Civil, Environmental, and Architectural Engineering

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
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

lt 3
lt 0.3 oF
15
Radiant Barriers

• Experimental Results Calibration (RB Case)
• Ceiling Heat Flux Indoor Air
  Temperature

lt 3
lt 0.3 oF
16
Radiant Barriers

• Experimental Results Effect of Radiant Barriers
  (28 Daily Heat Flow Reduction)

37.5
17
Radiant Barriers

• Experimental Results Installation
  ComparisonsHorizontal Configuration vs. Truss
  Configuration?

5
Slight Advantage for the Horizontal Configuration
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

• ModelingEnergy Balance (General)
• Energy Balance (Heat Transport Processes)
  
  ?Outdoor Energy BalanceIndoor 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 Configuration Truss
  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
31.6
33.1
No RB
Horizontal
Truss
32
Radiant Barriers

• Computer Simulations Attic Ventilation Pattern
  (Roof/Soffit)

Jun - Aug
26.2
31.4
No RB
Horizontal
Truss
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

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

42
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