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ASME Conference Presenter Attendance Policy and Archival Proceedings

2015;():V002T00A001. doi:10.1115/ES2015-NS2.
FREE TO VIEW

This online compilation of papers from the ASME 2015 9th International Conference on Energy Sustainability (ES2015) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Photovoltaics

2015;():V002T11A001. doi:10.1115/ES2015-49044.

At the design stage of a solar photovoltaic (PV) system, equipment’s information from the specifications provided by manufacturers is the most reliable information. Parameters used to describe the performance are obtained under laboratory conditions, but the information is the appropriate for estimating the performance of the components of the solar PV system. When a system is in operation, the engineering models used at the design stage can also be used to predict the performance of the system. However, under real conditions, many factors can affect the performance which suggests that statistical models developed with field data could give better results to predict the performance of a solar PV system. Experimental data used in this study correspond to the energy generated by a 7.5 kW PV system installed to supply electricity to a research house at the University of Texas at Tyler, as well as the outdoor temperature and global horizontal solar radiation (as energy) recorder on site. The data is used to develop a multiple linear regression model and compare this model with an engineering model. Results show that the statistical model has a better quality than the engineering model.

Commentary by Dr. Valentin Fuster
2015;():V002T11A002. doi:10.1115/ES2015-49456.

Padang, the capital city of West Sumatra in Indonesia, has experienced major power outage repeatedly every year since 2006, typically causing people to experience 4–12 hours without electricity per day. The area is mainly supported by three lake-based hydro power plants, Maninjau, Singkarak, and Batang Agam. The electrical supply problems appear during the dry season when water availability is limited. Power outage during dry season in Padang area also becomes inevitable because the Sumatra island electricity system is a 150 kV interconnection power grid and due to the limitation of the transmission power transfer capacity lines from the Southern part of Sumatra (max for 250 MW) the demand cannot be satisfied. This paper presents the 2012 data of power outage and power production in Padang area. Using PVsyst software, a simulation of 200 MW solar PV systems in the Padang location is studied. Three scenarios are described, the current conditions without solar PV, with solar PV, and with solar PV-hydro collaboration. The results show that solar PV-hydro collaboration reduces the power outages significantly and distributes it more uniformly for the 2012 data.

Commentary by Dr. Valentin Fuster
2015;():V002T11A003. doi:10.1115/ES2015-49481.

Standard glass and polymer covers on photovoltaic modules can partially reflect the sunlight causing glint and glare. Glint and glare from large photovoltaic installations can be significant and have the potential to create hazards for motorists, air-traffic controllers and pilots flying near installations. In this work, the reflectance, surface roughness and reflected solar beam spread were measured from various photovoltaic modules acquired from seven different manufacturers. The surface texturing of the PV modules varied from smooth to roughly textured. Correlations between the measured surface texturing (roughness parameters) and beam spread (subtended angle) were determined. These correlations were then used to assess surface texturing effects on transmittance and ocular impacts of glare from photovoltaic module covers. The results can be used to drive the designs for photovoltaic surface texturing to improve transmittance and minimize glint/glare.

Commentary by Dr. Valentin Fuster
2015;():V002T11A004. doi:10.1115/ES2015-49764.

In the absence of a simple technique to predict convection heat transfer on building integrated photovoltaic (BIPV) surfaces, a mobile probe with two thermocouples was designed. Thermal boundary layers on vertical flat surfaces of a photovoltaic (PV) and a metallic plate were traversed. The plate consisted of twelve heaters where heat flux and surface temperature were controlled and measured. Uniform heat flux condition was developed on the heaters to closely simulate non-uniform temperature distribution on vertical PV modules. The two thermocouples on the probe measured local air temperature and contact temperature with the wall surface. Experimental results were presented in the forms of local Nusselt numbers versus Rayleigh numbers “Nu=a * (Ra)b”, and surface temperature versus dimensionless height [Ts -T= c*(z/h)d]. The constant values for “a”, “b”, “c” and “d” were determined from the best curve-fitting to the power-law relation. The convection heat transfer predictions from the empirical correlations were found to be in consistent with those predictions made by a number of correlations published in the open literature. A simple technique is then proposed to employ two experimental data from the probe to refine empirical correlations as the operational conditions change. A flexible technique to update correlations is of prime significance requirement in thermal design and operation of BIPV modules. The work is in progress to further extend the correlation to predict the combined radiation and convection on inclined PVs and channels.

Commentary by Dr. Valentin Fuster
2015;():V002T11A005. doi:10.1115/ES2015-49770.

A project was recently undertaken with the objective of designing a novel photovoltaic module, which encloses groups of solar cells that can track the sun. This will allow the module itself to be mounted simply at a fixed tilt but still reap the substantial energy collecting benefits presently associated only with rotating active and passive solar tracking panels, while avoiding their significant additional complexity, cost and weight. The main ultimate goal is to design such a module to collect at least 25% more energy than a similarly-sized fixed-tilt solar panel, while limiting its added production cost to less than 25%. This paper describes the module’s specific design requirements, and the analysis and design embodiments that have led to a few closely related prototypes based on bimetallic coil actuators. It also presents outdoor test (in the state of Georgia, USA) results showing that the most recent such prototypes collected just over 6% more energy than a similarly-sized fixed-tilt solar panel.

Topics: Design
Commentary by Dr. Valentin Fuster

Renewable-Non-Renewable Hybrid Power System

2015;():V002T12A001. doi:10.1115/ES2015-49225.

Internal combustion (IC) engines typically have an efficiency of less than 35%. This is largely due to the fact that much of the energy dissipates into waste heat. However, the waste heat may be converted into electricity by using energy conversion modules made from bismuth telluride. In this work, it is demonstrated that electricity can be generated from waste heat due to the difference in temperatures. The thermal to electrical energy conversion is achieved by using a self-assembled thermoelectric generator (TEG). The TEG (thermoelectric generator) uses two different types of metallic compound semiconductors, known as n-typed and p-typed, to create voltage when the junctions are held at different temperatures. The work mechanism is based on the Seebeck effect. In this study, the TEGs are made from bismuth telluride (Bi-Te) with relatively high energy conversion efficiencies. In addition, it is readily available. The installation location of the TEG is studied. For testing purposes and convenience, the top of the radiator of a 1990 Mazda Miata car was chosen. The TEG and an aluminum finned heat sink were placed in order on the top of the radiator. Thermal paste was applied to both surfaces and secured with zip ties. A vent was cut on the hood of the car to promote airflow between the fins. Appropriate electrical wiring allowed the unit to output to a digital multi-meter which was located within the car for operator to take data. It is found from the measured results that 0.948 V is the maximum output and the average voltage is 0.751 V. The highest voltage came from driving mountain paths due to the heat sink and coolant temperature being higher than nominal. We estimate that placing an insulator between the heat sink and TEG would push the maximum voltage over 1.0 V. During the cool down phase, the TEG produced electricity continuously with a maximum voltage of 0.9 V right after engine cutoff. The voltage decreased to about 0.6 V within 40 minutes. It is found that the relationship between the temperature difference and output voltage is linear.

Commentary by Dr. Valentin Fuster
2015;():V002T12A002. doi:10.1115/ES2015-49226.

As world trade grows, fuel prices increase, and International Maritime Organization (IMO) emissions requirements tighten, there is more demand for the marine industry to employ innovative means of reducing the fuel consumption and emissions of shipping vessels.

The main engines of large shipping vessels produce a large quantity of low temperature heat, but this valuable heat energy is transferred to cooling systems and rejected to the oceans as waste. At the same time, the electrical needs of shipping vessels are sustained by burning diesel fuel to run generators.

Calnetix Technologies, in partnership with Mitsubishi Heavy Industries, has developed the Hydrocurrent™ 125EJW Organic Rankine Cycle (ORC), a modularized system capable of absorbing the waste heat of main engine jacket water and converting it into grid-quality electric power. By combining this renewable source with the existing non-renewable source (engine gensets) a unique renewable-non-renewable hybrid power system is realized with minimal changes to overall ship power train. This novel hybrid system can be applied to all new and existing ships and allow for further integration into ship systems with available waste heat.

Shipping vessels such as tankers, bulk carriers, and container vessels are typically equipped with a category 3 marine diesel engine for main propulsion. A 30 MW engine, a most common engine size, utilizes 200–300 m3/hr of jacket water regulated to a heated temperature of 80–95 C. When integrated into the jacket water and sea water loops, the ORC can produce up to 125 kW of gross grid-quality electric power. This adds an immense benefit to the ship. To produce the same amount of power, a diesel generator consumes as much as 250 metric tons of diesel fuel per year, generates emissions, and requires significant maintenance.

Calnetix Technologies has leveraged its core technologies to develop the ORC into a reliable, high efficiency, compact and modular design. The turbo-generator or Integrated Power Module (IPM) is a hermetically sealed, high speed radial turbine coupled to a permanent magnet generator supported by magnetic bearings. Power from the IPM is converted by a high efficiency power converter supplying the ship with reliable power. The integrated design of the ORC along with the sophistication of its controls systems ensures essential ship functions are undisturbed under all conditions. The ORC is designed to comply with Nippon Kaiji Kyokai and Lloyd’s Register marine regulations and sea trials are anticipated to take place in 2015.

Commentary by Dr. Valentin Fuster
2015;():V002T12A003. doi:10.1115/ES2015-49459.

Demand Side Management (DSM) has been recognized for its potential to counteract the intermittent nature of renewable energy, increase system efficiency, and reduce system costs. While the popular approach among academia adopts a social welfare maximization formulation, the industrial practice in the United States electricity market compensates customers according to their load reduction from a predefined electricity consumption baseline that would have occurred without DSM. This paper is an extension of a previous paper studying the differences between the industrial & academic approach to dispatching demands. In the previous paper, the comparison of the two models showed that while the social welfare model uses a stochastic net load composed of two terms, the industrial DSM model uses a stochastic net load composed of three terms including the additional baseline term. That work showed that the academic and industrial optimization method have the same dispatch result in the absence of baseline errors given the proper reconciliation of their respective cost functions. DSM participants, however, and very much unfortunately, are likely to manipulate the baseline in order to receive greater financial compensation. This paper now seeks to study the impacts of erroneous industrial baselines in a day-ahead wholesale market context. Using the same system configuration and mathematical formalism, the industrial model is compared to the social welfare model. The erroneous baseline is shown to result in a different and more importantly costlier dispatch. It is also likely to require more control activity in subsequent layers of enterprise control. Thus an erroneous baseline is likely to increase system costs and overestimate the potential for social welfare improvements.

