inadvertently because of hoods being left open came as something of a surprise. "I think with rising energy costs on campus, it really brought the issue to our attention."

THERE'S NOW a campaign at MIT to get researchers to close their hoods when they go home for the night. The positions of fume hood sashes are recorded by the building ventilation control system, and a monthly report of the average sash position is sent to each research group.

"The report makes it easy to spot areas that need improvement," says Jim Doughty, environmental health and safety coordinator for MIT's School of Science. "We're trying to bombard them with this information in as many different venues as we can."

Hood manufacturers are also getting in on the act, introducing measures that restrict a hood's opening or ensure the sash is closed when not in use. Zboralski says one popular trend is to install hoods with combination sashes. These hoods have sashes that can move vertically up and down but also have a panel that slides horizontally. This design, Zborlaski explains, gives access to elevated areas inside the hood without having to open the entire sash.

There are also some simple fixes, such as latches or stops that ensure a sash can only rise to a specified height. Other solutions, such as motorized sash closers that kick in when the operator steps away from the hood, are more complex.

"The widgets are there if somebody wants to pay for them," Zboralski says, but ultimately, you have to be sure the energy savings from those widgets are worth it. No matter what all the manufacturers do to their hoods to manage airflow, nothing can make the hood safer than just getting the user to put the glass in front of their face. It's such a simple thing."

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