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Using local sources (roof runoff, stormwater, graywater, and onsite wastewater) to meet non-potable water demands can minimize potable water use in buildings and increase supply reliability. In 2017, an Independent Advisory Panel developed a risk-based framework to identify pathogen log reduction targets (LRTs) for onsite non-potable water systems (ONWSs). Subsequently, California's legislature mandated the development and adoption of regulations--including risk-based LRTs--for use in multifamily residential, commercial, and mixed-use buildings. A California Expert Panel was convened in 2021 to (1) update the LRT requirements using new, quantitative pathogen data and (2) propose treatment trains capable of meeting the updated LRTs. This paper presents the updated risk-based LRTs for multiple pathogens (viruses, protozoa, and bacteria) and an expanded set of end-uses including toilet flushing, clothes washing, irrigation, dust and fire suppression, car washing, and decorative fountains. The updated 95th percentile LRTs required for each source water, pathogen, and end-use were typically within 1-log10 of the 2017 LRTs regardless of the approach used to estimate pathogen concentrations. LRT requirements decreased with influent pathogen concentrations from wastewater to graywater to stormwater to roof runoff. Cost and footprint estimates provide details on the capital, operations and maintenance, and siting requirements for ONWS implementation. [ABSTRACT FROM AUTHOR]

This paper evaluates two roof pond configurations combined with a water-to-air heat exchanger (WAHE). Test cells of 1.35 m × 1.35 m x 1.35 m with the same thermal properties, except for the roofs, are built in a hot-dry climate with mild winters. They are connected with a WAHE placed inside the roof pond's water by a pipe through which the indoor air is re-circulated. The first roof consists of a 0.35 m deep water pond covered with a floating polystyrene insulation 0.03 m thick, and a spray system located 0.5 m above it that operates at night. The second roof is covered with an aluminum plate separated by a 0.10 m air gap above a 0.25 m deep water pond. We ran multiple series and compared the results to a control cell that had a California energy code compliant insulated roof. Predictive equations are developed to dimension the WAHE system. Results demonstrate that the cells with roof ponds have better cooling performance than the code compliant control cell. The best performance is obtained in the cell with the WAHE operating continuously. In this case, the indoor temperature stayed below 24 °C even with ambient temperatures above 35 °C. • WAHE systems integrated in roof ponds provide an additional cooling opportunity. • Test cells have been monitored for over two years in a hot and dry climate. • The benefits of integrating WAHE in roof ponds are assessed with promising results. • Predictive equations to dimension the WAHE system are developed. [ABSTRACT FROM AUTHOR]

In 2006, California introduced the Global Warming Solutions Act (Assembly Bill 32), which requires the state to reduce greenhouse gas emissions to 1990 levels by 2020. “Cool community” strategies, including cool roofs, cool pavements, cool walls and urban vegetation, have been identified as voluntary measures with potential to reduce statewide emissions. In addition, cool community strategies provide co-benefits for residents of California, such as reduced utility bills, improved air quality and enhanced urban livability. To achieve these savings, Lawrence Berkeley National Laboratory (LBNL) has worked with state and local officials, non-profit organizations, school districts, utilities, and manufacturers for 4 years to advance the science and implementation of cool community strategies. This paper summarizes the accomplishments of this program, as well as recent developments in cool community policy in California and other national and international efforts. We also outline lessons learned from these efforts to characterize successful programs and policies to be replicated in the future. [ABSTRACT FROM AUTHOR]

The most populated state in the United States, California, is projected to add millions of new inhabitants through the end of the current century, requiring considerable landscape conversion to the built environment. A suite of continuous multiyear, medium-range resolution (20-km grid spacing), ensemble-based simulations is examined to assess urban expansion climate effects on California in 2100, and potential strategies to alleviate them. Summertime [June-August (JJA)] warming due to urban expansion of 1°-2°C is greater relative to any other season, and is completely offset by a range of adaptation strategies: green roofs (highly transpiring), cool roofs (highly reflective), and hybrid roofs (with combined biophysical properties of green and cool roofs). After offsetting of urban-induced warming, cool and hybrid roofs lead to a further 1°-2°C reduction in JJA 2-m temperature, highlighting enhanced efficacy of these adaptation strategies. Guided by medium-range-resolution results, additional high-resolution (2-km grid spacing) experiments are conducted for a subset of the JJA periods conducted on a coarser scale. Urban-induced 1°-2°C warming (local maximum warming exceeds 4°C) is simulated, and is offset by cool and green roof deployment. In agreement with coarser-resolution results, maximum near-surface cooling is greater for cool roofs relative to green roofs. Reduced daytime warming associated with both cool and green roofs also modifies the convective mixed layer, reducing turbulent kinetic energy and planetary boundary layer height, although this impact is less for green roofs than for cool roofs. The results presented here demonstrate the importance of future urban expansion in California and illustrate climatic consequences with implications for regional air quality. [ABSTRACT FROM AUTHOR]

