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Simulated Impact of Roof Solar Absorptance, Attic, and DuctInsulation, and Climate on Cooling and Heating Energy Use inSingle-Family Resi dential Buildings

Description: This report summarizes a comparative analysis of the impact of roof surface solar absorptance, attic, and duct insulation on simulated residential annual cooling and heating energy use in sixteen sunbelt climates. These locations cover a wide range of climates where cool roofs are expected to save energy and money, and are areas with high growth rates in new residential construction. The residences are single-story, single-family of new construction with either a gas furnace or an electric heat pump, and with ducts in the attic OT conditioned zone. The objective is to demonstrate that a residence with a cool roof could utilize a lower level of attic insulation than one with a dark roof with a zero net change in the annual energy bill. Annual energy use is simulated with DOE-2. lE, which was adapted with a validated residential duct-attic function, for dark and cool roofs and eleven attic insulation R-values ranging from 1 through 60. Analysis of the simulated energy savings from the light-colored roofs show that the savings can be transformed into an equivalent reduction in the level of attic insulation. Reductions in R-value are observed in varying degrees for residences with both gas and electric heat, all duct configurations, and all climates. In some cooling dominated climates there are cases where a cool roof could be implemented without attic insulation.
Date: October 26, 1998
Creator: Akbari, H. & Konopacki, S.
Partner: UNT Libraries Government Documents Department

Free convective laminar flow within the Trombe wall channel

Description: Free convective laminar heat transfer between the channel surfaces of the Trombe wall has been investigated. This study considered the velocity profiles normal and parallel to the direction of fluid flow, the pressure drop due to flow acceleration at the channel entrance, and the effect of a variety of dissimilar but uniform channel surface temperatures for a wide range of flow rates. A finite difference procedure was used to solve the governing equations in dimensionless form using air as the fluid. After comparison with available experimental data, results have been reduced, and several correlations developed to enable important performance characteristics to be estimated given the channel thickness, height, and surface temperatures.
Date: August 1, 1978
Creator: Akbari, H. & Borgers, T.R.
Partner: UNT Libraries Government Documents Department

Meteorological modeling applications in building energy simulations

Description: Researchers use sophisticated computer models to predict building energy use. These models require extensive input data including building characteristics and dimensions, load schedules, and weather data. The typical source for weather data is the weather station at the nearest airport. Specifically, hourly values of ambient air temperature are necessary. The data obtained from local airports, however, may be significantly different from the actual weather experienced by a nearby residential building. Thus, using local airport data when simulating a residential building may yield inaccurate results. Furthermore, researchers interested in evaluating the potential for heat island mitigation schemes (such as urban tree planting programs) to decrease building air-conditioning energy use need a method for modifying the local airport data accordingly.
Date: August 1, 1992
Creator: Sailor, D.J. & Akbari, H.
Partner: UNT Libraries Government Documents Department

End-use energy characterization and conservation potentials at DoD Facilities: An analysis of electricity use at Fort Hood, Texas

Description: This report discusses the application of the LBL`s End-use Disaggregation Algorithm (EDA) to a DoD installation and presents hourly reconciled end-use data for all major building types and end uses. The project initially focused on achieving these objectives and pilot-testing the methodology at Fort Hood, Texas. Fort Hood, with over 5000 buildings was determined to have representative samples of nearly all of the major building types in use on DoD installations. These building types at Fort Hood include: office, administration, vehicle maintenance, shop, hospital, grocery store, retail store, car wash, church, restaurant, single-family detached housing, two and four-plex housings, and apartment building. Up to 11 end uses were developed for each prototype, consisting of 9 electric and 2 gas; however, only electric end uses were reconciled against known data and weather conditions. The electric end uses are space cooling, ventilation, cooking, miscellaneous/plugs, refrigeration, exterior lighting, interior lighting, process loads, and street lighting. The gas end uses are space heating and hot water heating. Space heating energy-use intensities were simulated only. The EDA was applied to 10 separate feeders from the three substations at Fort Hood. The results from the analyses of these ten feeders were extrapolated to estimate energy use by end use for the entire installation. The results show that administration, residential, and the bar-rack buildings are the largest consumers of electricity for a total of 250GWh per year (74% of annual consumption). By end use, cooling, ventilation, miscellaneous, and indoor lighting consume almost 84% of total electricity use. The contribution to the peak power demand is highest by residential sector (35%, 24 MW), followed by administration buildings (30%), and barrack (14%). For the entire Fort Hood installation, cooling is 54% of the peak demand (38 MW), followed by interior lighting at 18%, and miscellaneous end uses by 12%.
Date: May 1, 1995
Creator: Akbari, H. & Konopacki, S.
Partner: UNT Libraries Government Documents Department

