hoods protect operators from breathing harmful fumes by capturing,
containing, and exhausting hazardous gases created in laboratory
experiments or industrial processes.
These box-like structures, often mounted at tabletop level, offer
users protection with a movable, window-like front “face” called a
sash. Fans draw fumes out
the tops of the hoods. (See Fig. 1)
hoods typically exhaust large volumes of air at great expense.
The energy to filter, move, cool or heat, and in some cases scrub
(clean) this air is one of the largest loads in most lab facilities.
A six-foot-wide hood typically exhausts 1200 cubic feet per
minute (cfm), 24 hours per day, and consumes three-times more energy
than an average house. The
annual operating cost of U.S. fume hoods is approximately $3.2 billion,
with a corresponding peak electrical demand of 5,000 megawatts.
This equates to the electrical output of about 20 electric power
plants (at 250 megawatts each), plus nearly 200 trillion cubic feet of
natural gas burned each year, for the associated cooling and heating of
outside make-up air. Consequently,
greenhouse-gas emission caused by operating this typical hood is
equivalent to six automobiles.