Haider Taha

Mitigation of urban heat islands: materials, utility programs, updates☆

Abstract Elevated temperatures in urban `heat islands increase cooling energy use and accelerate the formation of urban smog. Urban shade trees and light-colored surfaces can offset or reverse the heat island and conserve energy. Implementation of heat island mitigation measures is now a prominent part of President Clintons Climate Change Action Plan to control the emissions of greenhouse gases, necessitating a better understanding of the quantitative benefits of these control measures. We present recent measurements of the air-conditioning savings for houses in Sacramento and Florida, and air temperature measurements at White Sands National Monument, New Mexico. We also discuss the results of meteorological and smog simulations for the Los Angeles Basin. The albedo of a city may be increased gradually if high-albedo surfaces are chosen to replace darker materials during routine maintenance of roofs and roads. Such high-albedo surfaces may last longer than their conventional dark counterparts. Utility-sponsored incentive programs, product labeling, and standards could promote the use of high-albedo materials for buildings and roads, and several paint manufacturers have expressed interest in participating in a ‘cool surfaces’ labeling program. We examine the spectral reflectance of various white coatings and building materials that might be labeled in such a program.

Residential cooling loads and the urban heat island—the effects of albedo

Abstract The urban heat island has become the target of recent research aiming at improving urban climates and energy efficiency of cities. In the warm, mid- and low-latitude cities, the typical heat island intensity averages up to 3–5°C on a summer day, adding to discomfort and increasing the air-conditioning loads, whereas in some temperate and cold, high-latitude cities a 2°C heat island is considered as a mild asset in winter. Some of these cities have been built to retain the urban heat. The objective of our ongoing research is to identify ways to mitigate summer heat islands in hot climates, for example by increasing the urban albedo, expanding evaporative surfaces and vegetation covers, and increasing urban thermal mass. From the energy consumption point of view, simple techniques such as these can be effective in reducing air-conditioning costs by modifying and improving the urban micro- and meso-climates. In this work, we have correlated the residential cooling energy and power consumption in Sacramento, California, with the urban heat island intensity. The effects of selected strategies, such as the ones mentioned above, upon changing the urban micro-climate and reducing the heat island induced cooling loads were simulated. The main focus in this paper is placed on albedo. The simulations were performed using the DOE-2.1C building energy analysis program in conjunction with micro-climate and planetary boundary layer models that predict the effects of albedo modifications on ambient conditions and micro-climates. The simulations indicate that there exists significant potential energy and peak power savings by using such simple conservation strategies. Simulations for Sacramento indicate that whitewashing the buildings can result in direct savings of up to 14% and 19% on cooling peak power and electrical cooling energy, respectively. Modifying the overall urban albedo, in addition to whitewashing, can result in total savings of up to 35% and 62% respectively.

The impact of trees and white surfaces on residential heating and cooling energy use in four Canadian cities

We have investigated the potential of using vegetation and high-albedo materials in Toronto, Edmonton, Montreal, and Vancouver, Canada, to modify the urban microclimate, thereby saving residential heating and cooling energy use. Parametric computer simulations of microclimates and energy performance of prototypical houses were our primary analysis tools. The building prototypes included a detached one-story and a detached two-story single family house, as well as a row house. The simulations indicated that by increasing the vegetative cover of the neighborhood by 30% (corresponding to about three trees per house) and increasing the albedo of the houses by 20% (from moderate-dark to medium-light color), the heating energy in Toronto can be reduced by about 10% in urban houses and 20% in rural houses, whereas cooling energy can be reduced by 40 and 30%, respectively. The annual savings in heating and cooling costs for different houses ranged from

Heat island and oasis effects of vegetative canopies: Micro-meteorological field-measurements

30 to

National Urban Database and Access Portal Tool

180 in urban areas and from

Cool roofs as an energy conservation measure for federal buildings

60 to

The integrated WRF/urban modelling system: development, evaluation, and applications to urban environmental problems

400 in rural zones. In urban houses of Edmonton, Montreal, and Vancouver, savings in heating energy use were about 10%. Cooling energy can be totally offset in Edmonton and Vancouver, and average savings of 35% can be achieved in Montreal.

Urban Surface Modification as a Potential Ozone Air-quality Improvement Strategy in California : A Mesoscale Modelling Study

SummaryDry-bulb temperature, dew-point, wind speed, and wind direction were measured in and around an isolated vegetative canopy in Davis CA from 12 to 25 October 1986. These meteorological variables were measured 1.5 m above ground along a transect of 7 weather stations set up across the canopy and the upwind/downwind open fields. These variables were averaged every 15 minutes for a period of two weeks so we could analyze their diurnal cycles as well as their spatial variability. The results indicate significant nocturnal heat islands and daytime oases within the vegetation stand, especially in clear weather. Inside the canopy within 5 m of its upwind edge, daytime temperature fell by as much as 4.5 °C, whereas the nighttime temperature rose by 1 °C. Deeper into the canopy and downwind, the daytime drop in temperature reached 6 °C, and the nighttime increase reached 2 °C. Wind speed was reduced by ~ 2 ms−1 in mild conditions and by as much as 6.7 ms−1 during cyclonic weather when open-field wind speed was in the neighborhood of 8 ms−1. Data from this project were used to construct correlations between temperature and wind speed within the canopy and their corresponding ambient, open-field values.

Summer heat islands, urban trees, and white surfaces

Based on the need for advanced treatments of high-resolution urban morphological features (e.g., buildings and trees) in meteorological, dispersion, air quality, and human-exposure modeling systems for future urban applications, a new project was launched called the National Urban Database and Access Portal Tool (NUDAPT). NUDAPT is sponsored by the U.S. Environmental Protection Agency (U.S. EPA) and involves collaborations and contributions from many groups, including federal and state agencies, and from private and academic institutions here and in other countries. It is designed to produce and provide gridded fields of urban canopy parameters for various new and advanced descriptions of model physics to improve urban simulations, given the availability of new high-resolution data of buildings, vegetation, and land use. Additional information, including gridded anthropogenic heating (AH) and population data, is incorporated to further improve urban simulations and to encourage and facilitate decision sup...

Episodic Performance and Sensitivity of the Urbanized MM5 (uMM5) to Perturbations in Surface Properties in Houston Texas

We have developed initial estimates of the potential benefits of cool roofs on federal buildings and facilities (building scale) as well as extrapolated the results to all national facilities under the administration of the Federal Energy Management Program (FEMP). In addition, a spreadsheet calculator is devised to help FEMP estimate potential energy and cost savings of cool roof projects. Based on calculations for an average insulation level of R-11 for roofs, it is estimated that nationwide annual savings in energy costs will amount to