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Highly Insulating Glazing Systems using Non-Structural Center Glazing Layers

Description: Three layer insulating glass units with two low-e coatings and an effective gas fill are known to be highly insulating, with center-of-glass U-factors as low as 0.57 W/m{sup 2}-K (0.10 Btu/h-ft{sup 2}- F). Such units have historically been built with center layers of glass or plastic which extend all the way through the spacer system. This paper shows that triple glazing systems with non-structural center layers which do not create a hermetic seal at the edge have the potential to be as thermally efficient as standard designs, while potentially removing some of the production and product integration issues that have discouraged the use of triples.
Date: April 9, 2008
Creator: Kohler, Christian; Arasteh, Dariush; Goudey, Howdy & Kohler, Christian
Partner: UNT Libraries Government Documents Department

Field Evaluation of Low-E Storm Windows

Description: A field evaluation comparing the performance of low emittance (low-e) storm windows with both standard clear storm windows and no storm windows was performed in a cold climate. Six homes with single-pane windows were monitored over the period of one heating season. The homes were monitored with no storm windows and with new storm windows. The storm windows installed on four of the six homes included a hard coat, pyrolitic, low-e coating while the storm windows for the other two homeshad traditional clear glass. Overall heating load reduction due to the storm windows was 13percent with the clear glass and 21percent with the low-e windows. Simple paybacks for the addition of the storm windows were 10 years for the clear glass and 4.5 years forthe low-e storm windows.
Date: July 11, 2007
Creator: Drumheller, S. Craig; Kohler, Christian & Minen, Stefanie
Partner: UNT Libraries Government Documents Department

Modeling Windows in Energy Plus with Simple Performance Indices

Description: The building energy simulation program, Energy Plus (E+), cannot use standard window performance indices (U, SHGC, VT) to model window energy impacts. Rather, E+ uses more accurate methods which require a physical description of the window. E+ needs to be able to accept U and SHGC indices as window descriptors because, often, these are all that is known about a window and because building codes, standards, and voluntary programs are developed using these terms. This paper outlines a procedure, developed for E+, which will allow it to use standard window performance indices to model window energy impacts. In this 'Block' model, a given U, SHGC, VT are mapped to the properties of a fictitious 'layer' in E+. For thermal conductance calculations, the 'Block' functions as a single solid layer. For solar optical calculations, the model begins by defining a solar transmittance (Ts) at normal incidence based on the SHGC. For properties at non-normal incidence angles, the 'Block' takes on the angular properties of multiple glazing layers; the number and type of layers defined by the U and SHGC. While this procedure is specific to E+, parts of it may have applicability to other window/building simulation programs.
Date: October 12, 2009
Creator: Arasteh, Dariush; Kohler, Christian & Griffith, Brent
Partner: UNT Libraries Government Documents Department

Two-Dimensional Computational Fluid Dynamics and Conduction Simulations of Heat Transfer in Horizontal Window Frames with Internal Cavities

Description: This paper assesses the accuracy of the simplified frame cavity conduction/convection and radiation models presented in ISO 15099 and used in software for rating and labeling window products. Temperatures and U-factors for typical horizontal window frames with internal cavities are compared; results from Computational Fluid Dynamics (CFD) simulations with detailed radiation modeling are used as a reference. Four different frames were studied. Two were made of polyvinyl chloride (PVC) and two of aluminum. For each frame, six different simulations were performed, two with a CFD code and four with a building-component thermal-simulation tool using the Finite Element Method (FEM). This FEM tool addresses convection using correlations from ISO 15099; it addressed radiation with either correlations from ISO 15099 or with a detailed, view-factor-based radiation model. Calculations were performed using the CFD code with and without fluid flow in the window frame cavities; the calculations without fluid flow were performed to verify that the CFD code and the building-component thermal-simulation tool produced consistent results. With the FEM-code, the practice of subdividing small frame cavities was examined, in some cases not subdividing, in some cases subdividing cavities with interconnections smaller than five millimeters (mm) (ISO 15099) and in some cases subdividing cavities with interconnections smaller than seven mm (a breakpoint that has been suggested in other studies). For the various frames, the calculated U-factors were found to be quite comparable (the maximum difference between the reference CFD simulation and the other simulations was found to be 13.2 percent). A maximum difference of 8.5 percent was found between the CFD simulation and the FEM simulation using ISO 15099 procedures. The ISO 15099 correlation works best for frames with high U-factors. For more efficient frames, the relative differences among various simulations are larger. Temperature was also compared, at selected locations on the frames. Small ...
Date: December 1, 2008
Creator: Gustavsen, Arlid; Kohler, Christian; Dalehaug, Arvid & Arasteh, Dariush
Partner: UNT Libraries Government Documents Department

