URGENT: Window U-values: Total window assembly v/s Glass only

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Dear all,

I have a small question regarding entering window properties to eQUEST:

I have read a lot of emails in the forum discussing NFRC testing, LBNL
Window 5 import, and other topics that I haven't paid attention to
before.

The way I modelled my windows is the following:

1. I have manufacturer's specifications listing the glass U-values,
not the total assembly.
2. In the "Glass Types" (eQUEST Detailed Mode), I created glass
types, and entered the glass conductance, visible transmittance, SC, and
emissivity from the manufacturer's details I have.
3. When creating windows, I specify which glass type (from the ones
I created in step 2), in addition to the frame width and conductance.

I'm assuming that, given that I entered the u-values for the glass only,
and then I entered information about the frame, then I need not worry
about any conversions in U-values, since eQUEST has all the necessary
information to calculate the equivalent u-value of the whole pane +
frame assembly, right?

I appreciate your feedback / comments today if possible, as this has
become really urgent!

Many thanks,

Omar

___________________________

Omar Katanani

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Omar,

The answer depends on the purpose of your study. If you're trying to get
results for a client on the impact of the glazing on their energy
performance, this may be adequate. Make sure you've entered in the framing
information properly (metal vs. non-metal).

I'd recommend opening up your simulation output results file (xxxx.SIM) and
going to the either the last page of the LV-D report or sort through your
LV-E report to see what value eQUEST has calculated. Compare these values
to the ASHRAE Fundamentals results for overall assembly values including
frame to see how close you've come. I would not blindly trust that eQUEST
will give you an appropriate overall assembly value based on entering only
the center of glass number.

However, if this is for a LEED study, this is not adequate. This an excerpt
from an e-mail I sent out recently regarding LEED and NFRC requirements.

In order to meet LEED EAp2 Minimum Energy Performance, the project must
comply with all mandatory provisions of ASHRAE 90.1-2007. Section 5.4.2
Fenestration and Doors requires that fenestration performance be determined
per section 5.8.2. Section 5.8.2.4 U-factor requires that the U-factor for
the overall fenestration area (including framing) be determined in
accordance with NFRC 100. If you do not have NFRC data available, values
from section A8.2 are the only acceptable alternative.

*Robby Oylear, LEED**?** AP BD+C*

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Is the u-value listed for a manufacturer and specific model on the NRCAN website centre of glass or overall assembly?? Many windows are custom made to suit so I am unclear if each individual custom window would need to be tested.

In eQuest, when entering the window, if the u-value represents the whole window, including frame, do you need to enter a frame width, conductance etc as well under the Window Frame section under Window Properties?? Thanks.

Brad Robinson

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Dear Robby,

Yes, I am modeling for LEED purposes.
I'll look into A8.2. But at least, is my method correct for the
proposed scenario?

Brad: I think you need to enter the center of glass u-value in the
"Glass Type", and then enter the frame properties in the "Window"
properties...

Best,
Omar

Quoting Brad Robinson :

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Omar,

To directly answer your question:

"I?m assuming that, given that I entered the u-values for the glass only,
and then I entered information about the frame, then I need not worry about
any conversions in U-values, *since eQUEST has all the necessary information
to calculate the equivalent u-value of the whole pane + frame assembly,*
right?"

No. Your method will result in an assembly U-value based on your input
glass conductance and whatever default frame properties that the eQUEST
wizard will use. I have never tried to let eQUEST determine an assembly
value, as NFRC values are required for LEED and code compliance studies. I
would not be surprised if the values eQUEST is calculating (shown in LV-D
and LV-E reports like previously mentioned) are much different than what
you'll actually see in the test results.

Again, NFRC values are a LEED requirement, so unless you're just doing
preliminary analysis for a client, you need to receive NFRC simulation
reports or certified product directory numbers in accordance with NFRC 100.

*Robby Oylear, LEED**?** AP BD+C*

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Dear all,

Thank you for your responses.

1. Are the NFRC testing and the values in table A8.2 used for the
Baseline, Proposed, or both scenarios?

2. Let's say I do not have NFRC test results and decide to use the
values in table A8.2. For a clear double glazed and metal frame type, I
get an assembly U-factor of 5.1. How can I input this into eQUEST? As
far as I know, I can enter the glass properties and the frame
properties. Do I have to play with the glass properties and check the
LV-D report for the calculated Assembly u-value?

