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Abstract: This paper presents experimental studies on a solar-assisted ground coupled heat pump (SAGCHP) system for space heating. The system was installed at the Hebei Academy of Sciences in Shijiazhuang (lat. N38°03′, long. E114°26′), China. Solar collectors are in series connection with the borehole array through plate heat exchangers. Four operation modes of the system were investigated throughout the coldest period in winter (Dec 5th to Dec 27th). The heat pump performance, borehole temperature distributions and solar colleting characteristics of the SAGCHP system are analyzed and compared when the system worked in continuous or intermittent modes with or without solar-assisted heating. The SAGCHP system is proved to perform space heating with high energy efficiency and satisfactory solar fraction, which is a promising substitute for the conventional heating systems. It is also recommended to use the collected solar thermal energy as an alternative source for the heat pump instead of recharging boreholes for heat storage because of the enormous heat capacity of the earth. [Copyright &y& Elsevier]

Abstract: This paper considers the design of cooling systems in the context of piping costs, exchanger costs, pumping costs and its hydraulic and thermal performance. A methodology for designing coolers in the context of both process needs and cooling water system behaviour is introduced. It is recognised that cooling systems need to be flexible. One way of ensuring this is to design a system for the most demanding load and then use bypasses to control performance under reduced load. The hydraulic modelling is based on new formulations of flow resistance for pipes, pipe fittings and equipment items. By using volumetric flow rate rather than velocity as the prime variable it becomes possible to construct hydraulic models for cooling water systems quickly. These calculations then provide predictions of water flows to the individual heat exchangers in the cooling water network. Knowledge of these flows is fundamental to both the design of new coolers and the prediction of the thermal performance of exchangers of known geometry. Previous studies have ignored this aspect of design. [Copyright &y& Elsevier]

Abstract: The Integrated Energy and Climate Protection Program of the German government includes the political target of doubling the share of combined heat and power generation (CHP) in Germany from currently about 13% to 25% by 2020. In order to reach this goal, a new CHP law was enacted to improve the framework conditions for CHP generation. In this paper, we aim at identifying which CHP technologies are most likely to be installed in the near future to reach the CHP target stipulated by the German government. In our model, we apply Mean-Variance Portfolio (MVP) theory to consider return- and risk-related aspects of various CHP technologies. The analysis pays tribute to specific characteristics of CHP generation, such as promotion via guaranteed feed-in tariffs, additional revenues from heat sales, specific operational features, and specifics concerning the allocation of CO2 allowances. The investigation is based on four generic standard CHP technologies currently available on a commercial basis: large coal-fired CHP plants, combined-cycle gas turbines (CCGT-CHP), engine-CHP and micro-turbine CHP. As selection criteria for the portfolio performance we take, independently from each other, the net present value (NPV) of investment in CHP and the expected annual portfolio return, and compare the results obtained from both approaches. Irrespective of the chosen selection criteria, the analysis shows that CCGT-CHP and engine-CHP are the most attractive CHP technologies from a return perspective. A diversification of the portfolio with other kinds of CHP technologies can contribute to stabilizing portfolio returns. In view of the results obtained we conclude for the further development of CHP generation in Germany that a large portion of additional new CHP capacity will probably be built in the industrial sector. [Copyright &y& Elsevier]

Abstract: There are various governmental policies aimed at reducing the dependence on fossil fuels for space heating and the reduction in its associated emission of greenhouse gases. DHNs (District heating networks) could provide an efficient method for house and space heating by utilizing residual industrial waste heat. In such systems, heat is produced and/or thermally upgraded in a central plant and then distributed to the end users through a pipeline network. The control strategies of these networks are rather difficult thanks to the non-linearity of the system and the strong interconnection between the controlled variables. That is why a NMPC (non-linear model predictive controller) could be applied to be able to fulfill the heat demand of the consumers. The main objective of this paper is to propose a tuning method for the applied NMPC to fulfill the control goal as soon as possible. The performance of the controller is characterized by an economic cost function based on pre-defined operation ranges. A methodology from the field of experiment design is applied to tune the model predictive controller to reach the best performance. The efficiency of the proposed methodology is proven throughout a case study of a simulated NMPC controlled DHN. [Copyright &y& Elsevier]

