bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Evaluation and Outlook of Utility-Scale Linear Fresnel Technology
Authors: Zhu Guangdong , Wagner Mike , Wendelin Tim , Kutscher Chuck
Published: December 2013

As one of the viable concentrating solar power (CSP) technologies, linear Fresnel collectors differ from parabolic troughs by virtue of their low-profile mirror arrays and fixed receiver assemblies. This technology is capable of achieving high concentration ratios and so is applicable to high-temperature solar power plant designs. In addition, its low wind profile and linear nature lead to low system and operation and maintenance (O&M) costs.

In this report two linear Fresnel solar plant configurations, namely a direct steam generation (DSG) system and a direct high-temperature molten-salt plant, are examined via a levelized cost of electricity (LCOE) analysis. By treating LCOE as a function of the annual investment energy return (IER, or the ratio of annual net electricity to the total direct system cost) under various assumptions of O&M cost, a few plant scenarios employing high-temperature linear Fresnel technology are carefully configured to meet the aggressive LCOE goals of 8 cents/kWh and 6 cents/kWh. The latter is the Department of Energy (DOE) SunShot Initiative goal aimed at making CSP cost competitive in the current energy market. In particular, a linear Fresnel scenario with the potential to meet the SunShot goal is featured with a collector cost of $100/m2, an annual system energy efficiency of 18%, a storage system cost of $15/kWh-th, and an O&M cost of $7.5/MWh. One of the most aggressive assumptions is an advanced power block with about 52% cycle efficiency and a turbine inlet temperature of 700°C.

This work addresses unanswered questions regarding linear Fresnel cost and performance and identifies future research and development directions for linear Fresnel technology, including economic optimization of collectors and receivers, development of physical plant performance models, development of automated O&M mechanisms and sophisticated plant control software.
Improving the Efficiency of Stirling Engines for Use in Solar Distributed Electricity, Heating, and Cooling
Authors: Schubert Travis M. , Jouzdani Shirin , Hallinan Kevin P.
Published: December 2013

Limiting solar power is the inability to cost effectively store energy. The most cost effective means to store solar energy is thermally in the ground, which can then be used for direct conversion to electricity. However, doing so is limited by a historically poor thermal efficiency of such engines. A novel Stirling engine is posed which more closely mimics a Carnot heat engine. It does this through the use of a new passive thermal ‘switch’ which permits heat flow into the expansion chamber of the Stirling engine only when the temperature of the chamber is above a desired value. Ideally heat would be added only at the end of the compression stroke and the beginning of the expansion stroke. Central to this thermal switch is the use of a vanadium dioxide (VO2) low mass heat exchanger internal to the expansion chamber. This low mass heat exchanger allows the film material to track and react to the temperature changes within the expansion chamber, permitting it to transfer heat only when needed. An adiabatic model of this enhanced solar Stirling engine is developed. Results indicate that the thermal efficiency can be nearly doubled, delivering a second law efficiency of over 0.6. Further, a year round overall efficiency accounting for losses in the Stirling engine and solar thermal collectors of 7% appears to be feasible when this engine is integrated with ground solar storage, providing the necessary power to meet loads in a low energy residence. Such results demonstrate promise for future application of this technology.
Development of Ammonia-Water Absorption Heat Pump Water Heater for Residential and Commercial Applications
Authors: Garrabrant Michael , Stout Roger , Glanville Paul , Keinath Chris , Garimella Srinivas
Published: December 2013

Approximately half of the water heaters sold in the U.S. and Canada for residential and small commercial applications are natural gas fired storage water heaters, with a maximum theoretical thermal efficiency of 96%. A packaged water heater heated by a 2.9 kW absorption heat pump was designed and demonstrated in this study to achieve performance exceeding these limitations. The modeling and validation of the absorption cycle and of the natural gas-fired combustion system are discussed here. Heat transfer characteristics of the absorption components at expected operating conditions were used to model cycle performance. A single-effect system based on these models was fabricated and yielded a cyclic COP of 1.63, within 3% of predictions. A corresponding GAX cycle-based system yielded performance 20% lower than predicted values, indicating the need for larger heat and mass exchangers to achieve the expected system level performance. The gas-fired burner configuration required for this heat pump is governed by the water heater envelope, desorber geometry and process requirements, coupled with emissions requirements. Parametric CFD analyses were conducted to estimate the impact of chamber design on burner performance, and revealed a beneficial recirculation pattern within the combustion chamber that was strongly influenced by chamber height. Emission reductions depended on chamber diameter, and prototype burners with smaller outer diameter fabricated based on these designs met emission targets.
Optimization Study of a Hybrid Solar Air Conditioner
Authors: Al-Alili Ali , Hwang Yunho , Radermacher Reinhard
Published: December 2013

