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Role of Computer Simulation in Window Certification

Role of Computer Simulation in Window Certification. By: Dragan Ć ur č ija, Ph.D. Center for Energy Efficiency and Renewable Energy University of Massachusetts Amherst, MA U.S.A.

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Role of Computer Simulation in Window Certification

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  1. Role of Computer Simulation in Window Certification By: Dragan Ćurčija, Ph.D. Center for Energy Efficiency and Renewable Energy University of Massachusetts Amherst, MA U.S.A. Acknowledgements:This work was sponsored by the Assistant Secretary for Conservation and Renewable Energy, Office of Building and Community Systems, Building Systems Division of the United States Department of Energy

  2. BRIEF OVERVIEW • Evaluation of Thermal performance of windows done in two ways: • Physical testing • Computer modeling • In early days (before energy crisis in 70’s) only physical testing • Very limited number of products • Energy use was not concern, mostly comfort and liability issues (early failures) • First generation of testing standards

  3. EARLY COMPUTER MODELS • Research class computer models and general purpose commercial programs • Better understand energy performance of windows • Develop algorithms for simplified computer programs • More detailed than testing results • Not user friendly • Too costly for certification purposes • Early research programs later adopted for fenestration computer modeling tools

  4. RESAERCH CLASS COMPUTER MODELS

  5. PC BASED COMPUTER PROGRAMS • 20 years ago first computer programs for fenestration heat transfer • 1-D heat transfer and solar optical properties for center of glass • 2-D heat transfer in frames and edge of glass (few years later) • First 2-D programs were FDM based • Limited functionality • Inaccurate geometry representation • Long model preparation time

  6. ROLE OF EARLY COMPUTER PROGRAMS • Reduced cost of evaluating thermal performance vs. testing • Greater consistency of results • Complemented testing in design and research • Changed common wisdom of the role of computer models • Helped create modern certification bodies • Accelerated development of stricter code req. • Helped introduction of performance labels

  7. WINDOW 4.1

  8. MODERN FENESTRATION COMPUTER MODELING TOOLS • First program released in mid 90’s: THERM 1.0 • Based on FEM and programs initially developed for military and space research • Allows for accurate geometry representation • Imports AutoCAD drawings • Reduced model preparation time  decreased cost of evaluating fenestration products • Program(s) are developed through government funding and are free for public use

  9. THERM 2.0 • 2-D Conduction and Radiation heat transfer • Glazing cavity Convection • View-factor radiation modeling • Graphic tool to draw the model • Automatic meshing • Calculates 2-D Heat Transfer in Fenestration Products

  10. Mesh Refinement

  11. OTHER PROGRAMS • RESFEN 3.1 – Annual Energy Performance • OPTICS 5 – Virtual Glass Laboratory

  12. ENHANCED NEW VERSIONS • Windows based WINDOW+5 program

  13. COMPUTER TOOLS & CERTIFICATION • Validation studies showed that computer tools can be reliably used for certification • First started in North America (U.S. & Canada) 10 years ago • One validation test (U.S.) and one “quality control” test (production line testing) • Validation criteria 10% (often within 5%) • Limited number of products for which no good agreement

  14. NFRC LABEL B Title A B Contact Information C Overall Heat Transfer Coefficient D E F D F Visible Transmittance E Solar Heat Gain “Transmittance”

  15. INTERNATIONAL USE OF COMPUTER PROGRAMS IN CERTIFICATION • Computer programs based on best science • Physics is same everywhere in the world • Algorithms in WINDOW suite published in North American & international standards • Accepted for use in Russia • Considered for use in Baltic countries, U.K., European Union, etc.

  16. MAIN PHILOSOPHY • Complexity is hidden behind ease of use! • Complex algorithms • User friendly and convenient user’s interface • Premise: Accuracy does not have to be sacrificed in order to create simple & elegant computer tools

  17. CURRENT AREAS OF PROGRAM DEVELOPMENT • Condensation Resistance • Projecting Products • Highly Conducting Products • Improved accuracy in estimating annual energy performance • Laminates • Better integration • Database management

  18. CONCLUSIONS • New fenestration computer programs are reliable tools for estimating thermal performance • Computer modeling should become integral part of modern certification procedure • Computer modeling can effectively be used in the design of energy efficient windows • Further development is necessary to • improve accuracy for certain class of fenestration products • Further improve ease of use and simplicity of user’s interface

  19. For More Information Contact: Dragan Curcija Center for Energy Efficiency and Renewable Energy University of Massachusetts Amherst, MA U.S.A. Tel: +1 (413) 545-4454 Fax: +1 (413) 545-1027 Email: curcija@ceere.org Web: http://www.ceere.org/beep Also: http://windows.lbl.gov http://www.nfrc.org

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