Hand-Operated Positive Energy Control (HOPEC)

Published February 2000

A fume hood accessory used as a means of cutting total energy demands by 50 percent. In both vertical and horizontal hoods, HOPEC locks the sash in a half-raised position during use to avoid the energy expense of researchers working with the hoods wide open. The equation for measuring the energy efficiency of HOPEC is total exhaust capacity of fume hood in cfm = rate of flow x areas of full sash opening. For example, a four-foot hood that has a face opening of 8.6 square feet with face velocity air at 100 fpm uses 860 cfm; with HOPEC, the door opens only to 4.3 square feet, reducing the exhaust capacity by 430 cfm.