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 6.5.7.2 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