[Equest-users] Basic stuff - Infiltration

[Nick Caton]

Hi John - thanks for your thoughts!

 

I was relating some of the same concerns with others off-list ... I'm am
no infiltration-auditing expert (though some lurk among us here on the
lists ^_~), but one thing I can say based on my past attempts to build a
better mousetrap regarding infiltration is that where ASHRAE may be
generally vague on the topic - they are actually doing a lot to say (if
not always directly) that whole building infiltration is a very
difficult thing to quantify at best (sorry for excessive use of
parentheticals (I mean it!)...).

 

The best guidance imaginable that would still be practical in day-to-day
use would have to rely in some part on subjective observations (guesses)
regarding envelope constructions.  Two brick walls of certain
grout/masonry ratios weathered for the same period in the same climate
may still have different leakiness because the two masons used slightly
different grout mixes...  What I'm getting at is you couldn't
realistically construct a table that covered every variable, and many
variables are not "knowable." 

 

That's not to say the residential ACH table isn't useful for subjective
estimations, nor that research couldn't be undertaken to raise the bar a
notch.  As John is alluding, a table providing representative commercial
envelope constructions (with accompanying illustrations!) and/or layer
combinations could be undertaken that would provide infiltration
performance as a function of time.  Values could be given for new
construction, and after weathering for 1/5/10 years.  While new
constructions/layers could be assessed in a controlled environment,
initial research on aged constructions would need to be done sampling
within a single climate zone.  Separate/concurrent research could
explore determining multipliers on the weathering effects based on
varying climate and geography...  All things being equal, a beachside
wall built in Miami, FL with lots of sun/salt/torrential rain seasons
and the occasional hurricane will weather differently over a decade than
the same wall in a milder climate.  The net result of such research
could ultimately produce some really helpful tools in better assessing
existing and new constructions for a variety of industries and purposes
(energy modeling included).

 

Considering the growing presence and pressing need for better tools in
the world of energy modeling, I would put forward prime candidates for
whole construction assemblies would be ASHRAE 90.1 baseline
constructions as defined in Appendix A.  

 

For all I know, such research may be underway or completed years ago -
my ear is not quite so close to the ground with the academic world...
can anyone comment?

 

 

To another point you brought up - eQuest is quite capable of using your
personally developed CFM/ft2 values - in the wizards even!  In detailed
mode you'll find there are inputs for more involved estimations as well
if you wish to pursue other methods:

 

 

 

 

 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com 

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of John
Bixler
Sent: Wednesday, August 10, 2011 9:23 AM
To: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Basic stuff - Infiltration

 

My own personal opinion is that ASHRAE Fundamentals has not rescued us
here.

 

As Nick mentioned, the data presented there is for residential houses
and relies on incredibly vague and subjective judgment calls by the
modeler. 

 

Furthermore, the values presented are in the unit's of air changes per
hour.  To me, this is a terrible way to use the data.  Your entries for
infiltration then rely on the volume of the room to determine the amount
of infiltration.  The volume of the room (zone is probably a better
term) has NOTHING to do with the infiltration.  What if I have a gym
that's 150'x100'x50' tall, but it only has 10' wide by 50' tall of
exterior wall???  If I use the ASHRAE method and rely on air changes per
hour, the zone will be modeled with a HUGE GIGANTIC REALLY REALLY LARGE
amount of infiltration.  

 

Yet this seems to be the only recourse we have that is grounded in any
sort of defendable data.

 

I have looked and looked for a reliable report or other source for real
world commercial/institutional construction infiltration values to no
avail.  It would be so incredibly useful.

 

I have, over the course of my energy modeling career, developed a set of
seemingly practical infiltration values to use, using the units of "CFM
per sq ft of gross external wall area" available in Trane Trace (I don't
believe these units are an option in eQuest).  These values were
developed by taking a number of buildings with no infiltration and
arbitrarily adding infiltration in, until I get a reasonable utility
consumption value.  Hardly scientific and no way could I defend these
values if they came under scrutiny, other than to say "well, you got a
better idea????"

 

Some may say "Eh, who cares about infiltration anyway?".  Well, it makes
a bigger difference then you'd think.  

 

A novice user who relies on the ASHRAE air changes per hour is likely
significantly oversizing their cooling equipment in large rooms (ie
conference, assembly, gyms, etc) which is exactly where you don't want
to be oversizing cooling equipment.  

 

Think about the components of a heating load - envelope conduction
losses, taking in cold OA...and infiltration.  Envelope losses are
generally small, the design community likes to temper their OA
(rightfully so), so where is a major component of the heating
(consumption) load coming from?  Infiltration really adds up.  

 

How do you justify replacing leaky, wood sash windows?  How bout making
a switch to spray foam insulation?  How about modeling door seals?  

 

I've rambled enough.  Point being, we all are forced to use arbitrary
numbers for something that is a significant component of both equipment
sizing and energy modeling and it just makes me mad and embarrassed when
I have to explain to a client or colleague "well those are really
important, but completely imaginary, numbers..."

 

From: equest-users-bounces at lists.onebuilding.org
[mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bruce
Easterbrook
Sent: Tuesday, August 09, 2011 5:41 PM
To: John Bixler
Subject: Re: [Equest-users] Basic stuff - Infiltration

 

Since 1922!
Bruce Easterbrook P.Eng.
Abode Engineering
ASHRAE Member

On 09/08/2011 06:11 PM, lawrence Lile wrote: 

Good ol ASHRAE Fundamentals!  Why didn't I think of looking there?
Thanks!   

 

 

On Mon, Aug 8, 2011 at 11:36 AM, Nick Caton <ncaton at smithboucher.com>
wrote:

Hi Lawrence,

 

My copy of ASHRAE Principles of HVAC includes a table (5-1) excerpted
from ASHRAE Fundamentals, 2001 (Table 7, Ch 28).  This table provides
air change rates as a function of subjective envelope airtightness
("tight" / "medium" / "loose") and as a function of the outdoor design
temperature.  Upon reviewing the referenced Fundamentals chapter, I
learned this table is built from research surveying residential homes of
various vintages, so it helps to know that these are "tight" to "loose"
residential constructions.  

 

In any case, I've used and cited this resource before when modeling
infiltration and calculating sizing loads for non-residential projects
as well.  I've searched, but have yet to come up with an equivalent
table based on surveying and measuring commercial constructions from a
subjective/objective standpoint... That might be handier, but in the
meantime this is a good tool for "converting" your subjective
observations into the right ballpark.  

 

~Nick

 



 

NICK CATON, P.E.

SENIOR ENGINEER

 

Smith & Boucher Engineers

25501 west valley parkway, suite 200

olathe, ks 66061

direct 913.344.0036

fax 913.345.0617

www.smithboucher.com <http://www.smithboucher.com>  

 

From: equest-users-bounces at lists.onebuilding.org [mailto:
equest-users-bounces at lists.onebuilding.org] On Behalf Of lawrence Lile
Sent: Sunday, August 07, 2011 12:50 PM


To: equest-users at lists.onebuilding.org

Subject: [Equest-users] Basic stuff - Infiltration

 

In building modeling programs one always has to provide precise values
for infiltration.  In the real world, I will know one of two things:
almost nothing (The building appears to be kinda leaky with old
windows), or I will have a blower door test done at a specific pressure.
How do I convert subjective ("kinda leaky") or objective (Blower door
test) leakage into numbers that make sense in the program?  Is there a
guide one can use?  

 

 

--Lawrence

 





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