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Solid-state transformers can be applied in the AC/DC hybrid distribution network. The reliability and power density of a solid-state transformer is significantly influenced by the insulation design of the isolated DC-DC converter and, in particular, its medium-voltage medium-frequency transformer. This paper proposes an insulation design method for the medium-voltage medium-frequency transformer. A novel insulation structure is adopted to reduce the volume and improve the heat dissipation performance. Optimization of insulation distance parameters is performed based on finite element method simulations. The proposed method is applied to a 60 kVA/10 kHz transformer, and the simulation results verify the improved performances with the proposed insulation design method. A prototype is developed according to the proposed scheme, and the experimental results of a DC-DC converter and the partial discharge and applied voltage tests are presented.

Given that the passive performance simulation of buildings based on typical meteorological year data and specific design schemes makes it challenging to respond to climate change and refine design requirements on time, this article established a passive performance prediction model for future buildings considering multi-dimensional variables including climate change, building design, and operational characteristics. For high thermal insulation buildings under future climates, the mild climate zone is more sensitive than the others, cooling energy demand is more sensitive than heating demand, apartments are more sensitive than office buildings, and passive survivability is more sensitive than energy performance; for buildings of the same type located in the same climate zone, thermal design solutions determine the increase rate of cooling demand. The potential benefits of climate warming on heating demand reduction are almost zero, but the cooling demand increases significantly, with apartments and office buildings increasing up to 22.1% and 5.0%, respectively. Buildings generally overheat in the future, and the increase rate of the mild zone far exceeds other zones with duration and severity being 3004.8% and 877.7% for apartments, and 884.3% and 288.9% for office buildings, respectively.

Considering the comprehensive effect of building carbon emissions, cost savings is of great significance in nearly-zero-energy buildings (NZEBs). Previous research mostly focused on studying the impact of technical measures in pilot projects. The characteristics of different cities or climate zones have only been considered in a few studies, and the selection of cities is often limited. At times, only one city is considered in each climate zone. Therefore, this study selected 15 cities to better cover climate zone characteristics according to the variation in weather and solar radiation conditions. A pilot NZEB project was chosen as the research subject, in which the energy consumption was monitored and compared across different categories using simulated values by EnergyPlus software. Various NZEB technologies were considered, such as the high-performance building envelope, the fresh air heat recovery unit (FAHRU), demand-controlled ventilation (DCV), a high-efficiency HVAC and lighting system, daylighting, and photovoltaic (PV). The simulated carbon emission intensities in severe cold, cold, and hot summer and cold winter (HSCW) climate zones were 21.97 kgCO2/m2, 19.60 kgCO2/m2, and 15.40 kgCO2/m2, respectively. The combined use of various NZEB technologies resulted in incremental costs of 998.86 CNY/m2, 870.61 CNY/m2, and 656.58 CNY/m2. The results indicated that the HSCW region had the best carbon emission reduction potential and cost-effectiveness when adopting NZEB strategies. Although the incremental cost of passive strategies produced by the envelope system is higher than active strategies produced by the HVAC system and lighting system, the effect of reducing the building’s heating load is a primary and urgent concern. The findings may provide a reference for similar buildings in different climate zones worldwide.

Evidence indicates that improvement of thermal performance of building envelope has the potential for aggravating the indoor overheating risk in summer. On the other hand, evolving building standards continue to strengthen the requirements for thermal performance to achieve the energy-saving target. Therefore, this study quantifies the interaction effect between building standards-oriented building design, heating energy demand in winter, and indoor overheating risk in summer. Building databases with different energy efficiency levels are generated using a randomly generated method. Uncertain variables include not only 13 design parameters but also the running state of natural ventilation and external shading. The indoor overheating risk is assessed in terms of severity and duration. Finally, a multi-objective optimization model integrating metamodels and the non-dominated sorting genetic algorithm is proposed to balance heating energy demand in winter and indoor overheating risk in summer. Results indicate that building standards tend to aggravate overheating risk in summer: the duration and severity of high-performance buildings increased by 40.6% and 24.2% than that of conventional-performance buildings. However, window ventilation could offset the adverse effect, and mitigation of duration and severity can be up to 85.2% and 62.1% for high-performance buildings. Window ventilation can weaken the conflict between heating energy demand in winter and overheating risk in summer. As heating energy demand increased from 6.1 to 67.3 kWh/m2, the overheating risk changes little that the duration of overheating risk decreased from 17.5% to 15.6% and severity decreased from 8.7 °C to 8.3 °C.

