bluuebunny/crossref_metadata_2025 huggingface dataset:
Simulation of Energy Saving Control for a Central Air Conditioning System
Authors: Wei Bing , Pei Na , Liu Jing , Tang Juan
Published: March 2012

In recent years with the sustainable development of economy, the energy consumption of air conditioning system has accounted for over 40% of the total of buildings in China. Energy conservation has become an important issue. Various energy wastes exist in the operation process of central AC systems. So the central air conditioning system of energy saving has great potential. Central air conditioning load changes with time-varying characteristics, the load and operating conditions are influenced by various factors such as season, weather, traffic and environmental conditions changing and so on. They are always changing, and always fluctuating. Even in the day, morning and evening have temperature changes. According to statistics it is only a short time for the occurrence of most buildings’ maximum load time, and air conditioning systems are running at part load conditions in most time. If air conditioning system operating control way cannot change load according to the dynamic adjustment, which necessarily causes enormous energy waste. In this paper, with the help of a typical building located in Baoding, China, the simulation of a central air-conditioning system was carried out. First, the simulation models of main equipments of a central air conditioning system are established. Second, according to the actual loads, simulation of the different energy control modes and the operation schemes were carried through. Third, the simulation curves were obtained. Finally, based on the comparison of simulation curves, the optimal energy saving control mode and the operation scheme of the central air conditioning system were analyzed, the energy saving potentials existing in the actual operating process were proposed. All these above will be very important for the AC system operation optimization of building energy-efficient and air conditioning system operation and management.
Thermal Performance Estimation of the Office Building With the Building Integrated Photovoltaic System
Authors: Egrican Nilufer , Akguc Alpay
Published: March 2012

The Earth is faced to decreasing of energy resources due to increasing of energy consumption. This reason accelerates the global warming which leads the Earth to a place in which quality of life is reducing year by year. A considerable portion of total energy consumption is used in residential sector in the world. The usage of energy in residential sector effectively ensures large amount of energy saving. Nowadays, the buildings have been aiming to design which consume low energy and supply high comfort. In order to design energy efficient buildings, all the designing parameters which include passive systems must be taken into consideration together considering versatile interior and exterior conditions. In this study the energy efficient building was described and the applications were explained for the sample building. The office building designed to obtain LEED certification was taken into consideration as a current application in Turkey and it was modeled using TRNSYS simulation program during the year. The heating and cooling loads were calculated. According to results some suggestions were recommended for reducing the heating and cooling demands of the office building and any suggestion was simulated and analyzed for the designed building.
Use of SCADA Data for Failure Detection in Wind Turbines
Authors: Kim Kyusung , Parthasarathy Girija , Uluyol Onder , Foslien Wendy , Sheng Shuangwen , Fleming Paul
Published: March 2012

High operations and maintenance costs for wind turbines reduce their overall cost effectiveness. One of the biggest drivers of maintenance cost is unscheduled maintenance due to unexpected failures. Continuous monitoring of wind turbine health using automated failure detection algorithms can improve turbine reliability and reduce maintenance costs by detecting failures before they reach a catastrophic stage and by eliminating unnecessary scheduled maintenance. A SCADA (Supervisory Control and Data Acquisition System) -data based condition monitoring system uses data already collected at the wind turbine controller. It is a cost-effective way to monitor wind turbines for early warning of failures and performance issues. In this paper, we describe our exploration of existing wind turbine SCADA data for development of fault detection and diagnostic techniques for wind turbines. We used a number of measurements to develop anomaly detection algorithms and investigated classification techniques using clustering algorithms and principal components analysis for capturing fault signatures. Anomalous signatures due to a reported gearbox failure are identified from a set of original measurements including rotor speeds and produced power.
Development of a Fac¸ade Evaluation Facility for Experimental Study of Building Energy
Authors: Concina Wendell , Sadineni Suresh B. , Boehm Robert F.
Published: March 2012

The goal of the project is to evaluate various types of facades’ behavior and effects on building energy, focused primarily on building fenestrations such as windows. Development of the fac¸ade evaluation facility and requirements are presented in this paper. The test facility is a complete standalone unit designed to replicate a section of a building. Accommodation for facilitating a wide range of fenestrations was an important criterion. An effective solution was developed that allowed instant interchangeability of the fac¸ade setup. Although, due south orientated facades was of primary interest, integration of a rotating carousel base allowed flexibility in adjusting the orientation of the test facility. Experimental procedures and instrumentation layout are discussed in detail. The temperature of the indoor environment is continuously controlled and monitored. The measured fenestration characteristics include thermal and optical properties of the windows. The test results reveal the fenestration performance. The outcome of these tests enumerates the effects of the fac¸ade on the overall heating and cooling loads of buildings. Further investigation into these characteristics assists in improving building energy efficiency. Due to the versatility of the facility, quick replacement of the fac¸ade can accommodate several tests in short durations of time. Furthermore, correlation of the results can be scaled appropriately for residential or commercial settings providing practical information for wide utilization, contingent upon the window type.
Simulation of Flow Inside Heat Pipe: Sensitivity Study, Conditions and Configuration
Authors: Ahmed Nouman Zahoor , Singh Pawan K. , Janajreh Isam , Shatilla Youssef
Published: March 2012

