Fine EE folks,

I've got to go the ALTERNATIVE COMPLIANCE PATH for ASHRAE 62.2, and I need help with the NATURAL INFILTRATION CREDIT.  Either ...

  • Tables where these have been worked out for different "n-factor" locations.
  • a calculation or formula for how to derive these myself.

Please see the attachment for an example.  And yes, I've reached out to the Energy Trust in Ore. about this.  No response so far.

TIA!

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No attachment? What version of 62.2?

With that said, I don't much care for the credit - size to recommended & then tune it down with timers as much is overkill

http://thehtrc.com/2014/aci-great-ventilation-debate

Hey Sean, the 2007 version.  Example below.  

If you have thoughts on where tables like these might reside, or how I can calculate & create these myself, I'm totally game.

Thank you!

Melissa, there's a lot wrapped up in your question.

Is Energy Trust of Oregon somehow involved in your project? The reason I ask is because the table you posted would only be valid for the specific version of 62.2 that it was designed for (which should have been disclosed in the footnotes if not on the table itself). In particular, the way the infiltration credit is handled in 62.2 completely changed between 2010 and 2013. Then in 2016 it changed again.

That table is simply a shortcut for converting CFM50 to ACH-nat based on an assumed n-factor (and an unspecified average ceiling height, since ACH is based on volume.)  You can do the same thing more accurately with energy modeling software, which instead uses the Sherman-Grimsrud formula to convert from ACH50 to ACH-nat. The S-G formula involves several steps and thus is best done in software. For example, REM and Right-J will take your CFM50 input and convert that to ACH-nat or CFM-nat. No one should be using n-factors any longer!

Once you convert the blower door result to CFM-nat (infiltration), the credit under 62.2 depends on which version you're dealing with. For example, in 2010, the formula "7.5 CFM per occupant (# bedrooms + 1) + 1% of floor area" assumes a baseline infiltration credit of 2% of floor area, so you can only take infiltration credit to the extent that the blower door result (as CFM-nat) exceeds the 2% baseline. In 2013, the baseline credit was removed and the floor area component increased to 3%, so the infiltration credit is no longer optional, lest you end up over-ventilating with respect to what the standard requires.

NOTE: Residential Energy Dynamics website (http://www.residentialenergydynamics.com/) provides handy 50-Pascal-to-natural conversion tools for all versions of ASHRAE-62.2 since 2010.

Lastly, what exactly did you mean by 'alternative compliance path?

UPDATE: I just saw your update that you're working with ASHRAE 62.2-2007. Wow! To my knowledge, the residential i-codes didn't even require whole-house ventilation when that version of 62.2 was in effect! So it doesn't seem logical that any code currently in effect would refer back to that version of 62.2.

Also, I'm not sure if the 2007 version allowed for an infiltration credit. But I don't have a copy so perhaps someone else will chime in who can clarify how 2007 dealt with the infiltration credit.

Thanks, Dave.  You're always a source for nuanced answers.  

Yes, 2007.  It's a legacy version of LEED, and that's the referenced ASHRAE standard.  I think I got what I need from Energy Trust.  They're not my client, but they've been helpful in snapping the pieces together with this.  

FYI - They turned me onto the Wayback Time Machine - a Google archive with billions of old web pages that've ever been launched.  Just Google it.

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