Showing papers on "Efficient energy use published in 1998"

Adaptive frame length control for improving wireless link throughput, range, and energy efficiency

Abstract: Wireless network links are characterized by rapidly time varying channel conditions and battery energy limitations at the wireless mobile user nodes. Therefore static link control techniques that make sense in comparatively well behaved wired links do not necessarily apply to wireless links. New adaptive link layer control techniques are needed to provide robust and energy efficient operation even in the presence of orders of magnitude variations in bit error rates and other radio channel conditions. For example, research has advocated adaptive link layer techniques such as adaptive error control, channel state dependent protocols, and variable spreading gain. We explore dynamic sizing of the MAC layer frame, the atomic unit that is sent through the radio channel. A trade-off exists between the desire to reduce the header and physical layer overhead by making frames large, and the need to reduce frame error rates in the noisy channel by using small frame lengths. Clearly the optimum depends on the channel conditions. Through analysis supported by physical measurements with Lucent's WaveLAN radio we show that adaptive sizing of the MAC layer frame in the presence of varying channel noise indeed has a large impact on the user seen throughput (goodput). In addition, we show how that adaptive frame length control can be exploited to improve the energy efficiency for a desired level of goodput, and to extend the usable radio range with graceful throughput degradation. We describe the implementation of the adaptive MAC frame length control mechanism in combination with adaptive hybrid FEC/ARQ error control in a reconfigurable wireless link layer packet processing architecture for a low-power adaptive wireless multimedia node.

A worldwide perspective on energy, environment and sustainable development

Abstract: Problems with energy supply and use are related not only to global warming, but also to such environmental concerns as air pollution, ozone depletion forest destruction and emission of radioactive substances. These issues must be taken into consideration simultaneously if humanity is to achieve a bright energy future with minimal environmental impacts. Much evidence exists which suggests that the future will be negatively impacted if humans keep degrading the environment. There is an intimate connection between energy, the environment and sustainable development. A society seeking sustainable development ideally must utilize only energy resources which cause no environmental impact (e.g. which release no emissions to the environment). However, since all energy resources lead to some environmental impact, it is reasonable to suggest that some (not all) of the concerns regarding the limitations imposed on sustainable development by environmental emissions and their negative impacts can be in part overcome through increased energy efficiency. A strong relation clearly exists between energy efficiency and environmental impact since, for the same services or products, less resource utilization and pollution is normally associated with higher efficiency processes. Anticipated patterns of future energy use and consequent environmental impact (focusing on acid precipitation, stratospheric ozone depletion and the greenhouse effect) are comprehensively discussed in this paper. Also, some solutions to current environmental issues in terms of energy conservation and renewable energy technologies are identified and some theoretical and practical limitations on increased energy efficiency are explained. The relations between energy and sustainable development, and between the environment and sustainable development, are described, and an illustrative example is presented. Throughout the paper several issues relating to energy, environment and sustainable development are examined from both current and future perspectives. Finally, several conclusions and recommendations are drawn which may be useful to energy scientists and engineers and policy makers. © 1998 John Wiley & Sons, Ltd.

A framework for estimating and minimizing energy dissipation of embedded HW/SW systems

Abstract: Embedded system design is one of the most challenging tasks in VLSI CAD because of the vast amount of system parameters to fix and the great variety of constraints to meet. In this paper we focus on the constraint of low energy dissipation, an indispensable peculiarity of embedded mobile computing systems. We present the first comprehensive framework that simultaneously evaluates the tradeoffs of energy dissipations of software and hardware such as caches and main memory. Unlike previous work in low power research which focused only on software or hardware, our framework optimizes system parameters to minimize energy dissipation of the overall system. The trade-off between system performance and energy dissipation is also explored. Experimental results show that our Avalanche framework can drastically reduce system energy dissipation.

A comparison of MAC protocols for wireless local networks based on battery power consumption

Abstract: Energy efficiency is an important issue in mobile wireless networks since the battery life of mobile terminals is limited. Conservation of battery power has been addressed using many techniques. This paper addresses energy efficiency in medium access control (MAC) protocols for wireless networks. The paper develops a framework to study the energy consumption of a MAC protocol from the transceiver usage perspective. This framework is then applied to compare the performance of a set of protocols that includes IEEE 802.11, energy-conserving MAC (EC-MAC), PRMA, multiservices dynamic reservation-TDMA (MDR-TDMA), and distributed-queueing request update multiple access (DQRUMA). The performance metrics considered are transmitter and receiver usage times for packet transmission and reception. The analysis here shows that protocols that aim to reduce the number of contentions perform better from a energy consumption perspective. The receiver usage time, however; tends to be higher for protocols that require the mobile to sense the medium before attempting transmission.

Energy and Environmental Impacts: Present and Future Perspectives

Abstract: Today, world energy consumption contributes to pollution, environmental deterioration, and global greenhouse emissions. Increases in energy consumption are driven by population growth and economic ...

