Panel I: Connecting 2nd Law Analysis with Economics, Ecology and Energy Policy

The present paper is a review of several papers from the Proceedings of the Joint European Thermodynamics Conference, held in Brescia, Italy, 1–5 July 2013, namely papers introduced by their authors at Panel I of the conference. Panel I was devoted to applications of the Second Law of Thermodynamics to social issues—economics, ecology, sustainability, and energy policy. The concept called Available Energy which goes back to mid-nineteenth century work of Kelvin, Rankine, Maxwell and Gibbs, is relevant to all of the papers. Various names have been applied to the concept when interactions between the system of interest and an environment are involved. Today, the name exergy is generally accepted. The scope of the papers being reviewed is wide and they complement one another well

Comparison of rankine cycles for micro-CHP generation based on inward flow radial turbine or scroll expander

This contribution aims to analyze micro-CHP units based on Rankine cycles. Two types of expander are considered: a small scale inward flow radial turbine and a volumetric scroll type expander. This latter, should allow to overcome the limitation imposed by a standard steam-turbine that arise when the required shaft-power is very low. Moreover, the scroll expander will also allow to easily treat wet steams, which must be avoided when considering a turbo-expander. The final aim is to deduce which one of the two types of expander is more suitable, with a specified target performance and the availability of a certain hot source. In order to define the thermodynamic expansion process, the analysis uses a one-dimensional model of the radial turbine, previously developed by the authors, and of an estimation of the scroll expander efficiency. Also, the analysis is carried out for different working fluids, such as water, and two organic fluids, cyclohexane and toluene. Through the discussion of the results, for a specified set of constraints (e.g. expander inlet temperature, temperature of condensation, expander geometrical parameters) it is possible to deduce important indications on the most suitable expander for a given cycle layout

Part-load energy performance assessment of a pumped thermal energy storage system for an energy community

Research on pumped thermal energy storage (PTES) has gained considerable attention from the scientific community. Its better suitability for specific applications and the increasing need for the development of innovative energy storage technologies are among the main reasons for that interest. The name Carnot Battery (CB) has been used in the literature to refer to PTES systems. The present paper aims to develop an energy analysis of a CB comprising a high-temperature two-stage heat pump (2sHP), an intermediate thermal storage (latent heat), and an organic Rankine cycle (ORC). From a broad perspective, the CB is modeled considering two types of heat inputs for the HP: a cold reservoir in the ground (at a constant temperature of 12 °C throughout the entire year) and a heat storage at 80 °C (thermally-integrated PTES—TI-PTES). The first part defines simple models for the HP and ORC, where only the cycles’ efficiencies are considered. On this basis, the storage temperature and the kind of fluids are identified. Then, the expected power-to-power (round-trip) efficiency is calculated, considering a more realistic model, the constant size of the heat exchangers, and the off-design operation of expanders and compressors. The model is simulated using Engineering Equation Solver (EES) software (Academic Professional V10.998-3D) for several working fluids and different temperature levels for the intermediate CB heat storage. The results demonstrate that the scenario based on TI-PTES operation mode (toluene as the HP working fluid) achieved the highest round-trip efficiency of 80.2% at full load and 50.6% round-trip efficiency with the CB operating at part-load (25% of its full load). Furthermore, when the HP working fluid was changed (under the same scenario) to R1336mzz(Z), the round-trip full-load and part-load efficiencies dropped to 72.4% and 46.2%, respectively. The findings of this study provide the HP and ORC characteristic curves that could be linearized and used in a thermo-economic optimization model based on a Mixed-Integer Linear Programming (MILP) algorithm

Two-Level evolutionary multi-objective optimization of a district heating system with distributed cogeneration

The paper deals with the modeling and optimization of an integrated multi-component energy system. On-off operation and presence-absence of components must be described by means of binary decision variables, besides equality and inequality constraints; furthermore, the synthesis and the operation of the energy system should be optimized at the same time. In this paper a hierarchical optimization strategy is used, adopting a genetic algorithm in the higher optimization level, to choose the main binary decision variables, whilst a MILP algorithm is used in the lower level, to choose the optimal operation of the system and to supply the merit function to the genetic algorithm. The method is then applied to a distributed generation system, which has to be designed for a set of users located in the center of a small town in the North-East of Italy. The results show the advantage of distributed cogeneration, when the optimal synthesis and operation of the whole system are adopted, and significant reduction in the computing time by using the proposed two-level optimization procedure

Is the Evolution of Energy System Productive Structures Driven by a Physical Principle?

