Fumehoods and LEED

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I'm wrestling with an energy model for a lab building and have a quick question about fumehood exhaust.

ASHRAE 90.1 says the following about fume hood exhaust Fume Hoods. Buildings with fume hood systems
having a total exhaust rate greater than 15,000 cfm shall
include at least one of the following features:
(a) Variable air volume hood exhaust and room supply systems
capable of reducing exhaust and makeup air volume
to 50% or less of design values.
(b) Direct makeup (auxiliary) air supply equal to at least 75%
of the exhaust rate, heated no warmer than 2?F below
room setpoint, cooled to no cooler than 3?F above room
setpoint, no humidification added, and no simultaneous
heating and cooling used for dehumidification control.
(c) Heat recovery systems to precondition makeup air from
fume hood exhaust in accordance with (Exhaust
Air Energy Recovery) without using any exception.

My question is this:

If the lab is equipped with snorkels, does this count towards this calculation, or is this strictly for fumehoods? (My guess is the term "fume hood systems" includes snorkels.

My other question is this:

We are currently doing heat recovery (so we have criterion (c) covered). If we are using constant volume hoods with off peak hour setback, can we take credit for that, or do we need to reflect that in both the base model and the designed building? In reality since this is a teaching lab the hoods will be open most of the time, and the difference in performance with a VAV fumehood and a CAV hood with setback would be nonexistent.

Vikram Sami, LEED AP

Vikram Sami's picture
Joined: 2011-09-30
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My take is that you need to model the base using item c. That is heat recovery with thew fume. Hood exhaust as per

If your new building will have constant volume hoods, with 5O percent set back during unoccupied periods, thanb that is what you have to model. See if you can drop thje set back to 30 to 40 percent(provided the min air changes for the lab is maintained during the unoccupied hrs.

If the snorkels are on, then you should include them

Elmes, Wilmouth's picture
Joined: 2011-10-02
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