Heat pipes are widely used as a heat transporting device in a variety of applications. From space satellites, large industrial appliances to a heat sink for cooling electronic components and packages. Heat pipes are extremely efficient because of their high effective thermal conductivity, compactness, low cost and reliability. Therefore, the designers of heat sinks are often required to optimize the performance of the heat pipe itself in order to improve the overall thermal management system of any particular equipment. However, the detailed internal modeling of a heat pipe presents a challenging problem for an engineer. It is a multi physics problem including two phase flow within porous media and with conjugate heat transfer adding the solicited high capillary and surface tension effect. In this present study, detailed modeling of the heat pipe considering the mentioned effects is pursued. A basic review of the governing equations describing the complete heat pipe operation is given. The commercially available simulation tool Fluent 6.3 is used to describe and solve these equations in a coupled conjugate heat transfer set up. The geometry of heat pipe is divided in two different regions which solve simultaneously. The first region is core region where only vapor flow is assumed. The second region consists of wall and wick structure through which the mass transfer due to wettability and heat dissipates through conduction. Water was used as flowing fluids through wick porous structure. Previous experimental as well as numerical models regarding the heat pipes have been studied and used for the verification of the present model along with a standard grid convergence study. The effects of different heat pipe length, heat fluxes, wall thickness, wall material and porosity are investigated. The pressure drop and wall temperature increase with the value of heat flux. Similarly, porosity and wall material affect the wall temperature distribution. The effect of wall thickness and heat pipe length was not significant. In addition, a theoretical model is developed for the pressure drop across the heat pipe in vapor region and the respective output was used for the simulation. Finally, the temperature distribution in wall and wick is shown and discussed.
Fuel Use and CO2 Emissions Under Uncertainty From Light-Duty Vehicles in the U.S. to 2050
Authors: Bastani Parisa , Heywood John B. , Hope Chris
Published: March 2012

On-road transportation contributes 22% of the total CO2 emissions and more than 44% of oil consumption in the U.S. Technological advancements and use of alternative fuels are often suggested as ways to reduce these emissions. However, many parameters and relationships that determine the future characteristics of the light-duty vehicle fleet and how they change over time are inherently uncertain. Policy makers need to make decisions today given these uncertainties, to shape the future of light-duty vehicles. Decision makers thus need to know the impact of uncertainties on the outcome of their decisions and the associated risks. This paper explores a carefully constructed detailed pathway that results in a significant reduction in fuel use and GHG emissions in 2050. Inputs are assigned realistic uncertainty bounds, and the impact of uncertainty on this pathway is analyzed. A novel probabilistic fleet model is used here to quantify the uncertainties within advanced vehicle technology development, and life-cycle emissions of alternative fuels and renewable sources. Based on the results from this study, the expected fuel use is about 500 and 350 billion litres gasoline equivalent, with a standard deviation of about 40 and 80 billion litres in years 2030 and 2050 respectively. The expected CO2 emissions are about 1,360 and 840 Mt CO2 equivalent with a spread of about 130 and 260 Mt CO2 equivalent in 2030 and 2050 respectively. Major contributing factors in determining the future fuel consumption and emissions are also identified and include vehicle scrappage rate, annual growth of vehicle kilometres travelled in the near term, total vehicle sales, fuel consumption of naturally-aspirated engines, and percentage of gasoline displaced by cellulosic ethanol. This type of analysis allows policy makers to better understand the impact of their decisions and proposed policies given the technological and market uncertainties that we face today.
Energy Analysis and Thermoeconomic Assessment of the Closed Greenhouse: The Largest Commercial Solar Building
Authors: Vadiee Amir , Martin Viktoria
Published: March 2012

The closed greenhouse concept has been studied in this paper. The closed greenhouse can be considered as the largest commercial solar building. In principle, it is designed to maximize the utilization of solar energy through seasonal storage. In an ideal fully closed greenhouse, there is not any ventilation window. Therefore, the excess heat must be removed by other means. In order to utilize the excess heat at a later time, long and/or short term thermal storage technology (TES) should be integrated. A developed model has been evaluated due to different situations. The closed greenhouse is compared with conventional greenhouse using a case study respect to the energy analysis. A parameter has been defined in this paper in order to compare performance of the closed greenhouse concept in different conditions. This parameter has been called ESR. Finally a preliminary thermo-economical study has been assessed in order to investigate on feasibility of the closed greenhouse concept.
A Simulation Study for Single and Double Effect Absorption Solar Cooling Systems Operated Under Taiwan Climate
Authors: Yang Ru , Shen Jun-Long
Published: March 2012