Estimates of energy consumption by building type and end use at U.S. Army installations

Description: This report discusses the use of LBNL`s End-use Disaggregation Alogrithm (EDA) to 12 US Army installations nationwide in order to obtain annual estimates of electricity use for all major building types and end uses. The building types include barrack, dining hall, gymnasium, administration, vehicle maintenance, hospital, residential, warehouse, and misc. Up to 8 electric end uses for each type were considered: space cooling, ventilation (air handling units, fans, chilled and hot water pumps), cooking, misc./plugs, refrigeration, exterior and interior lighting, and process loads. Through building simulations, we also obtained estimates of natural gas space heating energy use. Average electricity use for these 12 installations and Fort Hood are: HVAC, misc., and indoor lighting end uses consumed the most electricity (28, 27, and 26% of total[3.8, 3.5, and 3.3 kWh/ft{sup 2}]). Refrigeration, street lighting, exterior lighting, and cooking consumed 7, 7, 3, and 2% of total (0.9, 0.9, 0.4, and 0.3 kWh/ft{sup 2})
Date: August 1, 1996
Creator: Konopacki, S. J. & Akbari, H.
Partner: UNT Libraries Government Documents Department

Proposed guidelines for using Energy Management and Control Systems for performance monitoring

Description: Monitoring of energy consumption and building operation are important parts of conservation savings analysis, although effective monitoring can be quite expensive. Energy management and Control Systems (EMCSS) contain all of the same equipment that is usually installed for monitoring, however, and can often be used for this application. Since EMCSs are installed in a growing number of commercial buildings, the addition of conventional energy monitoring equipment can be redundant. EMCSs are not designed with monitoring in mind, however. The characteristics of an EMCS are determined by the building`s control needs rather than by monitoring needs, so EMCS-based monitoring can have several complicating factors. Differences between the EMCS models, the installed options at sites with the same model, or the degree of system utilization at a site can mean the difference between a system that can be used for monitoring immediately, and one that cannot be used at all. In instituting monitoring programs that include EMCSs as tools, guidelines defining procedures and the required system capabilities would be quite helpful. In this paper, we propose guidelines for EMCS monitoring, based on our evaluation of monitoring procedures in earlier case studies. These guidelines could be used to help in determining whether EMCSs can be used for monitoring at particular sites. The guidelines also discuss how to find out if the necessary elements are present, and what to do if these elements are not present. Finally, we discuss how these guidelines could be used in the development of the EMCS-based monitoring technology, and the advantages that could be realized through that development.
Date: March 1, 1992
Creator: Heinemeier, K. & Akbari, H.
Partner: UNT Libraries Government Documents Department

Electrical energy and cost savings potential at DOD facilities

Description: The US Department of Defense (DOD) has been mandated to reduce energy consumption and costs by 20% from 1985 to 2000 and by 30% from 1985 to 2005. Reduction of electrical energy consumption at DOD facilities requires a better understanding of energy consumption patterns and energy and financial savings potential. This paper utilizes two independent studies--EDA (End-Use Disaggregation Algorithm) and MEIP (Model Energy Installation Program)--and whole-installation electricity use data obtained from a state utility to estimate electrical energy conservation potential (ECP) and cost savings potential (CSP) at the Fort Hood, Texas, military installation and at DOD nationwide. At Fort Hood, the authors estimated an annual electricity savings of 62.2 GWh/yr (18%), a peak demand savings of 10.1 MW (14%), and an annual energy cost savings of $6.5 million per year. These savings could be attained with an initial investment of $41.1 million, resulting in a simple payback of 6.3 years. Across the DOD, they estimated an annual electricity savings of 4,900 GWh/yr, a peak demand savings of 694 MW, and an annual energy cost savings of $316 million per year. The estimated cost savings is 16% of the total nationwide DOD 1993 annual energy costs. These savings could be attained with an initial investment of $1.23 billion, resulting in a simple payback of 3.9 years.
Date: June 1, 1996
Creator: Konopacki, S.; Akbari, H.; Lister, L. & DeBaille, L.
Partner: UNT Libraries Government Documents Department

