Matching Items (8)

A Review on the Generation, Determination and Mitigation of Urban Heat Island

Description

Urban Heat Island (UHI) is considered as one of the major problems in the 21st century posed to human beings as a result of urbanization and industrialization of human civilization.

Urban Heat Island (UHI) is considered as one of the major problems in the 21st century posed to human beings as a result of urbanization and industrialization of human civilization. The large amount of heat generated from urban structures, as they consume and re-radiate solar radiations, and from the anthropogenic heat sources are the main causes of UHI. The two heat sources increase the temperatures of an urban area as compared to its surroundings, which is known as Urban Heat Island Intensity (UHII). The problem is even worse in cities or metropolises with large population and extensive economic activities. The estimated three billion people living in the urban areas in the world are directly exposed to the problem, which will be increased significantly in the near future. Due to the severity of the problem, vast research effort has been dedicated and a wide range of literature is available for the subject. The literature available in this area includes the latest research approaches, concepts, methodologies, latest investigation tools and mitigation measures. This study was carried out to review and summarize this research area through an investigation of the most important feature of UHI. It was concluded that the heat re-radiated by the urban structures plays the most important role which should be investigated in details to study urban heating especially the UHI. It was also concluded that the future research should be focused on design and planning parameters for reducing the effects of urban heat island and ultimately living in a better environment.

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  • 2007-09-27

Building Thermal Performance, Extreme Heat, and Climate Change

Description

The leading source of weather-related deaths in the United States is heat, and future projections show that the frequency, duration, and intensity of heat events will increase in the Southwest.

The leading source of weather-related deaths in the United States is heat, and future projections show that the frequency, duration, and intensity of heat events will increase in the Southwest. Presently, there is a dearth of knowledge about how infrastructure may perform during heat waves or could contribute to social vulnerability. To understand how buildings perform in heat and potentially stress people, indoor air temperature changes when air conditioning is inaccessible are modeled for building archetypes in Los Angeles, California, and Phoenix, Arizona, when air conditioning is inaccessible is estimated.

An energy simulation model is used to estimate how quickly indoor air temperature changes when building archetypes are exposed to extreme heat. Building age and geometry (which together determine the building envelope material composition) are found to be the strongest indicators of thermal envelope performance. Older neighborhoods in Los Angeles and Phoenix (often more centrally located in the metropolitan areas) are found to contain the buildings whose interiors warm the fastest, raising particular concern because these regions are also forecast to experience temperature increases. To combat infrastructure vulnerability and provide heat refuge for residents, incentives should be adopted to strategically retrofit buildings where both socially vulnerable populations reside and increasing temperatures are forecast.

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  • 2016-11-11

Approaches to Study Urban Heat Island – Abilities and Limitations

Description

Urban Heat Island (UHI) has significant impacts on the buildings energy consumption and outdoor air quality (OAQ). Various approaches, including observation and simulation techniques, have been proposed to understand the

Urban Heat Island (UHI) has significant impacts on the buildings energy consumption and outdoor air quality (OAQ). Various approaches, including observation and simulation techniques, have been proposed to understand the causes of UHI formation and to find the corresponding mitigation strategies. However, the causes of UHI are not the same in different climates or city features. Thus, general conclusion cannot be made based on limited monitoring data.

With recent progress in computational tools, simulation methods have been used to study UHI. These approaches, however, are also not able to cover all the phenomena that simultaneously contribute to the formation of UHI. The shortcomings are mostly attributed to the weakness of the theories and computational cost.

This paper presents a review of the techniques used to study UHI. The abilities and limitations of each approach for the investigation of UHI mitigation and prediction are discussed. Treatment of important parameters including latent, sensible, storage, and anthropogenic heat in addition to treatment of radiation, effect of trees and pond, and boundary condition to simulate UHI is also presented. Finally, this paper discusses the application of integration approach as a future opportunity.

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  • 2010-04-11

Assessing the Effects of CO2 Reduction Strategies on Heat Islands in Urban Areas

Description

There has been a wide range of low-carbon solutions proposed to mitigate climate change. However, such measures must be compatible with the local environment and living standards of residents to

There has been a wide range of low-carbon solutions proposed to mitigate climate change. However, such measures must be compatible with the local environment and living standards of residents to be brought to fruition. Measures that adversely affect residential environments will be difficult to implement, so the impacts of measures on the local environment must be taken into consideration during implementation. This study assessed the effects on urban heat islands of efforts to reduce CO2 emissions, as one environmental impact associated with climate change. A simulated assessment was conducted, using an urban canopy model coupled with a building energy model (CM-BEM), to evaluate the effects of five specific measures: solar shading of windows using curtains and blinds, improvement of the thermal insulation of building walls and roof surfaces, implementation of energy-saving measures related to indoor appliances, installation of solar photovoltaic (PV) panels, and adjustment of preset cooling temperatures. The study focused on these effects as they occur within typical urban districts of office buildings, fire-resistant housing, and wooden housing. Results indicated that many of the energy-saving measures have slight temperature lowering effects, but solar panel installation and improved heat insulation, both associated with changes in surface heat balances, tend to raise daytime temperatures to some extent. However, effects on daytime temperatures were in the range of 0.1–0.2 °C and, as such, none of the CO2 reduction measures considered was deemed a significant factor in raising urban temperatures.

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  • 2016-04-27

Urban Heat Island Mitigation Strategies: Phoenix

Description

The growing urban heat island (UHI) phenomenon is having detrimental effects on urban populations and must be addressed in planning. The purpose of this research is to investigate the effectiveness

The growing urban heat island (UHI) phenomenon is having detrimental effects on urban populations and must be addressed in planning. The purpose of this research is to investigate the effectiveness of urban heat island effect reduction factors for Metropolitan Phoenix. Current strategies, case studies, and the ENVI-Met modeling software were used to finalize conclusions and suggestions to further progress Phoenix’s goals in combating urban heat islands. Results from the studies found that the implementation of green walls and roofs, the integration of wind towers into existing and new construction, improving building energy efficiency, and an establishment of a task force responsible for researching applying UHI strategies to the cities are all expected to halt Phoenix’s progression into a more intense UHI, and to reverse the adverse effects that city development has had on the environment.