Topics: Errors
Commentary by Dr. Valentin Fuster
2015;():V002T12A004. doi:10.1115/ES2015-49781.

Co-firing coal and biomass offers a sustainable renewable energy option. However, slagging and fouling have been identified as some of the major operational challenges associated with co-firing. The chemistry of individual fuels can be used to determine the slagging potential of the blend. Previously, we have developed a numerical slagging index (NSI) based on the ash content in coal and the chemical properties of the coal ash. The NSI has been tested on a wide range of coals, and very good prediction results were obtained. In this paper, the slagging potential of Nigerian coal and other coals from Australia, Colombia and South Africa have been numerically evaluated. The predicted results using the NSI indicate that the Nigerian coal has relatively low slagging propensity when compared with other coals tested in this paper. One of the Australian coals seems to have lower slagging potential, and this may be attributed to the extraordinary low ash content for the coal, as reported. It has been observed that the silica-rich coal ash composition can be used to select suitable coals that could be co-fired with the alkali-rich biomass, with low operational risk. However, detail information on the chemical properties of blend and the particle-particle interaction can improve the performance of the assessment tool.

Topics: Coal , Co-firing
Commentary by Dr. Valentin Fuster
2015;():V002T12A005. doi:10.1115/ES2015-49804.

Clean forms of renewable energy with low to no environmental impact are highly desirable. Pressure Retarded Osmosis (PRO) has been a growing form of “Blue Energy” [1], a renewable energy medium involving mixing bodies of salt and fresh water. PRO systems take advantage of the pressure difference seen between freshwater and seawater by forcing fresh water across a semipermeable membrane into a body of saltwater. This transfer, through the means of forward osmosis, yields an increase in pressure on the saltwater side of the membrane. This observable increase in pressure can be used for generating electricity. A popular thought proposed has involved taking a part of this newly created pressure and diverting it back into the system with the use of a pressure exchanger. Residual pressure would then be devoted to the generation of electricity. If done correctly, a net gain can be seen between the electricity gleaned from the output of the system, and the energy consumed to run the pumps necessary for operation. The group’s aim is to design and construct a variant of the traditional PRO system for the purpose of analysis in a laboratory setting. The design proposed consists of a compact, two-membrane system that allows for the testing and analysis of forward osmosis in a closed system. While the system is not intended for actual electrical generation, it provides a medium for future experimentation.

Topics: Pressure , Design , Osmosis
Commentary by Dr. Valentin Fuster
2015;():V002T12A006. doi:10.1115/ES2015-49815.

This paper approaches the argument of cogeneration in aircraft propulsion. It presents an effective design of a cogeneration system with thrust augmentation by heat recovery for aeronautic propulsion which can be installed inside an electrical ducted fan unit. The system optimization is based on constructal law. Energy comparison against potential competitors is produced together with an analysis in terms of GHG emissions.

Commentary by Dr. Valentin Fuster

Smart Grid, Micro-Grid Concepts; Energy Storage

2015;():V002T13A001. doi:10.1115/ES2015-49079.

This paper provides an overview of a 100 kw flywheel capable of 100 kW-Hr energy storage that is being built by Vibration Control and Electromechanical Lab (VCEL) at Texas A&M University and Calnetix Technologies. The novel design has a potential of nearly doubling the energy density of conventional steel flywheels. Applications include renewable energy source energy storage, frequency regulation at power plants, regenerative braking on vehicles and cranes and backup power at data centers and hospitals. The design and construction of this Department of Energy sponsored flywheel will be presented.

Commentary by Dr. Valentin Fuster
2015;():V002T13A002. doi:10.1115/ES2015-49143.

The use of finned tubes as enhancement method to increase the heat flow rate into a phase change material, which has in many cases a low thermal conductivity, is a common method. A highly efficient and easy-to-assemble solution for finned heat exchanger tubes is a key component for innovative thermal energy storage systems which play a key-role in electricity production and industrial heat management.

In the present article the results of the investigation for different designs of bimetallic heat exchanger tubes is presented. These tube designs are developed for the use in latent heat thermal energy storage systems (LHTES) at a medium temperature range. For the use in latent heat thermal energy storage systems, the probably high pressure of the heat transfer medium and the high temperature differences between the operating temperature and the ambient temperature are challenging. Therefore, the bimetallic finned heat exchanger tube consists of a steel tube, where the heat transfer fluid flows, and an aluminum tube with longitudinal fins, which should improve the heat transfer to the phase change material. Due to different thermal expansion coefficients, displacements of the tubes are given. To guarantee a high heat transfer rate between the two connected tubes the contact between aluminum and steel plays an important role.

In the present study 4 prototypes (including the new design) were designed, analyzed and compared on the connection strength. Long-term tests for simulating the application in a LHTES were done to determine the creep rupture properties of the compositions. All prototypes were tested successfully; the new design is convinced in many aspects of that challenge and is submitted to the Austrian patent office. Main advantages of the new design are the simple production and assembling compared to other analyzed prototypes. Furthermore, the new design shows the best results under the analyzed operation conditions and the layout of the geometry has a high optimization potential in terms of stresses.

Commentary by Dr. Valentin Fuster
2015;():V002T13A003. doi:10.1115/ES2015-49144.

The melting and solidification process of sodium nitrate, which is used as energy storage material, is studied in a vertical arranged energy storage device with two different bimetal finned tube designs (with and without transversal fins) for enhancing the heat transfer. The finned tube design consists of a plain steel tube while the material for the longitudinal (axial) fins is aluminum. The investigation analyses the influence of the transversal fins on the charging and discharging process. 3-dimensional transient numerical simulations are performed using the ANSYS Fluent 14.5 software. The results show that every obstruction given by transversal fins reduces the melting and solidification velocity in direction to the outer shell. In the present study also a comparison of the simulation results between 2D and 3D simulation of the melting and solidification behavior of the sodium nitrate is presented.

Commentary by Dr. Valentin Fuster
2015;():V002T13A004. doi:10.1115/ES2015-49145.

In this paper the results of a numerical investigation of the melting and solidification process of sodium nitrate, which is used as phase change material, will be presented. For the heat transfer to the sodium nitrate different finned tube designs, namely helical-, transversal- and longitudinal finned tubes, are used. The numerical results of the melting and solidification process for the different design cases will be compared. The numerical analysis of the melting process has shown that apart from the first period of the charging process natural convection is the dominant heat transfer mechanism. The numerical analysis of the melting process has also shown that for a fast melting process heat exchanger tubes should be designed in such a way that an unrestricted natural convection is guaranteed.

The numerical investigation for the solidification process has shown that the dominant heat transfer mechanism is heat conduction. The investigation has also shown that the solidification front grows more uniformly from the tube surface to the outer shell compared to the melting front. Therefore no significant differences between the different tube designs are detected concerning the solidification process.

Commentary by Dr. Valentin Fuster
2015;():V002T13A005. doi:10.1115/ES2015-49170.

A simplified mathematical model was developed to analyze a storage tank containing a stationary fluid with hot and cold heat exchanger coils. The model is to be used as a screening tool for determining tank size and configurations for operation with a given power generation unit in a combined cooling, heating and power (CCHP) system. As such, the model was formulated so that it requires minimal information about the thermo-physical properties of the fluids and design parameters in order to determine the temperature profiles of the stored fluid and the heat transfer fluid for turbulent flow inside the heat exchangers. The presented model is implemented computationally with varying number of nodes, before comparing it with a more detailed model that take into account the variation of thermo-physical properties, as well as the effects of thermal de-stratification and heat loss to the ambient. The simplified model provided accurate temperature predictions that could subsequently be used to design a stratified tank system for a given CCHP application.

Commentary by Dr. Valentin Fuster
2015;():V002T13A006. doi:10.1115/ES2015-49493.

An experimental study has been conducted to develop a test-bed for advanced vanadium redox flow battery (VRFB) for renewable energy applications. Lab scale experimental setup has been designed based on enhanced geometry of mechanical components and reduced power consumption in terms of fluid mechanics and thermodynamics. Two tests have been conducted with variations of flowrate, concentration of electrolytes and electrical input power. The VRFB project has been collaborated between Arkansas State University Jonesboro (ASUJ) and University of Arkansas Fayetteville (UAF) to integrate VRFB with micro-grid at UAF. To obtain comparable experimental data, a test bed made of two half cells was constructed and joined together by a permeable membrane designed to facilitate ion transfer between two separate vanadium electrolytes. This research aims to better understand and demonstrate the transient characteristics of VRFB in order to refine the system in hopes of improving efficiency. This paper will focus on the steps taken to experimentally validate preliminary performance of the VRFB test bed. An analytical model has been performed to validate design and test of VRFB. Future work will be addressed to develop a pilot-scale multiple cell stacks with enhanced efficiency and temperature limits.

Commentary by Dr. Valentin Fuster
2015;():V002T13A007. doi:10.1115/ES2015-49513.

Energy infrastructure in rural areas of developing countries is currently deployed on an ad-hoc basis via grid extension, public and private sector solar home system (SHS) service using photovoltaic (PV) panels, and community distributed generation systems, also called mini or micro grids. Universal access to energy is increasingly pursued as a policy objective via e.g. the U.N. Millennium Develop Goals (MDG), Sustainable Energy for All (SE4All), and U.S. Power Africa initiatives. Rational allocation of energy infrastructure for 1.6b people currently lacking access requires a screening process to determine the economic break-even distance and consumer connection density favoring topologically diverse energy technology approaches. Previous efforts have developed approaches to determine grid-connection break-even distances, but work on micro-grid and SHS break-even distance and density is limited.

The present work develops an open access modeling platform with the ability to simulate various configurations of PV, Concentrating Solar Power (CSP), and fueled generator backup systems with exhaust waste heat recovery. Battery and thermal storage options are examined, and typical meteorological year (TMY) data is combined with probabilistic and empirical load curve data to represent the appropriate physical dynamics. Power flow control strategy and infrastructure is optimized for a minimum tariff (USD/kWh) for cost recovery. Cost functions derived from manufacturers’ data enable performance and economic assessment for a case study micro grid in Lesotho.

Commentary by Dr. Valentin Fuster
2015;():V002T13A008. doi:10.1115/ES2015-49535.