Similarly, for the baseline, Tables 5.5-1 to 5.5-8 of ASHRAE 90.1
provide the assembly u-values for vertical glazing. How can I enter
these values into eQUEST?

3. I am attaching the specs of the proposed glazing. These numbers
are for the glass only (note that the u-values reported are NFRC ones).
Additionally, I know that the frame will be aluminium. Do I still need
NFRC U-values for the whole assembly, or is the NFRC usually for the
glass only? If yes, how can I calculate the whole assembly U-value
(given that eQUEST doesn't have the ability to calculate this)

Thanks for clarifying this, as my project is outside the US and we are
not too familiar with standards such as NFRC.

Best regards,

Omar Katanani

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Hi Bruce,

The project is in Lebanon, and there are pretty much no standards
relating to energy whatsoever!

The LEED Review I got is the following:

"It is It is unclear whether the window U-value of 0.26 and SHGC of 0.28
used for the Proposed case accounts for the impact of the window frames
on the whole assembly as required by ASHRAE modeling protocol. Please
provide additional information to confirm that the framed assembly
U-value was used for the Proposed case windows (e.g. showing that the
whole window assembly has been tested by NFRC, or verifying that LBNL
Window5 calculations have been provided for the whole assembly, or
verifying that the frame effects are captured within the energy modeling
software), or revise the model referencing ASHRAE 90.1-2007 Table A8.2
if needed."

Can we argue that the frame effects are captured within eQUEST, as per
the underlined phrase?

Do you recommend using table A8.2, or are its U-values too high?

Best regards,

Omar Katanani

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Thanks Bruce,

I have an additional question:

* In the "Glass prop.jpg" file attached, I entered the glass
conductance as 0.6 Btu/h-ft2-F

* In the "Window specs.jpg" file, I entered the frame width as
zero.

* However, when I look at my LV-D report, I notice that the
Average U-value for the windows is 0.509 Btu/h-ft2-F

Why is this number different from the glass conductance, given that I am
assuming the frame width zero (i.e, the window is only composed of
glass)?

I need to figure this out in order to argue with the LEED Reviewer that
eQUEST has the ability to capture frame effects.

Many thanks,

Omar Katanani

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If you look at the description for LV-D, it will tell you what all is
included in the U-value .It is either glass + internal film, or
glass+internal film+external film. What you enter in eQuest is either just
glass or glass + internal film (check the help on it to be sure). The values
you get from manufacturer are glass + internal film + outside film (someone
correct me if this is not the case).
So make sure that you are comparing the same combination of values.
-Rohini

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Omar,

If I was the reviewer in this case I'd have trouble understanding how eQUEST
is accounting for frame effects when you've set the frame width to zero.
Honestly, I think the only acceptable values you should be using are from
the table in Appendix A if you don't have an equivalent nationally
recognized certification program.

Also, your SHGC looks really low compared to your visible transmittance.
Unless you're using some pretty impressive glazing or low-e coatings I'd
expect the VT to be around 0.5-ish for a glazing assembly with an SHGC of
0.29.

*Robby Oylear, LEED**?** AP BD+C*

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Robby,

I was just doing some sensitivity analysis for my own sake when I put
the frame width into zero.

Should the values in table A8.2 be used for the Baseline? If that is the
case, then I should use 5.1W/m2-C (0.9 Btu/h-ft2-F) for my case, which
is much less stringent than the 3.41W/m2-C (0.6 Btu/h-ft2-F) and this
would be to my advantage :-)

However, if I am required to use A8.2 for the proposed, then I should
the figure of 0.9 Btu/h-ft2-F with the baseline u-value being
0.6Btu/h-ft2-F. This would definitely worsen my thermal model results
for LEED and very probably risk my 10% prerequisite of improvement over
the baseline!

The glazing is pretty impressive. I'm attaching the specs, highlighted
in yellow. The Glass U-value if 0.26 Btu/h-ft2-F.

Additionally, if I am to use the assembly U-value of 0.9 Btu/h-ft2-F for
my baseline, what is the best way to enter it to eQUEST? Shall I enter
the glass properties to 0.9 and zero out the frame width?

Many thanks,

Omar Katanani

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Omar,

Table A8.2 is for the proposed case, when you do not have certified values
for the overall assembly. They are intended to be worse than the baseline
to encourage projects to follow the code guidelines for certified testing.

Baseline values shall be determined in accordance with the tables in Section
5, which you've likely already done.

