Journal of Energy Engineering

The demand for renewable energy is first and foremost for environmental purposes and economic purposes. Wind energy, due to its many advantages, is receiving increasing attention. Thus, to evaluate wind energy properly, an accurate forecasting method is important for solving the problem. This paper proposes a hybrid model named discrete wavelet transform (DWT)—brain storm optimization (BSO)—back propagation neural network (BPNN) to forecast short-term wind speed, which uses a DWT to decompose the original wind speed into a low-frequency and high-frequency series, remove the high frequency noise sequence and reconstruct the remaining series. Next, the brain storm optimization algorithm is used to select the best parameters of a back propagation neural network. This paper also explores how to find the best parameter choice for the proposed model. To test the stability and availability of the developed model, a three-month wind speed time series from three observation sites of a wind farm located in Shandong Peninsula of China is used as the test set. Compared with linear regression, Auto Regressive Integrated Moving Average (ARIMA), BPNN, BSO-BPNN, Back Propagation Neural Network with Double Hidden Layer (BP-Hidden), First-order Adaptive Coefficient forecasting method (FAC), Elman Neural Network (Elman), Generalized Regression Neural Network (GRNN) and DWT-BPNN, the proposed model has better precision and robustness and is especially suitable for short-term wind speed forecasting at a large-scale wind farm in China.

Cement factories have more potential to generate power from waste heat compared to other industries. Pressurized water flashing into wet steam at the end of a boiler’s economizer augments 15% of the plant’s output by increasing waste heat recovery compared to a regular steam power plant (Rankine cycle with a deaerator). A double-flash steam power plant is considered for theoretical demonstration of power augmentation with a cement factory’s waste heat recovery compared to a regular steam power plant. The hot water from the final flash chamber is used for feedwater heating and the saturated steam from the two flash chambers is supplied to the turbine. The current work is focused on selection of heat-recovery steam generator’s (HRSG) pressure and location of the high-pressure flasher (HPF) and low-pressure flasher (LPF). The flash fluid mass can be analyzed for better heat recovery as it influences the exhaust gas temperature. A low pressure has been recommended for the HRSG as it increases the heat recovery and power production at a fixed pinch point. The suggested temperature ratio for HPF and LPF is 0.5. The theoretical results are validated with a case study conducted at a cement factory.

This paper analyzes the effects of relieving power transmission congestion to encourage the development of renewable energy (RE) under different regulatory policies. The present model is based on Cournot competition and incorporates uncertainty and the variability of both renewable resources and demand. Transmission congestion particularly affects the development of RE under subsidy policies (feed-in tariff and premium payment). By investing in flexible AC transmission system (FACTS) and/or other devices that increase transmission capacity, all policies have positive incentives from the social perspective. From a private perspective, the tax policy does not provide sufficient incentives. Higher levels of transmission investment are obtained from a social perspective than from a private perspective. Finally, the existence of multiple equilibria affects the resulting social welfare and market outcomes. In particular, ${\mathrm{CO}}_2$ emissions and social welfare may significantly vary from equilibrium to equilibrium.

Solar thermal heating analysis of a tube in the presence of metallic meshes, resembling the mobile thermal battery, is carried out. The influence of metallic meshes on the heat-transfer rates inside the tube is examined in detail. Structured aluminum meshes are incorporated into the tube while stagnant water is assumed as the working fluid inside the tube. Numerical analysis using the control-volume approach is incorporated to solve the governing equations of heat transfer and fluid flow inside the tube. The dimensionless temperature parameter is introduced to quantify the excessive local heating inside the tube with and without meshes under the solar-concentrated irradiation. It is found that aluminum meshes act like a conduction tree and enhance the heat-transfer rates in water inside the tube. The local excessive heating and large temperature difference are avoided inside the tube when the aluminum meshes are used inside the tube. The influence of natural convection current on the heat-transfer rates is found to be insignificant when the aluminum mesh is present inside the tube. This behavior is associated with the small mesh volumes, which are occupied by water; in this case, small temperature difference in the cell causes small variation in water density while suppressing the natural convection current formed in the cell. Small oscillation in the temperature parameter is observed along the $x$- and $y$-axes inside the tube because of the high rates of heat transfer toward water in the region close to the aluminum meshes.

