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ASME Conference Presenter Attendance Policy and Archival Proceedings

2017;():V001T00A001. doi:10.1115/ES2017-NS.
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This online compilation of papers from the ASME 2017 11th International Conference on Energy Sustainability (ES2017) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Batteries and Electrochemical Energy Storage

2017;():V001T01A001. doi:10.1115/ES2017-3407.

The use of lithium-based batteries, due to their high energy density, has become popular for power sources in portable electronic devices. Safety concerns over lithium cell applications have arisen due to their lower abuse tolerance compared to standard battery designs. Internal short circuits present one of the more dangerous abuse situations since there is a great potential of thermal runaway leading to fire and explosion. Field failures and recalls associated with internal short circuits demonstrate the risks of lithium batteries. Understanding the response of lithium cells under internal short circuit conditions is of great importance to ensure the safe development of lithium battery application. In this work, an internal short circuit test machine was designed to conduct nail penetration tests of lithium chemistry cells. The test machine successfully provides the required force to allow for multi-cell penetration. The test machine also provides accurate control of the penetrating nail’s position and velocity. This testing will support the development of models to simulate the mechanism of internal short circuits of lithium cells.

Commentary by Dr. Valentin Fuster

Biofuels, Hydrogen, Syngas, and Alternate Fuels

2017;():V001T02A001. doi:10.1115/ES2017-3058.

Computational Fluid Dynamics (CFD) study of compression ignition (CI) engines provides invaluable insights into in-cylinder conditions and processes, which greatly expands on the very limited detail provided by engine output measurements, fuel consumption measurements, and engine-out measurements of exhaust emissions. CFD modeling and simulation has therefore become an attractive alternative for engine analysis in place of full experimental testbed study in recent years. In this research work, the performance of a single cylinder four stroke diesel engine was investigated. Commercial simulation software ANSYS Forte was used to study the combustion and emission characteristics of a diesel engine, in order to establish strategies for improvement of in-cylinder combustion and emission control. Normal heptane (n-heptane) was used as the surrogate fuel to represent diesel. Simulation results are compared against data from experimental testbed studies in terms of in-cylinder pressure profiles, heat release rate and exhaust emission of oxides of nitrogen (NOx), soot and unburned hydrocarbon (UHC) levels. The pressure trace from the simulations is found to be within a reasonable error limit of 10%. The combustion process is simulated with special focus on exhaust emissions of soot, NOx and unburned hydrocarbon. Graphical plots for mass fraction of soot, NOx and UHC are presented and discussed to elucidate the formation of these emissions. Graphics contours of temperature, NO mass fraction and oxygen concentration within the combustion chamber are also presented and discussed. The effects of injection timing on engine in-cylinder pressure, heat release rate and exhaust emissions are also studied by varying the injection timing and maintaining constant injection duration. Results are compared for the three different injection timings investigated, namely start of injection (SOI) 18° bTDC, 15° bTDC and 12° bTDC. Emissions of soot and NOx are found to decrease with retarded injection timing. However, the peak in-cylinder pressure is greatly reduced and hence the output power is low. Injection timing is found to have no significant effect on emissions of UHC. The optimum injection timing that gives high output power and relatively low emission is 15° bTDC.

Commentary by Dr. Valentin Fuster
2017;():V001T02A002. doi:10.1115/ES2017-3097.

Anaerobic digestion (AD) is a viable method for conversion of food waste and other organic materials into methane-rich biogas. However, when used at high organic loading rates, using only food waste can lead to an unstable process. Process instability is indicated by frequent changes in pH, and increase in ammonia and hydrogen sulfide concentration. These uncontrolled changes combined with over-production of organic acids can inhibit biogas production and ultimately lead to digester failure. Therefore, certain co-substrates produced as wastes in the regional food sector were tested as stabilizing agents for food waste digestion with an objective of achieving stable non-manure based digestion. The substrates tested were acid whey, bread, manure, caffeinated drink, paper napkins and apple pomace. The biogas production was increased by 12% in reactors containing bread, by 10% with acid whey, and by 12% when the co-substrate was caffeinated drink. The reactors containing paper and manure showed decreased biogas production by 6% and 12% respectively, but these changes are relatively small and thus not considered inhibitory. Co-digestion with apple pomace was found to be inhibitory and resulted in digester failure. This initial study has demonstrated that the stability of AD systems may be improved by strategically combining available food waste feedstocks.

Topics: Food products
Commentary by Dr. Valentin Fuster
2017;():V001T02A003. doi:10.1115/ES2017-3126.

Anaerobic digestion (AD) has gained popularity as an effective way to treat organic materials, produce clean energy, and reduce greenhouse gas emissions. There is a significant number of large-scale AD facilities operating world-wide, largely treating livestock wastes, and used primarily for electricity production in industrialized countries. At the same time, there are millions of small, household-scale ADs deployed in developing countries, mostly to provide biogas resources for heating and cooking. Decentralized low-volume AD systems could provide a local, renewable energy source (for electricity, heating, or both), reduce or eliminate waste disposal costs, and limit discharges of high strength wastes. The purpose of this study was to evaluate the feasibility of deploying low-volume anaerobic digestion (LVAD) systems at institutions generating significant food waste, using Rochester Institute of Technology (RIT) as a case study. Mass flows and energy balance, net present value (NPV), and discounted payback period (DPP) were used to assess the feasibility of implementing an anaerobic digestion system utilizing the campus organic waste resources. Our study showed that a positive NPV can be achieved if subsidies and incentives were applied to offset the initial capital investment. However, the economics can be improved by driving down equipment cost and accepting food waste from other establishments to generate revenue from tipping fees.

Topics: Food products
Commentary by Dr. Valentin Fuster
2017;():V001T02A004. doi:10.1115/ES2017-3167.

In this paper, a novel coal gasification technology used for Integrated Gasification Combined Cycle (IGCC) power plants is proposed, in which a regenerative unit is applied to recover syngas sensible heat to generate steam and then the high temperature steam is used to gasify coke from pyrolyzer. Through such a thermochemical regenerative unit, the sensible heat with lower energy level is upgraded into syngas chemical energy with higher energy level, and therefore a higher cold gas efficiency (CGE) is expected. The Aspen Plus Software is selected to simulate the novel coal gasification system. Then the exergy and Energy-Utilization Diagram (EUD) analyses are applied to disclose the plant performance enhancement mechanism. It reveals that 83.2% of syngas sensible heat can be recovered into steam agent and so the CGE is upgraded to 90%. And with the enhancement of CGE, the efficiency of an IGCC plant based on the novel gasification system can be as high as 51.82%, showing a significant improvement compared to 45.2% in a Texaco coal gasification based plant. At the same time, the exergy destruction of gasification process is reduced from 132.5MW to 98.4MW through thermochemical reactions. Lift of accepted energy level (Aea), and decrease of released energy level (Aed) and heat absorption (ΔH) contribute to the exergy destruction reduction in the gasification process. Additionally, since oxygen agent is no longer used in the IGCC, 34.5MW exergy loss in the air separation unit is avoided. Thereby the novel coal gasification technology proposed in this paper has a good thermodynamic performance and may provide a quite promising way for high efficient and clean coal utilization.

Commentary by Dr. Valentin Fuster
2017;():V001T02A005. doi:10.1115/ES2017-3192.

A molten carbonate electrolysis cell (MCEC) is capable of separating carbon dioxide from methane reformate while simultaneously electrolyzing water. Methane reformate, for this study, primarily consists of carbon dioxide, hydrogen, methane, and a high percentage of water. Carbon dioxide is required for the operation of a MCEC since a carbonate ion is formed and travels from the reformate channel to the sweep gas channel. In this study, a spatially resolved physical model was developed to simulate an MCEC in a novel hybrid reformer electrolyzer purifier (REP) configuration for high purity hydrogen production from methane and water. REP effectively acts as an electrochemical CO2 purifier of hydrogen.

In order to evaluate the performance of REP, a dynamic MCEC stack model was developed based upon previous high temperature molten carbonate fuel cell modeling studies carried out at the National Fuel Cell Research Center at the University of California, Irvine. The current model is capable of capturing both steady state performance and transient behavior of an MCEC stack using established physical models originating from first principals. The model was first verified with REP experimental data at steady state which included spatial temperature profiles. Preliminary results show good agreement with experimental data in terms of spatial distribution of temperature, current density, voltage, and power. The combined effect of steam methane reformation (SMR) and water electrolysis with electrochemical CO2 removal results in 96% dry-basis hydrogen at the cathode outlet of the MCEC. Experimental measurements reported 98% dry-basis hydrogen at the cathode outlet.

Commentary by Dr. Valentin Fuster
2017;():V001T02A006. doi:10.1115/ES2017-3378.

There has been a global search for alternative fuels that are environmentally friendly to replace and or compliment the conventional fossil fuels used in running engines. This is in line with the global action to reduce CO2 emissions hence ameliorating the effect of climate change. Biodiesel fuels have been adjudged to be clean energy with minimal environmental pollution during combustion. Hence, biodiesel fuels for running compression ignition engines have been developed from various feedstocks such as vegetable oils, animal fat, and waste or used cooking oils. The properties of these biodiesels have been reported to be dependent on the feedstock type and therefore vary according to the source feedstock. In carrying out this present study on the effects of utilising biodiesel fuel on the compression ignition engine, a numerical study of temperature distribution in the cylinder liner of biodiesel-powered compression ignition engine is presented. Biodiesel produced from palm kernel oil is used. Eight nodes in the cylinder liner spanning the top section of the liner, midpoint and the interface between the liner and the block were used as data source as it is established that sharp-edged points are most likely regions for thermal stress. Of the eight nodes selected, four were edge nodes and the other four were nodes at the interface with varying conditions. Model equations used for the study were developed and subsequently transformed using the finite difference method. Numerical solutions were obtained from computer codes written in MATLAB programming language. The obtained results from this code were compared to results obtained from commercial software (ANSYS FLUENT) for same geometry and boundary conditions. Results on the cylinder liner showed steady state temperatures were reached in about five minutes using both the MATLAB code and ANSYS FLUENT and both results showed a similar trend of temperature distribution in the radial direction. However, the MATLAB code showed higher temperatures at the upper section of the liner material as compared to the midpoint of the liner whereas ANSYS FLUENT showed the midpoint section to possess maximum temperatures as compared to the cylinder head section. Both results agree with the lower section having least temperature distribution. Further analyses were carried out on the midpoint of the cylinder and the cylinder head section and factors responsible for the discrepancies discussed. The outcome of this study presents palm kernel based biodiesel as an alternative fuel in cylinder engines while highlighting sections of the engine that require design attention in terms of heat flux and engine stability.

Commentary by Dr. Valentin Fuster
2017;():V001T02A007. doi:10.1115/ES2017-3380.

A numerical study of temperature distribution in the cylinder liner of biodiesel-powered compression ignition engine is presented. The mathematical model equations developed were based on heat transfers in the cylinder liner and subsequently transformed using the finite difference method. Numerical solutions were obtained from computer codes written in MATLAB programming language. A biodiesel produced from Nigerian physic nut oil was used in the study. The result was compared with that obtained for conventional diesel fuel. The results revealed that the cylinder head section of the liner material presented higher temperature distribution compared to the oil sump section of the liner. Over a twelve-minute time range, the liner attained steady state with Jatropha-based biodiesel, recording a maximum temperature of 873.1°C. Conventional diesel recorded the lower temperature of 784.3°C. Results also showed that the cylinder head section of the liner material closest to the combustion chamber experienced the greatest temperature rise in comparison to other parts of the liner. These results show that though there are lots of publications confirming that a compression ignition engine previously running on diesel fuel can run on biodiesel fuel or its blend with diesel, there is a need for a further critical study on the development of engine parts like the cylinder liner.

Commentary by Dr. Valentin Fuster
2017;():V001T02A008. doi:10.1115/ES2017-3393.