Surplus heat generated from industrial sectors amounts to between 20% and 50% of the total industrial energy input. Smart reuse of surplus heat resulted from industrial sectors and power generation companies is an opportunity to improve the overall energy efficiency through more efficient use the primary energy sources. A potential solution to tackle this issue is through use of thermal energy storage (TES) to match user demand to that of the generated surplus heat. A mobile TES (M-TES) concept of transportation of industrial surplus heat from production sites to end customers has shown promising results. One commissioned demonstration project using industrial heat for swimming pool water temperature regulation in Dortmund, Germany proved the interest and attention given to this concept.

In this paper, a techno-economic case study in Sweden of transportation of surplus thermal energy to district heating in smart cities is presented. The application consists of heat storage at 110°C–130°C through the use of phase change materials (PCM) based TES, notably with use of Erythritol (90 kWh/ton) for the considered temperature range, to remote district heating network located at 48 km from the thermal energy generation site. The advantages of using latent heat based PCM are the high enthalpy density per unit volume and per unit mass, as well as the quasi-constant temperature during charging and releasing of heat. The M-TES in this study has a total storage capacity of 2.1 MWh, the optimization of charge/discharge time to the amount of stored/released energy and to that of energy transportation rate is presented in this paper. Contrary to logical thinking, it is shown through this work that under certain conditions, it is more cost-effective to operate at partial load of storage units albeit the increased number of transport trips and charge/discharge cycles.

Topics: Heat storage
Commentary by Dr. Valentin Fuster
2015;():V002T13A009. doi:10.1115/ES2015-49634.

In this paper we present an economical optimization model for a microgrid connected to the general electricity grid by minimizing the total operating cost over a given period in the presence of uncertain future grid electricity prices. The microgrid is modeled to consist of five distinct blocks, four of which make up the microgrid and the fifth one being the connection to the general electricity grid. Each of these components has various adjustable attributes, allowing for the simulation of different kinds of consumers as well as different storage and generation technologies. Consumption and intermittent generation are exogenous variables derived from existing datasets. Under uncertain future grid electricity prices, the storage component introduces a non-causal dependency into the model, to cope with this non-causality, we present various storage use strategies and analyze the resulting cost patterns using real electricity price data and Monte Carlo simulations.

Commentary by Dr. Valentin Fuster
2015;():V002T13A010. doi:10.1115/ES2015-49787.

Conventional power networks have experienced a gradual evolution from a centralized nature to distributed and localized structures. The upgrading of power system toward a smart grid is being developed to improve reliability and facilitate the integration of different types of renewable energies and improve load management. Due to different uncertainties linked to electricity supply in renewable MGs, probabilistic energy management techniques are going to be necessary to analyze the system. In this study, the short-term operation planning of a typical microgrid (MG) with diverse units for achieving the maximum profit, considering technical and economical constraints, for the next 24 hours, using gravitational search algorithm (GSA) with SPSS software is presented and the effect of wind generation in the planning is investigated. The MG consists of a diverse variety of power system components such as wind turbine, microturbine, photovoltaic, fuel cell, Hydrogen storage tank, reformer, a boiler, and electrical and thermal loads. Moreover, MG is connected to an electrical grid for exchange of power. The MG is managed and controlled through a central controller. The system costs include the operational cost, thermal recovery, power trade with the local grid, and hydrogen production costs. The system costs include the operational cost, thermal recovery, power trade with the local grid, and hydrogen production costs. Total obtained profit from the MG, considering with US electricity and natural gas prices is $5.312902×103.

Topics: Microgrids , Wind
Commentary by Dr. Valentin Fuster

Solar Chemistry

2015;():V002T14A001. doi:10.1115/ES2015-49199.

A volumetric solar receiver for superheating evaporated sulfuric acid is developed as part of a 100kW pilot plant for the Hybrid Sulfur Cycle. The receiver, which uses silicon carbide foam as a heat transfer medium, heats evaporated sulfuric acid using concentrated solar energy to temperatures up to 1000 °C, which are required for the downstream catalytic reaction to split sulfur trioxide into oxygen and sulfur dioxide. Multiple approaches to modeling and analysis of the receiver are performed to design the prototype. Focused numerical modeling and thermodynamic analysis are applied to answer individual design and performance questions. Numerical simulations focused on fluid flow are used to determine the best arrangement of inlets, while thermodynamic analysis is used to evaluate the optimal dimensions and operating parameters. Finally a numerical fluid mechanics and heat transfer model is used to predict the temperature field within the receiver. Important lessons from the modeling efforts are given and their impacts on the design of a prototype are discussed.

Commentary by Dr. Valentin Fuster
2015;():V002T14A002. doi:10.1115/ES2015-49334.

The current work is a follow-up of the idea described in previous publications, namely of combining active thermochemical redox oxide pairs like Co3O4/CoO, Mn2O3/Mn3O4 or CuO/Cu2O with porous ceramic structures in order to effectively store solar heat in air-operated Solar Tower Power Plants. In this configuration the storage concept is rendered from “purely” sensible to a “hybrid” sensible/thermochemical one and the current heat storage recuperators to integrated thermochemical reactors/heat exchangers. In addition, the construction modularity of the current state-of-the-art sensible storage systems provides for the implementation of concepts like spatial variation of redox oxide materials chemistry and solid materials porosity along the reactor/heat exchanger, to enhance the utilization of the heat transfer fluid and the storage of its enthalpy. In this perspective the idea of employing cascades of various porous structures, incorporating different redox oxide materials and distributed in a certain rational pattern in space tailored to their thermochemical characteristics and to the local temperature of the heat transfer medium has been set forth and tested.

Thermogravimetric analysis (TGA) studies described in previous works have shown that the Co3O4/CoO redox pair with a reduction onset temperature ≈ 885–905°C is capable of stoichiometric, long-term, cyclic reduction-oxidation under a variety of heatup/cooldown rates. Further such studies with the other two powder systems above, described herein, have demonstrated that the Mn3O4/Mn2O3 redox pair is characterized by a large temperature gap between reduction (≈ 950°C) and oxidation (≈ 780–690°C) temperature, whereas the CuO/Cu2O pair cannot work reproducibly and quantitatively since its redox temperature range is narrow and very close to the melting point of Cu2O. Thus, a combination of two such systems, namely Co3O4/CoO and Mn2O3/Mn3O4 has been further explored. Thermal cycling tests with these two powders together under the conditions required for complete oxidation of the less “robust” one, namely Mn3O4/Mn2O3, demonstrated in principle the proof-of-concept of the cascaded configuration, i.e. that both powders can be reduced and oxidized in complementary temperature ranges, extending thus the temperature operation window of the whole storage cascade. A suitably designed test rig where similar experiments in the form of cascades of coated honeycombs and foams can be performed has been built and further such tests are under way.

Commentary by Dr. Valentin Fuster
2015;():V002T14A003. doi:10.1115/ES2015-49355.

The unsteady 3D fluid flow coupled to radiative, convective, and conductive heat transfers are computed within a cavity-receiver that was successfully tested experimentally. A Monte-Carlo radiation model is used in the fluid regions of the reactor with source terms outside the cavity’s window to account for the concentrated radiative power input. Darcy’s law for the viscous regime and the Forchheimer’s term for the inertial regime are used in the momentum equation to account for the pressure drop within the porous region (RPC).

Two separate energy equations for the solid and for the fluid regions of the porous domain are solved in order to capture the non-equilibrium effects in that region. Rosseland diffusion approximation is used in the solid regions of the RPC domain. The material properties and boundary conditions were taken from published experimental measurements. The simulation results are compared to the measurement data collected during the pre-heating and the ceria reduction phases, which sum up to four different radiative power inputs. Results of the comparison are very good and constitute the verification that the numerical methods, physical sub-process models and material properties are adequately selected and implemented. An analysis regarding the heat balance, the recirculating flow and, the effect of dual-scale porosity is also presented.

Commentary by Dr. Valentin Fuster
2015;():V002T14A004. doi:10.1115/ES2015-49507.

An engineering design for a 1-kW dual-cavity solar-driven reactor to capture carbon dioxide via the calcium oxide based two-step carbonation-calcination cycle is presented. In the low temperature carbonation step, gas containing up to 15% carbon dioxide flows through a gas manifold and plenum into an annular reaction zone filled with calcium oxide particles. The carbon dioxide reacts with the calcium oxide, forming calcium carbonate. Carbon dioxide-depleted gas flows out of the reactor through a second gas manifold. In the high temperature calcination step, concentrated solar radiation enters the beam-up oriented, windowless reactor and is absorbed by the diathermal cavity wall, which transfers heat via conduction to the calcium carbonate particles formed in the previous step. The calcium carbonate dissociates into calcium oxide and carbon dioxide. Additional carbon dioxide is used as a sweep gas to ensure high purity carbon dioxide at the outlet. Mechanical and thermal analyses are conducted to refine an initial reactor design and identify potential design shortcomings. Numerically predicted temperature profiles in the reactor are presented and the final reactor design is established.

Commentary by Dr. Valentin Fuster

Solar Heating and Cooling

2015;():V002T15A001. doi:10.1115/ES2015-49027.

Milk spoilage is a common issue in remote dairy farms due to the unavailability of power grid. Many farmers rely on diesel engines to power their milk chillers. A sustainable approach is to replace the environmentally harmful diesel generators with solar powered chillers. Solar energy is attractive in such application because the peak cooling demand occurs at the peak solar irradiance. Solar energy can be converted to cooling through PV powered chiller or through thermally driven chillers. This concept was applied to a Modular Solar Bulk Milk Chiller (MilkPod™) which uses the solar energy to generate electricity in 6 kWp PV panels. The system cools 600 liters of milk per day as well as produces hot water for cleaning the milk tank. A detailed model was used in the design process and the system equipment were selected such that the system uses about 98% of its energy from the sun throughout the year. The effect of the solar energy utilization ratio, equipment supplied current as well as milk loading were investigated on the system performance.

Commentary by Dr. Valentin Fuster
2015;():V002T15A002. doi:10.1115/ES2015-49156.

As the demand for cooling increases in Canada, it creates a greater energy demand on the utility grid by placing peak loads during the summer months. As a result, air conditioning in the residential sector is responsible for a disproportionately large and increasing amount of CO2 emissions in Canada. One potential solution is the use of solar thermally driven absorption chillers, however before their widespread use in Canada is possible, extensive testing and optimization of the systems must be conducted to determine their feasibility in the Canadian climate. This paper discusses a full scale experimental test rig that has been recently constructed and commissioned to experimentally evaluate the performance of a commercially available solar absorption chiller with integrated thermal storage. The complete system is described, including the system’s test capabilities, the instrumentation installed, the control system developed, and the calibration and uncertainty analysis completed on each individual sensor and the system as a whole. Additionally, the paper examines the charge cycle of the solar absorption chiller being studied, and compares the results to simulation results obtained from a TRNSYS model of the test apparatus.