Abstract: A total momentum filtered energy selective electron (ESE) heat pump model with heat leakage is established in this paper. The analytical expressions of heating load and coefficient of performance (COP) for both the total momentum filtered (kr -filtered) ESE heat pump and the conventionally filtered (kx -filtered) ESE heat pump in which the electrons are transmitted according to the momentum in the direction of transport only are derived, respectively. The optimal performance of the kr -filtered ESE heat pump is analyzed by using the theory of finite time thermodynamics (FTT). The optimal regions of COP and heating load for the kr -filtered heat pump are obtained. By comparing the performance of the kr -filtered device with that of the kx -filtered device, it is found that the heating load performance and the COP versus heating load characteristic curves of the kr -filtered heat pump are totally different from those of the kx -filtered device; and the maximum COP and maximum heating load of the kr -filtered device are generally higher than those of the kx -filtered device. The influences of heat leakage, resonance width, hot reservoir temperature and chemical potential on the performance of the total momentum filtered ESE heat pump are further analyzed by numerical calculations. The obtained results can provide some theoretical guidelines for the design of practical electron systems such as solid-state thermionic heat pump devices. [Copyright &y& Elsevier]

Abstract: In this paper, the performance of wind energy system is assessed thermodynamically, from resource and technology perspectives. The thermodynamic characteristics of wind through energy and exergy analyses are considered and both energetic and exergetic efficiencies are studied. Wind speed is affected by air temperature and pressure and has a subsequent effect on wind turbine performance based on wind reference temperature and Bernoulli’s equation. VESTAS V52 wind turbine is selected for (Sharjah/UAE). Energy and exergy efficiency equations for wind energy systems are further developed for practical applications. The results show that there are noticeable differences between energy and exergy efficiencies and that exergetic efficiency reflects the right/actual performance. Finally, exergy analysis has been proven to be the right tool used in design, simulation, and performance evaluation of all renewable energy systems. [Copyright &y& Elsevier]

Abstract: According to the physical and chemical energy cascade utilization and concept of synthesis integration of variety cycle systems, a new humid air turbine (HAT) cycle with solar energy for methanol decomposition has been proposed in this paper. The solar energy is utilized for methanol decomposing as a heat source in the HAT cycle. The low energy level of solar energy is supposed to convert the high energy level of chemical energy through methanol absorption, realizing the combination of clean energy and normal chemical fuels as compared to the normal chemical recuperative cycle. As a result, the performance of normal chemical fuel thermal cycle can be improved to some extent. Though the energy level of decomposed syngas from methanol is decreased, the cascade utilization of methanol is upgraded. The energy level and exergy losses in the system are graphically displayed with the energy utilization diagrams (EUD). The results show that the cycle’s exergy efficiency is higher than that of the conventional HAT cycle by at least 5 percentage points under the same operating conditions. In addition, the cycle’s thermal efficiency, exergy efficiency and solar thermal efficiency respond to an optimal methanol conversion. [Copyright &y& Elsevier]

Abstract: Traditional methods of evaluating energy performance of building tend to focus on comparing the observed energy consumption with the average value of energy consumption by regression method or theoretical value calculated by simulation analysis. For evaluating and ranking the energy performance of buildings, this paper proposed a perspective of multiple objective outputs to evaluate the energy performance of buildings and then use a multiple attribute decision-making approach, Grey relational analysis (GRA), to rank the evaluated buildings. The energy performance of 47 office buildings in Taiwan were evaluated and ranked to serve as a case study to illustrate the procedure and effectiveness of the proposed approach. [Copyright &y& Elsevier]

Abstract: This paper proposes a four-regime bivariate Markov regime-switching model to estimate the daily time-varying minimum variance hedge ratios for West Texas Intermediate (WTI) crude oil, and evaluates its in- and out-of-sample hedging performances with two-regime model, CC-GARCH, TVC-GARCH, and OLS models. Empirical results reveal that the four-regime Markov switching model outperforms the other models for both in- and out-of-sample hedging performance. Based on Hansen’s SPA test (2005), the four-regime model significantly outperforms the other models for only in-sample hedging. [Copyright &y& Elsevier]

Abstract: Micro heat engines have attracted considerable interest in recent years for their potential exploitation as micro power sources in microsystems and portable devices. Thermodynamic modeling can predict the theoretical performance that can be potentially achieved by micro heat engine designs. An appropriate model can not only provide key information at the design stage but also indicate the potential room for improvement in existing micro heat engines. However, there are few models reported to date which are suitable for evaluating the power performance of micro heat engines. This paper presents a new thermodynamic model for determining the theoretical limit of power performance of micro heat engines with consideration to finite heat input and heat leakage. By matching the model components to those of a representative heat engine layout, the theoretical power, power density, and thermal efficiency achievable for a micro heat engine can be obtained for a given set of design parameters. The effects of key design parameters such as length and thermal conductivity of the engine material on these theoretical outputs are also investigated. Possible trade-offs among these performance objectives are discussed. Performance results derived from the developed model are compared with those of a working micro heat engine (P3) as an example. [Copyright &y& Elsevier]

