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 differences was found in the results from model to model.

Finally, the effectiveness of the ISO cavity radiation algorithms was examined by comparing results from these algorithms to detailed radiation calculations (from both programs). Our results suggest that improvements in cavity heat transfer calculations can be obtained by using detailed radiation modeling (i.e. view-factor or ray-tracing models), and that incorporation of these strategies may be more important for improving the accuracy of results than the use of CFD modeling for horizontal cavities.

1 aGustavsen, Arlid1 aKohler, Christian1 aDalehaug, Arvid1 aArasteh, Dariush, K. uhttps://facades.lbl.gov/publications/two-dimensional-computational-fluid01965nas a2200169 4500008004100000050001500041245010300056210006900159260002500228490000800253520136800261100002101629700002501650700002201675700002401697856007401721 2005 eng d aLBNL-6125000aTwo-Dimension Conduction and CFD Simulations for Heat Transfer in Horizontal Window Frame Cavities0 aTwoDimension Conduction and CFD Simulations for Heat Transfer in aOrlando, FLc02/20050 v1113 aAccurately analyzing heat transfer in window frames and glazings is important for developing and characterizing the performance of highly insulating window products. 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. Three representative complex cavity cross-section profiles with varying dimensions and aspect ratios are examined. The results presented support the ISO 15099 rule that complex cavities with small throats should be subdivided; however, our data suggest that cavities with throats smaller than 7 mm should be subdivided, in contrast to the ISO 15099 rule, which places the break point at 5 mm. The agreement between CFD modeling results and the results of the simplified models is moderate for the heat transfer rates through the cavities. The differences may be a result of the underlying ISO 15099 Nusselt number correlations being based on studies where cavity height/length aspect ratios were smaller than 0.5 and greater than 5 (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.

1 aGustavsen, Arlid1 aArasteh, Dariush, K.1 aKohler, Christian1 aCurcija, Dragan, C. uhttps://facades.lbl.gov/publications/two-dimension-conduction-and-cfd01448nas a2200169 4500008004100000050001500041245004400056210004300100520093100143100002001074700002201094700002501116700001801141700002201159700002401181856007301205 2003 eng d aLBNL-4825500aTHERM 5/WINDOW 5 NFRC Simulation Manual0 aTHERM 5WINDOW 5 NFRC Simulation Manual3 aThis 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 Users Manual and the WINDOW Users Manual. In general, this manual references the Users 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.

1 aMitchell, Robin1 aKohler, Christian1 aArasteh, Dariush, K.1 aCarmody, John1 aHuizenga, Charlie1 aCurcija, Dragan, C. uhttps://facades.lbl.gov/publications/therm-5window-5-nfrc-simulation02348nas a2200157 4500008004100000050001500041245015700056210006900213260002500282520171200307100002102019700002202040700002502062700002402087856007902111 2003 eng d aLBNL-5250900aTwo-Dimensional Computational Fluid Dynamics and Conduction Simulations of Heat Transfer in Window Frames with Internal Cavities - Part 1: Cavities Only0 aTwoDimensional Computational Fluid Dynamics and Conduction Simul aOrlando, FLc02/20053 aAccurately 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.

1 aGustavsen, Arlid1 aKohler, Christian1 aArasteh, Dariush, K.1 aCurcija, Dragan, C. uhttps://facades.lbl.gov/publications/two-dimensional-computational-fluid-001132nas a2200157 4500008004100000245008800041210006900129260003200198300001200230490001600242520057600258100002200834700002500856700002000881856007300901 2001 eng d00aTHERM Simulations of Window Indoor Surface Temperatures for Predicting Condensation0 aTHERM Simulations of Window Indoor Surface Temperatures for Pred aAtlantic City, NJc01/ 2002 a593-5990 v109, Part 13 aAs 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.

1 aKohler, Christian1 aArasteh, Dariush, K.1 aMitchell, Robin uhttps://facades.lbl.gov/publications/therm-simulations-window-indoor01204nas a2200193 4500008004100000245003700041210003600078260001200114300000800126520064300134100002000777700002200797700002500819700002900844700002200873700002400895700001800919856007300937 2000 eng d00aTHERM 2.1 NFRC Simulation Manual0 aTHERM 21 NFRC Simulation Manual c07/2000 a2603 aThis 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.

This paper studies the effectiveness of one commercial computational fluid dynamics (CFD) program for simulating combined natural convection and heat transfer in three dimensions for air-filled cavities similar to those found in the extruded frame sections of windows. The accuracy of the conjugate CFD simulations is evaluated by comparing results for surface temperature on the warm side of the specimens to results from experiments that use infrared (IR) thermography to map surface temperatures during steady-state thermal tests between ambient thermal chambers set at 0 °C and 20 °C. Validations using surface temperatures have been used in previous studies of two-dimensional simulations of glazing cavities with generally good results. Using the techniques presented and a noncontact infrared scanning radiometer we obtained surface temperature maps with a resolution of 0.1 °C and 3 mm and an estimated uncertainty of +/-0.5 °C and +/-3mm. Simulation results are compared to temperature line and contour plots for the warm side of the specimen. Six different cases were studied, including a simple square section in a single vertical cavity and two four-sided frame cavities as well as more complex H- and U-shaped sections. The conjugate CFD simulations modeled the enclosed air cavities, the frame section walls, and the foam board surround panel. Boundary conditions at the indoor and outdoor air/solid interface were modeled using constant surface heat-transfer coefficients with fixed ambient-air temperatures. In general, there was good agreement between the simulations and experiments, although the accuracy of the simulations is not explicitly quantified. We conclude that such simulations are useful for future evaluations of natural convection heat transfer in frame cavities.