Handbook on international comparisons of energy efficiency in the manufacturing industry

Abstract: The aim of this methodology handbook is to establish a conceptual framework to develop indicators for measuring energy efficiency in the manufacturing industry, and to use that framework to propose indicators for the most important sectors (from the energy perspective) of the manufacturing industry. Non-manufacturing industry is not included because of a relatively low share in total energy consumption and a lack of data. Energy efficiency indicators are proposed for the iron and steel industry, the aluminium industry, the cement industry, pulp and paper production, ammonia production, chlorine/alkali production, the petrochemical industry, refineries and the public electricity sector. For each sector relevant processes are described and the energy efficiency indicator pyramid is presented. Furthermore, structural aspects are identified. For each of the sectors required data, potential sources and methodological or data pitfalls are described. For each of the sectors some examples of the suggested indicators are presented. Each sectoral chapter contains a checklist of data required to make an international comparison of the energy efficiency. refs.

An energy/security scalable encryption processor using an embedded variable voltage DC/DC converter

Abstract: Security concerns for battery-operated wireless systems require the development of energy-efficient data-encryption techniques that can adapt to the time-varying data rates and quality-of-service requirements inherent in a wireless application. This work describes the design and implementation of a configurable encryption processor that allows the security provided to be traded off with respect to the energy that is dissipated to encrypt a bit. The processor features an embedded high-efficiency variable-output DC/DC converter that allows the supply voltage to be dynamically varied to match the time-varying throughput and quality requirements of the data stream being encrypted. The resulting processor consumes 134 mW at 2.5 V when encrypting data at a rate of 1 Mb/s using a maximum bit width of 512 bits. The converter efficiency is 96% at the peak load of 134 mW. A comparison of our processor to a software implementation running on a low-power programmable processor shows that our implementation is two to three orders of magnitude more energy efficient.

Energy and ventilation

Abstract: The energy statistics of OECD Countries show that between 30 and 50% of primary energy is consumed in non-industrial buildings (i.e. in dwellings, offices, hospitals, schools etc.) Of this, as much as 50% is dissipated from the building in the departing air stream. As buildings become more thermally efficient, the proportion of energy loss (either heating or cooling losses) associated with ventilation and air infiltration is expected to become the dominant thermal loss mechanism. Additional losses may be associated with the energy needed to operate mechanical ventilation systems. It is, therefore, essential to understand the role that air change plays in contributing to energy loss, and to identify methods to improve the energy efficiency of ventilation. Much of this area of activity is still ongoing, but the purpose of this paper is to present an overview of the current level of understanding and summarise the results of recent analytical work. Taking the building stock as a whole, the present analysis shows that airchange accounts for approximately 36% of total space conditioning energy and contributes to almost half of heating equipment losses. If fresh air supply was controlled to meet current recommended ventilation rates for health, then it is estimated that ventilation heat energy could be reduced to a quarter of its present value.

Energy efficiency of media access protocols for mobile data networks

Abstract: As mobile terminals are powered by a finite battery source, energy constraints play a major role in the design of wireless communications systems. In this letter, based on a general analytical framework, we study the energy efficiency of a class of multiple access schemes, using the average number of correctly transmitted packets for a given amount of allocated energy as an appropriate metric. We show that a good choice of the protocol rules can significantly improve the energy efficiency.

Simplified life-cycle analysis of PV systems in buildings: present situation and future trends

Abstract: The integration of photovoltaic (PV) systems in buildings shows several advantages compared to conventional PV power plants. The main objectives of the present study are the quantitative evaluation of the benefits of building-integrated PV systems over their entire life-cycle and the identification of best solutions to maximize their energy efficiency and CO2 mitigation potential. In order to achieve these objectives, a simplified life-cycle analysis (LCA) has been carried out. Firstly, a number of existing applications have been studied. Secondly, a parametric analysis of possible improvements in the balance-of-system (BOS) has been developed. Finally, the two steps have been combined with the analysis of crystalline silicon technologies. Results are reported in terms of several indicators: energy pay-back time, CO2 yield and specific CO2 emissions. The indicators show that the integration of PV systems in buildings clearly increases the environmental benefits of present PV technology. These benefits will further increase with future PV technologies. Future optimized PV roof-integrated systems are expected to have an energy pay-back time of around 1·5 years (1 year with heat recovery) and to save during their lifetime more than 20 times the amount of CO2 emitted during their manufacturing (34 times with heat recovery). © 1998 John Wiley & Sons, Ltd.

Energy integration of industrial sites: tools, methodology and application

Abstract: One of the most important conclusions of the energy integration techniques is that energy efficiency can only be analyzed with respect to the pinch point location of the system. Therefore, the problem boundaries cannot be limited to the chemical process level but should be extended at the site scale level. In this paper, we discuss how to adapt the pinch based techniques in order to solve the industrial site integration. In the proposed approach, each process requirement is defined by its respective hot and cold composite curves that become hot and cold streams for the site scale problem. The use of mathematical programming techniques allows us to target the minimum cost of energy requirement (MCER) of the total site, including the integration of the combined production of heat and power by the steam network. The illustrative example shows an energy saving of 35% of the total site energy consumption with a very small pay back time.

