Melvin Pomerantz

Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas

Abstract Elevated summertime temperatures in urban ‘heat islands’ increase cooling-energy use and accelerate the formation of urban smog. Except in the city’s core areas, summer heat islands are created mainly by the lack of vegetation and by the high solar radiation absorptance by urban surfaces. Analysis of temperature trends for the last 100 years in several large U.S. cities indicate that, since ∼1940, temperatures in urban areas have increased by about 0.5–3.0°C. Typically, electricity demand in cities increases by 2–4% for each 1°C increase in temperature. Hence, we estimate that 5–10% of the current urban electricity demand is spent to cool buildings just to compensate for the increased 0.5–3.0°C in urban temperatures. Downtown Los Angeles (L.A.), for example, is now 2.5°C warmer than in 1920, leading to an increase in electricity demand of 1500 MW. In L.A., smoggy episodes are absent below about 21°C, but smog becomes unacceptable by 32°C. Because of the heat-island effects, a rise in temperature can have significant impacts. Urban trees and high-albedo surfaces can offset or reverse the heat-island effect. Mitigation of urban heat islands can potentially reduce national energy use in air conditioning by 20% and save over

Cool communities: strategies for heat island mitigation and smog reduction

10B per year in energy use and improvement in urban air quality. The albedo of a city may be increased at minimal cost if high-albedo surfaces are chosen to replace darker materials during routine maintenance of roofs and roads. Incentive programs, product labeling, and standards could promote the use of high-albedo materials for buildings and roads. Similar incentive-based programs need to be developed for urban trees.

Cooling energy savings potential of reflective roofs for residential and commercial buildings in the United States

Abstract Adopting our ‘cool communities’ strategies of reroofing and repaying in lighter colors and planting shade trees can effect substantial energy savings, directly and indirectly. In our target city of Los Angeles, annual residential air-conditioning (A/C) bills can be reduced directly by about US

Reflective surfaces for cooler buildings and cities

100 M and, because these strategies serve to cool the air in the Los Angeles basin and reduce smog exceedance levels by about 10%, an additional savings of US

Preliminary evaluation of the lifecycle costs and market barriers of reflective pavements

70 M in indirect cooling and US

Solar access of residential rooftops in four California cities

360 M in smog-reduction benefits—a total savings of about US

Policies to reduce heat islands: Magnitudes of benefits and incentives to achieve them

1/2 B per year—is possible. Trees are most effective if they shade buildings, but the savings are significant even if they merely cool the air by evapotranspiration. In Los Angeles, avoided peak power for air conditioning can reach about 1.5 GW (more than 15% of the citys air conditioning). Generalized to the entire US, we estimate that 25 GW can be avoided with potential annual benefits of about US

Cooler Paving Materials for Heat-Island Mitigation

5 B by the year 2015. Recent steps taken by cities in the warm half of US towards adoption of cool communities include (1) incorporation of cool roofs in the revised ASHRAE building standards S90.1 and (2) inclusion of cool surfaces and shade trees as tradeable smog-offset credits in Los Angeles. Other step underway include (1) plans by the US Environmental Protection Agency (EPA) to approve heat island mitigation measures in the state implementation plan to comply with ozone standards and (2) plans for ratings and labeling of cool surfaces.

Cooler reflective pavements give benefits beyond energy savings: durability and illumination

We make quantitative estimates of the impact of roof reflectivity on cooling and heating energy use for buildings in the US. Prototypical buildings are simulated with reflective (light in color) and absorptive (dark in color) roofs. Differences of annual cooling and heating energy use and peak electricity demand between dark and light roofs yield the savings. The DOE-2 building energy simulation program is used for these calculations. Monetary savings are calculated using local utility rates. Savings are estimated for 11 US metropolitan statistical areas (MSAs) in a variety of climates. The total savings for all 11 MSAs are: annual electricity savings, 2.6 terawatt hours (TWh); net annual savings,

A simple tool for estimating city-wide annual electrical energy savings from cooler surfaces

194 M; and peak electricity demand savings, 1.7 gigawatt (GW). Extrapolating the savings from the 11 MSAs to the entire United States, we estimate annual electricity savings of about 10 TWh and a net savings of about