Abstract: Organic Rankine Cycle (ORC) could be used to recover low-grade waste heat. When a vehicle is running, the engine exhaust gas states have a wide range of variance. Defining the operational conditions of the ORC that achieve the maximum utilization of waste heat is important. In this paper the performance of different working fluids operating in specific regions was analyzed using a thermodynamic model built in Matlab together with REFPROP. Nine different pure organic working fluids were selected according to their physical and chemical properties. The results were compared in the regions when net power outputs were fixed at 10kW. Safety levels and environmental impacts were also evaluated. The outcomes indicate that R11, R141b, R113 and R123 manifest slightly higher thermodynamic performances than the others; however, R245fa and R245ca are the most environment-friendly working fluids for engine waste heat-recovery applications. The optimal control principle of ORC under the transient process is discussed based on the analytical results. [Copyright &y& Elsevier]

Abstract: In this paper, the performance of customer-owned distributed generation (DG) units is quantified from different perspectives through an uncertainty study. A Monte Carlo-based method is applied to assess the stochastic operation of the customer-owned DG units in the power distribution system. Several cases are studied to analyze the impact on system performance of using such generators, with the emphasis on benefits. The results of the studied cases show that proper operation of customer-owned DG units placed close to significant consumption centers offers several benefits which lead to significant energy savings and improvement in the performance indices while maintaining the cost-effectiveness. Furthermore, based on the energy demand, different electricity price scenarios considering a cost sensitivity analysis are performed to indicate how the variations in electricity price influence each scenario’s feasibility. It is concluded that implementation of a proper energy purchase policy, and allocating the benefits of DG units to the owners, improves the economic performance of their investments and encourages customer DG developers to connect DG to the distribution network. [Copyright &y& Elsevier]

Abstract: Turbine air inlet cooling is one of many available commercial methods to improve the efficiency of an existing gas turbine. The method has various configurations which could be utilized for almost all installed gas turbines. This paper presents a comparison between two commons and one novel inlet air cooling method using turbo-expanders to improve performance of a gas turbine located at the Khangiran refinery in Iran. These methods have been applied to one of the refinery gas turbines located at the Khangiran refinery in Iran. Two common air cooling methods use evaporative media or a mechanical chiller. The idea behind the novel method is to utilize the potential cooling and power capacity of the refinery natural gas pressure drop station by replacing throttling valves with a turbo-expander. The study is part of a comprehensive program with the goal of enhancing gas turbine performance at the Khangiran gas refinery. Based on the results, it is found that using turbo-expanders is the most economically feasible option and so is recommended to be utilized for improving gas turbine performance at the Khangiran refinery. [Copyright &y& Elsevier]

Abstract: This study analyses three feasible regulation methods of an in-service cogeneration plant. The main task is to study the potential energy savings, CO2 reduction and the increase in profitability compatible with the lowest transformation costs. The cogeneration system is composed of two General Electric LM2500 gas turbines and a heat recovery steam generator (HRSG). Two plant localizations in Spain have been considered; San Fernando (Cádiz) where the current plant is located, and Burgos. The latter has been taken into account to analyze the effect of cooler weather on the regulation methods. The paper has been divided into three parts. First, a revision of the current legislation regarding cogeneration in Spain is shown. Second, a description of the power plant and the proposed regulation methods are set out. Then, the cogeneration plant is modelled with the objective of evaluating the effects of the regulation methods in power, generated steam and thermal oil flow. Finally, the model was applied to analyze the profit obtained from different regulation combinations and to compare the benefits of those regulation methods in the two locations with different climatic situations. The main conclusion reached is the importance to meet the requirements of Spanish legislation in order to obtain advantages in the sale of electricity; an increased profit of up to 60% was obtained in the simulation. In addition, it is evident that the regulation is more important when ambient temperature is lower. [Copyright &y& Elsevier]

Abstract: Solar ponds provide the most convenient and least expensive option for heat storage for daily and seasonal cycles. This is particularly important for a desalination facility, if steady and constant water production is required. If, in addition to high storage capacity, other favorable conditions exist, the salt gradient solar ponds (SGSPs) are expected to be able to carry the entire load of a large-scale flash desalination plants without dependence upon supplementary sources. This paper presents a performance investigation of a SGSP coupled with desalination plant under Jordanian climatic conditions. This is particularly convenient in the Dead Sea region characterized by high solar radiation intensities, high ambient temperature most of the year, and by the availability of high concentration brine. It was found that a 3000m2 solar pond installed near the Dead Sea is able to provide an annual average production rate of 4.3Lmin−1 distilled water compared with 3.3Lmin−1 that would be produced by El Paso solar pond, which has the same surface area. Based on this study, solar ponds appear to be a feasible and an appropriate technology for water desalination near the Dead Sea in Jordan. [Copyright &y& Elsevier]

