Systematic Integration of Energy-Optimal Buildings With District Networks

The residential sector accounts for a large share of worldwide energy consumption, yet is difficult to characterise, since consumption profiles depend on several factors from geographical location to individual building occupant behaviour. Given this difficulty, the fact that energy used in this sector is primarily derived from fossil fuels and the latest energy policies around the world (e.g., Europe 20-20-20), a method able to systematically integrate multi-energy networks and low carbon resources in urban systems is clearly required. This work proposes such a method, which uses process integration techniques and mixed integer linear programming to optimise energy systems at both the individual building and district levels. Parametric optimisation is applied as a systematic way to generate interesting solutions for all budgets (i.e., investment cost limits) and two approaches to temporal data treatment are evaluated: monthly average and hourly typical day resolution. The city center of Geneva is used as a first case study to compare the time resolutions and results highlight that implicit peak shaving occurs when data are reduced to monthly averages. Consequently, solutions reveal lower operating costs and higher self-sufficiency scenarios compared to using a finer resolution but with similar relative cost contributions. Therefore, monthly resolution is used for the second case study, the whole canton of Geneva, in the interest of reducing the data processing and computation time as a primary objective of the study is to discover the main cost contributors. The canton is used as a case study to analyse the penetration of low temperature, CO2-based, advanced fourth generation district energy networks with population density. The results reveal that only areas with a piping cost lower than 21.5 kEuro/100 m(ERA)(2) connect to the low-temperature network in the intermediate scenarios, while all areas must connect to achieve the minimum operating cost result. Parallel coordinates are employed to better visualise the key performance indicators at canton and commune level together with the breakdown of energy (electricity and natural gas) imports/exports and investment cost to highlight the main contributors.

Method for the systematic integration of multi-energy networks and low carbon resources in cities

Luc Girardin, François Maréchal, Paul Michael Stadler, Raluca-Ancuta Suciu

The design and operation of building energy systems (BES) has become a subject of great interest, given the latest energy policies adapted around the world, namely increasing the energy efficiency and the share of renewable energy sources (RES) while reducing greenhouse gas emissions related to the provision of domestic energy services. Within the latter context, this work addresses the issue of optimal sizing and operation of BES while integrating an advanced CO2 based district energy network. Indeed, unlike common water based networks which use sensible heat, the former exploits the phase change enthalpy to realize the heat transfer when interacting with the different end users as well as with the environment [1]–[4]. The related optimization problem is formulated using a mixed integer linear programming (MILP) technique, a suitable method to represent both the continuous and discrete behaviour of BES [5]. The objective function is represented by the sum of the operating and annualized investment costs (i.e. the total annual project expenses) while the integrated system is subject to mass and energy balances, heat cascade and other additional constraints. In order to decrease the computational complexity of the aforementioned problem a PAM algorithm is implemented, thus generating several typical operating periods regarding the region of interest [6]. Different case studies are performed in view of fully assessing the potential of advanced CO2 based district energy network; the different technologies include water-water heat pumps, photovoltaic arrays, water based buffer tanks and electric storage units. In addition, in regard to the implemented model formulation [7], [8], heat might be stored directly in the dwelling, thus providing a further storage capacity. The presented study hence tackles multiple research questions among which, the optimal network distribution operating conditions (i.e. supply and return temperatures) when considering optimal on the end-user side. Indeed, in regard to the different temperature thresholds related to the different domestic heating requirements, trade-off solutions must be defined to assess the best system efficiency, i.e. considering the COPs of both the network and the dwelling operators. Another aspect considered is the building construction period, which has a strong impact on both the thermal energy demand and the required temperatures of supply. Therefore, two types of buildings are considered, namely existing and new, during the different case studies, based on their respective shares in the built environment. Finally, in order to address the impact of the novel district energy network on the use of electricity storage units, different RES penetration levels are analysed. References [1] C. Weber, “CO2 BASED DISTRICT ENERGY SYSTEM,” 2008. [2] S. Henchoz, C. Weber, F. Maréchal, and D. Favrat, “Performance and profitability perspectives of a CO2 based district energy network in Geneva’s City Centre,” Energy, vol. 85, pp. 221–235, Jun. 2015. [3] Raluca Suciu, Paul Stadler, Araz Ashouri, and François Maréchal, “Towards energy-autonomous cities using CO2 networks and Power to Gas storage, ECOS Proceedings 2016.” ECOS Proceedings 2016, 2016. [4] R. Suciua, L. Girardin, and F. Marechal, “Energy integration of CO2 networks and Power to Gas for emerging energy autonomous cities in Europe,” Submitt. 30th Int. Conf. Effic. Cost Optim. Simul. Environ. Impact Energy Syst., 2017. [5] A. Bemporad and M. Morari, “Control of systems integrating logic, dynamics, and constraints,” Automatica, vol. 35, no. 3, pp. 407–427, Mar. 1999. [6] J. M. F. Rager, “Urban Energy System Design from the Heat Perspective using mathematical Programming including thermal Storage,” EPFL thesis nr. 6731. [7] A. Ashouri, “Simultaneous Design and Control of Energy Systems,” Diss., Eidgenössische Technische Hochschule ETH Zürich, Nr. 21908, 2014, 2014. [8] L. Girardin, F. Marechal, M. Dubuis, N. Calame-Darbellay, and D. Favrat, “EnerGis: A geographical information based system for the evaluation of integrated energy conversion systems in urban areas,” Energy, vol. 35, no. 2, pp. 830–840, 2010.