In recent decades, environmental problems have enforced designers to estimate the level of environmental emission of building design and reduce their environmental impact. On the premise of ensuring indoor comfort, the cost-effectiveness of solutions for reducing the building’s greenhouse gas has become a critical issue. Based on the Life Cycle Assessment (LCA), this paper establishes a building performance trade-off framework for indoor thermal comfort, economics, and environmental implication. This framework consists of four parts: the establishment of the optimization model; sensitivity analysis; obtain of Pareto frontier solutions, and decision-making analysis. Optimization variables involve envelope type and some envelope physical parameters. The “design variables-building performances” database is obtained by using building simulation software combined with the Latin hypercube sampling algorithm. Sensitivity analysis is used to extract the key factors affecting building performance. The designer can prioritize these key factors and it can reduce the uncertainty of building performance. A multi-objective optimization method coupling Gradient Boosted Decision Tree (GBDT) and non-dominated sorting genetic (NSGA-II) algorithm is proposed to seek the trade-off between three performances (obtain Pareto frontier solutions). The Pareto solution provides a more comprehensive reference for the preferences of different stakeholders, and the set of alternative solutions is further shrunk. Finally, take a specific residential building in China’s cold climate zone as a showcase of the trade-off framework. According to the obtained Pareto frontier solution, the solution set is shrunk to a certain range, and the distribution ranges of Life Cycle Costs, the greenhouse gas emissions, and the annual thermal discomfort hour ratio are 122.3–137.1 USD/m2, 15.6–44.8 kg CO2/m2, and 19.1–25.2%, respectively. The trade-off framework adopts the order of objective Pareto optimal and then subjective preference selection, narrowing the scope of alternatives for designers and saving time-cost of decision-making.

Phase change material (PCM) can be integrated into floor heating system to store excess heat, releasing it when needed, thus effectively reducing the mismatch between energy supply and demand. In this study, a double pipe PCM floor heating system with three independent heating modules was proposed for clean energy heating in rural China. A 26-day experimental study was conducted to study the operation effect of the system under four different strategies. Strategy 1: partial power operation strategy; Strategy 2: daytime energy storage strategy; Strategy 3: nocturnal energy storage strategy; and Strategy 4: phased energy storage strategy. In the early stage of heating, the average temperature of experiment room was 18.9 °C and the daily temperature fluctuation was controlled within 2.1 °C, which showed an effective guarantee of indoor comfort under Strategy 1. In the late stage of heating, the differences in indoor temperature fluctuations could be caused by changes in outdoor climate and operation strategies. And operating strategy had less impact on indoor temperature distribution. Moreover, the experiment results revealed that the system could provide a comfortable indoor thermal environment while adjusting operational strategies. And the 3 °C average daily temperature fluctuation confirmed the feasibility of creating a comfortable environment with gentle temperature fluctuations via the PCM floor intermittent heating.

Operating room (OR) is an indispensable department in a hospital, while its ventilation system is an important engineering solution to ensure safety for surgical procedures. Suitable ventilation system in the OR should be defined as using the minimum energy consumption and lifecycle cost to meet both the requirements of clean air for safe surgeries and comfort for occupants. Therefore, this study aims to develop a flexible evaluation framework on the suitability evaluation for ventilation system performance in ORs from a holistic view instead of one aspect only. To achieve the objective, we adopted analytic hierarchy process (AHP) and fuzzy comprehensive evaluation (FCE) methods and conducted suitability evaluation for two ORs with laminar airflow (LAF) and mixing ventilation (MV) system in St. Olavs Hospital, Norway. The evaluation includes seven indexes under three main aspects: ventilation effectiveness, energy consumption and users’ satisfaction. The comprehensive evaluation results are obtained through site measurements during mock surgeries, data collection and calculation as well as the questionnaire survey. Due to the unsatisfactory performance in energy consumption and thermal comfort indexes, the evaluation result of the suitability performance of the case OR with MV system was “unsuitable” while the one with LAF system was “suitable”, which reflects the situation that the energy consumption and thermal environment are sacrificed, although a clean and safe operation environment is guaranteed. The evaluation can provide basis for the commissioning of the ventilation system in the ORs of St. Olavs Hospital and provoke thinking of the ventilation system design and operation in the future.

