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Highlights • The thermodynamic and thermo-economic models of SORC and DORC are built. • The thermodynamic and thermo-economic performances are optimized and compared. • The DORC can increase power output and show better thermo-economic performance. Abstract The goal of this paper is to study and evaluate the thermodynamic and the thermo-economic performance of dual-pressure and single pressure evaporation organic Rankine cycle (DORC and SORC) using isobutane as the working fluid. The effects of the two-stage pressures and the heat source inlet temperature on the system performances have been investigated. Then the performance comparisons between SORC and DORC have been conducted at the optimized condition. Results show that the DORC yields more net power than the SORC when the heat source temperature is between 100 and 177.2 °C, and the net power output gains of the DORC are higher at lower heat source temperature. The DORC no longer has the performance advantage as the heat source temperature is above 177.2 °C. The thermo-economic evaluations show that the optimized electricity production cost (EPC) decreases as the heat source temperature rises. Furthermore, optimized EPC of SORC and DORC are nearly equal at the same heat source temperature. For the heat source temperature of 100–177.2 °C, the DORC can significantly increase the net power output, but the thermo-economic performance of DORC is not reduced by system complexity compared to the SORC. [ABSTRACT FROM AUTHOR]

Highlights • An engine speed control model is established and identified by step experiments. • A gas engine speed control strategy is proposed and applied to control the engine speed of GEHPs. • The engine speed controller has a good performance in terms of settling time and overshoot. ABSTRACT The gas engine-driven heat pump (GEHP) system is an energy saving device for heating, cooling or hot water supply. As the power source of the system, the performance of gas engine speed control directly has a significant impact on the system stability and efficient operation. However, gas engine is typically a nonlinear dynamical system and easily disturbed by the load fluctuation, which increases the difficulty of control of gas engine speed. Therefore, a gas engine speed control strategy is proposed for a GEHP system. Aiming at achieving this objective, a test facility is developed and an engine speed controller is designed according to the characteristics of the gas engine and the GEHP system. Then the engine speed controller is applied to the GEHP system and experiments are performed under different conditions: engine speed setting control and anti-disturbance control. The experimental results show that it costs less than 40 s to make the engine speed steady without overshoot when engine speed setting changes. When the disturbances of superheat change occur, the error (accuracy) of the engine speed is controlled within ± 50 rpm. The engine speed control strategy can not only guarantee the stable operation but also satisfy the capacity adjustment performance of the GEHP system. Finally, performance characteristics of the GEHP are characterized by heating capacity and primary energy ratio (PER). The results indicate that engine speed is an important factor which influences the performance of the GEHP. The heating capacity increases with the increase of engine rotational speed, while PER of the GEHP decreases. In terms of energy saving, the GEHP system should operate at lower engine speed in the case of satisfying the system load. [ABSTRACT FROM AUTHOR]

About 2/3 of the combustion energy of internal combustion engine (ICE) is lost through the exhaust and cooling systems during its operation. Besides, automobile accessories like the air conditioning system and the radiator fan will bring additional power consumption. To improve the ICE efficiency, this paper designs some coupled thermal management systems with different structures which include the air conditioning subsystem, the waste heat recovery subsystem, engine and coolant subsystem. CO2 is chosen as the working fluid for both the air conditioning subsystem and the waste heat recovery subsystem. After conducting experimental studies and a performance analysis for the subsystems, the coupled thermal management system is evaluated at different environmental temperatures and engine working conditions to choose the best structure. The optimal pump speed increases with the increase of environmental temperature and the decrease of engine load. The optimal coolant utilization rate decreases with the increase of engine load and environmental temperature, and the value is between 38% and 52%. While considering the effect of environmental temperature and road conditions of real driving and the energy consumption of all accessories of the thermal management system, the optimal thermal management system provides a net power of 4.2 kW, improving the ICE fuel economy by 1.2%. [ABSTRACT FROM AUTHOR]