Deliberations in the Philippines are underway on the shift to 5% (B5) CME-diesel blend from the current B2 blend. In support to said deliberations, a fuel economy and gaseous emissions study of B1–B50 CME-diesel blends was conducted using an in-use Asian utility vehicle running on the Japanese 10–15 Mode drive cycle. Results show that adding CME up to 20% by volume (B20) has a small effect on the heating values, specific fuel consumption (SFC), mileage, and maximum power. Relative to neat diesel, the increase in SFC, and lower mileage and power beyond B20 were attributed to lower heating values at higher blends. CO was practically constant while THC and NOx generally decreased with increasing CME blends. The CO and THC trends were ascribed to overall lean mixtures and increased amount of oxygenated fuel at higher CME blends. The decreasing NOx trend needs further investigation as it seemed contrary to other studies. Based on these results, the shift to B5 would insignificantly affect fuel economy and likely lessen THC and NOx emissions. B20 yielded the most emissions reduction without performance loss.

Topics: Diesel , Emissions
Commentary by Dr. Valentin Fuster
2017;():V001T02A009. doi:10.1115/ES2017-3464.

The Philippine Department of Environment and Natural Resources (DENR) has issued Department Order 2015-04 (DAO 2015-04) or the “The Implementation of Vehicle Emission Limits for EURO 4/IV, and In-Use Vehicle Emission Standards”. This policy, coupled with the Philippine Biofuels Act of 2016 (RA 9367) should greatly reduce the environmental impact of local automobile emissions. Commercial fuel is a mix of local coconut methyl ester (CME) and neat diesel blend. However, commercial diesel fuel is still at 2% v/v as of 2016 in contrast to the 5% v/v set by the policy, part due to the fact that only few local studies are done to show the effects of higher percentage of CME, with most recent studies showing results against increased CME usage. The study shows the effects of the usage of higher CME percentage in accordance to the set schedule of RA 9367. Five fuel blends with varying CME percentages v/v (2%, 5%, 10%, 15%, and 20%) are used in a heavy duty turbocharged common rail direct injection (CRDI) engine. The engine is run on an eddy current dynamometer with steady state measurements at 50 to 500Nm with 50Nm intervals. Each fuel is tested at three pedal positions, alpha, (25%, 50%, and 60%) controlled directly from the engine control unit (ECU). Results show that higher CME usage does not result in reduction of power and achieved torque. There is, however, a significant increase in brake specific fuel consumption at higher percentages of CME. No significant change in carbon monoxide (CO) and unburned hydrocarbons of diesel (HCD) is observed but there is a significant increase in Nitrous Oxides (NOx) concentration as CME percentage is increased. However, brake specific CO and HCD were found to be out of standard for near no load and near full load operations. A similar trend is observed for brake specific. Brake specific NOx is particularly more problematic since all measurements were observed to be out of standard with maximum values of 1350% of the set EURO 4/IV standard. However, it is also seen that the performance of each blend does not significantly differ from each other. Nevertheless, there is still some potential in the usage of CME due to the fact that power and torque requirements are still met at the expense of higher fuel consumption; but with the opportunity of being self-sufficient as coconut-producing country.

Topics: Engines , Ester , Emissions
Commentary by Dr. Valentin Fuster
2017;():V001T02A010. doi:10.1115/ES2017-3503.

Much interest is given to the research in biodiesel these days. It is renewable and has similar properties to conventional diesel. Biodiesel is also generally seen to produce less emissions, hence it is seen as an attractive and a greener alternative source of energy. Biodiesels are also referred to as Fatty Acid Methyl Esters (FAME). They are obtained from the transesterification of oils from organic products such as animal fat or vegetable oil. Common biodiesel feedstocks are soybean (USA), rapeseed (Europe), palm, and coconut (Asia). The Philippines, being one of the largest producers of coconut in the world, should have a substantial interest in this. Biodiesel in the Philippines is obtained from coconut oil and is commonly called Coconut Methyl Ester (CME). There is a number of research works available that study the effects of biodiesel when used to run diesel engines, although there is notably less studies on CME and particularly Philippine-CME available. This work aims to show the fuel injection timing and duration of a Common Rail Direct Injection (CRDI) engine run by CME-diesel with neat diesel as baseline. There are two sets of injection parameters that describe the injection behaviour of an engine. The static injection parameters refer to the electronic commands given out by the Electronic Control Unit (ECU) while the dynamic injection parameters refer to the actual physical injection happening in the fuel injector nozzle. Knowledge of these information may help explain possible differences in performance and/or emissions observed in biodiesel-fed engines. The static injection commands were obtained by tapping into the solenoid signal wire from the ECU. The dynamic injection parameters were estimated from line pressure signals in the fuel injection line. All the tests were done on the AVL Eddy Current Engine Dynamometer in the University of the Philippines Vehicle Research and Testing Laboratory. Baseline data were recorded from 100% neat diesel, then volumetric blends B10 (10% CME biodiesel and 90% neat diesel) and B20 (20% CME biodiesel and 80% neat diesel) were mixed for the tests. The CRDI engine was ran at full load, sweeping the operating range at 400 RPM increments from 800 to 4000. The results showed no significant difference in the static injection parameters of the CME-diesel blend-fed engines as compared to being ran with neat diesel. As for the dynamic injection parameters, there were some significant differences observed in the higher engine speeds starting at 2800 RPM. The observed changes were attributed to the differences in the physiochemical properties of CME biodiesel as compared to neat diesel.

Commentary by Dr. Valentin Fuster

CHP and Hybrid Power and Energy Systems

2017;():V001T03A001. doi:10.1115/ES2017-3079.

Increasing grid penetration of intermittent renewable power from wind and solar is creating challenges for the power industry. There are times when generation from these intermittent sources needs to be constrained due to power transmission capacity limits, and times when fossil fuel power plant are required to rapidly compensate for large power fluctuations, for example clouds pass over a solar field or the wind stops blowing.

There have been many proposals, and some actual projects, to store surplus power from intermittent renewable power in some form or other for later use: Batteries, Compressed Air Energy Storage (CAES), Liquid Air Energy Storage (LAES), heat storage and Hydrogen being the main alternatives considered. These technologies will allow power generation during low periods of wind and solar power, using separate discrete power generation plant with specifically designed generator sets. But these systems are time-limited so at some point, if intermittent renewable power generation does not return to its previous high levels, fossil fuel power generation, usually from a large centralized power plant, will be required to ensure security of supplies. The overall complexity of such a solution to ensure secure power supplies leads to high capital costs, power transmission issues and potentially increased carbon emissions to atmosphere from the need to keep fossil fuel plant operating at low loads to ensure rapid response.

One possible solution is to combine intermittent renewables and energy storage technologies with fast responding, flexible natural gas-fired gas turbines to create a reliable, secure, low carbon, decentralized power plant. This paper considers some hybrid power plant designs that could combine storage technologies and gas turbines in a single location to maximize clean energy production and reduce CO2 emissions while still providing secure supplies, but with the flexibility that today’s grid operators require.

Commentary by Dr. Valentin Fuster
2017;():V001T03A002. doi:10.1115/ES2017-3095.

Due to fluctuation and intermittence, renewable energy sources (RESs) require high adjustability of power system. However, the existing combined heat and power (CHP) system has limited adjustability because of being controlled in the “heat-led” mode, which, consequently, hinders the development of the RESs. A solution of the problem is to introduce the heat storage (HS), which decouples heat supply from heat load. Although a number of researchers have studied in the design and the planning optimization of such CHP systems with RESs and HS, few people have paid attention to the seasonal variation of the heat load, which may vary the daily optimal planning of the systems. In this dissertation, we set up the model and optimize the planning of a CHP system with RESs and HS, with the consideration of the seasonal variation of the heat load. We find that in the beginning/ending of the heating season, the HS should store heat when the wind power is being abandoned and release heat in the rest of the days, while in the middle of the heating season, the HS should release heat when the wind power is being abandoned and store heat in the rest of the days.

Commentary by Dr. Valentin Fuster
2017;():V001T03A003. doi:10.1115/ES2017-3119.

Distributed peak-shaving heat pump technology is to use a heat pump to adjust the heat on the secondary network in a substation, with features of low initial investment, flexible adjustment, and high operating cost. The paper takes an example for the system that uses two 9F class gas turbines (back pressure steam) as the basic heat source and a distributed heat pump in the substation as the peak-shaving heat source. The peak-shaving ratio is defined as the ratio of the designed peak-shaving heat load and the designed total heat load. The economic annual cost is taken as a goal, and the optimal peak-shaving ratio of the system is investigated. The influence of natural gas price, electricity price, and transportation distance are also analyzed. It can provide the reference for the optimized design and operation of the system.

Commentary by Dr. Valentin Fuster
2017;():V001T03A004. doi:10.1115/ES2017-3396.

This paper summarizes results of a study conducted to minimize total cost of ownership of multistage air compressors by integrating it with compact and efficient off-the-shelf organic rankine power cycle units to recover low grade waste heat from inter-stage coolers with subsequent conversion to power. The paper also highlights challenges faced by the integration and provides guidance for future cost and technology targets for key components to make it a commercial scale reality. Various schemes for vaporization of the working fluid including direct and indirect as well as full or partial were explored. Also, in order to better understand interaction between cycle efficiency and capital cost of key components, design as well as operating parameters including evaporator approach temperature, compression stage suction temperature, number of compression stages and cooling water supply temperature were investigated. Configuration, size and hence the cost of evaporator/ inter-stage cooler was found to be one of the major factors governing the overall cost. Impact of various operating modes including turn-down and seasonal variations were also studied. Air flow and final discharge pressure from the multistage air compressor were kept constant throughout the study to facilitate a fair comparison.

Commentary by Dr. Valentin Fuster
2017;():V001T03A005. doi:10.1115/ES2017-3575.

A hybrid cooling, heating and power (HCHP) concept was recently demonstrated through a DOD innovative energy program. It included several high performance components for distributed energy systems and a unique drive-train design, which efficiently converts waste heat into useful energy in the form of cooling, heating and power depending upon the energy needs. Compared to a standard military environmental control unit (ECU) which puts an electric load on a diesel generator, the HCHP system uses engine exhaust heat as the primary energy input. Utilizing the exhaust heat can potentially provide 27% reduction on fuel consumption when operating in the cooling mode. When cooling is not needed, it is able to provide power output using engine waste heat — a potentially significant advantage over other heat activated cooling technologies.

Commentary by Dr. Valentin Fuster
2017;():V001T03A006. doi:10.1115/ES2017-3638.

From a practical perspective, economics drive the development of distributed energy resource (DER) systems. However, the adoption of a DER system provides an opportunity for the end user to completely control their environmental footprint. This work examines the process of designing a DER system while controlling carbon emissions. A mixed integer linear program (MILP) for sizing and dispatching a DER system is developed. The MILP includes a novel formulation of constraints that govern utility natural gas, generator operational state, and charging of thermal energy storage. The MILP is executed using real energy demand data for the University of California, Irvine to optimally design a DER system that minimizes cost while also reducing carbon emissions by a specified quantity. Two primary technology scenarios are explored (DER including storage with and without electrical export). A trajectory of DER technology adoption is determined for both technology scenarios. The different operational methods through which each system achieved lower carbon emissions at minimum cost is examined. Finally, the cost to reduce carbon emissions is calculated for both technology scenarios.

Commentary by Dr. Valentin Fuster
2017;():V001T03A007. doi:10.1115/ES2017-3670.