In order for the solar air conditioners (A/Cs) to become a real alternative to the conventional systems, their performance and total cost has to be optimized. In this study, an innovative hybrid solar A/C was simulated using the transient systems simulation (TRNSYS) program, which was coupled with MATLAB in order to carry out the optimization study. Two optimization problems were formulated with the following design variables: collector area, collector mass flow rate, storage tank volume, and number of batteries. The Genetic Algorithm (GA) was selected to find the global optimum design for the lowest electrical consumption. To optimize the two objective functions simultaneously, a Multi-Objective Genetic Algorithm (MOGA) was used to find the Pareto front within the design variables’ bounds while satisfying the constraints. The optimized design was also compared to a standard vapor compression cycle. The results show that coupling TRNSYS and MATLAB expands TRNSYS optimization capability in solving more complicated optimization problems.
Guidelines for CSP Yield Analysis: Definition of Elementary Terms
Authors: Hirsch Tobias , Bachelier Camille , Dersch Jürgen , Eck Markus , Feldhoff Jan Fabian , García-Barberena Labiano J. , Gertig Christian , Kretschmann David , Morin Gabriel
Published: December 2013

With the success of CSP technology in the last years more players are active in the market, inducing the need for harmonization of technical terms and methodologies. The mission of the SolarPACES “guiSmo” project which was started in 2010 is to develop a guideline for CSP yield analysis [1]. Activities carried out so far have shown that people have different understandings of many terms used in daily CSP practice. Especially for the development of guidelines, the essential terms need to be clearly defined in order to avoid inconsistencies within the same project. A first version of a nomenclature has been compiled by the “guiSmo” team and will undergo final discussion. The aim is to come to a harmonized version by Summer 2013 which will then be presented at the ASME Energy Sustainability conference. The compilation so far includes essential definitions of terms like direct normal irradiance, incident angles, heat flows, and efficiencies on a system level. The definitions presented will be discussed together with existing standards like the ISO 80000 (physical quantities and units of measurement), the ISO 9488 (Solar energy-vocabulary) and other relevant sources. Although the list of terms is primarily put together for the work in the “guiSmo” project, it might serve as a basis for standardization in the official councils. An international group of solar experts is involved in the preparation of the document in order to ensure high quality and international support for the results.
VAV System Operating in an Educational Building Under Tropical Conditions: Energy Analysis
Authors: Alvarez Oscar , Sanjuan Marco , Amaya Fabian , Bula Antonio
Published: December 2013

An educational building located in the Caribbean area of Colombia that uses a VAV system has been monitored in order to quantify the energy consumption. The energy values attained has been compared with a simulation of the building running with a constant volumetric flow system. The results show that a 43% and 18% energy reduction can be achieved for the ventilation system and for the entire air conditioning system that includes a chiller with variable primary pump, a variable air volume system and a variable cooling tower fan.
Morfoplane: Energetic Analysis of a Novel Green Aerial Vehicle Concept
Authors: Trancossi Michele , Dumas Antonio , Madonia Mauro
Published: December 2013

Costs of Helium are increasing more rapidly than provided by economic analysts because of the high demanded if compared with actual production possibilities. These economic disadvantages are slowing many airship projects, because of the necessary costs that need to be faced for initial inflation. They are forcing the definition of novel airship architectures which could use hydrogen as buoyant gas with a higher level of safety than in the past.

This paper starts from those economic issues to define a general model based on the variable volume airship defined in the MAAT cruiser-feeder airship project. It defines a future hydrogen airships concept which could avoid the disasters of the past and maximize the safety of people and goods.

The model has been compared with the results of an optimization of the very general airship conceptual design based on Constructal theory. The goal of the optimization has been defined in terms of maximization of solar energy caption possibility, minimization of frontal area, volume, and energy consumption at a predefined operative altitude. A surprising accordance of the proposed model with the results of the Constructal optimization results has been obtained.

A comparison with a traditional model of airship has been performed and results have been validated by CFD simulation at different altitudes.
Solar-Assisted Heat Pump Systems: A Review of Existing Studies and Their Applicability to the Canadian Residential Sector
Authors: Chu Jenny , Cruickshank Cynthia A.
Published: December 2013

Heat pumps are commonly used for space-heating and cooling requirements. The combination of solar thermal and heat pump systems as a single solar-assisted heat pump (SAHP) system is a promising technology for offsetting domestic hot water, space-heating and cooling loads more efficiently. Task 44 of the Solar Heating and Cooling Programme of the International Energy Agency is currently investigating ways to optimize SAHP systems for residential use. This paper presents a review of past and current work conducted on SAHP systems. Specifically, the key performance data from many studies are highlighted and different system configurations are compared in order to establish insight towards which system configurations are suitable for the Canadian residential sector.

