[Equest-users] Building Walls

[Bishop, Bill]

Yes, eQUEST simulates the exterior air film with different hourly values for each exterior surface, based on wind speed and surface roughness. I ran a custom hourly report to verify this for three random exterior walls. If you do this for your own model and scroll down to the yearly summary, you can get a sense of the building-wide average annual value. In the case below, the average value is approximately twice the R-0.17 value included in the ASHRAE 90.1 effective R-values for various exterior constructions. Granted, R-0.35 is small relative to a well-insulated wall, but it can be enough to impact the LV-D reported U-values.

Regards,
Bill

[cid:image001.png at 01CD9190.DD912ED0]

[Senior Energy Engineer 28Jun2012]<mailto:wbishop at pathfinder-ea.com>

From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Bruce Easterbrook
Sent: Wednesday, September 12, 2012 12:47 PM
To: Nick Caton
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Building Walls

As an adder to this the wind speed also varies with the height of the building.  The wind speed for a locations weather file is at a standard reference height and would also be adjusted for height of the building.
Bruce Easterbrook P.Eng.
Abode Engineering
On 12/09/2012 12:22 PM, Nick Caton wrote:
I can add a probable bit of method to the madness for those concerned:

The reason exterior air film is not entered as a static property, nor reported lumped in with the constructions' overall assembly U-values, is because it's actually a variable property.

The reference I have handy (Table 5-12, 2001 Fundamentals) lists multiple resistance values for moving air (at various speeds) and still air (for various surface orientations and directions of heat flow).

I take it as implicit that eQuest/DOE2 models this variable contribution from the exterior air film in consideration of the hourly windspeed data available from the weather file, so presenting any single value could be misleading.  I've had to make that clarification a few times for those scrutinizing the construction reports without the eQuest detailed simulation reports reference handy ;).

Hope that helps a bit!

~Nick
[cid:489575314 at 22072009-0ABB]

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> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Dahlstrom, Aaron
Sent: Monday, September 10, 2012 4:20 PM
To: Peter Hillermann; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Building Walls

Peter -

We've noticed the identical issue. Another way of stating it - the sequence of layers input for the baseline and the proposed should EXCLUDE contributions from air film. eQUEST adds the interior air film as a separate entry under the Layers tab.

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ASHRAE's regulations for baseline constructions include the contribution of the exterior air film at a specified windspeed. As far as I can tell, this is how the u-value displayed on the LV-D report is calculated. (Report says "includes exterior air film").

However, we have noticed that the value displayed inside eQUEST as "calculated u-value" does not match the u-value from the LV-D. My theory is that the item shown in eQUEST includes the interior air film but not the exterior air film. (From Vol 2 dictionary, under CONSTRUCTION:U-VALUE - "For exterior surfaces, equals the overall conductance of the surface including the inside air film but excluding the outside air film.")

[cid:image005.jpg at 01CD9190.DD912ED0]

I'm just learning about this issue, so any wisdom from more experienced folks would be welcome!

Aaron

Aaron Dahlstrom , PE, LEED(r) AP
In Posse - A subsidiary ofAKF| 1500 Walnut Street, Suite 1414, Philadelphia, PA 19102
d: 215-282-6753| m: | In Posse: 215-282-6800| AKF: 215-735-7290
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From: equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Peter Hillermann
Sent: Monday, September 10, 2012 2:02 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Building Walls

To All:

A general piece of information I got from our engineer when we had done the energy model for LEED and something to look out for. He let me know that in the baseline for wall construction to make sure you add in the air film (inside and out) otherwise LEED has an issue with your submission.

Our exact comment was this:
The Baseline Case roof and exterior wall U-values reported in Table 1.4.1A (U-0.048 and U-0.065, respectively) are
inconsistent with the U-values reported in the LV-D report (U-0.054 and U-0.063, respectively). Please ensure consistency
across construction drawings, software summaries, and the EAp2 Template.

Hope it helps.

I also don't know if anyone has this summarized, because I used the baseline walls from this forum that someone had posted and that was the response.

PS: Thank you to this forum, we ended up getting LEED Certified.

Thanks,

PETER HILLERMANN

peterh at westallarchitects.com<mailto:peterh at westallarchitects.com>

westall
architects
3404 pierce drive
chamblee, georgia 30341

o 770.458.4113
c 678.898.2936

westallarchitects.com
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