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Reflective Products: An Energy-Savings Solution for Post-Frame Buildings

Reflective Products: An Energy-Savings Solution for Post-Frame Buildings. David W. Yarbrough, PhD, PE R&D Services, Inc. Cookeville, TN Sponsored by The Reflective Insulation Manufacturers Association International.

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Reflective Products: An Energy-Savings Solution for Post-Frame Buildings

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  1. Reflective Products: An Energy-Savings Solution for Post-Frame Buildings David W. Yarbrough, PhD, PE R&D Services, Inc. Cookeville, TN Sponsored by The Reflective Insulation Manufacturers Association International

  2. Components of this Presentation Physical Basis: Design of Insulations Expected Performance Installation - Reflective Assemblies Savings – Reduce Heating/Cooling Hybrid Systems

  3. A Time Line • 1650-1850 The physics is established • 1850-1920 Air space resistance recognized • 1920-1950 Reflective systems appear • 1950-1985 Reflective data base is developed • 1985-2000 Product development • 2000- Advanced systems

  4. Product Categories • Reflective Insulations enclosed air space (0-10 in.) R-value ASTM C 1224, ASTM C 1363 • Radiant Barriers large (ventilated) air space (2-20 ft) reduction in heat flow ASTM C 1313, ASTM C 1340 • Interior Radiation Control Coatings Increases air film resistance (at surface) ASTM C 1321 A property in common to all of these products: low thermal emittance (low emissivity)

  5. Reflective Insulations Enclosed air space Small air gap ( 0-6 in. ) Thermal Resistance ( up to 14 ) Radiant Barriers (attic) Open air space (or ventilated space) Large air gap ( up to 10-15 ft. ) Thermal Resistance Reflective Insulations and Radiant Barriers have Low-Emittance Surfaces

  6. Large Scale Test Facility12 by 12 ft. specimen8 by 8 ft. metering area

  7. Design of Insulations Insulations Based on Air Mechanism Mass-TypeReflective-Type Conduction Increases Increases-slight Convection None Decreases (some exceptions) Radiation Decreases Almost Zero Increase in conduction because solids like glass, wood, concrete, or paper have much higher thermal conductivity than air. Air is an excellent thermal insulation.

  8. Thermal Conductivity of Air T (°F)k (Btu∙in./ft2∙h∙°F) R/inch 0 0.155 6.45 75 0.178 5.62 100 0.201 4.78 No Convection and No Radiation

  9. Thermal Emittance (ε) – A Property • A fraction 0 < ε < 1 that is measured. • ε = 0 no radiation • ε = 1 maximum radiation (black body)

  10. ^ ↓(radiation in, Qrad) | ↓ (radiation reflected, r) ___________________/_______________ |_ →→(radiation absorbed, a) |_ |__________________________________|_ ↓ ↓(radiation transmitted, t)

  11. Radiation Terminolgy • Qrad = Reflected + Absorbed + Transmitted • If opaque ,then transmitted is zero (t=0) • Expressed as fractions 1 = r + a but a = e so we have 1 = r + e If e is small, then r is large e= 0.03, r= 0.97 systems perform in both directions

  12. Total Hemispherical Emittance (all directions) Paints 0.8 < e < 1.0 Wood 0.8 < e < 0.9 Masonry 0.9 < e < 1.0 Metals 0.02 < e < 0.10 IRCC 0.15 < e < 0.25 aluminum foil 0.03<e<0.04 Al metallized film 0.04<e<0.06

  13. What to choose ? ε→0 At 75 °F (room temperature) Aluminum 0.03 Polished brass 0.03 Cadmium 0.02 Polished copper 0.03 Gold 0.02-0.03 Nickel 0.04 Platinum 0.03 Tin 0.05 Zinc 0.05 American Institute of Physics (early edition)

  14. Why Emittance is Key Property(Boltzmann Equation) Q/A = E * [ σ * (T42– T41)] ↑ 1/E=1/e1 + 1/e2 – 1 e1 e2 E % reduction no foil/film 1 1 1 0 Foil one side 1 0.03 0.03 97 Foil one side 0.03 1 0.03 97 Foil both sides 0.03 0.03 0.015 98.5

  15. Boltzmann 1844-1906 AustriaStefan published in 1879 Boltzmann published in 1884Stefan-Boltzmann Law and Stefan-Boltzmann Constant5.6704 x 10-8 W/m2·K4

  16. Insulation Assembly Design • Identify the space to be insulated. • Choices Attach RI to one side or the other to create a single reflective air space. Attach RI in center to form two reflective air spaces. Install RI that forms more than two reflective air spaces.

  17. Quick Estimate of Savings • Use HDD/CDD data • CLIMATOGRAPHY OF THE UNITED STATES No. 81 SUPPLEMENT NO. 2 • Title: “Annual Degree Days to Selected Bases” • Heating: 40 to 65 °F Cooling: 45 to 70 °F • Louisville HDD65 4352 CDD70 797 • Heat flow out HDD*24*Area/R • Utility Use HDD*24*Area/(R*E) • Heat flow in CDD*24*Area/R • Utility Use CDD*24*Area/(R*COP) • Convert from BTU/yr to KWH/yr multiply by 0.000293 • Kwh at 0.1 as example

  18. Calculation of SavingsLouisville – 1000 square feet

  19. Hybrid Systems Combine Technologies Examples: fiberglass + foam fiberglass + reflective foam + reflective Utilize air spaces to increase R-value

  20. Summary • Reflective technology is a mature area • Products: Insulation, radiant barriers, IRCCs • Evaluation: laboratory measurements and/or engineering calculations • Quick estimates of savings are possible • Combine technologies: Hybrids

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