• Energy Research

Abstract Energy efficiency in water systems contributes significantly towards achieving sustainable water management. Decentralized anaerobic fluidized bed membrane bioreactor (AFMBR) systems with energy recovery have been proposed for greywater recycling in domestic buildings for non-potable uses, such as toilet flushing. This study developed an eco-efficiency analysis (EEA) framework with the integration of life-cycle assessment (LCA) and economic analysis for the evaluation of different water systems. Four water management scenarios including (1) freshwater flushing system, (2) seawater flushing system, (3) greywater flushing system adopting aerobic membrane bioreactor (MBR), and (4) greywater flushing system adopting AFMBR, were analyzed in a case study in Hong Kong. The EEA results reveal the AFMBR greywater reuse scenario to be the most eco-efficient option as the system is capable of energy recovery, recycling of water resource and reduction of sewage treatment loadings. This study has demonstrated that the EEA framework is an effective tool to guide water management towards sustainability and provides a basis for further research on the application of greywater recycling systems on a larger scale.

Abstract The disparity of carbon dioxide emission abatement (CDEA) has been impeding more balanced improvement of energy efficiency worldwide. Energy service companies (ESCOs), which are present to varying degrees, have come to play an increasingly key role in reducing CO2 emission via energy efficiency retrofit projects. China, as the main contributor to carbon dioxide (CO2) emissions, has been promoting ESCOs for decades. This study aims to identify the factors influencing the spatial differences for CDEA and assess the provincial-level potentials for reducing CO2 emissions through ESCOs. Data from 3225 ESCO projects in Mainland China spanning from 2011 to 2015 were examined to map out the spatial patterns of CDEA using local Moran’s I index and local indicator spatial autocorrelation. Influencing factors were identified through spatial analysis based on Kaya identity and ordinary least squares. The results indicate that the national progress of CDEA can be attributed to the high efficiency of ESCO projects in coastal and northern China. It was observed that population, consumption of coal, and research & development input have a positive influence on CDEA, whereas per-capita GDP, energy industry investment, and industry value added have an inhibitory effect on CDEA.

Abstract Most cities import energy and water from their hinterlands. Both the nexus in a city and that between the city and its hinterlands should be considered for comprehensive management of water and energy. To examine the water-energy nexus associated with the city embedded in the hinterland, a city-hinterland water-energy mixed-unit input–output methodology is proposed to model the effects of growth under different water and energy production and consumption scenarios based on the growth of the demands for water and energy resources from the city. This study presents a demonstration of the water-energy mixed-unit input–output approach by analyzing Hong Kong and its associated hinterland in mainland China. A Sankey diagram and several indicators have been presented to illustrate the water–energy nexus in 2015, as well as the nexus for future city growth and the nexus incorporating the water and energy infrastructures planned in Hong Kong. Several indicators in the results compare the interaction between water and energy systems and the dependence on hinterland for different scenarios in Hong Kong. The modeling outcomes show that the current water infrastructures might be able to meet the demand for water treatment in 2050. The indicators obtained from this study suggest that all types of water for energy and energy for water will increase by 7.8–9%.

Abstract Climate change is receiving an ever-increasing attention due to the accelerated global warming. Undoubtedly, CO 2 from anthropogenic sources is the major contributor to this undesirable effect and thus, there has been a growing attempt to curb it. Utilization of biofuels to replace fossil fuels has been considered a viable method to mitigate CO 2 emissions. However, there has been some concern about the indirect greenhouse gas emissions from the production and consumption of biofuels, such as land-use change, carbon leakage, and biomass transportation. It was suggested that these indirect factors can increase the CO 2 emission and may offset the benefits of CO 2 sequestration from biofuel utilization. In this study, all these challenges in biofuel production have been comprehensively reviewed and the importance of using the agricultural residues for biofuel production in countries with high reliance on agricultural development has been emphasized upon. A case study for the utilization of the agricultural residues in the Great Mekong Subregion (GMS) for biofuel production has been presented and the carbon balance for different bioenergy production scenarios in five Southeast Asian countries has been calculated. The results of the regression models show that Thailand and Lao PDR have the highest and lowest amounts of biomass residues per unit mass crop, respectively, suggesting the substantial differences in the harvesting technologies and/or economics of those countries. The overall annual CO 2 sequestration potentials of the biomass for replacing gasoline through bioethanol production, and for substituting coal for power generation via anaerobic digestion and gasification have been determined to be approximately 104/ Tg and 488 Tg, respectively. It has been suggested that using the crop residues as feedstock for the second generation biofuel production without affecting the food market could indeed provide considerable carbon credits for sustainable agricultural development as the major industry in the developing countries.

