Ronnen Levinson

Weathering of Roofing Materials-An Overview

Deliverable for CEC Task 2.6.4. Report LBNL-59724. Submitted to Construction and Building Materials, February, 2006 Weathering of Roofing Materials-An Overview Paul Berdahl, Hashem Akbari, and Ronnen Levinson Lawrence Berkeley National Laboratory Berkeley, CA 94720 and William A. Miller Oak Ridge National Laboratory Oak Ridge, TN 37831 Abstract An overview of several aspects of the weathering of roofing materials is presented. Degradation of materials initiated by ultraviolet radiation is discussed for plastics used in roofing, as well as wood and asphalt. Elevated temperatures accelerate many deleterious chemical reactions and hasten diffusion of material components. Effects of moisture include decay of wood, acceleration of corrosion of metals, staining of clay, and freeze- thaw damage. Soiling of roofing materials causes objectionable stains and reduces the solar reflectance of reflective materials. (Soiling of non-reflective materials can also increase solar reflectance.) Soiling can be attributed to biological growth (e.g., cyanobacteria, fungi, algae), deposits of organic and mineral particles, and to the accumulation of flyash, hydrocarbons and soot from combustion. 1. Introduction Roofing materials are exposed to the elements, namely wind, sunlight, rain, hail, snow, atmospheric pollution, and temperature variations and consequently degrade over time. Even the most durable materials are modified by deposition of ambient dust and debris, and may provide an opportunity for colonization by biological organisms such as cyanobacteria, fungi and algae. In this paper, we broadly review how weathering occurs and discuss several engineering strategies that are employed for improving the performance of roofing materials. We have been engaged in a multi-year project to develop and commercialize cooler, solar-reflective roofing in conjunction with a number of industrial partners. These materials can save energy used for air conditioning and improve occupant comfort. Since reflective white materials are sometimes not suitable from an architectural standpoint, the work has included materials with specified visual colors but with high near-infrared reflectance [1]. This paper is a summary of what we have learned concerning the weathering of roofing materials.

Radiative forcing and temperature response to changes in urban albedos and associated CO 2 offsets

Radiative forcing and temperature response to changes in urban albedos and associated CO 2 offsets Surabi Menon 1 , Hashem Akbari 1* , Sarith Mahanama 2 , Igor Sednev 1 and Ronnen Levinson 1 Lawrence Berkeley National Laboratory, Berkeley, CA, USA Global Modeling and Assimilation Office, NASA Goddard Space Flight Center, Greenbelt, MD, USA *Now at the Dept. of Building, Civil and Environmental Engineering, Concordia University, Montreal, Quebec, Canada. Abstract The two main forcings that can counteract to some extent the positive forcings from greenhouse gases from pre-industrial times to present-day are the aerosol and related aerosol-cloud forcings, and the radiative response to changes in surface albedo. Here, we quantify the change in radiative forcing and land surface temperature that may be obtained by increasing the albedos of roofs and pavements in urban areas in temperate and tropical regions of the globe by 0.1. Using the catchment land surface model (the land model coupled to the GEOS-5 Atmospheric General Circulation Model), we quantify the change in the total outgoing (outgoing shortwave+longwave) radiation and land surface temperature to a 0.1 increase in urban albedos for all global land areas. The global average increase in the total outgoing radiation was 0.5 Wm - , and temperature decreased by ~0.008 K for an average 0.003 increase in surface albedo. These

Effects of composition and exposure on the solar reflectance of portland cement concrete

Increasing the solar reflectance (albedo) of a paved surface keeps it cooler in the sun, reducing convection of heat from pavement to air and thereby decreasing the ambient air temperature. Lower air temperatures decrease demand for cooling energy and slow the formation of urban smog. Variations with composition and environmental exposure of the albedos of portland cement concrete pavements were investigated through laboratory fabrication and exposure of 32 mixes of concrete. Concrete albedo generally correlated with cement albedo and sand albedo and, after abrasion, with rock albedo. Cement albedo had a disproportionately strong influence on the reflectance of concrete. Simulated weathering, soiling, and abrasion each reduced average concrete albedo, though some samples became slightly more reflective through weathering or soiling. Concrete albedo grew as the cement hydration reaction progressed, but stabilized within six weeks of casting.

