• Energy Research
• 11. Sustainability close
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• Applied Energy close

Abstract A variety of novel, recyclable and reusable, construction materials has already been studied within literature during the past years, aiming at improving the overall energy efficiency ranking of the building envelope. However, several studies show that a delicate control of indoor climating elements can lead to a significant performance improvement by exploiting the building’s savings potential via smart adaptive HVAC regulation to exogenous uncertain disturbances (e.g. weather, occupancy). Building Optimization and Control (BOC) systems can be categorized into two different groups: centralized (requiring high data transmission rates at a central node from every corner of the overall system) and decentralized 1 (assuming an intercommunication among neighboring constituent systems). Moreover, both approaches can be further divided into two subcategories, respectively: model-assisted (usually introducing modeling oversimplifications) and model-free (typically presenting poor stability and very slow convergence rates). This paper presents the application of a novel, decentralized, agent-based , model-free BOC methodology (abbreviated as L4GPCAO) to a modern non-residential building (E.ON. Energy Research Center’s main building), equipped with controllable HVAC systems and renewable energy sources by utilizing the existing Building Management System (BES). The building testbed is located inside the RWTH Aachen University campus in Aachen, Germany. A combined rule criterion composed of the non-renewable energy consumption (NREC) and the thermal comfort index – aligned to international comfort standards – was adopted in all cases presented herein. Besides the limited availability of the specified building testbed, real-life experiments demonstrated operational effectiveness of the proposed approach in BOC applications with complex, emerging dynamics arising from the building’s occupancy and thermal characteristics. L4GPCAO outperformed the control strategy that was designed by the planers and system provider, in a conventional manner, requiring no more than five test days.

Abstract In this paper, an open source tool is introduced to represent urban energy infrastructure in the City of Philadelphia, and different renewable energy scenarios are compared with respect to minimization of the standard deviation of the residual load. Renewable energy sources play a critical role in the world’s ongoing energy transition in response to climate change. Urban Energy Systems may be particularly sensitive to this transition due to the high energy demand density associated with urban environments. Open energy analysis and modeling tools can provide important information that can be used by urban energy planners, policy makers, and other stakeholders during this transition. In the present study, we apply FlexiGIS, an open energy modeling tool developed in a European context, to a case study in the City of Philadelphia. Due to the importance of open access to energy data, we pay particular attention to open energy data sources. Notably, OpenStreetMap was incomplete in its spatial coverage, but alternate open data resources were identified. This work conducts an optimization of the renewable energy mix to minimize the amount of balancing energy required for the residual load. We observe that Philadelphia has an optimal mix of renewables that favors a roughly even share of wind and solar, but that, compared to a previous case study in Oldenburg, Germany, requires more balancing energy at comparable levels of renewable penetration.

This paper examines the sources of changes in energy use of the Brazilian economy of industries and households from 1970 to 1996, using structural decomposition analysis based on the logarithmic mean divisia index technique. Energy use can be decomposed into eight factors that explain changes in overall energy use over the entire time period, and within five sub-periods. The growth of energy use between 1970 and 1996 was mainly influenced by changes in affluence, population and intersectoral dependencies, while changes in direct energy intensity and per capita residential energy use had a retarding impact on energy use. The novel contributions of the paper are the alignment of a previously disparate data set, the use of supply-use tables for SDA, and the application of such an SDA to a developing country. Both contributions involve solving a range of methodological issues pertaining to handling of large data sets.

Abstract The energetic use of residues from agriculture can foster the transition towards a more renewable energy supply. However, sustainability issues have to be considered along the entire provision chain as they affect the resource and energy potential as well as the achievable contribution to climate mitigation. Straw is one of the most important agricultural residues in Germany. It is not yet used for energy purposes extensively and compared to other agricultural feedstock it shows low competition with food, feed or fiber. This paper analyses on the one hand the sustainable potential of cereal straw for energy application in Germany considering the actual agricultural conditions, and on the other hand the global warming potential from different energy provision chains based on straw. Different humus-balance tools that are able to assess the organic matter (OM) demand to presume soil fertility. The analysis of straw potentials was applied at NUTS 3 level for Germany, based on statistical data. The results of this analysis were used as input data for the modeling of concepts for straw provision and use. Greenhouse gas (GHG) emissions were calculated for each concept in order to compare the global warming potential of various energy applications, to investigate the relative contribution of different production steps and to compare them with fossil energy applications. In total, 29.8 Tg of straw (fresh matter) are produced annually in Germany (1999–2007). Approximately 4.8 Tg of the total straw occurrence are annually required by animal husbandry. Between 7.97 and 13.25 Tg straw can be classified as sustainable straw. Highest straw potential (3.99 Mg ha−1) can be found in parts of Schleswig-Holstein, Mecklenburg–West Pomerania, North Rhine-Westphalia and Lower Saxony. But there are also regions that show a net deficit. The cumulated GHG emissions for the resulting concepts are between 8 and 35 g CO2-eq. MJ−1. In comparison to fossil energy applications, the highest reduction potential occurs for concepts for combined heat and power (CHP) provision, i.e. 223 g CO 2 -eq . MJ el - 1 . This study highlights the possible contribution of straw as renewable energy carrier, but also demonstrates that there are regional restrictions for straw use.