Use of Calibrated HVAC System Models to Optimize System Operation

Abstract: A calibrated simplified engineering modeling method has been developed to optimize HVAC system operation. This method can be used to optimize operating strategies and control schedules. It has also served to identify malfunctioning components on occasion. This method has been successfully applied to 18 LoanSTAR buildings where over $2.0 million per year in potential savings have been identified, and over $1.4 million per year have been implemented. The method is described in the context of a case study.

Potential Nationwide Improvements in Productivity and Health From Better Indoor Environments

Abstract: Published in the Proceedings of the 1998 Summer Study on Energy Efficiency in Buildings, Energy Efficiency in a Competitive Environment , American Council for an Energy-Efficient Economy, August 23-28, Asilomar, CA, pp. 8.85-8.97. LBNL-41849 Potential Nationwide Improvements in Productivity and Health From Better Indoor Environments William 1. Fisk* and Arthur H. Rosenfeld+ *Indoor Environment Department Environmental Energy Technologies Division Lawrence Berkeley National Laboratory, Berkeley, CA 94720 +U.S. Department of Energy Washington, D.C. 20585 May 1998 This work was supported by the Assistant Secretary of Energy Efficiency and Renewable Energy, Office of Building Technology, State, and Community Programs, Office of Building Systems of the U.S. Department of Energy (DOE) under contract No. DE-AC03-76SF00098.

Quadratic optimization of force distribution in walking machines

Abstract: Energy efficiency remains a problem in walking machines. One approach to improving energy efficiency involves solving for an optimal set of foot forces which minimizes the power supplied to DC motor actuators at each instant. Energy regenerated by the motors, which may be significant, is generally lost and should be explicitly taken into account to produce the optimal force distribution. A method to produce this optimal solution using quadratic programming is developed in this paper. The results are compared to three suboptimal quadratic programming approaches which minimize internal forces, a weighted norm of joint torques, and finally power without accounting for regeneration, all on a simulated hexapod. It is found that the common approach of minimizing internal forces may often result in poor energy efficiency.

Energy consumption performance of a class of access protocols for mobile data networks

Abstract: When user terminals powered by a finite battery source are used for wireless communications, energy constraints are likely to influence the choice of media access protocols. We use the average number of correctly transmitted packets for a given amount of allocated energy as an appropriate metric. In particular, we study different versions of a wireless access protocol operating over a mobile radio channel using a finite energy source with a flat power profile. The mobile radio channel itself is characterized by a correlated Rayleigh fading process, the correlation in the fading process being dependent on the speed of the user terminal. We show that the access protocol with an error detect feature is energy efficient for pedestrian user speeds, whereas for vehicular speeds a retransmission protocol is more efficient.

The Solid-State Spray Forming of Low-Oxide Titanium Components

Abstract: Figure 2. The SSF system for fabricating near-net-shape OFTi components. Editor’s Note: This paper was presented at the 1998 TMS Annual Meeting as part of the Innovations in Titanium symposium, which was sponsored by the Office of Industrial Technologies, Energy Efficiency and Renewable Energy, U.S. Department of Energy, Innovative Concepts program. This issue of JOM represents the proceedings of that symposium.

Improving energy efficiency: strategies for Supporting Sustained Market Evolution in Developing and Transitioning Countries

Abstract: This report presents a framework for considering market-oriented strategies for improving energy efficiency that recognize the conditions of developing and transitioning countries, and the need to strengthen the effectiveness of market forces in delivering greater energy efficiency. It discusses policies that build markets in general, such as economic and energy pricing reforms that encourage competition and increase incentives for market actors to improve the efficiency of their energy use, and measures that reduce the barriers to energy efficiency in specific markets such that improvement evolves in a dynamic, lasting manner. The report emphasizes how different policies and measures support one another and can create a synergy in which the whole is greater than the sum of the parts. In addressing this topic, it draws on the experience with market transformation energy efficiency programs in the US and other industrialized countries.

Turning Off the Heat: Why America Must Double Energy Efficiency to Save Money and Reduce Global Warming

Abstract: Global warming, the result of increasing carbon dioxide emissions from energy producers and users, has become a danger to humans. It threatens radical climate changes, severe storms, and ecological havoc. "Turning Off the Heat" targets a main source of overuse of fossil fuels - the energy producers themselves who, through their government-approved monopolies have led to energy inefficiency and needless pollution. A leading authority with 20 years experience developing and operating of energy projects, Casten clearly explains that the US and other nations of the world can, and must, double the efficiency of electric utilities. This efficiency improvement will lead to a reduction of electric prices by 30 to 40 per cent and cut carbon dioxide emissions (a greenhouse gas) in half. Two-thirds of the fuel used to make US electricity is wasted, resulting in higher energy prices and excess pollution. If market forces are unleashed and monopolies ended, competition will save money and fuel, Casten says. This is an essential volume for policy-makers, legislators, leaders in industry, environmentalists, and concerned citizens.