**Interlaboratory Comparison of Temperature Results for the Warm Surface
of Window Assemblies Subjected to Winter Conditions**

A Project Description for ASHRAE TC 4.5\
Subcommittees on Condensation Resistance and Joint US/Canada Research

Revised February 9, 2000

Prepared by:

Brent Griffith

Lawrence Berkeley National Laboratory

BLDG. 53 Room 101

Berkeley, CA 94720

Tel. 510-486-6061

Fax 510-486-6046

BTGriffith@lbl.gov

# INTRODUCTION

This proposal summarizes a joint research project that will compare
results for surface temperatures on the same set of fenestration
specimens at ASHRAE winter design conditions. Results are to be
generated blindly by different research groups conducting both
experiments and computer simulations. Experiments will subject specimens
to winter conditions typical of a Hot Box and map surface temperatures
on the warm side with non-contact infrared radiometers. Two dimensional
simulations will model the experimental situation with both routine
techniques for rating and more sophisticated research-level computations
that analyze conduction, convection, and radiation heat transfer. This
project is related to an earlier research project that studied seven
different flat-mounted IGUs. This project differs in that it will study
entire window products.

# PARTICIPANTS

In addition to the participation listed in Table 1, the project is to
remain open to other researchers who would like to contribute results.
Information sufficient for creating simulation input data is posted on a
web site (http://windows.lbl.gov/cr).

### Table 1---Participants, Type of Contribution, and Contact Person

  ---------------------------- -------------------- ----------------------
  Research Institution         Contribution         Contact

  LBNL                         Infrared             Brent Griffith
                               Measurements         

  LBNL                         THERM Simulations    Christian Kohler

  Univ. of Massachusetts       FIDAP and THERM      Dragan Curcija
                               Simulations          

  NRC                          Infrared and\        Hakim Elmahdy
                               U-Factor             
                               Measurements         

  ORNL                         Infrared and\        Andre Desjarlais
                               U-Factor             
                               Measurements         

  Univ. of Waterloo            Bravo Simulations    Roydon Fraser

  Univ. of Waterloo            FRAME/Vision         John Wright
                               Simulations          

  WESTLab & LBNL               Overview             Jeff Baker\
                                                    Brent T Griffith
  ---------------------------- -------------------- ----------------------

#  

# SCHEDULE

The current schedule is shown in Table 2. This schedule included changes
made at the Dallas subcommittee meeting and targets completing the
research and papers in time for the presentation at the ASHRAE meeting
in Cincinnati to be held in June, 2001.

Table 2---Research Steps and Schedule

![](media/image1.wmf){width="5.998611111111111in"
height="3.5027777777777778in"}

Schedule Discussion

1)  Finalize Project Proposal.\
    \
    Finished: June 1999\
    \
    Participating researchers agree on the overall plan, specimen list,
    and basic procedures so that the work can be performed. This current
    plan is outlined in this document. If changes are needed, please
    forward information to Brent Griffith so that this document and the
    project web site can be updated.

2)  Assemble and Document Information for Simulators\
    \
    Finished: Feb. 3, 2000\
    \
    Geometry and material property information have been collected and
    made available to simulators on a central, project specific web
    site, http://windows.lbl.gov/cr

3)  Develop Specimen Models using Standard Film Coefficients\
    Start: Feb 2000\
    Finish: July 2000\
    \
    Simulation researchers prepare models. Initial runs are conducted
    using standard surface heat transfer coefficients/conditions with
    the understanding that experimental conditions will differ and the
    models will need to be run again with "as-tested" conditions when
    those values become available later in the project.

4)  LBNL Experiments\
    \
    Finished: Nov 1999\
    \
    LBNL perform infrared measurements on the three primary specimens
    using both imaging and point infrared detectors. Air conditions
    within 4 mm from the specimen\'s glazing surface were also measured.
    Measurements were performed at both ASHRAE and ISO temperature
    conditions. A reusable shipping crate was built to transport the
    specimens to the other laboratories.

