Fume Hoods
The fume hood is designed to satisfy a convergence of human health, environmental, research and financial needs. Organizationally speaking, the fume hood is also operated to satisfy a convergence of faculty, administration and student needs, responsibilities and limitations. The fume hood is often intrinsically tied into the ventilation balance of laboratories which further complicates efficient management efforts.
A typical fume hood in the United States runs 24 hours a day, 365 days a year and uses 3.5 times more energy than the average house (Bell et al 2003). In an average U.S. climate, the energy to fuel the average fume hood costs over $4,300/year (LBNL 2002).
Harvard University operates close to 1000 fume hoods, of which around 40% are located on the Longwood Campus and the rest within the Faculty of Arts and Sciences in Cambridge. According to estimations based on national averages, which predict that each fume hood consumes 1000 CFM and are on all the time, fume hoods are costing Harvard University roughly $3.6 million each year, generating a significant volume of greenhouse gases.
Nationally, there are around 75,000 fume hoods that exist across the country, amounting to $3.2 billion each year in energy expenses (including the cooling load). This requires the equivalent electrical output of roughly 20 electric power plants (assuming they are 250 megawatts each) (LBNL 2002). In addition, these 75,000 fume hoods nation-wide consume roughly 200 trillion cubic feet of natural gas annually to heat the make-up air in laboratories (LBNL 2002).
While keeping the fume hood sash closed is one of the most important things that lab users can do both for their own safety and for energy efficiency, (Rois 1999), often hoods are kept open all the time and used infrequently.
Estimates of how much a "typical” fume hood is in use is hard to pin down. Interviews with 18 lab users at a biochemical laboratory revealed a wide variation. However, interviewees typically noted they used fume hoods from “never” to “maybe once a month to ten minutes a day” to once or twice a day for twenty minutes. Only one person out of eighteen answered several hours a day.”
A general estimate of average fume hood use across the country ranges from 1 to 2 hours (Grossman 1995) to between 1 and 11 hours in university labs (Rabis & Welkenbach 1993) to 1.5 hours a day in a typical pharmaceutical company (Phoenix Controls 2003). Of course, it is dependant on the kind of work being done in the laboratory and the variety of usage patterns is as great as the variety of labs. However, there is clearly opportunity to reduce the time that the average fume hood has its sash open.