High-power high-frequency transformer is a crucial component of isolated DC-DC converters. To optimize the structure and efficiency of high-frequency high-power transformer, high-precision estimation of transformer parameters is necessary. This paper proposes to adopt high-precision FEA simulations in parameter estimation including the dielectric strength for insulation design and the core loss. In addition, the difference of core loss estimation principle between different types of core material is pointed out. The proposed methods are applied to a specific case of transformer design to demonstrate the effects of the proposed methods in structure and efficiency optimization. Experiments will be performed in future research to verify the accuracy of the proposed core loss estimation methods and the feasibility and high efficiency of the proposed design scheme.

In the application of photovoltaic power generation integrated into the MVDC grid, the design of high-power and high-voltage converters is often a difficult point due to the limitations of devices and converters themselves. Aiming at high efficiency, adaptive voltage regulation and high power density, the interleaved-Boost and full-bridge LLC converter (IB-FBLLC) based on all SiC devices is studied and designed. For the core topology, LLC topology, a parameter design method based on high efficiency and wide bus voltage range is proposed. The losses of each part of the LLC converter as a function of main parameters are analyzed in this paper, and it is concluded that the switching loss is independent of the frequency when considering the maximum efficiency. In the design based on the wide bus voltage range, the FHA method is innovatively applied to the decoupling solution of resonance parameters by introducing intermediate variables k and Q, which significantly optimizes the parameter design process and simplifies calculations that are almost impossible to solve. It turns out that the maximum voltage gain or minimum bus voltage is independent of the switching frequency. These design methods and considerations are verified on a 80kW prototype, whose efficiency and power density reaches 98.08% and 1.562 W/cm3, respectively.

In recent years, the systematic application of phase change materials (PCM) is continuously developing. In this paper, an innovative PCM ceiling coupled with earth-air heat exchanger (EAHE) cooling system was proposed for building cooling. The system aimed to combine the cooling capacity of soil and the energy storage capacity of PCM, thus improving the indoor thermal environment. Performance of the system was tested by experimental method while data analysis focused on the indoor side. To research the effect of cold storage time on the performance of the system, two different operation strategies were adopted for comparison: 8-h cold storage strategy and 12-h cold storage strategy. Moreover, a control group was set up to observe the performance of the system on indoor temperature under the same weather conditions. The result showed that the experimental room in which we installed this system could reduce peak temperature by 2.1 &deg, C under 8-h timed cold storage strategy and 2.7 &deg, C under 12-h timed cold storage strategy. What is more, under the two operation strategies, temperature and heat flux of the PCM ceiling had similar distribution characteristics. Different strategies mainly affected the sustainability of the system and phase transition efficiency of the PCM ceiling.

In China, relevant standards about building energy efficiency and green buildings have resulted in corresponding requirements for the envelope thermal performance. However, improvement of the thermal performance of the envelope is accompanied by an increase of the environmental impact and cost. This study quantitatively analyzed the thermal performance, environmental impact, and cost of the green building envelope in cold areas and established a common practice database, as well as a multi-index evaluation model. The results show that the best thermal performance improvements are 40% in residential buildings and 30% in public buildings, respectively, based on the relevant standards. The exterior walls and windows have the greatest impact on building heat consumption. There is no significant correlation between the heat consumption and the comprehensive heat transfer coefficient of 10 green buildings. Therefore, the comprehensive heat loss coefficient is corrected. The verification results show that all errors except project 10 are within 15%. Additionally, the projects with balanced thermal performance improvement of exterior walls and windows showed a better performance. Finally, the best combination of residential building envelopes in the cold area was selected, using the evaluation model and quantitative database to calculate the comprehensive score.

Quickly detecting related primitive events for multiple complex events from massive event stream usually faces with a great challenge due to their single pattern characteristic of the existing complex event detection methods. Aiming to solve the problem, a multiple pattern complex event detection scheme based on decomposition and merge sharing is proposed in this article. The achievement of this article lies that we successfully use decomposition and merge sharing technology to realize the high-efficient detection for multiple complex events from massive event streams. Specially, in our scheme, we first use decomposition sharing technology to decompose pattern expressions into multiple subexpressions, which can provide many sharing opportunities for subexpressions. We then use merge sharing technology to construct a multiple pattern complex events by merging sharing all the same prefix, suffix, or subpattern into one based on the above decomposition results. As a result, our proposed detection method in this article can effectively solve the above problem. The experimental results show that the proposed detection method in this article outperforms some general detection methods in detection model and detection algorithm in multiple pattern complex event detection as a whole.