Commentary by Dr. Valentin Fuster
2015;():V002T15A003. doi:10.1115/ES2015-49236.

In order to meet global challenges to reduce greenhouse gas emissions, the implementation of solar systems for residential purposes is an emergent task. Commonly liquid-based solar systems are used to heat up shower and pool water. More recently space heating systems have become part of sustainable buildings. An alternative could be a solar system that uses air as energy carrier. This study analyses the retrofit of such a system into a 40-year-old building. Starting from the analysis of the energy demand of a selected room, a solar air heater was designed, simulated and evaluated experimentally. The solar efficiency of the constructed collector reached 60%.

Commentary by Dr. Valentin Fuster
2015;():V002T15A004. doi:10.1115/ES2015-49292.

Energy use for space cooling has increased by 156% from 1990 to 2010 in the Canadian residential sector. In many parts of the country, the increasing use of electrically driven air-conditioners has begun to shift the peak load on the electricity grid from the coldest days of winter to the hottest days of summer. Many of Canada’s major electric utilities providers rely on fossil fuels to generate the additional capacity needed to meet the peak demand, resulting in significant greenhouse gas emissions. Solar-driven sorption chillers remain one of the possible solutions for shaving the peak loads experienced by the electricity grid.

This paper presents a review of the recent developments in the research of adsorption and absorption chillers, as well as a comparison of the two technologies based on the latest published experimental results found in the literature. Adsorption chillers continue to evolve in their design, including the use of new consolidated and composite adsorbents, the integration of coated adsorbers into internal heat exchangers, and newly developed advanced cycles for heat and mass recovery. While the physical design of adsorption chillers continues to be advanced, the development of absorption chillers for solar cooling applications has largely been focused on optimizing the system as a whole through improved control strategies and the implementation of newly developed high performance solar collectors.

Finally, the paper aims to assess the current state of development of solar-driven sorption chillers to provide insight into their applicability in the Canadian residential sector, as well as the remaining challenges facing this technology.

Commentary by Dr. Valentin Fuster
2015;():V002T15A005. doi:10.1115/ES2015-49577.

In ejector refrigeration cycles, ejector working fluids include various refrigerants with different properties. In some cases, ejector works with mixture of two different refrigerants; that each refrigerant have distinct properties. The purpose of this paper is to evaluate the performance of an ejector used for suction of a mixture of air and water vapor. In this regard, the ejector performance was numerically studied under the operating condition that a mixture of air and steam with variable mass fractions, were sucked into the ejector. With the help of numerical simulation, various conditions for two perfect gas streams of air and water vapor were investigated. Initially, the numerical simulation was carried out for the case that pure water vapor was considered as the working fluid of ejector. After validation of initial case with experimental data, numerical method was expanded for a specific case that, water vapor was considered as the working fluid of motive flow and a mixture of air and water vapor was considered for suction flow. Numerical simulations were done for different mass fraction of air and water vapor for suction flow mixture. Results indicated that, variations of the mass fraction of air in suction flow, leads to obvious changes in ejector performance. Also, it was observed that the increment of suction flow pressure, leads to increment of the ejector performance sensitivity to variations of suction flow mass fraction.

Commentary by Dr. Valentin Fuster
2015;():V002T15A006. doi:10.1115/ES2015-49637.

This study investigates the techno-economic feasibility of solar-powered absorption cooling and heating systems for a large-sized hotel building in Sydney, Australia. The proposed plant primarily consists of evacuated tube solar collectors, a hot water storage tank, a single-effect absorption chiller, and a backup gas burner. Dynamic simulation of the system has been carried out using the TRNSYS environment. Several control strategies have been implemented in the model to increase the overall efficiency of the system. Solar fraction and levelized total cost of the system have been considered as energetic and economic indicators, respectively. The parametric study results reveal that the optimal values of the storage tank volume and specific collector area are 70 L/m2 and 4 m2 per kW cooling capacity of the chiller, corresponding to the solar fraction of ∼72% and levelized total cost of ∼874,000 AUD/year. Finally, the payback period of the solar equipment is calculated to be 30.8 years, reiterating this technology still needs a great deal of subsidy in order to be economically competitive with conventional air-conditioning systems.

Commentary by Dr. Valentin Fuster
2015;():V002T15A007. doi:10.1115/ES2015-49696.

A complete study for a solar dryer is shown. In this work the lemon drying process is considered. Also, results for temperature distribution, currents lines velocities and density distribution are presented inside of the dryer chamber. Curves for dried are obtained when the lost mass of the lemon is measured. For this purpose, a digital balance is used and during several intervals of time the measures are done. A Compact Field point device of National Instrument is used to measure temperatures inside of the chamber in the dryer. Thermocouples k-type were placed in different points. By acquisition data, the values of temperature were measured for the test. By means of software (ANSYS) is discretized the inner zone and using the temperatures as boundary conditions. Solving the system defined for the equations according to the mesh defined, temperature, velocities and densities are determined. The results allowing to identify what is the behavior inside of the dryer and how the drying process happens. This way to study the drying process can be useful when the behavior inside of the chamber wants to be evaluated. In addition, this work can be useful in the design of solar dryers because allows to know how the trays can be placed to take advantage in the best way the solar energy in solar dryers.

Topics: Drying , Solar energy
Commentary by Dr. Valentin Fuster
2015;():V002T15A008. doi:10.1115/ES2015-49699.

In this work, four different arrangements of solar cooker box-type with internal reflectors results, for irreversibility and second law efficiency are presented. The solar cooker has two glasses in its cover to diminish the losses of heat radiation and convection, which in turn creates the hot house effect inside the cooker. The interior of the cooker has flat mirrors placed at different angles to reflect the solar radiation toward recipient with water. The obtained results are based on the heated water temperatures. These are obtained by means of numerical simulation, which in turn allows the comparison under identical conditions for the cookers. The results reveal that the energy reaching the cookers, less than 5%, is used in the water heating process. Most of the available energy is “stored” into the cooker glass cover, which shows the need for further work on improving cover materials in order to diminish such a situation.

Topics: Solar energy
Commentary by Dr. Valentin Fuster
2015;():V002T15A009. doi:10.1115/ES2015-49828.

A large solar hot water system can be utilized to provide driving energy for heating system, heat-driven cooling system, as well as to provide hot water. This research addresses the effects of the storage tank design parameters on the performance of a large-scale solar hot water system with a horizontal storage tank. Most literatures only considered the stratification performance of the thermal storage tank itself instead of considering the overall system performance. Also, there is lack of experimental research data available for the design purpose. Therefore, this study employs a numerical simulation technique to study the design parameters effect of a horizontal thermal storage tank on the performance of a large-scale solar hot water system. In this study, the ANSYS-CFX program is employed to calculate the flow and temperature distributions inside horizontal thermal storage tank. Then the inlets and outlets of the tank are combined with the TRNSYS program to simulate the entire system performance under the weather of three representative cities of Taiwan, (Taipei, Taichung and, Kaohsiung). The results of the present study indicate that the vertical stratification baffles in the tank have important effects on system performance improvement. Quantitative increase of solar fraction of the total load is obtained. The comparison with the system with vertical storage tank is provided. The results of the present study can provide important reference for the large solar hot water system design in improving system efficiency.

Commentary by Dr. Valentin Fuster
2015;():V002T15A010. doi:10.1115/ES2015-49843.

Finding optimal operating conditions of solar-based power and cooling systems is always a challenge. Performance of these systems is highly dependent on several important parameters, which not only impact the long-term efficiency but also its technical and economic feasibility. This paper studies the operation/configuration problem of an ammonia-water power and cooling cycle using an exergetic analysis. Thermodynamic performance of the combined cycle was addressed by using analysis of variance and multiple linear regression analysis. Modeling was done in Matlab®, using Refprop 9.0 to calculate the thermodynamic properties of the ammonia-water mixture. Convergence issues were observed on the thermodynamic properties estimation carried out by Refprop when the stream had high ammonia mass fraction. To solve this issue an averaging algorithm was implemented online to estimate such properties using pure ammonia data and high, but stable, ammonia concentration data. After this implementation, small differences between current and reference model were seen.

Optimum operating conditions were obtained using response surface technique. The response variable used was the ratio between exergetic efficiency and exergy destruction. Results showed that the response variable is mainly influenced by the ammonia concentration, pressure ratio, turbine efficiency and temperature gradient in the heat exchanger. Finally integration of the power/cooling cycle with a solar field was performed using two types of concentrated solar collectors: Linear Fresnel Collector (LFC) and Parabolic Trough Collector (PTC). The analysis showed that LFC technology can be a viable alternative for small scale applications combined with power/cooling systems.

Commentary by Dr. Valentin Fuster

Sustainable Cities and Communities, Transportation

2015;():V002T16A001. doi:10.1115/ES2015-49089.

One of the clean energy initiatives at Missouri S&T is an electric shuttle bus service, the Ebus. It provides valuable operational data for a fleet-type electric vehicle (EV) operating over a fixed route. The primary aim of this study is to use the daily operational data obtained from the Ebus in order to formulate an optimal driving strategy. Existing research efforts to improve EVs focus on improvements to the architecture and the energy management strategy. However, they fail to provide the driver with an optimal driving strategy leading to suboptimal use of the stored battery energy. This shortcoming was addressed here by implementing a multi-objective approach to find an optimal driving strategy for an electric bus. The driving strategy was taken to comprise two parts: a constant trip speed and an acceleration value to achieve that speed. From the operational data, the efficiency and power consumption of the electric motor were computed for different speeds. By assuming the entire trip was executed at a constant speed, the range for each speed was calculated. The speeds were ranked based on their corresponding ranges. Then, to achieve the optimal speed, the acceleration duration and energy consumption for different acceleration values were computed. The values were ranked based on the trade-off between duration and energy. The choice of driving strategy (exact speed and acceleration values) is left to the driver since different strategies would be needed for different road conditions. This multi-objective approach gives flexibility to the driver and promotes optimal use of the stored battery energy, thereby enhancing the energy efficiency and range of the Ebus. It can be easily implemented in other electric vehicles as well.

Commentary by Dr. Valentin Fuster
2015;():V002T16A002. doi:10.1115/ES2015-49129.

