To predict the energy performance of a chilled water system more accurately, the hydraulic resistances of its water pipe network should be calibrated before simulation. However, it is a challenge to calibrate the hydraulic resistance of such a complex pipe network that are compose of chillers, terminal units, variable-speed pumps, valves and many pipes installed in different floors of a high-rise building. In this study, a new calibration method is proposed elaborately to adapt the vertical structure of the water pipe network in a high-rise building. The proposed calibration method utilized an optimization model and a general pipe network hydraulic solver. To overcome the severe nonlinear characteristic of the pipe network, Genetic Algorithm (GA) is used to solve the optimization model. Then, the proposed calibration method is validated in a real-life chilled water system in a high-rise building. With the hourly measured data from the chilled water system in operation in a typical summer day, the hydraulic resistances of 200 terminal units, 46 valves and 912 pipes are calibrated in detail. The calibrated hydraulic resistances are used to predict pressures and flow rates of the chilled water system in the next day. Compared with the uncalibrated simulation results, the average pressure error between the calibrated simulation results and measured data from the 42 onsite pressure meters is reduced from 2.2% to 0.6%. The average flow rate error between the calibrated simulation results and measured data from the 3 onsite flow rate meters is reduced from 5.3% to 0.9%.
In this study, we aim to find an optimally sized battery that can be installed to an existing grid-tied solar home system without a prior energy storage system, in order to maximize the user’s financial benefits while maintaining reliable power supply to the home. To solve this optimization problem, we formulate the objective function as the net present value of the investment on the battery. Solution to the optimization problem returns the optimal battery size, power flows and battery age status during a 10-year evaluation period. In order to identify the most favorable solution to the user, we apply the proposed optimization algorithm to five typical photovoltaic (PV) generation and home load levels, and find that the optimal battery size is very sensitive to the level of PV power generation and the home load. In addition, it is more financially viable to have the battery when the daily PV power generation is less than the home load.
This study aims at exploring the relationship between renewable energy consumption and carbon dioxide emissions in China, and through the significance of renewable energy consumption, the hypothesis of environmental Kuznets curve at individual country level is tested as well as. Autoregressive distributes lag bounds testing approach is employed for empirical analysis. The results show that a quadratic relationship between renewable energy and CO2 emission has been found for the period support EKC relationship, and there exists a negative causality from renewable energy consumption to CO2 emissions.
In order to better understand the real-life thermal performance of Solar domestic hot water (SDHW) systems, SDHW systems installed in dormitories in a university were selected for on-line monitoring. There are 50 dormitory buildings in this university, and each building contains around 430 students. A SDHW system is installed in each building, using the glass evacuated solar tube collector, with an average collector area of 260 m2 . Air source heat pumps are used as auxiliary heat sources in the collector side. All SDHW systems were equipped with data logging system and remotely monitored with online data. Thermal performance analysis and economic analysis of SDHW systems were presented in this paper. The results show that the thermal performance and economy of SDHW systems for dormitory buildings are very good because the domestic hot water demand of student dormitories is relatively concentrated in time and space. Therefore, SDHW systems has a good application prospect in dormitory buildings.
The development of renewable energy is a huge opportunity and challenge in the energy field. As the ultimate energy source, solar energy is one of the most reliable energy sources among the renewable energies. Solar water splitting for hydrogen production is one of the most promising technologies of solar energy utilization, in recent decades. As an ideal clean energy source, hydrogen has made a significant breakthrough in transportation and storage technologies and hydrogen is also of great significance for applications such as chemical synthesis and energy storage. This paper reviews the basic methods and development of hydrogen production from solar water splitting, including photovoltaic, photoelectrochemical, and photothermal methods. In view of the photothermal method-solar thermochemical hydrogen production technology, this paper analyzes the thermodynamics, summarizes its future development perspectives. Furthermore, this paper also points out some new ideas for the realization of solar-thermal water splitting for hydrogen production.
Carbon trading markets play an important role in emissions mitigation through financial tools. China has established seven carbon trading pilots in its major cities and provinces. This paper explores the evolution laws of the co-movement of daily prices between carbon markets using complex network theory. First, we combine the co-movement of prices in five continuous days to co-movement modes. Then, we construct a directed weighted complex network. The nodes are the co-movement modes. Edges are defined as the time adjacent relations of two nodes. The frequency of an edge is taken as its weight. Transaction prices for the pilots in Hubei and Shanghai are selected as the samples. Results show an appearance of 231 modes from the 243 possible patterns, indicating a scattering of co-movement modes. Among all modes, the most frequent one is the fully stable one, showing that the markets are inactive in most time. Compared to the full sample and other periods, the complex networks in the first sample period stands out due to its large nodes and the existence of rings. This finding indicates the exact mirroring of some successive co-movement modes. The method proposed in this paper helps in understanding the evolution of Intermarket co-movement.
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.