I agree that you should enter the frame as zero width if you are entering
the simplified values in as assembly values under the glass parameters.

Though Solarban is a great product as far as glass is concerned, if the
product uses a poorly insulated aluminum frame, the value could be much
worse than the baseline.

My big concern here would be that you don't know what the performance of
your glazing assembly is. If you can show project specifications that
clearly describe the type of thermally broken frame that will be provided,
you could argue that the values in ASHRAE Fundamentals could be used instead
of ASHRAE Table A8.2.

You need to provide some justification for whatever assembly U-factor, SHGC,
and VT you end up using in your proposed case. Be that NFRC testing, ASHRAE
Table A8.2, or ASHRAE Fundamentals values.

*Robby Oylear, LEED**?** AP BD+C*

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On Thu, Jul 28, 2011 at 5:40 AM, Omar Katanani wrote:

Fenestration
U-factors shall match the appropriate requirements in Tables 5.5-1 through
5.5-8. Fenestration SHGC shall match the appropriate requirements in Tables
5.5-1 through 5.5-8.
They are silent about frames but I would use one, match the frame width of
your proposed window. Use an Aluminum frame with no thermal break.

For your proposed building I highly recommend you use LBNL's Window program.
In it you can select your window type, e.g. casement, picture, etc,, select
your glass from their glass library, which is huge and definitely includes
Solarban, and then model your frame using whatever information the architect
gives you related to thermal breaks and spacers. After you run your window
in the program you can select to save it to a DOE 2 report which will
automatically go into your DOE 2 Window folder. Then you just have to select
it from the pull down menu.

Otherwise, input your glass values, as you are already, *and* input your
frame data, the same data you got from your architect, and model it that
way. When you look at your LV-D report you will likely see a variety of U
values. That's because they will vary based on window size.due to the frame
effect. You need to have a frame.

As far as NFRC, your Solarban glass data is NFRC rated which should be good
enough, I think. It's rare in commercial buildings to have a rating for the
entire window.

Carol

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Carol,

I have to take exception to this:
"As far as NFRC, your Solarban glass data is NFRC rated which should be good
enough, I think. It's rare in commercial buildings to have a rating for the
entire window."

In order to meet LEED EAp2 Minimum Energy Performance, the project must
comply with all mandatory provisions of ASHRAE 90.1-2007. Section 5.4.2
Fenestration and Doors requires that fenestration performance be determined
per section 5.8.2. Section 5.8.2.4 U-factor requires that the U-factor for
the overall fenestration area (including framing) be determined in
accordance with NFRC 100. If you do not have NFRC data available, values
from section A8.2 are the only acceptable alternative.

NFRC values for the glazing alone not "good enough". This is exactly what
the reviewer is trying to get at.

I'd hardly call NFRC certification rare. In the State of Washington NFRC
certification has been required for all glazing assemblies for over 10
years.

How do you justify certifying that your projects have met the mandatory
provisions of ASHRAE 90.1 without NFRC data?

*Robby Oylear, LEED**?** AP BD+C*

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This came off of the Window website:

WINDOW 6.3 is a publicly available computer program for calculating total
window thermal performance indices (i.e. U-values, solar heat gain
coefficients, shading coefficients, and visible transmittances). WINDOW 6.3
provides a versatile heat transfer analysis method consistent with the
updated rating procedure developed by the National Fenestration Rating
Council (NFRC) that is consistent with the ISO 15099 standard. The program
can be used to design and develop new products, to assist educators in
teaching heat transfer through windows, and to help public officials in
developing building energy codes.

* *

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Robby,

I would agree that NFRC values for the glazing alone would not be good
enough. That is why I recommended using Window.

I have not had the success you have had obtaining an NFRC rating for the
window+frame because the buildings I have been working on are using
site-built windows. In Washington, and Seattle in particular, you have had
John Hogan working on your codes. It's entirely possible that the level of
information you have available is greater than what I have seen.

Carol

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Carol,

We definitely have the energy code on our side up here forcing projects to
provide NFRC data. However, the way I interpret ASHRAE 90.1, the same
requirement exists.

ASHRAE 90.1 section 5.8.2.1 and 5.8.2.2 would indicate that U-factor, SHGC,
and air lekage rate are to be determined by a laboratory accredited by a
nationally recognized certification organization, such as the National
Fenestration Rating Council. If no label is provided, a signed and dated
certification (simulation report) should be provided.

This tells me that a simulation in WINDOW by the energy consultant would not
be enough to verify glazing properties.