Combined Cooling Heat and Power (CCHP) attained significant attention among energy professionals and academicians recently due to its superior thermal, economic and environmental benefit in comparison with conventional energy producing systems (internal combustion engine (ICE), micro-turbine, etc). Despite the abundance of literature on CCHP, only a few studies emphasized on the selection of appropriate prime mover for an economically sustainable CCHP system. Furthermore, the effect of part load efficiencies is commonly neglected during CCHP analysis. We had introduced these two new concepts of economic sustainability of specific prime mover and part load effects on efficiency to CCHP system in our previous paper. An algorithm based on hybrid load following method was utilized to determine the optimum prime mover for a particular location and weather type. No studies explored the effects of efficiency parameters and the selection strategies of prime mover in different building types for any particular location using this newly developed algorithm. Since building types dominates the electric, heating and cooling demand extensively, it is imperative to extend the prime mover selection analysis for building types for efficient CCHP operation. Economic, energy, and emission performance criteria have been utilized for the prime mover selection systems in different building types. Computer simulations were conducted for five different building categories (primary school, restaurant, small hotel, outpatient clinic and small office buildings) for each of three different types of prime movers (reciprocating internal combustion engine (ICE), micro-turbine and phosphoric acid fuel cell) in a cold climate zone (Minneapolis, MN). The simulation results of different prime movers were compared with the outcomes of a reference case (for each building in the same climate zone) that has a typical separate heating and power system. The cold climate zone (Minneapolis, MN) helped to explore the heating load effects on economic, energy, and emission performance of the buildings in comparison to other energy demands (i.e. electric and cooling demand). A hybrid load following method was executed, using improvements shown in our previous article. Performance parameters and other outcomes of this study showed that economic savings were observed for the ICE in all building types, and the micro-turbine in some building types. Internal rate of returns of ICE are 22.4%, 14.7%, 20.5%, 14.6% and 6.5% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. ICE also shows highest energy savings among all three prime movers with an energy savings of 20%, 17.2%, 25.7%, 23.8% and 9.7% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. For all types of prime mover based CCHP systems, lower CO2 emission was observed for all building types. However, unlike ICE, which is preferable in terms of economic and energy savings, emission analysis shows that micro-turbine poses better emission characteristics compared to other types of prime movers. CO2 emission for micro-turbine savings are 67.1%, 62.2%, 82%, 43.2% and 81.4% for primary school, restaurant, small hotel, outpatient clinic and small office respectively. The relationship between the power and thermal demand of the different buildings was determined to be a significant factor in CCHP system performance. A sensitivity analysis determining the effects of heat exchanger and heating coil efficiencies on the performance of CCHP systems shows that the economic performance was most sensitive to the heat exchanger efficiency, while energy consumption and emissions was most sensitive to the heating coil and boiler efficiency.

Commentary by Dr. Valentin Fuster

Commercial Applications of Energy Storage

2017;():V001T04A001. doi:10.1115/ES2017-3053.

Utilities in regulated energy markets manage power generation, transmission, and delivery to consumers. Matching peak demand with peak generation is costly, and the increasing penetration of renewable energy into the grid adds complexity due to fluctuations in supply. A few options exist for addressing the task of balancing supply and demand, including demand response, energy storage, and time-varying pricing (tariffs).

Arizona Public Service (APS), the largest electric utility company in Arizona, employs tariffs that charge more for electricity at certain times (on-peak periods) and a demand charge for the highest power demand throughout the billing period. Such tariffs incentivize end users to lower peak demand. Arizona State University (ASU), a public university with its largest campus in Tempe, AZ, participates in a time-of-use tariff structure with APS. Analysis in this paper shows that ASU’s 16MWdc of onsite solar capacity alone can lower its monthly electricity bills by over 10% by decreasing on-peak power demand.

A novel contribution of the paper is the analysis of the value of small scale, on-campus energy storage in lowering the demand charge. Most analyses consider savings from transferring off-peak electric power to peak-electric power, but this paper considers using stored electricity solely to reduce peak demand and thus lower the demand charge. Small amounts of electricity could greatly reduce overall cost. An algorithm was developed and executed in Python to decide when on-campus storage should be charged and discharged. The critical part of the algorithm is to decide when to discharge. Deploying too early, or too late, will not change peak demand.

The paper’s storage dispatch model is implemented alongside a financial model that calculates the savings in electricity bills and determines the net present value (NPV) of different storage technologies as a function of storage lifetime and installed capacity (kWh). The results show that, for all storage technologies considered, a positive NPV is realized. NPVs are very sensitive to actual power demand and thus vary from year to year. This is to be expected because the storage dispatch strategy operates on extreme values, which tend to include very rare events.

This analysis uses actual data from ASU, which allows us to extend the results to other universities and commercial customers. The favorable results suggest that a smarter dispatch algorithm based on machine learning would enable further cost savings by determining what can be thought of as a shadow price of electricity.

Topics: Energy storage
Commentary by Dr. Valentin Fuster
2017;():V001T04A002. doi:10.1115/ES2017-3288.

In order to reduce CO2 emissions in the residential sector, the installation of photovoltaics (PV) has been increasing extensively. However, such large-scale PV installations cause problems in the low-voltage distribution grid of the residential sector, such as PV related voltage surges. In this study, the utilization of suppressed PV output through energy storage devices was proposed. Using demand side energy storage devices reduces voltage surge, transmission loss, and CO2 emissions from the residential buildings. The objective of this study was to add voltage constraints of the low-voltage distribution grid to an operational planning problem that we developed for the residential energy systems, and to quantitatively evaluate the potential of heat pump water heater (HP) to utilize the PV surplus electricity, while considering the electrical grid constraints based on the minimization of CO2 emissions. We found that when a 4.5 kW HP with 370 L storage, which utilizes PV output, was added to the system, the reduction in CO2 emissions was more than twice compared with that in the case of adding 4 kWh battery (BT) to a PV and gas fired water heater configuration. Further, the effect of utilizing the suppressed PV electricity by HP was almost equivalent to that by the BT. Therefore, the potential of HP in utilizing PV surplus electricity is higher than that of the BT in terms of CO2 emissions reduction in the residential sector.

Commentary by Dr. Valentin Fuster

Concentrating Solar Power

2017;():V001T05A001. doi:10.1115/ES2017-3096.

Recently, Concentrated Solar Power (CSP) is attracting more research attentions because it can store the excessive heat from the solar field and extend the power generation at night, CSP can also levelized the mismatch between energy demand and supply. To make CSP technology competitive, thermal energy storage (TES) system filled with energy storage media is a critical component in all CSP plant.

TES system can be operated by using sensible materials, phase change materials (PCMs) or a combination of both. Because the phase change materials can store more heat due to the latent during the melting/freezing process, it becomes promising to use PCM in latent heat thermal energy storage (LHTES) system for large scale CSP application. Unfortunately, LHSS has relatively low energy storage efficiency compared to SHSS alone because of the fact that LHSS has more parameters to be controlled and optimized.

To realize a complete utilization of PCM and a high energy storage/extraction efficiency and a high exergetic efficiency, one approach is to adopt a cascade configuration of multiple PCMs modules in TES tank, which can also be called as a cascade latent heat thermal energy storage (CLHTES) system. The melting temperatures of the PCMs placed in the TES tank should be cascaded from low to high temperature, where the latent heat of PCM can completely be used to absorb the heat from the solar field for energy storage purpose.

Due to the complexity of a CLHTES system, it is necessary to provide a comprehensive study from the heat transfer perspective. This paper presents a preliminary parametric study of CLHTES system using a previously developed enthalpy-based 1D transient model for energy storage/extraction in CLHTES system. The effects of material properties (such as latent heat, specific heat at solid and liquid phase) and CSP plant operation conditions (such as charging/discharging time period) are to be explored. The results from the preliminary parametric study is expected to be beneficial to the community of solar thermal engineering.

Commentary by Dr. Valentin Fuster
2017;():V001T05A002. doi:10.1115/ES2017-3098.

Concentrating solar power (CSP) technology is moving toward high-temperature and high-performance design. One technology approach is to explore high-temperature heat-transfer fluids and storage, integrated with a high-efficiency power cycle such as the supercritical carbon dioxide (s-CO2) Brayton power cycle. The s-CO2 Brayton power system has great potential to enable the future CSP system to achieve high solar-to-electricity conversion efficiency and to reduce the cost of power generation. Solid particles have been proposed as a possible high-temperature heat-transfer medium that is inexpensive and stable at high temperatures above 1,000°C. The particle/heat exchanger provides a connection between the particles and s-CO2 fluid in the emerging s-CO2 power cycles in order to meet CSP power-cycle performance targets of 50% thermal-to-electric efficiency, and dry cooling at an ambient temperature of 40°C. The development goals for a particle/s-CO2 heat exchanger are to heat s-CO2 to ≥720°C and to use direct thermal storage with low-cost, stable solid particles. This paper presents heat-transfer modeling to inform the particle/s-CO2 heat-exchanger design and assess design tradeoffs. The heat-transfer process was modeled based on a particle/s-CO2 counterflow configuration. Empirical heat-transfer correlations for the fluidized bed and s-CO2 were used in calculating the heat-transfer area and optimizing the tube layout. A 2-D computational fluid-dynamics simulation was applied for particle distribution and fluidization characterization. The operating conditions were studied from the heat-transfer analysis, and cost was estimated from the sizing of the heat exchanger. The paper shows the path in achieving the cost and performance objectives for a heat-exchanger design.

Commentary by Dr. Valentin Fuster
2017;():V001T05A003. doi:10.1115/ES2017-3099.

Solid particles can operate at higher temperature than current molten salt or oil, and they can be a heat-transfer and storage medium in a concentrating solar power (CSP) system. By using inexpensive solid particles and containment material for thermal energy storage (TES), the particle-TES cost can be significantly lower than other TES methods such as a nitrate-salt system. The particle-TES system can hold hot particles at more than 800°C with high thermal performance. The high particle temperatures increase the temperature difference between the hot and cold particles, and they improve the TES capacity. The particle-based CSP system is able to support high-efficiency power generation, such as the supercritical carbon-dioxide Brayton power cycle, to achieve >50% thermal-electric conversion efficiency. This paper describes a solid particle-TES system that integrates into a CSP plant. The hot particles discharge to a heat exchanger to drive the power cycle. The returning cold particles circulate through a particle receiver to absorb solar heat and charge the TES. This paper shows the design of a particle-TES system including containment silos, foundation, silo insulation, and particle materials. The analysis provides results for four TES capacities and two silo configurations. The design analysis indicates that the system can achieve high thermal efficiency, storage effectiveness (i.e., percentage usage of the hot particles), and exergetic efficiency. An insulation method for the hot silo was considered. The particle-TES system can achieve high performance and low cost, and it holds potential for next-generation CSP technology.

Commentary by Dr. Valentin Fuster
2017;():V001T05A004. doi:10.1115/ES2017-3140.

When a coal-fired power plant is considered for closure, arguments are commonly made about the loss of jobs and unrealized investments. Facing this pressure, governments are reluctant to enact enforceable emission standards, and these plants continue to emit pollutants into the atmosphere. As the equipment ages, the plants may retire, but in their lifetime they will cause irreversible environmental damage. This report presents a method to mediate this damage, create jobs, maintain the efficiency of the turbine, and maintain or increase the capacity factor of the plant.

Solar parabolic troughs using molten salt technology are scalable and can meet the steam conditions of a standard Rankine cycle coal-fired power plant. A marriage of these technologies allows the parabolic trough field to be installed without new power generation equipment. The turbine, generator, and transmission equipment are already in place, and when compared to a standalone concentrated solar power (CSP) plant, can be amortized over a greater number of operational hours without the use of very large amounts of thermal storage. That allows for a reduction in capital investment compared to a greenfield CSP plant, and reduces the levelized cost of energy (LCOE) from the solar contribution to well below current US Department of Energy SunShot targets.

Coal-fired plant operators note that they typically cannot operate at partial power output without reducing the efficiency of their turbine accordingly. So, while a photovoltaic hybridization can take advantage of existing transmission infrastructure, it will require that the coal-fired system reduces its output and will consequently reduce the efficiency of the coal cycle. If we have to burn coal, we should do it in the most efficient way possible. Hybridizing with a molten salt parabolic trough installation makes use of the same turbine as the coal-fired system, which maintains the overall efficiency of the turbine at its design point and optimal load. With this model, the coal plant can operate at full power, reduce overall usage of coal while maintaining or even increasing employment opportunities, and reduce CO2 emissions.

Commentary by Dr. Valentin Fuster
2017;():V001T05A005. doi:10.1115/ES2017-3272.

Ceramic particles as a heat transfer fluid for concentrated solar power towers offers a variety of advantages over traditional heat transfer fluids. Ceramic particles permit the use of very high operating temperatures, being limited only by the working temperatures of the receiver components, as well as demonstrate the potential to be used for thermal energy storage. A variety of system configurations utilizing ceramic particles are currently being studied, including upward circulating beds of particles, falling particle curtains, and flows of particles over an array of absorber tubes. The present work investigates the use of gravity-driven dense granular flows through cylindrical tubes, which demonstrate solid packing fractions of approximately 60%. Previous work demonstrated encouraging results for the use of dense flows for heat transfer applications and examined the effect of various parameters on the overall heat transfer for low temperatures. The present work examined the heat transfer to dense flows at high operating temperatures more characteristic of concentrated solar power tower applications. For a given flow rate, the heat transfer coefficient was examined as a function of the mean flow temperature by steadily increasing the input heat flux over a series of trials. The heat transfer coefficient increased almost linearly with temperature below approximately 600°C. Above 600°C, the heat transfer coefficient increased at a faster rate, suggesting an increased radiation heat transfer contribution.

