Manifolded fume hood exhaust in complex laboratory buildings can provide substantial energy and first-cost savings. A manifolded system also offers opportunities for energy recovery, flexibility, redundancy, and better air quality. Neuman (1987) compares manifold and individual systems: "Proponents (of individual exhaust systems) feel that the isolation provided by the individual ducts and dedicated fume hood fans is worth the expenditure of cost and sacrifice of floor space," but "the individual fume hood scheme results in lower energy efficiency, more maintenance, and more roof penetrations." However Nelson (1986) points out that "The primary reason for using the individual system is that there is something unusually hazardous in the exhaust from the fume hood." Experience has shown that central exhaust systems are appropriate in large laboratories and in buildings with large numbers of fume hoods as well as in multi-floor, multi-section buildings. [Charneux, 2001] [Rydzewski, 1999] [Crockett, 1999] [Neuman, 1987]
Wendes (1990) stresses the point that, "...manifolded exhaust systems are characterized by lower energy consumption than individual fume hood systems." A single exhaust fan, with a back-up unit, in an optimized duct system has higher energy efficiency than numerous lower power fans working independently. The addition of any new fume hood would result in only a slight increase in the required energy of the manifolded system versus the energy required to operate a new independent exhaust system. [Neuman, 1987]
The central manifold presents an opportunity to recover the energy value contained in the conditioned air that is being exhausted from the laboratories. There are numerous design and operational challenges and problems with recovering this energy including: corrosion of the devices, added pressure drops for the air moving systems, increased maintenance costs, operational durability in the form of continued beneficial use, and control complexity, to name a few. See Chapter 5, for expanded review of heat recovery systems.
Secondary benefits of the manifolded fume hood exhaust systems can help in the decision to incorporate this design approach. They include:
Fume Hood Manifold Flexibility
Stack Exhaust Checklist