It was found that the most suitable configuration for Canadian residential buildings depend on a combination of factors which may include occupant behavior, building characteristics, operation parameters, system components, the performance criteria of interest and climate. A large variety of configurations and parameters exist for SAHP systems and this made analyzing a specific system, comparing differing systems and establishing an optimal design fairly difficult. It was found that different authors used various different performance criterions and this inconsistency also added to the difficulty of comparing the studies of different systems. Overall, a standard performance criterion needs to be established for SAHP systems in order to meaningfully compare different configurations and determine optimal configurations for certain requirements.
A 5 kWht Lab-Scale Demonstration of a Novel Thermal Energy Storage Concept With Supercritical Fluids
Authors: Ganapathi Gani B. , Berisford Daniel , Furst Benjamin , Bame David , Pauken Michael , Wirz Richard
Published: December 2013

An alternate to the two-tank molten salt thermal energy storage system using supercritical fluids is presented. This technology can enhance the production of electrical power generation and high temperature technologies for commercial use by lowering the cost of energy storage in comparison to current state-of-the-art molten salt energy storage systems. The volumetric energy density of a single-tank supercritical fluid energy storage system is significantly higher than a two-tank molten salt energy storage system due to the high compressibilities in the supercritical state. As a result, the single-tank energy storage system design can lead to almost a factor of ten decrease in fluid costs. This paper presents results from a test performed on a 5 kWht storage tank with a naphthalene energy storage fluid as part of a small preliminary demonstration of the concept of supercritical thermal energy storage. Thermal energy is stored within naphthalene filled tubes designed to handle the temperature (500 °C) and pressure (6.9 MPa or 1000 psia) of the supercritical fluid state. The tubes are enclosed within an insulated shell heat exchanger which serves as the thermal energy storage tank. The storage tank is thermally charged by flowing air at >500 °C over the storage tube bank. Discharging the tank can provide energy to a Rankine cycle (or any other thermodynamic process) over a temperature range from 480 °C to 290 °C. Tests were performed over three stages, starting with a low temperature (200 °C) shake-out test and progressing to a high temperature single cycle test cycling between room temperature and 480 °C and concluding a two-cycle test cycling between 290 °C and 480 °C. The test results indicate a successful demonstration of high energy storage using supercritical fluids.
Passive Cooling With Phase Change Material Energy Storage
Authors: Omojaro Peter , Breitkopf Cornelia , Omojaro Simon
Published: December 2013

A passive induced cooling system using phase change material (PCM) energy storage is presented in this analysis for providing indoor cooling and energy saving. Also, the latent heat performance of the PCM is analyzed. The supplied cooling capacity was evaluated using an indoor cooling temperature performance while the PCM characteristic performance was achieved by relating the applications sensible heat ratio efficiency to the charging and discharging effectiveness of the PCM. This is carried out for an office building in a warm humid climate. Obtained result delivered 24.54 % of the required indoor cooling load for 24°C indoor cooling temperature. Moreover, delivered indoor cooling capacity increased at constant increasing mean indoor temperature and PCM melting temperatures. Application sensible heat ratio efficiency was 77.66 % and average energy saving of 37.77 % in total energy operation cost was obtained. A CO2 emission reduction of 0.071 tons can also be achieved by the system.
Design and Analysis of Metal Foam Enhanced Latent Thermal Energy Storage With Embedded Heat Pipes for Concentrating Solar Power Plants
Authors: Nithyanandam K. , Pitchumani R.
Published: December 2013

Thermal energy Storage is a critical component of Concentrating Solar Power (CSP) plant, enabling uninterrupted operation of plant during periods of cloudy or intermittent solar weather. Investigations of Latent Thermal Energy Storage (LTES) which utilizes Phase Change Material (PCM) as a heat storage medium is considered due to its high energy storage density and low capital cost. However, the low thermal conductivity of the PCM restricts the solidification rate of the PCM leading to inefficient heat transfer between the PCM and the HTF which carries thermal energy to the power block. To address this, LTES embedded with heat pipes and PCM’s stored within the framework of porous metal foams possessing one to two orders of magnitude higher thermal conductivity than the PCM are considered in the present study. A transient, computational analysis of the metal foam (MF) enhanced LTES system with embedded heat pipes is performed to investigate the enhancement in the thermal performance of the system for different arrangement of heat pipes and design parameter of metal foams, during both charging and discharging operation.
Carbon Particle Generation and Preliminary Small Particle Heat Exchange Receiver Lab Scale Testing
Authors: Frederickson Lee , Kitzmiller Kyle , Miller Fletcher
Published: December 2013

High temperature central receivers are on the forefront of concentrating solar power research. Current receivers use liquid cooling and power steam cycles, but new receivers are being designed to power gas turbine engines within a power cycle while operating at a high efficiency. To address this, a lab-scale Small Particle Heat Exchange Receiver (SPHER), a high temperature solar receiver, was built and is currently undergoing testing at the San Diego State University’s (SDSU) Combustion and Solar Energy Laboratory. The final goal is to design, build, and test a full-scale SPHER that can absorb 5 MWth and eventually be used within a Brayton cycle.

