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

[Jon Evans]

In my experience modeling of infiltration has nothing to do with actual infiltration in a constructed building.  How much infiltration results in an actual building is 99.9% construction and 0.1% design and specification.  A well design building to minimize infiltration, with poor attention to details during construction and sloppy workmanship can end up having more infiltration than an average design with a good construction team.

I have looked in many plenums only to see daylight and cold-wintery air flowing into the building, even on LEED projects.

These issues make it very difficult to justify infiltration savings in an energy model.


Jon Evans, PE, LEED AP

Project Engineer | jevans at sustaineng.com



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431 Charmany Drive, Suite 102 | Madison, Wisconsin 53719

608.231.9664 ext. 13 | Fax: 608.231.9665

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________________________________
From: Marcus Sheffer [mailto:sheffer at energyopportunities.com]
Sent: Monday, August 24, 2009 8:22 AM
To: 'Paul Grahovac'; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] Air leakage, LEED, and Appendix G of ASHRAE 90.1

As I understand it the issue is that the 90.1 Standard does not establish a base line condition for air leakage so no savings can be claimed.  I certainly agree that the savings are real and should be counted.  I know that the Appendix G committee has this issue on their extensive "to do" list.

Marcus Sheffer, Chair - USGBC EA TAG
7group


From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Paul Grahovac
Sent: Wednesday, August 19, 2009 7:00 PM
To: bldg-sim at lists.onebuilding.org
Subject: [Bldg-sim] Air leakage, LEED, and Appendix G of ASHRAE 90.1

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<mailto:pgrahovac at prosoco.com>
web site  http://www.prosoco.com/


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