Abstract: In this paper, the double pass flat and v-corrugated plate solar air heaters are investigated theoretically and experimentally. Analytical models for the air heater with flat and v-corrugated plates are presented. Numerical calculations have been performed under Tanta (latitude, 30° 47′ N) prevailing weather conditions. The theoretical predictions indicated that the agreement with the measured performance is fairly good. Comparisons between the measured outlet temperatures of flowing air, output power and overall heat losses of the flat and v-corrugated plate solar air heaters are also presented. The effect of mass flow rates of air on pressure drop, thermal and thermo hydraulic efficiencies of the flat and v-corrugated plate solar air heaters are also investigated. The results showed that the double pass v-corrugated plate solar air heater is 11–14% more efficient compared to the double pass flat plate solar air heater. It is also indicated that the peak values of the thermo hydraulic efficiencies of the flat and v-corrugated plate solar air heaters are obtained when the mass flow rate of the flowing air is 0.02 kg/s. [Copyright &y& Elsevier]

Abstract: Large primary-secondary chilled water systems often suffer from low chilled water temperature difference (i.e., known as low delta-T central plant syndrome) during operation. This paper presents a detailed study to investigate the feasibility and potential benefits related to the use of a bypass check valve in the chiller decouple line to solve this operational problem and hence, to improve the overall system operating efficiency. The objective of this study is to provide some guidance and necessary confidence as well as the awareness of potential problems that may arise when a bypass check valve is considered to handle the low delta-T syndrome. Based on testing the effects of the low delta-T syndrome, the performances of the systems with and without the bypass check valve are then evaluated by using a simulated virtual system. In the tests, the low delta-T syndrome was introduced through air-side fouling by changing the air-side thermal resistance coefficient in the cooling coil model. The results show that, if the chilled water system suffered from 20% air-side fouling, about 6.77% total energy of the chilled water system studied can be saved when a bypass check valve is used, as compared to that without the bypass check valve. [ABSTRACT FROM AUTHOR]

Abstract: In the design of solar air heaters (SAHs), channel depth is a principal variable to be fixed. In this paper, the effect of the channel depth on the energy gain of type I and type III SAHs has been investigated by computational fluid dynamics (CFD) simulations. Laminar model and k–ω turbulence model of Wilcox are used for the prediction of flow and temperature field in SAHs. Our study shows that the heat transfer corresponding to the temperature distribution across the channel in SAH varies greatly with the change of channel depth. Based on the first and second laws of thermodynamics, the optimal channel depths for type I and type III SAHs with black-painted absorber are suggested as 10 mm. It is found that with selective coating, the absorber plate should be further from the cover glazing in order to prevent excessive convective heat loss, the distance is better of no less than 20 mm. In type III SAH, air flows in two channels above and below the absorber plate, the depth ratio of up channel to down channel should be no less than 1. [ABSTRACT FROM AUTHOR]

Abstract: Accurate hourly photovoltaic (PV) output data are useful for engineering design, cost-effectiveness evaluation, rate design, system operation, transmission planning, risk management, and policy analysis. However, a large sample of hourly metered PV data is seldom available, and engineering simulation is often the only practical means to obtain hourly PV output. Based on an analysis of net energy metering (NEM) funded by the California Public Utilities Commission (CPUC), this paper presents statistically adjusted engineering (SAE) modeling of metered output of 327 roof-top PV installations in California for the 12-month period of January–December 2008. The key findings are: (a) the metered PV output is on an average 80–90% of simulated performance; and (b) the simulated data have useful information for accurately predicting metered PV performance. Plausible causes for (a) include incomplete input data for PV simulation, occasional failures in metered data recording, and less than ideal conditions for PV performance in the real world. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents validated real-time energy models for small-scale grid-connected PV-systems suitable for domestic application. The models were used to predict real-time AC power output from a PV-system in Dublin, Ireland using 30-min intervals of measured performance data between April 2009 and March 2010. Statistical analysis of the predicted results and measured data highlight possible sources of errors and the limitations and/or adequacy of existing models, to describe the temperature and efficiency of PV-cells and consequently, the accuracy of power prediction models. PV-system AC output power predictions using empirical models for PV-cell temperature and efficiency prediction showed lower percentage mean absolute errors (PMAEs) of 7.9–11.7% while non-empirical models had errors of 10.0–12.4%. Cumulative errors for PV-system AC output power predictions were 1.3% for empirical models and 3.3% for non-empirical models. The proposed models are suitable for predicting PV-system AC output power at time intervals suitable for smart metering. [ABSTRACT FROM AUTHOR]

