Reflective Roofs Sustainable Communities Conference Sustainable Surfaces Track March 10, 2009 Dallas, TX R. Chappell
Roofs and Heat Flow The sun heats up the roof surface Heat transmits through the roof into and out of the building
Solar Reflectivity Amount of incoming solar energy a material reflects, also called albedo (usually in %) Emissivity Amount of energy a material releases that it has absorbed due to its own heat and temperature (usually in %) sun reflected emitted roof
Cool Reflective Roofs Reflectivity Standards: Low-Slope Commercial Roofing Products Reference Standard Energy Star (EPA) Minimum Initial Reflectance 65% Minimum Aged Reflectance 50% Minimum Initial Emittance n/a Certification Method Self-Report California Title 24 Product Standard 70% n/a 0.75 CRRC (2) California Title 24 Long-Term Value (1) n/a 50% n/a CRRC (2) (1) For energy calculation purposes (2) Cool Roof Rating Council Product Rating Program
Economic Benefits
Measured Energy Savings and Demand Reduction from a Reflective Roof Membrane on a Large Retail Store in Austin A study conducted by the Ernest Orlando Lawrence Berkeley National Laboratory S. Konopacki, H. Akbari Under a contract with the EPA and the DOE
100,000 sq. ft., Austin, TX
Methodology Instruments measured weather conditions on the roof, temperatures inside the building and throughout the roof layers, and air conditioning and total building power consumption With a black EPDM roof After replacement with a white thermoplastic roof (same insulation, HVAC systems left in place)
Without considering any tax benefits or other utility charges, annual abated energy expenditures totaled $7,200.00 ($0.07/ ft2)
Ecological Benefits
R.C. Willey Intermountain Distribution Center Salt Lake City, UT
Potential Benefits Of Cool Roofs On Commercial Buildings Conserving energy, saving money and reducing emission of greenhouses gases and air pollutants R. Levinson, H. Akbari Heat Island Group Lawrence Berkeley National Laboratory
Building energy simulation for 236 US cities Local energy prices and emission factors Cooling energy savings Heating-energy penalties Etc. Impact of substituting a weathered cool white roof (Sol. Ref.: 0.55) for a weathered conventional grey roof (Sol. Ref.: 0.20)
Retrofitting 80% of US Buildings Would Result in Annual Cooling energy savings:10,400 GWh Energy cost savings: $735 m CO2 reduction: 6.23 Mt Equivalent to reducing 1.2 m cars Nox reduction: 9.93 kt SO2 reduction: 25.6 Kt Equivalent to reducing 815 peak power plants
Do Cool Roofs Stay Cool?
Roofs will get dirty over time The degree of soiling will depend on: Location/ geography/ climate Surroundings Urban, agricultural, industrial Amount, type of discharge from the building Roof slope
Aged Reflectivity Both Energy Star and CA Title 24 Call for a minimum of 0.5 after 3 years exposure
Aged Reflectivity Although there will be some loss after exposure, reflectivity will continue to be significantly higher than that of traditional black materials Emissivity is not affected by ageing Even simple cleaning techniques can restore most of the original reflectivity Complete restoration of initial reflectivity is possible
Thermal Insulation ASHRAE Standard 90.1 1999 Energy Efficient Design of New Buildings Except Low Rise Residential Allows for a decrease in the minimum amount of thermal insulation when a reflective roof is used in locations where HDD65 > 3,600 We recommend reflective roofs be used to complement insulation rather than substitute for it
Reflective roofs over thermal insulations The thermal resistance of insulation materials installed immediately below a black membrane has been found to be up to 30% lower than advertised, when measured at peak summertime temperatures in Austin, Texas Konopacki and Akbari, 2001
BEYOND COOL TO SUSTAINABLE REFLECTIVE ROOF COATINGS, Leonard, J., Leonard, T., proceedings of the Cool Roofing Cutting Through the Glare Symposium, Atlanta, GA, May 12 & 13, 2005
Additional Benefits of Cool Roofs Lower roof top temperatures Allows HVAC equipment to operate more efficiently Slow the ageing process of roofing materials In unconditioned spaces, lower the interior temperature and increase comfort level
Cool Reflective Roofs Why Reflective Roofs? Reduced cooling costs Reduced peak electric consumption Reduced Urban Heat Island Effect Minimal, if any, cost premium Field studies suggest long-term benefit with minimal maintenance
Bottom Line --- Everyone Benefits from Cool Reflective Roofs Saving energy, no matter how you do it, reduces air pollution, saves money, and our environment. A Cool Reflective Roofing System is and will be the most cost-effective investment for a building owner and for our environment.
Reflective Roofs Sustainable Communities Conference Sustainable Surfaces Track March 10, 2009 Dallas, TX R. Chappell