eQUEST infiltration rate

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Hello all,

Does anyone remember where in ASHRAE is referenced the default value for infiltration (0.38 cfm/ft2) that eQUEST uses?
I can't seem to trace it back, yet I'm pretty sure it comes from ASHRAE.

Thank you,

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Patrick Lapierre_ing. BEMP, Charg? de projets
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Patrick Lapierre's picture
Joined: 2015-01-28
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Is that the default the wizard uses? I believe it?s been 0.4 cfm/ft2 (@ 0.3 in. of water) for the past few cycles of 90.1 at least (Section 5.4.3).

Regards,

Phil Jordan

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I believe that value ? though I believe it to be 0.038 cfm/ft? of gross exterior wall area -- goes all the way back to 90.1-1989:

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Brian Fountain
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d 416 572 8501 m 416 562 6831

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Thank you Brian, exactly what I was looking for!

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Patrick Lapierre_ing. BEMP, Charg? de projets
D?veloppement durable et Efficacit? ?nerg?tique
plapierre at bpa.ca | t: 5143833747x2807

De : Brian Fountain
Envoy? : 26 octobre 2020 12:46
? : Lapierre, Patrick
Cc : equest-users at lists.onebuilding.org
Objet : RE: eQUEST infiltration rate

I believe that value ? though I believe it to be 0.038 cfm/ft? of gross exterior wall area -- goes all the way back to 90.1-1989:

[cid:image002.png at 01D6AB9E.DCFC19E0]

Footprint

Brian Fountain
Associate
d 416 572 8501 m 416 562 6831

Patrick Lapierre's picture
Joined: 2015-01-28
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The 0.038 cfm/ft2 is the Wizard Default. We typically override it to a higher value, but not to 0.4 cfm/sf. That?s at a pressure well above typical building pressurization. We?ve used 0.04 and 0.05 in the past with no questions asked. ASHRAE 90.1-2016 G3.1.1.4 has defined a method to determine the infiltration rate.

Thanks,
DARIC ADAIR PE, CEM, BEMP
Mechanical Engineer, Energy Analyst

HENDERSON ENGINEERS
daric.adair at hendersonengineers.com

LICENSED IN KS

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I have been applying the ASHRAE 0.4 cfm/ft2 air leakage as follows, with a formula for AIR-CHANGES/HR and an alternate infiltration schedule.

The methodology in 90.1 Appendix G applies a multiplier of 0.112, giving 0.0448 cfm/ft2 (halfway between the 0.04 and 0.05 that Daric has been using). However, while the default infiltration in eQUEST is applied to above-ground exterior walls only, 90.1 applies it to the whole building envelope, ?including the lowest floor, any below-grade walls or above-grade walls, and roof?. So you end up with a larger value for calculated infiltration cfm, which you then apply as air changes/hour in eQUEST. (You could also apply it as cfm per floor area as INF-FLOW/AREA, but AIR-CHANGES/HR should be preferred because it has a correction for wind speed relative to the ASHRAE-referenced 10 mph.)

Additionally, there is some guidance from PNNL-18898 Infiltration Modeling Guidelines to use an infiltration schedule fraction of 1.0 when HVAC systems are off and 0.25 when HVAC systems are in operation. This differs from the default eQUEST infiltration schedule. (Special thanks to Maria Karpman of Karpman Consulting for sharing this guidance.)

The Appendix G methodology can be applied using an INF-METHOD of AIR-CHANGE and the following expression for AIR-CHANGES/HR, where the values for area and volume will vary per model, and the air leakage rate is defined using a parameter with a value of 0.4 or some other value for a parametric run:

/* Based on 90.1 G3.1.1.4 method with
46134 pressure boundary area, LV-D Building Window+Wall
and V=356358 building total volume, LV-B.
Air leakage is 0.4 cfm/ft2 per Table G3.1 or
0.08 cfm/ft2 per PHIUS. */
switch (#SV(#L("INF-METHOD")))
case 0 : unused
case 1 : 0.112*#PA("Air Leakage")*46134*60/356358
case 2 : unused
case 3 : unused
case 4 : unused
default : unused
endswitch

~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP
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Bill Bishop's picture
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I am not as read up on this matter as I have been in years past*, but I think an important thing to consider here is that 90.1 is prescribes envelope leakage corresponding to pressures typical of blower door tests, which in turn reflect pressures corresponding to rather extreme weather (wind velocity) conditions. Concurrently, eQuest is set to normalize infiltration around more modest wind pressures, with intent to allow natural ventilation to vary with hourly windspeed data from the weather BIN. Apples and oranges, in a sense.

I?ve attached messages from a prior [equest-users] thread, with contributions from myself and Keith Swartz. If ever someone were equipped/able to update the doe2 reference manual and provide commentary around infiltration inputs relative to 90.1 prescriptions and real-world envelope airtightness testing? they might find these to be a helpful resource =).

Kind regards!

~Nick

* At one point, in the course of one of the lowdown showdown competitions, I worked on developing a excel tool to bridge eQuest infiltration inputs and real-world blower testing results. That involved reading up a lot on blower testing methodology and how envelope airtightness is prescribed/executed in different municipalities and countries around the world. This entailed a sort of ?literature review? of prescriptive standards / green building standards / etc? If I learned anything, it was that this is a hard sort of tool to build that isn?t ultimately region/standard specific (down to an AHJ level), as variances in how blower test performances are performed/recorded can generate very different ideas of what constitutes good/acceptable/poor levels of infiltration for prescriptive purposes. This was however a number of years ago and it?s possible some national/international consistency may have developed (particularly among jurisdictions where infiltration testing is done with some regularity). I?d love to hear from anyone in such an area who has ?figured out? a defensible approach to marrying real-world blower testing (with specific methodology) to energy model inputs.

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????????, P.E. (US), BEMP
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ESS - ?????????????
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M JP
Email
785 . 410 . 3317
? TBD ?
nicholas.caton at se.com
15200 Santa Fe Trail Drive
Suite 204
Lenexa, KS 66219 USA
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Hi Nick,
Please see section 2.4.1 of the City of Vancouver Energy Modelling Guidelines (attached) for instructions on how to convert blower door test data to infiltration rates for energy modelling.
With kind regards,
Torsten

Torsten Ely | M.Sc, Dipl?Ing, CPHD
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