Cryo-compressed vessels have many advantages in storing hydrogen for automotive applications because of large storing density and thermal endurance. However, the cooling power of venting hydrogen in the processes of dormancy and discharge is not fully utilized. A throttling valve can be used to recycle the cooling power. A thermodynamic model is established to analyze the behavior of hydrogen in the insulated pressure vessel with a throttling valve. Different initial pressures and release pressures of hydrogen in the vessel are studied in the processes of dormancy, discharge and driving. The dormancy can be extended 55% with a throttling valve in the vessels of 2 MPa release pressure. The cooling capacity of the throttling valve decreases with the increase of the initial pressure. Simulations of hydrogen storage during the actual driving are performed at different initial pressures. The throttling valve in the lowinitial- pressure vessel can reduce the upper pressure limit of the vessel by 50% which reduces the manufacturing costs obviously. This work introduces the great potential of the throttling valve in the vessel for automotive applications.
In this paper, we develop a residential grid-level optimization model, which incorporates both electrical consumption scheduling (ECS) systems and energy storage devices (ESDs), so as to lower the peak-to- average ratio (PAR) of electricity demand and reduce the costs of electricity supply and consumption. This model consists of three levels: household consumption optimization (solo opt), grid consumption optimization (base opt) and ESD allocation optimization (ESD opt). To evaluate this model, a realistic residential population of 180 households subdivided into subpopulations by household sizes and income levels was simulated using a bottom-up randomization approach, with electricity supply from conventional thermal generation (CTG). The results show that PAR can ideally be reduced to 1 with an optimal allocation of ESDs among households with positive bills savings.
Modelling tools are frequently used to study China’s carbon policies while central and local governments initiate and implement carbon targets. Reviews of these low-carbon-planning tools and their usefulness, however, are not sufficient. In this regard, we review eight often used tools in China and suggest their applications and limitations. Tools are classified into four categories: computable general equilibrium, cost- optimization, benchmarking, and accounting tools. For China, application cases are recognized in addressing three research questions, i.e., emission scenario building, policy optimization, and carbon-policy impact analysis. From these studies, it is found that while tools usually require significant assumptions, the disclosure of them are in shortage and lack standardization and comparability. Tools also exclusively focus on policy- planning phase without attention to policy- implementation and policy-evaluation phases. Since the Chinese government has initiated three rounds of low- carbon-pilot-city programs, therefore, it is recommended that tool developers learn from some empirical evidence to integrate real policy outcomes into tools, e.g., policy effectiveness, expected implementation barriers, and required administrative power. Hence, analysts can complete a more holistic, evidence-based, and local-oriented policy suggestion. Standardization of model disclosure rules and evidence- based assumption-making are suggested to enhance comparability and mutual learning. Finally, modules to track progress in policy implementation and evaluation process can be added into tools for policy iteration and evidence collection.
Carbon-dioxide mitigation in residential building sector (CMRBS) has become critical for China in achieving its emission mitigation goal in the “Post Paris” period with the growing demand for household energy service in residential buildings. This is the first paper to investigate the factors that can mitigate carbon-dioxide (CO2) intensity and further assess CMRBS in China based on a household scale via decomposition analysis. Here we show that: Three types of housing economic indicators and the final emission factor significantly contributed to the decrease in CO2 intensity in the residential building sector. In addition, the CMRBS from 2001–2016 was 1816.99 MtCO2, and the average mitigation intensity during this period was 266.12 kgCO2 · (household · year)-1. Furthermore, the energy-conservation and emission-mitigation strategy caused CMRBS to effectively increase and is the key to promoting a more significant emission mitigation in the future. Overall, this paper covers the CMRBS assessment gap in China, and the proposed assessment model can be regarded as a reference for other countries and cities for measuring the retrospective CO2 mitigation effect in residential buildings.
Building layout is one of the most important factors of residential outdoor wind environment. Existing researches on the impact of building layout mainly focus on a certain layout or an actual case, which lacks comparisons and analysis of different typical models. Three typical residential models with different layouts are established in this paper. Based on the meteorological data in Shanghai, the influences of different layouts in different seasons are analyzed through the numerical simulation. The study helps to provide a reference for architecture design.