5)  NRC Experiments\
    \
    Start: Feb 2000\
    Finish: July 2000\
    \
    NRC will perform measurements on the three primary specimens. Data
    collected will include surface temperatures from non-contact
    infrared radiometer and U-factor.

6)  ORNL Experiments\
    Start: July 2000\
    Finish: Sept 2000\
    \
    ORNL will perform measurements on the three primary specimens. Data
    collected will include surface temperatures from non-contact
    infrared radiometer and U-factor.

7)  Write papers\
    Start: July 2000\
    Finish: September 29, 2000\
    \
    Participants prepare documentation to submit drafts by September 29,
    2000 in order to complete reviews and overview paper by winter
    ASHRAE meeting in Atlanta, January 2001.

8)  Provide "As-Tested" experimental conditions to simulators\
    Start: March 2000\
    Finish: September 2000\
    \
    To the extent possible, experimental participants will provide
    ancillary data on the conditions found during the tests to
    simulation participants. "As tested" data on mean and/or local film
    coefficients are particularly important. This will most likely
    consist of results from CTS experiments. Glazing deflections or
    other changes in geometry may also be reported. For conjugate CFD
    simulations, air flows and radiation conditions at model boundaries
    may also be desirable. Surface temperature and U-factor results are
    not to be disclosed.

9)  Finalize simulations with "as-tested" experimental conditions.\
    Start: August 2000\
    Finish: September 2000\
    \
    Simulations should use boundary conditions that closely approximate
    what was experienced by the individual specimens at the individual
    laboratories in order for results to be comparable.

10) Write Overview Paper\
    Start: October 2000\
    Finish: November 2000\
    \
    Results will be compiled from all participants into a summary paper
    that presents an overview, comparison, and discussion of the
    results.

11) ASHRAE reviews\
    Start: October 2000\
    Finish: January, 2001\
    \
    Symposium Chair organizes reviews. Chair cannot be an author.

12) ASHRAE Symposium, Cincinnati June 2001.\
    \
    Present results at ASHRAE Meeting

# SPECIMENS

The main focus of the interlaboratory project will be to study the three
specimens shown in Table 3. The primary set of specimens will be
circulated between all test facilities and ultimately returned to LBNL.
Drawings of the specimens are available as computer files on the project
web site (http://windows.lbl.gov/cr/) and are included as Figures x thru
y

Table 3---Primary Specimens

+---------+-----------+-----------+--------+--------------+-----------+
| S       | Man       | Type      | Frame  | Glazing      | Overall   |
| pecimen | ufacturer |           | Ma     | C            | Size      |
| Number  | (Mo       |           | terial | onfiguration |           |
|         | del/type) |           |        |              |           |
+---------+-----------+-----------+--------+--------------+-----------+
| 1       | LBNL      | Foam Core | N/A    | Foam Core\   | 2\' 0\" x |
|         |           | Heat Flux |        | ≈12.5 mm EPS | 3\' 0\"   |
|         | CTS       | T         |        |              |           |
|         |           | ransducer |        |              |           |
+---------+-----------+-----------+--------+--------------+-----------+
| 2       | Marvin\   | Fixed     | Wood   | Dual,        | 2\' 0\" x |
|         | 3-step    | Casement  |        | air-filled\  | 3\' 0\"   |
|         |           |           |        | Clear-Clear\ |           |
|         |           |           |        | 16.5 mm gap  |           |
+---------+-----------+-----------+--------+--------------+-----------+
| 3       | Marvin\   | Fixed     | Wood   | Dual,        | 2\' 0\" x |
|         | 3-step    | Casement  |        | air-filled\  | 3\' 0\"   |
|         |           |           |        | Clear-Low-e\ |           |
|         |           |           |        | 16.5 mm gap  |           |
+---------+-----------+-----------+--------+--------------+-----------+