This research numerically studies the performance of absorption solar cooling systems operated under climates of the major cities in Taiwan. Both single-effect and double effect absorption solar cooling systems are studied. The single-effect system uses flat-plate solar collectors and the double-effect system uses linear concentration collectors. The results show a promising solar fraction (the fraction of cooling load provided by solar energy) for most of Taiwan areas. In addition, the double-effect systems provide better solar fraction than the single-effect systems. This study provides design reference and system optimization for the development of absorption solar cooling systems in Taiwan.
Using the Energy Intensity Ratio as an Assessment Tool for Near Term US Energy Strategy in Transportation and Petrochemicals
Authors: Hill Davion M. , King Carey
Published: March 2012

Conventional fuels such as oil, natural gas, and coal have historically provided reasonable financial returns on investment as well as energy returned on energy invested (EROEI), despite the fact that continuous financial and energy inputs are required to use these fuels. Besides EROEI, the energy intensity ratio (EIR) is another measure for energy use and economics. The EIR is the ratio of energy bought per dollar to the energy it takes to make a dollar in the economy. In this case we are considering the cost of petroleum per barrel, and therefore we are discussing EIRp or EIR of oil based upon price. The EIRp is related to historical economical data and conclusions will be drawn about the value of EIRp as an economic indicator. Then, EIRp will be used as a tool to demonstrate the value of shifting energy resources from petroleum to alternatives, specifically for transportation and petrochemicals. The considerations for modern economic conditions as they compare to historical economic conditions will be explained, and the viability of policy and alternative technological transportation scenarios will be described in terms of EIRp and its relationship to vehicle miles travelled.
Solar-Augment Potential of U.S. Fossil-Fired Power Plants
Authors: Turchi Craig S. , Langle Nicholas , Bedilion Robin , Libby Cara
Published: March 2012

Concentrating Solar Power (CSP) systems utilize solar thermal energy for the generation of electric power. This attribute makes it relatively easy to integrate CSP systems with fossil-fired power plants. The “solar-augment” of fossil power plants offers a lower cost and lower risk alternative to stand-alone solar plant construction. This study ranked the potential to add solar thermal energy to coal-fired and natural gas combined cycle (NGCC) plants found throughout 16 states in the southeast and southwest United States. Each generating unit was ranked in six categories to create an overall score ranging from Excellent to Not Considered. Separate analysis was performed for parabolic trough and power tower technologies due to the difference in the steam temperatures that each can generate. The study found a potential for over 11 GWe of parabolic trough and over 21 GWe of power tower capacity. Power towers offer more capacity and higher quality integration due to the greater steam temperatures that can be achieved. The best sites were in the sunny southwest, but all states had at least one site that ranked Good for augmentation. Geographic depiction of the results can be accessed via NREL’s Solar Power Prospector at http://maps.nrel.gov/.
Design and Construction of an Automated Hybrid Lighting System
Authors: Pe´rez Sa´nchez Maria M. , Alonzo Chavarria Josue´ A. , Ordon˜ez Lo´pez Eduardo E.
Published: March 2012

The lighting systems of homes and workplaces today must be constantly redesigned to be environmentally friendly, sustainable, healthy and ergonomic. This requires maximizing the flow of daylight into indoors, minimizing the amount of pollutants used in their manufacture, long durability materials considered in the design, maximizing energy efficiency of the lighting system components, mimicking the spectrum of natural light and providing some control of lighting modes by the user. Taking into account all these considerations, it is proposed the design and construction of an intelligent lighting system that regulates the use of natural and artificial light, prioritizing the availability of the former over the latter in order to be implemented in housing in the region of the Yucata´n peninsula. To achieve this goal, it is designed and built a light sensor with its own signal conditioning circuit, a light tube of stainless steel with luminous flux control, a dimming circuit for a lamp that uses light-emitting diodes (LEDs) and a control system with a PIC18f4550 micro controller.
Design of a Modular Latent Heat Storage System for Solar Thermal Power Plants
Authors: Campbell Mark R. , Newmarker Marc , Lewis Nathaniel , George Christopher T. , Cohen Gilbert
Published: March 2012