1 aGustavsen, Arlid1 aGriffith, Brent, T.1 aArasteh, Dariush, K. uhttps://facades.lbl.gov/publications/three-dimensional-conjugate01203nas a2200181 4500008004100000050001500041245008900056210006900145260002600214520056200240100002200802700002500824700002900849700002000878700002400898700002400922856007500946 1999 eng d aLBNL-4399100aTHERM 2.0: A Building Component Model for Steady-State Two-Dimensional Heat Transfer0 aTHERM 20 A Building Component Model for SteadyState TwoDimension aKyoto, Japanc09/19993 aTHERM 2.0 is a state-of-the-art software program, available without cost, that uses the finite-element method to model steady-state, two-dimensional heat-transfer problems. It includes a powerful simulation engine combined with a simple, interactive interface and graphic results. Although it was developed primarily to model thermal properties of windows, it is appropriate for other building components such as walls, doors, roofs, and foundations, and is useful for modeling thermal bridges in many other contexts, such as the design of equipment.

1 aHuizenga, Charlie1 aArasteh, Dariush, K.1 aFinlayson, Elizabeth, U.1 aMitchell, Robin1 aGriffith, Brent, T.1 aCurcija, Dragan, C. uhttps://facades.lbl.gov/publications/therm-20-building-component-model01900nas a2200181 4500008004100000050001500041245014300056210006900199260002500268490001600293520122000309100002201529700002501551700002901576700002001605700002401625856006901649 1998 eng d aLBNL-4210200aTeaching Students about Two-Dimensional Heat Transfer Effects in Buildings, Building Components, Equipment, and Appliances Using THERM 2.00 aTeaching Students about TwoDimensional Heat Transfer Effects in aChicago, ILc01/19990 v105, Part 13 aTHERM 2.0 is a state-of-the-art software program, available for free, that uses the finite-element method to model steady-state, two-dimensional heat-transfer effects. It is being used internationally in graduate and undergraduate laboratories and classes as an interactive educational tool to help students gain a better understanding of heat transfer. THERM offers students a powerful simulation engine combined with a simple, interactive interface and graphic results. Although it was developed to model thermal properties of building components such as windows, walls, doors, roofs, and foundations, it is useful for modeling thermal bridges in many other contexts, such as the design of equipment. These capabilities make THERM a useful teaching tool in classes on: heating, ventilation, and air-conditioning (HVAC); energy conservation; building design; and other subjects where heat-transfer theory and applications are important. THERMs state-of-the-art interface and graphic presentation allow students to see heat-transfer paths and to learn how changes in materials affect heat transfer. THERM is an excellent tool for helping students understand the practical application of heat-transfer theory.

1 aHuizenga, Charlie1 aArasteh, Dariush, K.1 aFinlayson, Elizabeth, U.1 aMitchell, Robin1 aGriffith, Brent, T. uhttps://facades.lbl.gov/publications/teaching-students-about-two01730nas a2200157 4500008004100000050002100041245009800062210006900160520114800229100002901377700002001406700002501426700002201451700002401473856007501497 1998 eng d aLBL-37371 Rev. 200aTHERM 2.0: a PC Program for Analyzing Two-Dimensional Heat Transfer through Building products0 aTHERM 20 a PC Program for Analyzing TwoDimensional Heat Transfer3 aTHERM is a state-of-the-art, Microsoft Windows?-based computer program developed at Lawrence Berkeley National Laboratory (LBNL) for use by building component manufacturers, engineers, educators, students, architects, and others interested in heat transfer. Using THERM, you can model two-dimensional heat-transfer effects in building components such as windows, walls, foundations, roofs, and doors; appliances; and other products where thermal bridges are of concern. THERM's heat-transfer analysis allows you to evaluate a product?s energy efficiency and local temperature patterns, which may relate directly to problems with condensation, moisture damage, and structural integrity.

This version of THERM includes several new technical and user interface features; the most significant is a radiation view-factor algorithm. This feature increases the accuracy of calculations in situations where you are analyzing non-planar surfaces that have different temperatures and exchange energy through radiation heat transfer. This heat-transfer mechanism is important in greenhouse windows, hollow cavities, and some aluminum frames.

1 aFinlayson, Elizabeth, U.1 aMitchell, Robin1 aArasteh, Dariush, K.1 aHuizenga, Charlie1 aCurcija, Dragan, C. uhttps://facades.lbl.gov/publications/therm-20-pc-program-analyzing-two01300nas a2200145 4500008004100000050001500041245011600056210006900172260003800241520071500279100002000994700002501014700002701039856008801066 1996 eng d aLBNL-4225400aTransforming the Market for Residential Windows: Design Considerations for DOE's Efficient Window Collaborative0 aTransforming the Market for Residential Windows Design Considera aPacific Grove, CAbACEEEc08/19963 aMarket adoption of recent, commercially available technological advances that improve the energy performance of windows will lead to immediate economic and energy savings benefits to the nation. This paper is a scoping study intended to inform the design of a major DOE initiative to accelerate market adoption of these windows in the residential sector. We describe the structure of the U.S. residential window market and the interests of the various market players. We then briefly review five recent market transformation initiatives. Finally, we summarize our findings in a list of considerations we believe will be important for the DOE's initiative to transform the U.S. residential window market.

1 aEto, Joseph, H.1 aArasteh, Dariush, K.1 aSelkowitz, Stephen, E. uhttp://aceee.org/files/proceedings/1996/data/papers/SS96_Panel10_Paper05.pdf#page=1