The SPHER utilizes air mixed with carbon particles generated in the Carbon Particle Generator (CPG) as an absorption medium for the concentrated solar flux. Natural gas and nitrogen are sent to the CPG where the natural gas undergoes pyrolysis to carbon particles and nitrogen is used as the carrier gas. The resulting particle-gas mixture flows out of the vessel and is met with dilution air, which flows to the SPHER.

The lab-scale SPHER is an insulated steel vessel with a spherical cap quartz window. For simulating on-sun testing, a solar flux is produced by a solar simulator, which consists of a 15kWe xenon arc lamp, situated vertically, and an ellipsoidal reflector to obtain a focus at the plane of the receiver window. The solar simulator has been shown to produce an output of about 3.25 kWth within a 10 cm diameter aperture. Inside of the SPHER, the carbon particles in the inlet particle-gas mixture absorb radiation from the solar flux. The carbon particles heat the air and eventually oxidize to carbon dioxide, resulting in a clear outlet fluid stream.

Since testing was initiated, there have been several changes to the system as we have learned more about the operation. A new extinction tube was designed and built to obtain more accurate mass loading data. Piping and insulation for the CPG and SPHER were improved based on observations between testing periods. The window flange and seal have been redesigned to incorporate window film cooling. These improvements have been made in order to achieve the lab scale SPHER design objective gas outlet flow of 650°C at 5 bar.
Evaluation of Air Recirculation for Falling Particle Receivers
Authors: Ho Clifford K. , Christian Joshua M.
Published: December 2013

This paper presents simulations and designs of a prototype falling particle solar receiver with air recirculation as a means of mitigating heat loss and impacts of external wind on particle flow. The flow and dispersion of different sizes of ceramic proppant (CARBO HSP) particles (1 mm, 100 μm, and 10 μm) were simulated in recirculating air flows without heating effects. Particles on the order of 0.1–1 mm yielded desirable simulated flow patterns when falling through the cavity receiver with an air-injection velocity of 3 m/s. Simulations of smaller particles on the order of 10 microns yielded unstable flow patterns that may lead to large losses of particles through the aperture. A prototype cavity receiver with air recirculation was designed and fabricated to validate the unheated simulations. The blower nozzles and suction plenum were engineered to yield the most uniform flow pattern along the entire width of the aperture. Observed and simulated air velocity distributions around the aperture and particle flow patterns using CARBO HSP particles with an average diameter of ∼0.7 mm were found to be qualitatively similar.
Design and Construction of a Solar Thermal Refrigeration System for Patna, India
Authors: Winter Björn Oliver , Louco Lathom , Kissock Kelly , Mariadass Paul , Daniels Malcolm
Published: December 2013

This paper describes the design and construction of a solar thermal adsorption refrigerator in Patna, Bihar, India. After a brief description of the local situation and planning prerequisites the reasons for choosing an ethanol based adsorption system are explained. The following sections are focused on the description of the design and the theory behind the system. Lastly, practical aspects that arose during the construction of the first prototype are mentioned.
HVAC Sustainability Research Park
Authors: Shaligram Avinash , Deshpande Rajesh
Published: December 2013

Energy Crisis and Environment Balance have been occupying a leading position internationally in both, the sociopolitical arena and technological developments. A developing country like India is under dual pressure to provide economic prosperity to its burgeoning population while maintaining the energy-environment balance. Current challenging situation is a good opportunity to develop products and systems which not only provide customer satisfaction at competitive prices but also does it in a sustainable, resource-friendly way. This paper outlines a proposal to set up a Research Park in an academic institute with the theme of Sustainability in HVAC field. The idea is to collaborate with the industry and association partners so that the students and faculty together can work on joint R & D projects which ultimately will result into innovative energy-saving and environment-friendly technological products and systems. The metric on which the Research Park will base its output target is the reduction in greenhouse gas emissions through a multi-pronged approach. In this paper, a baseline of annual energy consumption by the HVAC sector in India has been drawn which works out to 137,026 GWh translating into 123.32 Million Metric Tonnes of CO2 equivalent emissions.
Gas Turbine-Based Combined Cycle Power Plant Modeling and Effects of Ambient Temperature
Authors: Shaw Paul , Zabihian Farshid , Fung Alan S.
Published: December 2013

This paper presents results of the combined cycle power plant (CCPP) modeling when the ambient temperature is varying. The model of the CCPP was developed using a gas turbine and a heat recovery steam generator (HRSG) models that had been already developed and validated. The model of the components was developed based on an actual existing power plant and then the operational data of the power plant was used to validate the model. The results of running the model for various ambient temperatures demonstrated that the performance of the gas turbine part of the cycle was heavily affected by the changes in the ambient temperature, particularly the output power of the gas turbines. However, the performance of the steam cycle was almost untouched by the changes of ambient temperature. This suggests that operation of the CCPP is more stable than stand-alone gas turbine in hot summer days especially if the cycle is not equipped with an inlet air cooling system.
Development of a Tool to Calibrate Vertical Ground Heat Exchanger Model Using Optimization
Authors: Mun Junghyon , Tao Yong
Published: December 2013

