[Equest-users] Spandrel Glass

Bishop, Bill bbishop at pathfinder-ea.com
Fri Dec 7 11:08:45 PST 2018 

Great conversation!
I agree that spandrel panels should be modeled as EXTERIOR-WALL components and not WINDOWs.
My comments/hints that weren’t already mentioned below:

  *   The 1/4in Spandrel Glass material from the library should be entered as the first material in LAYERS (which are ordered outside to inside for exterior walls).
  *   The default library only has 1/4in Spandrel Glass but you can make any material layer as thick as you want by changing the THICKNESS.
  *   Absorptance: The percentage of solar radiation absorbed by the wall is input as ABSORPTANCE. This is a keyword for the CONSTRUCTION and is shown on the main tab/sheet of the wall construction. I assumed a glass spandrel panel would have a different absorptance than the default value of 0.700. After looking into it, I couldn’t find a good alternative value and it is probably all over the place depending on the glazing coatings/paints, air spaces and backing materials.
  *   Surface Roughness: The outside air film coefficient for exterior surfaces is a function of the surface roughness and wind speed. The ROUGHNESS keyword input is also on the main CONSTRUCTION tab/sheet. Glass and smooth painted surfaces have a ROUGHNESS of 6 per the DOE-2 help description. The default is 3.
  *   Emissivity: Infrared (heat) radiation to/from exterior walls is specified by OUTSIDE-EMISS which is a keyword of the EXTERIOR-WALL (not the CONSTRUCTION). The default value of 0.9 is close to the typical value for glass (0.84).
  *   I finally understand why they’re called curtain walls. They are not structural members. They are exterior coverings, as a curtain covers a window.
~Bill

William Bishop, PE, BEMP, BEAP, CEM, LEED AP
Senior Energy Engineer

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From: Equest-users <equest-users-bounces at lists.onebuilding.org> On Behalf Of Nicholas Caton via Equest-users
Sent: Thursday, December 6, 2018 9:09 PM
To: David Eldridge <DEldridge at grummanbutkus.com>; jra_sac at yahoo.com; Paul Diglio <paul.diglio at sbcglobal.net>; equest-users at onebuilding.org
Subject: Re: [Equest-users] Spandrel Glass

I’ll toss some extra thoughts/experience into the pile:

My preferred approach to handling large amounts of spandrel glass is to start by taking advantage of the wizards’ capacity to generate separate “plenum” exterior wall sections (of height resulting from your ceiling inputs), to produce equivalent area to the spandrel glass on each orientation.  Those separate sections are in part a by-product of the intent to distinguish the conditioned space/zone volume relative to the floor-to-floor height, but we can repurpose them!

I do not create glass on those “plenums” wall sections, but rather just make a new “spandrel” exterior wall construction in detailed mode and use custom user default expressions to automate assigning “spandrel” vs. “normal” constructions to each exterior surface as a function of their Z coordinate (0 = normal wall, else spandrel construction).

This can be combined with post-wizard manipulation of interior space/ceiling heights (which do not have to line up with the “seams” separating plenum from normal walls), to capture cases where the spandrel actually extends below the ceiling line and ensure the conditioned volume is accurate around your perimeters.  Be mindful that if the spandrel glass is largely incident on the conditioned volume it may be more appropriate to move them off the plenum spaces and onto the occupied spaces.

There is an aesthetic “downside” to this approach to consider (according to some industry professionals I’ve worked with), but if someone *really* wants a pretty 3D model picture that looks like a fishbowl from the likes of eQuest (?), I’ll just add that you can generate some (apparently convincing) “forgery” of extra windows by mis-using MSPAINT – the duct tape of my graphical tool belt.  And yes, I sleep at night just fine, thank you.

@David:  I’m not sure about that library entry either, but I have in the past been convinced myself it was okay to use the simplified window glass definition option and

  *   specify a shading coefficient of zero (where SC is the ratio of solar energy transmitted relative to single pane float glass), and
  *   specify a U-value appropriate to the degree of insulation (though I’d leave this equivalent to the underlying glass layer(s) if it’s just painted panels – run into that a couple times).
This modeling approach doesn’t pick up on all of the actual nuances of radiative* emissivity for painted-over windows, but it has for me been good enough for (literally) government work where there were much bigger problems to focus the energy model’s development around… If anyone has developed further best practices for handling “high-e coatings” applied to mitigating unwanted transmissive solar gains, I am certainly all ears =).

~Nick


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Nick Caton, P.E., BEMP
  Senior Energy Engineer
  Regional Energy Engineering Manager
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  Schneider Electric

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From: Equest-users <equest-users-bounces at lists.onebuilding.org<mailto:equest-users-bounces at lists.onebuilding.org>> On Behalf Of David Eldridge via Equest-users
Sent: Wednesday, December 05, 2018 5:59 PM
To: jra_sac at yahoo.com<mailto:jra_sac at yahoo.com>; Paul Diglio <paul.diglio at sbcglobal.net<mailto:paul.diglio at sbcglobal.net>>; equest-users at onebuilding.org<mailto:equest-users at onebuilding.org>
Subject: Re: [Equest-users] Spandrel Glass


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Paul – to answer your question: painfully? It may not be that bad actually – what’s your base wall type? For a curtain wall that is half spandrel and half vision glass, make the exterior opaque surface equivalent to the spandrel sections as a defined opaque wall construction, and then add the vision glass to that – if you change the surface constructions in spreadsheet view it may not be that painful after all. The painful part will be deleting all of the current spandrel sections that are now defined as the base wall.

JRA – I’m not sure of the purpose of the spandrel glass type in the library, I don’t know if that window object model has the capability to perform as if it were an opaque surface although this spandrel glass definition may be available to be selected…I’m not sure it would be an accurate choice. I wonder if it is a research entry that isn’t meant for the modeling public. Anyone used it?

David


David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
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From: Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of John Aulbach via Equest-users
Sent: Wednesday, December 05, 2018 5:39 PM
To: Paul Diglio <paul.diglio at sbcglobal.net<mailto:paul.diglio at sbcglobal.net>>; Paul Diglio via Equest-users <equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>>; equest-users at onebuilding.org<mailto:equest-users at onebuilding.org>
Subject: Re: [Equest-users] Spandrel Glass

Paul,

As I recall there IS a wall component called spandex glass in the Library. See if that solves your need.

John
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On Wed, Dec 5, 2018 at 3:33 PM, Paul Diglio via Equest-users
<equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>> wrote:
I have a building with a very large amount of spandrel glass panels, which I modeled as glass since this seemed to be the only way to insert the panels into the exterior walls.

I would somehow like to re-assign the spandrel panels as another exterior component so they will be counted as part of the exterior walls in the LV-D report instead of glass.

Any idea on how this can be done?

Thank you,

Paul Diglio
87 Fairmont Avenue
New Haven, CT 06513
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