Peak power and cooling energy savings of high-albedo roofs

Akbari, Hashem; Bretz, Sarah; Kurn, Dan M.; Hanford, J.W.

doi:10.1016/s0378-7788(96)01001-8

Cited by 223 publications

(100 citation statements)

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“…Higher temperatures cause a significant increase of the buildings' energy consumption, since they affect the already onerous cooling demand [4][5][6][7][8][9][10]. It is indeed estimated that temperate and mid-latitude climates will experience the largest increase in annual energy consumption due to climate change and UHI scenarios, because cooling will be needed also in autumn and spring periods [11,12].…”

Section: Introductionmentioning

confidence: 99%

Assessing the urban heat island and its energy impact on residential buildings in Mediterranean climate: Barcelona case study

Salvati

Roura²,

Cecere

2017

Energy and Buildings

164

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Highlights The maximum urban heat island intensity(UHI) reaches 4.3°C during summer  During daytime, air temperatures at the street level are higher than the roof level  The sea breeze has a positive effect on the roof level temperatures during summer  The UHI determines an average increase of the cooling load between 18% and 28%  The energy impact of the UHI is more relevant for higher solar gains Abstract: The Urban Heat Island (UHI) effect is particularly concerning in Mediterranean zone, as climate change and UHI scenarios foresee a fast growth of energy consumption for next years, due to the widespread of air conditioning systems and the increase of cooling demand. The UHI intensity is thus a key variable for the prediction of energy needs in urban areas.This study investigates the intensity of UHI in Barcelona (Spain), the densest Mediterranean coastal city, and its impact on cooling demand of residential buildings.The experimental analysis is based on temperature data from rural and urban Weather Stations and field measurements at street level. The maximum average UHI intensity is found to be 2.8 °C in winter and 1.7°C in summer, reaching 4.3°C at street level. Simulations performed with EnergyPlus indicate that the UHI intensity increases the sensible cooling load of residential buildings by around 18% to 28%, depending on UHI intensity, amount of solar gains and cooling set point.In the light of the results, the UHI intensity in Mediterranean context should be properly considered in performing energy evaluations for urban contexts, since standard meteorological data from airport weather stations are not found to be accurate enough.

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Section: Introductionmentioning

confidence: 99%

Assessing the urban heat island and its energy impact on residential buildings in Mediterranean climate: Barcelona case study

Salvati

Roura²,

Cecere

2017

Energy and Buildings

164

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“…UHI mitigation via sustainable design of the urban environment has received increasing attention from ecologists, urban planners, and policymakers. Commonly practiced mitigation strategies include but are not limited to: increasing number of parks and coverage of green space near residential areas [17][18][19][20], installing green roofs or other cool roofs built with high-albedo materials [21][22][23][24], using cold pavement materials [25][26][27], and creating better urban design for air flow [28]. The goal of this paper is to use remotely sensed imagery and data processing to evaluate the contribution of residential rooftop properties and nearby vegetation in understanding urban heat.…”

Section: Introductionmentioning

confidence: 99%

Rooftop Surface Temperature Analysis in an Urban Residential Environment

et al. 2015

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Abstract:The urban heat island (UHI) phenomenon is a significant worldwide problem caused by rapid population growth and associated urbanization. The UHI effect exacerbates heat waves during the summer, increases energy and water consumption, and causes the high risk of heat-related morbidity and mortality. UHI mitigation efforts have increasingly relied on wisely designing the urban residential environment such as using high albedo rooftops, green rooftops, and planting trees and shrubs to provide canopy coverage and shading. Thus, strategically designed residential rooftops and their surrounding landscaping have the potential to translate into significant energy, long-term cost savings, and health benefits. Rooftop albedo, material, color, area, slope, height, aspect and nearby landscaping are factors that potentially contribute. To extract, derive, and analyze these rooftop parameters and outdoor landscaping information, high resolution optical satellite imagery, LIDAR (light detection and ranging) point clouds and thermal imagery are necessary. Using data from the City of Tempe AZ (a 2010 population of 160,000 people), we extracted residential rooftop footprints and rooftop configuration parameters from airborne LIDAR point clouds and QuickBird satellite imagery (2.4 m spatial resolution imagery). Those parameters were analyzed against surface temperature data from the MODIS/ASTER airborne simulator (MASTER). MASTER images provided fine resolution (7 m) surface temperature data for residential areas during daytime and night time. Utilizing these data, ordinary least squares (OLS) regression was used to evaluate the relationships between residential building OPEN ACCESSRemote Sens. 2015, 7 12136 rooftops and their surface temperature in urban environment. The results showed that daytime rooftop temperature was closely related to rooftop spectral attributes, aspect, slope, and surrounding trees. Night time temperature was only influenced by rooftop spectral attributes and slope.