Commentary by Dr. Valentin Fuster
2017;():V001T05A006. doi:10.1115/ES2017-3377.

Particle-based concentrating solar power (CSP) plants have been proposed to increase operating temperature for integration with higher efficiency power cycles using supercritical carbon dioxide (sCO2). The majority of research to date has focused on the development of high-efficiency and high-temperature particle solar thermal receivers. However, system realization will require the design of a particle/sCO2 heat exchanger as well for delivering thermal energy to the power-cycle working fluid. Recent work has identified moving packed-bed heat exchangers as low-cost alternatives to fluidized-bed heat exchangers, which require additional pumps to fluidize the particles and recuperators to capture the lost heat. However, the reduced heat transfer between the particles and the walls of moving packed-bed heat exchangers, compared to fluidized beds, causes concern with adequately sizing components to meet the thermal duty. Models of moving packed-bed heat exchangers are not currently capable of exploring the design trade-offs in particle size, operating temperature, and residence time. The present work provides a predictive numerical model based on literature correlations capable of designing moving packed-bed heat exchangers as well as investigating the effects of particle size, operating temperature, and particle velocity (residence time). Furthermore, the development of a reliable design tool for moving packed-bed heat exchangers must be validated by predicting experimental results in the operating regime of interest. An experimental system is designed to provide the data necessary for model validation and/or to identify where deficiencies or new constitutive relations are needed.

Commentary by Dr. Valentin Fuster
2017;():V001T05A007. doi:10.1115/ES2017-3524.

Previous research at Sandia National Laboratories showed the potential advantages of using light-trapping features which are not currently used in direct tubular receivers. A horizontal bladed receiver arrangement showed the best potential for increasing the effective solar absorptance by increasing the ratio of effective surface area to the aperture footprint. Ray-tracing analyses using SolTrace were performed to understand the light-trapping effects of the bladed receivers, which enable re-reflections between the fins that enhance the effective solar absorptance. A parametric optimization study was performed to determine the best possible configuration with a fixed intrinsic absorptivity of 0.9 and exposed surface area of 1 m2. The resulting design consisted of three vertical panels 0.584 m long and 0.508 m wide and 3 blades 0.508 m long and 0.229 m wide with a downward tilt of 50 degrees from the horizontal. Each blade consisted of two panels which were placed in front of the three vertical panels. The receiver was tested at the National Solar Thermal Test Facility using pressurized air. However, the receiver was designed to operate using supercritical carbon dioxide (sCO2) at 650 °C and 15 MPa for 100,000 hours following the ASME Boiler and Pressure Vessel Code Section VIII Division 1. The air flowed through the leading panel of the blade first, and then recirculated toward the back panel of the blade before flowing through one of the vertical back panels. The test results of the bladed receiver design showed a receiver efficiency increase over a flat receiver panel of ∼5 – 7% (from ∼80% to ∼86%) over a range of average irradiances, while showing that the receiver tubes can withstand temperatures > 800 °C with no issues. Computational fluid dynamics (CFD) modeling using the Discrete Ordinates (DO) radiation model was used to predict the temperature distribution and the resulting receiver efficiencies. The predicted thermal efficiency and surface temperature values correspond to the measured efficiencies and surface temperatures within one standard deviation. In the near future, an sCO2 flow system will be built to expose the receiver to higher pressure and fluid temperatures which could yield higher efficiencies.

Topics: Design , Testing
Commentary by Dr. Valentin Fuster
2017;():V001T05A008. doi:10.1115/ES2017-3573.

Supercritical carbon dioxide (sCO2) Brayton cycle is an emerging technology to be used as a power block with concentrated solar power (CSP) systems, tower type, sCO2 Brayton cycle has the potential to be competitive with traditional Rankine steam cycle. Most of the studies have been focused on the steady state analysis of this technology.

This research has developed numerical models for five configurations of sCO2 Brayton cycles operating under quasi steady state conditions. The studied cycles are connected directly to the solar central receiver tower, which is used to provide heat input to the cycles; consequently, the heat addition is changing over time as a function of solar radiation. During the off load operation, the mass flow rate of the cycle is changing with the goal of keeping the turbine inlet temperature at 700°C. The compressor and turbine use a partial load model to adjust velocities according to the new mass flow rate. Also, the heat exchangers effectiveness are adjusted as they present off-design operation. In the recompression cycle, the model permits to explore the relationship between recompression fraction and the ambient temperature. It is demonstrated that the power generated by the cycle may be improved more than 6 % if the recompression fraction is continuously changed and controlled as a function of the ambient temperature.

Commentary by Dr. Valentin Fuster
2017;():V001T05A009. doi:10.1115/ES2017-3590.

Supercritical carbon dioxide (sCO2) Brayton power cycles have the potential to significantly improve the economic viability of concentrating solar power (CSP) plants by increasing the thermal to electric conversion efficiency from around 35% using high-temperature steam Rankine systems to above 45% depending on the cycle configuration. These systems are the most likely path toward achieving the Department of Energy’s (DOE) Office of Energy Efficiency and Renewable Energy (EERE) SunShot targets for CSP tower thermal to electric conversion efficiency above 50% with dry cooling to air at 40 °C and a power block cost of less than 900 $/kWe. Many studies have been conducted to optimize the performance of various sCO2 Brayton cycle configurations in order to achieve high efficiency, and a few have accounted for drivers of cost such as equipment size in the optimization, but complete techno-economic optimization has not been feasible because there are no validated models relating component performance and cost.

Reasonably accurate component cost models exist from several sources for conventional equipment including turbines, compressors, and heat exchangers for use in rough order of magnitude cost estimates when assembling a system of conventional equipment. However, cost data from fabricated equipment relevant to sCO2 Brayton cycles is very limited in terms of both supplier variety and performance level with most existing data in the range of 1 MWe power cycles or smaller systems, a single completed system around 7 MWe by Echogen Power Systems, and numerous ROM estimates based on preliminary designs of equipment for 10 MWe systems. This data is highly proprietary as the publication of individual data by any single supplier would damage their market position by potentially allowing other vendors to undercut their stated price rather than competing on reduced manufacturing costs.

This paper describes one approach to develop component cost models in order to enable the techno-economic optimization activities needed to guide further research and development while protecting commercially proprietary information from individual vendors. Existing cost models were taken from literature for each major component used in different sCO2 Brayton cycle configurations and adjusted for their magnitude to fit the limited vendor cost data and estimates available. A mean fit curve was developed for each component and used to calculate updated cost comparisons between previously-reviewed sCO2 Brayton cycle configurations for CSP applications including simple recuperated, recompression, cascaded, and mixed-gas combined bifurcation with intercooling cycles. These fitting curves represent an average of the assembled vendor data without revealing any individual vendor cost, and maintain the scaling behavior with performance expected from similar equipment found in literature.

Commentary by Dr. Valentin Fuster
2017;():V001T05A010. doi:10.1115/ES2017-3597.

In this paper we present a dynamic three-dimensional volume element model (VEM) of a parabolic trough solar collector (PTC) comprising an outer glass cover, annular space, absorber tube, and heat transfer fluid. The spatial domain in the VEM is discretized with lumped control volumes (i.e., volume elements) in cylindrical coordinates according to the predefined collector geometry; therefore, the spatial dependency of the model is taken into account without the need to solve partial differential equations. The proposed model combines principles of thermodynamics and heat transfer, along with empirical heat transfer correlations, to simplify the modeling and expedite the computations. The resulting system of ordinary differential equations is integrated in time, yielding temperature fields which can be visualized and assessed with scientific visualization tools. In addition to the mathematical formulation, we present the model validation using the experimental data provided in the literature, and conduct two simple case studies to investigate the collector performance as a function of annulus pressure for different gases as well as its dynamic behavior throughout a sunny day. The proposed model also exhibits computational advantages over conventional PTC models-the model has been written in Fortran with parallel computing capabilities. In summary, we elaborate the unique features of the proposed model coupled with enhanced computational characteristics, and demonstrate its suitability for future simulation and optimization of parabolic trough solar collectors.

Commentary by Dr. Valentin Fuster
2017;():V001T05A011. doi:10.1115/ES2017-3615.

Solar thermal towers are a maturing technology that have the potential to supply a significant part of energy requirements of the future. One of the issues that needs careful attention is the heat flux distribution over the central receiver’s surface. It is imperative to maintain receiver’s thermal stresses below the material limits. Therefore, an adequate aiming strategy for each mirror is crucial. Due to the large number of mirrors present in a solar field, most aiming strategies work using a data base that establishes an aiming point for each mirror depending on the relative position of the sun and heat flux models. This paper proposes a multiple-input multiple-output (MIMO) closed control loop based on a methodology that allows using conventional control strategies such as those based on Proportional Integral Derivative (PID) controllers. Results indicate that even this basic control loop can successfully distribute heat flux on the solar receiver.

Commentary by Dr. Valentin Fuster
2017;():V001T05A012. doi:10.1115/ES2017-3628.

This paper presents a study of alternative heliostat standby aiming strategies and their impact on avian flux hazards and operational performance of a concentrating solar power plant. A mathematical model was developed that predicts the bird-feather temperature as a function of solar irradiance, thermal emittance, convection, and thermal properties of the feather. The irradiance distribution in the airspace above the Ivanpah Unit 2 heliostat field was simulated using a ray-trace model for two different times of the day, four days of the year, and nine different standby aiming strategies. The impact of the alternative aiming strategies on operational performance was assessed by comparing the heliostat slew times from standby position to the receiver for the different aiming strategies. Increased slew times increased a proxy start-up time that reduced the simulated annual energy production. Results showed that spreading the radial aim points around the receiver to a distance of ∼150 m or greater reduced the hazardous exposure times that the feather temperature exceeded the hazard metric of 160 °C. The hazardous exposure times were reduced by ∼23% and 90% at a radial spread of aim points extending to 150 m and 250 m, respectively, but the simulated annual energy production decreased as a result of increased slew times. Single point-focus aiming strategies were also evaluated, but these strategies increased the exposure hazard relative to other aiming strategies.

Topics: Hazards
Commentary by Dr. Valentin Fuster
2017;():V001T05A013. doi:10.1115/ES2017-3634.

A computational heat-transfer and thermodynamic-cycle model was developed to evaluate the performance of an integrated solar and combined-cycle power plant using a prototype linear Fresnel reflector. The solar receiver consists of a secondary reflector and single-tube absorber, with a selective surface and glass cover to optimize collector efficiency. The solar integration occurs in the high-pressure steam drum of the heat recovery steam generator, to boost power output when solar energy is available without the need for an auxiliary fossil-fueled boiler or thermal storage. The solar resource and weather data used in the model were for the municipality of Bom Jesus da Lapa, Brazil.

Results indicated that, over a year, 8.25 GWh of solar thermal energy was provided to the plant, with an incremental power plant output of 2.76 GWh. While these numbers were small relative to baseline power plant operation using only fossil-fuel sources, the utilization of additional solar thermal modules would produce a more significant impact.

Commentary by Dr. Valentin Fuster
2017;():V001T05A014. doi:10.1115/ES2017-3635.