Abstract: Fuel cells are clean generators that provide both electrical and thermal energy with a high global efficiency level. The characteristics of these devices depend on numerous parameters such as: temperature, fuel and oxidizer pressures, fuel and oxidizer flows, etc. Therefore, their influence should be evaluated to appropriately characterize behaviour of the fuel cell, in order to enable its integration in the electric system. This paper presents a theoretical and experimental analysis of the performance of two commercial Proton Exchange Membrane (PEM) fuel cells of 40 and 1200W, and introduces the application of the principle of geometrical similarity. Using the principle of geometrical similarity it is possible to extrapolate the results obtained from the evaluation of one fuel cell to other fuel cells with different ratings. An illustrating example is included. [Copyright &y& Elsevier]

Abstract: Buildings have direct and indirect impacts on the CO2 emissions. This paper presents a study on the impact of wall systems and cladding materials on the CO2 emissions and aims to analyse the performance of those systems in order to provide designers with reliable technical data. The studied systems include stucco, masonry veneer, aluminium siding, vinyl siding and the exterior insulation and finish systems (EIFS). To evaluate the economic performance, environmental performance and embodied energy, green building modelling system was used, while to estimate the impact of operational energy, a simulation model was first used and then simple bottom-up model constructed. A sensitivity analysis was conducted in order to determine the relative influence of each system on a representative educational building. It was found that some cladding materials reduce the direct CO2 emissions, but provide a moderate reduction in terms of operational energy, and vice versa. Others positively impact the embodied energy and environmental performance and can optimise the operational energy performance. Therefore, a careful evaluation should be carried out in selecting wall cladding systems and finishing materials in order to reduce the CO2 emissions effectively. [Copyright &y& Elsevier]

Abstract: This work presents an experimental evaluation, from an energy analysis point of view, for two of the most used inter-stage systems in two-stage vapour compression cycles driven by compound compressors: the direct liquid injection and subcooler systems. The evaluation, considers the two-stage cycle with no intermediate systems as reference cycle and was performed on a plant, driven by a compound compressor using the refrigerant R404A for an evaporating temperature range of −36 to −20 °C and for a condensing temperature range of 30–47 °C. The analysis of the results shows that the inter-stage systems determine the performance of the energy parameters, which are discussed in the paper. The configuration yielding the best results was the two-stage compression cycle with subcooler, since the cooling capacity and COP values for this configuration were the highest. Conversely, the two-stage compression cycle working with direct liquid injection showed lower performance from an energy point of view, though this configuration allows a substantial reduction of the discharge temperature. [Copyright &y& Elsevier]

Abstract: In this paper, the performance evaluation of a solid oxide fuel cell (SOFC)–micro gas turbine (MGT) hybrid power generation system under the part-load operation was studied numerically. The present analysis code includes distributed parameters model of the cell stack module. The conversions of chemical species for electrochemical process and fuel reformation process are considered. Besides the temperature distributions of the working fluids and each solid part of cell module by accounting heat generation and heat transfers, are taken into calculation. Including all of them, comprehensive energy balance in the cell stack module is calculated. The variable MGT rotational speed operation scheme is adopted for the part-load operation. It will be made evident that the power generation efficiency of the hybrid system decreases together with the power output. The major reason for the performance degradation is the operating temperature reduction in the SOFC module, which is caused by decreasing the fuel supply and the heat generation in the cells. This reduction is also connected to the air flow rate supplement. The variable MGT rotational speed control requires flexible air flow regulations to maintain the SOFC operating temperature. It will lead to high efficient operation of the hybrid system. [Copyright &y& Elsevier]

Abstract: This paper presents results of a study of the performance of solar air heaters with 60 ° v-down discrete rectangular cross-section repeated rib roughness on the air flow side of the absorber plate. A detailed investigation has been carried out using a mathematical model to study the effects of various ambient, operating and design parameters on the thermal efficiency and effective efficiency (based on the net gain after taking account of the pumping power) of such air heaters. The study shows that, at air mass flow rates less than about 0.04 kg s−1 per m2 of the absorber plate, roughened duct solar air heaters provide significant performance advantage over the smooth duct air heater. The thermal and effective efficiencies differ only marginally at low flow rates. With the increase in the flow rate, the difference between the thermal and effective efficiencies increases because of the increase in the pumping power. At the mass flow rate of about 0.045 kg s−1 m−2, the effective efficiencies of the roughened and smooth duct solar air heaters are practically the same. The results of the study are presented in the form of design plots. [Copyright &y& Elsevier]

Abstract: This paper presents the steady-state behavior of a series compensated (short-shunt) self-excited six-phase induction generator (SPSEIG) configured to operate as stand-alone electric energy source in conjunction with a hydro power plant. A purely experimental treatment is provided with the emphasis placed on operating regimes that illustrate the advantages of using SPSEIG. In particular, it is shown that the SPSEIG can operate with a single three-phase capacitor bank, so that the loss of excitation or fault at one winding does not lead to the system shutdown. The generator can also supply two separate three-phase loads, which represent an additional advantage. Experimental results include loading transients with independent three-phase resistive and resistive–inductive load at each of the two three-phase winding sets, and measured steady-state characteristics for various load and/or capacitor bank configurations. Practical results for long-shunt configuration are also given for comparative performance evaluation of series compensated SPSEIG. [Copyright &y& Elsevier]

