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Abstract District heating (DH) enables the utilisation and distribution of heating from sources unfeasible for stand-alone applications and combined with cogeneration of heat and power (CHP), has been the cornerstone of Denmark’s realisation of a steady national primary energy supply over the last four decades. However, progressively more energy-efficient houses and a steadily improving heat pump (HP) performance for individual dwellings is straining the competitive advantage of the CHP–DH combination as DH grid losses are growing in relative terms due to decreasing heating demands of buildings and relatively high DH supply temperatures. A main driver for the DH water temperature is the requirements for domestic hot water (DHW) production. This article investigates two alternatives for DHW supply: (a) DH based on central HPs combined with a heat exchanger, and (b) a combination of DH based on central HPs and a small booster HP using DH water as low-temperature source for DHW production. The analyses are conducted using the energyPRO simulation model and are conducted with hourly varying factors; heating demands, DH grid losses, HP coefficient of performance (COP) and spot market prices in order to be able to analyse the relative performance of the two options and their performance over the year. Results are also compared to individual boilers and individual HPs. The results indicate that applying booster HPs enables the DH system to operate at substantially lower temperature levels, improving the COP of central DH HPs while simultaneously lowering DH grid losses significantly. Thus, DH performance is increased significantly. Additionally, performance for the DH HP with booster combination is considerably better than individual boiler or HP solutions.

Bioplastics are alternatives of conventional petroleum-based plastics. Bioplastics are polymers processed from renewable sources and are biodegradable. This study aims at conducting an environmental impact assessment of the bioprocessing of agricultural wastes into bioplastics compared to petro-plastics using an LCA approach. Bioplastics were produced from potato peels in laboratory. In a biochemical reaction under heating, starch was extracted from peels and glycerin, vinegar and water were added with a range of different ratios, which resulted in producing different samples of bio-based plastics. Nevertheless, the environmental impact of the bioplastics production process was evaluated and compared to petro-plastics. A life cycle analysis of bioplastics produced in laboratory and petro-plastics was conducted. The results are presented in the form of global warming potential, and other environmental impacts including acidification potential, eutrophication potential, freshwater ecotoxicity potential, human toxicity potential, and ozone layer depletion of producing bioplastics are compared to petro-plastics. The results show that the greenhouse gases (GHG) emissions, through the different experiments to produce bioplastics, range between 0.354 and 0.623 kg CO2 eq. per kg bioplastic compared to 2.37 kg CO2 eq. per kg polypropylene as a petro-plastic. The results also showed that there are no significant potential effects for the bioplastics produced from potato peels on different environmental impacts in comparison with poly-β-hydroxybutyric acid and polypropylene. Thus, the bioplastics produced from agricultural wastes can be manufactured in industrial scale to reduce the dependence on petroleum-based plastics. This in turn will mitigate GHG emissions and reduce the negative environmental impacts on climate change.

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.

SummaryThe German government has adopted a law that requires sewage plants to go beyond the recovery of phosphorus from wastewater and to promote recycling. We argue that there is no physical global short‐ or mid‐term phosphorus scarcity. However, we also argue that there are legitimate reasons for policies such as those of Germany, including: precaution as a way to ensure future generations’ long‐term supply security, promotion of technologies for closed‐loop economics in a promising stage of technology development, and decrease in the current supply risk with a new resource pool.

A generalized optimal pulsewidth modulation (PWM) technique applicable to multilevel inverters for low-switching-frequency control of medium-voltage high-power industrial ac drives is presented. Proposed synchronous optimal PWM method allows setting the maximum switching frequency to a low value without compromising the harmonic distortion of machine currents. Low switching frequency reduces the switching losses of the power semiconductor devices, resulting in higher inverter power output and efficiency. The proposed optimization results in low harmonic distortion at low switching frequency. Experimental results of a five-level inverter drive using optimal PWM are presented.

Abstract Since the adoption of the Kyoto protocol in 1997 and its entry into force in 2005, as well its aftermath such as the Doha amendment and Paris agreement, national policies have become more conscious of the usage of clean energy, mostly the different forms of renewable energy and nuclear energy. Ratifying countries and signatories had committed themselves to binding targets for the reduction of greenhouse emissions by 8% with respect to 1990 levels until 2012, also based on the particular contribution to global emissions from each country. This paper examines the integrational properties of clean energy consumption from eight emerging economies which are also high greenhouse gas emitters. The empirical results show that the clean energy consumption is stationarity for Brazil and Philippines by using a quantile unit root test without smooth breaks (Koenker and Xiao, 2004). However, after capturing the smooth breaks (Bahmani-Oskooee et al., 2018), we find the clean energy consumption of China, Pakistan and Thailand are stationary. The time-varying deterministic trend with smooth breaks is more fitted to the path of clean energy consumption in comparison to the deterministic trend without smooth breaks. The paper suggests economic insights useful for policy making.

Abstract Biomass is an important renewable energy source that holds large potential as feedstock for the production of different energy carriers in a context of sustainable development, peak oil and climate change. In developing countries, biomass already supplies the bulk of energy services and future use is expected to increase with more efficient applications, such as the production of biogas and liquid biofuels for cooking, transportation and the generation of power. The aim of this study is to establish the amount of Ghana's energy demand that can be satisfied by using the country's crop residues, animal manure, logging residues and municipal waste. The study finds that the technical potential of bioenergy from these sources is 96 PJ in 2700 Mm3 of biogas or 52 PJ in 2300 ML of cellulosic ethanol. The biogas potential is sufficient to replace more than a quarter of Ghana's present woodfuel use. If instead converted to cellulosic ethanol, the estimated potential is seven times the estimated 336 ML of biofuels needed to achieve the projected 10% biofuels blends at the national level in 2020. Utilizing the calculated potentials involves a large challenge in terms of infrastructure requirements, quantified to hundreds of thousands of small-scale plants.

Abstract Energy efficiency improvement will reduce the effective price of energy services, and hence at least partially mitigate original expected energy conservation. Therefore, the magnitude of rebound effect is important for the design and timing of an effective energy conservation policy. Under the framework of translog cost share equations, we estimates the direct rebound effect for heavy industry in China for the first time by conducting an empirical research on the relationship between the direct rebound effect and the ease with which energy services can substitute for other inputs. Additionally, asymmetric price responses are specified in the model for the rebound effect estimation. Empirical results in our paper indicate that the rebound effect for heavy industry in China is about 74.3%. This reveals that energy efficiency improvement can save energy to a certain degree since the rebound effect is less than 100% (“back-fire”), but most of the expected reduction in heavy industry energy consumption is mitigated. These findings prove that energy pricing reforms and energy taxes should be further implemented to achieve effective energy conservation in China’s 12th Five Years Plan.