Exact computation of emergy based on a mathematical reinterpretation of the rules of emergy algebra

cited By (since 1996)5International audienceThe emergy algebra is based on four rules, the use of which is sometimes confusing or reserved only to the experts of the domain. The emergy computation does not obey conservation logic (i.e. emergy computation does not obey Kirchoff-like circuit law). In this paper the authors propose to reformulate the emergy rules into three axioms which provide (i) a rigourous mathematical framework for emergy computation and (ii) an exact recursive algorithm to compute emergy within a system of interconnected processes at steady state modeled by an oriented graph named the emergy graph.Because emergy algebra follows a logic of memorization, the evaluation principles deal with paths in the emergy graph. The underlying algebraic structure is the set of non-negative real numbers operated on by three processes, the maximum (max), addition (+) and multiplication (*). The maximum is associated with the co-product problem. Addition is linked with the split problem or with the independence of two emergy flows. And multiplication is related to the logic of memorization. The axioms describe how to use the different operators max, + and * to combine flows without any confusion or ambiguity. The method is tested on five benchmark emergy examples. © 2012 Elsevier B.V

waste heat integration in smart thermal networks a dynamic thermoeconomic approach

Abstract The transformation of large district heating networks (DHN) towards smart thermal networks is one way of contributing to a decarbonized integrated energy system. DHN might operate as a backbone receiving a variety of different energy vectors. As a smart thermal network, a DHN is therefore able to solve both spatial- and temporal mismatch of energy demand-supply, while its operation is mostly governed by fluctuating or batch-like supply of thermal exergy. Thermoeconomics is used to provide information upon third-party excess, exergetic destruction and the feasibility of waste-heat integration but currently mainly focuses on system evaluation. In this work, thermoeconomics is used to extend the information on operational level, focusing on the dynamic behavior of exergy flows in systems with various producers and consumers. The aim is to evaluate the individual contributions of energy service by the substations (the consumers on component level) to the thermoeconomic cost generation in the system. This is done through applying the principles of exergy costing to network nodes of a graph-based network model. Furthermore, product and fuel flows, which are intrinsic part of the theory of exergy cost, are defined on control volume level and on component level. A matrix formulation of the approach is developed which can be directly applied to graph-based models using the incidence matrix for topology representation. The thermoeconomic model is applied to a case study of a real existing DHN in current operation. The effect of waste-heat integration of a typical batch-like waste heat profile at 80 °C shows that the exergetic costs are dependent on the position of the network and can be quantified in economic terms, which provides important information for decentralized integration, third-party access and dynamic pricing

Energetic and exergetic assessment of solar and wind potentials in Europe

International audienceThis paper deals with a physics-based assessment of renewable energy potential in Europe, particularly solar and wind energy sources, using two literature models. A sensibility analysis with the weather data is first done. Actual temperature, pressure, relative humidity, global radiation and wind speed data are employed to develop energy and exergy maps for Europe, based on iso-areas of land-use. These maps are compared with similar existing ones. A good agreement is obtained. A paradoxical result is found for wind exergy efficiency. The yearly average exergy efficiency where wind speed is less than 5 m/s is greater than that where wind speed is greater than 7 m/s. This can be explained by the 'dome' shape of wind exergy efficiency. A solar efficiency map for Europe is also developed to serve as a useful guide for choosing a renewable energy form based on yearly energy production

Recycling flows in emergy evaluation: A mathematical paradox?

cited By (since 1996)4International audienceThis paper is a contribution to the emergy evaluation of systems involving recycling or reuse of waste. If waste exergy (its residual usefulness) is not negligible, wastes could serve as input to another process or be recycled. In cases of continuous waste recycle or reuse, what then is the role of emergy? Emergy is carried by matter and its value is shown to be the product of specific energy with mass flow rate and its transformity. This transformity (τ) given as the ratio of the total emergy input and the useful available energy in the product (exergy) is commonly calculated over a specific period of time (usually yearly) which makes transformity a time dependent factor. Assuming a process in which a part of the non-renewable input is an output (waste) from a previous system, for the waste to be reused, an emergy investment is needed. The transformity of the reused or recycled material should be calculated based on the pathway of the reused material at a certain time (T) which results in a specific transformity value (τ). In case of a second recycle of the same material that had undergone the previous recycle, the material pathway has a new time (T+T 1) which results in a transformity value (τ 1). Recycling flows as in the case of feedback is a dynamic process and as such the process introduces its own time period depending on its pathway which has to be considered in emergy evaluations. Through the inspiration of previous emergy studies, authors have tried to develop formulae which could be used in such cases of continuous recycling of material in this paper. The developed approach is then applied to a case study to give the reader a better understanding of the concept. As a result, a 'factor' is introduced which could be included on emergy evaluation tables to account for subsequent transformity changes in multiple recycling. This factor can be used to solve the difficulties in evaluating aggregated systems, serve as a correction factor to up-level such models keeping the correct evaluation and also solve problems of memory loss in emergy evaluation. The discussion deals with the questions; is it a pure mathematical paradox in the rules of emergy? Is it consistent with previous work? What were the previous solutions to avoid the cumulative problem in a reuse? What are the consequences?. © 2011 Elsevier B.V

Mineral resource assessment: Compliance between Emergy and Exergy respecting Odum's hierarchy concept

