Abstract

In order to obtain phase change materials with suitable melting point, latent heat and thermal conductivity, this paper employed the liquid paraffin with a melting point of 17°C and solid paraffin with a melting point of 41°C in different proportions to fabricate PCM composites. By adjusting the mixing ratio of short-chain hydrocarbons and long-chain hydrocarbons in paraffin wax, phase change materials with different phase change ranges were obtained to meet the requirements of practical applications. A variety of copper foam /paraffin composite phase change materials with different porosities and pore densities were prepared by the melt dipping method. The influence of the porosity and pore density on the thermal conductivity of copper foam/paraffin composite was explored. The experimental results show that mixed paraffin can control the melting point and latent heat of composite phase change materials. Copper foam can greatly increase the thermal conductivity of composite phase change materials with the porosity has a greater impact and the pore density has a less effect. The thermal conductivity of composites can be increased by a maximum 20 times.

Abstract

The refrigerant-direct radiant cooling (RDRC) systems have become increasingly popular owing to good thermal comfort and high energy efficiency. However, the existing RDRC terminal has complex structure and large occupation area. To tackle these problems, an aluminum column-wing type RDRC (ACT-RDRC) terminal is presented. The detailed numerical model is developed to explore the thermal performance of this system and validated with experimental data. Results shows that when the evaporating temperature increases from 6℃ to 14.0℃, the ratio of the natural convection, condensation latent and radiant cooling capacities changes from 4.6:2.1:1 to 4.5:1.4:1, which indicates that the natural convection is a main contributor in the heat transfer process of this system. To meet the thermal comfort requirements, the relative humidity less than 60% is recommended with the indoor air temperature of 28℃. A characteristic equation is proposed to accurately predict the cooling performance of the ACT-RDRC system, which is conductive to promote its application.

Abstract

Latent heat storage (LHS) system has obvious advantages in balancing energy supply and demand. However, the heat conductivity of PCM is extraordinarily low, which makes it difficult for the latent heat storage system to be applied in practice. For the sake of enhancing the productivity of phase transformation, the way of adding the area of heat conduction is adopted in this paper, such as adding fins. Two different fin combinations are designed under the condition that the total area of fins is unchanged. They design and analyze from two aspects of fins complexity and angle. The two dimensional model of energy storage equipment was established, and the system containing paraffin RT35 was numerically solved. The melting rate, total time required for melting, melting and temperature changes clouds. According to the analysis of the research results, it is found that the complex fin arranged at the bottom of the phase change material can penetrate deeper into the interior and enhance the melting of the phase change material at the bottom, thereby improving the overall melting rate of the system. When the angle between the fin and the horizontal axis is 0°, the melting rate of the system is faster. From the inner tube to the outer tube, the fins are arranged from short to long. Compared with the simple straight fins, the total melting time is reduced by 52.2%.

Abstract

As the increased frequency, intensity and duration of extreme weather events have significantly challenged power systems, greater attention has been focused on the development of resilient power systems. Taking a physical-cyber-human system perspective, this paper establishes a multi-criteria resilience evaluation framework for urban power systems, in which two principal elements responsible for power system function degradation are described, and fifteen (eleven objective and four subjective) power system resilience evaluation indicators are identified. Fuzzy hesitant judgement and a TOPSIS aggregation method are applied for the evaluation to minimize expert divergence and maximize group consensus. The evaluation method is then applied to four Chinese municipalities: Shanghai, Beijing and Chongqing, and Tianjin. It was found that Beijing’s resilience was the best of the four but overall the urban power system resiliencies were not enough in the face of extreme event challenges.

Abstract

The bioenergy with CO2 capture and storage (BECCS) is an important solution to reduce CO2 emissions. This paper proposed a new method that can accurately access CO2 capture potential from a biomass-fired combined heat and power (BCHP). Chemical absorption is used as CO2 capture technology. By carefully considering the temperatures of the heat required by district heating and CO2 capture, the allocation of the available heat from flue gas condensation and extracted steam condensation for different purposes has been optimized. By using a real BCHP with a thermal capacity of 200MW as a case study, results show that the captured CO2 was 23.42t/day without any change in heat and power supply, which was 1.77% of the total released CO2.