Abstract: The paper presents an optimization model of a distributed cogeneration system with a district heating network, applied to a real city centre situation. The distributed urban cogeneration system includes both a set of micro-gas turbines, located inside some public buildings, and a centralized cogeneration system based on a Internal Combustion Engine. The objective function adopted for the optimization is the Total Annual Cost for owning, maintaining and operating the whole system. To face the problem a Mixed Integer Linear Program (MILP) is defined and solved by a commercial software. Starting from the thermal and electrical demand of the buildings, the MILP model allows to define the possible installation of the centralized cogeneration ICE (Internal Combustion Engine) and the number of microturbines in the different buildings, the optimal lay-out of the district heating network and the optimal operation strategy for the whole system as well. In particular the energy performance and global CO2 emissions are evaluated. [Copyright &y& Elsevier]

Abstract: The fluctuation of heat source influences the performance of adsorption cooling systems greatly in practical applications. This paper mainly investigates the cyclic characteristics of silica gel–water adsorption cooling system under the condition of general variable heat source, in order to explore the system characteristics and access the related operation strategies. In this work, all practical variable heat sources are regarded as the combination of two different changes: the slow time-varying change (long change) and the fast time-varying change (short change). Based on a transient model of adsorption chiller verified by experiments, the characteristics of adsorption cooling system under both the two types of changes are presented. With the slow time-varying change, the heat source variation rate is a key factor that influences the system performance greatly. And for the fast time-varying change, concentration is being focused on the influence on chiller desorption process. The methods to minimize this effect, such as to change desorption time, is discussed. Moreover, the water tank capacity plays a very important role under both slow time-varying and fast time-varying heat sources. The analysis in this work will eventually contribute to operation strategies under different conditions and methods to decrease the influence of heat source fluctuation. [Copyright &y& Elsevier]

As an on-site energy supply system, combined cooling, heating and power (CCHP) system plays significant role. Thus, CCHP systems servicing four types of buildings were employed in this paper. Considering high initial investment and off-design operation, a multi-objective optimization model and a bi-level programming method integrated with operation and design were proposed. Nominal capacity configurations were optimized with no supportive policy. Then influence of capital subsidy and feed-in tariff policies to system comprehensive performance were illustrated. Results show that CCHP system servicing residential building could not achieve economic merits whatever energy policy was employed. CCHP system servicing hotel and hospital could realize better comprehensive performance than that of office. While the capacity of power generation unit was lower than 1.5 MW and capital subsidy was lower than 3000 ¥/kW, the capital subsidy policy had slight effect on system performance. For feed-in tariff policy, when feed-in tariff ratio (E sale / E grid) was quite low, nearly no change on system performance would be obtained. And when the feed-in tariff ratio was relatively high, the energy and environment performance would decrease significantly. If feed-in tariff ratio was in a reasonable price range, this policy would have a positive effect on CCHP system with different building types. • A bi-level programming method integrated with operation and design was proposed. • Comprehensive performance obtained by AHP is employed as the optimization objective. • The analysis is performed on energy system in different four types of buildings. • Performances are presented and compared under different energy policies. [ABSTRACT FROM AUTHOR]

The adaptation of rooftop solar PV systems has increased significantly in recent years. Batteries have become an essential part of the rooftop solar PV systems, which ensures maximum utilisation of solar energy. With a view to present a clear insight to benefits of a rooftop solar PV system, considering both the technical and economic benefits, a MATLAB based PVAnalytX software toolkit has been presented in this paper. The end users can evaluate both the technical and economic benefits of a rooftop solar PV system considering solar generation and electricity demand variability, as well the battery performance degradation over the course of its usage. In addition, the mechanism to generate forecasted solar power generation and electricity demand data is also included as a feature in the proposed software toolkit. Furthermore, the toolkit considers actual electricity imports and export tariffs that allow the end consumers to know their financial expenditures for electricity consumption and income generated through the export of access rooftop PV energy to the grid. A thorough validation of the proposed toolkit has been presented through two case studies using actual dataset of rooftop PV systems located at CBD region of Sydney, Australia. • Matlab based toolkit quantifying the expected benefits of the rooftop solar battery systems. • Useful for both non-technical and expert (researchers and industry experts) users. • Includes intermittencies of solar power generation, load demand and degradation of commonly used batteries. • Extensive case studies evaluating different aspects of rooftop solar battery systems. [ABSTRACT FROM AUTHOR]