This paper presents a calibration process and its tool of the vertical ground heat exchanger model used in a building energy simulation program, Energyplus. To adequately analyze the performance of the system, calibration of the system model is crucial. The calibration procedure is to estimate input data of the simulation that match the results of the simulation with measured data by an inverse method. The vertical ground loop heat exchanger consists of ground and borehole systems. The thermal properties of the borehole system usually can be found from manufacturer’s data. However, the thermal property of the ground is hard to evaluate. In this paper, an evaluation tool of the thermal properties of the ground around the borehole is developed using Matlab. This tool consists of three submodels. The first one is a G-function curve fit model which represents the relationship between variation of thermal conductivity and g-function values. The second model is the vertical ground loop heat exchanger model which predicts the return water temperature from a ground loop heat exchanger using the short time response factor method. The vertical ground loop heat exchanger model in Energyplus is converted to Matlab code and integrated into the calibration model for this research. The last sub-model is the optimization model that uses the Nelder and Mead simplex optimization scheme to find parameters which minimize the difference between the simulation results and the field measurement data. This tool estimates the ground thermal propertiesusing an optimization scheme based on data collected from field measurement. Far field ground temperature and the ground thermal conductivity are estimated to be used as input data of the vertical ground loop heat exchanger model in Energyplus. This program is validated using a case study which is performed for an actual building, ZOE which is located in the University of North Texas and its system. 2 weeks’ measurement data were compared with the simulation result. The average deviation between the simulation result and measurement data for 2 weeks is 0.27 °C.
Application Study of a CCHP System Operating With the Flue Gas and Geothermal Energy
Authors: Zhao Xiling , Fu Lin , Wang Xiao
Published: December 2013

Because of the performance of the power generation equipment is almost perfect, how to integrate the thermally-activated technologies and use the waste heat deeply are a critical issue for CCHP (Combined cooling heating and power) system. According to the characteristics of a typical end user’s demands, a CCHP system with the flue gas and geothermal energy is proposed. The system is composed of an internal combustion engine, a soil source absorption heat pump driven by the flue gas, and other assistant facilities, such as pumps, fans, and end user devices. In the winter, the flue gas is used to drive absorption heat pump to recover the waste heat of the soil source and the condensation heat of the flue gas simultaneously, and in the summer, the waste heat of the flue gas is used to drive absorption heat pump to cooling, and the heat sink is the soil. In the paper, the energy analysis of the system is done. Compared with the conventional CCHP system, the operation cost is lowered greatly and the increased investment could be returned within one year. It is show that the system is the efficient integration of clean energy, renewable energy, the discharge of the flue gas could be reduced to below 30°C, and the water steam could be catch to avoid the white smoke of the stack.
Phase Change Salt Thermal Energy Storage for Dish Stirling Solar Power Systems
Authors: White Maurice , Qiu Songgang , Galbraith Ross
Published: December 2013

The ability of thermal energy storage (TES) to avoid the major intermittency issues associated with solar photovoltaic power generation is a key differentiator for concentrating solar power (CSP) systems. Infinia Corporation is a pioneer in phase change salt TES systems, with one DOE contract based on heat pipes [1], and a second DOE contract that uses an inherently simpler, patented sodium pool boiler that is integral with the TES salt. This paper describes the Phase 1 results for that second contract, which is targeted for cost effective extended duration storage for CSP systems up to a level that can provide baseload power, with a particular focus on dish Stirling systems.
Comparison and Analysis for the Differential Heating Modes in the Large-Scale CHP System
Authors: Lin Zhen Xian , Fu Lin
Published: December 2013

With the process acceleration of China’s energy conservation and the full development of the market economy, the environmental protection is to coexist with the power plants’ benefits for thermal power plants. Relative to the traditional mode named “determining power by heat”, it is not adequate that the heating demand is only to be met, the maximizations of economy benefits and social benefits are also demanded. At present, several large-scale central heating modes are proposed by domestic and foreign scholars, such as the parallel arrangement and series arrangement of heating system for the traditional heating units and NCB heating units (NCB heating unit is a new condensing-extraction-backpressure steam turbine and used to generate the power and heat, it has the function of extraction heating turbine at constant power, back pressure turbine or extraction and back pressure heating turbine and extraction condensing heating turbine.), and running mode with heating units and absorbed heat pumps, and so on. Compare and analyze their heating efficiency, heating load, heating area, power generation, and the impact on the environment. The best heating mode can be found under the different boundary conditions, it can be used to instruct the further work. The energy utilization efficiency will be further improved.
Heat Pipe Solar Receivers for Concentrating Solar Power (CSP) Plants
Authors: Cao Yiding
Published: December 2013