Thermal energy storage systems designed to use phase change material can benefit from accounting for the reduction in heat transfer that results from fouling on the heat transfer surface or employing a system to minimize the amount of build-up on the heat transfer surface. This paper describes the modeling and design of a modular latent heat thermal energy storage system that can use an internal heat exchanger and a mechanical system to increase heat transfer to and from the phase change material. Theoretical heat transfer modeling of a 100 kWht storage system was performed, candidate phase change materials were tested, and mechanical material removal experiments were conducted. The results of this work led to a design that is in construction and will be operated in the future. The system is predicted to be capable of reaching 93% round trip efficiency while providing 2 hours of discharge at a nearly constant temperature.
Hydrodynamic Modeling of CO2-Saturated Brine Injection in Geologic Formations for Carbon Sequestration Using the Lattice Boltzmann Method
Authors: Ebrahimi A. , Ellis J. S. , Bazylak A.
Published: March 2012

We present the implementation of the conventional lattice Boltzmann method (LBM) with single-relaxation time (SRT) to model the injection of CO2-saturated brine into underground porous rocks. The aim is to describe the “surface dissolution” technique of carbon sequestration, whereby CO2 is dissolved in brine extracted from the designated storage site and this CO2-brine solution is pumped back into underground formations. In the two-dimensional numerical model here, a small subsection of underground porous rock formation is represented as a staggered periodic array of disks. From a single unit cell of the porous structure, we have determined the domain size and lattice spacing required to reach a stable solution. By modeling single-phase flow, the permeability k could be calculated and compared over various lattice sizes to determine a mesh size-independent solution. A constant pressure gradient was imposed across the length of the domain to simulate the injection of the incompressible CO2-saturated brine solution into the domain. From these simulations, velocity fields within the pore structure were obtained, and the effects of porosity on the permeability were explored. Such porosity effects may prove important at the transition between different rock layers within a storage site.
Novel Two-Stage Concentrating Solar Air Unit Achieves Heating Goals, Minimizes Tracking and Uses Off-the-Shelf Materials for Construction
Authors: Mendell Christopher N.
Published: March 2012

Available solar heaters, particularly for baking, have not enjoyed wider success because of their inability to address issues of ease-of-integration to existing infrastructure, unit size, frequent tracking adjustment, tracking system failure, use of ‘exotic’ materials, glare, and reflector fouling from the exposure of the optical system to the close proximity of the cooking vessel. The author created a series of ‘user-friendly’ features and criteria for a proposed unit to meet these challenges.
Exergy Analysis of Coal Energy Conversion With Carbon Sequestration Via Combustion in Supercritical Saline Aquifer Water
Authors: Mobley Paul D. , Pass Rebecca Z. , Edwards Chris F.
Published: March 2012

Decarbonization of electricity production is a vital component in meeting stringent emissions targets aimed at curbing the effects of global climate change. Most projected pathways toward meeting those targets include a large contribution from carbon capture and storage. Many capture technologies impose a large energy penalty to separate and compress carbon dioxide (CO2). Also, injected neat CO2 in a deep saline aquifer is buoyant compared to the aquifer brine and requires an impermeable seal to prevent it from escaping the aquifer. An alternative technology was recently proposed by Heberle and Edwards [1] that burns coal in supercritical water pumped from a saline aquifer. The entire effluent stream is sequestered, capturing all carbon and non-mineral coal combustion products in the process. This stream is denser than the aquifer brine and therefore offers a higher level of storage security, and can utilize aquifers without suitable structural trapping. This technology also increases energy security in the U.S., allowing for the use of its coal resources while avoiding atmospheric pollution. In this paper, a complete architecture employing supercritical water oxidation is proposed, including a liquid-oxygen-pumped air separation unit and regenerator system that heats and desalinates the incoming brine. A thermodynamic model calculates the overall thermal efficiency of the plant, including all separation and storage energy penalties. In addition, an exergy analysis gives insights into the least efficient parts of the proposed system. The details and assumptions of the model are discussed. Insights from the model and these analyses elucidate how the proposed system may be operated as a zero-emission electricity source and the technical challenges that must be addressed for deployment.
Standardization of CSP Performance Model Projection: Latest Results From the guiSmo Project
Authors: Hirsch Tobias , Eck Markus , Blanco Manuel J. , Wagner Michael , Feldhoff Jan Fabian
Published: March 2012