Energy and exergy analysis is very useful to optimize the design, operation and evaluation of calcium carbide production process. In this paper, a new calcium carbide production process of coal-coke-electricity grading substitution method (GSM) is proposed and evaluated by inter grating the first and second laws of thermodynamics according to the actual operation data from an actual calcium carbide production enterprise. Three typical calcium carbide production processes of GSM, electro thermal method (ETM) and oxygen thermal method (OTM) are compared based on the comprehensive energy and exergy consumption indexes of multiple products. The results show that, for the GSM, the mixed pellet brings into the highest proportion of energy and exergy of 69.36% and 71.85%, while the calcium carbide brings out the highest proportion of energy and exergy of 71.97% and 69.09%. Among the various heat losses, calcium carbide furnace gas takes the most heat, accounting for 15.9% of the total heat output. The power consumption per unit product of GSM is only 2.48 kWh/kg-CaC2, which is 23.93% lower than 3.26 kWh/kg-CaC2 of ETM. According to the energy and exergy analysis, when CaC2 is the only target product, the GSM has the lowest comprehensive energy consumption of 10.22 kWh/kg-CaC2 and the lowest comprehensive exergy consumption of 9.15 kWh/kg-CaC2. Compared with the traditional ETM and OTM, the GSM has obvious advantages.

Due to the continuous penetration of renewable energy in the building sector, its instability increases the importance of energy storage in balancing energy demand and supply. However, the low thermal conductivity of phase change materials limits its application. This paper proposes a shell-tube latent heat thermal energy storage device with fins to enhance heat transfer. The ANSYS software is used to establish a three-dimensional simulation model of the device, considering of the nature convection. Furthermore, for this study, an experimental platform is built, and the influence of factors on the device during the charging and discharging period is analyzed. Simulation results show that the melting effects of the device vary with the fin and tube pitch; their optimization results are 40 mm and 90 mm, respectively. Experimental results exhibit that the inlet temperature influences the storage effect of the device, but as long as the phase change material is completely melted, pursuing excessively high temperature is not necessary. The same pattern was observed with the flow rate when the heat exchange fluid reached a turbulent state. After optimization, the effective energy release efficiency of the device reaches 77%, and the corresponding inlet temperature, heat storage flow, and heat release flow are 60 °C, 0.144 m3/h, 0.288 m3/h, respectively.

The application of solar energy for heating in buildings has the problem of heat supply and demand time mismatch. In this paper, an interlayer ventilated phase change material (PCM) component (IVPC) that can be coupled with solar air collector was proposed. The thermal performance of IVPC was tested through experiments. The results show that if IVPC completes latent heat storage, the optimal air supply temperature of solar hot air is 35∼45℃ and the air supply speed is 3∼4m/s. The latent heat release time can be maintained for 5 hours. To build an IVPC coupled with solar air collector system (IVPSS) in TRNSYS, to simulate the improvement effect of IVPC on heating temperature fluctuations, a rural building in cold regions of China was selected. IVPSS can maintain the indoor temperature of the building in the range of 8∼16℃. Compared with buildings without IVPSS, the room temperature throughout the day can be increased by 5∼8℃. IVPC can effectively use solar energy to peak load shifting, reduce room temperature fluctuations, improve indoor thermal comfort, and provide solutions for farmhouses in cold regions to use clean energy for heating.

In-depth studies on the supply-side and demand-side are required to realize the on-demand heating of the heating system. At present, a lot of researches have conducted on the supply-side for obtaining the accurate heat consumption prediction, and researches on the demand-side are mainly concentrated on the single-family. For the large residential buildings, occupancy rate is an important factor affecting building heat consumption, but it is often ignored. In this paper, taking buildings in Tianjin as an example, the heat transfer relationship between households was analyzed firstly, and obtained that the heating condition of up household had a greater influence on object household than left, right and down households. Secondly, the influencing factors of heat consumption of household in different locations were analyzed, the number of classes for households in buildings with and without basement were determined, and the numerical relationship of heat consumption of classes for building with different energy-saving standard were further determined. Finally, the building heat consumption calculation method and household heat consumption distribution method with different occupancy rates were determined, and the correctness and necessity of their application in practical engineering were verified, that will provide theoretical guidance for refined heating.