# Testing

The specimens will be tested in laboratory hot-box chambers according to
ASTM C-1199 (Revision 6) wherever this standard is applicable. If
possible, two sets of tests could be completed at different temperature
settings, -17.8 and 21.1C as well as 0 and 20C. (LBNL has completed
measurements at both settings.) The foam core of the surround panel
should have a nominal thickness of 150 mm. Specimen #1, the Calibrated
Transfer Standard, will be mounted 25 mm in from the surround panel
weather side surface. Specimen #1 should be tested first in order to
verify (or adjust so) that the mean surface heat transfer rates are
within 5% of 7.7 W/m^2^-K on the warm side and 29 W/m^2^-K on the cold
side. Specimens \# 2 and \# 3 will be mounted in the surround panel with
their weather side surfaces flush with the weather side surface of the
surround panel. Perimeter joints between the test specimen and the
surround panel will be sealed with tape on both sides of the test
specimen.

A separate document has been prepared as a draft ASTM test method that
provides guidance on performing the surface temperature measurements
using infrared thermography.

# SIMULATIONS

Simulations will model heat transfer through the window assemblies and
related fluid movements. This is a research project and not a routine
effort to simulate window U-factors. The final results will include
U-factor, but of more interest is obtaining results for the surface
temperature along the warm side surface. The surface temperatures are
what determine the performance with regards to moisture condensation.
Two-dimensional models will simulate the performance of the entire
vertical cross section of a specimen and not just the edge of glass. The
geometry for each two dimensional model is that of the vertical cross
section along the centerline of the specimen. The surround panel should
be included in the model for a distance of 75 mm above and below the
specimen opening.

**Boundary Conditions**

One goal of this project is to investigate the effect that environmental
boundary conditions have on the accuracy of computer simulations that
attempt to predict the condensation resistance of a window product.
Boundary conditions are comprised of free stream air temperatures and
surface heat transfer rates. The main focus of the project is to use
AHSRAE winter design conditions where free stream temperature conditions
are 21.11°C on the warm side and 17.78°C on the cold side. Secondary
results are desired for ISO conditions of 20.0°C on the warm side and
0.0°C on the cold side.

Simulations are also to be conducted with a variety of surface heat
transfer rates or film coefficients. Some models will use only the total
film coefficient that includes both radiative and convective heat
transfer rates. Models that directly calculate radiation exchange will
need the convective portion of the total film coefficient. It has been
suggested to use three different sources for mean overall surface heat
transfer coefficients, (1) NFRC/W4.1, (2) SPC142a/ISO 15099, and (3)
measured values from CTS experiments. It is also possible to use
*localized* convection surface heat transfer coefficients rather than
mean values. (1) results from simulations at UMass and (2) measurements
using traverse data from LBNL.) Thus, for each specimen, several sets of
simulation results will be obtained corresponding to different film
coefficient boundary conditions. Note that an iterative approach is
necessary in some cases because some modeling boundary conditions depend
on the surface temperatures, which are not known.

**NFRC/W4.1 Fixed Boundary Conditions**

NFRC has defined fixed boundary conditions for use in simulating frame
sections and relies on the algorithms in Window 4.1 for the glazings.
Table 1 lists final values for coefficients that should be used for the
various regions of the three specimens. These values were determined
from low-level operation of the W4.1 program (puke files) in order to
provide this project a set of fixed boundary conditions. This will allow
initial modeling efforts to proceed directly without having to iterate
with boundary conditions that vary with surface temperature. (Window 4.1
has already performed temperature iterations to come up with the values
for the glazing regions.) NFRC has fixed values for the total
coefficient on the frame. Assuming a surface temperature of 12°C and
calculating radiation using equation 10, allows separating out the
convective and radiative parts of the warm side film coefficient. For
the cold side, the correlation used by Window 4.1 for forced convection
was used to determine the convective portion. (The \"?s\" in Table 1
reflect the fact that it would be useful to know the exact methodology
used by NFRC to arrive at their fixed values.)

