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Energy Code Terminology

Energy Code Terminology. The new energy requirements and terms are being added to the energy codes. Solar Reflectance - the ability of the surface to reflect solar radiation away from that surface

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Energy Code Terminology

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  1. Energy Code Terminology The new energy requirements and terms are being added to the energy codes. • Solar Reflectance - the ability of the surface to reflect solar radiation away from that surface • Infrared Emittance - the ability of a material to emit or radiate heat energy that builds up in the material. • Cool Roof Color - A cool roof color is required for a conditioned building and it must meet the energy code Cool Roof finish values for Solar Reflectance and Infrared Emittance. These values will vary based upon the energy code requirements being met. • Maximum Required U-Factor – The energy codes are lowing the established maximum required U-Factors for building construction. These new requirements will result in increased R-Values • Conditioned Buildings - For a conditioned building, to get a building permit, a Building Envelope Energy Calculation will be required showing that the building is energy efficient. A building is conditioned if it has a system with heating capacity of more than 3.4 Btu/hr-ft2 or cooling capacity of more than 5 Btu/hr-ft2 .

  2. Cool Roofing Terminology (cont’d) • Solar Spectrum - radiation energy originating from the sun, including ultraviolet, visible and near infrared radiation. • Conduction - the passing of heat through a roof material into the layer in contact directly beneath the surface • Convection - the heating of the air that passes over a hot surface

  3. Energy Balance on Roof Surface Total Solar Radiation Re-Emitted Energy Reflected Radiation Convection Roof Surface Layer Absorbed Energy Net Heat Flux Into Roof

  4. Ultraviolet (UV) 3% of total energy responsible for sunburn Visible (VIS) 40% of total energy visible light Infrared (IR) 57% of total energy felt as heat! Solar Energy Spectrum

  5. Cool Roofing Testing Methods • ASTM E-903 - Reflectance (Laboratory) • ASTM E-1918 - Reflectance (field test for variegated surfaces) • ASTM C-1549 - Reflectance (portable device) • ASTM E-408 - Emittance (Laboratory) • ASTM C-1371 - Emittance (portable device)

  6. High reflectivity Initial reading  65% ASTM E-903-96 or ASTM E-1918-97ORMinimum Solar Reflectance Index (SRI)of 75% ASTM E-1980 for moderate wind conditions Cool Roof Requirements • High emissivity • 80% • ATSM E 408-71 (1996)

  7. SOLAR ENERGY SPECTRUM

  8. rsolarANDeIRARE BOTH VERY IMPORTANT Total Solar Irradiation Convection Net Infrared Radiation hair(tair-ts) It rsolarIt Reflected eIRDR with DR=s(Ts4-Tsky4 ) (asolarItAbsorbed) Net Heat Flux into Roof

  9. Most Efficient 1.0 .75 .50 .25 0 Absorbed Reflected Least Efficient Measuring Solar Reflectivity • Solar Reflectivity describes an object’s ability to REFLECT solar radiation away from its surface. • It is measured in the UV, IR and visible light wavelengths and therefore should not be confused with gloss/sheen which is based solely on visible light reflection • Don’t confuse reflectivity with GLARE!

  10. Total Solar Reflectance A measure of reflectivity of an object over the entire spectrum of sunlight that hits the Earth’s surface, weighted by the intensity of sunlight at each wavelength.

  11. Solar Reflectance • Solar reflectance describes an objects ability to REFLECT solar radiation away from its surface • It is measured in the UV, IR and visible light wavelengths and therefore should not be confused with gloss/sheen which is based solely on visible light reflection • Don’t confuse reflectivity with GLARE!

  12. Gloss/Sheen vs. Solar Reflectance • GLARE is a CONCERNfor commercial metal roofs • Glare is the reflection of sunlight that can impair vision and create an ANNOYANCE • This becomes CRITICAL around airports (impaired vision of pilots) and in tightly built residential neighborhoods • The GLARE of a coated surface is controlled by the SHEEN • Low Sheen = Low Glare Gloss/Sheen and Solar Reflectance are totally independent properties and do not have an affect on one another. A change in gloss and sheen does not change solar reflectance and vice versa.

  13. Suns Energy 6% Ultraviolet 52% Visible 42% Infrared 100% Sunlight Sunlight UV - Visible - Infrared UV - Visible - Infrared Low IR Reflectance High IR Reflectance Same Color Roof Low IR Pigments High IR Pigments Low IR Reflectance = Higher Temperature High IR Reflectance = Lower Temperature The same color roof can be cool or hot depending on the pigment in the roofing!!!

  14. UV - Visible - Infrared Sunlight Low IR Reflectance Infrared Suns Energy 6% Ultraviolet 52% Visible 42% Infrared 100% Low IR Pigments High IR Reflectance Visible UV - Visible - Infrared UV Same Color Low IR Reflectance = Higher Temperature Careful selection of weatherable IR reflective pigments can produce dark, aesthetically pleasing colors that meet Energy Star roofing requirements. Infrared Visible UV High IR Pigments Energy Star (High Slope) (over 2:12 roof pitch) 25% Total Reflectance (Initial) 15% after 3 years • Lower cooling costs • Reduced Heat Island Effect • Potential for for longer life cycle due to lower temperature High IR Reflectance = Lower Temperature The same color roof can be cool or hot depending on the pigment in the roofing!!!