Electricity yield projection is one of the essential tasks related to concentrating solar thermal power plants. Currently, the project engineers and other stakeholders cannot refer to standardized methods for calculation of the annual electricity outcome of such plants. In autumn 2010, the first steps were taken to initiate an international project within SolarPACES Task I that targets the development of reliable methodologies for yield projection [1, 2]. More than 80 international participants from academia, industry, and finance agreed to work together within the guiSmo project (Guidelines for CSP performance modelling). Intended as an open project with publicly available results, CSP stakeholders are invited to join the team. Since initiation of the project, a coordination team and supervisory board have been founded. The challenging task is subdivided into ten “work packages” that cover all aspects of CSP project analysis — from elementary plant models to transient effects and financial evaluation approaches. This paper provides an overview of recent achievements and upcoming activities in the guiSmo project. The focus is on the definition of three quality levels for yield projection as they will be required during the various project development phases.
Multivariate and Multimodal Wind Distribution Model Based on Kernel Density Estimation
Authors: Zhang Jie , Chowdhury Souma , Messac Achille , Castillo Luciano
Published: March 2012

This paper presents a new method to accurately characterize and predict the annual variation of wind conditions. Estimation of the distribution of wind conditions is necessary (i) to quantify the available energy (power density) at a site, and (ii) to design optimal wind farm configurations. We develop a smooth multivariate wind distribution model that captures the coupled variation of wind speed, wind direction, and air density. The wind distribution model developed in this paper also avoids the limiting assumption of unimodality of the distribution. This method, which we call the Multivariate and Multimodal Wind distribution (MMWD) model, is an evolution from existing wind distribution modeling techniques. Multivariate kernel density estimation, a standard non-parametric approach to estimate the probability density function of random variables, is adopted for this purpose. The MMWD technique is successfully applied to model (i) the distribution of wind speed (univariate); (ii) the distribution of wind speed and wind direction (bivariate); and (iii) the distribution of wind speed, wind direction, and air density (multivariate). The latter is a novel contribution of this paper, while the former offers opportunities for validation. Ten-year recorded wind data, obtained from the North Dakota Agricultural Weather Network (NDAWN), is used in this paper. We found the coupled distribution to be multimodal. A strong correlation among the wind condition parameters was also observed.
Integrated Thermal-Fluids System Modeling of an Ocean Thermal Energy Conversion Power Plant for Analysis and Optimization
Authors: Upshaw Charles R. , Webber Michael E.
Published: March 2012

This report focuses on the development of an integrated model of a closed-cycle Ocean Thermal Energy Conversion (OTEC) power plant for the purpose of analyzing the relative effects of key design parameters on the performance of the plant’s main sub-systems. The model was then used to analyze the effects of cascaded stages within the power cycle, as an example of using the model for analysis and optimization. The analysis led to the conclusion that 2–5 stages are most beneficial. A simplified thermodynamic model of the power cycle was developed to estimate the power produced, as well as the water mass flow rates required for the necessary heating and cooling rates. A simplified pipe flow model was then integrated into the power plant model to calculate the pumping power required to run the power cycle. The pumping power demand was subtracted off the thermodynamic model to provide the net power out of the cycle. Since the thermodynamic efficiency of the OTEC power cycle is inherently low, the water flow rates are substantial, and so are the power requirements of their pumps. Therefore, it is important to optimize the design parameters of an OTEC plant to minimize water mass flow rate relative to the power output of the plant. The thermodynamic performance analysis consists of first establishing a base-line reference power plant and a reference set of input variables. Plant design variables, such as the number of power cycle stages, are then varied up and down about the reference point; the outputs are then compared to the reference output.
Carbon Catalyzed Methane Decomposition for Enhanced Solar Thermal Cracking
Authors: Shilapuram Vidyasagar , Ozalp Nesrin
Published: March 2012

This study presents thermal decomposition of methane, laden with two activated charcoal samples, namely Fluka 05105 and Fluka 05120, which were used laden with methane in a vortex flow solar reactor and seeded in a tornado flow solar reactor. Previously, we presented our thermo gravimetric experiment results on the carbon-hydrogen reaction to show whether the injected carbon particles react with the formed hydrogen. In this work, we expanded our thermogravimetric analysis to study carbon-methane reaction at various concentrations of methane feed gas to study the favorable effect of carbon laden flow experiments for catalytic methane decomposition. Results were analyzed to discuss the threshold temperature, ultimate mass gain, average hydrogen production, amount of carbon formed, type of carbon sample, and concentration of methane in the feed gas. It is observed that average hydrogen production rate is increased with an increase in the methane volume fraction in the feed gas. Higher hydrogen and carbon production is observed when Fluka 05105 is used. For different partial pressures of methane, different ultimate mass gain is observed.
A Comprehensive Measure of the Energy Resource Potential of a Wind Farm Site
Authors: Zhang Jie , Chowdhury Souma , Messac Achille , Castillo Luciano
Published: March 2012