Am I reading this incorrectly? Are you bypassing these requirements because
of the "*manufactured *fenestration" part? ASHRAE 90.1 doesn't clearly
define the difference between site-built and manufactured.

-Robby

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Regarding Omar's first question, I would also clarify that adding a frame to the baseline is probably not the correct approach unless you are adjusting the U-value to a center of glass value and accounting for the frame and edge effects such that the total fenestration performance is equal to the 90.1 prescribed value.

'They are silent about frames but I would use one, match the frame width of your proposed window. Use an Aluminum frame with no thermal break.'

Baseline Table 5.5-1 through 5.5-8 specify 'fenestration assembly' values which include the effect of the frames and edge of glass. Modeling a frame in the Baseline will further degrade the overall fenestration U-value (unless your frame outperforms the glazing) and result in overestimating the savings relative to the fenestration performance. If you use the Table values for your window performance, frames shouldn't be included. If you include a frame, you should create a 90.1 compliant product using WINDOW and use the appropriate frame and glazing performance values as eQuest inputs such that your overall frame and glazing performance matches the A90.1 Table value.
Regards,
Bill

Bill Talbert PE, LEED(r) AP

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I know in Canada they specifically mention using Window 5.x to determine the rating. This is contained in the LEED Canada 2009 Supplementary Energy Modelling Guidelines:

"Specialized software packages such as FramePlus or LBNL Window 5.x may be used to calculate
window performance parameters."

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>From the 90.1 User's Manual pg 5-12:

"With Addendum 90.1ag (published
with Standard 90.1-2001) glazed wall
systems, including glass curtain walls used
on large buildings, storefront glazing
systems, and other similar products that
are assembled at the construction site, as
opposed to at the factory, must either be
rated using NFRC procedures or the
default U-factor, SHGC and VLT from
Table A8.2. Since the performance values
in Table A8.1A are based on uncoated
clear glass in poorly performing metal
frame, they do not offer any credit for
low-e coatings, thermal break frames or
any other advanced feature. In general,
values from Table A8.1A will not achieve
compliance with the fenestration
requirements.
The NFRC procedure for site-built
fenestration is described in NFRC 100.
The NFRC ratings are based on computer
simulations of various product options at
standard sizes. (For curtain walls, the
standard size specified is 2000 mm by
2000 mm, or approximately 79 in. by 79
in.) Multiple glass options can be included
in one simulation matrix. The entire
simulation matrix is then validated by a
single physical test at the standard size. If
the matrix for a product has previously
been validated, then a new glass option
can be added to the matrix by simulation
alone. Simulations and tests must be done
by an NFRC-accredited simulation and
test laboratories."

Also, the LEED Reference Guide for Green Building Design and Construction,
pg 275 specifically references Tables A8.1 and A8.2 or requires that the
products be certified and labeled in accordance with NFRC.

Not seeing any statements that would allow the modeler to perform their own
fenestration assembly performance calculations.

-Robby

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Well, this is what the whole introductory page says on the LBNL website:
http://windows.lbl.gov/software/window/window.html.I'd like to hear what
some of the glass guys say about this. Alexx? Anyone else?

WINDOW *WINDOW 6.3**
(For NFRC Certification and modeling Complex Glazing Systems)* *WINDOW 5.2
(older version)* * Download WINDOW
6.3
*
(for NFRC Certification and complex glazing systems) * Download 5.2 (older
version)
*(Contains WINDOW 5.2.17a (bug fixes for DOE2 and EnergyPlus Files) and
Version 17.1 of the International Glazing Database) * Knowledge
Base
*
(Check here first if you are experiencing a problem with the software)
* Knowledge
Base *
(Check here first if you are experiencing a problem with the software) * New
Features * New
Features *
Documentation *
(includes documentation for both
WINDOW 4.1 and 5)
*Documentation
*
(includes documentation for both
WINDOW 4.1 and 5) * Window Glass Library
Update
* * Window Glass Library
Update
* * System Requirements
* *System Requirements
*

WINDOW 6.3 is a publicly available computer program for calculating total
window thermal performance indices (i.e. U-values, solar heat gain
coefficients, shading coefficients, and visible transmittances). WINDOW 6.3
provides a versatile heat transfer analysis method consistent with the
updated rating procedure developed by the National Fenestration Rating
Council (NFRC) that is consistent with the ISO 15099 standard. The program
can be used to design and develop new products, to assist educators in
teaching heat transfer through windows, and to help public officials in
developing building energy codes.