  15. 80% Cool Roof Requirement 0.25.50.751.0 Least Efficient Most Efficient Measuring Infrared Emissivity • Efficiency of a surface ability to emit heat by radiation; the ratio of the radiant energy emitted by a surface to that emitted by a blackbody at the same temperature. • Decreasing emittance may lead to increased energy use. • Values are expressed from 0 to 1.0 • Same type of values as solar reflectance

  16. Roof Surface Temperature Infrared Emittance Has a Lesser Impact Than Solar Reflectance (Example for Air Temperature of 98° F) Source: LBNL, ASTM D1980 solar reflectanceemittancetemperature (F) 0.700.75 124 0.700.90 122 0.550.75139 0.700.75125 0.800.75115 T = 2° F T = 10 - 14° F

  17. Color Selection • Light and medium shades usually meet the 0.25 requirement • Dark colors can usually be reformulated to meet the 0.25 requirement

  18. The Primary Energy Concern is the Heat in the Building • Dark materials ABSORB MORE HEAT from the sun. • When those dark surfaces are roofs, some of the heat is TRANSFERRED INSIDE • When that happens, the Urban Heat Island Effect becomes a factor.

  19. The Problem – Metal Stability • Metal Expansion and Contraction: • Standing seam applications are subject to DISTORTION by heat • The temperature variations create MOVEMENT within the standing seam leg, WEAR, and OILCANNING • Oil Canning: • The STRESS in the platform angles of the LEG causes distortion, exasperated by heat absorption

  20. Cool Coating Benefits • Heat is REFLECTEDaway from buildings • All the advantages of greater reflectivity can be had WITHOUT SACRIFICING COLOR CHOICE • Dramatically increases the reflectivity of medium to dark colors to such a degree that the product will meet the ENERGY STAR specifications for STEEP SLOPE Cool Roofs • Smog is REDUCED when environmental temperatures arereduced

  21. Impact on Temperature and Energy Consumption • Rule of Thumb: • FOR EVERY 1% INCREASE IN ROOF REFLECTANCE, TEMPERATURE DECREASES 1°F • example: Improving reflectance from 10% to 50% lowers surface temperature 40°F • FOR EVERY 10% INCREASE IN ROOF REFLECTANCE, COOLING/HEATING ENERGY COSTS DROP 2¢/ft2 (warm climates) Per LBNL: based on DOE 2 model, LBNL models, ORNL calculator, EnergyPlus model

  22. Roofing Material Thermal Properties Initial Solar Reflectance Metal(unpainted)0.60-0.80 0.04-0.10 Metal(painted and granular coated)0.10-0.75 * 0.75 + Comp Asphalt Shingles 0.05-0.25 0.90 Modified Bitumen 0.05-0.25 0.90 Built Up Roofing 0.05-0.80 0.90 Concrete/Clay Tile 0.20-0.70 0.90 White Single Ply Membrane 0.70-0.80 0.85 + Source: ORNL and LBNL Infrared Emittance * depending on color Emissivity is generally high in coatings and paint films, but very low in unpainted metallic surfaces

  23. Roof Surface Temperature Infrared Emittance Has Less Impact Than Solar Reflectance (Example for Air Temperature of 98° F) Source: LBNL, ASTM D1980 solar reflectanceemittancetemperature (F) 0.700.75 124 0.700.90 122 0.550.75139 0.700.75125 0.800.75115 T = 2° F T = 10 - 14° F

  24. Urban Heat Island Effect • Urban Heat Island - a built environment wherein the large proportion of dark surfaces such as asphalt paving and dark roofs absorb solar radiation and radiate the heat back into the atmosphere causing higher ambient temperatures and higher pollution levels • Urban areas are 6-8 °F warmer than suburbs (Dark pavements, dark roofing and less vegetation) • Roof surface temperature has an effect on the following items: (lower temperature = less smog, less pollution, lower peak energy demand) • High reflectance/emittance = low surface temperatures

  25. Thermal Image of Washington, DC Hottest Surface Colored in Red

  26. Smog Formation Heat is a catalyst for smog The air in Los Angeles is noticeably cleaner during winter, yet the number of cars on the road is approximately the same as in summer.

  27. Roof Energy Savings White Membrane Unpainted Galvalume Aluminum Coating $0.25 R-5 R-15 $0.20 White Membrane or White Painted Metal $0.15 Unpainted Galvalume Savings, $/ft² per year $0.10 Aluminum Coating $0.05 $0.00 Knoxville Phoenix Chicago Knoxville Phoenix Chicago City

  28. Heating Degree Day • The sum of the degree days for heating, using a common base of 65°F, used with other factors to evaluate the energy requirements of a heating season. • Example for HDD Base 65º F For any one day, when the mean temperature is less than 65 °F, there are as many degree-days as degrees F temperature difference between the mean temperature for the day and 65°F. Annual heating degree-days are the sum of the degree-days over a calendar year.

  29. 3600 HDD Isothermal Line

  30. Building Envelope • One of most important factors in designing energy-efficient buildings • Strongly affects heating and cooling loads (HVAC Energy) • Investment in insulation or energy-efficient windows can result in smaller HVAC systems to help pay for the better envelope

  31. Envelope Compliance Methods • Prescriptive • Trade-off • Energy Cost Budget (Whole Building)

  32. Prescriptive Method Roof Umax 0.065 • Specified for Location • ASHRAE 90.1 – 16 Climate Zones • Insulation for Opaque Components • Maximum U-Factor or Minimum R • Roofs, Walls, Floors • Fenestration • Maximum SHGC and U-Factor • Windows, Skylights

  33. Trade-Off • Offers flexibility • Thermal performance of one envelope component can fail to meet prescriptive requirement as long as other components perform better than what is required • Proof of compliance is more involved • Overall Heat Loss • Overall Heat Gain

  34. NAIMA Prescriptive Solutions Screw Down w/R-19 U=0.098 SSR w/R-19 U=0.065 ASHRAE = 0.065 SSR 2 Layers R-19 U=0.046

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