This paper introduces separate-type heat pipe (STHP) based solar receiver systems that enable more efficient operation of concentrated solar power plants without relying on a heat transfer fluid. The solar receiver system may consist of a number of STHP modules that receive concentrated solar flux from a solar collector system, spread the high concentrated solar flux to a low heat flux level, and effectively transfer the received heat to the working fluid of a heat engine to enable a higher working temperature and higher plant efficiency. In general, the introduced STHP solar receiver has characteristics of high heat transfer capacity, high heat transfer coefficient in the evaporator to handle a high concentrated solar flux, non-condensable gas release mechanism, and lower costs. The STHP receiver in a solar plant may also integrate the hot/cold tank based thermal energy storage system without using a heat transfer fluid.
Spherical Tanks for Use in Thermal Energy Storage Systems
Authors: Khan Fahad , Savilonis Brian J.
Published: December 2013

Thermal energy storage (TES) is a vital component of concentrated solar power (CSP). TES makes up for intermittent solar radiation, bad weather, and peak power demand. Currently, a sensible heat storage system using two tanks containing molten salt is considered the most practical and economical TES. Yet further system development is needed in order to improve its performance and economics.

In this study of molten salt storage tanks, spherical tanks were investigated as an alternative to cylindrical tanks. Structural and thermal aspects of cylindrical tanks with varying H/D ratios (0.25–5) and spherical tanks of the same volume were compared.

Comparison showed that utilization of spherical instead of cylindrical tanks resulted in significant savings in shell building material (28–47%). Heat transfer from the spherical tank’s shell is at least 35% less than cylindrical tanks. Reduction in building material, foundation, and insulation cost can lead to significant cost savings.
Experimental Study of Natural Gas Combustion Flue Gas Waste Heat Recovery System Based on Direct Contact Heat Transfer and Absorption Heat Pump
Authors: Zhou Xian , Liu Hua , Fu Lin , Zhang Shigang
Published: December 2013

Condensing boiler for flue gas waste heat recovery is widely used in industries. In order to gain a portion of the sensible heat and latent heat of the vapor in the flue gas, the flue gas is cooled by return water of district heating through a condensation heat exchanger which is located at the end of flue. At low ambient air temperature, some boilers utilize the air pre-heater, which makes air be heated before entering the boiler, and also recovers part of the waste heat of flue gas. However, there are some disadvantages for these technologies. For the former one, the low temperature of the return water is required while the utilization of flue gas heat for the latter one is very limited. A new flue gas condensing heat recovery system is developed, in which direct contact heat exchanger and absorption heat pump are integrated with the gas boiler to recover condensing heat, even the temperature of the return water is so low that the latent heat of vapor in the flue gas could not be recovered directly by the general condensing technologies. Direct contact condensation occurs when vapor in the flue gas contacts and condenses on cold liquid directly. Due to the absence of a solid boundary between the phases, transport processes at the phase interface are much more efficient and quite different from condensation phenomena on a solid surface. Additionally, the surface heat exchanger tends to be more bulky and expensive. In this study, an experimental platform of the new system is built, and a variety of experimental conditions are carried out. Through the analysis of the experimental data and operational state, the total thermal efficiency of the platform will be increased 3.9%, and the system is reliable enough to be popularized.
Demonstration Study of High-Efficiency Natural Gas CCHP
Authors: Liu Hua , Zhou Xian , Fu Lin , Zhao Xiling , Li Feng
Published: December 2013

Combined cooling heating and power (CCHP) systems based on natural gas is widely applied abroad, which have resulted in increasing domestic attention to distributed energy systems (DES). In order to reduce heat loss of exhaust-gas and recover condensation heat of it, an innovative system is advanced by Tsinghua, which can recover exhaust-gas condensation heat utilizing an exhaust-gas-driven absorption heat pump (AHP). In 2007, Tsinghua bears a research task from National Ministry of Science and Technology, that is, ‘Integration and Demonstration study of high-efficiency natural gas CCHP technique’. As a part, a natural gas CCHP system based on AHP has been set up at the Tsinghua University energy-saving building, in Beijing, China, and a lot of research has been made. As another part, a combined cooling heating and power (CCHP) project based on the gas-powered internal combustion engine (ICE) (electricity volume MW) is built in Beijing Southern Station. This paper mainly analyzes and introduces the running condition of this demonstration project.
Waste From Metallurgic Industry: A Sustainable High-Temperature Thermal Energy Storage Material for Concentrated Solar Power
Authors: Calvet Nicolas , Dejean Guilhem , Unamunzaga Lucía , Py Xavier
Published: December 2013

The ambitious DOE SunShot cost target ($0.06/kWh) for concentrated solar power (CSP) requires innovative concepts in the collector, receiver, and power cycle subsystems, as well as in thermal energy storage (TES).

