[Equest-users] Infiltration issues whith more than one shell

Wed Mar 7 22:48:03 PST 2018

Thanks everyone, that’s very helpful! I’ll start checking post-wizard, especially when I have a complex building with many shells and/or core/perimeter that are only separated by ‘air walls’.

Cheers,
Menush
From: Nicholas Caton <Nicholas.Caton at schneider-electric.com>
Sent: Wednesday, March 07, 2018 4:17 PM
To: Joe Huang <yjhuang at whiteboxtechnologies.com>; Bruce Easterbrook <bruce5 at bellnet.ca>; Menush Akbari <makbari at missiongreenbuildings.com>
Cc: equest-users at onebuilding.org
Subject: RE: [Equest-users] Infiltration issues whith more than one shell

To round back and answer Menush’s query directly – you aren’t doing anything wrong!

eQuest wizards do not take into account adjoining shells when determining whether a zone is “core” vs. “perimeter” for the purposes of assigning the static-but-tiny “core” infiltration rate of .001 cfm/ft2 vs. those derived from other infiltration rate inputs for each shell.

For many models, this isn’t of much consequence, but I do recommend for any model where infiltration rates are a focus to give careful review post-wizards for where infiltration is applied.  The wizards’ default behavior is sensible enough for most cases, but  sometimes requires correction beyond the adjoining shell “quirk,” such as when core zones include clerestories or similar features subjecting them to more infiltration than a typical core zone.  You may also wish to ensure core/perimeter HVAC zones who are in reality only separated by “air walls” (i.e. open office with exposed perimeter) distribute the infiltration loads instead of isolating to just the perimeter.

If you’re thinking ahead, you can “trick” the wizards into treating shell-perimeter-but-adjoining-another-shell zones as “core” by pull the associated vertices a small bit off of the associated shell footprint… but that’s some next level shenanigans and you won’t be avoiding giving the whole model a pass later… I think just correcting core vs. other infiltration rates is probably most time-efficiently done immediately post-wizards.

~Nick

[cid:image001.png at 01D3B66D.1CA719C0]
Nick Caton, P.E., BEMP
  Senior Energy Engineer
  Regional Energy Engineering Manager
  Energy and Sustainability Services
  Schneider Electric

D  913.564.6361
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E  nicholas.caton at schneider-electric.com<mailto:nicholas.caton at schneider-electric.com>

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Suite 204
Lenexa, KS 66219
United States

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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Joe Huang via Equest-users
Sent: Friday, March 02, 2018 12:45 AM
To: Bruce Easterbrook <bruce5 at bellnet.ca<mailto:bruce5 at bellnet.ca>>; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Infiltration issues whith more than one shell

Bruce,

I have to say that DOE-2 normalizing the Leakage-Fraction by the floor area is not a quirk, but a result of the infiltration studies done to date that are predominantly, almost exclusively, done on single-family residences.  I'm thinking here of the work by Max Sherman and David Grimsrud at LBNL that produced the Sherman-Grimsrud Model, the only infiltration model I know of that's physically based, i.e., the model related the infiltration to the temperature difference and wind pressure, coupled with the leakage area of the building.  For single-family residences, that leakage area is best scaled by the floor area, since a large part of the leakage area is in the ceiling. Therefore, I don't agree that leakage scales better with the wall area than the floor area.  On an intuitive basis, it should probably scale by the exterior surface area, i.e., walls + windows + ceiling, but I have yet to see any study that quantified the amount of leakage through each of these components.  As we move to multi-family or commercial buildings, the surface/volume ratio will clearly dominate and for interior floors with only the wall and windows exposed to the outside, yes, the infiltration probably does scale with the exposed wall area. However, there's a dearth of information on the normalized leakage of walls.

Joe

Joe Huang

White Box Technologies, Inc.