A fixed bed pyrolysis reactor is used to prepare biochars and co-pyrolysis chars at different temperatures (723 and 823 K). The effect of final pyrolysis temperature and additives on the combustion property of chars is investigated. In order to simulate the injection of chars into the blast furnace through tuyeres, a drop tube test was carried out. Combustion experiments indicate that pyrolysis process and additives elevated the burnout index of pyrolysis chars; in particular, the burnout index of the chars obtained by adding iron oxide red in the co-pyrolysis process was dramatically increased to 98% at final temperature of 823 K. Scanning electron microscope (SEM) results revealed that iron oxide red catalyzes coal pyrolysis and enhances the quantity of the pores and cracks on the surface of co-pyrolysis chars. X-ray diffraction (XRD) analysis demonstrated that iron oxide red significantly increases amorphous carbon structures in chars by inhibiting the trend of graphitization of coal during the pyrolysis process. Consequently, the pyrolysis process and additives improve the combustion reactivity of pyrolysis chars.

The expansion of the Panama Canal will be completed by 2015. The route through the Panama Canal will shorten voyages from North America to Japan by more than 7,500 nautical miles. However, the competition for use of the Canal is high because it is a major route for container ships and other vessels including crude oil, metal ores, and other materials. Therefore, several questions have been raised regarding how much the capacity of the Panama Canal will be available for liquefied natural gas (LNG) passages and how much LNG will go through the Canal. Applying the 2014 version of the World Gas Model, a large-scale, game theory-based global gas model, this paper investigates the influence of the Panama Canal capacity level for LNG tankers on global gas markets and LNG exports from the Gulf of Mexico through five scenarios. The model results show that without the Panama Canal route with its expanded capacity, it is unprofitable to export LNG from the Gulf of Mexico to Asian markets. However, there may be noneconomic reasons such as energy security to motivate such trade. In addition, when Panama Canal capacity is limited, the United States becomes a swing LNG exporter who supplies both Asian and European markets.

This article investigates how hydrofluorocarbon (HFC) refrigerant affects compressor operating conditions and system performance using experimental testing under different conditions. In a heat pump or refrigerator cycle, it is necessary to move the fluid in the system to achieve heating or cooling. The compressor is the responsible component in fluid movement and so is a key factor in system power consumption. For this reason, it is essential to discover ways to increase compressor energy efficiency. R404a refrigerant was selected to evaluate the influence of refrigerant on compressor performance. Compressor inlet and discharge temperatures and pressures were measured experimentally. For the tested refrigerant, compressibility factor ($Z$) and deviation from ideal gas behavior were analyzed cautiously to compute power consumption, isentropic work, coefficient of performance, energy and exergy state, and compressor efficiency. Also analyzed were the influence of condenser water flow rate and the effect of evaporator inlet temperature. The study discussed here provided results that can be used to enhance the performance of compressors in heating/cooling systems.

A solution to the inordinate amount of energy used for climate control in buildings is of paramount importance if we are to significantly reduce our dependence on fossil fuels in a relatively short time. A large quantity of low-grade energy is available in the earth surrounding a typical residential structure. This energy is often tapped for use in heating and cooling in conjunction with a ground source heat pump. Efficient use of this energy source can be realized without the expense of a heat pump by designing a green system directly integrating the ground source with a dynamic building envelope. This paper explains the concept of the ground-coupled dynamic (GCD) wall, which can be easily retrofitted in some form to most existing structures to capture and use this low-grade energy. It makes use of clean renewable resources without excessive amounts of expensive or high-tech equipment. The paper demonstrates that in conjunction with an exergy management system, the application of this concept could significantly lower residential fossil fuel consumption.

Addressing air leakage and its influencing factors in buildings is very important for further improvement of buildings’ energy efficiency. The evaluation of how energy use is influenced by the design parameters of buildings is also crucial for architects in early design stages when there is a need for rapid assessment of the effect of minor and major design changes in overall energy demand. This paper helps fill the information gap on predictive models for this field, which became evident during literature review. This work examines the relationship between energy demand, air-tightness, and their influencing factors including volume, treated floor area, building age, compactness, window-to-wall ratio, and frame-length factor of 18 dwellings constructed between 2005 and 2014 in Estonia. The buildings involved in the study are mostly energy-efficient buildings, e.g., there were two passive houses and one net-zero energy building that also qualifies as a plus-energy building. The paper employs the ANOVA to compare the means of air tightness and energy demand in relation to other individual factors. Important contributions of this paper include two novel linear functions to predict energy demand based on four and seven common building variables. This proof-of-concept approach demonstrates a possible paradigm shift for the building industry, where such predictive equations derived by multiple approaches and using conventional parameters can serve as a practically useful guide for designers at early stages of the design process to achieve energy efficiency. The findings from the developed predictive model for estimating the energy demand of dwellings with the multiple-regression technique should contribute in predicting the influence of design parameters on achieving air tightness and energy efficiency on buildings.