Ganged-heliostats have the potential for large cost reductions with enhanced solar collector field optimization. Unlike typical heliostats that require dual axis tracking actuators and a base or foundation, ganged-heliostats can share actuation and a support structure. This membership greatly reduces system infrastructure and installation costs. However, concentrating solar power (CSP) heliostats are subjected to wind-induced loads, vibration, and gravity-induced deformations. These effects could impact performance and reliability of these structures, where despite the many advantages for the utility of ganged heliostats, modal limitations exist from wind perturbations. In this investigation, an introductory multiphysics finite element analysis (FEA) model was developed using SolidWorks Simulation software to validate experimental measurements of a novel small-scale ganged heliostat system, parametrically under varying azimuth rotations, facet pitch levels, and cable tension levels. The ganged heliostat design featured a number of mirrors resting on two guide wires which were tensioned and rotated to align with any given target. Experimentally, several standard modal tests were conducted on the ganged heliostat, which was designed to operate under a number of orientations, where for this investigation two scenarios were selected to be representative of an operational heliostat. The heliostat was oriented at a 0° (face up) and 45° orientations for the modal test configurations. The modal tests were computationally validated in good agreement with the experiments to within 2.8% and 6.3% error for 0° and 45° orientations respectively.

Commentary by Dr. Valentin Fuster
2017;():V001T05A015. doi:10.1115/ES2017-3677.

Solar electricity can be generated by either photovoltaic panels or concentrating solar power (CSP), which uses a thermal cycle. The recent historic drop in photovoltaic panel prices has encouraged the opinion that CSP, with its higher levelized cost of energy, has poor prospects outside of niche deployments. We review evidence for the contrary view, supported by the International Energy Agency and others, that CSP’s market prospects are in fact bright.

Commentary by Dr. Valentin Fuster
2017;():V001T05A016. doi:10.1115/ES2017-3689.

Novel particle release patterns have been proposed as a means to increase the thermal efficiency of high-temperature falling particle receivers. Innovative release patterns offer the ability to utilize light-trapping and volumetric heating effects as a means to increase particle temperatures over a conventional straight-line particle release pattern. The particle release patterns explored in this work include wave-like patterns and a series of parallel curtains normal to the incident irradiation that have shown favorable results in previous numerical studies at lower particle temperatures. A numerical model has recently been developed of an existing falling particle receiver at the National Solar Thermal Test Facility at Sandia National Laboratories to evaluate these patterns at elevated temperatures necessary to evaluate radiative and convective losses. This model has demonstrated that thermal efficiency gains of 2.5–4.6% could be realized using these patterns compared to the conventional planar release depending on the particle mass flow rate. Increasing the number of parallel curtains, increasing the spacing between curtains, and shifting the particle mass flow rate deeper in the receiver cavity was also found to increase the thermal efficiency. These effects became less significant as the particle mass flow rate increased.

Commentary by Dr. Valentin Fuster

Environmental, Economic, and Policy Considerations of Advanced Energy Systems

2017;():V001T06A001. doi:10.1115/ES2017-3693.

This paper analyzes some of the existing incentives for solar photovoltaic (PV) energy generation in the U.S. to investigate how effectively those existing incentive policies can promote PV adaptions in the U.S. market. Two common building types (i.e., hospitals and large hotels) located in five different U.S. states, each having their own incentives, are selected and analyzed for the PV incentive policies. The payback period of the PV system is chosen as an indicator to analyze and critique the effectiveness of each incentive by comparing the payback periods before and after taking the incentive into consideration. In this way, the existing incentive policies implemented by utility companies in each state are analyzed and critiqued. Finally, a parametric analysis is conducted to determine the influence of the variation in key parameters, such as PV system capacity and PV capital cost, on the performance of PV system. The results show how the existing incentives can be effectively used to promote the PV systems in the U.S. and how variations of the parameters can impact the payback period of the PV systems. Through the evaluation of the existing incentive policies and the parametric study, this paper demonstrates that the type and level of incentives should be carefully determined in policy-making processes to effectively promote the PV systems.

Commentary by Dr. Valentin Fuster

Geothermal Power, Hydro/Ocean Power, and Emerging Energy Technologies

2017;():V001T07A001. doi:10.1115/ES2017-3038.

The control of a three-degree-of-freedom (3-DOF) wave energy converter (WEC) is considered in this paper. Recently, several methods have been developed in the literature for this problem. This paper is a comparison between three methods: the non-linear model predictive control, the pseudo-spectral method, and the time-variant linear quadratic optimal control. Comparison between the three methods is presented in terms of the harvested energy.

Commentary by Dr. Valentin Fuster
2017;():V001T07A002. doi:10.1115/ES2017-3372.

The use of pumps as turbines (PAT) has gained importance in the recent years as a possible alternative to specifically developed turbine for mini/micro hydropower plants. The use of production pump for hydropower generation reduces the capital cost of the plant but the energy conversion efficiency can be remarkably lower.

The paper analyses the performance of a production centrifugal pump running both in direct and reverse mode. The analysis calculates theoretically the behavior of the PAT under the best efficiency point and extends the investigation to other operating points using both a combined theoretical approach and CFD simulation under dynamic conditions.

The effects of possible modifications to the initial design of the pump are investigated when running in turbine mode and their influence on the standard pump operation is also determined.

Numerical simulation demonstrates that the impeller trimming leads to improvement in the PAT efficiency in some operating conditions. Conversely, the rotational speeds close to the values typical for the electric generator reduce the PAT performance. Finally, the modification of the impeller geometry at the turbine inlet increases the PAT efficiency but lowers the performance of the machine when running in pump mode.

Commentary by Dr. Valentin Fuster
2017;():V001T07A003. doi:10.1115/ES2017-3425.

In this paper, a numerical simulation of tether undersea kites (TUSK) used for power generation is undertaken. The effect of varying key design parameters in these systems is studied. TUSK systems consist of a rigid-winged kite, or glider, moving in an ocean current. One proposed TUSK concept uses a tethered kite which is connected by a flexible tether to a support structure with a generator on a surface buoy. The numerical simulation models the flow field in a three-dimensional domain near the rigid undersea kite wing by solving the full Navier-Stokes equations. A moving computational domain method is used to reduce the computational run times. A second-order corrector-predictor method, along with Open Multi-Processing (OpenMP), is employed to solve the flow equations. In order to track the rigid kite, which is a rectangular planform wing with a NACA 0021 airfoil, an immersed boundary method is used. The tension force in the elastic tether is modeled by a simple Hooke’s law, and the effect of tether damping is added. PID control methods are used to adjust the kite pitch, roll and yaw angles during power (tether reel-out) and retraction (reel-in) phases to obtain the desired kite trajectories. During the reel-out phase the kite moves in successive cross-current motions in a figure-8 pattern, the tether length increases and power is generated. During reel-in the kite motion is along the tether, and kite hydrodynamic forces are reduced so that net positive power is produced. The effects of different key design parameters in TUSK systems, such as the ratio of tether to current velocity, and tether retraction velocity, are then further studied. System power output, kite trajectories, and vorticity flow fields for the kite are also determined.

Commentary by Dr. Valentin Fuster
2017;():V001T07A004. doi:10.1115/ES2017-3442.

There has been a recent surge in interest for Tesla turbines used in renewable energy applications such as power extraction from low-quality steam generated from geothermal or concentrated solar sources as well as unfiltered particle-laden biomass combustion products. High interest in these bladeless turbines motives renewed theoretical and experimental study.

Despite this renewed interest, no systematic Tesla turbine design process based in foundational theory has been published in the peer reviewed engineering literature. A design process is thus presented which is flexible, allowing an engineering designer to select and address goals beyond simply maximizing turbine output power. This process is demonstrated by designing a Tesla turbine where Reynolds number can be easily varied while holding all other parameters fixed. Tesla turbines are extremely sensitive to inter-disk spacing. It is therefore desirable to design the experiment to avoid turbine disassembly/reassembly between tests; this assures identical disk spacing and other parameters for all tests. It is also desirable to maintain similar working fluid mass flow rate through the turbine in all tests to minimize influence of losses at the nozzle impacting shaft power output differently across experiments.

Variation in Reynolds number over more than two orders of magnitude is achieved by creating a set of two-component working fluid mixtures of water and corn syrup. Increasing mixture mass fraction of corn syrup achieves increased working fluid viscosity but only small increase in density with a corresponding decrease in working fluid Reynolds number.

The overall design goal is to create a turbine that allows modulating Reynolds number impact on Tesla turbine performance to be evaluated experimentally. The secondary goal is to size the turbine to maximize sensitivity to changes in Reynolds number to make experimental measurement easier.

The presented example design process results in a Tesla turbine with 8-cm-outer-diameter and 4-cm-inner-diameter disks. The turbine will be able to access a range of Reynolds numbers from 0.49 < Rem < 99.50. This range represents a Reynolds number ratio of Rem,max/Rem,min = 202.8, more than two orders of magnitude and spanning the lower part of the laminar range. The turbine’s expected power output will be = 0.47 Watts with a delivered torque of 0.024 mN-m at a rotation rate of ωmax = 1197 rev/min.

Combining the analytical equations underpinning the design process with similarity arguments, it is shown that shrinking the Tesla turbine’s physical scale drives the Reynolds number toward 0. The resulting velocity difference between the working fluid and the turbine disks gets driven toward infinity, which makes momentum transfer and the resulting turbine efficiency extremely high. In other words, unlike conventional turbines whose efficiency drops as they are scaled down, the performance of Tesla turbines will increase as they are made smaller.

Finally, it is shown through similarity scaling arguments that the 8-cm-diameter turbine resulting from the design process of this paper and running liquid Ethylene Glycol working fluid can be used to evaluate and approximate the performance of a 3-mm-diameter Tesla turbine powered by products of combustion in air.

Commentary by Dr. Valentin Fuster
2017;():V001T07A005. doi:10.1115/ES2017-3490.

Hydro power has always been a major source of electricity generation among different renewable energy technologies. However, due to the construction of dams, the conventional hydro energy extraction techniques cause disturbance to the ecology by diverting the natural flow of water and migrating population from their native land. Of late, energy extraction from the natural flow of water is considered as potential source of renewable power since it is clean and reliable. In view of this, the present study deals with the development and performance characterization of a vertical-axis helical-bladed hydrokinetic turbine. Considering the various design parameters, a NACA 0020 bladed vertical-axis turbine of solidity ratio 0.38 and aspect ratio 1.0 has been developed. In-situ experiments have been carried out at an irrigation sluice having a water velocity of 1.1 m/s. Further, its performance characteristics are evaluated at different mechanical loading conditions with the help of a mechanical dynamometer. It has been observed that the developed helical-bladed turbine demonstrates a peak power coefficient of 0.16 at a tip-speed ratio of 0.85. The present experimental investigation has clearly demonstrated the usefulness of the hydrokinetic turbine. It has also been logged that the average water velocity at the concerned site has a great importance on the turbine design.

Commentary by Dr. Valentin Fuster

Photovoltaics

2017;():V001T08A001. doi:10.1115/ES2017-3270.

In this study, prototype electrodynamic dust shield (EDS) devices large enough to cover commercial photovoltaic (PV) modules were fabricated and tested in the lab and in the field. The EDS device consisted a polyethylene terephthalate (PET) substrate with screen-printed silver electrodes, and a PET cover sheet that bonded to the substrate using a synthetic rubber adhesive. The voltage-current characteristics of the EDS device was measured while square wave high voltage was applied to the device, so as to determine the power consumption of the EDS device. The EDS device was also tested in the field to determine its effectiveness in soiling mitigation.

Measurements showed that the EDS capacitance varied from approximately 600 pF in the air-conditioned lab to 2 nF in the field when the EDS device temperature reached 45 °C. The variation of the capacitance has significant relevance to the capacity requirements for the high voltage sources needed to energize the EDS device and its power consumption. Under laboratory conditions, the EDS power consumption was found to be 0.3 W m−2 at 6 kVp-p and 1 Hz, and roughly proportional to the voltage squared.

In the field test electrode damage was observed, due to electrical discharge at the electrode lines. As a result, the EDS operation did not show significant effect of soiling mitigation.

The results of this study are useful for designing high voltage sources for EDS operation, and for modifying the design and fabrication methods in order to produce EDS devices that can effectively repel dust in the field.

Topics: Dust
Commentary by Dr. Valentin Fuster
2017;():V001T08A002. doi:10.1115/ES2017-3388.

