Five-year field study confirms accelerated thermal aging method for polyisocyanurate insulation

In 1989, industry produced some experimental, permeably-faced polyisocyanurate (PIR) laminated board insulation blown with HCFC-141b and a second batch blown with CFC-11, which has undergone continuous field thermal performance monitoring for 5.5 years (June 1989 until February 1995). From these boards, several thin-sliced specimens were prepared and laboratory k-factors periodically measured on these core foam specimens. This work was conducted as part of a six-year joint research project between The Society of the Plastics Industry, Inc. (SPI). Polyisocyanurate Insulation Manufacturers Association (PIMA), National Roofing Contractors Association (NRCA), and the U.S. Department of Energy (DOE) Oak Ridge National Laboratory (ORNL). One of the major research products from this cooperative research effort was the development of an accelerated method for predicting full thickness lifetime thermal conductivities ("in-service R-values") of permeably-faced polyisocyanurate products. This paper compares the prediction of the field installed permeably-faced boards generated from the accelerated aging procedure to the actual measured field performance. The field applications consist of loose-laid boards under ethylene propylene diene terpolymer (EPDM) membranes in a low-sloped roof installed in the ORNL Roof Thermal Research Apparatus (RTRA). For the 5.5 years, each test roof was monitored hourly for temperature and heat flux. This data provides a time series of boundary conditions for a computer program PROPOR (Properties-Oak .Ridge) to compute weekly thermal conductivities. PROPOR is an application of one-dimensional inverse heat transfer analysis. Every six months the test specimens were pulled from the roof and tested under steady state conditions in the laboratory according in American Society of Testing Materials (ASTM) C 518-91. This field validation of an accelerated aging procedure concludes that the thin slicing and laboratory k-factor measurements, within the first six months, accurately predict five years of full thickness, in-situ thermal performance of HCFC-141b permeably-faced polyisocyanurate insulation boards. A computer program was developed which uses the thin slice data set of a specific manufacturer's insulation. The design service life and full product thickness is input, and the in-service R-value is estimated. This value will vary depending on results from the thin slice testing. This work is leading toward an acceptable industry standard to determine the in-service R-value, which is defined as the design thermal resistance of insulation over the normal life of a roof system containing foams which thermally age. At the National Roof Contractors Association 110th Annual Convention Feb. 4, 1997 in Orlando, Florida, the Polyisocyanurate Insulation Manufacturers announced that by January 1,1998 each PIMA member-insulation manufacturer would have available aped thermal nerformance data.