Abstract

Data generated in the cities have great potential to assist in studies on urban metabolism and urban energy transition. Several cities around the world have already adopted the open data portals to share data and increase their capabilities. However, much of these data are of low resolution, diverse formats, and mostly lack real energy measurements of buildings. In this paper, we address this issue by using an example of Energy Hub data portal “NRGYHUB”, an urban energy portal for open data for the city of Västerås, Sweden. Granular electricity, district heating and water consumption data were collected and matched to their corresponding buildings. The data are stored into a database and will be available for public through a GIS-driven interface. The challenges that were faced during the data access process are briefly described. The potential of NRGYHUB data portal as a tool to develop urban policies is discussed.

Abstract

In this paper, the concept of electric energy storage by a fluidized bed (EESFB) is introduced and validated. In this novel EESFB system, sand is used as the medium for energy storage. In the heating mode, sand is heated up in a fluidized bed by a group of embedded electric heating elements to a high temperature and then stored in thermally insulated tank. In the heat release mode, the stored thermal energy can be released to generate hot air, steam and electricity as necessary. Compared with other thermal energy storage technologies, EESFB is prevailing in cost-effective, environmental-friendly, high efficiency, high energy density, high flexibility to meet load fluctuations and always-ready characteristics to supply high-temperature thermal energy. It also could have a potential for massive energy storage. An experimental system with 100 kW input power was setup to study the feasibility of the novel technology. Results showed that EESFB system can be operated smoothly and sand can be efficiently heated up to a high temperature with embedded heating elements in the fluidized bed.

Abstract

This paper investigates a collective control problem for a parking-based large-scaled EVs. A parking under electric energy management by a virtual power plant is targeted under assumption of decentralized charging/discharging rate control of the individual EVs. A decentralized charging control strategy is proposed by solving a mean-field game problem with the cost function that balancing between the collective charging behavior and the charging level of each EV. Simulation results is finally demonstrated to validate the proposed control strategy.

Abstract

Combined cooling, heating and power (CCHP) system is a promising distributed energy system, which is usually installed close to the terminal user and satisfies the diverse energy supply. Whereas, the demand-response characteristics is critical for the system feasible and efficient operation. In this work, an alternative adjust method based on the thermochemical recuperation is developed for optimizing the CCHP production, the exhaust high-temperature gas from the prime mover is first used to drive the endothermic reaction of methanol decomposition before the absorption refrigeration, thereby the exhaust waste heat realizes the enhanced cascade utilization and improves its energy level by transited into the chemical form. Both the thermodynamic performances and the flexible demand response characteristics of the system were also comprehensively investigated. Regarding to the case studies of building application in China, two scenarios of the gas turbine and the internal combustion engine as the prime movers are considered, the system thermal efficiency for CCHP production is increased by 0.82%-13.71% accompanying with a considerable fuel saving. Furthermore, the system is able to automatically adjust the recuperation thermal ratio based on the simultaneous changed terminal energy loads, the operation flexibility of source-demand matching is thus enhanced and optimized. The reasonable operation characteristics approve this promising method to achieve efficient waste heat recovery and feasible multi-energy production.

Abstract

The charging/discharging characteristics of lithium-ion battery are mainly dependent on itself temperature which is determined by the balance both the heat generated by battery itself and the heat removed by the battery thermal management system (BTMS). Consequently, study on the heat generation behaviors of the lithium-ion battery is necessary for designing the BTMS which is capable of maintaining batteries at optimum temperature ranging from 20℃ to 40℃. In this study, the heat generation behaviors and electro-thermal characteristics of a prismatic LiFePO4 battery with a high nominal capacity of 280Ah at the charging rates of 0.5C and 1C and initial temperatures of 15℃, 25℃ and 35℃ were comprehensively explored using an electrochemical-calorimetric method. The experimental results show that the charging capacity at the end of charging is nearly independent on the above mentioned charging rates and initial temperatures, which is due to the positive effect of heat generated by the battery itself in accelerate calorimeter rate (ARC). However, it is noted that the heat generation rates during the charging process (especially for the beginning of charging) significantly increases with the growth of charging rate and the decrease of initial temperature. At the state of charge (SOC) equal to 0.1 and initial temperature of 15℃, the heat generation rates at charging rates of 0.5C and 1C are about 20.2 W and 76.6 W respectively, that is to say, the heat generation rate at high charging rate of 1C is nearly 3.8 times than that at moderate charging rate of 0.5C. These findings indicate that the battery own the excellent charging efficiency (short charging time and charging capacity nearly equal to nominal capacity) at the high charging rate of 1C, however, significant rise of heat generation rate inevitably brings the huge challenge for the BTMS. This study may also provide some guidance for the design of BTMS.