[Equest-users] Adjacent Shells

[Nick Caton]

Hey Jeremy,

If I can correctly assume most of these are "sandwiched" walls as you've described them as adjacent shells (thus shading each other from solar gains)...  Pretty simply, the impact or "degree of error" such phantom skin loads introduces will vary primarily with how heavily the annualized exterior conditions differ from the conditioned set points inside.  More specifically:  If it's a building in a very mild & temperate climate (San Diego comes to mind), the extraneous loads introduced will be much less severe than somewhere like Kansas City.

That said, "a pretty big deal" could describe the impact for your project just about anywhere.  Particularly if you're making comparisons with/without self-shading, a la LEED.

I agree the fastest approximation to address this in detailed mode is probably to simply delete all 'false' exterior perimeter walls, as suggested.  This might actually be MUCH easier using the 2D plan view option over the 3D view however.  It'll show you one shell at a time (depending on what's highlighted in the tree), and you can very easily/accurately use the graphic to select the appropriate walls from the component tree (if you're familiar enough with the layout in 2D to recognize which walls go away).

I reckon correcting this may very well help bring your lighting consumption effects to the forefront.  If not, the benefits of reducing installed watts should be easy enough to demonstrate with simple math however, outside of an energy model ;).

Regards,

~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] On Behalf Of Jeremy Poling
Sent: Wednesday, January 23, 2013 5:21 PM
To: Sami, Vikram
Cc: equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Adjacent Shells

Thanks Bill and Vikram - with most buildings this would be an easy solution, but with this particular building the problem involves hundreds of these exterior surfaces.  Unfortunately, the changes in building geometry are not minor enough to simplify - bump outs exceeding 20 feet, changes in direction and angle of the building, etc.  I should have noted that the 4M+ SF is spread across 4 floors...

I'll take a look at it once the architecture is finally complete in the model.  I'll have to do it as best as possible in the 3D view since without a pan feature I can't get close enough to the tails of the building to visualize the sections that are exterior.

If anyone does have an idea on what percentage of the load these phantom skin loads can add up to in more typical cases, that would be helpful: following ASHRAE 14 there's room for some small percentage error adjustments due to things like this.  To put it a little differently, we're recommending the owner finish changing the last few incandescents to alternate sources (depending on application, LED or CFL) but the threshold for showing up as a percentage of energy use in the building is so high all of the incandescent sources remaining wouldn't show up on the simplified results in eQuest. :)  Fun "little" project, yes?
Jeremy R. Poling, PE, LEED AP+BDC



On Wed, Jan 23, 2013 at 3:48 PM, Sami, Vikram <Vikram.Sami at perkinswill.com<mailto:Vikram.Sami at perkinswill.com>> wrote:
I agree with Bill - don't leave them as exterior walls - you will get non existent skin loads in those zones.

Another thing worth trying (if you are going through the wizard) is to make the building footprint slightly bigger than the zone footprint on that side of the building.  Like this:

[cid:image004.jpg at 01CDF990.CB3A39D0]

You will end up with interior walls in those zones like so:

[cid:image005.png at 01CDF990.CB3A39D0]

Hope this helps


Vikram Sami, LEED AP BD+C
Sustainable Design Analyst
1315 Peachtree St. NE, Atlanta, GA 30309
t: 404-443-7462<tel:404-443-7462>    f: 404.892.5823<tel:404.892.5823>       e: vikram.sami at perkinswill.com<mailto:vikram.sami at perkinswill.com>   www.perkinswill.com<http://www.perkinswill.com/>
Perkins+Will.  Ideas + buildings that honor the broader goals of society


From: equest-users-bounces at lists.onebuilding.org<mailto: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 Bishop, Bill
Sent: Wednesday, January 23, 2013 2:59 PM
To: Jeremy Poling; equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Adjacent Shells

Jeremy,

Well, every one of those extraneous exterior walls (and roofs) is going to be simulated as envelope loads on those spaces. The model doesn't know that they aren't actually exposed to the outdoors. I would certainly delete them for any model, calibrated or otherwise, if it were me. You could determine the impact, relatively quickly, by modifying the U-factor of your wall construction based on the ratio of modeled exterior wall area to actual exterior wall area. Get your modeled wall area from the last page of the LV-D report, and divide by the actual wall area of the existing building. Divide the wall construction U-factor by the modeled-to-actual wall ratio, and modify the wall construction accordingly. Simulate and see how much the energy is reduced. Okay, never mind that sounds like too much work. Just delete the walls.

If you're in that much of a hurry, don't replace the exterior walls with interior walls. Just delete the exterior surfaces and be done with it. I usually add the interior walls, especially if the adjacent spaces have different thermostat setpoints or different internal loads. These edits can be pretty quick when you modify the 3-D view to more easily see where the extra surfaces are:

[cid:image006.jpg at 01CDF990.CB3A39D0]

Regards,
Bill

[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> [mailto:equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>] On Behalf Of Jeremy Poling
Sent: Wednesday, January 23, 2013 2:33 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Adjacent Shells

Two questions in the same day...I may have more still :)

Has anyone taken the time (maybe Nick?) to determine if there is a major impact due to leaving walls of adjoining shells as exterior instead of changing them to interior, air-walls, or deleting them?  I only ask because I have a 4M+ SF building that is requiring 20+ shells stacked and adjacent and I'm looking for every time saver I can find.  I simplified the shells as much as possible, but due to geometry this is the smallest number I can squeak by with from an orientation/geometry/overlap.

I should note, this is an existing building and the model is being more or less calibrated, so just having a rough idea of the impact of this nuance will allow me to decide to take the time or to chalk it up in my model error.

Thanks much!
Jeremy R. Poling, PE, LEED AP+BDC



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