Infiltration Schedule

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Howdy Bldg Sim peers!

While working on LEED Equest simulations I find that in an effort to simplify I end up deleting the P-Inf and C-Inf Infiltration Schedules all of the time and end just use "undefined" to simulate a constant infiltration rate. I was curious to know if anyone uses the actual Infiltrations schedules, to emulate winds and or building pressurization, and if so do you typically achieve more energy savings, and do you find it worth the extra effort?

Thanks all and be well.

Joshua W. Talbert P.E., LEED-AP

vt_powskier's picture
Joined: 2011-09-30
Reputation: 1

Hi all:

We do building envelope consulting and are very curious as to what folks do
and what rates they use whatever approach. When looking at buildings we
find that most infiltrate much more in the real world than designers
estimate and that the fluctuations are far greater than predicted. We would
also love it if anyone has any experiences which can be shared.


Andy Hoover

Andy hoover's picture
Joined: 2011-10-02
Reputation: 0

JRR wrote;

I won an ASME regional design contest prize with my Solar House
design, a graduating
semester design project. It was later fully detailed and built in
1986. We moved in Jan
1987. It is basically a LEED Platinum building, one story with
finished basement, 2x6
studs 24 OC upstairs with 1" XPS sheathing, brick vernier 100%, etc.

The main surprises vis a vis air infiltration were / are

1) The porosity of the above grade basement CMUs allowing air
2) The top or finish course of CMUs was not always sealed from an
air infiltration
point of view and many of these CMU cores were hidden behind
finish dry wall
for years.
3)The air return duct through the attic even though sealed with
metal tape and covered
with R-25 batts was not sealed to the attic penetration / wood
surround for years.
4) One bathroom had an outside wall stud space with no insulation at
all - it contained
the plumbing vent stack. The framing crew and insulation crews
thought we were
'over insulated' and just didn't need it.
5) None of the plumbing stacks were sealed at the attic penetration
on the outside
by the work crews.
6) The Active Solar plumbing penetrations were not sealed at the
attic penetration
by the work crews.
7) Rodentia bent the clothes dryer outside vent flap so severely
that it would not close
completely on its own, but we never had mice enter the house via
this access.
8) Conventional plumbing stack boots, black rubber, were utterly
destroyed by the
heat from the Active Solar pipes. We made silicon rubber fittings
to replace them.
We run an oversquare ( more sq ft collector than gal of tankage )
system with 6/12
slope 20 degrees W of S at ~ 38:45 N. We use the active system
for more than
domestic hot water. Since we sabotaged the evil tempering valve =-O
we have all metal bodied valves through out the house and a
stainless steel tub on the
9) None of these problems was detected by a military grade IR video
shot from outside
the house in freezing cold weather. IR shot inside the attic was
extremely revealing.
10) Leak testing has to be done during windy weather -- the leaks
act in concert., and
CFD considerations show that differing pressures exist at
specific locations.

Our all electric bill for 4500 sq ft this last December was $72.00

We are developing a new version of this house with architectural as well
as energy improvements.

John R Ross III PE

JRR's picture
Joined: 2011-10-01
Reputation: 0

I tend to model an air exchange rate of 0.15 ACH in perimeter spaces during
unoccupied hours (e.g. outside air fans are off with dampers closed) for new
buildings (even if they have air barriers). Vestibules, conditioned loading
docks, etc usually get higher air change rates. Zones with no exterior
exposure should not be modeled as having any infiltration since there is not
a way for air at outside conditions to make it to these zones. I assume no
infiltration into plenum zones.

I am curious to know whether or not this seems reasonable based on real
world experience. Andy, any thoughts?



Eric Studer's picture
Joined: 2011-09-30
Reputation: 200

Dear Andy and Eric,

My past experience with industrial buildings (manufacturing, assembly,
warehouses, etc) indicates that a good building has an AVERAGE winter AC/hr
of ~0.2. Poor buildings are on the order of 0.5 (or more!)

This doesn't address residences (which often have much higher infiltration
rates) offices or high rises, but it may be helpful. Most of the literature
I'm familiar with indicates that infiltration is normally a lot higher than
is generally assumed. My experience confirms that.

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

James V. Dirkes II  P.E.'s picture
Joined: 2011-10-02
Reputation: 0

Is the 0.2 to 0.5 ACH based on blower door testing? Did you apply some
sort of conversion to get from the blower door pressure differential to
a typical real world pressure?

Doug Maddox

Doug Maddox's picture
Joined: 2011-09-30
Reputation: 0

You don't really do blower door testing on 100,000 - 1,000,000 sq.ft factory
buildings, however we did something that was roughly equivalent. My
company's air handler product normally used a control loop that monitored
differential pressure between the building and the outdoors, and then
controlled the outdoor air amount to maintain a slight (0.01") positive
pressure. Since the controls were very often digital and we could obtain
data from the AHU performance, we knew what the outdoor air control was
doing over the course of a day, or weeks, or months.

new projects.

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

James V. Dirkes II  P.E.'s picture
Joined: 2011-10-02
Reputation: 0

Hey folks:

We have done similar things to control outside air and create positive
pressure then look at the losses in a variety of ways and have seen reports
of work done by various labs and even reports on whole buildings with the
giant tractor trailer blower unit. They always see much much higher than
predicted/designed infiltration and higher energy cost/comfort issues but
not always significantly (5% is significant to me but not to all) higher
cost in heavy cooling areas due to what seems to be both the infiltration
that occurs when the conditioned air is cooler/less humid on the interior
and the comparatively low cost to cool.

We have very limited experience in industrial but in office, commercial,
retail, and similar have seen from James numbers (his range is mostly the
low end we have seen) to 5 times them and even more. The numbers tend to
go completely crazy when we have tried to look at real world effects and
apply parameters such as actual in use conditions for office, commercial or
retail buildings. We have never seen an existing building that was at the
'design parameters'. I am not saying that as a negative toward anyone who
did or does design nor about the assumptions in the models but am saying
that it needs to be looked at as we need to end up saving most of our
energy, carbon, cost, whatever all you care about through work on existing
structures. We can not build our way to enough savings of any type
particularly in a 10 to 30 year horizon.

I would not presume no infiltration at plenums (2 years after a building is
up seal up an area, pressurize it and see what you get) and would assume
significant infiltration at penthouses, elevator rooms, and so on.

Eric, my thought would be that if you are going to apply a number across the
board, so to speak, you may want to go to .20 bare minimum and I would
suggest .25. My bet is James does a lot of .4 to .5 in design work with
very tight structures.

We have not yet done anything specifically following the letter of the newer
large building standards/suggestions for testing from ASTM/ASHRAE et al.


Andy Hoover

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Joined: 2011-10-02
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Jesse Thompson's picture
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