Evolution of Cool-Roof Standards in the US

Abstract Roofs that have high solar reflectance and high thermal emittance stay cool in the sun. A roof with lower thermal emittance but exceptionally high solar reflectance can also stay cool in the sun. Substituting a cool roof for a non-cool roof decreases cooling electricity use, cooling power demand and cooling equipment capacity requirements, while slightly increasing heating energy consumption. Cool roofs can also lower the citywide ambient air temperature in summer, slowing ozone formation and increasing human comfort. Provisions for cool roofs in energy efficiency standards can promote the building and climate-appropriate use of cool roofing technologies. Cool-roof requirements are designed to reduce building energy use, while energy-neutral cool-roof credits permit the use of less energy-efficient components (e.g. larger windows) in a building that has energy-saving cool roofs. Both types of measures can reduce the life-cycle cost of a building (initial cost plus lifetime energy cost). Since 1999, several widely used building energy efficiency standards, including ASHRAE 90.1, ASHRAE 90.2, the International Energy Conservation Code and Californias Title 24 have adopted cool-roof credits or requirements. This chapter reviews the technical development of cool-roof provisions in the ASHRAE 90.1, ASHRAE 90.2 and California Title 24 Standards, and discusses the treatment of cool roofs in other standards and energy efficiency programmes. The techniques used to develop the ASHRAE and Title 24 cool-roof provisions can be used as models to address cool roofs in building energy efficiency standards worldwide.

A Review of Methods for the Manufacture of Residential Roofing Materials

Shingles, tiles, and metal products comprise over 80% (by roof area) of the California roofing market (54-58% fiberglass shingle, 8-10% concrete tile, 8-10% clay tile, 7% metal, 3% wood shake, and 3% slate). In climates with significant demand for cooling energy, increasing roof solar reflectance reduces energy consumption in mechanically cooled buildings, and improves occupant comfort in non-conditioned buildings. This report examines methods for manufacturing fiberglass shingles, concrete tiles, clay tiles, and metal roofing. The report also discusses innovative methods for increasing the solar reflectance of these roofing materials. We have focused on these four roofing products because they are typically colored with pigmented coatings or additives. A better understanding of the current practices for manufacturing colored roofing materials would allow us to develop cool colored materials creatively and more effectively.

Sealing ducts in large commercial buildings with aerosolized sealant particles

LBNL-42414 Sealing Ducts in Large Commercial Buildings with Aerosolized Sealant Particles M. P. Modera, O. Brzozowski ** , F. R. Carrie * , D. J. Dickerhoff, W. W. Delp, W. J. Fisk, R. Levinson, D. Wang Abstract Electricity energy savings potential by eliminating air leakage from ducts in large commercial buildings is on the order of 10 kWh/m 2 per year (1 kWh/ft 2 ). We have tested, in two large commercial buildings, a new technology that simultaneously seals duct leaks and measures effective leakage area of ducts. The technology is based upon injecting a fog of aerosolized sealant particles into a pressurized duct system. In brief, this process involves blocking all of the intentional openings in a duct system (e.g., diffusers). Therefore, when the system is pressurized, the only place for the air carrying the aerosol particles to exit the system is through the leaks. The key to the technology is to keep the particles suspended within the airstream until they reach the leaks, and then to have them leave the airstream and deposit on the leak sites. The principal finding from this field study was that the aerosol technology is capable of sealing the leaks in a large commercial building duct system within a reasonable time frame. In the first building, 66% of the leakage area was sealed within 2.5 hours of injection, and in the second building 86% of the leakage area was sealed within 5 hours. We also found that the aerosol could be blown through the VAV boxes in the second building without impacting their calibrations or performance. Some remaining questions are (1) how to achieve sealing rates comparable to those experienced in smaller residential systems; and (2) what tightness level these ducts systems can be brought to by means of aerosol sealing. Ecole Nationale Superieure d’arts et Metiers (ENSAM), Paris, France On leave from Ecole Nationale des Travaux Publics de l’Etat, Laboratoire des Sciences de l’Habitat, DGCB – URA CNRS 1652, 2 rue Maurice Audin, 69518 Vaulx-en-Velin Cedex, France