For the TES, one innovative approach is to recycle waste from metallurgic industry, called slags, as low-cost high-temperature thermal energy storage material. The slags are all the non-metallic parts of cast iron which naturally rises up by lower density at the surface of the fusion in the furnace. Once cooled down some ceramic can be obtained mainly composed of oxides of calcium, silicon, iron, and aluminum. These ceramics are widely available in USA, about 120 sites in 32 States and are sold at a very low average price of $5.37/ton. The US production of iron and steel slag was estimated at 19.7 million tons in 2003 which guarantees a huge availability of material.

In this paper, electric arc furnace (EAF) slags from steelmaking industry, also called “black slags”, were characterized in the range of temperatures of concentrated solar power. The raw material is thermo-chemically stable up to 1100 °C and presents a low cost per unit thermal energy stored ($0.21/kWht for ΔT = 100 °C) and a suitable heat capacity per unit volume of material (63 kWht/m3for ΔT = 100°C). These properties should enable the development of new TES systems that could achieve the TES targets of the SunShot (temperature above 600 °C, installed cost below $15/kWht, and heat capacity ≥25 kWht/m3). The detailed experimental results are presented in the paper.

After its characterization, the material has been shaped in form of plates and thermally cycled in a TES system using hot-air as heat transfer fluid. Several cycles of charge and discharged were performed successfully and the concept was validated at laboratory scale. Apart from availability, low-cost, and promising thermal properties, the use of slag promotes the conservation of natural resources and is a noble solution to decrease the cost and to develop sustainable TES systems.
A Computational Analysis: A Honeycomb Flow Distributor With Porous Approximation for a Thermocline Thermal Energy Storage System
Authors: Afrin Samia , Ortega Jesus D. , Kumar Vinod , Bharathan Desikan
Published: December 2013

Conversion of direct solar energy, in particular the Concentrated Solar Power (CSP) technologies, has a significant role on conventional energy cost and efficiency. A single tank thermocline Thermal Energy Storage (TES) system is accountable for the overall efficiency of this conversion system. A single tank TES system has a thermocline region that produces the temperature gradient between hot and cold storage fluid by density difference. The overall energy storage capacity depends on sustaining of this region at uniform manner. This paper analyzes how the difference in the percentage of porous medium influences the effectiveness of the flow-distribution and hence, the overall performance of the TES system. The effectiveness is assessed by the optimal flow distribution. The optimal distribution is obtained by examining the velocity profile at any horizontal plane. This plane should be uniform for sustaining the thermocline region during the operation period. To achieve a uniform velocity distribution, two symmetric perforated plate flow distributors were placed in the tank. The distributors were positioned near the inlet and outlet, and checked the performance by varying the percentage of porous medium since the distribution is influenced by the porosity. Porous distributors with hexagonal shape pore were considered and Hitec® molten salt was used as a heat transfer fluid. These respective percentages of porosity affect the flow distribution throughout the tank during the flow distribution. The standard deviations of the velocity field at different positions along z-plane and thermal diffusivity were analyzed. The analyses of our cases were done to distinguish a configuration for the minimum thermal diffusivity and velocity deviation from the mean flow.

A finite volume based computational fluid dynamics software was used to execute the computational analysis.
Electric Mobility as Part of City Transportation Systems
Authors: Weber B. , Chávez G. , Durán M. D.
Published: December 2013

Nowadays there is a trend that more people prefer to live in cities than in rural areas, so there is the necessity of different urbanization strategies with various transportation schemes. While in most cities in the US the population density is very low with an interval of 20 to 50 inhabitants per hectare, in cities like Hong Kong more than 250 inhabitants live on an area of one hectare. As a consequence transportation needs are different, for example gasoline driven cars as preferred transportation systems for US citizens, giving rise to an average consumption of 2000 liters per year for every inhabitant; in comparison to Hong Kong, where average consumption is only 300 Liters per year. So there is a great challenge to reduce these emissions. Apparently solutions are not planned in relation to studies by the International Energy Agency that places the United States as biggest crude oil producer in the year 2017, due the increments of tight oil exploitation. In the shown scenery electro mobility can be a solution for sustainable transportation, when it is combined with PV systems.

This study starts with the feasibility of such a combination, and shows the coverage of population where this system can be implemented. From the analysis of economy results: It can be observed that the return of investment of a PV-system can be reduced when it is combined with electric mobility. Today cars driven by an electronic motor with cost of 0.035±0.015 USD/km afforded for transportation energy are more efficient than gasoline motors (based on fuel costs of 0.5±0.1 USD/km for economic cars with a coverage of 14 km/L). So it’s demonstrated that the return of investment is minor than 5 years for the PV system. It’s worth mentioning that charging batteries of electric cars could help to smooth energy peaks in the grid caused by renewables like sun and wind energy (a challenge for further grid systems). Besides the economic study the ecological impact has to be evaluated.
A Cost/Performance Evaluation of Advanced Low-Cost Heliostat Reflective Facets
Authors: Yellowhair Julius , Andraka Charles E.
Published: December 2013

Heliostat reflective facets have traditionally been constructed with glass/silver and a metal back support. During the past year, Sandia National Laboratories evaluated low-cost materials and alternative manufacturing methods to construct facets with the goal of reducing current facet cost by at least 25% while maintaining surface slope errors at 1 milli-radians rms or below. Several companies developed prototype facet samples, which were optically evaluated at Sandia and compared to baseline facet samples using a proposed cost-to-performance metric.