Comprehensive global decarbonization will require that transportation services cease to rely on fossil fuels. Here we develop a generic life-cycle cost model to address two closely related questions central to the emergence of sustainable transportation: (i) the utilization rates (hours of operation) that rank-order alternative drivetrains in terms of their cost, and (ii) the cost-efficient share of clean energy drivetrains in a vehicle fleet of competing drivetrains. Calibrating our model framework in the context of urban transit buses, we examine how the comparison between diesel and battery-electric buses varies with the specifics of the duty cycle (route). We find that even for less favorable duty cycles, battery-electric buses will entail lower life-cycle costs once utilization rates exceed 20% of the annual hours. Yet, the current economics of that particular application still calls for a one-third share of diesel drivetrains in a cost-efficient fleet.

Abstract Microgrids integrating local renewable energy sources at low-voltage level show promising potentials in realizing a reliable, efficient, and clean supply of electricity. Further improvements are expected when such a microgrid is operated based on direct current (dc) instead of alternating current (ac) infrastructure for power distribution commonly in use today. Our study aims to systemically quantify the gap between environmental impacts of microgrids at building level using the case study of power distribution within office buildings. For this purpose, a scalable comparative life cycle assessment (LCA) is conducted based on a technical bottom-up analysis of differences between ac and dc microgrids. Particularly, our approach combines the micro-level assessment of required power electronic components with the macro-level requirements for daily operation derived from a generic grid model. The results indicate that the environmental impacts of employed power electronics are substantially reduced by operating a microgrid based on dc power distribution infrastructure. Our sensitivity analyses show that efficient dc microgrids particularly lead to savings in climate change impact emissions. In addition, our study shows that the state-of-the-art scaling rules of power electronics currently used in LCAs leads to inaccurate results. In contrast, the proposed methodology applies a more technical approach, which enables a detailed analysis of the environmental impacts of power electronic components at system level. Thus, it provides the foundation for an evaluation criterion for a comprehensive assessment of technological changes within the framework of energy policy objectives.

Abstract One of the first rehabilitated passive energy standard office buildings in Europe was extensively monitored over two years to analyse the cooling performance of a ground heat exchanger and mechanical night ventilation together with the summer comfort in the building. To increase the storage mass in the light weight top floor, phase change materials (PCM) were used in the ceiling and wall construction. The earth heat exchanger installed at a low depth of 1.2 m has an excellent electrical cooling coefficient of performance of 18, but with an average cooling power of about 1.5 kW does not contribute significantly to cooling load removal. Mechanical night ventilation with 2 air changes also delivered cold at a good coefficient of performance of 6 with 14 kW maximum power. However, the night air exchange was too low to completely discharge the ceilings, so that the PCM material was not effective in a warm period of several days. In the ground floor offices the heat removal through the floor to ground of 2–3 W m−2 K−1 was in the same order of magnitude than the charging heat flux of the ceilings. The number of hours above 26 °C was about 10% of all office hours. The energy performance of the building is excellent with a total primary energy consumption for heating and electricity of 107–115 kW h m−2 a−1, without computing equipment only 40–45 kW h m−2 a−1.

[EN] District heating systems (DHSs) play an important role for urban areas as they enable an efficient and cost-effective heat supply. Existing DHSs are primarily based on fossil fuel energy and therefore need to be transformed in the coming years to meet the climate goals of the Paris Agreement. Lowering system temperatures is relevant to convert the fossil-based generation to renewable energy sources. However, there is a lack of a systemic methodology that can properly promote the required changes of the system temperatures during operation. This paper contributes a first part to such a methodology: a method to evaluate the average variable costs of heating plants that supply DHSs. The novelty of the approach lies in a systematic way to consider the impact of supply temperature and momentary thermal power on the variable costs of a plant. The method¿s requirements, application, results, and conclusions are demonstrated in three case studies of renewable heating plants: a solar thermal, a geothermal and an industrial surplus heating plant. The specific results of these case studies show that different set-points for the supply temperature and for thermal power of each plant have an impact on the variable cost of production. A comparison of the results demonstrates that the method increases the cost transparency in general. It is concluded that the supply temperature should be used as a variable in the operational optimization in DHSs. Further, the method should be part of a more comprehensive methodology for entire DHS infrastructures including storages, the network, and the customers. This work was supported by the Federal Ministry for Economic Af-fairs and Energy of Germany in the project "Smart Heat Grid Hamburg" [grant number 03ET1458A]