Research Needs: Glass Solar Reflectance and Vinyl Siding

Description: The subject of glass solar reflectance and its contribution to permanent vinyl siding distortion has not been extensively studied, and some phenomena are not yet well understood. This white paper presents what is known regarding the issue and identifies where more research is needed. Three primary topics are discussed: environmental factors that control the transfer of heat to and from the siding surface; vinyl siding properties that may affect heat build-up and permanent distortion; and factors that determine the properties of reflected solar radiation from glass surfaces, including insulating window glass. Further research is needed to fully characterize the conditions associated with siding distortion, the scope of the problem, physical properties of vinyl siding, insulating window glass reflection characteristics, and possible mitigation or prevention strategies.
Date: July 7, 2011
Creator: Hart, Robert; Curcija, Charlie; Arasteh, Dariush; Goudey, Howdy; Kohler, Christian & Selkowitz, Stephen
Partner: UNT Libraries Government Documents Department

Evaluating Fenestration Products for Zero-Energy Buildings: Issuesfor Discussion

Description: Computer modeling to determine fenestration product energy properties (U-factor, SHGC, VT) has emerged as the most cost-effective and accurate means to quantify them. Fenestration product simulation tools have been effective in increasing the use of low-e coatings and gas fills in insulating glass and in the widespread use of insulating frame designs and materials. However, for more efficient fenestration products (low heat loss products, dynamic products, products with non-specular optical characteristics, light re-directing products) to achieve widespread use, fenestration modeling software needs to be improved. This paper addresses the following questions: (1) Are the current properties (U, SHGC, VT) calculated sufficient to compare and distinguish between windows suitable for Zero Energy Buildings and conventional window products? If not, what data on the thermal and optical performance, on comfort, and on peak demand of windows is needed. (2) Are the algorithms in the tools sufficient to model the thermal and optical processes? Are specific heat transfer and optical effects not accounted for? Is the existing level of accuracy enough to distinguish between products designed for Zero Energy Buildings? Is the current input data adequate?
Date: July 25, 2006
Creator: Arasteh, Dariush; Curcija, Charlie; Huang, Joe; Huizenga,Charlie & Kohler, Christian
Partner: UNT Libraries Government Documents Department

Developing Low-Conductance Window Frames: Capabilities and Limitations of Current Window Heat Transfer Design Tools

Description: While window frames typically represent 20-30% of the overall window area, their impact on the total window heat transfer rates may be much larger. This effect is even greater in low-conductance (highly insulating) windows that incorporate very low-conductance glazing. Developing low-conductance window frames requires accurate simulation tools for product research and development. Based on a literature review and an evaluation of current methods of modeling heat transfer through window frames, we conclude that current procedures specified in ISO standards are not sufficiently adequate for accurately evaluating heat transfer through the low-conductance frames. We conclude that the near-term priorities for improving the modeling of heat transfer through low-conductance frames are: (1) Add 2D view-factor radiation to standard modeling and examine the current practice of averaging surface emissivity based on area weighting and the process of making an equivalent rectangular frame cavity. (2) Asses 3D radiation effects in frame cavities and develop recommendation for inclusion into the design fenestration tools. (3) Assess existing correlations for convection in vertical cavities using CFD. (4) Study 2D and 3D natural convection heat transfer in frame cavities for cavities that are proven to be deficient from item 3 above. Recommend improved correlations or full CFD modeling into ISO standards and design fenestration tools, if appropriate. (5) Study 3D hardware short-circuits and propose methods to ensure that these effects are incorporated into ratings. (6) Study the heat transfer effects of ventilated frame cavities and propose updated correlations.
Date: September 11, 2008
Creator: Gustavsen, Arild; Arasteh, Dariush; Jelle, Bjorn Petter; Curcija, Charlie & Kohler, Christian
Partner: UNT Libraries Government Documents Department