The aim of the paper is to identify the consequence of the Constructal Principle in the field of Thermoeconomics of (energy) production systems. This Principle has been recently formulated as an extension of the Maximum Entropy Production Principle and it has been used in literature to explain the shape and structure of all kind of flowing systems. First, the concept of Thermoeconomic Environment is defined consistently with the consumption of environmental resources and residual emissions, which inherently characterize every kind of production system. This approach allows to infer that the evolution of any energy system is strictly related to the exploitation of resources from the Thermoeconomic Environment. Moreover, the widely accepted assumption that energy systems have to be optimized by minimizing the specific resource (exergy) cost of products, has to be regarded as a consequence of a physical principle that tells us which energy systems can persist in time (to survive) and which others would be selected for extinction. The paper shows how the creation of a recycle may allow a reduction of the unit exergy cost of the product, obtaining a more sustainable behavior of the macro-system, made up by the production process together with its supply chains, consistently with the Constructal Principle. Finally, the definition of the Thermoeconomic Environment allows (at least in principle) to properly identify the resource (exergy) cost of disposing off residues and sub-products directly in the environment, without any kind of additional operation. As a consequence, residues and sub-products have to be generally converted into some kind of product by different (new) production processes, supporting the paradigm of the Circular Economy and highlighting the importance of recycling not only for system efficiency, but for system surviving. More generally, the results obtained may be regarded as the physical justifications of the evolutionary tendency toward the more and more complex and highly circular pathways that can be observed in both natural and artificial (energy) production systems

Constructal law & thermoeconomics

In spite of evident differences, Constructal Theory and Thermoeconomics (in particular thermoeconomic optimization) have also some similarities. For instance, they both suggest the optimal allocation of two different types of losses: high permeability vs. low permeability flow losses in the Constructal Theory, while local losses inside the process vs. external losses for making available all resources actually consumed, at local level, by a component or a process in the thermoeconomic optimization. The paper discusses this one and related aspects, highlighting how the optimal criterion of minimum energy cost of the product can be derived from the Constructal Law, when the flow of useful product through the productive structure is considered as the characteristic flow of the system. In this context, the evolution of energy systems toward highly interrelated productive structures, with recycling flows, can be regarded as a consequence of the Constructal Law

A Review of Small\u2013Medium Combined Heat and Power (CHP) Technologies and Their Role within the 100% Renewable Energy Systems Scenario

The energy transition towards a scenario with 100% renewable energy sources (RES) for the energy system is starting to unfold its effects and is increasingly accepted. In such a scenario, a predominant role will be played by large photovoltaic and wind power plants. At the same time, the electrification of energy consumption is expected to develop further, with the ever\u2010increasing diffusion of electric transport, heat pumps, and power\u2010to\u2010gas technologies. The not completely predictable nature of the RES is their well\u2010known drawback, and it will require the use of energy storage technologies, in particular large\u2010scale power\u2010to\u2010chemical conversion and chemical\u2010to\u2010power re\u2010conversion, in view of the energy transition. Nonetheless, there is a lack in the literature regarding an analysis of the potential role of small\u2013medium CCHP technologies in such a scenario. Therefore, the aim of this paper is to address what could be the role of the Combined Heat and Power (CHP) and/or Combined Cooling Heat and Power (CCHP) technologies fed by waste heat within the mentioned scenario. First, in this paper, a review of small\u2013medium scale CHP technologies is performed, which may be fed by low temperature waste heat sources. Then, a review of the 100% RE scenario studied by researchers from the Lappeenranta University of Technology (through the so\u2010called \u201cLUT model\u201d) is conducted to identify potential low temperature waste heat sources that could feed small\u2013medium CHP technologies. Second, some possible interactions between those mentioned waste heat sources and the reviewed CHP technologies are presented through the crossing data collected from both sides. The results demonstrate that the most suitable waste heat sources for the selected CHP technologies are those related to gas turbines (heat recovery steam generator), steam turbines, and internal combustion engines. A preliminary economic analysis was also performed, which showed that the potential annual savings per unit of installed kW of the considered CHP technologies could reach EUR 255.00 and EUR 207.00 when related to power and heat production, respectively. Finally, the perspectives about the carbon footprint of the CHP/CCHP integration within the 100% renewable energy scenario were discussed

