Monitoring and adaptation of existing buildings to a hydraulic network Impact of the retrofit of buildings and heat distribution systems on the system performance

Based on the audits realised on buildings by the UNIGE-CUEPE in 2007 [2], [3], the present work studies the conditions of the integration of the energy conversion system and of the building refurbishment options to fit with the GLN network and to prepare the data for integration using the tools developped in the frame of GE WP1.1. The method developed for designing and optimising the large scale integration through low temperature networks of district area is based on the data generated using the method described in [1]. When existing buildings are considered, the data obtained by extrapolation of statistical measures may be replaced by the data measured in the building. In order to maximise the efficiency of the building integratiojn, it is important to realise the study of the integration of existing buildings, considering on the one hand the results of the measurement done in the building and on the other hand the possible options related to the building refurbishment and the reuse of existing equipment. This report explains the approach developed to study the audited buildings inorder to generate the data needed to apply the so called DESD(OP)2 program (``District Energy System Design and OPeration Optimisation'') which has been developped in the frame of the WP1.1. The measured information from the audits carried out by the UNIGE-CUEPE are needed to set the problem with the different building signatures, annual energy quantities and the corresponding temperature levels. The climatisation distribution loops only have been audited, no data was available from these reports regarding heating and sanitary hot water values and therefore for these data the statistical values will be used.

Méthodologie de la synthèse des systèmes énergétiques industriels

Raffaele Bolliger

This work presents a synthesis method that leads to the preliminary design of industrial energy systems. Such systems are composed of several technologies that transform, through a set of physical unit operations, raw materials and energy into products and energy services. The purpose of the preliminary synthesis is to define which technologies form the system, to calculate their technical characteristics, their operating conditions and their interactions, based on performance indicators such as for example the cost of the system or its environmental impact. This area is studied since a long time and many synthesis approaches are available. However, these methods have significant limitations, particularly in their ability to face the study of more and more complex systems. The main goal of the method presented in this work is to enable the study of large systems and promote the use of the experience gained from previous studies in the form of models and methodological approaches. The synthesis method of industrial energy systems is based on the overall system optimization using a model that is obtained by assembling several modules, representing each a set of physical unit operations and whose equations are formulated with the black box technique, and an integration model that can represent the possible interactions within the system. Optimization is performed using a multi-objective evolutionary algorithm, whose objective functions are defined on the basis of calculation of several performance indicators based on the model of the system. To simplify the resolution of this complex system, the optimization problem is decomposed into a master problem, responsible for calculating the characteristics of the units and their operating conditions, and an optimization slave subproblem, which selects the units being part of the system and their interconnections. To ensure its robustness, the slave subproblem is formulated as a mixed-integer linear optimization problem. The slave subproblem is formulated by using process integration techniques, which are extended in this work to allow the synthesis of multiple heat and mass transfer networks. The synthesis problem can thus be defined using an explicit superstructure or by one generated automatically, either implicit or explicit. This work also introduces a technique that greatly reduces the number of degrees of freedom of the integration model. Instead of separately optimizing each ΔTmin/2 associated with heat streams, a formula is applied to calculate their value from a reference case. The ΔTmin/2 optimization is thus reduced to the optimization of a single decision variable related to the reference case, regardless of the size of the problem. The proposed method uses a set of heterogeneous elements, including flowsheeting software for modeling physical unit operations, mathematical programming tools for the formulation of the integration problem, methods for calculating performance indicators and calculation tools such as the optimization algorithm. This work introduces new tools developed to systematically apply the proposed methodology and to automate recurring operations of data transfer and the call of the various used software. In particular, a syntax description is defined as an abstraction layer to describe and to structure the exchanged information. A computing platform has been created to support the application of the method and to ensure the data transfer between its components. Two case studies are presented to illustrate the various aspects of the synthesis method. A first case, involving the synthesis of two combined cycles, has been chosen to illustrate the different application stages of the method and to show the potential reuse of certain modules. Through the integration techniques, it has been possible to identify potential heat recovery that can increase the performance of one of the cycles beyond what had been expected by experts using conventional simulation techniques. The second case study is about the treatment of waste generated by an industrial site active in the field of fine chemicals. Waste treatment can recover different materials and energy services useful for process units, thereby reducing the quantities purchased in the market. The model of multi-network integration can easily solve the complexity of the problem of waste management in developing strategies for allocating waste to the various treatments available for different objective functions related to operating costs and environmental impact.

EPFL2010

Environmental impacts and benefits of information and communication technology infrastructure and services, using process and input-output life cycle assessment