State-of-the-Art Highly Insulating Window Frames - Research and Market Review

Description: This document reports the findings of a market and research review related to state-of-the-art highly insulating window frames. The market review focuses on window frames that satisfy the Passivhaus requirements (window U-value less or equal to 0.8 W/m{sup 2}K ), while other examples are also given in order to show the variety of materials and solutions that may be used for constructing window frames with a low thermal transmittance (U-value). The market search shows that several combinations of materials are used in order to obtain window frames with a low U-value. The most common insulating material seems to be Polyurethane (PUR), which is used together with most of the common structural materials such as wood, aluminum, and PVC. The frame research review also shows examples of window frames developed in order to increase the energy efficiency of the frames and the glazings which the frames are to be used together with. The authors find that two main tracks are used in searching for better solutions. The first one is to minimize the heat losses through the frame itself. The result is that conductive materials are replaced by highly thermal insulating materials and air cavities. The other option is to reduce the window frame area to a minimum, which is done by focusing on the net energy gain by the entire window (frame, spacer and glazing). Literature shows that a window with a higher U-value may give a net energy gain to a building that is higher than a window with a smaller U-value. The net energy gain is calculated by subtracting the transmission losses through the window from the solar energy passing through the windows. The net energy gain depends on frame versus glazing area, solar factor, solar irradiance, calculation period and U-value. The frame research review also discusses heat ...
Date: January 1, 2007
Creator: Gustavsen, Arild; Jelle, Bjorn Petter; Arasteh, Dariush & Kohler, Christian
Partner: UNT Libraries Government Documents Department

Performance Criteria for Residential Zero Energy Windows

Description: This paper shows that the energy requirements for today's typical efficient window products (i.e. ENERGY STAR{trademark} products) are significant when compared to the needs of Zero Energy Homes (ZEHs). Through the use of whole house energy modeling, typical efficient products are evaluated in five US climates and compared against the requirements for ZEHs. Products which meet these needs are defined as a function of climate. In heating dominated climates, windows with U-factors of 0.10 Btu/hr-ft{sup 2}-F (0.57 W/m{sup 2}-K) will become energy neutral. In mixed heating/cooling climates a low U-factor is not as significant as the ability to modulate from high SHGCs (heating season) to low SHGCs (cooling season).
Date: October 9, 2006
Creator: Arasteh, Dariush; Goudey, Howdy; Huang, Joe; Kohler, Christian & Mitchell, Robin
Partner: UNT Libraries Government Documents Department

Experimental and Numerical Examination of the Thermal Transmittance of High Performance Window Frames

Description: While window frames typically represent 20-30percent of the overall window area, their impact on the total window heat transfer rates may be much larger. This effect is even greater in low-conductance (highly insulating) windows which incorporate very low conductance glazings. Developing low-conductance window frames requires accurate simulation tools for product research and development. The Passivhaus Institute in Germany states that windows (glazing and frames, combined) should have U-values not exceeding 0.80 W/(m??K). This has created a niche market for highly insulating frames, with frame U-values typically around 0.7-1.0 W/(m2 cdot K). The U-values reported are often based on numerical simulations according to international simulation standards. It is prudent to check the accuracy of these calculation standards, especially for high performance products before more manufacturers begin to use them to improve other product offerings. In this paper the thermal transmittance of five highly insulating window frames (three wooden frames, one aluminum frame and one PVC frame), found from numerical simulations and experiments, are compared. Hot box calorimeter results are compared with numerical simulations according to ISO 10077-2 and ISO 15099. In addition CFD simulations have been carried out, in order to use the most accurate tool available to investigate the convection and radiation effects inside the frame cavities. Our results show that available tools commonly used to evaluate window performance, based on ISO standards, give good overall agreement, but specific areas need improvement.
Date: June 17, 2010
Creator: Gustavsen Ph.D., Arild; Goudey, Howdy; Kohler, Christian; Arasteh P.E., Dariush; Uvslokk, Sivert; Talev, Goce et al.
Partner: UNT Libraries Government Documents Department

THERM 2.1 NFRC simulation manual

Description: This document, the ''THERM 2.1 NFRC Simulation Manual'', discusses how to use THERM to model products for NFRC certified simulations and assumes that the user is already familiar with the THERM program. In order to learn how to use THERM, it is necessary to become familiar with the material in the THERM User's Manual. In general, this manual references the THERM User's Manual rather than repeating the information. If there is a conflict between the THERM User's Manual and the THERM 2.1 NFRC Simulation Manual, the THERM 2.1 NFRC Simulation Manual takes precedence. The CD that is included with the manual includes all sample files that are referenced in the manual as well as some additional samples.
Date: July 1, 2000
Creator: Mitchell, Robin; Kohler, Christian; Arasteh, Dariush; Finlayson, Elizabeth; Huizenga, Charlie; Curcija, Dragan et al.
Partner: UNT Libraries Government Documents Department

