Infiltration

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Hello,

While performing energy modeling, I am guessing it is enough if we account
infiltration just for the zones in contact with the exterior environment? Am
I right?
Or do we have to include interior zones in infiltration calc?

Thank you.

Regards,
Vinay

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That's typical in my experience.

Infiltration is figured primarily based on temperature and pressure
differential (wind speed vs.interior pressurization) across an exterior
surface, among other things. Lacking any exterior surfaces, I would
presume any "interior cross-zonal infiltration" is generally negligible,
unless you might be dealing with a large positively pressurized
unconditioned space...?

NICK CATON, E.I.T.

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Vinay et. al:

Understanding and Estimating Large Building Infiltration.... One of those
'Defense of the Dark Arts' courses at Hogwarts!

Reminds me of a quote from Donald Rumsfield: "... because as we know, there
are known knowns; there are things we know we know. We also know there are
known unknowns, that is to say we know there are some things we do not know.
But there are also unknown unknowns - the ones we don't know we don't know"

Chew on that one for awhile...

If there was such a course, I'd recommend the attached pdf be in the list of
required reading.. If nothing else it's a gold mine refererence for
explaining to your client why 'measuring' infiltration rates in his/her
building, while theoetically possible, it most likely would require an
ENORMOUS amount of cash and airflow to generate a meaningful "reference
pressure". This document is "solid" on the fundamentals.

So, if you want to do it 'right' - this pdf will help you correctly specify
a infiltration measurement test procedure to be performed by a qualified
'Testing Agency. I'd bring several bags of cash with me.

The fallback here that many of us may find useful are the 'standards' tables
on pages 5, 6, and 7. If you don't measure, you will have to estimate, and
atleast these 'standards' will give you a sense of how 'non-standard' your
final estimate is.. We have to work with what we have..

ASHRAE's RP-935: "Protocol for Field Testing of Tall Buildings to Determine
Envelope Air Leakage Rate" - (Available free to ASHRAE members through the
ASHRAE bookstore) is another good reference to get familiar with possible
methods for better understanding the "known unknowns".... As for the
"unknown unknowns" - thank god for ASHRAE research.

All the Best,

Chris Balbach, PE, CEM BEMP, CMVP

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Amen to that!

Stated another way, almost anyone who thinks they know (with any precision)
the infiltration rate of any building is misinformed.

Thanks, Chris, for the references. I was unfamiliar with them, probably due
to giving up hope for any accurate way to estimate infiltration long ago.

That said, more effort is being spent on understanding and reducing
infiltration in recent years and, while the estimation of infiltration may
not improve, the construction practices which allow infiltration may very
well improve as a result!

James V. Dirkes II, P.E., LEED AP

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There is active research in this area: ASHRAE RP 1478 Measuring Air-tightness of Mid- and High-Rise Non-residential Buildings. This project is focussing on buildings constructed after 2000.

When complete this will go some way to providing data to some of the unknowns...

Dr. Iain Macdonald, Ph.D.

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+++ James V Dirkes II, PE [2010-07-02 09:47 -0400]:

Do you not feel that door blower tests on small, airtight domestic
buildings, as required for passivhaus certification, are not
reasonably accurate?

I quite agree that for large or very leaky buildings there is a real
problem, but I don't agree that there is no such thing as
sufficiently-accurate testing, and the passivehaus people are nothing
if not careful and rigorous about the science.

Wookey

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Dear Wookey,

A blower door test is probably the best way to get a good idea of
infiltration / leakage. It is, however, an extrapolation of a VERY limited
test. If you limit your test buildings to small and "airtight" (i.e.,
constructed purposefully by a knowledgeable contractor to be tight) and the
HVAC system does not affect the building pressure, the blower door probably
does a good job. I was thinking of a much broader type of building.

James V. Dirkes II, P.E., LEED AP

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