For the heating system with thermal inertia, accurate prediction of heating parameters is the premise of achieving on-demand heating. The existing prediction models do not evaluate the historical operation data before model training, which may lead to the establishment of non-on-demand models and affect their application in actual project. In this paper, firstly, the data evaluation method and application process were proposed based on heating professional mechanism and actual operation data. Secondly, the proposed method was used to evaluate the historical data of a heating substation, and the relationship between outdoor temperature and heating parameters (daily secondary supply temperature and daily heating consumption) for different indoor temperature intervals were obtained. Finally, the prediction models were training by historical data with and without evaluation method, and compared them from evaluation criteria and professional mechanism. The results showed that the accuracy of prediction model established by historical data with evaluation method was greatly improved, and can be used to guide the energy-saving operation of heating substation. In addition, it was also obtained that the prediction model established by big data can be used for prediction guidance at the middle heating period, and linear regression method was suitable for the end of heating period.

Due to the increasingly serious shortage of resources, new energy-using technologies and new energy sources have received widespread social attention. CCHP system, as an efficient and stable way of energy utilization, has wide application prospect, which can achieve energy ladder utilization and multi-energy complementary. In this study, a correlation model for configuration and operation optimization based on a bi-level model construction method is established for a CCHP coupled multi-energy system. A solution method based on sequence control configuration methods, sequential quadratic programming algorithm and feedback correction mechanism is proposed for the optimization model and a CCHP coupling multi-energy system optimization tool is developed using MATLAB. Then taking a commercial area in Tianjin as a specific case, after calculating, the optimized system has significant economic benefit, whose total annual operating cost can be reduced by 36.2% compared with the traditional sub-system. The study found an effective method for the design optimization of CCHP coupled multi-energy system, and gives a new idea for solving similar optimization problems.

This article describes how quickly picking up some valuable information from massive RFID event stream often faces with the problem of long detection time, high memory consumption and low detection efficiency due to its stream characteristics of volume, velocity, variety, value and veracity. Aim to solving the problems above, an efficient complex event processing method based on NFA-HTBTS (Nondeterministic Finite Automaton-Hash Table B+ Tree Structure) is presented in this article. The achievement of this article lies in that we successfully use the union of NFA and HTBTS to realize the detection of complex event in massive RFID event stream. Specially, in our scheme, after using NFA to match related primitive events from massive RFID event stream, we use hash table and B+ tree structure to successfully realize the detection of complex event from large matched results above, as a result, these problems existed in current methods above can be effectively solved by our scheme. The simulation results show that our proposed scheme outperforms some general methods for massive RFID event stream.

A modular DC/DC conversion system with distributed MPPT and centralized step-up converter for photovoltaic energy integrated into HVDC grids is proposed in this paper. The conversion system consists of two power stages, with MPPT converter as the first stage and a step-up converter as the second stage. Both stages are modular structures. For the distributed MPPT stage, interleaved boost topology is utilized to effectively reduce the input and output ripples without adding extra components. For the centralized step-up stage, narrow-switching-frequency-variation LLC topology is employed, with the modules being configured as input-parallel-output-series structure. Full-range soft-switching property is achieved in the LLC stage to minimize switching losses. Theoretical analysis is carried out for the system voltage gain and design principles. Simulation and experimental results of a 3kW prototype system are presented to verify the theoretical analysis of the proposed system.

With the gradual increase of building energy consumption in recent years, the application of phase change energy storage materials in buildings has become the focus of researches. Phase change material (PCM) embedded in the envelope can increase the building inertia to keep the temperature stable. It can also store energy and release energy when needed. In this paper, the system of PCM radiant floor combined with PCM wall attached with sunspace was established. The thermal characteristics and the energy consumption of the building are studied through analyzing the data from the experimental investigation including the temperature and the heat flux. Two different buildings were built between the PCM room and the conventional room with the same dimension and building. The main test conditions are divided into passive and active control stages by comparing the air temperatures, envelope temperatures, phase transition temperatures, heat fluxes and power consumptions between the two rooms. It is concluded that the average room temperature of the experimental room is 7.15 °C higher than that of the conventional room in the passive energy storage stage. While the average energy-saving rate of PCM room was 54.27% compared with the conventional room in the active control stage.