A first-generation prototype dynamic residential window

Description: We present the concept for a ''smart'' highly efficient dynamic window that maximizes solar heat gain during the heating season and minimizes solar heat gain during the cooling season in residential buildings. We describe a prototype dynamic window that relies on an internal shade, which deploys automatically in response to solar radiation and temperature. This prototype was built at Lawrence Berkeley National Laboratory from commercially available ''off-the-shelf'' components. It is a stand-alone, standard-size product, so it can be easily installed in place of standard window products. Our design shows promise for near-term commercialization. Improving thermal performance of this prototype by incorporating commercially available highly efficient glazing technologies could result in the first window that could be suitable for use in zero-energy homes. The unit's predictable deployment of shading could help capture energy savings that are not possible with manual shading. Installation of dynamically shaded windows in the field will allow researchers to better quantify the energy effects of shades, which could lead to increased efficiency in the sizing of heating, ventilation, and air conditioning equipment for residences.
Date: October 26, 2004
Creator: Kohler, Christian; Goudey, Howdy & Arasteh, Dariush
Partner: UNT Libraries Government Documents Department

THERM Simulations of Window Indoor Surface Temperatures for Predicting Condensation

Description: As part of a ''round robin'' project, the performance of two wood windows and a Calibrated Transfer Standard was modeled using the THERM heat-transfer simulation program. The resulting interior surface temperatures can be used as input to condensation resistance rating procedures. The Radiation and Condensation Index features within THERM were used to refine the accuracy of simulation results. Differences in surface temperatures between the ''Basic'' calculations and those incorporating the Radiation and/or Condensation Index features are demonstrated and explained.
Date: May 18, 2001
Creator: Kohler, Christian; Arasteh, Dariush & Mitchell, Robin
Partner: UNT Libraries Government Documents Department

Improving information technology to maximize fenestration energyefficiency

Description: Improving software for the analysis of fenestration product energy efficiency and developing related information technology products that aid in optimizing the use of fenestration products for energy efficiency are essential steps toward ensuring that more efficient products are developed and that existing and emerging products are utilized in the applications where they will produce the greatest energy savings. Given the diversity of building types and designs and the climates in the U.S., no one fenestration product or set of properties is optimal for all applications. Future tools and procedures to analyze fenestration product energy efficiency will need to both accurately analyze fenestration product performance under a specific set of conditions and to look at whole fenestration product energy performance over the course of a yearly cycle and in the context of whole buildings. Several steps have already been taken toward creating fenestration product software that will provide the information necessary to determine which details of a fenestration product's design can be improved to have the greatest impact on energy efficiency, what effects changes in fenestration product design will have on the comfort parameters that are important to consumers, and how specific fenestration product designs will perform in specific applications. Much work remains to be done, but the energy savings potential justifies the effort. Information is relatively cheap compared to manufacturing. Information technology has already been responsible for many improvements in the global economy--it can similarly facilitate many improvements in fenestration product energy efficiency.
Date: June 6, 2001
Creator: Arasteh, Dariush; Mitchell, Robin; Kohler, Christian; Huizenga,Charlie & Curcija, Dragan
Partner: UNT Libraries Government Documents Department

THERM 5 / WINDOW 5 NFRC simulation manual

Description: This document, the ''THERM 5/WINDOW 5 NFRC Simulation Manual', discusses how to use the THERM and WINDOW programs to model products for NFRC certified simulations and assumes that the user is already familiar with those programs. In order to learn how to use these programs, it is necessary to become familiar with the material in both the ''THERM User's Manual'' and the ''WINDOW User's Manual''. In general, this manual references the User's Manuals rather than repeating the information. If there is a conflict between either of the User Manual and this ''THERM 5/''WINDOW 5 NFRC Simulation Manual'', the ''THERM 5/WINDOW 5 NFRC Simulation Manual'' takes precedence. In addition, if this manual is in conflict with any NFRC standards, the standards take precedence. For example, if samples in this manual do not follow the current taping and testing NFRC standards, the standards not the samples in this manual, take precedence.
Date: June 1, 2003
Creator: Mitchell, Robin; Kohler, Christian; Arasteh, Dariush; Carmody, John; Huizenga, Charlie & Curcija, Dragan
Partner: UNT Libraries Government Documents Department

Solar absorption in thick and multilayered glazings

Description: Thick and multilayered glazings generally have a nonuniform distribution of absorbed solar radiation which is not taken into account by current methods for calculating the center of glass solar gain and thermal performance of glazing systems. This paper presents a more accurate method for calculating the distribution of absorbed solar radiation inside thick and multilayered glazings and demonstrates that this can result in a small but significant difference in steady-state temperature profile and Solar Heat Gain Coefficient for some types of glazing systems when compared to the results of current methods. This indicates that a more detailed approach to calculating the distribution of absorbed solar radiation inside glazings and resulting thermal performance may be justified for certain applications.
Date: February 1, 2002
Creator: Powles, Rebecca; Curcija, Dragan & Kohler, Christian
Partner: UNT Libraries Government Documents Department

