[Bldg-sim] Really need some deep DOE-2 theology on this one..

[Nick Caton]

To be clear, for an eQuest/DOE2 model I'm pretty sure only a single surface need be defined to transfer heat between two zones.  It can be defined under either space and thermally linked to the other space via the "NEXT-TO" parameter.

I believe defining a surface in both spaces, each linking the other space, for the same real-world construction plane would in effect double the surface area for transfer between the spaces.

In the common scenario of a plenum in between floors (meaning three zones), a minimum of two surfaces (representative of the "ceiling" and "floor/deck" constructions) are required to model heat transfer between all three zones.

I agree there are cases where inter-floor heat transfer cannot be dismissed as negligible, I simply mean to highlight there are scenarios where this case can be made, which can simplify how to address the posed issue of incorrect roof surface areas.  As with any consideration of simplification in an energy model, if one is ever unsure it's usually better to err on the side of "more accurate," time allowing.  This allows you to explore either option and gain first-hand experience that will help you make such judgements in the future.

You could say I'm one of those self-taught/home-schooled energy modelers however (many of us on these lists are), so please do not hesitate to correct or inform me if I'm missing anything commonly taught in the formal programs!  One of the most valuable lessons I've learned to apply to the field of energy modeling, paraphrasing Donald Rumsfeld<http://en.wikipedia.org/wiki/There_are_known_knowns>: There are always things you know, things you don't know, and things you don't know you don't know.

Sincerest 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: Kevin Kyte [mailto:KKyte at watts-ae.com]
Sent: Thursday, October 03, 2013 3:44 PM
To: Nick Caton; Karen Walkerman; Patrick J. O'Leary, Jr.; John Aulbach (jra_sac at yahoo.com)
Cc: bldg-sim at lists.onebuilding.org
Subject: RE: [Bldg-sim] Really need some deep DOE-2 theology on this one..

I would recommend deleting the roofs where roofs are actually not and create a floor and a ceiling.  In order for two spaces to most accurately model heat transfer between them, each space needs to have a construction at the joining surface.

For example, a single space per floor that is two storey's will need a ceiling construction on the first floor and a floor construction on the second floor.

Also, as mentioned...a construction will need to be created for all spaces that have adjoining surfaces.
Take the example above and make the second storey two spaces, the single space on the first floor will need two separate ceiling constructions as the second floor spaces will have two floor constructions.

This is the kind of stuff they don't talk about at home 'building energy modeling' school.  I suppose either way might not matter much for green building rating systems but I have seen it make a difference in unmet hours, usage, etc.

Thanks,
Kevin

From: Nick Caton [mailto:ncaton at smithboucher.com]
Sent: Thursday, October 03, 2013 12:43 PM
To: Karen Walkerman; Patrick J. O'Leary, Jr.; John Aulbach (jra_sac at yahoo.com<mailto:jra_sac at yahoo.com>)
Cc: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] Really need some deep DOE-2 theology on this one..

I'm with Karen - I don't think you can simply explain this one away to a LEED reviewer and will need to address/correct the issues you've identified

If I'm not mistaken, "adiabatic" isn't an option for exterior surfaces however, at least through the eQuest detailed mode interface.  You could make a distinct roof construction which has an impossibly low U-value to severely limit heat transfer (to/from exterior conditions), but that won't correct the roof area figures your reviewer is tuned into.

In my opinion, the easiest reasonable thing to do would to assert (if you can) the thermostat setpoints are the identical between floors and therefore it's reasonable to not model heat transfer between floors, which means you can simply delete those "non-exposed" roofs.  Re-defining those surfaces to be adiabatic ceiling/floor (using an interior wall construction) would have the same net effect except to define additional thermal mass for the associated spaces.

The "partially correct" roof surface(s) on the other hand, which are both exposed and sandwiched, ought to be modified equally in both models to correct the exposed portion.  How simple/involved this is depends on your project's geometries.

Here's a procedure for a correcting a partially sandwiched, single surface roof.  This is done in detailed mode and assumes wizard-based model assembly:

-          Navigate to 3D view, highlight the roof surface to be edited

-          Open properties window for that surface via the component tree or right-click context menu.

-          Identify the referenced space polygon (green text) in the surface properties

-          Scroll down to that polygon in the component tree, right click, create a new polygon, copy the one you identified - name it anything you'll easily find in a long list.

-          Re-highlight that roof surface in the 3D view and open its properties window

-          Re-assign the polygon (green text) to the copied polygon with a unique name (will now be red text).  Click Done.  3D view should look like nothing has changed at this point.

o   Save a copy of your project separately before proceeding!