To achieve reliable and efficient operation of generic polycrystalline silicon solar cell under concentrated sunlight, a novel structure of the cell layers is proposed along with effective cooling technique using microchannel heat sink (MCHS). In the novel structure, Boron Nitride with the volume fraction of 20%, 40%, and 60% as a filler is incorporated in the Ethylene Vinyl Acetate (EVA) matrix to form a new composite. The new composite is used instead of the conventional EVA layer in the solar cell. Various solar cell structures integrated with MCHS are studied and compared with the conventional structure. To determine the performance of the developed concentrated photovoltaic thermal (CPVT) system, a comprehensive three-dimensional model of the solar cell with heat sink is developed. The model is numerically simulated and validated. Based on the validated results, it is found that the novel structure with EVA-60% BN composite along with aluminum foil back sheet attains 30% increase in the gained solar cell electric power with 10.9 % reduction in the cell temperature compared with the conventional solar cell structure at the same cooling mass flow rate of 50 g/min and concentration ratio of 20. However at CR = 20, Vw = 1m/s and Ta = 30°C a significant damage of the conventional solar cell structure will occurs if no effective cooling technique is used. Moreover, the developed design of solar cell achieves a higher CPVT-system thermal efficiency compared with the conventional one.

Commentary by Dr. Valentin Fuster
2017;():V001T08A003. doi:10.1115/ES2017-3397.

The goal of a recent study was to design, and determine the effectiveness of, a fixed-tilt solar panel module that contains strands of photovoltaic cells, which are rotated by a very small motor to track the sun. The motivation was that such a configuration enjoys the advantage of increased energy collection over static solar panels due to sun tracking ability, while it mitigates some key difficulties associated with stabilizing and rotating bulky panels as current active and passive tracking systems need to do. Most critically, such a module allows the benefits of sun tracking to be reaped by sloped roof panel installations, which at present almost always consist of fixed-tilt solar panels rather than rotating tracking panels. The study’s result is an active tracking system design in a fixed-tilt module configuration that generated over 10% more daily energy typically, during the test period, compared to a static panel, thus substantially offsetting its added complexity and higher initial cost.

Commentary by Dr. Valentin Fuster

Sustainable Building Energy Systems

2017;():V001T09A001. doi:10.1115/ES2017-3092.

Conventional residential building energy auditing needed to identify opportunities for energy savings is expensive and time consuming. On-site energy audits require quantification of envelope R-values, air and duct leakage, and heating and cooling system efficiencies. There is a need to advance lower cost automated approaches, which could include aerial and drive-by thermal imaging at-scale in an effort to measure the building R-value. However, single-point in time thermal images are generally qualitative, subject to errors stemming from building dynamics, background radiation, wind speed variation, night sky thermal radiation, and error in extracting temperature estimates from thermal images from surfaces with generally unknown emissivity. This work proposes two alternative approaches for estimating roof R-values from thermal imaging, one a physics based approach and the other a data-mining based approach. Both approaches employ aerial visual imagery to estimate the roof emissivity based on the color and type of roofing material, from which the temperature of the envelope can be estimated. The physics-based approach employs a dynamic energy model of the envelope with unknown R-value and thermal capacitance. These are tuned in order to predict the measured surface temperature at the time of the imaging, given the transient weather conditions prior to the imaging. The data-mining approach integrates the inferred temperature measurement, historical utility data, and easily accessible or potentially easily accessible housing data. A data mining regression model, trained from this data using residences with known R-values, is used to predict the roof R-value in the unknown houses. The data mining approach was shown to be a far superior approach, demonstrating an ability to estimate attic/roof R-value with an r-squared value of greater than 0.88 using as few as nine training houses. The implication of this research is significant, offering the possibility of auditing residences remotely at-scale via aerial and drive-by thermal imaging coupled with utility analysis.

Commentary by Dr. Valentin Fuster
2017;():V001T09A002. doi:10.1115/ES2017-3105.

Advanced energy management control systems (EMCS), or building automation systems (BAS), offer an excellent means of reducing energy consumption in heating, ventilating, and air conditioning (HVAC) systems while maintaining and improving indoor environmental conditions. This can be achieved through the use of computational intelligence and optimization. This paper evaluates model-based optimization processes (OP) for HVAC systems utilizing any computer algebra system (CAS), genetic algorithms and self-learning or self-tuning models (STM), which minimizes the error between measured and predicted performance data. The OP can be integrated into the EMCS to perform several intelligent functions achieving optimal system performance. The development of several self-learning HVAC models and optimizing the process (minimizing energy use) is tested using data collected from an actual HVAC system.

Using this optimization process (OP), the optimal variable set points (OVSP), such as supply air temperature (Ts), supply duct static pressure (Ps), chilled water supply temperature (Tw), minimum outdoor ventilation, and chilled water differential pressure set-point (Dpw) are optimized with respect to energy use of the HVAC’s cooling side including the chiller, pump, and fan. The optimized set point variables minimize energy use and maintain thermal comfort incorporating ASHRAE’s new ventilation standard 62.1-2013.

This research focuses primarily with: on-line, self-tuning, optimization process (OLSTOP); HVAC design principles; and control strategies within a building automation system (BAS) controller. The HVAC controller will achieve the lowest energy consumption of the cooling side while maintaining occupant comfort by performing and prioritizing the appropriate actions. The program’s algorithms analyze multiple variables (humidity, pressure, temperature, CO2, etc.) simultaneously at key locations throughout the HVAC system (pumps, cooling coil, chiller, fan, etc.) to reach the function’s objective, which is the lowest energy consumption while maintaining occupancy comfort.

Commentary by Dr. Valentin Fuster
2017;():V001T09A003. doi:10.1115/ES2017-3200.

This paper aims to evaluate the thermal performance and feasibility of integrating the Earth-Air Heat Exchanger (EAHE) with the building’s vapor compression air cooling system. In the proposed system, the ambient air is forced by an axial fan through an EAHE buried at a certain depth below the ground surface. EAHE uses the subsoil low temperature and soil thermal properties to reduce the air temperature. The outlet air from the EAHE was used for the purpose of cooling the condenser of the vapor compression cycle (VCC) to enhance its coefficient of performance (COP). The potential enhancement on the COP was investigated for two different refrigerants (i.e. R-22 and R410a) cooling systems. A mathematical model was developed to estimate the underground soil temperature at different depths and the corresponding outlet air temperature of EAHE was calculated. The obtained results showed that the soil temperature in Dubai at 4 meters depth is about 27°C and remains relatively constant across the year. In order to estimate the effect of using EAHE on the performance of the VCC system, a sample villa project was selected as a case study. The obtained results showed that EAHE system contributed efficiently to the COP of the VCC with an overall increase of 47 % and 49 % for R-22 and R410a cycles, respectively. Moreover, the calculated values were validated against Cycle_D simulation model and showed good agreement with a maximum deviation of 5%. The payback period for this project was found to be around two years while the expected life time is about 10 years which makes it an attractive investment.

Commentary by Dr. Valentin Fuster
2017;():V001T09A004. doi:10.1115/ES2017-3563.

This paper discusses a Fiber-Optic Hybrid Day-Lighting system that can cut energy consumed by buildings for lighting significantly. This system is designed for mobile applications such as military shelters. The system is comprised of two primary components: the solar collector and the Solar Hybrid Lighting Fixture. The first component, the solar collector, consists of a housing, structural stand, a dual axis tracking system, Fresnel Lenses, secondary optics, and fiber-optic cables. The collector is integrated into a dual-axis tracker, which is then mounted on a tripod. The tripod can be staked into the ground and weighed down to protect the system from any wind loading and the collector height can be adjusted so that there is no shading of the collector by nearby structures. The collector with an aluminum housing holds eight 10-inch diameter Fresnel Lenses that focus sunlight onto eight secondary optics based on TIR (total internal reflection) which filter UV/IR and deliver uniform light to the fiber-optic cables. The secondary optic is coupled to the fiber-optic cable with index matching gel so that Fresnel reflection losses are minimized. The solar collector tracks the sun’s movement through the day with a dual-axis tracker (azimuth/tilt), ensuring the light is concentrated into the fiber-optic cables. The optics has been designed to have a high half-acceptance of 1.75° and can accommodate a tracking accuracy of 1.50° or better.

The opposite end of the fiber-optic cable attaches to the second part of the Day-Lighting system, the Solar Hybrid Light Fixture (SHLF). The SHLF comprises of two lighting systems: 1) a solar fiber-optic system and 2) an LED system. The fiber-optic cable is coupled to an acrylic light diffusing rod that evenly delivers the light into the room. During sunny periods, depending on the length of the cable, solar fiber-optic lighting could provide full illumination of the space. In order to keep lighting uniform even during fluctuations of the light output from the sun during cloudy periods, the LED portion of the light will allow for constant lighting at a lower power consumption. The LED lighting has dimming capabilities due to a photosensor that regulates the light output of the LEDs based on how much solar light is delivered by the fiber-optic cables. On a typical sunny day with an overall concentration factor of ∼400 from the Fresnel Lens system to the optical fiber, it is possible to generate an output of 2,000 lumens with a 20-foot cable, with each fiber-optic cable experiencing a 1% loss of light per foot of cable. The LED portion of the hybrid light fixture produces about 1,800 lumens as well.

Topics: Fibers , Daylighting
Commentary by Dr. Valentin Fuster
2017;():V001T09A005. doi:10.1115/ES2017-3582.

This paper is an ASHRAE Level 3 study of the energy audit process carried out in an institutional building, The Umm Shaif Building, of The Petroleum Institute, Abu Dhabi, UAE. It undertakes the study by collecting data and conditional surveys. The energy loss locations are highlighted through psychrometric and infrared camera analysis. The detailed dynamic model has been simulated using the EnergyPlus® simulation engine. The details of the building envelope, and fenestration, the occupancy schedules, the equipment energy consumption and HVAC details are presented. The detailed building model is used to allocate the energy usage and identify key energy consumers. The main results are reported using monthly total energy consumption. The validation and calibration are performed through different statistical metrics including Coefficient of Determination (R2), Root Mean Square Error (RMSE) and Coefficient of Variance Root Mean Square Error (CVRMSE). Finally, energy conservation measures are suggested with the energy and cost savings.

Commentary by Dr. Valentin Fuster
2017;():V001T09A006. doi:10.1115/ES2017-3601.

Indoor Air Quality (IAQ) studies the air quality inside different types of environments and relates it to the health and comfort of occupants. Understanding and controlling common pollutants indoors can help in decreasing effects and the risks associated with these pollutants. Unhealthy indoor environment could lead to serious problems in people health and productivity. According to ASHRAE, 80–90% of personal time is spent indoors. As a result, indoor air pollution has gained a lot of interest and the number of studies on occupant health inside buildings grew very significantly in the last decades. The purpose of this study is to investigate the effect of indoor air quality inside an educational buildings on occupants’ comfort and performance. Various indoor pollutant such as, Carbon dioxide, Carbon monoxide, Volatile organic compounds, Particulates, and formaldehyde, are measured. The indoor air contaminants will be detected using IAQ measurement devices. The value of the pollutants is compared to maximum allowed values in ASHRAE standard 62.1. In addition, the occupant thermal comfort is reported using two indices which are Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD). The relationship between the performance and the indoor air quality is also discussed. The results will discover the sources of the indoor air pollutants and accordingly suggestions will be given toward improving the indoor air quality. The final results showed that the IAQ is generally in a good condition for the majority of classrooms except for the TVOC which was always at high concentrations. Also, for some classrooms, the CO2 level and the relative humidity were exceeding the maximum limit. Regarding the thermal comfort, all the classrooms do not comply with ASHRAE Standard 55-2013. Therefore, they are not thermally comfortable.

Topics: Air pollution
Commentary by Dr. Valentin Fuster
2017;():V001T09A007. doi:10.1115/ES2017-3666.

Building energy audits are both expensive, on the order of $0.50(US)/sf [1], and there aren’t enough auditors to survey the entire building stock in the U.S. Needed are lower cost automated approaches for rapidly evaluating the energy effectiveness of buildings. A key element of such an approach would be automated measurements of envelope R-values. Proposed is the use of single point-in-time thermal images potentially obtainable from drive-by thermal imaging to infer wall and window R-values. A data mining based approach is proposed, which seeks to calibrate the measured exterior wall temperatures to known and measured R-values for a small subset of residences. In this approach, visual imagery is first used to determine the wall emissivity based on the color of the wall siding in order to yield an estimate of the wall temperature. A Random Forest model is developed using the training set comprised of the residences with known R-value. This model can then be used to estimate R- and C-values of other houses based upon their measured exterior temperatures. The results show that the proposed approach is capable of accurately estimating envelope thermal characteristics over a spectrum of envelope R-values and thermal capacitances present in residences nationally. The resulting error for the houses considered is maximally 12% using as few as nine training houses. The data mining approach has significantly greater accuracy than modeling-based approaches in the literature.

