[Bldg-sim] LEED and infiltration

[Leslie Jones]

I think using 0.25 cfm/ft2 is a bit excessive for energy modeling purposes, unless, maybe, you are varying infiltration rate to account for wind & stack effects and the 0.25  is a peak value. (The 0.05 was a  value picked by the energy code Task group after discussions with NRC staff specializing in infiltration & modeling for the sole purpose of demonstrating compliance with the Code)
For the sample office/retail building in EE4, using 0.05 leakage results in an infiltration load that represents around 18% of the net envelope peak heat loss. Ramping it up to 0.25 put the value up to more than 1/2 the envelope load. I don't believe we are building buildings that poorly in Canada.

Since  the value was chosen solely to be used for demonstrating compliance it should not be construed as a design value for load estimation. Note too that in the EE4 compliance model, this rate occurs over all faces of the building which in practice cannot happen, what goes in must come out!

Hope this helps

Les Jones

-----Original Message-----
From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Genest, Frederic
Sent: Wednesday, January 25, 2012 4:46 PM
To: Brian A. Turner; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] LEED and infiltration

Hello Brian.

We ran into a similar case for a project designed to exceed MNECB 1997 (Canadian model energy code).

The answer we got was that, in fact, they had no idea what would be the infiltration rate of a building designed to meet code, basically because usual material testing is done to obtain infiltration rates based on material type, but not on overall assembly and typical construction practices. Thus, they have no way to establish an absolute numeric reference infiltration rate.

Looking at ASHRAE 90.1-2007, I don't see infiltration requirements with better (more specific/detailed) requirements than what we see in MNECB. So I'd expect you'll run into the same limitation.

For information: The energy software used for modeling against MNECN 1997 (EE4/DOE-2) assumes a fixed infiltration rate of 0.05 cfm/ft² of gross outside wall, both for the reference and the proposed building (without being able to assume a different value). OTOH, recent discussions I had with people involved in this field have indicated that the actual typical infiltration rate for commercial buildings is more in the range of 0.25 cfm/ft².

Regards,


Frédéric Genest,

Pageau Morel et associés inc.

ing., M.Sc.A., PA LEED BD+C / Eng., M.A.Sc., LEED AP BD+CASHRAE HBDP Chargé de projet / Project Manager Associé / Associate fgenest at pageaumorel.com

210, boul. Crémazie O., bur. 110
Montréal (Québec) H2P 1C6
T 514.382.5150 (203)
F 514.384.9872
www.pageaumorel.com

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-----Message d'origine-----
De : Brian A. Turner [mailto:bturner at ClarkNexsen.com] Envoyé : 24 janvier 2012 21:52 À : bldg-sim at lists.onebuilding.org Objet : [Bldg-sim] LEED and infiltration

All,

I am working on the design of a project which includes specification of an air barrier in the building envelope and post-construction testing to confirm its performance.  I would like to take credit for this in my energy modeling calculations for LEED EAc1.  I have seen previous discussions on this mailing list about the lack of a baseline number for air leakage in ASHRAE 90.1 Appendix G being an issue.  I am also aware of the fact that performing a precise simulation of infiltration for a building would be complex and take into account wind pressures/directions, building pressurization, massing, etc. etc.  However, page 36 of the Advanced Energy Modeling for LEED Technical Manual appears to reference a scenario in which credit can be taken for reduced infiltration, and there are CIRs that state that such credit can be taken if proper documentation is supplied.  My question is:  has anyone received a favorable review of an energy model that claimed savings due to reduced infiltration as part of LEED project documentation?  If so, what methodology/baseline data was employed?  Any insights would be greatly appreciated.

Thanks in advance,

Brian A. Turner P.E., CEM, LEED AP BD+C
Mechanical Engineer

CLARK NEXSEN
Architecture & Engineering
6160 Kempsville Circle Suite 200A
Norfolk, VA 23502
757.961.7991 Tel.
757.455.5638 Fax
bturner at clarknexsen.com
www.clarknexsen.com
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