Membrane filtration, which replaces standard microfiber glass filtration, can reduce energy consumption. Membrane filters remove particles more efficiently than microfiber filters and at a lower pressure drop; however, membrane filters can cost more per unit area. Life-cycle cost analysis and determination of optimum pressure drop, as described above, may justify the additional expense. According to McIlvaine (1995) , "The [energy-efficiency] impact of membrane filters could be substantial. It could reduce air movement energy cost by as much as 15 percent." [McIlvaine, 1995]