Currently, the quality of wind measure of a site is assessed using Wind Power Density (WPD). This paper proposes to use a more credible metric namely, one we call the Wind Power Potential (WPP). While the former only uses wind speed information, the latter exploits both wind speed and wind direction distributions, and yields more credible estimates. The new measure of quality of a wind resource, the Wind Power Potential Evaluation (WPPE) model, investigates the effect of wind velocity distribution on the optimal net power generation of a farm. Bivariate normal distribution is used to characterize the stochastic variation of wind conditions (speed and direction). The net power generation for a particular farm size and installed capacity are maximized for different distributions of wind speed and wind direction, using the Unrestricted Wind Farm Layout Optimization (UWFLO) methodology. A response surface is constructed, using the recently developed Reliability Based Hybrid Functions (RBHF), to represent the computed maximum power generation as a function of the parameters of the wind velocity (speed and direction) distribution. To this end, for any farm site, we can (i) estimate the parameters of wind velocity distribution using recorded wind data, and (ii) predict the maximum power generation for a specified farm size and capacity, using the developed response surface. The WPPE model is validated through recorded wind data at four differing stations obtained from the North Dakota Agricultural Weather Network (NDAWN). The results illustrate the variation of wind conditions and, subsequently, its influence on the quality of a wind resource.
A Model for a Geothermal Well in a Hydraulic Groundwater Flow for Ground Source Heat Pump Systems
Authors: Woods Kevin D. , Ortega Alfonso
Published: March 2012

Heat pumps are mechanical systems that provide heating to a space in the winter, and cooling in the summer. They are increasingly popular because the same system provides both cooling modes, depending on the direction of the cycle upon which they operate. For proper operation, the heat pump must be connected to a constant temperature thermal reservoir which in traditional systems is the ambient air. In ground source heat pumps however, subterranean ground water is used as the thermal reservoir. To access the subterranean groundwater, “geothermal” wells are drilled into the formation. Water from the building heating or cooling system is circulated through the wells thereby promoting heat exchange between the coolant water and the subterranean formation. The potential for higher efficiency heating and cooling has increased the utilization of ground source heating ventilating and air conditioning systems. In addition, their compatibility with a naturally occurring and stable thermal reservoir has increased their use in the design of sustainable or green buildings and man-made environments. Groundwater flow affects the temperature response of thermal wells due to advection of heat by physical movement of groundwater through the aquifer. Research on this subject is scarce in the geothermal literature. This paper presents the derivation of an analytical solution for thermal dispersion by conduction and advection from hydraulic groundwater flow for a “geothermal” well. This analytical solution is validated against asymptotic analytical solutions. The traditional constant linear heat source solution is dependent on the ground formation thermal properties; the most dominant of which is the thermal conductivity. The results show that as hydraulic groundwater flow increases, the influence of the ground formation thermal conductivity on the temperature response of the well diminishes. The diminishing influence is evident in the Peclet number parameter; a comparison of thermal advection from hydraulic groundwater flow to thermal conduction by molecular diffusion.
Performance and Economic Analysis of Double Pass Solar Air Collector
Authors: Gupta Akhilesh , Kumar Ravi , Ramani Bharat
Published: March 2012

Solar collector is a type of heat exchanger which transfers solar radiation energy into the heat energy. Conventional solar air collectors have poor thermal efficiency primarily due to high heat losses and low convective heat transfer coefficient between the absorber plate and flowing air stream, leading to higher absorber plate temperature and greater thermal losses. Attempts have been made to improve the thermal performance of conventional solar air collectors by employing various design and flow arrangements. Double pass counter flow solar air collector with porous material in the second air passage is one of the important and effective design improvement that has been proposed to improve the thermal performance. This paper presents the performance and economic analysis of double pass solar air collector with and without porous material. Effects of various parameters on the thermal performance and pressure drop characteristics have been studied experimentally. The study concludes that double pass arrangement with porous material is economical and having short payback period. Also, the thermal performance of double pass solar air collector with porous material is significantly higher compared to double pass solar air collector without porous material and single pass arrangement.
Power Output Fluctuation Analysis of Grid-Connected Wind Turbine-Generator System With Limiting Maximum Power Output
Authors: Wakui Tetsuya , Yokoyama Ryohei
Published: March 2012

The reduction in the power output fluctuation of grid-connected wind turbine-generator systems is strongly required to further increase their total installed capacity in Japan. This study focuses on limiting the maximum electric power output by changing the set point of the power output control as a reduction technique. The influence of limiting the maximum electric power output of a 2 MW-system, which adopts the variable speed operation, on the power output fluctuation characteristic is analyzed through numerical simulation conducted by using an observed field wind data. The focus is on the power output fluctuation, which is important for management of commercial power systems including power plants, of the 2 MW-system with six cases of the maximum electric power output. The results show that limiting the maximum electric power output does not have an influence on the power output fluctuation characteristic and control performance during the pitch angle operation at high wind speeds. However, the year-round simulation reveals that limiting the maximum electric power output brings a tradeoff between the reduction in the power output fluctuation and the generating performance.
Life Cycle Energy and Exergy Analysis for Building Cooling Systems: A Comparison Between a Solar Driven Absorption Chiller and an Electric Driven Chiller
Authors: Hu Yang , Schaefer Laura A. , Hartkopf Volker
Published: March 2012