Yves Jon Césare Loerincik

Sustainable development and the Information Society are two concepts that are not commonly associated. However, both could have a major impact on the other. Information and communication technologies (ICT) may have important negative impacts on the environment. At the same time, ICT can also bring improvements. To provide guidance on how ICT devices and applications can be oriented towards positive effects, new methodology and tools are needed to understand and assess these various effects. In that respect, Life Cycle Assessment (LCA) is a pertinent approach, potentially enabling a holistic and in-depth analysis. This thesis proposes to develop appropriate Life Cycle tools and methodology and to apply them to measure the sustainability of ICT devices and of their applications. Specific objectives are: to explore the possibilities of combining Process LCA (PLCA) and Input-Output LCA (IOLCA), and to develop an operational method for ICT applications; to apply the developed method to assess the direct impacts of a computer network, including software and maintenance and developing strategies, to account for the high renewal rate in ICT technologies; to extend the method to consider not only negative impacts, but also benefits of ICT; to develop a method to address effects on lifestyles and rebound effects, and apply it to assess the impacts and benefits of innovative ICT services; Chapter 1 is a short introduction describing the environmental impacts of ICT and how this work addresses them. Chapter 2 presents the main methodological developments: It looks in detail at how PLCA and IOLCA can be compared and used in a complementary way. A method is developed to compare the two approaches in detail and to evaluate the cut-offs processes – the processes that are not traditionally considered in a PLCA – of two specific ecoinvent processes. The conclusions are that a full integration of PLCA and IOLCA remains difficult with our present level of knowledge. IOLCA could be use to complement PLCA when no other evaluation is available, but IOLCA should also be used as a quality check for PLCA and to determine priorities. Chapter 3 assesses comprehensively the environmental impacts of the computer network of the Ecole Polytechnique Fédérale de Lausanne. The LCA shows that the computers have the highest environmental impact, but also that short-term technology changes can reduce significantly their impact. The use phase dominates the impacts, but the production phase is also significant. Finally, using the Input-Output (IO) approach leads us to the conclusion that the service-linked contribution included in the total cost of ownership - that is, all of the costs associated with the computer network - has a significant impact on the environment. Chapter 4 evaluates the impacts and benefits of the ICT application to help the management of urban networks. The CREM, in Switzerland, uses a telemonitoring system to assess the water, electricity, district heating, and natural gas networks to increase the efficiency of their management. We want to know how the environmental and economical costs of the infrastructure and its maintenance compare with the savings. An LCA has been performed using a tiered hybrid approach. It shows that the savings overcome largely the cost and environmental impacts of the infrastructure. Chapter 5 analyses an innovative service developed by France Telecom. The visiophonic station enables the substitution of physical interviews by virtual interviews. A PLCA of the service shows that the saved km due to the shift from physical to virtual interviews dominates the effects on the environment and that the potential savings are therefore important. However, depending on what is consumed when using the time and financial resources made available by the service, the related impacts counterbalance the savings. Rebound effects must therefore be considered, studied, and addressed in the development as well as the implementation of new ICT services. Chapter 6 concludes with recommendations towards environmental beneficial uses of ICT and identifies what is needed for the necessary further LCA developments.

EPFL2006

Multi-objective design and optimization of district energy systems including polygeneration energy conversion technologies

Céline Weber

In the present context of finding ways to decrease CO2 emissions linked with human activity, district energy systems including polygeneration energy conversion technologies are likely to play a major role. District energy systems meet the heating, hot water, cooling and electricity requirements of a district. Because they meet several types of energy requirements, and for more than one single building, district energy systems represent good opportunities to implement polygeneration energy conversion technologies. Polygeneration energy conversion technologies indeed provide different energy services simultaneously, helping to decrease the CO2 intensity compared to energy conversion technologies that meet only one energy service. Moreover, when providing energy to a whole district, polygeneration energy conversion technologies can take advantage of the various load profiles of the buildings by compensating the fluctuations and having therefore a smoother operation. A district energy system comprises essentially two parts: the plant with the polygeneration energy conversion technologies, and the distribution networks (heating and cooling). When designing the energy system for a district, one has therefore to define which type of polygeneration energy conversion technologies are best suited for the district, as well as which building are worse connecting to the system and which buildings shouldn't be connected (for instance if they are located too far away from the other buildings or if they have too small requirements to justify a connection from the plant). Moreover the operation strategy needs to be defined. In the present thesis, a method is developed that helps designing and optimizing district energy systems, from the structuring of the information available for the district (energy consumption profiles, location of the buildings, available energy sources, possible layouts for the pipes,...), over the thermo-economic modelling of the energy conversion technologies, the design of the network and the simulation of its operation strategy, and finally the evaluation of the results in terms of CO2 emissions and costs. The design and optimization of the district energy system is a multi-objective Mixed Integer Non Linear Programming problem. To solve this problem, a decomposition strategy including a master and a slave problem was developed. The master optimization problem takes care of the energy conversion technologies, whereas the slave optimization problem optimizes the network part. The two sub-problems are solved iteratively and result in the definition of a Pareto optimal curve that gives the trade-offs between the emissions and the costs for various configurations satisfying the requirements of the district. A configuration is characterized by given types and sizes of energy conversion technologies, their location in the district, the network layout, as well as the operation strategy of the technologies. Due to the time dependent energy consumption profiles and the geographical location of the buildings and plant, the method developed combines two well known types of problems, namely the multi-period optimization problems and the network problems. The method developed allows to take into account various constraints such as limited availability of energy sources, forbidden connections between buildings (for instance if a large river separates these two buildings), or else space limitations in underground technical channels. The capabilities of the method are demonstrated by means of a test case, as well as a real case in the Canton of Geneva. The results show the importance of considering all the energy services together (and not separately). Energy systems including a gas engine or a gas turbine combined cycle, together with heat pumps, indeed help decreasing both the emissions and the costs compared to the actual configurations. In the Geneva case study for instance, emissions can be decreased by up to 45%, with a simultaneous costs reduction of 24%. However, the method only deals with water networks, while in some cases space limitations and safety issues make the use of water impossible. A new type of district energy system based on CO2 as energy transfer medium (instead of water), is therefore developed in order to take such issues into account. This new system, that led to the submission of a patent, meets all the different types of energy requirements with only two pipes (instead of three or four like in conventional water based system), and uses the latent heat of CO2 as driving force, instead of the specific heat.

EPFL2008