Measuring savings in energy savings performance contracts using in-place energy management systems -- A case study

Description: Energy Management Control Systems (EMCSs) have been used in many projects as a monitoring device to provide information necessary for estimating savings from efficiency measures. This paper discusses a case study that looked in great depth at that use for evaluating savings in Energy Savings Performance Contracting (ESPC). ESPC is one of the increasingly important mechanisms for profiting from energy efficiency in commercial buildings. With ESPC, a contractor finances and installs energy-conversion measures, and the resulting savings in energy bills are shared between the contractor and the building owner. Hence, the method used for determining savings is key to the success of this financing scheme. As a part of their effort to establish measurement and verification methods, the Federal Energy Management Program (FEMP) carried out a pilot study of ESPC, and the EMCS was used in the savings verification for this ESPC contract. This case study also serves as a detailed and quantitative comparison of EMCS and conventional monitoring techniques, according to the guidelines developed in earlier work. This paper discusses the concept of different levels of monitoring savings for ESPC and presents an assessment of the use of EMCS for these levels of monitoring.
Date: August 1, 1996
Creator: Heinemeier, K.E.; Akbari, H. & Kromer, S.
Partner: UNT Libraries Government Documents Department

Impact of the temperature dependency of fiberglass insulation R-value on cooling energy use in buildings

Description: Building energy models usually employ a constant, room-temperature-measured value for the thermal resistance of fiberglass roof insulation. In summer, however, the mean temperature of roof insulation can rise significantly above room temperature, lowering the insulation`s thermal resistance by 10% to 20%. Though the temperature dependence of the thermal resistance of porous materials like fiberglass has been extensively studied, it is difficult to theoretically predict the variation with temperature of a particular fiberglass blanket, from first principles. Heat transfer within fiberglass is complicated by the presence of three significant mechanisms - conduction through air, conduction through the glass matrix, and radiative exchange within the matrix - and a complex, unknown internal geometry. Purely theoretical models of fiberglass heat transfer assume highly simplified matrix structures and require typically-unavailable information about the fiberglass, such as its optical properties. There is also a dearth of useful experimental data. While the thermal resistances of many individual fiberglass samples have been measured, there is only one practical published table of thermal resistance vs. both temperature and density. Data from this table was incorporated in the DOE-2 building energy model. DOE-2 was used to simulate the roof surface temperature, roof heat flux, and cooling energy consumption of a school bungalow whose temperature and energy use had been monitored in 1992. The DOE-2 predictions made with and without temperature variation of thermal conductivity were compared to measured values. Simulations were also run for a typical office building. Annual cooling energy loads and annual peak hourly cooling powers were calculated for the office building using both fixed and variable thermal conductivities, and using five different climates. The decrease in the R-value of the office building`s roof led to a 2% to 4% increase in annual cooling energy load.
Date: August 1, 1996
Creator: Levinson, R.; Akbari, H. & Gartland, L.
Partner: UNT Libraries Government Documents Department

Cooling energy savings potential of light-colored roofs for residential and commercial buildings in 11 US metropolitan areas