Analysis of the effect of vegetation on albedo in residential areas: case studies in suburban Sacramento and Los Angeles, CA

Increasingly “urban greening” is being implemented in order to meet goals of sustainability. Tree planting is part of these efforts that provide climate and environmental benefits. Albedo is an important factor in climatological and ecological functioning. Using GIS, this study assesses albedo changes of suburban communities resulting from trees. Based on orthophotos and LiDAR, a shading algorithm is used to examine how tree shading changes albedo throughout the year. For comparison, changes in community albedo were calculated with low and high assumptions for tree albedo. Under the low tree albedo assumption (0.14), community albedo was decreased (–0.07) by the effect of tree shading at all times modeled during the year. Using a high albedo for trees (0.20), the albedo changes were slight (<–0.01). This indicates the importance of considering the albedo of both the trees planted and the surfaces that are shaded when developing urban greening policies.

Modeling the climate impacts of deploying solar reflective cool pavements in California cities

Solar reflective “cool pavements” have been proposed as a potential heat mitigation strategy for cities. However, previous research has not systematically investigated the extent to which cool pavements could reduce urban temperatures. In this study we investigated the climate impacts of widespread deployment of cool pavements in California cities. Using the weather research and forecasting model (WRF), we simulated the current climate of California at 4 km spatial resolution. Comparing this simulation to 105 weather stations in California suggested an overall mean bias (model minus observation) of -0.30 °C. Widespread pavement albedo increases of 0.1 and 0.4 in California cities were then simulated. Comparing temperature reductions for each scenario showed that the climate response to pavement albedo modification was nearly linear. Temperature reductions at 14:00 local standard time were found to be 0.32 °C per 0.1 increase in grid cell average albedo. Temperature reductions were found to peak in the late morning and evening when boundary layer heights were low, and solar irradiance (late morning) or heat accumulation in the pavement (evening) was high. Summertime temperature reductions were found to be larger than corresponding reductions during winter, as expected. After scaling the results using realistic data-derived urban canyon morphologies and an offline urban canyon albedo model, annual average surface air temperature reductions from increasing pavement albedo by 0.4 ranged from 0.18 °C (Palm Springs) to 0.86 °C (San Jose). The variation among cities was due to differences in baseline climate, size of the city, urban fraction, and urban morphology.

Inclusion of cool roofs in nonresidential Title 24 prescriptive requirements

Roofs that have high solar reflectance (high ability to reflect sunlight) and high thermal emittance (high ability to radiate heat) tend to stay cool in the sun. The same is true of low-emittance roofs with exceptionally high solar reflectance. Substituting a cool roof for a noncool roof tends to decrease cooling electricity use, cooling power demand, and cooling-equipment capacity requirements, while slightly increasing heating energy consumption. Cool roofs can also lower the ambient air temperature in summer, slowing ozone formation and increasing human comfort. DOE-2.1E building energy simulations indicate that use of a cool roofing material on a prototypical California nonresidential building with a low-sloped roof yields average annual cooling energy savings of approximately 300 kWh/1000 ft2 [3.2 kWh/m2], average annual natural gas deficits of 4.9 therm/1000 ft2 [5.6 MJ/m2], average source energy savings of 2.6 MBTU/1000 ft2 [30 MJ/m2], and average peak power demand savings of 0.19 kW/1000 ft2 [2.1 W/m2]. The 15-year net present value (NPV) of energy savings averages

Near-ground cooling efficacies of trees and high-albedo surfaces

450/1000 ft2 [