Commentary by Dr. Valentin Fuster

Sustainable Infrastructure and Transportation

2017;():V001T10A001. doi:10.1115/ES2017-3389.

Air pollution is a leading public health concern that needs to be tackled. About 30% of the total greenhouse gas emissions, such as CO, HC and NOx are due to automobiles. By 2030, the US Department of Transportation aims to reduce light duty vehicle emissions by 18%. This can be achieved by public policy approaches such as implementing emission control norms and performance improvements such as exhaust system design.

In this work, the implementation of a pure Zeolite catalyst to reduce the exhaust CO2 emission of a SI engine is studied theoretically and experimentally. The complete exhaust system including the catalytic converter, muffler, and pipes is modeled in a 3D CAD modeling software, using the engine specifications. Current expensive precious metals in the catalytic converter are replaced with a binding agent along with Zeolite catalyst. The exhaust system is fabricated and the experimental tests are performed at the maximum engine RPM to obtain threshold emission reduction values. The results showed obtaining an emission reduction of CO2 at a lower cost. Furthermore, it is found that employing Zeolite sieves can further reduce the pollutant emission at a similar cost.

Commentary by Dr. Valentin Fuster
2017;():V001T10A002. doi:10.1115/ES2017-3589.

Cyber-physical systems (CPS) are smart systems that include engineered interacting networks of physical and computational components. The tight integration of a wide range of heterogeneous components enables new functionality and quality of life improvements in critical infrastructures such as smart cities, intelligent buildings, and smart energy systems. One approach to study CPS uses both simulations and hardware-in-the-loop (HIL) to test the physical dynamics of hardware in a controlled environment. However, because CPS experiment design may involve domain experts from multiple disciplines who use different simulation tool suites, it can be a challenge to integrate the heterogeneous simulation languages and hardware interfaces into a single experiment. The National Institute of Standards and Technology (NIST) is working on the development of a universal CPS environment for federation (UCEF) that can be used to design and run experiments that incorporate heterogeneous physical and computational resources over a wide geographic area. This development environment uses the High Level Architecture (HLA), which the Department of Defense has advocated for co-simulation in the field of distributed simulations, to enable communication between hardware and different simulation languages such as Simulink® and LabVIEW®. This paper provides an overview of UCEF and motivates how the environment could be used to develop energy experiments using an illustrative example of an emulated heat pump system.

Commentary by Dr. Valentin Fuster
2017;():V001T10A003. doi:10.1115/ES2017-3613.

Sustainability of natural gas transmission infrastructure is highly related to the system’s ability to decrease emissions due to ruptures or leaks. Although traditionally such detection relies in alarm management system and operator’s expertise, given the system’s nature as large-scale, complex, and with vast amount of information available, such alarm generation is better suited for a fault detection system based on data-driven techniques. This would allow operators and engineers to have a better framework to address the online data being gathered.

This paper presents an assessment on multiple fault-case scenarios in critical infrastructure using two different data-driven based fault detection algorithms: Principal component analysis (PCA) and its dynamic variation (DPCA).

Both strategies are assessed under fault scenarios related to natural gas transmission systems including pipeline leakage due to structural failure and flow interruption due to emergency valve shut down. Performance evaluation of fault detection algorithms is carried out based on false alarm rate, detection time and misdetection rate. The development of modern alarm management frameworks would have a significant contribution in natural gas transmission systems’ safety, reliability and sustainability.

Commentary by Dr. Valentin Fuster

Thermal Energy Storage Systems

2017;():V001T11A001. doi:10.1115/ES2017-3094.

In this contribution we introduced an integrated energy system consists of thermal power plants, combined heat-power (CHP) plants and wind power plants, and aimed to supply electricity and heat to users simultaneously. A large-scale battery, a TES device and heat transfer devices are included also. During the operation time of the battery, the TES device stores the generated heat and meanwhile supplies heat to users. Applying the power flow method, the electro-thermal analogy and the entransy dissipation-based thermal resistance method, we constructed the power flow model of the system. Besides, we optimized the system aimed to minimize wind curtailments. Optimization results presented for a typical day the system reduces wind curtailment percentage from 40.63 % to 13.70 % and supply 5% heat load. Besides, the operation strategy of the battery is to charge at night and discharge in the day.

Commentary by Dr. Valentin Fuster
2017;():V001T11A002. doi:10.1115/ES2017-3253.

In the sugar mill in Tanegashima which is an isolated island in Japan, raw sugar production process produces raw sugar and bagasse simultaneously. Raw bagasse is not storable because of its perishability due to high moisture content. Actually, the bagasse boiler burns more bagasse than that is required for the sugar mill. Hence, the temperature of flue gas increases and a massive amount of unused heat at around 200 °C is exhausted during sugar mill operation period. On the other hand, many other factories in this island burn imported oil at package boilers to generate process steam up to 120 °C all year around. To resolve this spatial and seasonal mismatch, we employed thermochemical energy storage and transport system using zeolite steam adsorption and regeneration cycle. We introduced a basic design of heat release device which is called “Zeolite boiler”, that is a moving bed with indirect heat exchanger. Adsorbed steam is assumed to be generated by a package boiler. A small zeolite boiler with 20 kg/h of zeolite was designed by using a developed quasi-2D simulation code that numerically solves mass and heat conservation equations of the counter-flow reactor model. As the result of single injection from the top of chamber, the zeolite boiler could generate 4.95 kg/h of dry saturated steam at 0.2 MPa when 4.0 kg/h of steam was injected from the package boiler. Multi injection process was considered to improve the heat recovery rate. By injecting 3.0 kg/h and 1.0 kg/h of steam separately from the top and the middle of the chamber, 5.9 kg/h of steam was generated and heat recovery rate was increased by 13 points.

Commentary by Dr. Valentin Fuster
2017;():V001T11A003. doi:10.1115/ES2017-3276.

Researchers are committed to develop robust and responsive technologies for renewable energy sources to avert from reliance on fossil fuels, which is the main cause of global warming and climate change. Solar energy based renewable energy technologies are valued as an important substitute to bridge gap between energy demand and generation. However, due to varying and inconsistent nature of solar energy during weather fluctuations, seasonal conditions and night times, the complete utilisation of technology is not guaranteed. Therefore, thermal energy storage (TES) system is considered as an imperative technology to be deployed within solar energy systems or heat recovery systems to maximise systems efficiency and to compensate for varying thermal irradiance. TES system can capture and store the excess amount of thermal energy during solar peak hours or recover from systems that would otherwise discard this excess amount of thermal energy. This stored energy is then made available to be utilised during solar off peak hours or night times.

Phase change material (PCM) based TES system is appraised as a viable option due to its excellent adoption to solar and heat recovery systems, higher thermal storage density and wide range of materials availability. However, due to its low thermal conductivity (≅ 0.2 W/mK), the rapid charging and discharging of TES system is a challenge. Therefore, there is a need for efficient and responsive heat exchange mechanism to boost the heat transfer within PCM.

In this study, transient analysis of two-dimensional computational model of vertical shell and tube based TES system is conducted. Commercial grade paraffin (RT44HC) is employed in shell as thermal storage material due to its higher thermal storage density, thermo-physical stability and compatibility with container material. Water is made to flow in tubes as heat transfer fluid. In this numerical study, the parametric investigations are performed to determine the enhancement in charging rate, discharging rate and thermal storage capacity of TES system. The parametric investigations involve geometrical orientations of tubes in shell with and without fins, inlet temperature and volume flow rate of HTF.

It is evident from numerical results that due to increase in effective surface area for heat transfer by vertical fins, the charging and discharging rate of paraffin based TES system can be significantly increased. Due to inclusion of vertical fins, conduction heat transfer is dominant mode of heat transfer in both charging and discharging processes. Furthermore, vertical fins do not restrict natural convection or buoyancy driven flow as compared to horizontal fins. Similarly, the inlet temperature has a noticeable impact on both charging and discharging process. In melting process, the sensible enthalpy is boosted due to rise in inlet temperature and thus the whole system thermal storage capacity is enhanced. Likewise, the effect of volume flow rate of HTF on charging and discharging rate is moderate as compared to inlet temperature of HTF. The numerical results are validated by experimental results.

To conclude, these findings present an understanding into how to increase charging and discharging rate of TES system so as to provide feasible design solutions for widespread domestic and commercial utilisation of TES technology.

Commentary by Dr. Valentin Fuster
2017;():V001T11A004. doi:10.1115/ES2017-3370.

Liquid Air Energy Storage (LAES) is one of the methods to store energy, which takes the advantage of high expansion ratio of air from liquid state to gaseous state. It uses liquefied air to create a potential energy reserve, by storing air in liquid form at −196°C, in insulated, unpressurized vessels and exposing them to ambient temperatures followed by an electricity generation process by driving a turbine. Off-peak electricity is used to liquefy air, and liquid air will be drawn from the tank, pumped to high pressure and used to drive a turbine to generate electricity when this stored energy is needed. Thermal storage loops (cold recycle) within the cycle as well as integration of waste cold (using the cold released during regasification of LNG) or waste heat (utilizing a waste heat stream during the expansion of air) are the key benefits of this technology and strengthen its competitive position among other energy storage methods.

In this paper, a grid scale, long duration energy storage system based on the liquid air cycle has been analyzed. The performance of a modified LAES system is evaluated to find out critical components and processes, which have a major impact on overall system performance. An economic study has been conducted by assuming a grid-scale LAES operating in Turkish market. LAES appears to be a promising solution as long as its full potential is unlocked by integration of waste cold and waste heat, resulting in an energy dense and cost competitive easily scalable energy storage solution.

Commentary by Dr. Valentin Fuster
2017;():V001T11A005. doi:10.1115/ES2017-3578.

Successful deployment of large amounts of renewable solar and wind energy has created a pressing need for significant additions of grid connected energy storage. Excess renewable generation is increasingly necessitating curtailment or derating of renewable or conventional generators. The CAISO Duck Curve [8] illustrates the challenge caused by very large quantities of solar generation. Both large scale energy storage and flexible ramping are needed for renewable resources to be financially sustainable and to meet CO2 reduction goals.

The Dispatchable Solar Combined Cycle (DSCC) integrates Concentrating Solar Power (CSP) with Thermal Energy Storage (TES) in a holistic combined cycle configuration to meet the challenges of the CAISO Duck Curve by delivering flexible capacity with dispatchable solar power. Energy cost from DSCC is comparable to that from a Combined Cycle Power Plant (CCPP), and substantially below the alternatives: Photovoltaic plus battery or Photovoltaic plus combustion turbine. DSCC also enable far higher integration of renewable power and far larger renewable capacity factors than the Integrated Solar Combined Cycle (ISCC), which typically has no storage.

The innovative DSCC system:

• uses energy storage to deliver power when it is most valuable,

• increases the capacity factor to deliver more renewable energy,

• improves the power plant Heat Rate to reduce fuel consumption, and

• reduces the cost of power while addressing RPS and storage mandates.

In DSCC, the CSP and TES are used primarily for latent heat: the evaporation of steam, and the Combustion Turbine (CT) exhaust gas is used primarily for sensible heating, especially superheating steam. This simplifies the integration of low-cost storage media, such as paraffinic oils or concrete, instead of molten salt, since high temperature storage is not needed. A single pressure, non-reheat steam cycle suitable, allowing for simplicity of design and operation, reducing costs and facilitating faster startup and ramping.

With DSCC, the steam turbine generates about the same power as the CT, unlike a typical CCPP where about half the power comes from the steam cycle. The additional steam production reduces the Heat Rate about 25% compared to CCPP.

The DSCC approach is ideally suited for repowering existing CSP plants, to provide firm capacity that can dispatch at valuable evening peak periods, increase the power output, and reduce fossil fuel use compared with conventional CCPP or peaking plants.

