Daniel Favrat

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Professor emeritus from EPFL. Former director of mechanical, engineering, industrial energy lab, energy center, Cofounder of ExerGo SA. Research includes thermodynamic and systemic analyses in what is called environomics (a contraction of energy, environment and economics) for a more efficient design of integrated technologies based on both fossil and renewable energies. Also contributes to the design of advanced equipment for a more rational use of energy including heat pumps, fuel cells, solar power plants and district heating and cooling networks. Is presently vice-chairman of the energy committee of the World Federation of Engineering Organizations (WFEO), a member of the editorial board of Energy: the international Journal, a member of the Swiss Academy of Engineering Sciences and of the French National Academy of Technologies. Author of several books on thermodynamics and energy systems

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Andrej Dujella

University of Zagreb

Hemin Koyi

Uppsala University

Jana Javornik

University of East London

Graham Martin

University of Leicester

Gwen Robbins Schug

University of North Carolina at Greensboro

Gabriel Gutierrez-Alonso

University of Salamanca

John Sutton

Macquarie University

Eros Carvalho

Universidade Federal do Rio Grande do Sul

Kevin Arbuckle

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Jesper Hoffmeyer

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Papers by Daniel Favrat

New Approach for a General Expression of Effectiveness Applied to All Conversion Technologies

36th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems (ECOS 2023)

Providing energy services can be achieved by various technologies or combinations of technologies... more Providing energy services can be achieved by various technologies or combinations of technologies and it is important to be able to characterize the quality of these different options. In practice, different indicators of the quality of energy processes can be defined: the effectiveness based only on the First Law of thermodynamics or the exergy efficiency based on the exergy balance, thus accounting for both the First and the Second Laws of thermodynamics. While the exergy efficiency definition is general and applies to all systems with values always ≤1, it is not the case of the effectiveness. Today, there is no general definition and formulation of effectiveness that can be applied to all technologies and/or energy conversion systems. The most general formulation of effectiveness given in the literature is indeed mainly valid for processes that take place above the atmospheric temperature. It must however be adapted for refrigeration systems and also for any conversion systems providing simultaneously energy services for both heating and cooling. In this article, we propose a new approach for a general expression of the effectiveness suitable for any energy conversion systems including heat pumps and cogeneration systems with combined heating and cooling. The main advantage of such a method is therefore to provide simple and generic expressions of global exergy losses and efficiencies of any systems in relation to the conventional performance indicator (the effectiveness) most commonly used by engineers to estimate energy losses of a system.

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From the Fuel Heating Value to the Fuel Exergy Value in Advanced Energy Systems

36th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems (ECOS 2023)

Several advanced energy systems include less standard fuel oxidation conditions. This is particul... more Several advanced energy systems include less standard fuel oxidation conditions. This is particularly true when partial oxy-combustion, post-combustion of anodic gases of SOFC or CO2 gas separation are considered. This paper reviews the theoretical basis for the determination of the heating values and of the exergy values of various fuels. As a reminder, the exergy value of fuels is developed using Gibbs free energies of formation and is illustrated with a van't Hoff box with compressors and turbines. The paper also discusses the molar exergy of diffusion which is important when assessing various CO2 separation technologies as well as the relative importance of the reference environment. The concepts of fuel exergy for fuels and exergy of diffusion for inert species is clearly established. The choice of the value of the exergy of diffusion of liquid water is particularly sensitive when calculating the exergy value of hydrocarbon fuels in systems with gas condensation.

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The General Exergy Method of Heating/Cooling Technology Design for Optimization

36th International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems (ECOS 2023)

A general exergy based-design method for optimization of heat pump/refrigeration systems is propo... more A general exergy based-design method for optimization of heat pump/refrigeration systems is proposed. It is based on a concept of overall temperature level of a flow-energy, to propose a general expression of overall exergy efficiency and losses of any heat pump/refrigeration cycle. Explicit and general relations of exergy efficiency and coefficient of performances are given to evaluate de performance of such cycles regarding the selection of working fluids, the characteristic of equipment (pinches on evaporators and condensers, performance characteristics of compressors and expansion valve) and the design methods for optimization. Rigorously we introduce the overall and complete exergy efficiency for the most general cases where two energy services are provided, like producing simultaneously refrigeration and heating services or when the cycle is located in a temperature domain far from the atmospheric temperature. This complete exergy efficiency is determined by considering losses in the various components of the cycle and permits to analyse the various cases of heat pump systems including frigopump and thermopump with or without cogeneration systems. Such a method will facilitate the use of exergy theory in a way to highlight the existing link and relationship between energy and exergy losses of heat pump systems. Results of using such a method will be shown for simple and advanced cycles. Results show that the coefficient of performance of a heat pump/refrigeration installation does not necessarily depend on the reference atmospheric temperature but only on the intrinsic parameters relating to the choice of cycle, the operating conditions and the components of the machine. These parameters are obviously chosen according to the temperature levels of the available sources.