Description: The U.S. Environmental Protection Agency (EPA) sponsored this project to estimate potential energy and monetary savings resulting from the implementation of light-colored roofs on residential and commercial buildings in major U.S. metropolitan areas. Light-colored roofs reflect more sunlight than dark roofs, so they keep buildings cooler and reduce air-conditioning demand. Typically, rooftops in the United States are dark, and thus there is a potential for saving energy and money by changing to reflective roofs. Naturally, the expected savings are higher in southern, sunny, and cloudless climates. In this study, we make quantitative estimates of reduction in peak power demand and annual cooling electricity use that would result from increasing the reflectivity of the roofs. Since light-colored roofs also reflect heat in the winter, the estimates of annual electricity savings are a net value corrected for the increased wintertime energy use. Savings estimates only include direct reduction in building energy use and do not account for the indirect benefit that would also occur from the reduction in ambient temperature, i.e. a reduction in the heat island effect. This analysis is based on simulations of building energy use, using the DOE-2 building energy simulation program. Our methodology starts with specifying 11 prototypical buildings: single-family residential (old and new), office (old and new), retail store (old and new), school (primary and secondary), health (hospital and nursing home), and grocery store. Most prototypes are simulated with two heating systems: gas furnace and heat pumps. We then perform DOE-2 simulations of the prototypical buildings, with light and dark roofs, in a variety of climates and obtain estimates of the energy use for air conditioning and heating.
Date: May 1, 1997
Creator: Konopacki, S.; Akbari, H. & Gartland, L.
Partner: UNT Libraries Government Documents Department

ASTM standards for measuring solar reflectance and infrared emittance of construction materials and comparing their steady-state surface temperatures

Description: Numerous experiments on individual buildings in California and Florida show that painting roofs white reduces air conditioning load up to 50%, depending on the thermal resistance or amount of insulation under the roof. The savings, of course, are strong functions of the thermal integrity of a building and climate. In earlier work, the authors have estimated the national energy savings potential from reflective roofs and paved surfaces. Achieving this potential, however, is conditional on receiving the necessary Federal, states, and electric utilities support to develop materials with high solar reflectance and design effective implementation programs. An important step in initiating an effective program in this area is to work with the american Society for Testing and Materials (ASTM) and the industry to create test procedures, rating, and labeling for building and paving materials. A subcommittee of ASTM E06, E06.42, on Cool Construction Materials, was formed as the vehicle to develop standard practices for measuring, rating, and labeling cool construction materials. The subcommittee has also undertaken the development of a standard practice for calculating a solar reflectance index (SRI) of horizontal and low-sloped surfaces. SRI is a measure of the relative steady-state temperature of a surface with respect to a standard white surface (SRI = 100) and a standard black surface (SRI = 0) under standard solar and ambient conditions. This paper discusses the technical issues relating to development of these two ASTM standards.
Date: August 1, 1996
Creator: Akbari, H.; Levinson, R. & Berdahl, P.
Partner: UNT Libraries Government Documents Department

Cooling energy savings potential of light-colored roofs for residential and commercial buildings in 11 US metropolitan areas

Description: Light-colored roofs reflect more sunlight than dark roofs, thus they keep buildings cooler and reduce air-conditioning demand. Typical roofs in the United States are dark, which creates a potential for savings energy and money by changing to reflective roofs. In this report, the authors make quantitative estimates of the impact of roof color by simulating prototypical buildings with light- and dark-colored roofs and calculating savings by taking the differences in annual cooling and heating energy use, and peak electricity demand. Monetary savings are calculated using local utility rates. Savings are estimated for 11 U.S. Metropolitan Statistical Areas (MSAs) in a variety of climates.
Date: May 1, 1997
Creator: Konopacki, S.; Akbari, H.; Pomerantz, M.; Gabersek, S. & Gartland, L.
Partner: UNT Libraries Government Documents Department

Energy Savings Calculations for Heat Island Reduction Strategies in Baton Rouge, Sacramento and Salt Lake City