Methodology for energy audits in the framework of the Energy Efficiency Directive

François Maréchal, Elfie Marie Méchaussie, Greta Martha Van Eetvelde

The Energy Efficiency Directive 2012/27/EU (EED) was released in October 2012 and transposed in June 2014 by Member States. The Directive requires large companies to carry out an energy audit before December 2015, which has to be repeated every 4 years. A possibility for companies to be exempted from regular energy audits is to be or become certified by an approved energy management system (EnMS), most likely the international standard ISO 50001. In both cases it means that companies have to set plans and define actions to comply with European and national requirements that aim at improving their energy efficiency. Considering the differences across European countries regarding the awareness and involvement of the industrial sector in terms of energy management, a large number of companies still lack systematic and comprehensive systems to understand, monitor and improve their energy consumption in a cost-effective and sustainable way. This paper presents a methodology to carry out indicative energy audits in compliance with the European standard EN 16247-1 and including the ISO 50001 requirements of the energy planning phase (e.g. energy review, energy baseline and energy performance indicators). The proposed methodology follows a top down approach, starting from the energy bill and identifying major energy sources. It covers the evaluation of the actual system’s energy efficiency, identifies energy savings opportunities and presents an innovative approach for energy consumption monitoring via surrogate models of processes. It makes use of state-of-the-art techniques such as data reconciliation, heat integration via total site pinch analysis and statistical tools. Since natural gas and electricity usually take up the largest share of the total energy consumption in industry, the focus is put on these two energy carriers. One of the interesting aspects of the methodology concerns the data gathering and processing phases. Here the required data are targeted and classified in a systematic way in order to characterise the energy consumers and identify the areas of significant energy use presenting a potential for energy efficiency improvement. Once the energy review step is carried out, strategies for energy consumption monitoring should be developed. The methodology proposes an innovative approach to generate specific energy consumption models of industrial processes (surrogate models) that could be used to monitor units, online or offline, and detect deviations from expected behaviour.

2015

Electrochemical systems for hydrogen fuel cell and battery electric vehicle infrastructure

Yorick Ligen

Thermodynamics and heat engines are the core disciplines which enabled the development of the thermo-industrial society during the 20th century. Liquid hydrocarbon fuels are one of the easiest and most convenient solutions offered by the thermophysical constraints of our world. However, an alternative to these dense energy carriers is required to enable a transition to a low carbon transport sector. Climate change mitigation, local air pollution reduction and energy independency are some of the key advantages that hydrogen fuel cell and battery electric vehicles can bring in this context. Beyond a shift from fossil fuels, the entire value chain, from primary energy to powertrains must be reconsidered, redesigned and redeployed to include renewable energies, robust powergrids, charging stations and electric powertrains. The prominent role of the infrastructure in terms of energy efficiency is demonstrated in chapter 2, introducing a grid to mobility segmentation for life cycle studies. In addition, the shortcomings of local and off-grid solutions are highlighted in the same chapter. Nevertheless, the grid integration also requires innovative solutions to comply with the physical constraints of current networks. In particular, the role and the sizing of stationary buffer batteries is detailled in chapter 3. The stochastic nature of charging events is used to develop a battery sizing algorithm including grid tie constraints. This research was intrinsically motivated by the perspective of infrastructure operators. A full scale demonstrator is at the core of the scientific questioning of this thesis. The design, the construction and the operation of a grid to mobility demonstrator is reported in chapter 4. Including a 200 kW / 400 kWh Vanadium redox flow battery, a 50 kW alkaline electrolyser, and a hydrogen refueling station, this demonstrator enabled a better understanding and characterization of process engineering, of control and programming and of electrochemical phenomenons. In particular, the data analysis on the electrolysis side and purification solutions are reported in chapter 5. Finally, the intrinsic characteristics of air driven gas boosters, a robust small scale compression solution, are analyzed in chapter 6 and the challenges for a full scale hydrogen mobility are discussed with an economic and logistics perspective.

EPFL2020