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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 l.jpg

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


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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


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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



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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


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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



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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


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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



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OTHER PROGRAMS

  • RESFEN 3.1 –

    Annual Energy Performance

  • OPTICS 5 –

    Virtual Glass Laboratory


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ENHANCED NEW VERSIONS

  • Windows based WINDOW+5 program


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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


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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”


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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.


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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


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CURRENT AREAS OF PROGRAM DEVELOPMENT

  • Condensation Resistance

  • Projecting Products

  • Highly Conducting Products

  • Improved accuracy in estimating annual energy performance

  • Laminates

  • Better integration

  • Database management


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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


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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