As one of the pivotal aspects for the flexible generation, the technique of long-term stable low-load operation plays an important role in the increasing scale of renewable energy power connected into grid, but it is still unable to be fully realized. Based on the unique capacity of circulating fluidized bed (CFB), including huge energy storage capacity and combustion method, the research on the long-term low-load operation may lead to a breakthrough in this area. With reasonable retrofits on a 330 MW CFB unit, several low-load operation tests are successfully carried out, and a performance evaluation framework for CFB low-load operation is structured in this paper. The framework is based on the use of process data that can represent the fluidization and combustion stability as well as the boiler efficiency. It is found that the key of long-term stable operation is to maintain compatible fluidization and heat distribution in the CFB boiler, which is controlled by the adjustment of primary air volume. With reliable data analysis and research, a novel low-load control strategy for primary air volume has been proposed and verified by actual operation. • Several 30% low-load operation tests are carried out on a 330 MW CFB unit. • A new evaluation framework for CFB low-load operation is structured. • A novel control strategy for primary air volume has been proposed to maintain long-term low-load operation. • The evaluation framework and control strategy are discussed and validated with actual operation. [ABSTRACT FROM AUTHOR]

This paper aims to evaluate the effects of fin arrangement in a vertical finned double-pipe latent heat storage system based on the locations, thickness and diameter of the fins in melting and solidification mechanisms. The PCM is placed in the outer tube while water is passed through the inner tube. The fins are circularly placed around the inner pipe in the PCM zone considering a constant fins number. The results show significant advantages of fins addition in reducing the melting time along with a lower advantage on the solidification time. For the uniform fin array compared with the non-fined case, the melting and solidification times reduces by 41.4% and 9.7%, respectively. For the best fin array compared with the uniform case, the melting time reduces by 23.9%. For the solidification process, the best case is the uniform distribution of the fins when the rate of heat recovery increases by 11.4% compared with the non-finned case. Furthermore, the melting time reduces by decreasing the thickness of the fins. The evaluation of fins' diameter shows that after a certain diameter, increasing the diameter of the fins shows an adverse effect due to suppressing the natural convection effect. • Evaluate the thermal performance of a vertical finned double-pipe LHS system. • Evaluate the fins array to have a higher heat storage/recovery rate. • 41.4/9.7% reduction in melting/solidification time using a uniform fins array. • 54% reduction in melting time in the best distribution of the fins. • Higher effect of fins array on natural convection for higher fins' diameters. [ABSTRACT FROM AUTHOR]

The development of automotive energy recovery technologies which mainly include the recovery of braking, vibration and exhaust energy have been highly promoted due to pressing energy issues. Nonetheless, the comprehensive study of energy recovery technologies applied simultaneously to a vehicle rarely receives attention. The recovered energy introduces further complications for the power sources system, which drives the refinement of the existing energy management strategy. This paper presents a novel comprehensive automotive energy recovery system. Energy conversion mechanism and energy saving potential are thoroughly explored based on the developed comprehensive energy recovery models. Bench tests are conducted to demonstrate the energy recovery performance and the effectiveness of the proposed scheme. Based on the analysis of energy flow, a novel assistant power balance strategy is developed to ensure the fair use and storage of the recovered energy and increase the energy conversion efficiency. Comparative analyses in typical cycles with various road disturbance are carried out to validate the effect of developed energy management method. The results indicate that profit of proposed strategy increases with the amount of the recovered energy and fuel economy can be well improved. • A comprehensive automotive energy recovery system is developed. • Experimental validations are performed on energy recovery test bench. • Vibration energy recovery can benefit more from the high speed driving conditions. • Engine efficiency is improved and power balance is achieved by proposed strategy. • Fuel economy can be improved with the proposed system. [ABSTRACT FROM AUTHOR]

The effects of flow variations to the aerodynamic performance of turbomachinery blades are considerable in the real world. Uncertainty quantification of aerodynamic performance is useful for evaluating the mean performance change, robust design, etc. The paper studies the performance impact of inlet and outlet flow variations for transonic compressor rotor blades using polynomial chaos. An adaptive sparse grid technique is employed to construct the model of adaptive non-intrusive polynomial chaos (ANIPC). Through statistical evaluation of performance changes for NASA Rotor 67, the response performance of ANIPC is firstly verified. Then the ANIPC is used to evaluate the changes of adiabatic efficiency and mass flow rate of Rotor 67 considering the variations of inlet total pressure and outlet back pressure at different operation conditions. The results reveal that the performance changes exhibit evident nonlinear dependence on the inlet and outlet pressure variations. Moreover, performance changes of the rotor blade in the whole operation range are evaluated and illustrated. Finally, by Monte Carlo simulation, the flow solutions along span and in the blade passage are statistically analyzed to demonstrate the impact mechanisms of inlet and outlet pressure variations to the performance changes. • An adaptive sparse grid based NIPC method is proposed for uncertainty quantification. • By the adaptive-NIPC-based method, computational cost is significantly reduced. • Performance changes increase as the operation condition approaches stall. • Uncertainty effects to the flow make the most contribution to performance changes. • The uncertainty quantification method potentially paves the way for robust design. [ABSTRACT FROM AUTHOR]