The ski industry in Colorado is the largest in the United States and makes up a significant portion of the state’s tourism revenue, but changes in the climate threaten the future of this highly weather-dependent business. In recent years, many ski resorts have taken steps to reduce greenhouse gas emissions in an effort to mitigate the effects shorter winters, less snowfall, and continued drought are having on the future viability of the industry. Energy efficiency and renewable energy projects are common strategies to reduce emissions; less common, however, are resort-wide analyses of distributed generation (DG) systems combining traditional and alternative energy sources. The intent of this study is to evaluate the economic and technical feasibility of a hybrid conventional-renewable DG system at Vail Resort.

Electrical and thermal loads for Vail’s mountain operations were used to analyze three DG technologies; combined heat and power (CHP), photovoltaics (PV), and horizontal axis wind turbines. Technologies were chosen based on a resource assessment as well as input from site managers and analyzed using the Hybrid Optimization Model for Electric Renewables (HOMER). The results indicate that the most cost-competitive DG system is a 700 kilowatt (kW) natural gas-fired CHP plant used to meet the site’s base load during the summer months. Although CHP systems are generally most effective at displacing conventional grid-based power for facilities with little seasonal load variation, the findings of this study align closely with an existing system at Snowbird Resort in Utah.

A small 700 kW CHP system could provide approximately 31% of annual electricity use and 24% of annual thermal energy needs based on the energy model used in this analysis. Furthermore, annual energy costs could be reduced by 3% and carbon emissions by 11%. Additional analyses are needed to more precisely determine the optimal system for Vail and the authors recommend that future studies include the energy use from base operations in addition to the mountain area considered in this analysis. The additional base area energy load during the summer could potentially make a larger CHP system more viable with subsequent cost and carbon emission savings. Additionally, site-specific resource data such as biomass production and ridge top wind speeds could aid in more definitively eliminating these technologies from consideration.

Commentary by Dr. Valentin Fuster
2015;():V002T16A003. doi:10.1115/ES2015-49130.

This paper presents the results from an economic and environmental feasibility study on photovoltaic PV and wind technologies for a community of 200 homes in Superior, CO. The electrical load profile assumed for the community, the solar resources available, and the wind resources are defined. Specific PV modules and wind turbines are identified. A simulation model was created in HOMER software and the specific model assumptions and reasoning presented. The results of the simulation show that the baseline scenario of grid electricity use is the best economic decision under the status quo system parameters. However, it is shown through sensitivity analyses and requirements for specific levels of renewable energy use, that the best possible system for the community should not be evaluated solely on the status quo economic parameters. PV is shown to be the best renewable technology to consider while wind energy proves to be a poor choice for the specific location of the community. Emissions of CO2 and other pollutants are greatly reduced under the recommended system design.

Topics: Wind
Commentary by Dr. Valentin Fuster
2015;():V002T16A004. doi:10.1115/ES2015-49171.

Airports are key components of the global transportation system and are the subject of continuous sustainability improvements. Promoting clean energy sources and energy-efficient practices can help attain major sustainability goals at airports around the world. Although small airports are greater in number, most of the “sustainability” attention has been given to large airports. Small airports are typically located in rural areas, making them excellent candidates for renewable energy. This paper focuses on the planning and selection of renewable energy systems as a strategic method to reduce energy use and increase electric power reliability at small-scale airport facilities. The target system may use a combination of renewable energy sources to produce electrical power for the on-site facilities. The framework details include methods of energy collection, power production, and energy storage that are environmentally sound. A small airport serving a dual role as a flight training facility was used as case study. In the case study, systems engineering methodology was adapted to the small airport/ renewable energy domain in order to effectively identify stakeholders and elicit user requirements. These, coupled with industrial standards, relevant government regulations, and a priori constraints, are used to derive the initial requirements that serve as the basis for a preliminary design. The proposed framework also contains provisions for an on-site assessment of existing airport energy needs, sources, providers, and location-specific assets and challenges.

Commentary by Dr. Valentin Fuster
2015;():V002T16A005. doi:10.1115/ES2015-49313.

For transit agencies looking to implement Zero Emission Vehicles (ZEV), Fuel Cell Electric Buses (FCEBs) represent an opportunity because of the similar range and refueling times compared to conventional buses, but with improved fuel economy. To assure an environmentally sensitive hydrogen infrastructure that can respond to the wide range of needs and limitations of transit agencies, a systematic evaluation of options is essential. This paper illustrates the systematic evaluation of different hydrogen infrastructure scenarios for a transit agency. The Orange County Transportation Authority (OCTA) in California was selected for the study.

Three different hydrogen infrastructure configurations are evaluated and compared to the existing paradigm of compressed natural gas buses and diesel buses. One additional scenario is analyzed in order to compare feasibility and environmental benefits of FCEBs with Plug-in Electric Buses. Each scenario represents (1) a specific mix and percentage of contribution from the various hydrogen generation technologies (e.g., on-site electrolysis, central SMR, and on-site SMR), (2) defined paths to obtain the corresponding feedstock for each generation process (e.g., biogas, natural gas, renewable energies), (3) detailed hydrogen distribution system (e.g., mix of gaseous/liquid truck delivery), and (4) the spatial allocation of the generation location and fueling locations (e.g., on-site / off-site refueling station) while also accounting for constraints specific to the OCTA bases.

This systematic evaluation provides Well-to-Wheel (WTW) impacts of energy and water consumption, greenhouse gases and criteria pollutant emissions of the processes and infrastructure required to deploy FCEBs and Plug-in Electric Buses at OCTA. In addition, this evaluation includes a detailed analysis of the space requirements and operations modifications that may be necessary, but yet feasible, for the placement of such infrastructure.

Topics: Fuel cells , Hydrogen , Buses
Commentary by Dr. Valentin Fuster
2015;():V002T16A006. doi:10.1115/ES2015-49445.

In the last 50 years, the province of Ontario has lost electrical power at various times, which has challenged Ontario’s emergency-response capabilities. In addition to the loss of electricity supply, there were concerns regarding access to diesel fuels and gasoline due to loss of electrical power to pump the fuel. However, natural gas and propane are a viable alternative energy supply in an emergency scenario.

The purpose of this project is to assess the role of natural gas in an emergency scenario and potential areas for further optimization to meet energy needs within the region of Durham, Ontario. An energy management model for the region of Durham has been developed for both electricity and natural gas. This model can be used to assess the impact of an emergency scenario on energy supply. This was achieved by researching different types of critical facilities such as hospitals, emergency services, schools, water/sewage facilities, community centers, shopping centers and gas stations and their reliance upon electricity and natural gas. Major shopping centers were included within this project as they provide communities with medical, grocery and basic needs.

Data gathered for 415 facilities was incorporated into a Visual Basic model. The data was based on floor space, population, fleet size, water consumption, fuel types and energy use behavior. Facilities were divided into categories based on sizes of less than 5,000 m2, between 5,000 m2 and 15,000 m2, and greater than 15,000 m2 for the purposes of the model. Unique facilities such as the six water treatment facilities and the ten E.M.S stations were assessed individually. The data was then used to create a model that related the available electricity and natural gas to the various types of facilities in the Durham Region.

The results show that natural gas infrastructure is already in place in the Region of Durham and many critical facilities currently use natural gas to supply heat energy. Hence, modest changes (cogeneration plants/ micro gas turbines) in the current infrastructure could be implemented to ensure emergency power is available from natural gas in a loss of electricity scenario and further improve the resiliency of the region of Durham in an emergency scenario.

Commentary by Dr. Valentin Fuster
2015;():V002T16A007. doi:10.1115/ES2015-49628.

The global population is expected to reach over 9 billion by 2050. The ‘second wave of urbanization’ indicates that developing world cities are growing much faster than their developed world counterparts, and most of these people will live in African and Asian cities where city growth rates are the highest.

This, ‘second wave of urbanization’ is a core driver of change in the 21st century and follows the first wave of urbanization that took place in developed countries from 1750, lasted 200 years and resulted in the urbanization of 400 million people. By contrast, the second wave of urbanization is projected to see over 3 billion additional people living in cities in a time-span of just 80 years, bringing unprecedented challenges to city doorsteps.

In the current era of development, urban sustainability is threatened by heightened global uncertainty and change. In broad terms, these changes consist of the following global factors: economic change, scarcity of resources, rapid technological and social change, environmental and climate change effects. These drivers of change have broad reach, and threaten multiple sectors — such as food, water, energy, transport and waste — that are critical for urban sustainability.

In response, this paper discusses cities’ transition to urban energy sustainability and the role of infrastructures, with focus on transportation planning. The paper highlights the case of Egypt as an example of developing countries.

The objectives of the paper are; firstly to identify the different factors affecting Egyptian cities’ transition to sustainability, and secondly to analyze the strategic urban planning process in Egypt which is a bottom-up participatory approach leading to urban sustainability.

The paper presents a case study from Egypt, illustrating the preparation of a future urban strategic plan for a small Egyptian city. The case study shows how participatory approach can result in innovative solutions leading to sustainable urban energy planning with focus on transportation.

Commentary by Dr. Valentin Fuster
2015;():V002T16A008. doi:10.1115/ES2015-49713.

The underpinning elements of sustainable communities are centered on economic security, renewable energy resources, reliable infrastructure, and ecological protection. The geomorphology of urban areas is altered due to human activity leading to change in land use characteristics and resources availability. Research has shown that global population has increased drastically over the last three decades resulting in depleted efficiency of regional resources. Because of this, obtaining sustainable energy platforms is a world-wide concern. In evaluating the ability of urban communities to support sustainable elements, both spatial and temporal influences must be considered. As a result a spatial analysis model will be used to assess the geomorphological and land use aspects of urban watersheds to support sustainable communities’ platform. These data will provide insight in essential components in need of environmental restoration that contribute to future renewable resources which can then be applied on a global scale.

Commentary by Dr. Valentin Fuster

Symposium on Integrated/Sustainable Building Equipment and Systems

2015;():V002T17A001. doi:10.1115/ES2015-49071.

In 2007, Chinese Ministry of Education (MOE) and Ministry of Housing & Urban-Rural Development (MOHURD) carried out the Campus Resource Conservation Actions, in order to take full use of resources and to improve the energy efficiency. However, due to the large amounts of universities, the total energy consumption and the energy efficiency situation have no objective statistics. Taking modeling the energy consumption of university buildings as the starting point, this paper analyzes the characteristics of university buildings in China. Then, we do the prediction, trend and potential analysis of the total energy consumption in 2020. In addition, four strategies for energy efficiency management are carried out, which might be helpful for all the university managers and related departments.

