[Bldg-sim] Air leakage, LEED, and Appendix G of ASHRAE 90.1

[Paul Grahovac]

The National Institute of Standards and Technology (NIST) did an
extensive study documenting a greater than 40% natural gas savings and a
greater than 25% electricity savings across the nation for building
energy consumption if buildings were uniformly constructed with air
barrier systems installed.  They evaluated 116 existing buildings and
computer modeled several different building types.  The purpose of their
study was to provide information to ASHRAE concerning whether it would
be desirable to add an air barrier requirement to ASHRAE 90.1.

 

As a result, I've always thought that Appendix G to ASHRAE 90.1 allows
you to change the air leakage rate off the default and onto a rate
corresponding to an air barrier installation, so that you could claim
LEED points for the corresponding energy savings.  However, an architect
at a presentation I did said you could not do that under the LEED and
ASHRAE requirements.  (I know the models will do it, because I've done
it on the TRANE model and obtained results that support the NIST
findings.)

 

I see in Appendix G that:  "G3.1.2.5. Ventilation.  Minimum outdoor air
ventilation rates shall be the same for the proposed and baseline
building designs."  However, I searched the document for "outdoor air
ventilation" and the phrase occurs only in the context of mechanical
systems that are designed to intentionally bring air into the building.
If this section is the basis for concluding that air leakage barriers
should be left out of the modeling, then I have trouble understanding
why.

 

Appendix G says that all components of the building are to be modeled as
designed.  That would preclude modeling as if an air barrier system did
not exist in the design.  It says the baseline building model is to have
steel-framed above-grade walls, and it is silent about the design
building, but the User's Manual says that if the design building walls
are block or cast concrete, then "the mass is credited in the building
performance rating method."  Likewise, if the walls are wood stud
instead of steel, then the Manual says credit is given for the superior
energy performance of wood frame versus steel frame.  The User's Manual
states that it:  "Offers information on the intent and application of
Standard 90.1."  Given these examples in the Manual based on existing
thermal mass energy-saving data and wood-versus-steel stud energy data,
it is difficult to conclude that a wall that is constructed with
materials meeting the air leakage limits and installation requirements
of the Air Barrier Association of America and determined to produce
significant energy savings by the NIST study based on those same limits
and requirements should be modeled as if it leaked air like a building
without an air barrier. 

 

Please let me know what you think, and if you know of any reason why it
is not proper to change the air leakage rate through the building
envelope in the design model to show the benefit of air barriers.

 

Thanks,

 

Paul Grahovac, LEED AP

R-GUARD Air & Water-Resistive Barrier Product Manager

PROSOCO, Inc.

3741 Greenway Circle

Lawrence, Kansas  66046

(785) 830-7355

(888) 376-3417 fax

pgrahovac at prosoco.com

web site  http://www.prosoco.com/

 

 

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