Two-dimensional computational fluid dynamics and conduction simulations of heat transfer in window frames with internal cavities - Part 1: Cavities only

Description: Accurately analyzing heat transfer in window frame cavities is essential for developing and characterizing the performance of highly insulating window products. Window frame thermal performance strongly influences overall product thermal performance because framing materials generally perform much more poorly than glazing materials. This paper uses Computational Fluid Dynamics (CFD) modeling to assess the accuracy of the simplified frame cavity conduction/convection models presented in ISO 15099 and used in software for rating and labeling window products. (We do not address radiation heat-transfer effects.) We examine three representative complex cavity cross-section profiles with varying dimensions and aspect ratios. Our results support the ISO 15099 rule that complex cavities with small throats should be subdivided; however, our data suggest that cavities with throats smaller than seven millimeters (mm) should be subdivided, in contrast to the ISO 15099 rule, which places the break point at five mm. The agreement between CFD modeling results and the results of the simplified models is moderate. The differences in results may be a result of the underlying ISO correlations being based on studies where cavity height/length (H/L) aspect ratios were smaller than 0.5 and greater than five (with linear interpolation assumed in between). The results presented here are for horizontal frame members because convection in vertical jambs involves very different aspect ratios that require three-dimensional CFD simulations. Ongoing work focuses on quantifying the exact effect on window thermal performance indicators of using the ISO 15099 approximations in typical real window frames.
Date: April 15, 2003
Creator: Gustavsen, Arild; Kohler, Christian; Arasteh, Dariush & Curcija, Dragan
Partner: UNT Libraries Government Documents Department

Rapid field testing of low-emittance coated glazings for product verification

Description: This paper analyzes prospects for developing a test device suitable for field verification of the types of low-emittance (low-e) coatings present on high-performance window products. Test devices are currently available that can simply detect the presence of low-e coatings and that can measure other important characteristics of high-performance windows, such as the thickness of glazing layers or the gap in dual glazings. However, no devices have yet been developed that can measure gas concentrations or distinguish among types of coatings. This paper presents two optical methods for verification of low-e coatings. The first method uses a portable, fiber-optic spectrometer to characterize spectral reflectances from 650 to 1,100 nm for selected surfaces within an insulated glazing unit (IGU). The second method uses an infrared-light-emitting diode and a phototransistor to evaluate the aggregate normal reflectance of an IGU at 940 nm. Both methods measure reflectance in the near (solar) infrared spectrum and are useful for distinguishing between regular and spectrally selective low-e coatings. The infrared-diode/phototransistor method appears promising for use in a low-cost, hand-held field test device.
Date: February 1, 1998
Creator: Griffith, Brent; Kohler, Christian; Goudey, Howdy; Turler, Daniel & Arasteh, Dariush
Partner: UNT Libraries Government Documents Department

High-performance commercial building facades

Description: This study focuses on advanced building facades that use daylighting, sun control, ventilation systems, and dynamic systems. A quick perusal of the leading architectural magazines, or a discussion in most architectural firms today will eventually lead to mention of some of the innovative new buildings that are being constructed with all-glass facades. Most of these buildings are appearing in Europe, although interestingly U.S. A/E firms often have a leading role in their design. This ''emerging technology'' of heavily glazed fagades is often associated with buildings whose design goals include energy efficiency, sustainability, and a ''green'' image. While there are a number of new books on the subject with impressive photos and drawings, there is little critical examination of the actual performance of such buildings, and a generally poor understanding as to whether they achieve their performance goals, or even what those goals might be. Even if the building ''works'' it is often dangerous to take a design solution from one climate and location and transport it to a new one without a good causal understanding of how the systems work. In addition, there is a wide range of existing and emerging glazing and fenestration technologies in use in these buildings, many of which break new ground with respect to innovative structural use of glass. It is unclear as to how well many of these designs would work as currently formulated in California locations dominated by intense sunlight and seismic events. Finally, the costs of these systems are higher than normal facades, but claims of energy and productivity savings are used to justify some of them. Once again these claims, while plausible, are largely unsupported. There have been major advances in glazing and facade technology over the past 30 years and we expect to see continued innovation and product development. It ...
Date: June 1, 2002
Creator: Lee, Eleanor; Selkowitz, Stephen; Bazjanac, Vladimir; Inkarojrit, Vorapat & Kohler, Christian
Partner: UNT Libraries Government Documents Department