This publication is one in series of best practice guides for ''Laboratories for the 21st Century,'' a joint program of the U.S. Environmental Protection Agency and the U.S. Department of Energy Federal Energy Management Program. It is intended for those who plan to design and construct public and private-sector laboratory buildings. This guide describes how implementing low-pressure-drop design strategies established in the early stages of the design process will result in much lower energy costs through the system's life.