[Equest-users] eQUEST infiltration rate

Thu Oct 29 06:39:15 PDT 2020

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
Senior Energy Engineer
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From: Equest-users <equest-users-bounces at lists.onebuilding.org> On Behalf Of Daric Adair via Equest-users
Sent: Wednesday, October 28, 2020 9:39 AM
To: Phil Jordan <phil.jordan at clearesult.com>; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] eQUEST infiltration rate

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

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From: Phil Jordan <phil.jordan at clearesult.com<mailto:phil.jordan at clearesult.com>>
Sent: Monday, October 26, 2020 11:15 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] eQUEST infiltration rate

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

From: Equest-users <equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>> On Behalf Of Lapierre, Patrick via Equest-users
Sent: Monday, October 26, 2020 9:09 AM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] 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,

  [cid:image001.jpg at 01D6ADC3.9402D590] <https://nam12.safelinks.protection.outlook.com/?url=http%3A%2F%2Fwww.bpa.ca%2F&data=04%7C01%7Cphil.jordan%40clearesult.com%7C922b1ea6029c41fc47bd08d879c97b84%7Cc505a74550c6477fa1107be89b513acc%7C1%7C0%7C637393253562115145%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=VPNlBW3wH2ut04ohxLoqGoZ%2FAl6RTkjd9Yv5fv3kXiY%3D&reserved=0>

Patrick Lapierre_ing. BEMP, Chargé de projets
Développement durable et Efficacité énergétique
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