"Qualified" energy modeling tools for LEED NC v2.2

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Tim,

I have the impression that Type 56 in TRNSYS is not a geometrical, but
rather a analytical, representation of buildings, by which I mean that Type
56 does not seem to understand what is the relationship between different
building elements, such as east wall, west wall, window, roof, shading, etc.
Am I right or wrong?

How do you input building definition in TRNSYS?

Thanks,
Chaoqin

Zhai Chaoqin's picture
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Chaoqin,
There are three parts to the geometry issue.

For internal radiation exchange, you are correct that TRNSYS is a
non-geometrical model and that two surfaces do not have any knowledge of
their mutual view factor. Like many of the other building models out
there, TRNSYS uses a star-network in which each surface "radiates" to
the air node and vice versa.

For external geometry, one defines orientations in the building
processor (TRNBuild) and then defines corresponding surfaces (slope and
azimuth) in the weather data reader. Solar radiation from a particular
weather data reader surface is then linked to the appropriate Type56
inputs for each orientation defined in TRNBuild.

For external shading (including building self-shading), one places a
series of wingwall and overhang components between the unshaded solar
radiation calculated by the weather data reader and the building, in
effect cutting down on the amount of radiation incident on the building.
It is a flexible methodology but a bit of a cumbersome one. One of the
main pushes in the current development of TRNSYS 17 is a much more
automated methodology for doing building self-shading. The Type56
developers are also working on a true view-factor methodology for
internal radiation exchange within a zone.

Kind regards,

David BRADLEY

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David,

I am not familiar with TRNBuild. Does it have a built-in CAD interface that
one can draw a building? Can one define building surfaces by coordinates?
Can one import a 2-D or 3-D CAD drawing? As I recall in Type56, one needs to
pre-calculate the wall and window areas by orientation for each zone and
input the area value into TRNSYS. I am not sure if this is still the case.

Thanks,
Chaoqin

Zhai Chaoqin's picture
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Chaoqin -

There is not a CAD interface for Type56. TRNBuild is a program that
allows you to define your zones and enter the wall and window areas and
define orientations and adjacencies of the walls, along with defining your
internal gains, infiltration flows, ventialtions flows, etc.

Regards,

Timothy McDowell

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Do Type56 and TRNBuild refer to the same thing?

Zhai Chaoqin's picture
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TRNBuild is a front-end program that allows for the input of the
parameters of Type56 in a more user-friendly manner. Type56 is the TRNSYS
type which does the actual calculations.

Regards,

Timothy McDowell

Timothy McDowell's picture
Joined: 2011-10-02
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Hello Zhai Chaoqin:

Here is a response from Sonia Punjabi from USGBC in Wash, DC:

"LEED Energy and Atmosphere Credit 1 references ASHRAE 90.1. Section 11 of
90.1 lists criteria as requirements for an acceptable modeling tool.

"Because of the wide range of modeling tools being used in the market, USGBC
has not undertaken an initiative to quantify which tools are and are not
acceptable for use to document LEED EA c1. Generally speaking, most program
architects incorporate the 90.1 Section 11 criteria into their programs.
That said, it is still vital that you verify that the model you are
selecting for use meets the criteria.

"Modeling tools that deviate from Section 11 of 90.1 are approved for use in
LEED on a case by case basis. In certain circumstances modeling tools that
deviate from Section 11 offer a cost benefit that far outweighs any
potential inaccuracy. It is advisable to submit a CIR that clearly details
the modeling tools deficiencies and why the modeling tool is an acceptable
compliance path for your building program prior to submitting LEED EA c1
documentation that is based on a non-Section 11 compliant modeling tool."

Hope this helps!

Larry O. Degelman, P.E. 

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