LEED/Appendix G - Laboratory Question

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Hi all,

I have a question related to modeling a laboratory building via Appendix G methodology for LEED 2009. I have an inclination as to the answer based on my experience using Appendix G, but I'm looking to cite the specific section(s)/argument as to whether or not the following would be allowed:

It is common practice for lab buildings to utilize one mechanical system type throughout the building to maintain flexibility for conversion of spaces between offices and labs and vice versa. These buildings therefore rely on a 100% exhaust system in all spaces no matter the function. Our building's proposed design makes a conscientious energy efficiency decision to reduce exhaust air and associated makeup by installing a second mechanical system (not 100% exhaust) type to serve these office areas. This design decision also comes with additional first costs (another mechanical system), and hence should be considered an energy efficiency strategy of the proposed building.

Is it allowed for the baseline and proposed energy models to consider different exhaust requirements for the systems serving the office areas, the baseline's requiring a 100% exhaust system, while the proposed building's does not?

There may be other more relevant sections to coming up with a correction interpretation on this, but so far, I've noted that 90.1-2007 Section provides an exception for energy recovery for a. VAV hood exhaust and room supply systems capable of reducing exhaust and makeup air volume to 50% or less of design values. This to me suggests and confirms that the base system would be one that is a 100% exhaust type.

I am very interested to know if anyone has direct experience applying this same/similar logic in LEED models, or has learned of an interpretation that is acceptable by ASHRAE & LEED.

Joe Chappell PE

Joe Chappell3's picture
Joined: 2015-04-14
Reputation: 0


I have always modeled lab spaces with a separate system for the baseline
design according to section G3.1.1 ( exception c or d). In this case lab
spaces will have a separate system than the rest of the building (office
spaces). The ventilation rate shall be the same in both cases (G3.1.2.5)
until additional controls are provided for the proposed design (CO sensors,
DCV ventilation, or any specific controls that are not described in section
6 of the ASHRAE 90.1).
The baseline design shall be modeled meeting all mandatory and prescriptive
options of section 6. If 90.1-2007 Section provides an exception
for energy recovery, then it should be modeled in the Baseline Design too.
If you provide more energy efficiency controls that are not described in
section 6 and appendix G, then you can take a credit for the Proposed
Design. For example you reduce air to 75% or 100% during unoccupied hours ,
but in the baseline design you reduce it only to 50% as G 3.1.1 exception d
says or section

I hope my understanding helps you. But I would like to know other opinions
too, and if it is any exceptional cases are possible.


*Genia Gorbachinsky, LEED GA*

Energy Engineering Specialist


Kroz's picture
Joined: 2010-10-05
Reputation: 0

I agree with Genia - you should probably model a separate air handler for offices and Labs (in the baseline).

Another strategy sometimes used in Lab buildings is to cascade the airflow from the offices to the labs. Generally the ventilation requirements for Labs are exhaust based (if you need 10 air changes - that's saying you need to exhaust 10 air changes). Your supply can be a combination of fresh air and makeup air from the offices. This will actually reduce the overall outside air used (more than 2 separate air handlers) - your total fresh air intake = lab exhaust, whereas in the two air handler situation your total fresh air intake = lab exhaust+ ventilation requirements for the office.

Vikram Sami
Associate Partner


vsami's picture
Joined: 2013-05-31
Reputation: 1