The energy management strategy (EMS) plays an important role in the power system of hybrid-powered fuel cell vehicles in order to reduce hydrogen consumption and fuel cell performance degradation. This paper proposes a robust EMS based on the min-max game theory, where the EMS and the driver behavior are set as two virtual game players making decisions for opposite goals. First, a mathematical model of the hybrid-powered fuel cell vehicle is introduced, that include a transmission system, an ultracapacitor system, a fuel cell system, and the DC/DC converter. Then, a min- max game framework is constructed to describe the energy management problem of fuel cell/ultracapacitor hybrid-powered vehicle with uncertain environment. Finally, the high efficiency and robustness of the proposed strategy are validated by comparing it to the PID-based strategy in the dynamic driving condition.
This present study uses a panel of 24 countries over the period of 1990-2015 to analyze proposed determinants of energy consumption in Africa. The panel is categorized into LI, LMI and UMI African economies. Applying econometric tests and DCCE estimator through a specified DHPD model, issues of heterogeneity and cross-sectional reliance were considered. Our established findings indicated that, GDP, OP, URB, and POPg are potential drivers of EC when capital stock and labor are used as control variables. Further, with the exception of URB-EC, POPg-EC, POPg-GDP, and POPg-URB nexus whose direction of causality were common across country groups, variations occurred for the causalities amid GDP-EC, OP-EC, OP-GDP and URB-GDP nexus for the different income level groups. We therefore conclude that, factors unique to the various country groups in terms of income levels influence the causal affiliations between analyzed variables. Policy recommendation are briefly discussed.
Application of heat recovery units in building HVAC systems can significantly save the energy consumed by conditioning fresh air. The indirect evaporative cooler (IEC), used as a pre-cooling device for fresh air in the hot-humid area, recovers both latent and sensible energy from the exhaust air. In this paper, a year-around on-site performance test was carried out in a wet market located in Hong Kong. The energy performance of the two A/C systems with exhaust air heat recovery units was analyzed and compared: an IEC coupled to an AHU; a traditional heat recovery wheel (HRW) coupled to an AHU. The heat recovery of IEC and HRW were collected under typical summer operation conditions. The results show that the HRW has better dehumidification performance than IEC, but the IEC can largely reduce the fresh air temperature by handling the sensible cooling load. During the whole year, the difference in the total heat recovery between IEC and HRW is within 2%. In cooling seasons, the energy efficiency of the two systems with IEC and HRW for exhaust air heat recovery can be improved by 27.6% and 25.7% respectively.
natural gas system (IEGS), operating reserve and gas storage are both useful support to cope with contingencies in IEGS. This paper proposes a day-ahead SCUC model for the IEGS to schedule the operating reserve and gas storage simultaneously. The multi-state models for generating units and gas wells are firstly established. Based on the multi-state models, the expected unserved energy cost (EUEC) criterion is proposed based on probabilistic methods considering random failures of generating units and gas wells. Then, the EUEC criterion is incorporated into the day-ahead SCUC model, which is nonconvex and mathematically transformed into a solvable mixed integer linear programming (MILP) problem. The proposed model is studied using a 6-bus-6-node IEGS with natural gas storage.
There are already numerous small-scale solar energy collectors on the roofs of buildings in many cities in China, which are used to provide domestic hot water in most circumstances. However, these separated small-scale solar energy collectors usually do not work sufficiently as expected, particularly for fear of pipe freezing crack in severe cold winter. On the other hand, these distributed small-scale solar energy collectors would have very convenient access to local district heating system. Hence, the buildings can consume the thermal energy from local district heating system and simultaneously produce heat to local district heating system when the solar energy collectors on their roofs are available. Therefore, the buildings can become solar heat prosumers to local district heating system. In this study, a configuration on solar heat prosumers is proposed to integrate with a general district heating system. Then a thermo-hydraulic model is developed to simulate the energy performance of distributed small-scale solar heat prosumers in district heating system. The proposed model is validated in a real life case study in a north Chinses city. The simulation results showed that the solar energy penetration was about 13% of the total heat consumption in heating season of 120 days.