-          Keeping a clear view of the roof section to be edited, now scroll down and double click on the new copied polygon to pull up its vertices.

-          From here, play around with manually removing vertices to identify which consecutive series bounds the sandwiched portion of the surface. You will observe which vertices go away or move in the 3D view behind if you delete/edit these inputs.

-          Determine whether you need to define any new vertices, to define the "seam" edge where exposed roof meets exposed wall.  If so, experiment with editing a vertex to determine appropriate X/Y coordinates.

-          Once you've identified the vertices to remove and add, for eQuest stability reasons I try to edit existing polygon vertices before removing anything from the list (you'll typically end up with fewer vertices than you started).  This is hard to put to words but bear with me:  From the first vertex, identify the range which should remain (if any), then edit the following vertex points to any new coordinates you may have determined for additional points, then copy the series of vertices to remain from the end of the list up, then finally right-click and restore default to remove all vertices remaining in the list, starting from the bottom.

-          For context, I personally do not treat new/edited vertex coordinates super-precisely typically - anything that looks close to right in the 3D view is good enough for LEED.  Remember you'll be doing the same edits to both models.  Don't get worked up over small seams/holes in the picture - they don't cause roof leaks in in the model!

Procedure for a multi-surface roof (one per space/plenum) is the similar except you do it for each partially sandwiched roof section (don't worry this gets quicker/easier after the first couple).  Those fully-sandwiched sections can either be fully deleted per the above logic, or else re-defined as interior floor/ceiling surfaces if deemed necessary.

Until you wrap up such polygon geometry edits, save separately and often, and run a simulation to test everything is working okay.  I've had some mixed results doing such edits with eQuest interface open.  You may see errors/cautions pop up that can be simply clicked through without consequence.

When all is said and done, one piece of good news is you can save, close, and copy/paste all modified custom polygons between your baseline/proposed models, which makes doing the same edits on the other model as simple as re-assigning polygons (with 3D view up to check your work).

~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: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Karen Walkerman
Sent: Sunday, September 29, 2013 5:11 PM
To: Patrick J. O'Leary, Jr.
Cc: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: Re: [Bldg-sim] Really need some deep DOE-2 theology on this one..


If the "roofs" don't have a zone as the outside boundary condition, then the model views them as roofs exposed to the exterior.  You need to fix this. If the spaces on the other side have the same thermostat setpoints, then the easiest thing to do is set the roof type to "adiabatic". This will save you from having to define new polygons if the floor above has different zone shapes.  For a roof that is only partially covered by the floor above, you need to create the new polygons. Sorry.

--
Karen
On Sep 28, 2013 9:41 PM, "Patrick J. O'Leary, Jr." <poleary1969 at gmail.com<mailto:poleary1969 at gmail.com>> wrote:
this sounds like you have multiple shells in one model for this to occur?  i'm pretty sure equest views an exterior wall/roof as an exterior wall/roof even if it is bounded by an interior wall.  i had this problem come up on one of my own models where i ended up having a building wing meet the building trunk & as i had put them in as 2 separate shells equest did not recognize the dividing wall where the wing met the trunk as being an interior wall & assigned it (via the wizard) an exterior wall definition.  i didn't catch this until reviewing the unmet load hour ss-r & s-va reports & couldn't figure out why the load was so high.  changed the definition of the wall to interior (with a door) in detailed mode and the unmet load hours went to zero and the load came down.

my understanding (in my case) is that if you create multiple shells and place them with a common wall that you want to be an interior the shell rotations need to be zero, even if you have the separation between the two shells occur at a 45 deg angle (then ask mr. architect about that one).

On 9/28/13 4:47 PM, John Aulbach wrote:
Hi Gang:

I need to elite for this one, and you know who you are..

I am reviewing another party's eQuest model submitted for LEED. The reviewer noted that the roof area far exceeded the actual building footprint.

Well, guess why? Somehow, the other party made several floors ROOFS instead of ceilings. I might be able to simply turn the exterior spaces into interior ceilings, but one roof (over an unheated underground garage) is partially uder the building and partially exposed to the "sidewalk/entrance" of the building.

The BIG Kahuena is this..if a space is crammed next to an adjacent space and one of the spaces claims an Exterioir surface between them, does DOE-2 think that Exterior surface is seeing outdoor conditions? Or does it ignore such a thin and merely considers the heat transfer between the spaces (like the wall/roof is NOT exposed to the outdoors)?

My approach is this (unless you disagree)..leave the Exterior wall/roof along and explain that the model (now in Detailed Edit form) would need major surgery to correct to show actual roof area. Having the "roofs" there versus floors will not change the thermodynamics of heat transfer.

I yield to the floor.

John Aulbach, PE





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