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“Radiant Barrier Technology – A Must in Green Architecture”. Mario A. Medina, Ph.D., P.E. Introduction. “ Preventing the sun's radiation from entering through the roof can make a significant contribution to comfort and reduction in cooling bills/needs. ”
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“Radiant Barrier Technology – A Must in Green Architecture” Mario A. Medina, Ph.D., P.E. Civil, Environmental, and Architectural Engineering The University of Kansas
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
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)
Radiant Barriers • Installation Configurations Pre-laminated Roof Sheathing
Radiant Barriers • How are they installed?
Radiant Barriers • How are they installed?
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.
Radiant Barriers • Modes of Heat Transfer (Source: Btubusters)
Radiant Barriers Heat transfer schematic Radiant Barrier Radiant Barrier
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
Radiant Barriers • Experiments: Test Houses
Radiant Barriers • Experiments: Sensors
Radiant Barriers • Experiments: Monitoring Equipment
Radiant Barriers • Experimental Results: Calibration (No RB Case) Ceiling Heat Flux Indoor Air Temperature < 3 % < 0.3 oF
Radiant Barriers • Experimental Results: Calibration (RB Case) Ceiling Heat Flux Indoor Air Temperature < 3 % < 0.3 oF
Radiant Barriers • Experimental Results: Effect of Radiant Barriers (~28% Daily Heat Flow Reduction) 37.5%
Radiant Barriers • Experimental Results: Installation ComparisonsHorizontal Configuration vs. Truss Configuration? ~ 5 % Slight Advantage for the Horizontal Configuration
Radiant Barriers • Experimental Results: Shingle Temperatures Horizontal Configuration Truss Configuration vs. No RB Case vs. No RB Case No difference in shingle temperature
Radiant Barriers • Experimental Results: Effects of Daily Solar Radiation
Radiant Barriers • Experimental Results: Effects of Attic Ventilation
Radiant Barriers • Experimental Results: Effects of Attic Insulation Level 42% 34% 25%
Radiant Barriers • Modeling: Based on Energy Balance Approach at Each Enclosing Surface
Radiant Barriers • ModelingEnergy Balance (General) Energy Balance (Heat Transport Processes)Outdoor Energy BalanceIndoor Energy Balance
Radiant Barriers • Modeling: Solar Modeling
Radiant Barriers • Verification of Model/Experiments (No RB Case)
Radiant Barriers • Verification of Model/Experiments Horizontal Configuration Truss Configuration
Radiant Barriers • Verification of Model/Experiments (Winter) No Radiant Barrier Configuration Horizontal Configuration 15 % Reduction in Heat Leaving Across the Attic
Radiant Barriers • Verification of Model/Experiments No Radiant Barrier Configuration Horizontal Configuration
Radiant Barriers • Computer Simulations: Yearly Performance Horizontal Configuration Truss Configuration 34 % Jun - Aug 32 % Jun - Aug
Radiant Barriers • Computer Simulations: Yearly Performance
Radiant Barriers • Computer Simulations: Attic Ventilation Pattern (Soffit/Soffit) Jun - Aug 31.6% 33.1% No RB Horizontal Truss
Radiant Barriers • Computer Simulations: Attic Ventilation Pattern (Roof/Soffit) Jun - Aug 26.2% 31.4% No RB Truss Horizontal
Radiant Barriers • Computer Simulations: Attic Ventilation Pattern (Soffit/Ridge) Jun - Aug 32.3% 28.2% No RB Truss Horizontal
Radiant Barriers • Computer Simulations: Impact of Radiant Barrier on Cooling Demand as a Function of Insulation Degradation
Radiant Barriers • Computer Simulations: Climate Influence
Radiant Barriers • Computer Simulations: Climate Influence
Radiant Barriers • Computer Simulations: Climate Influence
Radiant Barriers • Computer Simulations: Climate Influence
Radiant Barriers • Computer Simulations: Climate Influence
Radiant Barriers • Computer Simulations: Climate Influence
Radiant Barriers • Computer Simulations: Climate Influence
Radiant Barriers • Parametric Analyses: Outdoor Air Temperature
Radiant Barriers • Parametric Analyses: Mean Hourly Relative Humidity
Radiant Barriers • Parametric Analyses: Mean Hourly Global (H) Radiation
Radiant Barriers • Parametric Analyses: Latitude
Radiant Barriers • Parametric Analyses: Altitude
Radiant Barriers • Parametric Analyses: Roof Solar Absorptivity
Radiant Barriers • Parametric Analyses: Radiant Barrier Emissivity
Radiant Barriers • Parametric Analyses: Attic Airflow Rate
Radiant Barriers • Parametric Analyses: Roof Slope