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Abstract The sustainable indicators are characterized by a low degree of aggregation and a high amount of information. An indicator must show a synthetic representation of a real environmental, by using a value or a parameter, so that they can be easily used by policy makers. It is necessary to connect, therefore, the various systems in an appropriately integrated sustainable system. The indicators need to be aggregated based on the structure of the data. Each indicator must to be defined through a weight with reference to another weighted indicator. In this paper is illustrated the calculation of the assigned weights that uses a procedure based on fuzzy logic and to define a model that allows us to estimate the sustainability of a city. The final result is, therefore, a combination of values assigned by expert opinion for the various criteria, processed using fuzzy logic to obtain a weight with significant objectivity and as it is possible to estimate the sustainability of the city through the weights.

Abstract This paper presents a novel dynamic simulation model for the analysis of a hybrid turboexpander system coupled with innovative high-vacuum solar thermal collectors. The model is developed in MatLab and it is able to dynamically calculate the energy, exergy, environmental, and economic performances of the investigated system, by taking into account the hourly fluctuation of thermodynamic and economic parameters (e.g. electricity cost, natural gas temperature, and flow rates, etc.). In addition, a computer-based Design of Experiment (DoE) approach was implemented for achieving the optimal design of the proposed system. A suitable case study is presented in order to show the capabilities of the developed simulation tool. Conventional and non-conventional decompression systems located in the weather zone of Messina (South-Italy) are investigated with the aim of assessing the optimal system configuration. By means of the computer-based DoE analysis, the optimal values of several design parameters (such as the number of solar thermal collectors, the volume of the hot water storage tank, and the size of the water loop pump) are calculated. Numerical results show significant primary energy savings (1.36 TWh/year) and avoided carbon dioxide emissions (348 tCO2/year). From the economic point of view, a feasible simple pay-back period of 4.51 years is achieved. The destroyed exergy of the system components are calculated, obtaining the highest value for the turbo-expander, equal to 12.0 TWh/year.

Abstract In this paper a thermoeconomic analysis of a novel hybrid Renewable Polygeneration System connected to a district heating and cooling network is presented. The plant is powered simultaneously by solar and geothermal sources, producing electricity, desalinated water, heat and cooling energy. System layout includes Parabolic Through Collector (PTC) field, geothermal wells, Organic Rankine Cycle (ORC) unit and a Multi-Effect Desalination (MED) system. Cooling and thermal demands are calculated by suitable building dynamic simulation models, calibrated for Pantelleria Island. Electrical demand is obtained by measured data. A detailed control strategy has been implemented in order to prevent any heat dissipation, to match the appropriate operating temperature levels in each component, to avoid a too low temperature of geothermal fluid reinjected in the wells and to manage the priority of space heating and cooling process. A 1-year dynamic simulation has been performed and results analyzed on daily, monthly and yearly basis. The system achieved an SPB equal to 8.50 and it resulted capable to cover the energy demands of a small community. Moreover, the plant is capable to cover the fresh water demand of the Pantelleria Island.

Abstract Aspects of successful market transformation are investigated both theoretically and empirically. At the theoretical level, success factors for single promotion activities are first discussed and classified, then for market transformation as a whole the emphasis is laid on the interactions between actors. Combined Action-Flow graphs are introduced as a tool for visualising the interconnections. In the empirical section, European experience with market penetration of condensing boilers is analysed. Thereby, both international comparisons and detailed customer surveys for several promotion activities in one country are used to identify the role of actors' interaction and promotion design factors in addition to usually considered technical and economic factors.

Potato, ranked third among food crops, gives rise to huge amounts of plant residues largely unutilized owing to the presence of toxic compounds. The fundamentals of the pyrolytic runaway of these residues are investigated for a packed bed heated at a temperature of 570 K. The feedstock variability (five samples of different harvest year and cultivar), corresponding to variable average plant ageing, causes remarkable differences in the char acteristic times (values between 6 and 42 s), heating rates (maxima between 5 and 155 K/s) and temperature overshoots (maxima between 220 and 410 K) of the runaway. On the other hand, the total gas and char yields are approximately the same (60–63 wt%), in consequence of the always fast and severe self-heating, also leading to evenly distributed and intense melting phenomena. The very high potassium contents (about 5–8 wt%) and a cellular structure with low porosity are the chief properties responsible for the significant exothermicity, resulting in intrinsically fast, in-situ catalyzed pyrolysis. The enhancement in the thermal severity of the pyrolytic runaway with longer plant ageing can be attributed to higher cellulose/starch contents, producing larger amounts of more reactive vapors, and thicker stem walls, confirming the key role of secondary reactions for the process.

Abstract The paper presents the validation of a 1D compressor model (1DCM) applied to the simulation of deep-surge operation. The compressor is described following an enhanced map-based approach, where proper "virtual pipes" are placed upstream and downstream the compressor to deal with the mass and energy storage and wave propagation effects. The proposed methodology, which takes into account main flow and thermal loss mechanisms, is based on the employment of "extended" compressor maps obtained through a steady version of the 1DCM. The tuning and validation of the 1DCM have been carried out comparing its results with the experimental data. Preliminarily, the steady version of the 1DCM is tuned against to the measured map for various rotational speeds. Subsequently, it is used to derive the extended map, including both direct and reverse flow branches. Finally, the unsteady version of the 1DCM is validated against experimental data denoting a satisfactory agreement, especially in terms of pulse frequency, amplitude and global shape. Summarizing, the proposed model, combining the reduced computational effort typical of 1D simulation with the adoption of advanced features such as "virtual pipe" and extended compressor map, shows the capability to capture the phenomenology of the compressor surging.

Abstract It is one of the most important requirements for reactor safety to guarantee the removal of nuclear decay heat from the core in any accident condition. Today it is well known that pebble bed fuel elements stay intact, if the accident temperature is below 1600°C. Therefore the reduction of the maximum accident temperature below 1600°C is necessary and can be done in a realistic way by passive, natural lawed heat-transfer mechanism for small and even for medium sized high temperature reactors.

Abstract The utilization of low temperature heat sources, e.g. waste heat, for power generation in Organic Rankine Cycles has become more and more important in recent decades. In this work, exhaust gas as the heat transfer medium is considered. Five organic working fluids in three cycle designs at three different scales are investigated in Aspen Plus V7.3. Additionally, two different constraints have been applied to the exhaust gas temperature: A minimum of 180 °C in order to avoid the acid dew point and a minimal temperature approach, where the pinch point in the exhaust gas heat exchanger is fixed at 10 K. The investigated turbine-bleeding process with regenerative pre-heating benefits higher exhaust gas outlet temperatures for further combined heat and power applications in conjunction with enhanced system performances. Also noteworthy is the lower total heat exchanger area of the process compared to the reference designs. Economic analyses are carried out in order to outline the economic merits of the turbine-bleeding cycle.