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  • 2017-04-12

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Experimental Measurements of Power Output of a Cu/Cu2+ Thermogalvanic Brick using Effective Electrode Surface Area Alterations

Description

The research analyzes the transformation of wasted thermal energy into a usable form through thermogalvanic devices. This technology helps mitigate international growing energy demands. Building energy efficiency is a critical

The research analyzes the transformation of wasted thermal energy into a usable form through thermogalvanic devices. This technology helps mitigate international growing energy demands. Building energy efficiency is a critical research topic, since the loads account for 40% of all energy demand in developed nations, and 30% in less developed nations. A significant portion of the energy consumed for heating and cooling, where a majority is dissipated to the ambient as waste heat. This research answers how much power output (µW·cm-2) can the thermogalvanic brick experimentally produce from an induced temperature gradient? While there are multiple avenues for the initial and optimized prototype design, one key area of interest relating to thermogalvanic devices is the effective surface area of the electrodes. This report highlights the experimental power output measurements of a Cu/Cu2+ thermogalvanic brick by manipulating the effective surface area of the electrodes. Across three meshes, the maximum power output normalized for temperature was found to be between 2.13-2.87 x 10-3 μWcm-2K-2. The highest normalized power output corresponded to the mesh with the highest effective surface area, which was classified as the fine mesh. This intuitively aligned with the theoretical understanding of surface area and maximum power output, where decreasing the activation resistance also reduces the internal resistance, which increases the theoretical maximum power.

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  • 2019-05

Effect of Pavement Thermal Properties on Mitigating Urban Heat Islands: A Multi-Scale Modeling Case Study in Phoenix

Description

Engineered pavements cover a large fraction of cities and offer significant potential for urban heat island mitigation. Though rapidly increasing research efforts have been devoted to the study of pavement

Engineered pavements cover a large fraction of cities and offer significant potential for urban heat island mitigation. Though rapidly increasing research efforts have been devoted to the study of pavement materials, thermal interactions between buildings and the ambient environment are mostly neglected. In this study, numerical models featuring a realistic representation of building-environment thermal interactions, were applied to quantify the effect of pavements on the urban thermal environment at multiple scales. It was found that performance of pavements inside the canyon was largely determined by the canyon geometry. In a high-density residential area, modifying pavements had insignificant effect on the wall temperature and building energy consumption. At a regional scale, various pavement types were also found to have a limited cooling effect on land surface temperature and 2-m air temperature for metropolitan Phoenix. In the context of global climate change, the effect of pavement was evaluated in terms of the equivalent CO2 emission. Equivalent CO2 emission offset by reflective pavements in urban canyons was only about 13.9e46.6% of that without building canopies, depending on the canyon geometry. This study revealed the importance of building-environment thermal interactions in determining thermal conditions inside the urban canopy.

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  • 2016-08-22

Indoor-Outdoor Environmental Coupling and Exposure Risk to Extreme Heat and Poor Air Quality During Heat Waves

Description

Mortality and morbidity associated with extreme summer heat and poor air quality continues to be one of the most pressing human health challenges in cities and is likely to be

Mortality and morbidity associated with extreme summer heat and poor air quality continues to be one of the most pressing human health challenges in cities and is likely to be exacerbated in the future due to urban growth and climate change. Heat is currently the leading weather-related cause of death in the developed world (e.g. CDC 2004), and future heat vulnerability for the elderly is projected to increase substantially in the coming decades (Sheridan et al., 2012).

Recent extreme heat events such as the May 2015 heat wave in India that saw record temperatures near 50oC and resulted in more than 2500 deaths, have underlined the importance and urgency of the problem. Traditional epidemiological studies of the health effects of heat and air quality focus on outdoor environmental conditions. This approach is suitable for assessing heat-health risks for populations that spend much of their time outdoors (e.g. homeless, construction workers, etc). However, as was the case of the European heat wave of 2003, the particularly vulnerable population was the elderly, and in particular, elderly who lived on the top floor of a building that lacked air conditioning (Mavrogianni et al., 2012). Typical urban residents spend more than 85% of their time indoors (Klepeis et al., 2001)—and some of the most vulnerable populations (e.g., the elderly) spend an even higher fraction of time indoors.

While the indoor environment is coupled with the outdoor environment there are key differences both in terms of air quality and thermal conditions. With respect to thermal environment, for buildings without air conditioning, this coupling includes variations in indoor air temperature that depend on building construction characteristics, location within building (e.g. top floor, south façade), occupant behavior, internal loads, ventilation, and infiltration. Indoor air quality, on the other hand, is driven by the relative magnitude of each mode of air exchange (e.g. infiltration vs. filtered mechanical ventilation) and emissions and secondary reactions of air pollutants indoors.

Hence, there is a need to better understand the relationship between indoor and outdoor environments, and how this relationship is affected by occupant behavior and building construction and management practices. In the case of air conditioned and mechanically ventilated buildings a scenario of particular interest is that of coincident heat waves and power outages producing very unhealthy indoor environments. This paper discusses a newly funded research project that addresses these issues, with an emphasis on assisted living facilities using the city of Houston Texas, USA as the research test bed. It will introduce some of the key mechanisms that drive differences in indoor and outdoor conditions and present some early findings related to risks of coincident heat waves and power outages or equipment failures in buildings.

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  • 2015-06-15