David W. Yarbrough

Measurement of Apparent Thermal Conductivity by the Thermal Probe Method

Three thermal probes were constructed in accordance with ASTM D 5334 and calibrated using heat-flow metre data. The temperature-time response of the thermal probes for determining apparent thermal conductivity λ under transient state conditions was logged at 1 s intervals. The instrumentation used reduced the determinate error associated with voltage and current measurements to a negligibly small value that made the uncertainty in λ dependent on the uncertainty of the slope dT/dlnt. A test method was run in 1000 s, in which a criterion of 2.5% spread among three consecutive slope values was used to determine the extent of the linear segment of the T–ln t curve. The probes demonstrated repeatability within ±3.5% but had definite individual bias indicating a need for individual calibration. Using individual probe calibration factors, the experimentally de termined λs for all-purpose sand, sifted sand, and soil were deter mined to be 0.520, 0.445, and 2.11 W/moK, respectively.

Use of Radiation Control Coatings to Reduce Building Air-Conditioning Loads

Abstract Radiation control coatings (RCCs) are used on building exteriors to reduce the absorption of solar energy. Reduced solar energy absorption results in lower exterior surface temperatures, and, consequently, less heat flow across the building envelope, and reduced electrical requirements to maintain air-conditioned space. Solar reflectance (r) and ambient temperature emittance (e) are key properties for RCC performance. RCC products typically have r values greater than 0.75 and e values greater than 0.8. A review of typical values for r and e along with the dependence of these properties on RCC thickness is presented. The performance of RCCs depends on a number of variables including r, e, solar flux, sol-air temperature, and the thermal resistance of the parts of the building envelope that are coated. The building simulation code DOE-2 has been used to calculate benefits of RCCs for selected values of the previously listed variables. Energy savings can be significant in hot climates where building...

Buildings with environmental quality management, part 1: Designing multifunctional construction materials

The quest for a sustainable built environment has resulted in dramatic changes in the process of residential construction. The new concepts of an integrated design team, building information modeling, commissioning of the building enclosure, and passive house standards have reached maturity. Global work on development of new construction materials has not changed, but their evaluation is not the same as in the past when each material was considered on its own merits. Today, we look at the performance of a building as a system and on the material as a contributor to this system. The series of white papers—a research overview in building physics undertaken in European and North American researchers—is to provide understanding of the process of design and construction for sustainable built environment that involves harmony between different aspects of the environment, society, and economy. Yet, the building physics is changing. It merges with building science in the quest of predicting building performance, it merges concepts of passive houses with solar engineering and integrates building shell with mechanical services, but is still missing an overall vision. Physics does not tell us how to integrate people with their environment. The authors propose a new term buildings with environmental quality management because the vision of the building design must be re-directed toward people. In doing so, the building physics will automatically include durability of the shell, energy efficiency, and carbon emission and aspects such as individual ventilation and indoor climate control. This article, which is part 1 of a series, deals with materials, and other issues will be discussed in following papers.

Low temperature formation of silicon oxide

Abstract Silicon oxide films have been formed at temperatures as low as 25°C, using a reaction of Si with a vapor mixture containing either NO, HF and H 2 O or NO, HF, H 2 O and O 2 . Experimental data relating silicon oxide film growth with processing parameters such as vapor composition, temperature and time are presented. Conditions for the growth of silicon oxide films of specific thicknesses are outlined.

Buildings with environmental quality management, part 2: Integration of hydronic heating/cooling with thermal mass:

The quest for a sustainable built environment brought dramatic changes to architectural design because of the integrated design process. The integrated design process is the modern way to realize “performance architecture,” that is, design with a view to field performance. Integrated design process permits merging of concepts from passive-house designs, solar engineering, and an integration of the building enclosure with mechanical services. In part 1 of this series, the emergence of many new multi-functional materials was discussed. Yet, current innovation is guided by lessons from history. Thermal mass in heavy masonry buildings allowed periodic heating. The authors postulate integration of a hydronic heating system with the walls and the use of smart temperature control of the heating system to modify and optimize the thermal mass contribution. To use the mass of a building, one must accept transient temperature conditions where the indoor temperature varies but is confined by comfort requirements for both summer and winter conditions. On the other side, resiliency requirements dictate that in the absence of electricity the air temperature does not fall below about 12°C over a period of several hours. This requirement implies that summer cooling will likely be separated from the heating systems and that operation of a low-energy building is heavily dependent on the design of smart control systems. Analysis of control systems provided in this article for earth-to-air heat exchangers and cooling of houses with lightweight walls lead us to the requirements of separation between heating and ventilation and needs for different sources of fresh air. Finally, a new concept emerges.