Description: In 1997, the US Environmental Protection Agency (EPA) established the ''Heat Island Reduction Initiative'', to quantify the potential benefits of Heat Island Reduction (HIR) strategies (i.e., shade trees, reflective roofs, reflective pavements and urban vegetation) to reduce cooling energy use in buildings, lower the ambient air temperature and improve urban air quality in cities, and reduce CO2 emissions from power plants. Under this initiative, the Urban Heat Island Pilot Project (UHIPP) was created with the objective to investigate the potential of HIR strategies in residential and commercial buildings in three initial UHIPP cities: Baton Rouge, Sacramento and Salt Lake City. This paper summarizes our efforts to calculate the annual energy savings, peak power avoidance and annual C02 reduction of HIR strategies in the three initial cities. In this analysis, we focused on three building types that offer most savings potential: single-family residence, office and retail store. Each building type was characterized in detail by old or new construction and with a gas furnace or an electric heat pump. We defined prototypical building characteristics for each building type and simulated the impact of HIR strategies on building cooling and heating energy use and peak power demand using the DOE-2.IE model. Our simulations included the impact of (1) strategically-placed shade trees near buildings [direct effect], (2) use of high-albedo roofing material on building [direct effect], (3) combined strategies I and 2 [direct effect], (4) urban reforestation with high-albedo pavements and building surfaces [indirect effect] and (5) combined strategies 1, 2 and 4 [direct and indirect effects]. We then estimated the total roof area of air-conditioned buildings in each city using readily obtainable data to calculate the metropolitan-wide impact of HIR strategies. The results show, that in Baton Rouge, potential annual energy savings of $15M could be realized by rate-payers from the combined ...
Date: March 1, 2000
Creator: Konopacki, S. & Akbari, H.
Partner: UNT Libraries Government Documents Department

A new approach to estimate commercial sector end-use load shapes and energy use intensities

Description: We discuss the application of an end-use load shape estimation technique to develop annual energy use intensities (EUIs) and hourly end-use load shapes (LSs) for commercial buildings in the Pacific Gas and Electric Company (PG&E) service territory. Results will update inputs for the commercial sector energy and peak demand forecasting models used by PG&E and the California Energy Commission (CEC). EUIs were estimated for 11 building types, up to 10 end uses, 3 fuel types, 2 building vintages, and up to 5 climate regions. The integrated methodology consists of two major parts. The first part is the reconciliation of initial end-use load-shape estimates with measured whole-building load data to produce intermediate EUIs and load shapes, using LBL`s End-use Disaggregation Algorithm, EDA. EDA is a deterministic hourly algorithm that relies on the observed characteristics of the measured hourly whole-building electricity use and disaggregates it into major end-use components. The end-use EUIs developed through the EDA procedure represent a snap-shot of electricity use by building type and end-use for two regions of the PG&E service territory, for the year that disaggregation is performed. In the second part of the methodology, we adjust the EUIs for direct application to forecasting models based on factors such as climatic impacts on space-conditioning EUIs, fuel saturation effects, building and equipment vintage, and price impacts. Core data for the project are detailed on-site surveys for about 800 buildings, mail surveys ({approximately}6000), load research data for over 1000 accounts, and hourly weather data for five climate regions.
Date: August 1, 1994
Creator: Akbari, H.; Eto, J.; Konopacki, S.; Afzal, A.; Heinemeier, K. & Rainer, L.
Partner: UNT Libraries Government Documents Department

Measured energy savings of light colored roofs: Results from three California demonstration sites

Description: Measured data and computer simulations have demonstrated the impact of roof albedo in reducing cooling energy use in buildings. Savings are a function of both climate and the amount of roof insulation. The cooling energy savings for reflective roofs are highest in hot climates. A reflective roof may also lead to higher heating energy use. Reflective coatings are also used in commercial buildings to protect the roofing membrane, and hence, maintain and prolong the useful life of the roof. Reflectivity of coatings changes with weathering and aging which in turn could have an effect on building cooling-energy savings. For that reason, reflective roof coatings are not primarily marketed for their energy savings potential. To monitor the field performance of reflective coatings, the authors initiated a demonstration project where three commercial buildings in California were painted with light-colored roof coatings. The buildings are two medical care centers and one drug store. At all sites, the roof reflectance, both fresh and aged, and cooling energy use were monitored. In addition, they measured temperature throughout the roof systems and inside the conditioned space. In the monitored buildings, increasing the roof reflectance from an initial value of about 20% to 60%, dropped the roof temperature on hot summer afternoons by about 45 F. Summertime standard-weekday average daily air-conditioning savings were 18% (198 kWh) in the first medical office building, 13% (86 kWh) in the second medical office building, and 2% (13 kWh) in the drug store. The overall u-value of the roofs had dictated the impact of roof reflectance.
Date: June 1, 1998
Creator: Akbari, H.; Gartland, L. & Konopacki, S.
Partner: UNT Libraries Government Documents Department

