[Equest-users] Building Geometry

Haynes, Glenn Glenn.Haynes at dnvgl.com
Fri Mar 13 10:04:21 PDT 2015

Here are my two cents:

If you want to obtain valid results that also look good in the 3D drawing, specify outside surfaces  to calculate skin loads and scale the inside loads (lights, equipment, infiltration, etc.) to the inner wall dimensions.  Specify window setback if they are not at the outside planes of their walls.  I do not think that LEED cares about the corner effects, but if you want to get the wall masses correct you can sacrifice the beauty of the 3D drawing by leaving gaps.  Just subtract half the thickness of the adjacent corner wall from the actual wall width, leaving the wall to start at the original position, and you get one gap; all you have to change is wall Width.  If your wall spans the full building width, you must subtract the two corner wall half thicknesses.

DOE-2 fails to subtract thickness (which is not always specified in the input) from the outer dimensions to calculate internal volumes.  Remember that thermal boundaries (building shell) are assumed by DOE-2 to face outward, where the default tilt for walls is 90 degrees, horizontal roofs is zero and floors is 180.  Material layers, if user specified, must be entered in the order of outside to inside.

Best regards
for KEMA Services Inc., USA

Glenn Haynes, PE
Senior Engineer, Policy Advisory and Research
DNV GL - Energy

E-mail glenn.haynes at dnvgl.com<mailto:glenn.haynes at dnvgl.com>
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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Nicholas Caton
Sent: Thursday, March 12, 2015 4:17 PM
To: Charudatta Joshi; Singhal, Harshul
Cc: Equest-users
Subject: Re: [Equest-users] Building Geometry

Hi everyone,

I have tread this path a few times before, and my position on the matter has evolved over time.  Here’s my current understanding of the issue:

1.       Tracing the outside will result in:

a.       Inaccurately large interior volumes and

b.      Inaccurately large perimeter space areas (pertinent for area-dependent inputs like LPD, plug loads).

2.       Tracing the inside will result in:

a.       Inaccurately small exterior surface areas for the purposes of determining skin loads.

3.       Tracing the middle of the construction results in ALL the inaccuracies above, but to a lesser degree.

I consider the implications between these approaches on your baseline model for Appendix G / LEED / etc. to be arbitrary in nature.  Your choice should reflect the degree of accuracy desired relative to the actual/Proposed case and the time you have to invest in your results.

[TIER 1 EFFORT] You could make the case that #1 or #2 is the lesser of two evils, considering the implications (and you might be right either way depending on the circumstances of the project).  #3 is a compromise between #1 & #2, and is my first suggestion if you’d rather not get bogged down in such hypotheticals AND need to perform a fast study, acknowledging the above inaccuracies.

[TIER 2 EFFORT] However, a more correct/accurate approach is to put slot yourself into either camp #1 or #2 and then make the necessary corrections in detailed mode (post-wizards) for the known/stated inaccuracies with that approach.

Of the two, I personally think #1: tracing the outside and making corrections for space volume and lighting/rcpt inputs, is the more intuitive approach and has the (subjective) advantage of a model that will look correct in 3D view.  Others will trend towards the second approach, and I wouldn’t fault them for it.

This isn’t really part of the original “black/white” question, but it seems worthwhile to insert a heads up:

To first speak to what’s happening “under the hood,” I believe it’s most correct to say eQUEST/DOE2 doesn’t actually “simulate” the thickness of a construction (i.e. “outward-in” vs. “inward-out”), rather the construction and heat transfer is 1-dimensional.  (I swear, this is rather pertinent for a thick-wall study – bear with me!)  While we DO enter thickness of materials/layers for exterior constructions in eQUEST, those inputs are used only to determine the construction’s thermal mass and conductivity.  This means each hour of the simulation, heat is determined to be moving either in or out, perpendicular to the surface.  Heat is not simulated to move “sideways” within the construction (as actually happens at building corners and where materials change along/within the assembly, such as with stud wall assemblies) – that would be what people are referring to when they speak of 2-dimensional heat transfer. Usually, we make efforts to define our construction layers in uniform terms (i.e. for a stud/insulation layer), and call it a day.

So what does all this mean for a thick wall study?  (Consider how heat would travel through the cross-section of a vertical building corner…)  It means the “effective” 1-dimensional exterior surface area for a space with skin loads actually lies somewhere between options #1 and #2, above.  A “most correct” eQUEST model might most closely resemble approach #3, above.