**ISO 15099/SPC142A Temperature Dependent Boundary Conditions**

These draft standards both provide essentially the same methods for
determining surface film coefficients (and they differ from NFRC/W4.1)
except for the cold side convective coefficient. The surface heat
transfer coefficients are determined through the use of temperature
dependent equations that are available elsewhere.

Table 1 Boundary Conditions: NFRC/W4.1Surface Heat Transfer Coefficients

+---------+------------+------------------+-------------+------------+
| S       | Region     | Boundary         | Warm/Indoor | Co         |
| pecimen |            | Condition:\      | Side\       | ld/Outdoor |
|         |            | Mean Coef.       | (W/m⋅K)     |            |
|         |            |                  |             | Side\      |
|         |            |                  |             | (W/m⋅K)    |
+---------+------------+------------------+-------------+------------+
| 1       | Glazing    | Convective       | 3.10        | 25.46      |
+---------+------------+------------------+-------------+------------+
| CTS     |            | Radiative        | 4.60        | 3.21       |
+---------+------------+------------------+-------------+------------+
|         |            | Total            | 7.70        | 28.66      |
+---------+------------+------------------+-------------+------------+
| 2       | Glazing    | Convective       | 3.40        | 25.46      |
+---------+------------+------------------+-------------+------------+
| Clear   |            | Radiative        | 4.51        | 3.23       |
+---------+------------+------------------+-------------+------------+
| window  |            | Total            | 7.91        | 28.69      |
+---------+------------+------------------+-------------+------------+
| 3       | Glazing    | Convective       | 3.07        | 25.46      |
+---------+------------+------------------+-------------+------------+
| Low-E   |            | Radiative        | 4.62        | 3.21       |
+---------+------------+------------------+-------------+------------+
| window  |            | Total            | 7.69        | 28.67      |
+---------+------------+------------------+-------------+------------+
| 1, 2,   | Frame &    | Convective       | ?2.92       | ?25.46     |
| &3      |            |                  |             |            |
+---------+------------+------------------+-------------+------------+
|         | Surround   | Radiative        | ?4.69       | ?3.57      |
+---------+------------+------------------+-------------+------------+
|         | Panel      | Total            | 7.61        | 29.03      |
+---------+------------+------------------+-------------+------------+

**Material Properties**

Table 2 Thermal Properties of Materials in Specimens 1, 2 and 3

  ------------------------- ----------------------- ---------------------
  Material                  Thermal Conductivity\   Emissivity
                            W/m-K                   

  Glass                     1.0                     0.84

  Low-E Coating (Spec. 3)   N/A                     0.10

  Wood                      0.14                    0.90

  Butyl Rubber              0.24                    0.90

  Steel ANSI 30 Stainless   14.3                    0.2

  PVC flexible              0.12                    0.9

  EPS foam, CTS core        0.034                   0.9

  EPS foam, Surround panel  0.036                   0.9

  Silica gel desiccant      0.03                    0.9
  ------------------------- ----------------------- ---------------------

# DATA PRESENTATION

Measuring and modeling efforts need to arrive at data sets that allow
for relatively simple comparison of results. Each set of temperature
results should be presented in two different coordinate systems with the
origin of both systems placed at the sill sightline of the window
assembly or the bottom edge of the CTS. The first system will present
data with the form *(x, y, T),* where **x** is a spatial coordinate
directed in the plane of the glazing, **y** is a spatial coordinate
directed away from the plane of the glazing, and **T** is surface
temperature. The second system would present data with the form *(l, T)*
where **l** is the accumulated path length (from the origin) along the
warm side surface of the profile. Data should be provided for 75 mm of
the surround panel above and below the specimen, as well as the entire
centerline section of the specimen. In order to help ensure that
comparable coordinate systems are used, The description of specimen
geometry for simulators will provide x and y locations of profile
vertices and the associated values for path length. Small fillets and
rounds will be neglected when determining accumulated distances along a
frame profile.

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