This paper proposes a modified refrigeration cycle (MRC) with zeotropic mixture R290/R600a for refrigerator-freezer applications. In the MRC, the use of two parallel compressors enables the two evaporators to be operated at two proper evaporation temperatures, which reduces the irreversibility of evaporator heat transfer processes. Noted that a subcooler is installed between the two loops for improving the system performance. Moreover, the MRC applies a phase separator to ensure more low-boiling point refrigerant to go to the freezer evaporator for increasing the freezer evaporation pressure. Energy and exergy performances of MRC are investigated based on a thermodynamic model. The simulation results indicate that compared with the conventional refrigeration cycle (CRC), the COP and exergy efficiency of MRC obtain the same improvement of 30.4% at a fixed condensation temperature of 35 °C. In addition, from the viewpoint of exergy analysis, the high priority in need of improvement for the MRC is ordered as the compressors, condensers, expansion valves, two evaporators, subcooler and internal heat exchanger. Generally, applying the MRC could be an effective and practical method to enhance refrigerator-freezer energy efficiency. • A modified parallel compression refrigeration cycle with R290/R600a is proposed. • Influence of various operating parameters on performance of the cycle is investigated. • Irreversibility of each component and exergy efficiency of the cycle are examined. • The cycle outperforms the conventional cycle in both energetic and exergetic aspects. [ABSTRACT FROM AUTHOR]

This paper presents a coupled electrical-thermal model for solar photovoltaic (PV) modules, under an unsteady state and various conditions, including ambient temperature, solar radiation and wind velocity. Validation shows that the electrical and thermal models present high agreement with the experimental data. The developed model after validation is then applied to investigate the distribution of thermal resistance, the influence of environmental conditions and cooling methods. Results show that the radiative and convective thermal resistances play a significant role in PV electrical-thermal performance, while conductive thermal resistance can be neglected for simplification in some cases. The results also demonstrate the effects of weather conditions including solar radiation, ambient temperature and wind velocity on PV performance vary and they need to be selected carefully during parameters design. Moreover, a dynamic estimation of different seasons and a long-term evaluation of an entire year for a specific PV array have been done to assess the performance of the coupled model. The simulated results are in good agreement with the experimental data in spite of the weather conditions, in which the relative errors of daily energy in four different seasons are just 1.06%–6.17%, while the average monthly energy based on the proposed model (1185.4 kWh) only deviates 4.66% from that extracted by PVsyst software (1132.6 kWh), which both verify the accuracy of the proposed model again. • A coupled electrical-thermal model is developed to predict PV temperature and electrical power simultaneously. • Unsteady state conditions are considered in the model to make it more accurate than NOCT and Sandia model. • The radiation and convection thermal resistance play an irreplaceable role in PV electrical-thermal performance. • The relative error between simulated and measured electrical energy in four different seasons is 1.06%–6.17%. [ABSTRACT FROM AUTHOR]

In this paper, an electrodialysis regeneration experimental system was set up to evaluate the performance of electrodialysis regeneration system using lithium bromide solution, whose concentration is much higher than that of LiCl solution. The effects of cycling flow rate, initial concentration, and operating current on the current efficiency of the electrodialysis regeneration system using LiBr solution were studied. The current efficiency model and regeneration result model of the electrodialysis regenerator for LiBr solution were acquired based on experimental results. The results show that the ED regenerator can regenerate the LiBr solution reliably, and the current efficiency of the ED regenerator using LiBr solution is lower than that for LiCl solution. To enhance the capability of electrodialysis regenerator, the difference in cycling flow rates between dilute and concentrate chambers should be controlled. The current efficiency of the electrodialysis regenerator and COP of electrodialysis regeneration system decreased with the increase of the operating current and initial concentration. When the concentration of LiBr solution is 45% and the operating current is 3A, the electrodialysis regeneration system has the maximum current efficiency of about 30.365% and the maximum COP of 4.26. • Electrodialysis (ED) regenerator with 30 cell pairs experimental system is set up. • Current efficiency and concentration increase models of LiBr solution are got. • Increasing flow rate can improve performance of ED regenerator and whole system. • Flow rate difference should be controlled to optimize ED regenerator performance. • Excessive initial concentration and operational current are harmful to the system. [ABSTRACT FROM AUTHOR]