* Program Updates*

The main change from WINDOW 5 to WINDOW 6 is the ability to model complex
glazing systems, such as venetian blinds and roller shades. In addition,
many bugs have been fixed.

* Program Features*

WINDOW 6.3 includes all of the WINDOW 5.2 capabilities such as:
[image: bullet]

a state of the art Microsoft WindowsTM interface
[image: bullet]

updated algorithms for the calculation of total fenestration product
U-values and Solar Heat Gain Coefficient consistent with ASHRAE SPC142,
ISO15099, and the National Fenestration Rating Council
[image: bullet]

a Condensation Resistance Index in accordance with the NFRC 500 Standard
[image: bullet]

a surface temperature map
[image: bullet]

an integrated database of properties
[image: bullet]

links to other LBNL window analysis software:

[image: bullet]

THERM 6, for calculating 2-D frame and edge effects
[image: bullet]

RESFEN, for calculating the energy effects of windows in typical houses
throughout the United States
[image: bullet]

Optics5 for the optical properties of all coated and uncoated glazings,
laminates, and applied films.

Program Capabilities

WINDOW 6.3 offers the following features:
[image: bullet] The ability to analyze products made from any combination
of glazing layers, gas layers, frames, spacers, and dividers under any
environmental conditions and at any tilt;
[image: bullet] The ability to model complex glazing systems such as
venetian blinds and roller shades.

[image: bullet] Directly accessible libraries of window system components,
(glazing systems, glazing layers, gas fills, frame and divider elements),
and environmental conditions;

[image: bullet] The choice of working in English (IP), or Systeme
International (SI) units;

[image: bullet] Help Screens and a manual;

[image: bullet] A print feature which generates detailed results for a
window, window component, or library;

[image: bullet] The ability to specify the dimensions and thermal
properties of each frame element (header, sills, jamb, mullion) in a
window;

[image: bullet] A multi-band (wavelength-by-wavelength) spectral model;

[image: bullet] A Glass Library which can access spectral data files for
many common glazing materials from the Optics5 database;

[image: bullet] A night-sky radiative model;

[image: bullet] A link with the DOE-2.1E and EnergyPlus building energy
analysis program. Performance Indices and Other Results

For a user-defined fenestration system and user-defined environmental
conditions, WINDOW calculates:
[image: bullet] The U-value, solar heat gain coefficient, shading
coefficient, and visible transmittance for the complete window system;

[image: bullet] The U-value, solar heat gain coefficient, shading
coefficient, and visible transmittance for the glazing system (center
-of-glass values);

[image: bullet] The U-values of the frame and divider elements and
corresponding edge-of-glass areas (based on generic correlations);

[image: bullet] The total solar and visible transmittance and reflectances
of the glazing system;

[image: bullet] Color properties, i.e. L*, a*, and b* color coordinates,
dominant wavelength, and purity for transmitted and reflected (outdoor)
solar radiation;

[image: bullet] The damage-weighted transmittance of the glazing system
between 0.3 and 0.38 microns;

[image: bullet] The angular dependence of the solar and visible
transmittances, solar and visible reflectances, solar absorptance, and solar
heat gain coefficient of the glazing system;

[image: bullet] The percent relative humidity of the inside and outside
air for which condensation will occur on the interior and exterior glazing
surfaces respectively;

[image: bullet] The center-of-glass temperature distribution.

Updated: 05/17/11

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Firstly - congratulations to all contributors - I think this is probably the first time (that I recall) that all of the posts on this list have been on a single thread. I couldn't resist being a part of this so I'm going to add my 2 cents:

90.1 baseline values & SHGC are assembly u-values so your frame needs to be calculated into this. To get the derated value - you could either use the handy little XL spreadsheet that comes with the install of eQUEST (under the data\window folder) called eQUEST-DOE2 Glass Library.xls. This gives you COG values AND glass+frame NFRC values. They have separate table where it is sorted by U-value and SHGC - I use it all the time (screenshot below).

[cid:image004.png at 01CC4E0E.0897B350]

So you can select your values in conjunction with the values below from the DOE2 help file to get what you need.