Commentary by Dr. Valentin Fuster
2015;():V002T17A002. doi:10.1115/ES2015-49128.

In this paper, passive cooling strategies have been investigated to evaluate their effectiveness in reducing cooling thermal loads and air conditioning energy consumption for residential buildings in Kingdom of Saudi Arabia (KSA). Specifically, three passive cooling techniques have been evaluated including: natural ventilation, downdraft evaporative cooling, and earth tube cooling. These passive cooling systems are applied to a prototypical KSA residential villa model with an improved building envelope. The analysis has been carried using detailed simulation tool for several cities representing different climate conditions throughout KSA. It is found that both natural ventilation and evaporative cooling provide a significant reduction in cooling energy for the prototypical villa located in Riyadh. Natural ventilation alone has reduced the cooling energy end-use by 22% and the total villa energy consumption by 10%, while the evaporative cooling system has resulted in 64% savings in cooling energy end-use and 32% in the total villa energy consumption. When applying both passive cooling systems together to the villa, the cooling energy end-use is significantly reduced by about 84.2% and the total villa energy savings by 62.3% relative to the un-insulated basecase residential building model. Moreover, natural ventilation is found to have a high potential in all KSA climates, while evaporative cooling can be suitable only in hot and dry climates such as Riyadh and Tabuk.

Commentary by Dr. Valentin Fuster
2015;():V002T17A003. doi:10.1115/ES2015-49233.

Dense urban environments are exposed to the combined effects of rising global temperatures and urban heat islands. This combination is resulting in increasing trends of energy consumption in cities, associated mostly with air conditioning to maintain indoor human comfort conditions. During periods of extreme summer weather, electrical usage usually reaches peak loads, stressing the electrical grid. The purpose of this study is to explore the use of available, high resolution weather data by effectively preparing a building for peak load management.

The subject of study is a 14 floor, 620,782 sq ft building located in uptown Manhattan, New York City (40.819257 N, −73.949288 W). To precisely quantify thermal loads of the buildings for the summer conditions; a single building energy model (SBEM), the US Department of Energy EnergyPlus™ was used. The SBEM was driven by a weather file built from weather data of the urbanized weather forecasting model (uWRF), a high resolution weather model coupled to a building energy model. The SBEM configuration and simulations were calibrated with winter actual gas and electricity data using 2010 as the benchmark year. In order to show the building peak load management, demand response techniques and technologies were implemented. The methods used to prepare the building included generator usage during high peak loads and use of a thermal storage system. An ensemble of cases was analyzed using current practice, use of high resolution weather data, and use of building preparation technologies. Results indicated an average summer peak savings of more than 30% with high resolution weather data.

Commentary by Dr. Valentin Fuster
2015;():V002T17A004. doi:10.1115/ES2015-49546.

This paper describes an approach for performing fast demand response involving a cluster of buildings. This approach is adaptive as well as distributed in nature. The approach is adaptive in the sense that the amount of targeted demand reduction, in an interval, is adjusted based on the performance of demand response actions executed in the last interval. The approach is distributed because the demand reduction is performed in each building in such a way that a global demand reduction target is met while the costs of performing the demand reduction actions are minimized. The developed method was implemented on a cluster of three buildings situated at U.S. Air Force Academy in Colorado Springs, CO. The results show that the developed approach was able to meet the demand reduction target, which was based on the amount of actual load that were deemed controllable for the DR events.

Commentary by Dr. Valentin Fuster
2015;():V002T17A005. doi:10.1115/ES2015-49583.

Recent trends for denser cities and associated levels of human activity reflected in energy demands are requiring new ways for quantifying human environmental impacts in cities. There is little information on human-induced environmental heat fluxes from very dense urban environments, and far less information on the anthropogenic sensible/latent heat flux partition. To address this, a surface energy model that takes into account evaporation from impervious surfaces and from cooling towers from buildings was implemented in the multilayer urban canopy model (BEP+BEM) of the Weather Forecasting Research (WRF) model to estimate the overall sensible/latent heat fluxes from urban surfaces and from air condition (A/C) systems from buildings in complex urban environments. The scenario used as case study was New York City (NYC) during summers (2010 & 2013). Urban canopy parameters from the Department of City Planning of NYC were assimilated into WRF with BEP+BEM at 250 meters horizontal resolution to have an accurate representation of the city topology. The modeling approach was calibrated with surface weather stations in NYC showing general good agreement with slight tendency to overestimate maximum temperatures and underestimate moisture content at nighttime. The A/C component was estimated in 150W/m2 latent heat due to cooling towers, and close to 40 W/m2 in sensible. Evaporative cooling technology diminishes between 80 and 90% the amount of sensible heat which is transformed into latent heat. Impacts of anthropogenic in the Planetary Boundary Layer (PBL) reflect warm season increases in the PBL height, and significant increases of atmospheric instability.

Commentary by Dr. Valentin Fuster
2015;():V002T17A006. doi:10.1115/ES2015-49701.

Natural ventilation has been studied as an effective strategy in order to reduce energy consumption without compromising occupant’s hygrothermal comfort in warm-humid climates. However, the main concern about the current state of art in the use of Building Energy Simulation (BES) as an approach to natural ventilation is the definition of input data which usually do not represent the real state of the buildings in the studied region. Within this context, the main contribution of this research is to propose a methodology through which the real state of buildings can be evaluated. By this analysis, valid input parameters was found to exploit the capabilities of BES and CFD simulations to fulfill the main objective of this study, which is to assess the impact of natural ventilation strategies in the energy consumption of HVAC systems and occupants hygrothermal comfort. Four natural ventilation strategies were evaluated: single sided ventilation, cross ventilation, solar chimney and double façade. The results show that the exclusive use of natural ventilation is ineffective to ensure hygrothermal comfort in a building with high thermal loads in a warm-humid climate like Guayaquil. However, by using a hybrid system (natural ventilation/dehumidification and cooling) cooling energy consumption can be reduced in up to 10.6% without compromising occupant’s hygrothermal comfort. Due to the promising results regarding energy savings, further research will aim to evaluate the impact of other passive strategies in energy consumption.

Topics: Ventilation , Climate
Commentary by Dr. Valentin Fuster
2015;():V002T17A007. doi:10.1115/ES2015-49805.

Floods are among the most common natural hazards in Florida. They are threatening the safety and economic welfare of Floridians. Every year Florida spends millions of dollar to mitigate direct flood damages. Amongst the effective solutions to these flood damages is the control of urban drainage in school buildings and nearby grounds to conserve and preserve natural resources and to promote sustainable thinking.

This paper discusses how public schools in Florida can benefit from sustainable techniques by applying the sustainable urban drainage system (SUDS) to school designs. The article also illustrates how Florida can use school sites as double functions to provide an active educational environment and to manage storm water runoff at the same time. Construction costs estimation for sustainable techniques is calculated based on data available for the year 2011 and compared with the conventional construction methods for schools.

The result indicates a high initial cost that can easily be offset by considering the cost of conventional drainage structure, conserved storm water, flooding impact, storm water sewage disposal, and other measures.

Commentary by Dr. Valentin Fuster

Thermofluid Analysis of Energy Systems Including Exergy and Thermoeconomics

2015;():V002T18A001. doi:10.1115/ES2015-49053.

This paper examines the economic benefits of various operation strategies for a thermal energy storage (TES) system in a solar thermal power plant. A thermodynamic model developed to evaluate different design options has been utilized to calculate system performance and assess the impact of operation strategies, storage capacity, and market prices on the value of TES. The overall performance is also investigated through several parametric studies, such as solar multiple, geographic location, and choice of HTF. The influence of these parameters has been evaluated in consideration of exergy destruction due to heat transfer and pressure drop. By incorporating exergy-based optimization alongside traditional energy analyses, the results of this study evaluate the optimal values for key parameters in the design and operation of TES systems, as well as highlight opportunities to minimize thermodynamic losses. Annual performance for each case is characterized both by nominal and part-load efficiency. Levelized cost of electricity (LCOE) is calculated for all cases, illustrating a set of optimal parameters that yield a minimum LCOE value.

Commentary by Dr. Valentin Fuster
2015;():V002T18A002. doi:10.1115/ES2015-49057.

This study investigates the drying mechanisms of corn when it is exposed to air at elevated temperature and velocity within a cross-flow packed bed dryer. A highly-instrumented laboratory-scale experimental test dryer was constructed to batch-dry samples of 0.03 m3 (1 ft3) of high moisture corn. This is achieved using a perforated wall drying chamber with forced air at temperatures ranging from 180–240°F. The high temperature, high velocity air entering the column is supplied by a variable speed fan and a variable Wattage electric heating coil through a 0.09 m2 (1 ft2) square air duct. This device is able to precisely control the drying air temperate and flow rate, while also measuring the temperature and humidity of the air exiting the dryer. In creating and instrumenting this apparatus, tests were performed to analyze both energy use and drying rate to determine the operating conditions that find a balance between energy and time requirements for moisture removal. This study used a variety of supply air temperatures and air flow rates in drying samples of corn at two initial moisture contents (19%MC and 24%MC) to 15%MC. This is done to determine if there are notable differences in energy requirements (Btu/pound water removed) between different operating conditions. This study determined that corn undergoes a significant pre-heating process before peak drying efficiency is achieved. Current grain dryer designs should focus the most energy just after that pre-heating process for highest overall efficiencies. Additionally, this study found an inverse relationship between dry time and energy efficiency, which showed that an optimum balance between those two factors should be identified.

Topics: Drying , Testing , Cross-flow
Commentary by Dr. Valentin Fuster
2015;():V002T18A003. doi:10.1115/ES2015-49092.

In this study, turbulent natural convection heat transfer during the charge cycle of a Thermal Energy Storage system was studied computationally and analytically. The storage fluids were supercritical CO2 and liquid toluene which are stored in vertical and sealed storage tubes. A computational model was developed and validated to study turbulent natural convection during the charge cycle. The results of this study show that the aspect ratio of the storage tube (L/D) has an important effect on the heat transfer characteristics. A conceptual model was developed that views the thermal storage process as a hot boundary layer that rises along the tube wall and falls in the center to replace the cold fluid in the core. This model shows that dimensionless mean temperature of the storage fluid and average Nusselt number are functions of a Buoyancy-Fourier number.

Commentary by Dr. Valentin Fuster
2015;():V002T18A004. doi:10.1115/ES2015-49110.