High-albedo materials for reducing building cooling energy use

Description: One simple and effective way to mitigate urban heat islands, i.e., the higher temperatures in cities compared to those of the surrounds, and their negative impacts on cooling energy consumption is to use high-albedo materials on major urban surfaces such as rooftops, streets, sidewalks, school yards, and the exposed surfaces of parking lots. High-albedo materials can save cooling energy use by directly reducing the heat gain through a building's envelope (direct effect) and also by lowering the urban air temperature in the neighborhood of the building (indirect effect). This project is an attempt to address high-albedo materials for buildings and to perform measurements of roof coatings. We search for existing methods and materials to implement fighter colors on major building and urban surfaces. Their cost effectiveness are examined and the possible related technical, maintenance, and environmental problems are identified. We develop a method for measuring albedo in the field by studying the instrumentation aspects of such measurements. The surface temperature impacts of various albedo/materials in the actual outdoor environment are studied by measuring the surface temperatures of a variety of materials tested on an actual roof. We also generate an albedo database for several urban surfaces to serve as a reference for future use. The results indicate that high-albedo materials can have a large impact on the surface temperature regime. On clear sunny days, when the solar noon surface temperatures of conventional roofing materials were about 40{degrees}C (72{degrees}F) warmer than air, the surface temperature of high-albedo coatings were only about 5{degrees}C warmer than air. In the morning and in the late afternoon, the high-albedo materials were as cool as the air itself. While conventional roofing materials warm up by an average 0.055{degrees}C/(W m{sup {minus}2}), the high-albedo surfaces warm up by an average 0.015{degrees}C/(W m{sup {minus}2}).
Date: January 1, 1992
Creator: Taha, H.; Sailor, D. & Akbari, H.
Partner: UNT Libraries Government Documents Department

Analysis of energy use in building services of the industrial sector in California: Two case studies

Description: Energy-use patterns in many of California's fastest-growing industries are not typical of the existing mix of industries in the US. Many California firms operate small- and medium-sized facilities housed in buildings used simultaneously or interchangeably over time for commercial (office, retail, warehouse) and industrial activities. In these industrial subsectors, the energy required for building services (providing occupant comfort and necessities like lighting, HVAC, office equipment, computers, etc.) may be at least as important as the more familiar process energy requirements -- especially for electricity and on-peak demand. Electricity for building services is sometimes priced as if it were base loaded like process uses; in reality this load varies significantly according to occupancy schedules and cooling and heating loads, much as in any commercial building. Using informal field surveys, simulation studies, and detailed analyses of existing data (including utility commercial/industrial audit files), we studied the energy use of this industrial subsector through a multi-step procedure: (1) characterizing non-process building energy and power use in California industries, (2) identifying conservation and load-shaping opportunities in industrial building services, and (3) investigating industrial buildings and system design methodologies. In an earlier report, we addressed these issues by performing an extensive survey of the existing publicly available data, characterizing and comparing the building energy use in this sector. In this report, we address the above objectives by examining and analyzing energy use in two industrial case-study facilities in California. Based on the information for the case studies, we discuss the design consideration for these industrial buildings, characterize their energy use, and review their conservation and load-shaping potentials. In addition, we identify and discuss some research ideas for further investigation.
Date: September 1, 1991
Creator: Akbari, H. & Sezgen, O.
Partner: UNT Libraries Government Documents Department

Workshop proceeding of the industrial building energy use

Description: California has a large number of small and medium sized industries which have a major impact on the demand growth of California utilities. Energy use in building services (lighting, HVAC, office equipment, computers, etc.). These industries constitute an important but largely neglected fraction of the total site energy use. The ratio of energy use in building service to the total site energy use is a function of the industrial activity, its size, and the climate at the site of the facility. Also, energy use in building services is more responsive to weather and occupant schedules than the traditional base-load'' industrial process energy. Industrial energy use is considered as a base-load'' by utility companies because it helps to increase the utilities' load factor. To increase this further, utilities often market energy at lower rates to industrial facilities. Presently, the energy use in the building services of the industrial sector is often clubbed together with industrial process load. Data on non-process industrial energy use are not readily available in the literature. In cases where the major portion of the energy is used in the building services (with daily and seasonal load profiles that in fact peak at the same time as systemwide load peaks), the utility may be selling below cost at peak power times. These cases frequently happen with electric utilities. 30 figs., 6 tabs.
Date: January 1, 1988
Creator: Akbari, H. & Gadgil, A.
Partner: UNT Libraries Government Documents Department

