Civil, Environmental, and Architectural Engineering The University of Kansas 1 “Radiant Barrier Technology – A Must in Green Architecture” Mario A. Medina, Ph.D., P.E.

2 Introduction  “ ”  “Preventing the sun's radiation from entering through the roof can make a significant contribution to comfort and reduction in cooling bills/needs.” From: Sustainable Building Sourcebook Chapter: Energy

3 Definition A radiant barrier consists of a layer of metallic foil, with low emittance, that significantly reduces the transfer of heat energy radiated from “hotter” surfaces to “colder” surfaces (e.g., the deck of an attic to the attic floor). Among the benefits of installing radiant barriers are energy savings, $ savings, and comfort. (Source: Florida Solar Energy Center)

4 Radiant Barriers  Installation Configurations Pre-laminated Roof Sheathing

5 Radiant Barriers  How are they installed?

6 Radiant Barriers  How are they installed?

7 Radiant Barriers  How they work: –Radiant barriers reduce radiated heat transfer rate by the combination of the low emittance/high reflectance properties of the foil.

8 Radiant Barriers  Modes of Heat Transfer (Source: Btubusters)

9 Radiant Barriers Heat transfer schematic Radiant Barrier

10 Radiant Barriers  In the present study, the performance of radiant barriers was assessed via: –Experiments Side by side monitoring of pre- and post-retrofit data. –Modeling Mathematical representation of thermal sciences that describe the processes that take place. Implemented using computer programming (e.g., FORTRAN). –Model/Experiment Validation

11 Radiant Barriers  Experiments: Test Houses

12 Radiant Barriers  Experiments: Sensors

13 Radiant Barriers  Experiments: Monitoring Equipment

14 Radiant Barriers  Experimental Results: Calibration (No RB Case ) Ceiling Heat Flux Indoor Air Temperature < 3 %< 0.3 o F

15 Radiant Barriers  Experimental Results: Calibration (RB Case) Ceiling Heat Flux Indoor Air Temperature < 3 %< 0.3 o F

16 Radiant Barriers  Experimental Results: Effect of Radiant Barriers (~28% Daily Heat Flow Reduction) 37.5%

17 Radiant Barriers  Experimental Results: Installation Comparisons Horizontal Configuration vs. Truss Configuration? Slight Advantage for the Horizontal Configuration ~ 5 %

18 Radiant Barriers  Experimental Results: Shingle Temperatures Horizontal Configuration Truss Configuration vs. No RB Case vs. No RB Case No difference in shingle temperature

19 Radiant Barriers  Experimental Results: Effects of Daily Solar Radiation

20 Radiant Barriers  Experimental Results: Effects of Attic Ventilation

21 Radiant Barriers  Experimental Results: Effects of Attic Insulation Level 42% 34% 25%

22 Radiant Barriers  Modeling: Based on Energy Balance Approach at Each Enclosing Surface

23 Radiant Barriers  Modeling Energy Balance (General) Energy Balance (Heat Transport Processes)  Outdoor Energy Balance Indoor Energy Balance 

24 Radiant Barriers  Modeling: Solar Modeling

25 Radiant Barriers  Verification of Model/Experiments (No RB Case)

26 Radiant Barriers  Verification of Model/Experiments Horizontal Configuration Truss Configuration

27 Radiant Barriers  Verification of Model/Experiments (Winter) No Radiant Barrier Configuration Horizontal Configuration 15 % Reduction in Heat Leaving Across the Attic

28 Radiant Barriers  Verification of Model/Experiments No Radiant Barrier Configuration Horizontal Configuration

29 Radiant Barriers  Computer Simulations: Yearly Performance Horizontal ConfigurationTruss Configuration 34 % Jun - Aug 32 % Jun - Aug

30 Radiant Barriers  Computer Simulations: Yearly Performance

31 Radiant Barriers  Computer Simulations: Attic Ventilation Pattern (Soffit/Soffit) Jun - Aug 33.1% 31.6% HorizontalTruss No RB

32 Radiant Barriers  Computer Simulations: Attic Ventilation Pattern (Roof/Soffit) Jun - Aug 31.4% 26.2% Horizontal Truss No RB

33 Radiant Barriers  Computer Simulations: Attic Ventilation Pattern (Soffit/Ridge) Jun - Aug 32.3% 28.2% Horizontal Truss No RB

34 Radiant Barriers  Computer Simulations: Impact of Radiant Barrier on Cooling Demand as a Function of Insulation Degradation

35 Radiant Barriers  Computer Simulations: Climate Influence

36 Radiant Barriers  Computer Simulations: Climate Influence Climate Summer Monthly Dry Bulb Air Temperature o C ( o F) Summer Monthly Relative Humidity (%) Summer Monthly Wind Speed km/h (mi/h) Area Covered km 2 (mi 2 ) Percent Area Covered (%) Humid Subtropical 29 (84) (8.5) 1,939,636 (750,430) Humid Continental Warm Summer 25 (77) (8.8) 1,655,112 (640,350) Desert 28 (83) (8.1) 1,223,467 (473,350) Humid Continental Cool Summer 21 (70) (8.7) 905,291 (350,250) Steppe 17 (62) (7.9) 739,043 (285,930) 9.15 Marine West Coast 15 (59) (8.3) 560,259 (216,760) 6.94 Mediterranean 17 (63) (10.0) 508,837 (196,865) 6.30 Western High Areas 20 (68) (8.5) 481,581 (186,320) 5.97 Tropical Savanna 28 (83) (8.0) 59,484 (23,014) 0.74 TOTAL 8,072,711 (3,123,269)

37 Radiant Barriers  Computer Simulations: Climate Influence

38 Radiant Barriers  Computer Simulations: Climate Influence

39 Radiant Barriers  Computer Simulations: Climate Influence

40 Radiant Barriers  Computer Simulations: Climate Influence

41 Radiant Barriers  Computer Simulations: Climate Influence ClimateSample Station Sample Summer Integrated Percent Reduction (SIPR) (%) Average Peak-Hour Percent Reduction (PHPR) (%) Humid Subtropical San Antonio, TX New York- NY Atlanta, GA Humid Continental Warm Summer Topeka, KS Indianapolis, IN Desert Las Vegas, NV Tucson, AZ Humid Continental Cool Summer Minneapolis, MN Detroit, Michigan Steppe Pocatello, ID Helena, MT Marine West CoastAstoria, OR9.6 ~100 MediterraneanSan Francisco, CA Western High AreasBoulder, CO Tropical SavannaMiami, FL

Radiant Barriers  Parametric Analyses: Outdoor Air Temperature

43 Radiant Barriers  Parametric Analyses: Mean Hourly Relative Humidity

44 Radiant Barriers  Parametric Analyses: Mean Hourly Global (H) Radiation

45 Radiant Barriers  Parametric Analyses: Latitude

46 Radiant Barriers  Parametric Analyses: Altitude

47 Radiant Barriers  Parametric Analyses: Roof Solar Absorptivity

48 Radiant Barriers  Parametric Analyses: Radiant Barrier Emissivity

49 Radiant Barriers  Parametric Analyses: Attic Airflow Rate

50 Radiant Barriers  Parametric Analyses: Roof Slope

51 Radiant Barriers  In Conclusion….

52 THANK YOU