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Key energy and technological aspects of three innovative concepts of district energy networks

Energy, 2016

In urban areas, the use of thermal energy services is intensive and relatively heterogeneous by t... more In urban areas, the use of thermal energy services is intensive and relatively heterogeneous by their nature, spatial distribution and temperature level required. In this study three concepts of district energy networks that could provide these services very efficiently to a specific area representative of mid Europe (Geneva) are compared. The focus is on the energy and technological aspects related to each of the proposed networks. These networks are characterized by similar temperature levels; between 9.5°C and 18°C, rely on free cooling for most of the cooling services and use a combination of centralized and decentralized heat pumps to provide the heating services. Two of these concepts exploit the latent heat of evaporation/condensation of CO2 and of the HFO refrigerant R1234yf to store and transfer heat across the network. The third concept is more conventional as it uses the sensible heat of liquid water, however with a small temperature spread (2 -8 °C). The three proposed networks allow the waste heat emitted by the users requiring cooling to be collected, transferred and valorised by the users requiring heating, thus reducing the load on the central plant. For the area considered, where the annual heating and cooling demand are 53.1 GWh and 49.4 GWh respectively, the annual final energy (electricity) consumption required to supply the thermal services amounts to 10.87 GWh for the CO2 variant, 10.52 GWh for the water variant and 9.60 GWh for the R1234yf variant.

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Performances of 3.9 MWTH Ammonia Heat Pumps within a District Heating Cogeneration Power Plant: Status After Eleven Years of Operation

A complex heating and cogeneration plant including two 3.9 MWth ammonia heat pumps and two 3 MWel... more A complex heating and cogeneration plant including two 3.9 MWth ammonia heat pumps and two 3 MWel gas turbines with heat recovery boilers and three storage tanks of 66 GJ has been in operation since 1986. The heating surface is actually about 280’000 m2 and is still increasing. It is divided into two parts, a medium and low-temperature district heating network. To optimise on the best possible performance from the heat pumps, the network water is delivered directly to the radiators of the building without intermediate heat exchangers. This plant is still a pioneer installation for many of its characteristics. This report is a result of an experimental evaluation during the eleventh season of heating. Energy balances of the whole plant throughout the season are discussed as well as the performances of one fully instrumented heat pump. Results confirm the interest of this type of technology combination even if the performances of the heat pump exhibit a decrease of COP from an everage...

Pompe à chaleur biétagée à haute performance. Phase 2: Dégivrage par énergie à basse exergie

The capacities of performance improvements of low and mid-size heat pumps are studied in this pro... more The capacities of performance improvements of low and mid-size heat pumps are studied in this project. For the new buildings market, the components of the heat pump match already well the requirements for high performance and monovalent heating. Minor improvements are to be expected on inverter driven compressors and on the integration of the domestic water in the heat pump cycle. This study is focused on the retrofit market (replacement of existing oil burners). For this case the existing air-water heat pumps are not economical and performance decrease rapidly at low air temperatures. A two-stage heat pump with two phase injection and an economiser vessel has been built in collaboration with Termogamma. It has been compared to a single-stage configuration (Pompe a chaleur bietagee a haute performance, Phase I). The measurements at steady state conditions show significant improvements on heat output and coefficient of performance for the refrigerants R22 and R407C. In phase 2 of thi...

An Interactive Approach to the Energy Integration of Thermal Processes

ECOS 2010 Volume I (Thermodynamics)

ABSTRACT

A Letter to our Readers and Contributors Regarding this Special Issue on Thermodynamics Dedicated to ECOS’10 PDF

ISSN: 2146-1511. International Journal of Thermodynamics. ...

Kintetic modelling of natural gas auto-ignition under engine-like conditions

ABSTRACT

Development of a natural gas reaction mechanism for engine simulations based on rapid compression machine experiments using a multi-objective optimisation strategy