346 Rheem Blvd., Suite 205A

Moraga CA 94556

yjhuang at whiteboxtechnologies.com<mailto:yjhuang at whiteboxtechnologies.com>

http://weather.whiteboxtechnologies.com for simulation-ready weather data

(o) (925)388-0265

(c) (510)928-2683

"building energy simulations at your fingertips"
On 3/1/2018 9:19 PM, Bruce Easterbrook wrote:
Thank's Joe, I didn't realize that.  There are many quirks with DOE2 and eQuest.  I haven't looked at that part of the fine print recently.  Leakage does depend on the wall area and not the floor area in real terms.  Buildings have many different wall heights, plenums or not, ducted or not, etc.  I would guess after normalization that one would have to be careful with how manipulations in geometry are done to achieve other effects in the model.  Infiltration can have a serious effect on a model.
I can remember a past model where I used this technique for an actual butting of 2 industrial spaces/buildings.  The one area was a cable casing thermal setting zone, 1/2 height of the warehouse/machinery high bay zone that was adjacent to it.  I was more concerned with the door and seal between the 2 buildings.  I possibly missed the infiltration difference seeing it was based on floor area and not wall area.   I will have to re-read the fine print.
Bruce
On 3/1/2018 10:32 PM, Joe Huang via Equest-users wrote:

I don't think Bruce's comment is germaine to the problem posed by Menush, since Menush is asking about infiltration and not heat transfer through interior walls.  As far as I know from DOE-2 (always have to add that caveat because I don't work much in eQUEST), infiltration rates are normalized per floor area, rather than external wall area, mainly because that's how the infiltration models have been developed, i.e., effective leakage areas have always been defined as per floor area.  If you don't think that's right, you can always adjust the input values by the ratio of the external wall area to the floor area, as you've described, but then you're on your own in coming up with the correlation,

Joe

Joe Huang

White Box Technologies, Inc.

346 Rheem Blvd., Suite 205A

Moraga CA 94556

yjhuang at whiteboxtechnologies.com<mailto:yjhuang at whiteboxtechnologies.com>

http://weather.whiteboxtechnologies.com for simulation-ready weather data

(o) (925)388-0265

(c) (510)928-2683

"building energy simulations at your fingertips"
On 3/1/2018 6:44 PM, Bruce Easterbrook via Equest-users wrote:
Hi Menush,
I don't think you have the same thing.  eQuest will treat 2 shells butted to each other differently than a single interior wall separating 2 zones in a shell.  It treats the 2 butted walls as exterior walls with a tiny space between.  They are the same wall in your thinking but they are not.  You can delete one of them and make the remaining wall an interior wall and assign the proper butting spaces on each side of the wall as sharing the wall and transferring heating and cooling through the wall.  Or you can add an interior wall to the original space and separate it into 2 zones.  As you have noticed there is a difference in the way eQuest treats your 2 solutions.  It is particular.  Now you need to pick the configuration that matches what you are trying to model in such a way that eQuest does/treats the wall in the way you want it to work.
Bruce Easterbrook P.Eng.
Abode Engineering
On 3/1/2018 5:23 PM, Menush Akbari via Equest-users wrote:
Hi all,

I’m having an issue with infiltration and wondering if anyone else has noticed this. When I’m in wizard mode, I build a very simple rectangular shell and I change the infiltration rate for perimeter zones to 0.05cfm/ft2. I leave the core zone infiltration rate to the eQuest default value (0.001cfm/ft2). From my understanding, the perimeter zone entered value in wizard mode is based on exterior gross wall area. When I move on to detail mode, eQuest changes the value to an infiltration value per floor area instead of exterior wall area. The values so far make sense and I can do the math and get the same numbers eQuest calculates in detail mode. No problems here.

The problem however happens when I create different shells. For example, let’s say I have the same rectangular building as mentioned above, but I split this up into two different shells next to each other (two square shells), therefore one of the walls of each square shell is an interior wall, which means I should not see an infiltration of 0.05 cfm/ft2 of the gross wall area. However when I finish building these two shells in detail mode (which would be identical to one rectangular shell), the infiltration value is not accurate anymore. Instead of the same numbers as my first model (one rectangular shell), the second model calculates an exterior wall infiltration value for the interior walls that are budded up against each other.

Has anyone come across this? Is this a quirk with eQuest and just needs to be changed manually in detail mode, or am I doing something wrong here?

Thanks for the help.

Cheers,

Menush Akbari
BEng, PEng, BEMP, CMVP
Senior Energy Engineer
Mission Green Buildings
(Mission Green Buildings is the trading name of Mission Green Limited)

t. 250 777 3380
makbari at missiongreenbuildings.com<mailto:makbari at missiongreenbuildings.com>
http://missiongreenbuildings.com<http://missiongreenbuildings.com/>

[MGB 5 Years 2]

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