I will insert here:  I have done some homework in the way of self-educating to read up on the topic & attend related seminars, and I even passed a thermodynamics course back in college, but I do not presently consider myself an expert on multi-dimensional heat transfer in building assemblies, and haven’t had a ton of experience putting this to practice.  I do know others on this list are more solidly situated in those camps and are welcome/encouraged to fill in gaps & participate!

So take approach #3 as a framework:  To arrive at a “most-correct” study using eQUEST (and it may be prudent at this stage to instead consider software with 2D/3D heat transfer baked-in):  Rather than arbitrarily define walls along the centerlines of your envelope, I would propose estimating at what mean construction thickness (between the interior and exterior thicknesses) you would achieve the same result in 1-dimensional transfer as you would with a more sophisticated 2D (or even 3D) analysis.  You would still need to later make corrections for interior volume and space-dependent internal loads, as suggested under approach #1.

Procedurally, I would not be surprised to learn others have come up with tools or a rule of thumb to estimate such an “effective 1-dimensional thickness,” accounting for the surface perimeter:area ratio in addition to the usual conductive variables.  You might also use a separate study/software to externally determine what this effective thickness should be.  Again, I haven’t tread this path in practice, and am hopeful others may chime in with suggestions along these lines.

I hope this was illuminating/helpful to some (even if only to help you fall asleep!),



Caton Energy Consulting
  1150 N. 192nd St., #4-202
  Shoreline, WA 98133
  office:  785.410.3317

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>] On Behalf Of Charudatta Joshi
Sent: Thursday, March 12, 2015 1:21 PM
To: Singhal, Harshul
Cc: Equest-users
Subject: Re: [Equest-users] Building Geometry

Inside edge is better in your case. Just make sure you model exterior constructions using the layers input, so you account for thermal mass.

(Larger projects can be modeled with outside edge of walls so your modeled area matches what's declared as total building area in the architectural drawings, or in other LEED credits, as applicable).

On Mar 12, 2015 1:05 PM, "Singhal, Harshul" <HSinghal at thorntontomasetti.com<mailto:HSinghal at thorntontomasetti.com>> wrote:
Hi Maria,

We have done one university block recently which had 2.5 feet thick walls (retrofit) and we modeled using inner dimensions. Whether it’s thick or thin, its advised to use inner dimensions although project requirements vary sometimes. Thanks!

Harshul Singhal, LEED AP BD+C
Project Consultant
Thornton Tomasetti
386 Fore Street, Suite 401
Portland, ME  04101
T +<tel:%2B1.207.245.6060>  F +<tel:%2B1.207.245.6061>
D +<tel:%2B1.207.245.6074>
HSinghal at ThorntonTomasetti.com<mailto:HSinghal at ThorntonTomasetti.com>

From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>] On Behalf Of Maria Elisa Rumeo
Sent: Thursday, March 12, 2015 2:51 PM
To: Farid Pour
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Building Geometry

Does anyone have experience with modelling thick-wall retrofits who can also answer my question?
It is a small house, so if I trace the interior dimensions I will get significantly different results than tracing exterior dimensions

On Thu, Mar 12, 2015 at 2:11 PM, Farid Pour <farid.pour at hok.com<mailto:farid.pour at hok.com>> wrote:
As far as I know, it goes in.

From: Maria Elisa Rumeo [mailto:rumeomar at gmail.com<mailto:rumeomar at gmail.com>]
Sent: Thursday, March 12, 2015 1:10 PM
To: Farid Pour
Cc: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: Re: [Equest-users] Building Geometry


It is a low-energy retrofit and the walls are really thick!
My fear is that by using the outside dimensions, then if the wall contruction goes 'outward' of these defined lines, then I am modelling a larger house ( the volume of the house in the model is greater than the actual volume) .

please help :)!



On Thu, Mar 12, 2015 at 2:05 PM, Farid Pour <farid.pour at hok.com<mailto:farid.pour at hok.com>> wrote:
It should not make that much of difference unless your walls are rally thick.   I suggest you trace the outside wall and then make sure of the wall thermal properties.
From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>] On Behalf Of Maria Elisa Rumeo
Sent: Thursday, March 12, 2015 1:03 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Subject: [Equest-users] Building Geometry


Can someone please help me with this:

I have an AutoCAD file of an old home that was retrofitted with thick (insulated walls). When I import this file and trace it to define the building footprint on eQuest,should I be tracing the OUTSIDE of the building (the brick face) or the INTERIOR of the building (the interior walls)? or should I draw a line in the middle of them and use that as my building footprint?

do you know the wall construction goes INWARD or OUTWARD from the building footprint you set?



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