Abstract The United Nations Sustainable Development Goal 7 (UNSDG 7) “Affordable and Clean Energy” strives to increase renewable energy share in energy consumption. Building-integrated photovoltaics generate renewable energy and offset fossil fuels carbon emissions. As roof space availability varies among different buildings, the potential to utilize rooftops as photovoltaic systems is uncertain. This study's aim is justified by the need to develop a systematic modeling framework to examine photovoltaic rooftops with varying roof availability and to propose peak shaving strategies for reducing peak load and carbon emissions. The framework incorporates computational simulations to model the building power demand and evaluate different peak shaving strategies. By identifying building peak loads, peak shaving offsets part of the loads with photovoltaic electricity . This framework can be applied globally given suitable data, and is demonstrated on a 10-story reference office building with photovoltaic installations occupying 10%, 30%, and 50% of the roof area. In this demonstration, 9 peak shaving strategy options are considered for covering a varying number of peaks that last for different durations on weekdays. Peak load reduction and carbon emission saving in each option are assessed, optimal peak shaving options are identified according to seasonal changes and available area for photovoltaics. For example, when 50% of the roof's area is available, a full-office-hour strategy is proposed in summer, saving approximately 595 kg CO 2 per weekday. In winter, solar generation is reduced. A proposed strategy covering full-office-hour except lunch hours yielded an estimated 271 kg CO2 saving per weekday. Based on these findings, policies are recommended to encourage utilization of existing rooftops, construct photovoltaic-ready roofs on new buildings, and guide urban planning to avoid excessive shading.

This study develops a hybrid prediction system to forecast 1-day-ahead electricity consumption of air conditioners in office spaces. The hybrid system combines a linear autoregressive integrated moving average model and a nonlinear nature-inspired metaheuristic optimization-based prediction model. To evaluate the efficacy of the proposed system, a smart grid-based monitoring device was installed in an office space, which consists of smart meters, environmental monitoring sensors, infrared sensors, and fan adjustment systems. Data were retrieved to train and test the proposed system. Sensitivity analyses were performed to identify the optimal parameters of the model and inputs for future use. Evaluation results confirmed that the proposed hybrid system outperformed the conventional linear and nonlinear models, showing good agreement between predicted and actual electricity consumption of air conditioners. Particularly, the proposed system obtained the correlation coefficient R of 0.71 and total error rate of 4.8%. The hybrid system can facilitate facility managers in forecasting electricity consumption of air conditioners.

Energy service companies (ESCOs) have emerged to carry out energy efficiency retrofit projects, playing an essential role in mitigating carbon dioxide (CO2) emissions in China. However, it remains unclear how exactly ESCOs contribute to CO2 mitigation during urbanization and industrialization. We conducted regression analyses on data collected in 29 provinces in China as the first case study to investigate the moderating effect of ESCOs in relationships between urbanization, industrialization, and CO2 emissions. The results indicate that urbanization had a significantly negative influence on CO2 emissions. In contrast, industrialization displayed a statistically significant positive impact on CO2 emissions. ESCOs have a significant moderating effect on the relationship between industrialization, urbanization, and CO2 emissions. The analysis also revealed that ESCOs have a better performance in areas with lower industrialization and greater urbanization. ESCOs may invest more in regions with limited ESCO activities and huge CO2 emission reduction demand, while energy-saving technology innovation should be advocated in regions with sufficient ESCO activities.

Energy performance contracting is increasingly employed to promote energy conservation toward sustainable development. This study characterizes these services in China through an analysis from 2011 to 2020 that reveals imbalances in the energy services company (ESCO) sector with respect to trade route, customer base, and energy conservation technology. More specifically, analyses of inter- and intra-province trade networks show that Beijing was the lead provider of ESCO projects, whereas Hebei was the lead customer. Jiangsu, Liaoning, and Inner Mongolia have risen to be new significant players during the 13th Five Year Plan (FYP) period (2016–2020). Although a wide range of energy conservation measures were deployed, ESCO projects were most prevalent in the industrial sector, with particular emphasis on residual heat, pressure and gas recovery. However, the building sector become an increased focus for ESCO projects during the 13th FYP. We further find that national guidelines alone may not lead to significant advances in energy conservation without additional and complementary provincial support. Such heterogeneity, especially at the provincial level, may help explain observed imbalances in ESCO projects. While prior studies usually focus on national guidelines, the more general implication and call of our study is that greater attention should be placed on subnational (provincial) guidelines around energy conservation.