Andre Omer Desjarlais

The Simulated Impact of Climate on the Drying Times of a Wetted Low-Slope Roof System

The 1991 National Roofing Contractors Association Annual Roof ing Survey predicts increases in recover, the reroofing practice of installing a new roof over an existing failed roof. For 1992, the survey estimates that

The Thermal Resistance of Spray-Applied Fiber Insulations

5¼ billion will be spent on recover. Market trends suggest that recover will become an increasingly more popular option in reroofing. The most controversial aspect of recover pertains to the presence of water in the failed roof. For recover to be a viable reroofing option, this water must have a means of escaping the roof system; entrapped water in the roof would lead to the eventual mechanical failure of the deck and fasteners The rate that water can be driven from a roof system will dictate whether recover can be con sidered as a reroofing option for that system

A rule-based expert system applied to moisture durability of building envelopes

The thermal resistances of four cellulosic and three mineral fiber spray-applied m- sulations have been determined using the flat Nichrome screen-heater apparatus de veloped at the Oak Ridge National Laboratory. Measurements were also made at Dynatech Scientific, Inc., on two of the same specimens of the cellulosic material and one similar specimen of the same mineral fiber product using conventional guarded hot plate and heat flow meter apparatuses. The experimental data obtained at ORNL were used to calculate R-values at 75°F from data obtained in the range 81 to 133 ° F The R-values obtained at Dynatech in cluded measurements at 75°F as well as measurements from 50 to 100°F for cellu losic insulations and 25 to 150°F for a mineral fiber insulation. The results from the two laboratories for the thermal resistance of identical specimens of spray-applied cellulose agreed to better than 1% while the agreement on similar specimens of a spray-applied mineral fiber insulation differed by less than 3%. The data discussed in this paper include spray-applied insulations that span the density range 1 to 8 lb/ft3 and the results show that material R -values for the spray- applied products can be predicted to within ± 10%, using correlations for the ap parent thermal conductivities of loose-fill insulation of the same type and density. They show further that existing plate and similar longitudinal heat flow methods are most appropriate for evaluating the performance of these types of materials.

Surface reflectance degradation by microbial communities

The moisture durability of an envelope component such as a wall or roof is difficult to predict. Moisture durability depends on all the construction materials used, as well as the climate, orientation, air tightness, and indoor conditions. Modern building codes require more insulation and tighter construction but provide little guidance about how to ensure these energy-efficient assemblies remain moisture durable. Furthermore, as new products and materials are introduced, builders are increasingly uncertain about the long-term durability of their building envelope designs. Oak Ridge National Laboratory and the US Department of Energy’s Building America Program are applying a rule-based expert system methodology in a web tool to help designers determine whether a given wall design is likely to be moisture durable and provide expert guidance on moisture risk management specific to a wall design and climate. The expert system is populated with knowledge from both expert judgment and probabilistic hygrothermal simulation results.

High Performance Window Retrofit

Building envelope, such as a roof, is the interface between a building structure and the environment. Understanding of the physics of microbial interactions with the building envelope is limited. In addition to the natural weathering, microorganisms and airborne particulate matter that attach to a cool roof tend to reduce the roof reflectance over time, compromising the energy efficiency advantages of the reflective coating designs. We applied microbial ecology analysis to identify the natural communities present on the exposed coatings and investigated the reduction kinetics of the surface reflectance upon the introduction of a defined mixture of both photoautotrophic and heterotrophic microorganisms representing the natural communities. The findings are (1) reflectance degradation by microbial communities follows a first-order kinetic relationship and (2) more than 50% of degradation from the initial reflectance value can be caused by microbial species alone in much less time than 3 years required by the current standard ENERGY STAR® test methods.

Summary Report: Development of a New ASTM Standard Test Method for Phase Change Materials

The US Department of Energy (DOE) Office of Energy Efficiency and Renewable Energy (EERE) and Traco partnered to develop high-performance windows for commercial building that are cost-effective. The main performance requirement for these windows was that they needed to have an R-value of at least 5 ft2 F h/Btu. This project seeks to quantify the potential energy savings from installing these windows in commercial buildings that are at least 20 years old. To this end, we are conducting evaluations at a two-story test facility that is representative of a commercial building from the 1980s, and are gathering measurements on the performance of its windows before and after double-pane, clear-glazed units are upgraded with R5 windows. Additionally, we will use these data to calibrate EnergyPlus models that we will allow us to extrapolate results to other climates. Findings from this project will provide empirical data on the benefits from high-performance windows, which will help promote their adoption in new and existing commercial buildings. This report describes the experimental setup, and includes some of the field and simulation results.

Effect of Steel Framing in Attic/Ceiling Assemblies on Overall Thermal Resistance

Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. PREFACE Materials used for thermal insulation and storage, along with other construction and building envelope components, are subjected to transient thermal conditions which can include dynamically changing temperature, moisture content, surface heat transfer, specific heat, etc. In addition, most building design and energy-related standards are based on a steady-state criterion (R-values using the apparent thermal conductivity measurements). This mismatch between the steady-state principles used in design and code requirements and the dynamic operation of buildings can result in lower thermal efficiency than achievable or higher cost (due to addition of more insulation than required). This mismatch can also lead to a gross underestimation of the performance of materials that store energy under cyclic temperature conditions, for example phase change materials (PCM). Although some experimental methods for transient analysis of building envelopes have been developed, there are no standardized testing procedures available to quantitatively characterize materials and systems under dynamic conditions. Data on dynamic material characteristics are needed to improve thermal design and analysis, whole-building simulations, and energy code-related work. This led to the development of a proposed ASTM Standard Test Method for characterizing PCM products under dynamic conditions.

Metal stud wall systems: Thermal disaster, or modern wall systems with highly efficient thermal insulation?

Experiments have been performed to assess the impact of cold-formed-steel framing on the thermal performance of attic/ceiling assemblies. Test configurations duplicated features of full-sized, truss-based and conventional joist-and-rafter assemblies away from the edges of the ceiling. Steady-state tests were done at winter conditions in a climate simulator. In truss systems, strong thermal bridges due to framing members that penetrated through the insulation to the bottom chords persisted as the insulation level increased. Without penetrations, the effect of steel framing eventually disappeared as insulation level was increased. For negligible effect of the framing, framing spaced 41 cm oc required greater insulation depth than did framing spaced 61 cm oc. Without penetrations but with enough insulation to cover framing with depths of 8.9 cm, 20.3 cm and 30.5 cm, greater framing depth yielded slightly poorer thermal performance. In some tests, a continuous layer of extruded polystyrene foam insulation was placed between the C-shaped bottom chords of trusses and the gypsum board ceiling. System R-values improved slightly more than the R-value of the foam insulation. A three-dimensional model of the thermal behavior of the assemblies was used to extend the test results to the entire range of steel-framed attic/ceiling configurations. Equations generated from this and related work can be the basis for changes in codes and standards that reflect the effect of steel framing on the thermal performance of attic/ceiling assemblies and discourage allowing steel framing to extend beyond insulation in the assemblies.

Insulation materials, testing, and applications

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 studs 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%.