Abstract A novel energy system which serves public buildings with large interior zones was proposed in this study. The proposed system integrates a modified water loop heat pump (WLHP) with a natural-gas-fueled SOFC plant. The distributed SOFC plant is employed to complete the conversion from chemical energy to electricity and heat, and the modified WLHP which retrieves the waste heat of the SOFC plant is used for space cooling or heating. A "standards-oriented" model was built, and an "as-designed" approach was adopted to estimate the performance of the WLHP. For understanding the energy saving potential and CO 2 emission reduction of the proposed system, a reference system, representative of the general level of energy production and consumption, is brought about for comparison. The IEER (integrated energy efficiency ratio) and CO 2 emission trend show that the proposed system offers a much higher primary energy efficiency and realizes an obvious CO 2 emission reduction compared to the reference system. Although the estimate of the IEER and CO 2 emission reduction is conservative for some imperfections of the built models, the results of this study will still help significantly in guiding China's future CO 2 emission reduction efforts. Highlights • A modified WLHP was presented with an increased COP and a wider applicability. • A novel energy system integrated the modified WLHP with an SOFC plant was proposed. • An "as-designed" approach based on a "standards-oriented" model was adopted. • The IEER was defined to perform the evaluation of the primary energy efficiency. • Performance of the proposed system was studied by comparison with a reference system. [ABSTRACT FROM AUTHOR]

The organic Rankine cycle (ORC) technology is an attractive candidate for waste heat recovery and clean energy utilization. The operating condition of ORC system would change constantly under fluctuant heat source and a dynamic model is able to predict the transient behavior. The ORC dynamic model generally contains some unknown parameters while their identification is often ignored. This paper proposes a detailed calibration mechanism for ORC dynamic model including subcritical and transcritical system. Component models including pump, expansion valve and evaporator are well calibrated and the integrated calibrated system model is validated based on experimental data. Results indicate that calibrated model can capture the system dynamic behavior well. For key system state parameters such as working fluid evaporator pressure and outlet temperature, model prediction can achieve mean absolute relative deviation of less than 2% for both subcritical and transcritical system. Meanwhile, the conventional expansion valve model for transcritical system is found not efficient enough and a modification form is provided. This work can contribute to the calibration mechanism of similar thermodynamic system and enhance the confidence in model application. • An ORC dynamic model applying to subcritical and transcritical system. • A modified expansion valve flow equation for transcritical system. • Two types of correction multipliers in evaporator calibration. • The mean absolute relative deviation of less than 2% for model prediction. [ABSTRACT FROM AUTHOR]

• Various kinds of SOFC-based systems for building applications were reviewed. • System configurations and characteristics were analyzed and discussed. • Means, by which the system performance was assessed, were detailed. • An all-around performance demonstration of the systems was presented. • Possible strategies for a brighter prospect of development were discussed. Energy consumption in buildings has long been a target for reduction efforts, and in these efforts, adopting advanced technologies to design high efficient energy systems dominates buildings' energy supply side. To date SOFC systems are regarded as one of the most adaptable technologies for building applications in terms of efficiency, flexibility and environmental protection. In this paper, a comprehensive review of SOFC-based energy systems for building applications is presented from the aspect of system layouts and performance assessments. The first half of this review is structured by the way of distinguishing SOFC systems in power capacities, provided energy forms and thermal management, based on which the types of SOFC systems used in buildings are defined and classified, and various system configurations and characteristics are reviewed and analyzed. The latter part gives a thorough review on the performance assessment of SOFC systems designed to be used in buildings. The system-level model widely adopted to predict the system performance is presented. With regard to the SOFC module, a common electrochemical model evolved from the conservation laws of mass and energy is discussed. For performance demonstrations and specific building load features are inextricable, building loads calculations and system matching strategies in relevant literatures are discussed before presenting the review of energy efficiency, and economical and environmental benefits. Guided by the ever-growing environmental concerns, the end of this paper discusses possible strategies for a brighter prospect of SOFC systems for building applications. [ABSTRACT FROM AUTHOR]