This paper will outline the DSCC concept, and provide performance estimates for a reference plant.

Commentary by Dr. Valentin Fuster

Thermodynamic Analysis of Energy Systems

2017;():V001T12A001. doi:10.1115/ES2017-3174.

This study focuses on the power cycles such as organic Rankine cycle (ORC) and combined regenerative Brayton/ORC. The selection of working fluids and power cycles is traditionally conducted by trial and error method and performing a large number of parametric calculations over a range of operating conditions. A methodology for selection of optimal working fluid based on the cycle operating conditions and thermophysical properties of the working fluids was developed in this study. Thermodynamic performance (thermal efficiency and net power output) of a simple subcritical and supercritical ORC was analyzed over a range of operating conditions for a number of working fluids to determine the effect of operating parameters on cycle performance and select the best working fluid. New expressions for thermal efficiency of a simple ORC are proposed. In case of a regenerative Brayton/ORC, the results show that CO2 is the best working fluid for the topping cycle. Depending on the exhaust temperature of the topping cycle, Isobutane, R11 and Ethanol are the preferred working fluids for the bottoming (ORC) cycle, resulting in highest efficiency of the combined cycle. Finally, a performance map is presented as guidance for selection of the best working fluid for specific cycle operating conditions.

Commentary by Dr. Valentin Fuster
2017;():V001T12A002. doi:10.1115/ES2017-3369.

The paper investigates the performance of a combined heat and power system by means of a fully dynamic numerical approach. An ad-hoc library for the simulation of energy conversion systems is developed under the OpenModelica open source platform; the library includes the main components that usually equip a Combined Heat and Power (CHP) system and they can be connected as they are logically connected in the real plant. Each component is modelled by means of equations and correlations that calculate their performance on a time dependent basis. Therefore, many configurations can be evaluated not only in terms of cumulative annual results or average performance, but the instantaneous behavior can be investigated. The numerical library is constructed using the lumped and distributed parameter approach and it is validated by comparing the numerical results with the measured values over a one-year time period. The prediction capabilities of the proposed numerical approach are evaluated by simulating a case study of a health spa. This case study is selected since it is characterized by significant requirements of both thermal and electric energy. The comparison demonstrated that the calculated results are in good agreement with the measurements in terms of both annual values and distribution over the reference period.

Furthermore, an optimization algorithm is adopted and linked to the developed library in order to estimate the best size of different components of the CHP system according to a number of constraints. This feature is particularly important when addressing the energy efficiency of a complete system that is depending on a number of interdependent variables. Therefore, the case study is investigated by accounting also for additional technologies that can be further enhance the performance of the system both in terms of energy consumption and economic investment. In particular, the numerical model is used to optimized the CHP energy efficiency by estimating the best trade-off between the reduction of the energy purchased and the overall cost of the system. The application of PV panels and electric energy accumulators is also investigated and the simulation demonstrates that the size of the cogeneration unit equal to 48 kW, the number of PV panels of 299 and the battery capacity of 45 kWh provide the lowest amount of energy purchased, while the best return of investment is obtained by the CHP unit of 40 kW along with 109 PV panels and a battery of 40 kWh.

Commentary by Dr. Valentin Fuster
2017;():V001T12A003. doi:10.1115/ES2017-3462.

Excess temperatures in photovoltaic panels may cause degradation in the panels’ electrical performance in short term. Moreover, photovoltaic cells may be damaged in the long term due to high operating temperatures. Therefore, photovoltaic thermal collectors (PVT)s have been proposed in order to solve these issues. PVT collectors allow the cooling of photovoltaic panels by heat extraction using a working fluid such as water or air. PVT collectors provide higher electrical output than standalone Photovoltaic (PV) panels while occupying a smaller area compared to a single solar thermal and a PV panel for the same capacity. In this study, the performance of a liquid cooled flat PVT collector under the climatic conditions of the United Arab Emirates is going to be investigated. The transient system simulation software (TRNSYS) is used to simulate the PVT system. The PVT system includes the PVT collectors, thermal storage tank, electrical storage, DC/AC inverter, pumps, and controllers. The effect of various design variables on the PVT electrical and thermal output is going to be studied. The design variables are the collector azimuth angle, slope of the collector, volume of the storage tank, and water mass flow rate through the PVT collector. The electrical and thermal outputs of the sized PVT system will be compared to that of a standalone PV panel electrical output and a standalone flat plate collector thermal output. Based on the obtained results, conclusions on the feasibility of using PVT collectors, under the weather conditions of the United Arab Emirates, will be deduced.

Topics: Flat plates
Commentary by Dr. Valentin Fuster
2017;():V001T12A004. doi:10.1115/ES2017-3469.

To investigate the performance of photovoltaic/thermal (PV/T) collectors, the steady-state model is not sufficient. Therefore, a dynamic model of the PV/T collector is required to capture the PV/T electrical and thermal output variation throughout the day. This article presents a dynamic model of a water type flat-plate PV/T collector. The model can be used to carry out in depth analysis of the PV/T transient thermal and electrical performance. It is developed based on the energy analysis of each component of the PV/T collector. The energy balance equations are solved by employing an explicit Runge-Kutta method using MATLAB program. The model is then validated with an experimental work. The thermal and electrical performance of a certain PV/T collector on a typical summer day is investigated under the hot and humid weather conditions of Abu Dhabi, the United Arab Emirates. A parametric study is also performed in order to study the effect of various parameters, namely: the inclination angle of the PV/T collector, the thermal conductance of the adhesive layer between the PV cells and the absorber plate, and the water mass flow rate.

Commentary by Dr. Valentin Fuster
2017;():V001T12A005. doi:10.1115/ES2017-3640.

This paper presents the organic Rankine cycle performance comparison of several working fluids with low global warming potential and low ozone depletion potential at several heat source temperatures. At an evaporating temperature of 80°C, maximum first law efficiency of 5.8% was achieved with ammonia, while at 145°C and 180°C, diethyl ether provides the maximum cycle efficiencies of 11.4% and 13% respectively. For the best operating conditions of the ORC model, a suitable two-stage scroll geometry was modeled and its performance was evaluated. Stage I and stage II scroll geometries with volume ratios of 5.3 each were modeled for the supply conditions of 180°C and 2.6 MPa. The geometries provided a combined shaft work of 8.7 kW at combined expander efficiency of 89% accounting for the losses due to the leakage in the expander.

Commentary by Dr. Valentin Fuster

Wind Energy Systems and Technologies

2017;():V001T13A001. doi:10.1115/ES2017-3441.

Vertical axis wind turbines present several advantages over the horizontal axis machines that make them suitable to a variety of wind conditions. However due to the complexity of VAWT aerodynamics, available literature on VAWT performance in steady and turbulent wind conditions is limited. This paper aims to numerically predict the performance of a 5kW VAWT under steady wind conditions through computational fluid dynamics modeling by varying turbine configuration parameters. Two dimensional VAWT models using a cambered blade (1.5%) were created with open field boundary extents. Turbine configuration parameters studied include blade mounting position, blade fixing angle, and rotor solidity. Baseline case with peak Cp of 0.31 at tip speed ratio of 4 has the following parameters: mounting position at 0.5c, zero fixing angle, 3 blades (solidity = 0.3). Independent parametric studies were carried out and results show that a blade mounting position of 0.7c from the leading edge produces best performance with maximum Cp = 0.315 while worst case is a mounting position of 0.15c with peak Cp = 0.273. Fixing angle study reveals a toe-out setting of −1° producing the best performance with peak Cp of 0.315 and the worst setting at toe-in of 1.5° with peak Cp of 0.287. The solidity study resulted in a best case of 4 blades (solidity = 0.4) with peak Cp = 0.316 and worst case of 2 blades (solidity = 0.2) with peak Cp = 0.283.

Commentary by Dr. Valentin Fuster
2017;():V001T13A002. doi:10.1115/ES2017-3544.

This paper presents an optimization procedure which integrates lightning strike analysis into design reliable and economical composite wind turbine blades. A high-fidelity 5-MW composite wind turbine blade is applied into the lightning strike analysis and the optimization procedure under four different lightning severity levels. The lightning-strike-induced electric field along the wind turbine blade at the top vertical position is calculated using finite element analysis. The dielectric breakdown strength of the composite wind turbine blade is considered as a function of laminate thickness. The lightning safety ratio is then calculated as the ratio between the dielectric breakdown strength and the magnitude of the lightning-strike-induced electric field. Subjected to the lightning constraints and fatigue constraints, the optimization procedure minimizes the total composite material cost by fine-tuning the laminate thickness design variables of the blade model. Both the lightning strike analysis and the optimization results indicate that the blade tip is the most vulnerable region against lightning strike damage. The obtained optimum designs under the four lightning severity levels increase the lightning safety ratio by 36% – 45% and increase the fatigue life more than 15 times compared with the initial blade design.

Commentary by Dr. Valentin Fuster
2017;():V001T13A003. doi:10.1115/ES2017-3568.

Improved understanding of wind gust climates may be of great value to the wind energy industry, and is currently hampered by a lack of high-quality in situ data in wind resource rich environments. Thus, we are examining the potential to supplement anemometry with data from seismometers, including those deployed as part of the USArray Transportable Array (TA). Two models of the relationship between gust magnitude and ground motion are evaluated based on their skill at describing the distribution of gust wind speeds over 1 year using seismic data.

The approach is illustrated, using observed gust magnitudes obtained from sonic anemometers located at or near the 15 TA seismic stations. One deterministic and one probabilistic wind-seismic model are conditioned using one year of 5-minute resolution data and tested on a second year of independent data. Both models relate the variance of ground acceleration in the frequency range of 0.01 to 0.1 Hz (P) to gust speed (Ug) but differ in their functional form. The probabilistic model is found to perform well in predicting the gust distribution in independent data, and at the 15 sites considered herein has an integrated error across the entire cumulative probability distribution that is only 5% of the mean gust magnitude.

Topics: Wind
Commentary by Dr. Valentin Fuster
2017;():V001T13A004. doi:10.1115/ES2017-3595.

The utilization of a ground-based testing facility for full-size wind turbine drivetrains is growing. Several test benches have been developed to apply torque and non-torque loads. These mechanical loads can be the loads used to design the drivetrain components or loads obtained from field measurements. Irrespective of the reason for testing a drivetrain, the selected test bench should have the capability to impose the loads of interest. The design of these test benches and their capabilities vary, and the loads of interest vary between drivetrain designs. A systematic method to evaluate the capability of a test bench to impose the loads of interest has been developed. This method can be applied to any test bench and drivetrain design. Part I of this paper presents the methodology and recommendations for presenting and interpreting the results. The demonstration of the method is the focus of part II. Overall, this two-part paper aims to establish guidelines for consideration by the IEA task force 35 for ground based testing for wind turbines and their components.

Commentary by Dr. Valentin Fuster
2017;():V001T13A005. doi:10.1115/ES2017-3611.

The systematic evaluation of wind turbine drivetrains using hardware-in-the-loop strategies (previously presented in Part I) is demonstrated using a state-of-the-art multi-MW drivetrain design and a 7.5-MW test bench. The test bench has the capability to apply both torque and non-torque loads to the electro-mechanical drivetrain. The proposed method to evaluate the capability of a test bench to impose the loads of interest uses design loads of the drivetrain and the test bench load application unit limits as inputs. The design loads are defined by stochastic time series of the longitudinal, lateral, and vertical forces as well as the yawing and nodding bending moments that the load application unit can concurrently apply to the drivetrain (i.e., combined loading). A total of 14 time series sets are considered to capture the minimum and maximum values of the longitudinal, lateral, vertical, and resultant forces as well as the yawing, nodding, and resultant moments. These time series are processed individually to calculate two metrics: the coverage and the capability ratio of the test bench. The former is a percentage of the time series that be applied by the test bench, and the latter indicates an excess (or deficit) in load application capability as compared with the selected design loads. The results are presented and interpreted using the previously described methodology. The findings suggest a good match between test bench capability and the loads of interest in general, and also points to challenges. These discoveries establish a basis for the experimental verification and the development of compensation methods to enhance test bench capabilities.

Commentary by Dr. Valentin Fuster

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