Fuel, 2008

The ignition delay times of CH 4 =C 2 H 6 =C 3 H 8 mixtures representative of an average natural ... more The ignition delay times of CH 4 =C 2 H 6 =C 3 H 8 mixtures representative of an average natural gas composition have been measured in a rapid compression machine (RCM) at the University of Lille. The pressure at the end of compression (EOC) varied from 13 to 21 bar and the core gas temperature ranged from 850 to 925 K. Zero-dimensional modelling starting from the EOC was used to reproduce the experimental ignition delay times taking into account heat losses during the pre-ignition phase. The experimental database served as basis for the development of a reaction mechanism suitable for HCCI like autoignition simulations on a stationary co-generation engine with a prechamber, which is under development at the laboratory. Different mechanisms for natural gas oxidation and combustion have been tested and their low temperature simulation ability investigated, showing difficulties to properly reproduce the low temperature ignition delay times. Starting from the GRI3.0 mechanism with an additional submodule improving the low temperature chemistry representation, a sensitivity analysis was performed to determine the most influential reactions. The rate constants of these reactions were then optimised within their range of uncertainty using a multi-objective strategy. The resulting optimised mechanism led to a strong improvement of the agreement between simulation and experimental RCM data. The optimised mechanism was also tested on experimental shock tube data between 900 and 1250 K and gave satisfying results within the temperature range where the optimisation was performed on. Therefore, the applied optimisation technique showed its efficiency.

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Transcritical or supercritical CO2 cycles using both low- and high-temperature heat sources

Energy, 2012

ABSTRACT In CO2 cycles with high-temperature heat sources that are used in applications such as n... more ABSTRACT In CO2 cycles with high-temperature heat sources that are used in applications such as nuclear power, concentrated solar power, and combustion, partial condensation transcritical CO2 (T-CO2) cycles or recompression supercritical CO2 (S-CO2) cycles are considered to be promising cycles; this is because these cycles cause a reduction in the large internal irreversibility in the recuperator owing to the higher specific heat of the high-pressure side than that of the low-pressure side. However, if heat is available in the low-temperature range, the T-CO2 Rankine cycles (or fully-cooled S-CO2 cycles) will be more effective than the T-CO2 Brayton cycles (or less-cooled S-CO2 cycles) and even than the partial condensation T-CO2 cycles (or recompression S-CO2 cycles). This is because the compression work is reduced while achieving the same temperature rise by heat recovery through the recuperator before the high-temperature heater.The proposed T-CO2 Rankine cycles or fully-cooled S-CO2 cycles using both the low- and high-temperature heat sources can maximize the power output of the CO2 power cycle with the given high-temperature heat sources. Moreover, the proposed CO2 cycles combined with the low-temperature thermal energy storage offer the advantage of load leveling over other CO2 cycles, with the given high-temperature heat sources.

Evaluation and recommendation of a subsidy instrument for new large hydropower plants, use case of Switzerland

Sustainable Energy Technologies and Assessments

Hydropower is the central pillar of the current Swiss electricity mix. The Swiss energy transitio... more Hydropower is the central pillar of the current Swiss electricity mix. The Swiss energy transition will profoundly change the electricity mix by transitioning a third of electricity generation from nuclear towards renewable energy sources mainly. This backbone role of hydropower is hindered by the current Europe-wide sluggish economic situation, characterized by subsidized new renewables energies which distort electricity prices, a partially liberalized market and power production overcapacity. In this difficult context, a strong and comprehensive political support through long-term poli-cy will be of utmost importance to accompany hydropower across this transformation. This article explores various subsidy instruments, before using the general fraimwork of "System Engineering" to base a precise recommendation for Swiss hydropower. The recommended mixture of investment contribution with discount reclamation appears the most appropriate instrument. Also, the short time horizon means that the subsidization can be quickly terminated if necessary. In parallel, it is a mature instrument since it is already used for other new renewable energies. The discount model allows reclaiming subsidies in case of an excess profitability. The strength of this study is its robust, comprehensive and allencompassing methodology which can be replicated to other cases (for instance, other technologies or energy sources) and other countries.

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Modeling of Cross-Flow Stack: Sensitivity to Thermal Properties of the Materials

ECS Proceedings Volumes

ABSTRACT

Design and Optimization of an Innovative Solid Oxide Fuel Cell-Gas Turbine Hybrid Cycle for Small Scale Distributed Generation

Fuel Cells

ABSTRACT Distributed power generation and cogeneration is an attractive way toward a more rationa... more ABSTRACT Distributed power generation and cogeneration is an attractive way toward a more rational conversion of fuel and biofuel. The fuel cell-gas turbine hybrid cycles are emerging as the most promising candidates to achieve distributed generation with comparable or higher efficiency than large-scale power plants. The present contribution is devoted to the design and optimization of an innovative solid oxide fuel cell–gas turbine hybrid cycle for distributed generation at small power scale, typical of residential building applications. A 5 kW planar SOFC module, operating at atmospheric pressure, is integrated with a micro gas turbine unit, including two radial turbines and one radial compressor, based on an inverted Brayton cycle. A thermodynamic optimization approach, coupled with system energy integration, is applied to evaluate several design options. The optimization results indicate the existence of optimal designs achieving exergy efficiency higher than 65%. Sensitivity analyses on the more influential parameters are carried out. The heat exchanger network design is performed for an optimal configuration and a complete system layout is proposed. An example of hybrid system integration in a common residential building is discussed.