This paper reports apparent thermal conductivity (k) values from field and laboratory aging tests on a set of industry-produced, experimental polyisocyanurate (PIR) laminated boardstock foamed with hydrochlorofluorocarbons (HCFCs) as alternatives to chlorofluorocarbons (CFCs). The PIR boards were blown with five gases: CFC-11, HCFC-123, HCFC-141b, and 50/50 and 65/35 blends of HCFC-123/ HCFC-141b. The k-values were determined at mean temperatures from 0 to 50°C (30 to 120°F) using techniques that meet ASTM C 1114 (Thin Heater Apparatus) and ASTM C 518 (Heat Flow Meter Apparatus) test methods. Results on laminate boards with facers provide an independent laboratory check on the increase in k observed for field exposure in the ORNL Roof Thermal Research Apparatus (RTRA). The observed laboratory increase in k was between 8% and 11% for all three blowing agent foams for a 240 day field exposure in the RTRA. A thin-specimen aging procedure established the long-term thermal resistance of gas-filled foams. Thin specimens were planed from the industry-produced boardstock foams and aged at 24 and 65°C for up to 300 days. An exponential dependency of k with the quantity (diffusion coefficient X time)½/thickness, provided effective diffusion coefficients for air components into the foams and blowing agent out of the foams. The foams blown with alternative blowing agents exhibited k-values 8 to 16% (average 12.7%) above CFC-11 foams under similar conditions. Field exposures were conducted on specimens under single ply EPDM membranes in the RTRA for over 400 days. Hourly averages of panel temperature and heat flux were analyzed to obtain k as a function of mean temperature on a week by week basis. The k-values derived from the field data provided effective diffusion coefficients for air components in the foam, which were greater than those obtained from the thin-specimen aging procedure at 24°C by 20 to 70%, but were less than the 65°C aging values by 20 to 80%. The relative performance of test specimens of HCFC-141b under a black and under a white membrane is reported. The field data suggests that the percent increase in k over that of the foam blown with CFC-11 is, after one year of aging, 4.3% for HCFC-123 and 10.2% for HCFC-141b. This leads to the same ordering of foams as derived from the thin-specimen analysis.
This paper describes a research program targeted towards the significant potential for energy savings from improved residential building foundations design. A recent study at the University of Minnesota estimates that less than 5% of foundations in the present building stock are optimally insulated. In addition, this study indicates that the potential national savings from upgraded basements, crawl spaces, and slab-on-grade foundation systems in residential and small commercial buildings is about 0.5 quads/year (0.523 × 1018 J/year). This research program is based upon a research needs assessment developed by the Building Foundations Research Review Panel. This panel was established by the U.S. Department of Energy (DOE) and Oak Ridge National Laboratory to assist in the formulation of DOE foundations research policy and the development of a technology transfer strategy to get this research to the marketplace. Half of the panel members are from private industry. One of the first tasks the panel addressed was to formulate a prioritized list of building foundation research needs. Building foundations research needs include: widescale dissemination of existing information on good practices for energy-efficient construction and retrofit, accurate characterization of the thermal properties of soils, validated foundation heat and mass transfer algorithms coupled into whole-building simulation models, an experimental data base from one or more well-characterized test sites, and design tools to effectively transfer the results of research into practice.
Metal stud wall systems for residential building are gaining in popularity. Thanks to their low cost, construction simplicity, and similarity to the existing wood frame technology, metal stud wall systems can share a considerable part of the residential and commercial markets, very soon. The prognosis of American Iron and Steel Institute predicts that in 1997 about 25% of the new residential buildings will be assembled with the use of metal stud's technologies in the U.S.A. The application of the light gage metal technologies in building has either economical or environmental aspects, because the replacement of the construction lumber by metal wall and roof components can reduce construction costs but also save a forest. In addition, metal studs are 100% recyclable material. The authors believe that tremendous markets are available around the world for the deployment of the metal stud wall technologies. A deployment of the metal stud wall technologies can create a great chance for modern, low-cost and energy efficient buildings in many world regions. This system has been already successfully introduced in Europe, Central and South America, Australia and New Zealand. However, these technologies require serious redesign to improve their thermal performances. Commonly, commercially available metal stud wall systems are initially designed by simple replacement of wood studs, joists, headers, etc., by structurally equivalent metal components. Metal substitutes of the wood structure are very often being installed without consideration of the difference in thermal conductivity between wood and metal. Strong thermal bridges caused by highly conductive metal components worsen thermal performance of these walls. In metal stud walls, the reduction of the in-cavity R-value can reach 50%. Because steel has higher thermal conductivity than wood and intense heat transfer occurs through the metal wall components, thermal performances of a metal stud wall are significantly lower than for similar wood stud walls. A reduction of the in-cavity R-value caused by the wood studs is about 10% in wood stud walls. That is why metal stud walls are believed to be considerably less thermally effective than similar made of wood. However, properly designed metal stud walls can be as thermally effective as wood stud walls. Relatively high R-values may be achieved by installing insulating sheathing, which is widely used as a remedy for a weak thermal performance of metal stud walls. A series of the promising metal stud wall configurations is analyzed using results of finite difference computer modeling and guarded hotbox tests. Some of these walls were designed and tested in the ORNL Building Technology Center, some were tested in other laboratories, and some walls were developed and forgotten long time ago. Also, a novel concept of combined foam -metal studs is considered. The main aim of the present paper is to proof that it is possible to build metal stud walls performing as well as wood stud walls. The key lies in designing; metal stud wall systems have to be treated in special way with particular consideration to the high thermal conduction of metal components. In the discussed collection of the efficient metal stud wall configurations, reductions of the in-cavity R-value caused by metal studs are between 10 and 20%.
A closed-cell foamboard insulation containing chlorodifluoromethane (HCFC-22) has been monitored in the laboratory and in the field for about three years. Experimental data for this developmental extruded polystyrene insulation has been obtained in two laboratories using three apparatuses. A correlation of apparent thermal conductivity with time gives the thermal resistivity of the two-inch-thick unfaced foamboards to within 3% with 95% confidence. A thermal resistivity of 30.2 m∙K/W (4.36 ft2∙h∙°F/Btu∙in) was calculated from the correlation for time equal 180 days after manufacture. Based on three years of data, the predicted thermal resistivity is 27.6 m∙K/W (3.98 ft2∙h∙°F/Btu∙in) as time since manufacture becomes large. Field measurements confirm the decrease with time of the thermal resistivity that was observed in the laboratory. A three-dimensional model for heat transfer through foamboard was used to predict thermal resistivity as a function of time. A comparison of the experimental results with the model shows a radiative contribution to the total heat flux of about 30%. A one-dimensional model was used to show the effect of initial foamgas pressure and thickness on thermal performance.
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