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.
As energy and environmental issues become more and more serious, we need to further improve the overall energy efficiency of modern cities. The operation of the urban energy system is affected by the characteristics of human social behavior, which increases the complexity of the problem. Therefore, cities must find how to conduct a comprehensive analysis of the energy use behavior of social residents from the perspective of smart cities and energy Internet, and then carry out effective guidance and management, assist the transformation and upgrading of the urban energy system, reasonable planning, and realize the improvement of urban comprehensive energy efficiency, cleanliness, and low carbon. The social-physical behavior model of residents formed by the corresponding population mobility attributes and energy attributes can reflect economic conditions and the behavior habits of various groups, thereby assisting the investment decision-making of urban infrastructure construction, and providing a basis for urban and power grid planning.
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.
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.
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.
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%.
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.
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.
The reform of electricity market in China has made the market participants more active, which has posed a series of challenges for the power system planning with high penetration of renewable energy. This paper proposed a price-driven bi-level model for transmission expansion planning. At the upper level, the investment cost and operation cost of the transmission system is comprehensively considered. While at the lower level, the market clearing model is established, i.e., energy market and reserve market. The local marginal prices are obtained to guide the expansion planning of the upper level. By integrating the market clearing model of the lower level using Karush-Kuhn-Tucker condition, a mixed-integer nonlinear programming problem is formulated, which is further solved by a Heuristic method. In the case study, a modified Garver-6 bus system is utilized to verify the validity of the proposed method.
Two-phase loop thermosyphon is promising in free cooling of data center, base station, and other industrial buildings with high temperature heat source. The large-scale circulation loop of its natural phase-change cycle is complex with high internal flow resistance in these context and thus is hardly related to the thermodynamic properties of working medium, which has yet to be revealed in detail. In this study, a distributed steady-state model was implemented to verify the heat transfer performance of a two-phase loop thermosyphon with different working mediums under high internal flow resistance for building air-conditioning. Simulative study shows that the behaviors of R744 and R410A are relatively superior, and R744 is outstanding at the extreme high thermal resistance condition. The operating states with different mixed refrigerants are more stable in comparison with pure refrigerants. Eco-friendly mixed refrigerants with low cost and high safety are alternative selections for two-phase loop thermosyphon in building applications.