Frame Type

FRAME-CONDUCT (excludes OA film)

U-valuea

Thermally unbroken aluminum

3.037 (17.24)

1.90 (10.79)

Thermally broken aluminum

1.245 (7.07)

1.00 (5.68)

External flush glazed aluminum

0.812 (4.61)

0.70 (3.97)

Wood with or without cladding

0.434 (2.46)

0.40 (2.27)

Vinyl

0.319 (1.81)

0.30 (1.70)

a U-value includes OA film at 15 mph [6.7 m/s] windspeed
FRAME-CONDUCT = [(U-value)-1 - 0.197]-1 Btu/ft2-F-h
FRAME-CONDUCT = [(U-value)-1 - 0.035]-1 W/m2-K

Alternately, you can select a COG value to match what you want, set your frame to zero and your spacer to UE-EQ-UC (this will give you a uniform COG conductance across the assembly).

I am curious about LBNL window imports. When you set up your assembly in window - it includes frames, but you import it in as a glass type - should you zero out the frame (as in the second case) if you import from window?

Vikram Sami, LEED AP BD+C

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Great thread-

To answer Vikram's question - When using WINDOW, you are slightly limited in the output file (for example, if I create an NFRC-type model to figure out U-value for a curtainwall system, I will need to simply the window to export it into a DOE-2 report format). When you do import a WINDOW Report for DOE-2 into eQUEST it does not load any frame information with it - it presents the COG glass performance. My process is to adjust the spacer type and frame width+conductance to make an object that matches what WINDOW tells me my window performance is.

I don't model for LEED, so am less familiar with what is required for that - since I work for a window manufacturer I usually have access to all the data I need to determine frame-inclusive u-value and SHGCs, i.e. no need to rely on 90.1 defaults.

Since the conversation was about using NFRC data - let me ask this question: NFRC data for windows (curtainwall assemblies included) is for a "default" size. I believe for curtainwall a mulled unit is modeled at 2m x 2m (or 78.54" x 78.54") - as shown below:

[cid:image001.jpg at 01CC4DF9.F0308990]

This is an example, but let's say that the NFRC value is U-0.34. If your building has a smaller or larger window (which will change the glass-to-frame ratio) the U-value will be different.

Is it still appropriate to use the NFRC value in that case, where it is entered as a frame-inclusive U-factor and SHGC? I'm curious as to how others approach this issue when dealing with models for compliance.

Kind regards,

Alex Krickx, LEED AP

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I was reading this while revisiting my window settings and read up some more on this. 

So basically as we all know there are two ways to model glazing in equest...

by Glass library code or simplified (with custom values for the glazing - which does not include the frame)

if you click on a glass type in "building shell" component tree and click "spreadsheet"  you will see all the settings.  Equest uses two methods for calculating glass heat transfer and solar gain.....

GLASS-TYPE-CODE      indicates that glass data will be selected from windows in the library

SHADING-COEF           indicates that the glass shading coefficient will be specified and the ASHRAE shading coefficient method will be used for the window solar-thermal calculation

Glass codes are obviously already lab tested through NFRC and approved for modeling.  But there are some NFRC tested glazings that are not in the DOE2 window library.

If you are planning on using manual inputs (simplified method) for the proposed model, you are basically saying that you are using the "ASHRAE shading coefficient method" for modeling the glazing because it is the only acceptable alternative to using a pre-tested glass type code (which applies to buildings being modeled for LEED).

The tables 5.5-1 thru 5.5-8 in ASHRAE 90.1 have all the assembly max factors for baseline window assemblies as prevoiusly mentioned.  So if you are modeling your glazing U-factor as "X" and that value is directly from the 5.5 tables, you must omit the frame or the assembly max would be off.

If you use ASHRAE manual inputs for both models, you are likely shorting your proposed model additional energy efficiency.  My opinion is that manual inputs tell the reviewer this - The proposed windows perform the same as the baseline and no energy efficiency improvement is being claimed for windows at all.

When the proposed manual inputs don't match the baseline manual inputs I can see why there would be a red flag raised - because if you go that route the values should be the same per ASHRAE 90.1.

For the baseline, I don't see why you wouldn't just model your baseline without a frame, then use "simplified" glazing values from the 5.5 tables.  The LEED reviewer will see that your values match up and that your windows assembly max values are ASHRAE compliant.

I should mention that currently for LEED-NC 2009 submissions you should be using the 5.5 table values in ASHRAE 90.1 (2007) for your climate zone.  You can use the more stringent window values in later publications of ASHRAE 90.1 but they likely won't care as long as you don't go beyond the max allowed in 2007 version of ASHRAE.

Chris Baker2's picture
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Joined: 2014-03-25
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