Adiabatic Walls in EnergyPlus

asked 2014-11-10 16:44:51 -0500

Thierry Nouidui
1507 ●13 ●7 https://nouidui.com/in...

updated 2015-07-10 14:59:48 -0500

I just simulated a 9 zone models in EnergyPlus using the latest release version. The system model has a couple of adiabatic walls. After the simulation successfully terminated, I looked at the Envelope Summary report and couldn't see the adiabatic (interior) walls listed. Does anyone know why they do not show up? How does EnergyPlus treats adiabatic walls during execution?

Update:

@Neal Kruis, @Annie Marston Thanks to both of you but it is still not clear to me why those walls do not appear in the report.

The InputOutputReference.pdf says following:

Envelope Summary

The Envelope Summary report (key: EnvelopeSummary) produces a report that includes the following tables:

Opaque which includes all opaque surfaces and includes the name of the construction, reflectance, U-Factor, gross area, azimuth, tilt, cardinal direction.
Fenestration which includes all non-opaque surfaces and includes the name of the construction, areas (glass, frame, divider, single opening, multiplied openings), U-Factor, SHGC (the solar heat gain coefficient based on summer conditions), visible transmittance, conductance (frame, divider), indication of shade control, the name of the parent surface, azimuth, tilt, cardinal direction.

Shouldn't those walls not be included in this report?

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@Thierry Nouidui I edited your question to include the update you posted. In general, if people aren't providing the answer you're looking for it probably means that you need to clarify your question. The best way to do that is by editing the question itself, but add something like Update to let people know that the question has changes since it was originally asked. Let me know if this works for you.

Neal Kruis ( 2014-11-12 15:11:22 -0500 )edit

It works. Thanks!

Thierry Nouidui ( 2014-11-12 15:43:29 -0500 )edit

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answered 2014-11-12 08:50:42 -0500

Neal Kruis

4675 ●9 ●17 http://bigladdersoftware.com/

updated 2014-11-12 09:46:26 -0500

Adiabatic walls in EnergyPlus are simulated by imposing the same boundary condition to both sides of the construction, and not by creating a zero-heat flux boundary condition as one might think. This allows heat to transfer in from both sides of the construction for thermal storage--although keep in mind that the thermal zone only sees the inside of the surface; heat transferred through the outside surface "disappears" into the ether. This is described also in the EnergyPlus Engineering Reference. This is the same way the InternalMass object works.

If you want heat to be exchanged from both sides of an interior surface with the zone then you will have to create two mirror constructions and two surfaces in the same zone with the other-side boundaries referencing each other.

At one point I created simulations using all three approaches (Adiabatic boundary, InternalMass, and a mirror surface boundary in the same zone) and confirmed that they all give the same result.

I don't believe that any of these options will have the surface appear in the Envelope Summary, but I might be wrong about the two surface approach.

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@Neal Kruis Your explanation of how adiabatic surfaces are modeled is correct, except I would strike "heat transferred through the outside surface "disappears" into the ether. Because the boundary conditions are symmetrical, heat never transfers through an adiabatic surface, whatever goes in from the zone returns to the zone or remains stored in the surface.

MJWitte ( 2014-11-20 17:06:54 -0500 )edit

You're right. Energy is certainly conserved from the zone's perspective, but algorithmically heat is still transferred into, transferred out-of, and stored in the side of the surface that is not seen by the zone. My understanding is that this heat comes from nowhere, and goes to nowhere (the ether). It doesn't effect the simulation since that heat cannot flow across the plane of symmetry.

Neal Kruis ( 2014-11-20 17:17:25 -0500 )edit

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answered 2014-11-12 11:49:14 -0500

Archmage

7185 ●3 ●11

I believe the explanation lies in the meaning of the word envelope here. It means thermal envelope of the building and that does not include interior partitions, only those surfaces that separate the indoors from the outdoors. If you want a report that includes the interior partitions then you can get details for all surfaces out of the EIO file.

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Thanks! This is not obvious to see from the definition below. In addition, there is in fact in the Envelope Summary a table for Interior and Exterior Fenestration... But as you said, I could get additional info from the EIO. Thanks! Thierry

Thierry Nouidui ( 2014-11-12 12:51:23 -0500 )edit

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answered 2014-11-12 08:36:43 -0500

Annie Marston
4297 ●4 ●31 http://www.resustain.com

I don't think interior walls show up in the envelop summary in energyplus, if I remember correctly the envelop summary just shows exterior constructions. I think with adiabatic walls, and please anyone correct me if I am wrong, I think that the heat does not transfer through them like it would a normal construction, rather it just acts as a physical barrier between the two spaces.

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