International audienceIn this paper, authors suggest to combine the exergoecology and the emergy concept in order to evaluate mineral resources, taking into account their abundance, their chemical and physical properties and the impact of their extraction. The first proposition of this work is to consider that every group of mineral, dispersed in the Earth's crust, is a co-product of the latter. The specific emergies of dispersed minerals are, then, inversely proportional to their abundance. The results comply with the material hierarchy as the specific emergy of a dispersed mineral rise with its scarcity. The second is an emergy evaluation model based on the chemical and concentration exergy of the mineral, its condition in the mine and its abundance. This model permits to assess the decline of mineral reserves and its impact on the ecosystem. The dispersed specific emergy of 42 main commercially used minerals has been calculated. Furthermore, the emergy decrease of some Australian mineral reserves has been studied, as well as the land degradation of US copper mines

Support Vector Machine in Prediction of Building Energy Demand Using Pseudo Dynamic Approach

Building's energy consumption prediction is a major concern in the recent years and many efforts have been achieved in order to improve the energy management of buildings. In particular, the prediction of energy consumption in building is essential for the energy operator to build an optimal operating strategy, which could be integrated to building's energy management system (BEMS). This paper proposes a prediction model for building energy consumption using support vector machine (SVM). Data-driven model, for instance, SVM is very sensitive to the selection of training data. Thus the relevant days data selection method based on Dynamic Time Warping is used to train SVM model. In addition, to encompass thermal inertia of building, pseudo dynamic model is applied since it takes into account information of transition of energy consumption effects and occupancy profile. Relevant days data selection and whole training data model is applied to the case studies of Ecole des Mines de Nantes, France Office building. The results showed that support vector machine based on relevant data selection method is able to predict the energy consumption of building with a high accuracy in compare to whole data training. In addition, relevant data selection method is computationally cheaper (around 8 minute training time) in contrast to whole data training (around 31 hour for weekend and 116 hour for working days) and reveals realistic control implementation for online system as well.Comment: Proceedings of ECOS 2015-The 28th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems , Jun 2015, Pau, Franc

Analyse du recyclage par la méthode émergétique

International audienceLe recyclage matière est a priori considéré comme éco-favorable par rapport à l'exploitation de minerais provenant de mines, par nature en quantité finie et donc s'épuisant. Néanmoins, une vision holistique du recyclage requiert l'analyse de l'ensemble des ressources mobilisées pour effectuer cette opération. De plus, en suivant le déplacement/cheminement de la matière dans le temps, il devient alors nécessaire de connaître l'ensemble de l'historique de la matière considérée. Les auteurs établissent une équation théorique décrivant l'évolution à temps discret de l'émergie d'un produit : le pas d'échantillonnage est le temps du cycle. L'équation peut se réduire à une suite géométrique de raison, la fraction à recycler, sous certaines hypothèses. L'aluminium est ensuite proposé comme exemple d'application

Impact of building material recycle or reuse on selected emergy ratios

cited By (since 1996)1International audienceWhile the emergy evaluation method has been used successfully in recycling processes, this area of application still requires further development. One of such is developing emergy ratios or indices that reflect changes depending on the number of times a material is recycled. Some of these materials may either have been recycled or reused continuously as inputs to a building, for example, and thus could have various impacts on the emergy evaluation of the building. The paper focuses on reuse building materials in the context of environmental protection and sustainable development. It presents the results of an emergy evaluation of a low-energy building (LEB) in which a percentage of input materials are from recycled sources. The corresponding impacts on the emergy yield ratio (EYR B) and the environmental loading ratio (ELR B) are studied. The EYR which is the total emergy used up per unit of emergy invested, is a measure of how much an investment enables a process to exploit local resources in order to further contribute to the economy. The ELR however, is the total nonrenewable and imported emergy used up per unit of local renewable resource and indicates the stress a process exhibits on the environment. The evaluation provides values for the selected ratios based on different recycle times. Results show that values of the emergy indices vary, even more, when greater amounts of material is recycled with higher amount of additional emergy required for recycling. This provides relevant information prioritizing the selection of materials for recycling or reuse in a building, and the optimum number of reuse or recycle times of a specific material. © 2012 Elsevier B.V. All rights reserved

Pseudo Dynamic Transitional Modeling of Building Heating Energy Demand Using Artificial Neural Network

International audienceThis paper presents the building heating demand prediction model with occupancy profile and operational heating power level characteristics in short time horizon (a couple of days) using artificial neural network. In addition, novel pseudo dynamic transitional model is introduced, which consider time dependent attributes of operational power level characteristics and its effect in the overall model performance is outlined. Pseudo dynamic model is applied to a case study of French Institution building and compared its results with static and other pseudo dynamic neural network models. The results show the coefficients of correlation in static and pseudo dynamic neural network model of 0.82 and 0.89 (with energy consumption error of 0.02%) during the learning phase, and 0.61 and 0.85 during the prediction phase respectively. Further, orthogonal array design is applied to the pseudo dynamic model to check the schedule of occupancy profile and operational heating power level characteristics. The results show the new schedule and provide the robust design for pseudo dynamic model. Due to prediction in short time horizon, it finds application for Energy Services Company (ESCOs) to manage the heating load for dynamic control of heat production system