Buildings in the United States utilize 39% of the primary energy, and more than 60% of that energy consumption is provided for heating and cooling in buildings. Most of the heating and cooling systems commercially available in the market today are driven by electricity and natural gas, which are high exergy resources, while the operating temperature in the building from a year-round perspective is closer to the reference environmental temperature. Thus, from a thermodynamic point of view, there exists a gap between the high exergy resources/supply and low exergy application/demand in buildings. This paper extends the traditional means of energy comparison between solar driven absorption chillers and electric driven chillers. A life cycle energy and exergy analysis is developed with the assumption that the fossil fuel for electricity generation is a different form of storing solar energy in the long run. Thus, both the systems are driven by solar energy, and the only difference is that the solar absorption chiller is an instantaneous solar energy utilization, while the electricity chiller utilizes the stored solar energy. A simple absorption chiller model is developed, and is calibrated using a paper published by the Center for Building Performance and Diagnostics in Carnegie Mellon University, using a 4-ton 2-stage absorption chiller provided by Broad Air Conditioning. The energy and exergetic efficiencies in each process are analyzed and provided in the two systems. This paper is useful in understanding the fundamental life cycle energy and exergy in chiller applications for building cooling.
Residential Energy Analysis: Regression Analysis of Heating Degree Days With Temperature Setback for Selected ASHRAE Climate Zones
Authors: Kearns Patrick A. , Krarti Moncef
Published: March 2012

Heating Degree Days (HDDs), calculated from hourly weather data, are often used to estimate energy savings for a variety of energy efficiency measures (EEMs) to be applied to conditioned spaces in buildings. More specifically, application of HDDs is useful for estimating savings from weather-dependent EEMs. For first order estimation, it is often problematic to calculate HDDs for a given base temperature, when temperature setbacks are used in the conditioned spaces. This paper provides a set of correlations to characterize HDDs for selected ASHRAE Climate Zones as functions of three key parameters including the base temperature, setback temperature level (delta-T), and setback duration. In addition to the well-documented pattern of decreasing HDDs for decreasing base temperature, it was also shown that HDDs are inversely proportional to both setback duration and temperature setback differential levels. In the analysis presented in this paper, corrections to estimate HDDs when temperature setbacks are used for typical residential space heating schedules during unoccupied periods which occurred from 8 am to 5 pm Monday through Friday. In particular, regression correlations using two- and three-parameter models have been developed to estimate HDDs for multiple US locations that account for the impact of temperature setbacks on the heating requirements of residential buildings. For the two-parameter model, the input variables for the regression correlations are setback hours and delta T; for the three-parameter model, the input variables for the correlations include setback hours, delta T, and base temperature. The prediction accuracy for the energy savings, due to a set of EEMs, obtained from the HDD method —using the developed correlations— is tested against whole-building detailed energy simulation analysis for two single family homes. Detailed energy audits including utility data analysis have been carried out for both homes to calibrate the detailed simulation model and evaluate the effectiveness of the EEMs in reducing building energy use. The results from the detailed simulation analysis are then compared to those obtained from the HDD with temperature setbacks.
Development of a Reactor for Continuous Electrochemical Reduction of CO2 Using Solid Electrolyte
Authors: Aeshala L. M. , Rahman S. U. , Verma A.
Published: March 2012

This paper reports the development of an electrochemical reactor for electrochemical reduction of carbon dioxide using anionic and cationic solid electrolyte. Cast nafion membrane was used as cation exchange membrane and alkali doped polyvinyl alcohol cross-linked with glutaraldehyde was used as anion exchange membrane. The anion exchange membranes (solid electrolytes) were characterized using TGA, XRD, FTIR, anionic conductivity, and mechanical strength. The anode electrode was prepared using Pt/C spraying over porous carbon paper. The cathode electrode was prepared using copper electroplating technique over porous carbon paper. The prepared electrodes were characterized using scanning electron microscope. The reactor was assembled with the electrolyte, electrodes, machined graphite plates, and end plates with the required accessories. The preliminary study of the reactor was evaluated for carbon dioxide electrochemical reduction under anionic and cationic electrolytes. The products of the electrochemical reduction of CO2 were analyzed using GC and HPLC.
Life Cycle Assessment of a Reflective Foil Material and Comparison With Other Solutions for Thermal Insulation of Buildings
Authors: Desideri U. , Proietti S. , Zepparelli F. , Sdringola P. , Cenci E.
Published: March 2012

