Some discuss about the Calculation Method of the software

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Hi all:

Below are some situations always puzzle me:

1. If you modify the Floor's Z-axis coordinate like this , you
will find the 2 floors has been separated, but the calculation result
didn't show any different.

2. As above, you can also move some wall like this, there is still
no different.

3. But , if you directly delete this wall, the result show
different.

The questions are :

1. Absolutely from the 1st situation, we can see that the software
can't judge if the two space are adjacent from the coordinate, is that
right? Further , how should the software judge if two spaces adjacent?

2. If there is a hole on the wall, I don't think the software
should deal with it as natural ventilation, so , how should the software
to deal with it?

3. If some wall been deleted as 3rd situation, the software still
can be run, so I think there should be some default boundary conditions,
and which should be the default boundary condition?

I have used this software half of one year, but I can't sure if my
calculation result is right, I think I need a higher level to understand
this software.

Any suggestions would be appreciated.

I have learn a lot from you guys ,Thank you.

Joey

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Joey Jiao

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1. Absolutely from the 1st situation, we can see that the software can't judge if the two space are adjacent from the coordinate, is that right? Further , how should the software judge if two spaces adjacent? The software judges adjacent spaces by the surface that separates them. In interior spaces you have to specify an adjacent space that it shares the space with.

2. If there is a hole on the wall, I don't think the software should deal with it as natural ventilation, so , how should the software to deal with it?

3. If some wall been deleted as 3rd situation, the software still can be run, so I think there should be some default boundary conditions, and which should be the default boundary condition?

The software doesn't (as far as I know) calculate holes. It will calculate heat transfer through a surface. In terms of boundary - it calculates heat transfer to a space from exterior conditions through an exterior wall, and from adjacent spaces through interior walls. The absence of a surface (I think) makes that area adiabatic - no heat transfer, mass, or any exchanges. It also means there is no daylight coming into the space from that wall. As far as natural ventilation goes - I think the way to model that is as an infiltration with a schedule.

Hope this helps

Vikram Sami, LEED AP BD+C

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Hi Joey,

Your observations are based on the fact that the underlying simulation
engine for eQuest (DOE2) has little actual understanding of 3 dimensional
space. I think it's easiest to start with your second example when you
move the wall out of the space. The program itself doesn't understand that
the original space bounded by the floor, ceiling and 4 walls consisted of a
volume. Therefore, when the wall is moved it doesn't understand that there
is a hole. The wall is still in the program, it is still facing the same
cardinal direction, it is still assigned by the same zone, and in both
cases, it is not shaded by any other objects, so the program will model
model conduction through the wall and solar gain through the windows. The
program does not understand the hole.

When you delete the wall, the program no longer models conduction through
the wall or solar gain through the windows. Basically, there is no longer
a boundary there, although it's easier to think of it as an adiabatic
boundary with no mass. This effect can be advantageous because if you need
to create custom geometry in detailed mode and need to change the polygons,
it can be difficult to get all walls to match exactly. Having a small gap
or small hole is acceptable and doesn't lead the program to model natural
ventilation. If you want to model natural ventilation, I believe you do
this in detail mode under the "Internal Loads" tab.

Your first example is the only one that should show a tiny amount of
difference in the result - this is because I believe that the elevation of
the building is accounted for in the calculation. However, the internal
ceiling of the first floor is still internal and is still specified as
being adjacent to the internal floor of the second floor.

Regarding space adjacency - when you enter spaces into the wizard, it does
a decent job of figuring out which spaces are adjacent. If it knows a
space is adjacent to another space, it will set that wall to interior. If
the space is not adjacent, it will set the wall to exterior. Be careful
and double check in detailed mode that everything you expect to be interior
and exterior actually came through that way. When you make a change in
detailed mode, you need to make sure everything agrees.

--
Karen

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Vikram and Karen's response are right on - I can fill in a few gaps as well:

- Elevation of a building can have an effect on eQuest's infiltration calculations, depending on the method you choose to use for defining infiltration. Much to read on the topic in the help files if you're interested, but FYI the default coming out of the wizards is not elevation-sensitive (AIR-CHANGE ? INF-FLOW/AREA).

- To help clarify the first example: Moving spaces away from each other does not break the "adjacency ties" that existed (or not) prior. I would not expect any changes of the first example, because you have the flexibility to move the spaces all over the place. If you intend to separate the floors, you should simultaneously re-assign the "next to" property or or removing the interior surfaces that joined them to begin with. Note coming out of the wizards, you may not actually find there to be a surface defining that connection, depending on how you defined the shell(s).

- I can confirm to my understanding that eQuest does not recognize "holes" in any sense. eQuest does recognize the relative XYZ coordinates of exterior surfaces and of building shades when determining solar loads incident on exterior walls, roofs, and windows. You should be able to confirm this by moving the wall in the 2nd example right next to another (and keeping the 'self-shading' property on for all exterior surfaces).

~Nick

NICK CATON, P.E.

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Hi, Sami:

Thank you for your light, I didn??t use these method before , I will try that.

Thanks very much again.

Joey

??????: Sami, Vikram
????????: 2012??1??31?? 22:18
??????: Jiao, Joey; Nick Caton; Karen Walkerman
????: RE: [Equest-users] Some discuss about the Calculation Method of thesoftware

Have you tried using a different infiltration model like the S-G model or the crack method? Both of those allow you to specify a neutral level, so I??m guessing the zone height will make a difference there.

Vikram Sami, LEED AP BD+C

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