OSHA’s Laboratory Standard 1910 calls for “4-12 room air changes per hour.”

It’s possible to save energy by reducing air changes to the bottom of this range in labs that aren’t housing extremely toxic research processes, says Bill Odell, HOK sustainable design principal. “We try to look at the science being done and, without ever compromising safety, question if that air change rate could be lower.”

It helps that the nature of science is changing. More of what used to be chemistry and biology experiments are being done with computers. Scientists also are using smaller quantities of materials, which reduces exposure.

Air Circulation
Many studies have shown that safety is more affected by the way air is distributed in a space than the rate of air changes itself.

Ventilation rates should be selected either by minimum air exchanges for safety or based on the amount needed to make up for exhaust. Labs with high heat-generating equipment often need more air for cooling. When this is the case, William Tao & Associates President Rich Janis recommends using fan coils to provide the additional cooling rather than increasing the ventilation rate. “It’s simpler to add fan coils in labs as equipment loads change rather than having to modify the ventilation system. So it’s a more flexible solution.”

Air change requirements in most buildings can be controlled by carbon dioxide monitoring. For labs, though, this generally is not practical because there are many other pollutants to guard against. One often-overlooked method for reducing air exchange requirements is simply to use air distribution systems that avoid short circuiting supply to exhaust and distribute air with enough velocity to purge the entire space of odors and pollutants. “This requires the engineer to take great care to provide good circulation without causing turbulence around fume hoods,” says Janis.

Energy-Efficient Hoods
When a researcher pushes up a fume hood’s sash and it is operating on “high,” the effect is like opening a window to the outside. A new breed of fume hoods captures the air more efficiently and at a much slower face velocity.

These new fume hoods adjust the amount of exhaust changes so that they decrease when the sash is shut and the threat is reduced.

At the U.S. Environmental Protection Agency’s 1.1 million-square-foot research campus in Research Triangle Park, North Carolina, fume hoods were designed to operate at an 80% sash height in most situations.

At Bristol-Myers Squibb’s research campus near Princeton, N.J., the new 147,000-square-foot chemistry building’s once-through VAV air supply and exhaust system includes hood occupancy sensors. Fume hood face velocity is reduced when labs are not in use.

SC Johnson’s labs feature manually operated fume hood sashes. Occupants can minimize the volume of air changed in labs when not using the fume hoods.

Another energy-saving trend is a move toward lower fume hood face velocity. “For years we have been specifying the face velocity at 100 cubic feet per minute (CFM) in order to ensure fume capture,” says Jeff Strohmeyer, a senior lab designer at HOK. “To determine the volume of air each of these fume hoods takes, we multiply the required average face velocity and the fume hood maximum face opening in square feet. For example, a 6'-0"-wide hood with a 30"-high sash operating at 100 feet per minute (FPM) has an air volume total of 1,500 CFM."

Instead of 100 FPM, the slower-face velocity hoods might run at 60, says Strohmeyer. “So there is potential to save energy through reduced air flow provided the hoods still capture fumes effectively.” In addition, overall air distribution in the laboratory can have a significant impact on the overall effectiveness of the fume hood performance.