The whole wall thermal performance calculator—On the net

The trend toward system performance codes, standards, and contracts leads to the need for a quick method of estimating the whole wall R-value for exterior envelope systems. Calculation of the actual whole wall R-value of traditional dimensional wood-framed wall systems is, in general, well understood by the residential designer and building contractor. However, the accuracy of estimating the thermal performance of other viable wall systems falls off rapidly, particularly if several different types of wall systems are being considered at the building conceptual design stages. At the Envelopes VI conference in 1995, a new methodology was presented for addressing this need. Three years later, more than 15 wall system manufacturers have submitted 40 different wall systems for generation of a whole wall R-value based on full-scale wall hot box tests. The hot box tests occasionally generated some unexpected results but provide a very credible check on computer modeling. This paper describes results from both steady-state and dynamic hot box tests using ASTM C-1363-97. The tests are the starting point for development of uniform whole wall R-values for inclusion in “The Whole-Wall Thermal Performance Calculator.” The following wall systems have been tested and are available for comparison: structural insulating panels with compressed straw core, conventional steel C-stud frame (2 in. × 6 in.[5 cm × 15.4 cm] and 2 in. × 4 in. [5 cm × 10 cm]), conventional metal frame with different types of sprayed foam insulation, novel metal studs, autoclaved concrete block, structural straw bale, and an insulating concrete form. This paper describes “The Whole-Wall Thermal Performance Calculator,” which is available at <http:/ /www.ornl.gov/roofs+walls/whole_wall/wallsys.html>. This interactive calculation tool can accept a simple description of custom building plans and enable the Internet user to compare uniform whole wall R-values of at least 40 different wall systems. This provides the comfort of knowing that all are based on hot box measurements by a recognized, objective, and qualified third party in cooperation with the manufacturers of each wall system.