Lab Core&Shell Modeling

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We are working on a laboratory building that will be pursuing LEED Core &
Shell. We are trying to confirm the modeling requirements for heat recovery
and laboratory supply airflow control. It appears that these two questions
are interrelated.

Based on Appendix G section 3.1.2.10, it appears that if we model heat
recovery in the proposed case, we will need to model it in the base building
also. (Note the building is in climate zone 5a) Can anyone please confirm
that lab heat recovery can not be counted as savings? It is my
understanding that this supersedes Section 6.5.6.1 discussion of energy
recovery, is this correct?

The core air handling units design supply and exhaust rates are based on 2.0
cfm/sf. The design team expects that the lab supply and exhaust will be
VAV, but since this is a Core & Shell design the minimum required flow rates
are unknown. Also, the potential for resetting air flow rates during
unoccupied hours is unknown. It is my understanding that baseline and
proposed models will need to assume the same supply and exhaust rates, but
is not clear what those flows should be. According to Section 6.5.7.2,
buildings with fume hood exhaust rates greater than 15,000 cfm (the building
under consideration) shall include at least one of the following:

(a) VAV Exhaust and Supply capable of minimum flows of 50% or less of
design.

(b) Will not be met...

(c) Heat recovery

What minimum supply and exhaust flow rates do we need to assume? Do we
assume that the flows are constant (24/7) at the design values? Or, do we
follow item A listed above?

Any insight into lab Core & Shell makeup/exhaust flow and/or heat recovery
modeling requirement is appreciated.

Thanks,

Mickey Bush

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Mickey -

I am not too dialed into the LEED issues you reference. Much of lab design is not really addressed by LEED. The folks at Labs21 are working on that.

Addressing the air flow though, here are the issues.

1) Each lab space must maintain, at a minimum, the owner's specified Air Change per Hour rate. The owner can select his own value, but Labs21 folks are suggesting 6 ACH in the absence of any compelling reason to do otherwise.

2) Chemical fume hoods must, at a minimum, exhaust 25 CFM per square foot of fume hood work surface. If you are using VAV, you will most likely be controlling the hood's face velocity to 100 lineal feet per minute once the minimum is reached.

3) VAV systems do a great job of minimizing the exhaust volume when the sashes are closed, but rely on the users to do so. As a rule, they aren't that good at keeping the hoods closed. You might look at the New Tech Automatic Sash Positioning System to accomplish that. (www.newtechtm.com) With ASPS installed, the exhaust volumes should be much less than 50% of max.

By the way, since you will be reducing the demand on the supply and exhaust system, you can also reduce the size of your heating and cooling equipment, and supply and exhaust fans and some of the ductwork.

I hope this is helpful.

David Sweitzer

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