During September, October, November, and December 2005, eight configurations of 2x4 steel-framed walls insulated with R-13 (3.5-in. thick) fiberglass batts were tested in the Oak Ridge National Laboratory (ORNL) guarded hot-box using ASTM C-1363 procedure. These wall assemblies were built on request from the Lennar Family of Builders.
According to the report prepared in 2002 by Enermodal Engineering for California Energy Commission (CEC), there is 27% framing in current residential walls in California. A similar study performed by ASHRAE in 2003 has concluded an average 25% of framing factor for all US residential buildings. The test walls were following findings of the CEC and ASHRAE projects findings. In all walls 2x4 steel studs were installed either at 24-in. or at 16-in. on center as shown on Figure 1. The amount of framing members for all these walls was between 22% and 25%. Conventional ½-in. thick OSB sheathing and ½-in. thick gypsum boards were used for exterior and interior wall finish. Detailed dimensions are presented on Figures 2 and 3.
Figure 3. Layout of the test wall with studs installed at 16-in. O.C.
In the test walls “steel 2” and “steel 3”, steel framing was additionally insulated using ¾-in. thick layers of rigid XPS foam of R-4. In the wall “steel 2” XPS foam sheathing was installed directly on steel studs and it was covered by ½-in. OSB sheathing. In the walls “steel 3”and “steel 12” XPS foam sheathing was installed on top of the OSB sheathing.
In the test walls “steel 6” and “steel 16”, steel framing was additionally insulated using 1-in. thick layers of rigid XPS foam of R-5. XPS foam sheathing was installed on top of the ½-in. OSB sheathing.
For the wall “steel 4” no foam sheathing was utilized. This wall was additionally insulated with ¼-in. thick and 2.5-in. wide aerogel strips which were installed on top of the stud flanges on the side where gypsum board was used. Aerogel insulation is a nano-technology which has been utilized by NASA for aerospace applications. Thermal resistivity of the aerogel insulation is about R-12 per in.
Personnel from the ORNL BTC constructed all test wall assemblies on site. Steel framing members were installed according to specifications showed on Figures 2 and 3. Cavity insulation (R-13 fiberglass batts) was custom-cut for each wall configuration to ensure the perfect fit.
The completed test wall measured 8-ft. wide x 8-ft. tall and was positioned in the test frame such that the wall was centered both vertically and horizontally over the metering chamber opening. The bottom and top tracks were even with the bottom and top metering chamber gaskets.
The hot-box conditions for this test were 100°F and 50°F in the metering and climate chambers, respectively. Array of thermocouples were installed on the both hot and cold sides of the test walls. The arrays for both surfaces were installed to monitor temperatures over the wall cavities, over the studs, over clusters of studs, and over the top and bottom track. The average temperatures of the hot and cold wall surfaces were determined by averaging all of the thermocouples attached to the individual components. An area weighting method was used to determine overall external average surface temperatures. The weighting factors used for the individual components will be discussed later in this report. Figure 4 shows the typical wall installation schedule within the test frame.
The area of the test frame surrounding the specimen wall on both sides and the top was filled with expanded polystyrene insulation to the same thickness as the test wall. The entire perimeter of the test wall was caulked and taped to prevent air leakage.
Figure 4. Schematic of the installation of a typical wall within the hot-box test frame.
Test wall assemblies were installed into a specimen frame which is mounted on a moveable dolly. The specimen frame has an aperture of 13-ft. long by 10-ft. high. The specimen frame/test assembly is inserted between two “clam-shell” chambers of identical cross-section. The placement of the test wall assembly between the chambers allows the chamber temperatures to be independently controlled, thereby creating a temperature difference across the specimen. The chambers are designated as the climate (cold) and metering/guard (hot) chambers. A photograph of the RGHB is shown on Figure 5.
Figure 5. ORNL BTC hot-box.
For More Information Contact Dr. Jan Kosny