A Thermal Resistance (R-Value) Correlation for Blow-in-Blanket Mineral Fiber Insulation

A correlation between the apparent thermal conductivity, measured at 75°F, and density of mineral fiber insulation has been developed for the fiber most commonly used in Blow-in-Blanket (BIB) applications. The correlation describes the data obtained for specimens prepared by six contractors to within ±5% in the den sity range 1.6 to 3.0 1b/ft3. R-value per inch increased from 3.85 ft2.hr.°F/Btu.in to 4.22 ft2·hr·°F/Btu·in for densities increasing from 1.6 1b/ft 3 to 3.0 lb/ft3. Thermal measurements obtained with purposely compressed test specimens were not sig nificantly different from results for uncompressed specimens at the same density. The apparent thermal conductivities for three fiberglass BIB products and one rock wool BIB product were a few percent greater than those for the corresponding loose-fill insulation. The thermal data were obtained using heat flux meters located at Ten nessee Technological University and the Oak Ridge National Laboratory.

Thermal Resistance of Air Ducts with Bubblepack Reflective Insulation

A series of measurements to determine overall heat-transfer coeffi cients for air-handling ducts was used to obtain the R-value added to the ducts by bubblepack reflective insulation Heat fluxes determined from steady-state energy balances were combined with temperature measurements to determine U-values and R-values. The five configurations tested were no insulation, reflective insulation ap plied directly to the inside or outside wall of the duct, and exterior reflective insula tion installed with two types of spacers to form 0.75 inch air gaps. The R-values added to the initial value of 1.56 ft2·h·°F/Btu varied from 0.82 to 4.09 ft2·h·°F/Btu for the configurations tested.

Buildings with environmental quality management: Part 4: A path to the future NZEB:

The previous part of this article starts 100 years ago, at the time of the humble beginnings of building science, and brings us to the current stage of the net zero energy buildings (NZEB). We see how, over the years, knowledge from the observed failures of buildings has accumulated to become the basis for current building science. The strong interactions between energy efficiency, moisture management, and indoor environment and the need for their simultaneous analysis led to the concept of environmental assessment. More than 40 years of experience with passive houses (the first 10 were built in Canada in 1977) in process that would collect those developments into the mainstream of NZEB technology permits extrapolation to the future. As the first priority, we see a need for a fundamental change in the approach to NZEB—instead of improving the separate pieces of the puzzle before assembling them, we need first to establish the conceptual design of the whole system. Only after determination of the basic requirements for each subsystem and each assembly may materials that would fulfill the specific requirements of this assembly be selected. In this design process, the actual climate and socio-economic conditions (including construction cost) vary, so we must deal with a set of design principles rather than a description of a specific construction technology. A guiding set of considerations is presented below to establish a system of environmental quality management (EQM).

Buildings with environmental quality management, part 3: From log houses to environmental quality management zero-energy buildings

The discussion in this article starts in the 1920s, that is, at the time of the humble beginnings of building science and brings us to 2020s with the development of net-zero energy buildings. The knowledge accumulated by explaining observed failures in the practice of construction slowly formed a basis for moving toward a predictive capability and to an integration of modeling and testing. Furthermore, we have learned that interactions between energy efficiency, indoor environmental quality, and moisture management are so critical that the three issues must be considered simultaneously. Effectively, a change in the low energy is needed to ensure durability of materials and cost considerations for these buildings. At this stage, one could observe a clear change in the mind-set of the scientific community. Forty years after construction of the first 10 passive homes, we made a shocking observation—an adequate technology has been developed, but our lack of vision prevents effective use of this technology. Again, we need to modify our vision and change the design paradigm to balance comfort, building durability, and cost-effectiveness. If the quest for sustainable buildings is our ultimate objective, then we should learn more from the surrounding nature; termites appear to master the art of hygrothermal control better than humans because they can optimize transient conditions to maintain a stable interior comfort zone. Thus, in the article to follow a new compact building envelope design package is proposed, applicable to different climates with specific modifications of critical hygrothermal material properties. This approach is called the Environmental Quality Management. This will be the second step for a building science (physics) needed to become a leading force in the transition to sustainable built environments.

Use of a hot-box facility to evaluate hybrid reflective insulation assemblies

The determination of the thermal performance of hybrid insulation assemblies that include an enclosed reflective airspace and a separate layer of insulation is being done using a hot-box test facility operated in accordance with ASTM C1224, the Standard Specification for Reflective Insulation. The thermal resistance determination of the insulated region requires a hot-box test with known thermal insulation to determine heat flow through the framing. Factors that affect the result for the hybrid insulation assembly will be discussed along with results obtained using the ASTM C1224 protocol. The thermal resistance obtained using the hot-box apparatus will be compared with calculated values obtained from published correlations. The uncertainty in the hybrid insulation assembly and the enclosed reflective airspace due to uncertainty in the thermal resistance of the calibration material are of particular interest.