Micro and minichannel are progressively used in heat exchangers nowadays. The application of these heat exchanger types in refrigeration and air conditioning fields show various advantages such as high efficiency, low air side pressure, reducing refrigerant charge and the compactness size. The aim of this study is to investigate the two phase flow heat transfer coefficient and pressure drop of R410A during evaporation.

The experimental data were observed in aluminum channel with the hydraulic diameters of 1.14 and 1.16 mm, mass fluxes of 50–150 kW/m2s heat fluxes of 3–6 kW/m2, saturation temperature of 6°C and vapor quality from 0.1 to 0.9. The effect of mass flux, heat flux, and hydraulic diameter on heat transfer coefficient and pressure drop were analyzed. The database was compared with numerous well-known heat transfer coefficient and pressure drop correlations. Finally, a modify heat transfer coefficient correlation was developed that showed a good prediction against the database.

Commentary by Dr. Valentin Fuster
2015;():V002T18A005. doi:10.1115/ES2015-49159.

In previous work the authors have demonstrated that when hydrogen is combusted in stoichiometric proportions at 1 atm and 1200 K, and singlet oxygen comprises 0–20% of the oxidizer, an optimal range of exergetic efficiency exists. The maximum exergetic efficiency occurs at approximately 10%. Over this range, roughly 60% of the total exergy destruction occurs prior to ignition. This is a significant result because it suggests that the exergetic efficiency of combustion might be improved at a fundamental level by chemical means, thereby inherently increasing the efficiency of fuel use for a desired energy application.

The objective of the study presented in this paper is to analyze the reaction mechanisms for combustion with varying percentages of singlet oxygen, to determine which reaction pathways most influence the observed trends in exergy destruction and exergetic efficiency. This was accomplished by performing both sensitivity and rate-of-production analyses of the hydrogen-oxygen combustion mechanism. The results of the analysis show that the presence of singlet oxygen governs the rate of production of hydroxyl and other key radicals. These key radicals directly affect the phenomenological processes associated with chemical induction and thermal induction during ignition. Therefore, the observed optimum exergetic efficiency correlates to the quantity of singlet oxygen in the inlet charge that minimizes exergy destruction by fostering chemical reactions due to radical formation to a greater extent than thermal heat release. The results of this analysis are noteworthy and provide new insight regarding how the exergetic efficiency of combustion may be optimized by introducing singlet oxygen, thereby altering the reaction pathways to enhance energy conversion in a fundamental way that could have important implications for improved fuel use.

Topics: Combustion , Hydrogen , Oxygen
Commentary by Dr. Valentin Fuster
2015;():V002T18A006. doi:10.1115/ES2015-49350.

Thermal energy storage (TES) technologies have been developed using Phase Change Materials (PCM) at various power plants to utilize waste heat sources. The melting process of PCM has been investigated experimentally and numerically to construct a fundamental database of TES systems. D-Mannitol was selected as a PCM for medium TES systems in this study. The experimental apparatus consisted of the cartridge heater, thermocouples, test tube, acryl tube, vacuum pump, pressure indicator, volt slider and shunt resistance. The temperatures near the cartridge heater were measured by K-type thermocouples. The heat inputs were ranged from 10W to 15W. As a result, temperature of D-mannitol increased with time linearly under the solid state until the fusion temperature. When D-mannitol changed from the solid phase to the liquid phase, temperatures remained constantly due to the latent heat. Moreover, the numerical simulation was conducted using the commercial CFD code, ANSYS FLUENT. As a result of the numerical simulation, it was understood that the melting process was affected by the natural convection at the inner wall. As the heat flux of the cartridge heater input from the inner wall, the liquid fraction increased from the inner wall to the outer wall. The numerical result was compared with the experimental data. It was understood that the temperature of numerical simulation was approximately consistent with that of the experiment during the phase change process.

Topics: Melting , Storage
Commentary by Dr. Valentin Fuster
2015;():V002T18A007. doi:10.1115/ES2015-49427.

The design of expanders for organic fluids is gaining an increasing attention due to the large opportunities opened by the ORC as a way to recover low grade heat. The possibility of recovering at least a fraction of the energy related to throttling in inverse cycles could have interesting relapses on the market of heating (heat pumps) and refrigeration machines. The main challenge to be faced is the management of a highly wet fluid (typical quality is in the 0–0.6 range), which puts off side dynamic expanders like turbines. For this reason, piston technology is proposed and analyzed. The potential recovery from the throttling of a 20 kW target domestic heat pump cycle is determined by modeling the real expansion cycle with two different codes, a commercial one (largely widespread and very easy to use) and a purposely developed one, which is much more customizable and may include different approaches to the physical behavior of the two–phase expansion.

The results show interesting possibility of energy recovery from this generally wasted source, which opens the way to improvements of the heat pump COP from 4% to about 7%, depending on the working (i.e. seasonal) conditions. The analysis also points out the agreement in the results of two different adopted simulation tools (commercial AMESim® and self-made customizable EES®), which can be thus considered valuable in the design, analysis and optimization of the proposed expander.

Due to the biphasic nature of the working fluid, the performance of the expander is strongly influenced by the inlet conditions of the fluid from the condenser of the heat pump to the cylinders, such as throttling of the inlet/outlet valves and friction through the ducts.

On the whole, this expander technology has very interesting chances to effectively manage fluids under highly wet conditions, like those related to the throttling from upper to lower pressure of inverse cycles.

Topics: Pistons , Refrigerants
Commentary by Dr. Valentin Fuster
2015;():V002T18A008. doi:10.1115/ES2015-49492.

A concept and the associated device of thermal-driven water treatment to fully separate water and solute have been proposed. The device is integrated to a conventional multi-effect-distillation water treatment system to achieve high energy efficiency and 100% water extraction using high temperature thermal energy. In the water treatment system, water for reclamation is sprayed into droplets which fall into hot, dry air and creates very effective convective heat transfer between water droplets and hot airflow. During the heat transfer process, water is vaporized for pure water collection while the crystallized solute from the reclamation water settles down to the bottom for collection. The current study investigates the energy consumption versus water treatment in the system, the correlation of the size of droplets and the temperature of hot air, and the mass heat distribution in subsystems or devices. Results from the study provide important guidance to the design of such a water treatment system.

Commentary by Dr. Valentin Fuster
2015;():V002T18A009. doi:10.1115/ES2015-49702.

Open expansion tanks are applied vastly in central heating and air-conditioning systems. Central heating systems are subjected to great deals of energy losses, owing to the lack of proper design. In this paper, the structure of Open Expansion Tanks is revised and some modifications for reducing energy and heat loss are made to their elements. Moreover, some common designs available in the market are studied in order to better recognize their defects and capabilities. To reach an efficient design, several scenarios are tested using Computational methods (CFD based). In order to validate the new design, an experimental model was created and heat and energy survey operations were performed. The results of energy auditing were analyzed to show the convergence of numerical and experimental models. Additionally, the proposed model was economically evaluated. The final presented model named “Optimized OET with twin containers” is capable of reducing the energy loss by 85 to 95 percent.

Topics: Central heating
Commentary by Dr. Valentin Fuster
2015;():V002T18A010. doi:10.1115/ES2015-49823.

A gas turbine normally suffers significant penalties in power output and heat rate during hot days. Turbine inlet chilling is an effective approach to reduce these penalties. Reducing the inlet air temperature increases the density of turbine inlet air and as a result, more air mass flow enters the compressor, resulting in more power produced. Cooling towers and liquid desiccant (Lithium Bromide, LiBr) regenerators are important components in a turbine inlet chilling system. Understanding of their heat and mass transfer performance, particularly the performance of LiBr regenerators, is of importance for system design and integration. 1-dimensional finite difference heat and mass transfer models were developed in this study to simulate the cooling capability of cooling towers and the efficiency of water removal of LiBr regenerators. The models were used to perform sensitivity analysis on the performance of the regenerator to understand the effects of major parameters such as Lewis factor (Lef), the ratio of the air to solution mass flow and the temperature of the LiBr solution at the inlet. The simulation results show that the performance is insensitive to Le. Reducing the ratio of the air to solution mass flow or increasing the temperature of the solution at the inlet increases the thermal efficiency of the regenerator.

Commentary by Dr. Valentin Fuster

Wind Energy Systems and Technologies

2015;():V002T19A001. doi:10.1115/ES2015-49009.

WINDGRABBER™ (WG) is a novel new roof or pole top mounted wind turbine system proposed for product commercialization up to 50 kWe. WG is projected to be cost-attractive in an environmentally friendly manner. The WG system uses the available energy in the wind via (1) a passively yawed air impact inlet air scoop, (2) a flow tube, (3) an air turbine and (4) a multiphased air inlet with an air impact - drag type outlet section.

The WG wind turbine system preferentially utilizes a combination enclosed - radial out-flow, cross-flow, reaction-impulse air turbine of squirrel cage configuration, using either a single or double axial flow inlet of centrifugal fan design with backwardly curved, air foil air blades mounted on the discharge end of a flow tube. The WG wind turbine design is based on the air power instead of the wind power equations, combined with duct resistance, wind impact and wind drag calculations, to determine system wind energy conversion effectiveness with respect to the Betz limit, as well as overall system efficiency. Low pressure drop screens may be provided at the various inlets and outlets to protect birds and small mammals from being drawn into rotating components. A currently proposed Phase I – CAE modeling for conceptual design verification, system optimization and 300 watt pilot plant test program, followed by a Phase II – design improvement and scale up to 3,000 watt prototype demonstration program and followed by a Phase III cost reduction, product improvement and scale up to a 5,000 watt commercial demonstration program is currently being considered by BCK Consulting, L.L.C. (BCK) and West Texas A & M University (WTAMU).

The history of WG, up to and including its latest developmental status, will be discussed in this paper with projections offered regarding its future product commercialization prospects. Please see ASME paper ES2010-90062 presented previously [Ref.1].

Commentary by Dr. Valentin Fuster
2015;():V002T19A002. doi:10.1115/ES2015-49052.