In the last twenty years, the exploitation of non-renewable resources and the effects of their applications on environment and human health were considered central topics in political and scientific debate on European and worldwide scale. This kind of resources have been used in different sectors, as energy systems, technological research, but also in private/public buildings and production of consumer goods, involving significantly domestic and ordinary life of every human being. Studies about the effect of this exploitation carried out discouraging results, in terms of climate changes and energy sustenance; this determined a progressive approach process to a new concept of development, able to couple the qualitative standard of modern life with the respect of planet and its inhabitants. Starting from this reflection, scientific community moved towards research on alternative resources and developed a new way to conceive planning process and technical innovations, in order to exploit renewable energies and recycled materials, promote energy savings and reduce environmental pollution. In this context the present paper aims at evaluating benefits relating to different solutions of thermal insulation in building envelope. In fact a high grade of insulation ensures better comfort conditions in inner spaces, reducing energy consumptions due to heating and cooling conditioning. The paper presents the results of a detailed Life Cycle Assessment (LCA) of the reflective foil ISOLIVING, conceived and produced by an Italian company. The Life Cycle Assessment methodology allows to consider all stages of the life cycle, from the extraction of raw materials to the product’s disposal, in an optics “from cradle to grave.” In particular, the study takes into account the production phase of the reflective foil ISOLIVING, the installation phase, the transport of all components to the production site and also the end of life scenario of the material. The possibility to collect many detailed information about the production phase adds value to the study. The analysis is carried out according to UNI EN ISO 14040 and UNI EN ISO 14044, which regulate the LCA procedure. The LCA modeling was performed using SimaPro software application. The results of the analysis allow to make an important comparison concerning the environmental performances, between the reflective foil ISOLIVING and other types of insulating materials.
Analysis of Distribution Feeder Losses due to Addition of Distributed Photovoltaic Generators
Authors: Tuffner Francis , Singh Ruchi
Published: March 2012

Distributed generators (DG) are small scale power supplying sources owned by customers or utilities and scattered throughout the power system distribution network. Distributed generation can be both renewable and non-renewable. Addition of distributed generation is primarily to increase feeder capacity and to provide peak load reduction. However, this addition comes with several impacts on the distribution feeder. Several studies have shown that addition of DG leads to reduction of feeder loss. However, most of these studies have considered lumped load and distributed load models to analyze the effects on system losses, where the dynamic variation of load due to seasonal changes is ignored. It is very important for utilities to minimize the losses under all scenarios to decrease revenue losses, promote efficient asset utilization, and therefore, increase feeder capacity. This paper will investigate an IEEE 13-node feeder populated with photovoltaic generators on detailed residential houses with water heater, Heating Ventilation and Air conditioning (HVAC) units, lights, and other plug and convenience loads. An analysis of losses for different power system components, such as transformers, underground and overhead lines, and triplex lines, will be performed. The analysis will utilize different seasons and different solar penetration levels (15%, 30%).
The Wind Shear Exponent: Comparing Measured Against Simulated Values and Analyzing the Phenomena That Affect the Wind Shear
Authors: Bratton Daniel C. , Womeldorf Carole A.
Published: March 2012

When assessing a region for wind energy the wind shear is a key factor to consider because of its profound effect on power density as a function of height. Traditionally, wind shear parameters are derived either from local velocity measurements at two or more heights or from surface roughness characteristics to predict the wind speed at hub height for a particular site. However, recent measurements in a complex terrain (non-mountainous) region indicate that the measured wind shear exponent is significantly higher than the value predicted by land use characteristics and modeled results. Virtual wind shear parameters: alpha and zo, created by the modeled flow fields of the complex terrain of southeastern Ohio’s Appalachian foothills are determined with computational fluid dynamics simulations designed for complex terrain. Then the first year’s measurements from the extra-tall tower in the region provide a direct evaluation of the wind shear parameters: alpha and zo. These values, characteristic of the measurements, are compared against values determined from the local land use characteristics as well as those found by modeling with a computational fluid dynamics wind simulator. It has been found that the measured value of the wind shear exponent is larger, by a factor of 2, than the values currently used in published state wind maps. Phenomena affecting wind shear are also analyzed. Diurnal and changes in reference heights have large effects on the measured wind shear. It is demonstrated that for this site an overall annual average value of the wind shear coefficient is an inaccurate representation of the wind shear because of the range of variability that occurs seasonally. It is also shown that extrapolating from near-surface measurements to hub heights can yield inaccurate predictions of wind speed and, more importantly, wind power.