A cost-performance metric for comparing facets was developed by modeling and optimizing a 200 MWe power tower plant scenario in DELSOL, a computer code for system-level modeling of power tower systems. We varied the slope error on the facets and adjusted the cost on the facets to maintain the constant plant levelized cost of energy. The result of these models provides a chart of the facet optical performance and the allowable facet cost for a constant plant LCOE.

The size of the prototype facet samples ranged from 1.4 to 3 m2. The measured optical slope errors were between 1 and 2 milli-radians rms when compared to a flat mirror design shape. Despite slope errors greater than 1 mrad rms, some of the prototype samples met the cost goals for this project using the cost-performance metric. Next steps are to work with the companies to improve the manufacturing processes and further reduce the cost and improve on the optical performance to reach DOE SunShot goal of $75/m2 for heliostats.
Thermal Patterns in PV Arrays Operating in Tropical Conditions: A Preliminary Approach
Authors: Soler-Bientz Rolando , Ricalde-Cab Lifter , Riech Méndez Inés
Published: December 2013

This paper presents preliminary results of a field study focused in the study of the heat patterns of a PV array in tropical conditions. The research system is comprised by four sub arrays of four mono-crystalline Silicon PV Modules. The system was installed facing to the South direction in a static configuration according to the geographical location of the study site. A set of temperature sensors were installed on the back of the PV module in order to monitor their thermal patterns on daily basics. Ambient temperature, solar radiation on the PV surface and on the horizontal surface as well as the wind speed and wind direction have been also monitored concurrently with the thermal patterns of the whole PV array under study.
Thermoeconomic Analysis of Combined Cycle Coupled With Parabolic Trough Solar Plant
Authors: Duran M. D. , Rincón E. A. , Martínez I. , Lentz A.
Published: December 2013

Parabolic trough technology is currently one of the most extended solar thermal systems for the production of electricity.

This paper describes a thermo-economic study of an integrated, combined-cycle parabolic trough power plant. The parabolic trough plant is considered an economizer or a superheater of the HRSG (heat recovery steam generator). The main objective is to obtain the optimum design of the different sections of the boiler and the size of the parabolic field. The configurations analyzed are two pressure levels with and without a reheater. A Euro Trough (ET) concentrator was used in this study, the working fluid being water with direct steam generation. There will be no problem with the evaporation in the absorber, since the solar plant will be the economizer of the HRSG and an approach point greater than 3°C is considered.

The methodology applied for the optimization is Genetic Algorithms. This methodology was employed in previous works developed by the authors and yielded good results. So that method is applied to the configurations analyzed but including the parabolic trough plant. As a result, a thermoeconomic optimum design of a parabolic trough plant used as the section of the HRSG is obtained. The results show that the solar field increases the power and efficiency of the combined-cycle plant during the operation and makes it less susceptible to load variations.
Electric Power Generation Using Buoyancy-Induced Vortices Sustained by Entrained Solar-Heated Air
Authors: Simpson Mark W. , Reeve Hayden M. , Pearlstein Arne J. , Glezer Ari
Published: December 2013

Thermally-stratified air layers over solar-heated ground are exploited for a scalable, low-cost method of power generation by the deliberate formation of intense buoyancy-induced vertical columnar vortices, similar to naturally-occurring desert “dust devils.” Such vortices collect low-grade thermal energy in solar-heated air in regions with high surface heating rates, and convert the (gravitational) potential energy in the concentrated buoyant air into “solar-induced wind” with significant kinetic energy. Unlike dust devil vortices that are typically free to wander laterally and are therefore susceptible to cross winds, the anchored columnar vortex is deliberately triggered and anchored within a cylindrical domain bounded by an azimuthal array of stationary ground-mounted vertical vanes sustained by continuous entrainment of the heated air through these vanes. Solar energy collected by the ground plane sustains the anchored vortex and electric power is generated by using the air motion to drive a vertical-axis turbine to form a simple, low-cost electric power generating unit. In terms of cost-of-energy, intermittency, mechanical simplicity, and environmental impact, the approach has significant advantages compared to solar PV, CSP, and conventional wind turbines. Meter-scale laboratory experiments have demonstrated the nucleation, anchoring, and sustainment of strong, buoyancy-driven vortices centered within an azimuthal array of stationary vertical vanes above a controlled thermal ground plane. Outdoor tests of a meter-scale prototype have demonstrated autonomous start-up, formation, anchoring, and sustainment of a buoyancy-induced vortex generated solely by absorbed solar energy.