Compressor fouling is a permanent concern for engine users, as it increases fuel consumption and decreases available useful power. Compressor performance can be restored provided certain measures are taken, e.g., regular washing of the flow path. The current study proposes a model that qualifies and, to a certain extent, quantifies compressor performance degradation attributable to fouling. The proposed model is built for the case of an axial flow compressor and it is embedded into a throughflow, streamline curvature tool called synthesis of correlations for the rapid assessment of turbomachine engine systems (SOCRATES). It is an integral model, integrated into the computational tool, that accounts separately for every effect that fouling introduces to the flow as the air passes through an axial compressor stage. In particular, the validity of the model is demonstrated on the NASA stage 37. Researchers in the past, studied the performance of this axial compressor stage, under cleaned and fouled conditions, using a commercial Reynolds-averaged Navier-Stokes (RANS) computational fluid dynamics (CFD) code. Fouling in these numerical simulations is modeled based on a set of input values of surface roughness and the deposit’s layer thickness. The proposed model, receives the same set of inputs. The effect of blade surface roughness is introduced to the flow through the fouling profile loss factor and the modified deviation angle. The deposit’s layer thickness decreases the cascade throat surface area. Comparison of the results between the two computational tools, for a certain fouling scenario, showed a good qualitative and an adequate quantitative agreement. The proposed model makes SOCRATES as a computational tool attractive to engine users, who are in need of assessing the impact of compressor fouling on gas turbine engine performance.

A novel single-pass all-glass parabolic trough receiver (SPAG-PTR) was developed and the parabolic trough solar collector with concentration ratio of 7.5 was built to investigate the thermal performance of the SPAG-PTR. The indoor heat loss tests were settled as well as the outdoor experiments in quasi-steady-state and transient-state test conditions. The heat loss per unit absorber area of the SPAG-PTR in the average absorber temperature from 100 to 287°C was within the range of $85–674\mathrm{W}/{\mathrm{m}}^2$, which represents a better heat loss performance ($-15\%$) upon the Sanle-3 receiver (Nanjing Sanle Electronic Information Industry Group, Nanjing, China). The experimental efficiency in transient state was within the range of 0.53–0.73 with the experimental relative error of approximately 3.6–6.5%. In addition, the experimental efficiency curve in quasi-steady-state was obtained. In quasi-steady-state, the experimental efficiency was approximately 0.65–0.71 when the inlet heat transfer fluid temperature was in the range of 100–160°C. These verify that this kind of SPAG-PTR is very promising for intermediate temperature applications.

The exergy analysis of a compression ignition (CI) engine for quantification of fuel to available energy could be the most effective tool to determine the fuel efficiency and effectiveness. During this investigation a few diesel-biodiesel blends were investigated for performance analysis in diesel engines under different load conditions using an exergy-based study. From this focused investigation, it was ascertained that biodiesel blends of B10 and B20 for apricot, argemone, karanja, nahar, and neem showed relatively better performance than petrodiesel at 80% load. As much as 30% of available input energy was estimated for shaft operation. Also diesel showed higher destroyed availability, whereas all other blends showed 1–3% less than diesel, which is a significant finding of this work. Among all the diesel-biodiesel blends, Argemone mexicana (ARB20) was found to be the best both in terms of biodiesel production and performance parameters. Thus, biodiesel blend B20 was found equally efficient in terms of virtual available energy and could be effectively used as a substitute for petrodiesel without compromising the shaft efficiency.

The object of the study is to present a method of thermodynamic optimization of power generating plants, in a mode that consolidates and simplifies the analysis of data on heat-work interaction of the plant components. The optimization scheme identifies the technical and process parameters that can improve the thermodynamic performance of the plant with respect to an objective variable, and further, the required thermodynamic measures necessary to improve the operating condition of the plant. Simple but effective tools are used to evaluate the optimal and suboptimal power generating capacities vis-à-vis the fundamental variables—namely, the thermodynamic quantity ratio (TQR) and the power-energy quantity ratio (PQR)—without routing optimization procedures. Beyond the optimal value of the objective variable, the power generation capacity of the plant is affected. The determination of the optimal value of the objective variable can also be approached by computerization; for fixed prescriptions of the boiler, superheater, and turbine parameters, variables such as boiler pressure and temperature can be optimally selected.

