Monitoring peak power and cooling energy savings of shade trees and white surfaces in the Sacramento Municipal Utility District (SMUD) service area: Project design and preliminary results

Akbari, Hashem; Bretz, Sarah; Hanford, J.W.; Rosenfeld, Arthur H.; Sailor, David J.; Taha, Haider; Bos, W.

doi:10.2172/10129204

Cited by 19 publications

(21 citation statements)

References 3 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…After the first year, the degradation slowed, with data indicating small losses in albedo after the second year. We use data from Akbari et al (1993) to estimate the effects of weathering of white roofs on seasonal cooling energy savings and estimate a 20% reduction from first year energy savings for all subsequent years (2-10). Although washing the roofs with soap is effective at restoring albedo, calculations show that it is not cost-effective to hire someone to clean a high-albedo roof only to achieve energy savings.…”

mentioning

confidence: 99%

Long-term performance of high-albedo roof coatings

Bretz

Akbari

1997

Energy and Buildings

218

View full text Add to dashboard Cite

Cooling energy savings of 10 to 70% have been achieved by applying high-albedo coatings to residential buildings in California and Florida. Since dirt accumulation can alter the performance of high-albedo roofs as an energy efficiency measure, we examined some high-albedo coatings at various stages of exposure to determine the magnitude of the effect.We conclude that most of the albedo degradation of coatings occurred within the first year of application, and even within the first two months of exposure. On one roof, 70% of the drop in albedo for the entire first year occurred within the first two months. After the first year, the degradation slowed, with data indicating small losses in albedo after the second year. We use data from Akbari et al. (1993) to estimate the effects of weathering of white roofs on seasonal cooling energy savings and estimate a 20% reduction from first year energy savings for all subsequent years (2-10). Although washing the roofs with soap is effective at restoring albedo, calculations show that it is not cost-effective to hire someone to clean a high-albedo roof only to achieve energy savings. Instead, it would be useful to develop and identify dirtresistant high-albedo coatings. 6 ,. ..... 00 J

show abstract

mentioning

confidence: 99%

Long-term performance of high-albedo roof coatings

Bretz

Akbari

1997

Energy and Buildings

218

View full text Add to dashboard Cite

show abstract

“…Akbari et al 1992b report measurements of summer urban heat islands in California, Japan, and China. Akbari et al 1992a andAkbari et al 1993 monitored peak power and cooling energy savings due to shade trees and white surfaces in Sacramento, CA, where they found that tree shading of two small houses resulted in seasonal cooling energy savings of 30% and peak cooling energy demand savings of 27 to 42%. They also found that the application of a high-albedo coating to the roof of one of the houses yielded seasonal cooling energy savings of 80%.…”

Section: Methodsmentioning

confidence: 99%

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

Levinson

1997

View full text Add to dashboard Cite

Portions of thisDaytime summer urban heat islands arise when the prevalence of dark-colored surfaces and lack of vegetation make a city warmer than neighboring countryside. Two frequentlyproposed summer heat island mitigation measures are to plant trees and to increase the albedo (solar reflectivity) of ground surfaces. This dissertation examines the effects of these measures on the surface temperature of an object near the ground, and on solar heating of air near the ground. Near-ground objects include people, vehicles, and buildings.The variation of the surface temperature of a near-ground object with ground albedo indicates that a rise in ground albedo will cool a near-ground object only if the object's albedo exceeds a critical value. This critical value of object albedo depends on wind speed, object geometry, and the height of the atmospheric thermal boundary layer. It ranges from 0.15 to 0.37 for a person. If an object has typical albedo of 0.3, increasing the ground albedo by 0.25 perturbs the object's surface temperature by -1 to +2 K.Comparing a tree's canopy-to-air convection to the reduction in ground-to-air convection induced by tree shading of the ground indicates that the presence of a tree can either increase or decrease solar heating of ground-level air. The tree's net effect depends on the extent to which solar heating of the canopy is dissipated by evaporation, and on the fraction of air heated by the canopy that flows downward and riiixes with the ground-level air.A two-month lysimeter (plant-weighing) experiment was conducted to measure instantaneous rates of water loss from a tree under various conditions of weather and soil-moisture. Calculations of canopy-to-air convection and the reduction of ground-to-air convection based on this data indicate that canopy-induced heating would negate shadowinduced cooling if approximately 45% of the canopy-heated air mixed with ground level air. This critical fraction is comparable to typical downward mixing fractions, so the tree's net heating or cooling effect on near-ground air is small. 2

show abstract

“…Another area of urban climatological research has been the effect of roof color on cooling costs, conducted at UC Berkeley's Lawrence Livermore Laboratory (Akbari et al, 1993;Taha, 1996). While not within the direct scope of American Forest's interest in trees, a module on energy consequences of roof albedo is included in CITYgreen (American Forests, 2000a).…”

Section: Scientific Basis For Citygreen Modulesmentioning

confidence: 99%

“…In the summer the increased shade offsets the decreased cooling from lessened air circulation caused by trees (Huang et al, 1987). The research in this area has largely been conducted on small residential buildings (Huang et al, 1987;Akbari et al, 1993). These studies model and measure cooling benefits for structures of less than 2,000 square feet and one or two stories.…”

Section: Energy Conservationmentioning

confidence: 99%

Applicability of Citygreen Urban Ecosystem Analysis Software to a Densely Built Urban Neighborhood

Longcore

Wilson

2004

Urban Geography

View full text Add to dashboard Cite

Abstract:In efforts to increase greenspace in cities, planners have relied on a series of arguments about the benefits of parks and other greenspace, including their economic value. The commercially available software program, CITYgreen 4.0, an extension of ArcView, calculates economic values for this purpose. The software evaluates the benefits of trees and other landscape features for energy use, stormwater runoff, air pollution, carbon sequestration, and wildlife habitat. While many examples are available of the use of CITYgreen in suburban morphologies, we set out to evaluate the applicability of CITYgreen for assessing these effects in a densely populated urban neighborhood. We inventoried 146 acres of urban land uses (commercial, residential, and institutional) in a Los Angeles neighborhood. CITYgreen does not calculate energy savings for structures larger than single-family residences, reducing its utility in densely built urban environments. The stormwater runoff reduction module works well when the field data themes were clipped so that the highest canopy (i.e., trees, shrubs, grass, or impermeable surface but no combination thereof) was recorded in every part of the study area. Carbon sequestration and air pollution removal modules worked well, but do not incorporate the best available science. Wildlife analysis falls short of its potential, given the extensive field data collected to use the program. [Key words: urban ecosystem analysis, GIS, urban forestry.]

show abstract

Monitoring peak power and cooling energy savings of shade trees and white surfaces in the Sacramento Municipal Utility District (SMUD) service area: Project design and preliminary results

Cited by 19 publications

References 3 publications

Long-term performance of high-albedo roof coatings

Long-term performance of high-albedo roof coatings

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

Applicability of Citygreen Urban Ecosystem Analysis Software to a Densely Built Urban Neighborhood

Contact Info

Product

Resources

About