Measured impact of neighborhood tree cover on microclimate

Description: In this paper we present results of our investigation into the relationship between urban microclimate and the local density of tree cover as measured in Sacramento, California. These results were obtained through analysis of data collected in a two-month long monitoring program with automatic weather stations installed at 15 residential locations throughout the city. Measured wind speeds showed a highly negative correlation with respect to tree cover. Daily peak air temperatures showed significant variation often differing from site to site by 2 to 4{degrees}C ({approx}3.5 to 7{degrees}F). A complex interaction between several competing factors is discussed leading to the conclusion that additional tree cover may actually increase urban air temperatures on synoptically cool days. It is suggested that this does not have a significant adverse affect in terms of overall summer urban cooling load. This is supported by an integrated analysis of the temperature data which yielded preliminary estimates indicating that residential cooling local (as measured by cooling degree days) may decrease by 5 to 10% per 10% increase in tree cover.
Date: August 1, 1992
Creator: Sailor, D. J.; Rainer, L. & Akbari, H.
Partner: UNT Libraries Government Documents Department

Modeling the effects of reflective roofing

Description: Roofing materials which are highly reflective to sunlight are currently being developed. Reflective roofing is an effective summertime energy saver in warm and sunny climates. It has been demonstrated to save up to 40% of the energy needed to cool a building during the summer months. Buildings without air conditioning can reduce their indoor temperatures and improve occupant comfort during the summer if highly reflective roofing materials are used. But there are questions about the tradeoff between summer energy savings and extra wintertime energy use due to reduced heat collection by the roof. These questions are being answered by simulating buildings in various climates using the DOE-2 program (version 2.1E). Unfortunately, DOE-2 does not accurately model radiative, convective and conductive processes in the roof-attic. Radiative heat transfer from the underside of a reflective roof is much smaller than that of a roof which absorbs heat from sunlight, and must be accounted for in the building energy model. Convection correlations for the attic and the roof surface must be fine tuned. An equation to model the insulation`s conductivity dependence on temperature must also be added. A function was written to incorporate the attic heat transfer processes into the DOE-2 building energy simulation. This function adds radiative, convective and conductive equations to the energy balance of the roof. Results of the enhanced DOE-2 model were compared to measured data collected from a school bungalow in a Sacramento Municipal Utility District monitoring project, with particular attention paid to the year-round energy effects.
Date: August 1, 1996
Creator: Gartland, L.M.; Konopacki, S.J. & Akbari, H.
Partner: UNT Libraries Government Documents Department

Electricity savings potentials in the residential sector of Bahrain

Description: Electricity is the major fuel (over 99%) used in the residential, commercial, and industrial sectors in Bahrain. In 1992, the total annual electricity consumption in Bahrain was 3.45 terawatt-hours (TWh), of which 1.95 TWh (56%) was used in the residential sector, 0.89 TWh (26%) in the commercial sector, and 0.59 TWh (17%) in the industrial sector. Agricultural energy consumption was 0.02 TWh (less than 1%) of the total energy use. In Bahrain, most residences are air conditioned with window units. The air-conditioning electricity use is at least 50% of total annual residential use. The contribution of residential AC to the peak power consumption is even more significant, approaching 80% of residential peak power demand. Air-conditioning electricity use in the commercial sector is also significant, about 45% of the annual use and over 60% of peak power demand. This paper presents a cost/benefit analysis of energy-efficient technologies in the residential sector. Technologies studied include: energy-efficient air conditioners, insulating houses, improved infiltration, increasing thermostat settings, efficient refrigerators and freezers, efficient water heaters, efficient clothes washers, and compact fluorescent lights. We conservatively estimate a 32% savings in residential electricity use at an average cost of about 4 fils per kWh. (The subsidized cost of residential electricity is about 12 fils per kWh. 1000 fils = 1 Bahrain Dinar = US$ 2.67). We also discuss major policy options needed for implementation of energy-efficiency technologies.
Date: August 1, 1996
Creator: Akbari, H.; Morsy, M.G. & Al-Baharna, N.S.
Partner: UNT Libraries Government Documents Department