In the present study, energy and exergy analyses of two commonly used heating systems, including floor heating and skirting board heating, were investigated in a room. For this purpose, first the energy analysis of each heating system was carried out using an in-house computer code along with the computational fluid dynamics (CFD) method. The room temperature distributions as well as the energy efficiencies of the both heating systems were found and compared with each other in the same conditions. Second, the exergy analyses of the both systems were evaluated. Then, the exergy destructions of these two systems were obtained and discussed. Results showed that with equally generated heat flux in the both systems, the total thermal efficiency of the skirting board heating system was 8% more than that of the floor heating system. However, the skirting board heating system could not provide good thermal conditions in the room, especially when there was a window on the room’s walls. The exergy analysis also showed that the thermodynamic second law efficiency of the thermal skirt system was 4% higher than that of the floor heating system. Although the exergy destruction between the supplied hot water and the room air in the skirting board heating system was more than that of the floor heating system (i.e., 40%), the overall exergy performances of these two systems were still close to each other. Furthermore, it was concluded that the floor heating system followed more closely the criteria of thermal conditions in comparison with the skirting board heating system.

Electricity sector restructuring has introduced competition to the electric power industry by establishing appropriate pricing signals that can maintain the security and economic performance of the power market and help minimize stability problems. In this paper, a market-clearing model for pricing system security in a hybrid power market utilizing pool and bilateral transactions is proposed. The market-clearing procedure uses small-perturbation stability-constrained optimal power flow (SSC-OPF) to help independent system operators (ISOs) adhere to required stability criteria. A contingency screening method in which only transmission line outages that threaten system stability are also considered to reduce the size of the SSC-OPF problem. Using a decomposition method, the determination of small-signal instabilities under an N-1 contingency criterion is specifically divided from the main SSC-OPF problem, and the results of the required stability criteria, along with those of decomposition formulae that adequately price electricity by computing nodal prices (NPs) and nodal congestion prices (NCPs), are demonstrated in terms of market solutions. To verify the effectiveness of this proposed market-clearing scheme, it is analyzed using an IEEE 14-bus test system; the results show that the proposed approach can be used to improve market and system operation by more accurately modeling system stability.

When a pump is running in turbine mode, susceptibility to cavitation increases, and it may be more severe than that in conventional hydro turbines. To accomplish the basic aim of making a compact machine with a high setting, a certain amount of cavitation can be allowed, then the erosion risk may be predicted. In the present study, experimental investigations were carried out on cavitation characteristics of a pump running in turbine mode in the nondimensional speed ($N^{*}$) range of 0.64–1.07. For cavitation analysis, an additional suction creation system was installed, and different techniques were applied for cavitation detection viz pressure measurement, visual inspection, and vibration analysis. The performance of pump as turbine was found better in the $N^{*}$ of 0.71–0.86 in terms of higher efficiency and lesser possibility of cavitation. From the sigma test, the critical value of $\sigma$ was found as 0.595. The study revealed that, when a pump is operated as a turbine, it might be suffering from traveling bubble and von Karman vortex cavitation near impeller blades and vortex rope cavitation in the draft tube.

Battery switch stations (BSSs) are regarded as important infrastructure for the development of electric vehicles (EVs). However, studies on the optimal configuration of BSSs are still limited. In order to assist the design of BSS, an optimal configuration framework based on operational planning method is proposed. An optimal model is formulated to minimize investment, maintenance, and electricity cost of BSSs. The extra waiting time (EWT) of EVs is taken as a constraint for service quality. A simulation model for operations of a BSS is designed and the states of EVs and batteries under different operation strategies can be simulated so the EWT for each EV can be calculated. Furthermore, differential evolution (DE) is used to solve the optimal configuration model. Finally, the actual data and parameters of electric taxis and electric buses are used for the case study. Results show the quantitative relations among EVs, batteries, and chargers under different levels of average EWT can be obtained. This method provides a practical auxiliary tool for designers to configure the batteries and chargers in BSS.

Recovering energy using microhydropower turbines on the flow of wastewater into or out of treatment plants has been shown to be a viable method of increasing the sustainability of the process. This paper examines the selection and design optimization of turbines at four wastewater-treatment plants in Ireland. Investigations were conducted to examine the impact of variation in flow rate due to storm events and changes in water demands on the optimal design of turbines. Turbine selection was also investigated in this setting, highlighting the optimum design in terms of power output and cost. Low-cost options for this low-head setting were examined through the use of multiple pump-as-turbines in parallel. The result highlights significant differences between power output estimates, using average flow rates and turbine efficiency, and those conducted using detailed design optimization. Underestimates of up to 12% were shown. The optimized systems efficiencies obtained across the sites ranged from 73 to 76%. Turbine costs ranged from 315 to $1,708€/\mathrm{kW}$ depending on the type. Using pump-as-turbines produced system efficiencies of 58–62%. Using two pump-as-turbines, arranged in parallel, was shown to increase efficiency of these low-cost systems by a further 5%.

