Selected Highlights of the Labs21 2007 Annual Conference

VAV Fume Hoods vs. Low-Flow Fume Hood

Victor Neuman, P.E., Precision Environments Group of TAC

Abstract

With the general introduction of low-flow fume hoods over the last five years, a war has been brewing. In many people's minds, the low-flow fume hood could or should push variable air volume (VAV) fume hood controls into obsolescence.

If it comes to war, both VAV fume hood controls and low-flow fume hoods have their advantages.

VAV fume hood controls have been with us for 25 years now and have proven safe and reliable. They increase safety of hood operation.  VAV fume hoods have higher first costs but greater utility cost savings for the more beneficial life cycle costing.

The current generation of low flow fume hoods seem to add a measure of greater safety compared to older hoods.  These hoods have lower first costs than VAV fume hoods but cannot save as much energy when used as constant volume devices.

Instead of seeing this as a two sided war, the better approach is to see these as two choices on your fume hood menu.

Other choices include fume hood sash closers, hood occupancy sensors, and active chemical monitoring to control laboratory air change rates.

The economics and energy cost analysis of the laboratory using fume hoods is dependent on how many fume hoods are installed into each laboratory and how this compares to minimum ventilation rates and heat loads.

Examples are given of some of the options:

  • Base Case: 50 hoods at 1200 cubic feet per minute (cfm) each, $3/cfm per year = $180,000 per year total
  • Low-Flow Hoods: 50 hoods at 720 cfm each at $3/cfm per year = $108,000. Payback: 1.25 years                 
  • VAV hoods: 1200 cfm for 50 hoods for 1,000 hours per year, 600 cfm for 1,000 hours/year, 300 cfm for 6,760 hours /year = $67,000 per year.  Payback: 2.65 years


View this entire presentation in PDF format (159 KB, 30 pp)


Biography

Victor Neuman started specializing in laboratory building design at X-nth (formerly Earl Walls Associates) where he was on design teams for 106 laboratory buildings from 1983 to 1990. Later he served as a laboratory mechanical engineer and principal with GPR Planners. Since 1988, he has served as a co-author of ANSI Z9.5 and has received ASHRAE's Distinguished Service Award.

His particular interests include sustainable laboratories, fume hoods, chemical exhaust fans, and laboratory ventilation controls.

Currently, Victor is with Precision Environments Group of Tour Andover Controls. They are a laboratory and cleanroom specialty contractor doing design/build contracts for owners all over North America and the world.