Examples of cooler reflective streets for urban heat-island mitigation : Portland cement concrete and chip seals

Description: Part of the urban heat island effect can be attributed to dark pavements that are commonly used on streets and parking lots. In this paper we consider two light colored, hence cooler, alternative paving materials that are in actual use in cities today. These are Portland cement concrete (PCC) pavements and chip seals. We report measurements of the albedos of some PCC and chip sealed pavements in the San Francisco Bay Area. The albedos of the PCC pavements ranged from about 0.18 to 0.35. The temperatures of some PCC pavements are also measured and calculated. We then consider how the albedos of the constituent materials of the PCC (stone, sand and cement) contribute to the albedos of the resulting finished concrete. The albedos of a set of chip sealed pavements in San Jose, CA, were measured and correlated with the times of their placement. It is found that the albedos decrease with age (and use) but remain higher than that of standard asphalt concrete (AC) for about five years. After t hat, the albedos of the chip seals are about 0.12, similar to aged AC. The fact that many PCC pavements have albedos at least twice as high as aged AC suggests that it is possible to have pavement albedos that remain high for many years.
Date: April 30, 2003
Creator: Pomerantz, M.; Akbari, H.; Chang, S.-C.; Levinson, R. & Pon, B.
Partner: UNT Libraries Government Documents Department

Thermal energy storage for cooling of commercial buildings

Description: The storage of coolness'' has been in use in limited applications for more than a half century. Recently, because of high electricity costs during utilities' peak power periods, thermal storage for cooling has become a prime target for load management strategies. Systems with cool storage shift all or part of the electricity requirement from peak to off-peak hours to take advantage of reduced demand charges and/or off-peak rates. Thermal storage technology applies equally to industrial, commercial, and residential sectors. In the industrial sector, because of the lack of economic incentives and the custom design required for each application, the penetration of this technology has been limited to a few industries. The penetration rate in the residential sector has been also very limited due to the absence of economic incentives, sizing problems, and the lack of compact packaged systems. To date, the most promising applications of these systems, therefore, appear to be for commercial cooling. In this report, the current and potential use of thermal energy storage systems for cooling commercial buildings is investigated. In addition, a general overview of the technology is presented and the applicability and cost-effectiveness of this technology for developed and developing countries are discussed. 28 refs., 12 figs., 1 tab.
Date: July 1, 1988
Creator: Akbari, H. (Lawrence Berkeley Lab., CA (USA)) & Mertol, A. (Science Applications International Corp., Los Altos, CA (USA))
Partner: UNT Libraries Government Documents Department

Measured commercial load shapes and energy-use intensities and validation of the LBL end-use disaggregation algorithm

Description: The Southern California Edison Company (SCE) has conducted an extensive metering project in which electricity end use in 53 commercial buildings in Southern California has been measured. The building types monitored include offices, retail stores, groceries, restaurants, and warehouses. One year (June 1989 through May 1990) of the SCE measured hourly end-use data are reviewed in this report. Annual whole-building and end-use energy use intensities (EUIs) and monthly load shapes (LSs) have been calculated for the different building types based on the monitored data. This report compares the monitored buildings' EUIs and LSs to EUIs and LSs determined using whole-building load data and the End-Use Disaggregation Algorithm (EDA). Two sets of EDA determined EUIs and LSs are compared to the monitored data values. The data sets represent: (1) average buildings in the SCE service territory and (2) specific buildings that were monitored.
Date: January 1, 1993
Creator: Akbari, H.; Rainer, L.; Heinemeier, K.; Huang, J. & Franconi, E.
Partner: UNT Libraries Government Documents Department