Abstract: Contaminants from cool-pigmented roof samples exposed at seven California sites were analyzed for elements and carbons to identify those that degrade or enhance solar reflectance. The losses in solar reflectance varied by site and the color of the sample. The least reflectance drop was observed in the alpine climate, while the largest drop occurred in sites near urban development. The change of reflectance appears cyclical with the onset of seasons having more rainfall. A deposition model suggests that chromium ranks first, iron second, and elemental carbon third in importance to soil light absorption. [Copyright &y& Elsevier]

The article focuses on the Oakland, California Kaiser Center Roof Garden which will qualify as a National Historic Landmark on its 50th anniversary in 2010. The Kaiser Center Roof Garden was reportedly conceptualized by California industrialist Henry J. Kaiser as a symbol of his career. Also noted is the life and career path of Henry J. Kaiser and the light-weight soil mix used on the Roof Garden by Osmund & Stanley landscaping company.

• Two photocatalytic architectural membranes were exposed alongside a control sample. • Specimens exposed at three California sites with different weather & pollution levels. • Photocatalytic samples showed excellent self-cleaning performance after two years. • De-NO x efficacy depended on weather, pollution, and type of photocatalytic material. • De-NO x efficacy showed seasonal effects associated with raining/dry periods. Photocatalytic self-cleaning "cool" roofs and walls can maintain high albedos, saving building cooling energy, reducing peak power demand, and mitigating the urban heat island effect. Other environmental benefits result from their de-polluting properties. Specimens from two different photocatalytic architectural membranes and a non-photocatalytic control were exposed alongside vertically, facing west, for two years at three California sites, and retrieved quarterly for testing. Photocatalytic materials showed excellent self-cleaning performance, retaining albedos of 0.74 – 0.75. By contrast, the control material exhibited an albedo loss of up to 0.10, with appreciable soiling observed by scanning electron microscopy. De-pollution capacity was assessed by quantifying NO removal and NO x deposition rates at 60 °C. Efficacy varied with exposure location, weather conditions, and the nature of the photocatalytic material. Seasonal effects were observed, with partial inhibition during the dry season and reactivation during the rainy season. [ABSTRACT FROM AUTHOR]

Green roofs and rooftop solar photovoltaic (PV) systems are two popular mitigation strategies to reduce the net building energy demand and ease urban heat island (UHI) effect. This research tested the potential mitigation effects of green roofs and solar photovoltaic (PV) systems on increased buildings energy demand caused by climate change in Los Angeles County, California, USA. The mitigation effects were assessed based on selected buildings that were predicted to be more vulnerable to climate change. EnergyPlus software was used to simulate hourly building energy consumption with the proper settings of PV-green roofs. All buildings with green roofs showed positive energy savings with regard to total energy and electricity. The savings caused by green roofs were positively correlated with three key parameters: Leaf Area Index (LAI), soil depth, and irrigation saturation percentage. Moreover, the majority of the electricity-saving benefits from green roofs were found in the Heating, Ventilation, and Cooling (HVAC) systems. In addition, this study found that green roofs have different energy-saving abilities on different types of buildings with different technologies, which has received little attention in previous studies. [ABSTRACT FROM AUTHOR]

The author describes the new building of the California Academy of Sciences in San Francisco, California. He asserts that the building could boost efforts to spread green roofs in the U.S. He cites the benefits of green roofs in terms of energy savings and storm-water reduction. He also mentions the development and adoption of green-roof technology in various countries in Europe.