When we were building our facility we explored the low flow hoods as well. Labconco allowed us to visit their testing facility and performed the ASHRAE tests on a hood that they let me clutter up. There were no abnormalities and the hoods are really well designed. They even allowed us to test their hoods below minimum specifications because I asked and I liked the results, but can't go into the details because it was non-standard. The primary issue with the Labconco Xstream hoods is their depth. They are approximately 40 inches deep versus the 36 inches of a normal hood. We had the space so this was not an issue. If you have a small room those 4 inches might become an issue.

We did look at the other models and the reason for selecting Labconco came down to the simplicity. The air flow has to go down before it goes up and that is why they need the extra space. They accomplish this by having a solid baffle with a gap on the bench top that you don't see behind the top to bottom slotted front baffle. This creates a laminar flow straight back. We liked this design because you don't have to worry about the moving parts on adjustable baffles being clogged up over the years and stop moving 5 or 10 years down the road. I would recommend having the sales reps for all of your design considerations come out and meet with you and then go tour the company/s before you make your final choice. We were only purchasing 15 hoods, but all companies under consideration treated us well and did a good job at describing why they designed their hoods. Regardless of your final choice I highly recommend a low-flow hood because the energy savings is tremendous. The estimated pay-back in reduced heating and cooling bills for our facility is 16 months.

Dennis

Dennis R. Compton, Ph.D
Director of Chemistry
Obiter Research, LLC
2809 Gemini Ct
Champaign, IL 61822
Phone (217) 359-1626
dennis.compton**At_Symbol_Here**obires.com


-----Original Message-----
From: DCHAS-L Discussion List [mailto:DCHAS-L**At_Symbol_Here**LIST.UVM.EDU] On Behalf Of Ralph Stuart
Sent: Thursday, January 17, 2008 7:03 AM
To: DCHAS-L**At_Symbol_Here**LIST.UVM.EDU
Subject: [DCHAS-L] Low flow hood selection

We have several lab design or renovation projects concurrently
underway. All of the engineers and project managers involved are
interested in the use of low flow fume hoods (i.e. face velocity of
around 60 feet per minute) to help support their LEED ratings and are
asking our advice about 1) whether such hoods are acceptable to the
institution and 2) which model is best.

The first question is relatively easy to answer; if they perform in
the ASHRAE containment test similarly to traditional hoods, then they
are ok. Either type of hood requires significant user education for
them to be used effectively.

The second question is proving more challenging because of the short
history of the low flow installations we've been able to identify.
We've found three models which seem to operate on different design
strategies:
- Air Sentry hoods use automatically adjusting baffles at the rear of
the hood and an aerodynamically designed hood entrance to protect the
containment vortex as cross-drafts, etc. threaten to disrupt it.
- Labconco Xtreme hoods use perforated back baffles to avoid the
development of the vortex and maintain laminar flow through the hood
- Hamilton Fisher Concept hoods appear to rely on well crafted hood
entrances to maintain containment at 60 fpm
I have talked about the Air Sentry hoods with colleagues who've had
them in place for three years and who report no unusual problems with
them.

I wonder if other people have evaluated these various options and
decided that one design approach was preferable to the others from the
users' point of view. My primary interest is maintaining some level of
uniformity on campus, since our hood users travel randomly from
building to building and we already have significant confusion on
campus as to the different operating procedures for different hoods
because of motion detector protocols, high low switches, etc.

Thanks for any help on this question (which I know other campuses are
asking as well).

- Ralph

Ralph Stuart, CIH
Environmental Safety Manager
University of Vermont
Environmental Safety Facility
667 Spear St. Burlington, VT  05405

rstuart**At_Symbol_Here**uvm.edu
fax: (802)656-8682

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