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“…Akbari and Rainer (2000) measured daily a/c energy savings of 33Wh/m 2 (3.1Wh/ft 2 ) (1%) in two Nevada telecommunication regeneration buildings. Konopacki et al (1998) Akbari et al (1997a) have shown from an increase in roof reflectance in one monitored Sacramento house daily summertime cooling-energy savings of 14Wh/m 2 (1.3Wh/ft 2 ) (63%) and peak-power reduction of 3.6W/m 2 (0.33W/ft 2 ) (25%), and in a Sacramento school bungalow, cooling-energy savings of 47Wh/m 2 (4.4Wh/ft 2 ) (46%) and peak-power reduction of 6.8W/m 2 (0.63W/ft 2 ) (20%). In an office, museum and hospice with reflective roofs in Sacramento, Hildebrandt et al (1998) measured daily a/c savings of 10 Wh/m 2 (0.9 Wh/ft 2 ), 20 Wh/m 2 (1.9 Wh/ft 2 ) and 11Wh/m 2 (1.0Wh/ft 2 ) (17%, 26% and 39%) .…”

Section: Literature Reviewmentioning

confidence: 99%

Energy impacts of heat island reduction strategies in the Greater Toronto Area, Canada

Konopacki¹,

Akbari²

2001

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In 2000, the Toronto Atmospheric Fund (TAF) embarked on an initiative to quantify the potential benefits of Heat Island Reduction (HIR) strategies (shade trees, reflective roofs and pavements) in reducing cooling energy use in buildings, lowering the ambient air temperature and improve air quality. This report summarizes the efforts of Lawrence Berkeley National Laboratory (LBNL) to assess the impacts of HIR measures on building cooling-and heating-energy use. We discuss our efforts to calculate annual energy savings and peak-power avoidance of HIR strategies in the building sector of the Greater Toronto Area. The analysis is focused on three major building types that offer most saving potentials: residence, office and retail store. Using an hourly building energy simulation model, we quantify the energy saving potentials of (1) Results show potential annual energy savings of over $11M (with uniform residential and commercial electricity and gas prices of $0.084/kWh and $5.54/GJ) could be realized by ratepayers from the combined direct and indirect effects of HIR strategies. Of that total, about 88% was from the direct impact roughly divided equally among reflective roofs, shade trees and windshielding, and the remainder (12%) from the indirect impact of the cooler ambient air temperature. The residential sector accounts for over half (59%) of the total, offices 13% and retail stores 28%. Savings from cool roofs were about 20%, shade trees 30%, wind shielding of tree 37%, and indirect effect 12%. These results are highly sensitive to the price of gas. Assuming a residential gas price of $10.84/GJ (gas price during December 2001), the net annual savings are reduced to about $10M; about 78% resulted from wind-shielding, 16% from shading by trees, and 5% from cool roofs. Potential annual electricity savings were estimated at about 150GWh or over $12M, of that about 75% accrued from roofs and shade trees and only 2% from wind shielding. The indirect effect was 23%. Potential peak-power avoidance was estimated at 250MW with about 74% attributed to the direct impacts (roofs about 24%, shade trees 51% and wind-shielding a small negative %) and the remainder (26%) to the indirect impact. The greatest part of avoided peak power (about 83%) was because of the effects of the residences and the rest shared by offices (7%) and retail stores (9%). Executive SummaryIn 2000, the Toronto Atmospheric Fund (TAF) embarked on an initiative to quantify the potential benefits of Heat Island Reduction (HIR) strategies (i.e. shade trees, reflective roofs, reflective pavements and urban reforestation) to reduce cooling energy use in buildings, lower the ambient air temperature and improve air quality. This report summarizes the efforts of Lawrence Berkeley National Laboratory (LBNL) to assess the impacts of HIR measures on building coolingand heating-energy use. A companion report will address the air quality aspect (Taha et al., 2002). Background During the summer, solar-reflective roofs (also known as "high-albedo § " or "coo...

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Peak power and cooling energy savings of high-albedo roofs

Cited by 223 publications

References 1 publication

Assessing the urban heat island and its energy impact on residential buildings in Mediterranean climate: Barcelona case study

Assessing the urban heat island and its energy impact on residential buildings in Mediterranean climate: Barcelona case study

Rooftop Surface Temperature Analysis in an Urban Residential Environment

Energy impacts of heat island reduction strategies in the Greater Toronto Area, Canada

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