Wind energy has been identified as an important source of renewable energy. In this study, several wind turbine designs have been analyzed and optimized designs have been proposed for low wind speed areas around the world mainly for domestic energy consumption. The wind speed range of 4–12 mph is considered, which is selected based on the average wind speeds in the Atlanta, GA and surrounding areas. These areas have relatively low average wind speeds compared to various other parts of the United States. Traditionally wind energy utilization is limited to areas with higher wind speeds. In reality a lot of areas in the world have low average wind speeds and demand high energy consumption. In most cases, wind turbines are installed in remote offshore or away from habitat high wind locations, causing heavy investment in installation and maintenance, and loss of energy transfer over long distance. A few more advantages of small scale wind turbines include reduced visibility, less noise and reduced detrimental environmental effects such as killing of birds, when compared to traditional large turbines. With the latest development in wind turbine technology it is now possible to employ small scale wind turbines that have much smaller foot print and can generate enough energy for small businesses or residential applications. The low speed wind turbines are typically located near residential areas, and are much smaller in sizes compared to the large out of habitat wind turbines. In this study, several designs of vertical and horizontal axes wind turbines are modeled using SolidWorks e.g. no-airfoil theme, airfoil blade, Savonius rotor etc. Virtual aerodynamic analysis is performed using SolidWorks Flow simulation software, and then optimization of the designs is performed based on maximizing the starting rotational torque and ultimate power generation capacity. From flow simulations, forces on the wind turbine blades and structures are calculated, and used in subsequent stress analysis to confirm structural integrity. Critical insight into low wind speed turbines is obtained using various configurations, and optimized designs have been proposed. The study will help in the practical and effective utilization of wind energy for the areas around the globe having low average wind speeds.

Commentary by Dr. Valentin Fuster
2015;():V002T19A003. doi:10.1115/ES2015-49123.

This paper presents a new approach allowing Numerical Weather Prediction (NWP) grid model forecasting to be applied to a desired “sub-grid” location. It permits observations from a NWP model using a novel bank of 24 Kalman Filters (KFs) operating simultaneously to accurately predict the wind speed (Zt) 24 hours ahead for a campus based wind turbine at Cork Institute of Technology (CIT) at 20m above sea level (asl) at sub grid location. The NWP model outputs wind speed predictions (mt) for Cork Airport at 152m asl (2.5km distant from CIT) at grid level. The Kalman Filter (KF), acting as a post processing tool with a moving time averaging window, derives a 24 hour ahead predicted wind speed schedule for CIT by applying a wind speed bias model polynomial to map and filter the wind speed bias offset between the two locations. To ensure a robust model, with good modelling and error noise disturbance rejection capabilities inclusive of model offsets [1], the accuracy of the model has been investigated using a particularly turbulent wind data set for December 2013 [2].

It is shown that a 4th order polynomial adaptive wind speed model bias remover is the optimum choice to employ in conjunction with the KF which uses a 3 point a priori moving window averager to adequately eliminate systematic error. The application of a KF to wind speed prediction is implemented in MATLAB software and results are provided in this paper to demonstrate the accuracy and fidelity of the procedure. Hypothesis testing along with statistical analysis has returned wind velocity prediction estimates that demonstrate the accuracy of the KF estimator. This also provides confidence enhancement of the polynomial model choice as a suitable wind velocity bias eliminator. The accuracy of the hourly wind velocity estimate are of strategic importance in wind power prediction where installed wind turbine scheduling is an issue for cost effective electrical network operation with a consequent beneficial economic return on wind generator capital investment.

Commentary by Dr. Valentin Fuster
2015;():V002T19A004. doi:10.1115/ES2015-49164.

World is facing a big problems for fossil fuel as it deals with the issues like availability, environmental effect like global warming etc, which forces us to explore new renewable sources of energy like solar, tidal, geothermal, wind etc. Among all the energies wind energy is the effective form of energy. As evaluated from the research, main cause for reduction of energy output in wind farm is the positioning of the wind turbine, as it is a function of wake loss. Present paper investigates an effective meta-heuristics optimization method known as Teaching–Learning-Based Optimization (TLBO), to optimize the positioning of the wind turbine in a wind farm. Two different scenarios of wind speed and its direction distribution across the wind site is considered like, (a) uniform wind speed of 12 m/s with uniform direction and (b) uniform wind speed of 12 m/s with variable wind direction. The results show that the implementation of TLBO is effective then other existing strategy, in terms of maximized expected power output and minimum wake effect of turbines by each other.

Commentary by Dr. Valentin Fuster
2015;():V002T19A005. doi:10.1115/ES2015-49188.

The understanding of atmospheric flows is crucial in the analysis of dispersion of a contaminant or pollutant, wind energy and air-quality assessment to name a few. Additionally, the effects of complex terrain and associated orographic forcing are crucial in wind energy production. Furthermore, the use of the Reynolds-averaged Navier-Stokes (RANS) equations in the analysis of complex terrain is still considered the “workhorse” since millions of mesh points are required to accurately capture the details of the surface. On the other hand, solving the same problem by means of the instantaneous governing equations of the flow (i.e., in a suite of DNS or LES) would imply almost prohibitive computational resources. In this study, numerical predictions of atmospheric boundary layers are performed over a complex topography located in Nygårdsfjell, Norway. The Nygårdsfjell wind farm is located in a valley at approximately 420 meters above sea level surrounded by mountains in the north and south near the Swedish border. Majority of the winds are believed to be originated from Torneträsk lake in the east which is covered with ice during the winter time. The air closest to the surface on surrounding mountains gets colder and denser. The air then slides down the hill and accumulates over the lake. Later, the air spills out westward towards Ofotfjord through the broader channel that directs and transforms it into highly accelerated winds.

Consequently, one of the objectives of the present article is to study the influence of local terrain on shaping these winds over the wind farm. It is worth mentioning that we are not considering any wind turbine model in the present investigation, being the main purpose to understand the influence of the local surface topography and roughness on the wind flow. Nevertheless, future research will include modeling the presence of a wind turbine and will be published elsewhere. The governing equations of the flow are solved by using a RANS approach and by considering three different two-equation turbulence models: k-omega (k–ω), k-epsilon (k–ε) and shear stress transport (SST). Furthermore, the real topographical characteristics of the terrain have been modeled by extracting the required area from the larger digital elevation model (DEM) spanning over 100 km square. The geometry is then extruded using Rhino and meshed in ANSYS Fluent. The terrain dimensions are approximately 2000×1000 meter square.

Topics: Flow (Dynamics) , Wind
Commentary by Dr. Valentin Fuster
2015;():V002T19A006. doi:10.1115/ES2015-49218.

A wind turbine blade performance depends on various parameters of which the shape of the blade is one of the most important one. In this work the shape of the tip of original NREL Phase-VI blade (S809 airfoil) has been modified to determine the changes in the blade aerodynamic performance. The chord length of new blade is kept similar to the original NREL blade up to 90% of the span. Last 10% was modified to a pointed tip at the pitch axis. This paper presents a comparative study of the effect of pointed tip on aerodynamic loads. CFD simulations were performed on both original NREL shape and pointed tip shape blades. The simulation results of pointed tip blade were compared with both experimental and simulation results of original blade. Ansys geometry modeler was used to draw the geometry and to generate the grids. Ansys CFX solver and post processor were used for simulation and calculation of the results. To predict the near wall transitional effect SST Gamma Theta turbulence model was used. Results of pressure coefficient along the chord at various blade sections of the pointed tip blade were found to be almost similar to the original NREL blade CFD results. Tangential and normal force along the span of pointed tip blade at different wind speeds showed some similarity in results compared with CFD results of original NREL blade. From the velocity contour the separation of flow with the increase of wind speed can clearly be observed. Thrust and torque effects are also observed at various wind speeds. The torque values for the pointed tip blade were found to be higher in the pre-stall and stall region but slightly lower in post-stall region. But compared to the torque values the difference in thrust at the same region is found to be negligible. Pointed tip thrust values are in better agreement at high wind speeds with respect to the experimental data. The flow separation at high wind speed is also found to be less with pointed tip blade compared to the original blade.

Topics: Blades
Commentary by Dr. Valentin Fuster
2015;():V002T19A007. doi:10.1115/ES2015-49593.

An optimization method that changes the control strategy of the Horizontal Axis Wind Turbine (HAWT) from passive- to active-pitch has been developed. The method aims to keep the rated power constant by adjusting the blade pitch angle while matching the rotor and the drive torques. The method is applied to an optimized wind turbine model. Further, numerical simulations were performed to validate the developed method and for further investigations of the flow behavior over the blades.

Commentary by Dr. Valentin Fuster
2015;():V002T19A008. doi:10.1115/ES2015-49765.

Acoustic noises emitted from wind turbine blades should be reduced to an acceptable level for the uptake of wind energy in buildings and in the urban environment. This paper reports on effectiveness of, Owl-wing-serrations (OWS), two-dimensional trip-wires, and Active-noise-cancellation (ANC) in minimization of aerodynamic noises in a micro model turbine. The OWS and trip wires were attached to the blade leading edges and trailing edges in the wind turbine. The model was operated in the fan mode as a single row. Combined effects of OWS and ANC were also tested in a counter rotating double-row Fan. Air velocity (m/s), shaft-revolution (rpm); electric-power (W), amplitude of acoustic noise (dB) and its Centre frequency (CF in Hz) were measured at a reference location, for a number of spacing. Experimental results were plotted in the forms of dB vs. Tip Speed Ratio (TSR), dB vs. CF, and Efficiency or Coefficients of Performance COP vs. TSR.

It was noticed that

• In the single row operations, 3mm trip wires and OWS attached to blades have influenced on the emitted aerodynamic noises. OWS reduced dB and increased Cf more than the trip-wires. For example, at a fixed TSR, amplitude of noise (dB) decreased with trip wires or OWS with the lowest dB occurring with the OWS alone. At a fixed dB, Centre frequency (Cf) increased with the highest frequency Cf occurring with OWS alone. Minor changes in efficiency (COP) were noticed with the trip wires or Owl-wing serrations. It may suggest that larger eddies are converted into small turbulences with lower amplitudes and higher frequencies.

• Active-noise-cancellation (ANC) in the double row operation affected acoustic noises as spacing/gap between the counter-rotating rows changed. At a fixed TSR, dB decreased in the double row operations in comparison with the single-row operations, the reduction in dB increased at higher TSR. At a fixed dB, Centre frequency (Cf) increased by 100% with the highest frequency Cf occurring at the spacing of 50mm. Efficiency or COP decreased by 50% when ANC was implemented with a minor change due to spacing between rows.

• Combined effects of OWS and ANC were moderate comparing to ANC alone, reducing both dB and COP by around 35% while doubling Cf as compared to the single raw fan conditions. The minimum dB and maximum Cf occurred at the gap/spacing of 50mm. No significant change was noticed at COP with combined OWS and ANC.

Commentary by Dr. Valentin Fuster

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