Wind power and carbon capture power plants (CCPPs) are two important viable options to reduce ${\mathrm{CO}}_2$ emission in low-carbon power systems. Especially, the combination of the two options, i.e., the CCPP integrating wind power, can effectively cut the ${\mathrm{CO}}_2$ emission of the power plant. This paper presents a low-carbon dispatch model for a CCPP integrating wind power, considering the ramping cost, fuel cost, and carbon emission cost. To simplify the model, the flexibility of the CCPP is defined as the capture percentage. Then, the impact of the ramping cost on the operation of the CCPP integrating wind power is studied under different carbon taxes. Numerical examples based on an IEEE 30-bus tested system show that the carbon taxes for the dispatch model including the ramping cost can be divided into two zones: the flexible zone and the inflexible zone. The simulation results demonstrate that within the flexible zone, considering the ramping cost for the dispatch model can effectively improve the economy of the CCPP integrating wind power.

The capillary tube is used in most air-conditioning systems due to its low cost and not requiring sensitivity. In this study, the improvement of energy parameters was examined by adjusting the length of capillary tubes as well as using alternative refrigerants for an air conditioner operating with R22. The cooling capacity, coefficient of performance (COP), and electricity consumption results as well as pressure and temperature measurements in the system were investigated for the available length of capillary tube in the unit and shorter lengths (i.e., cutting 20 and 40 cm from the original length, respectively) with R422D and R417A refrigerants at ambient temperatures of 25–45°C. Evaporator inlet pressure and evaporation temperature increased as a result of decreasing the capillary tube length. According to the results of study, the most suitable capillary tube length may be suggested as 80 cm, which developed an increase in COP by about 0.9–2.8% compared to the original capillary tube length for studied ambient temperatures using R422D and R417A.

Dedicated outdoor air systems (DOASs) with energy recovery ventilators (ERVs) are increasingly popular in new buildings and have the potential to greatly reduce building energy consumption through elimination of zone-level summer reheat and free preconditioning of outdoor ventilation air through energy recovery with building exhaust air, often using an enthalpy wheel heat exchanger. In practice, many of these systems, however, are run suboptimally or are designed with complex and counterintuitive configurations that require detailed engineering analysis to understand optimal control sequences. Three real-world case studies from commercial building retuning are presented where control deficiencies in DOASs with ERVs led to excess energy consumption. An analysis of the potential energy savings from correcting these deficiencies as well as a discussion of how each analysis was performed during the retuning audit is included. Energy savings can vary significantly based on the climate and the baseline system’s specific suboptimal operation; however, opportunities for saving energy have been documented in these case studies.

In the United States, the City of Gainesville in Florida was the pioneer in the implementation of a long-term feed-in-tariff model to purchase solar electricity generated by privately owned systems located in the public utility’s service territory, accelerating the investments in renewable energy. Based on the German model, the city implemented the feed-in-tariff program using 20-year agreements with suppliers. This program is funded by the electricity ratepayers through an increment in the electricity bill. A flat purchase rate is calculated using solar electric system costs and varies based on the type and size of installation. This cost-based purchase rate ensures a safe return margin to investors and is reduced annually for new contracts as market installation costs go down to promote the technology development in the region and encourage investors to act. Gainesville adopted this renewable energy policy in 2009 to diversify its generation portfolio, respond to community demands and meet carbon reduction goals, and discovered in this program a tool to expand distributed renewable generation, help reduce carbon emissions in the city. The program provided a rise from near 300 kW of solar energy installed capacity in 2008 to approximately 20.5 MW by April of 2014 (18.55 MW through FIT and 1.99 MW through net metering), and this deployment of more than 260 installations created a solar market in the region and contributed to sustained construction and solar employment through a difficult economy. This significant success in the adopted scheme turned Gainesville into a global leader in solar energy installed capacity per capita, surpassing more mature markets such as the state of California. Using some lessons learned from Gainesville’s experience and from dozens of nations across the world, similar feed-in-tariff programs have been adopted in larger municipal utility markets and some states. Also known as CLEAN in some U.S. jurisdictions (Clean Local Energy Accessible Now), municipal utilities including Palo Alto, Sacramento, Ft. Collins, Long Island Power Authority, and Los Angeles have similar programs, as does the State of Vermont.