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Feature from Environmental Building News
April 1, 1998

Sidebar: Mass-Enhanced R-Value of Agriboard Panels

Mass-Enhanced R-Value of Agriboard Panels

Computer Modeling of Agriboard House

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*DBMS is the Dynamic Benefit for Massive Systems. It is a multiplier showing how much higher the mass-enhanced R-value is than the steady-state R-value for Agriboard 77⁄8” panels in that climate. The steady-state R-value used is 16.47.
Data from J. Kosny, A. Desjarlais, and J. Christian, “Whole Wall Rating/Label for Agriboard Wall Systems with Double Core Structural Insulating Panels: Part II, Dynamic Thermal Analysis,” Oak Ridge National Laboratory, January 30, 1998. These are preliminary results that may be adjusted slightly following review.
Results are based on computer modeling using DOE-2.1E of a 1540 sq. ft. single-story ranch house with double-pane clear windows, R-30 roof insulation, interior wall mass of 3.57 lb/ft2 of floor area (specific heat 0.26 Btu/lb°F), and furniture mass of 3.30 lb/ft2 of floor area (specific heat 0.30 Btu/lb°F).

Researchers at Oak Ridge National Laboratory have carried out extensive testing and modeling of Agriboard straw-core structural insulated panels. This testing was referred to in the article “Agriboard’s Inflated R-Value Claims” in the January 1998 issue of EBN, though the results had not yet been released at that time. While the steady-state R-value testing indeed showed R-values significantly lower than Agriboard had claimed (R-16.5 vs. R-28), Agriboard—to their credit—also funded sophisticated dynamic testing and modeling of their panels to arrive at mass-enhanced R-values under various climates. These results are very interesting.

Following the steady-state R-value testing, researchers used a guarded hot box to measure conductivity of Agriboard panels under dynamic conditions. One side of an 8’ x 8’ wall assembly was kept at a constant 100°F, while the other side was held at 60°F for a period of time, then gradually dropped to 30°F. The results from this testing were used to calibrate a computer model that was then used to simulate energy performance of a simple one-story house built of Agriboard panels for comparison to ten different frame wall configurations ranging from R-2.3 to R-37. By simulating the performance of these houses in six different climates, investigators were able to determine the mass-enhanced R-value of the Agriboard panels under these conditions—in other words, how well insulated a conventional (low-mass) frame wall would have to be in those climates to achieve the same energy performance as the Agriboard house—see table.

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