Optimization of a Distributed Cogeneration System with solar district heating

The aim of the paper is to identify the optimal energy production system and its optimal operation strategy required to satisfy the energy demand of a set of users in an industrial area. A distributed energy supply system is made up of a district heating network, a solar thermal plant with long term heat storage, a set of Combined Heat and Power units and conventional components also, such as boilers and compression chillers. In this way the required heat can be produced by solar thermal modules, by natural gas cogenerators, or by conventional boilers. The decision variable set of the optimization procedure includes the sizes of various components, the solar field extension and the thermal energy recovered in the heat storage, while additional binary decision variables describe the existence/absence of each considered component and its on/off operation status. The optimization algorithm is based on a Mixed Integer Linear Programming (MILP) model that minimizes the total annual cost for owning, maintaining and operating the whole energy supply system. It allows to calculate both the economic and the environmental benefits of the solar thermal plant, cooperating with the cogeneration units, as well as the share of the thermal demand covered by renewable energy, in the optimal solutions. The results obtained analyzing different system configurations show that the minimum value of the average useful heat costs is achieved when cogenerators, district heating network, solar field and heat storage are all included in the energy supply system and optimized consistently. Thus, the integrated solution turns out to be the best from both the economic and environmental points of view

Exergy Analysis of an ORC Fed by a Thermal Storage with Variable Ambient Conditions

In a recent paper the derivation of flow and non-flow exergy if ambient reference temperature (T\ub0) and pressure (P\ub0) vary in time has been revised, highlighting that, in the expression of the exergy balance of a generic control volume, besides the well-known terms, two additional terms appear, that take into account the available work (exergy) destruction related to the variation of ambient condition during the considered time interval. In the present paper, that result is applied to a system made up by a solar collector with a thermal storage and a cogeneration unit, based on an Organic Rankine Cycle (ORC). The storage is regarded to be charged during day time, then the stored heat is used to feed the ORC during the night time, in order of producing electric energy during night also. The different evaluations of exergy destruction, with and without taking into account the actual ambient reference temperature variations during the whole process, are highlighted in the analysis. The results show that neglecting ambient reference temperature variations implies an error in the evaluation of exergy destruction and efficiency up to 10% for the system considered

The Thermoeconomic Environment and the exergy-based cost accounting of technological and biological systems

The paper is focused on the presentation of the Thermoeconomic Environment (TEE), showing the motivations for introducing this new concept, the consistency of the TEE with some important and recent updates of the extended exergy accounting methodologies, as well as the new perspectives that the concept of TEE allows us to identify. The TEE is a consistent ultimate boundary of the exergy cost accounting, where various exergy reservoirs, of limited content, are immersed in a background with no exergy (the zero-exergy matrix). The exergy reservoirs are kept separated from the zero-exergy matrix by some confinement constraints. Based on this very simple, but meaningful framework, some of the main issues of extended exergy accounting methodologies are reviewed and some possible new perspectives are highlighted for the exergy cost accounting of polluting emissions and of the products of biological systems. In addition the paper discusses the exergy cost of mineral resources, of capital and of human work