• Energy Research

Abstract The aim of the present research is to evaluate future primary energy consumption in the Italian thermoelectric sector. Despite its importance in the European context, researches addressing the primary energy consumption in the Italian power sector are not available in the literature. Therefore, to bridge this gap, a detailed representation of the power generation sector is proposed by modeling each individual thermal power station by considering its main features (i.e. maximum power, minimum stable level, efficiency, etc.), in order to estimate the future energy balances and the trend of power prices. An evolution of the generation fleet is designed according to available information from different sources and a simulation based on plant by plant competition is performed up to the year 2022. The impact of different fuel and carbon price scenarios is analyzed in terms of primary energy consumption. The analysis has shown that a high level of CO 2 prices does not foster the coal to gas transition, but it causes a relevant increase of power prices. In fact in the best case, it is detected that in 2022, for a carbon price of 30 €/t and a “base” price scenario for fossil fuels, there is a decrease of coal consumption of ∼5.6% and an increase of power price of +19% with respect to the base carbon prices. Therefore, it follows that final users are penalized, because they are expected to pay much higher electricity bills to obtain a modest reduction of coal consumption and carbon emissions.

The goal of this article is the comparison of global warming potential, estimated according to IPCC 2013 methodology, between bottled water and a drinking water dispenser made of pine wood. The functional unit is 1 L of water. Two cases are considered: in the first case is considered 1 L of refrigerated water supplied by a water dispenser, in the second case, it is also considered how users come back home with their water. The global warming potential for bottled water packed in polyethylene terephthalate is taken by literature, its average value is equal to 0.16 kg CO2 eq./L. In the first case, the water dispenser has a global warming potential value equal to 6.89 × 10−2 kg CO2 eq./L, the percentage difference between bottled water and water dispenser is about 43% in 100 years. In the end, a comparison of vehicles used by users to come back home is performed. The comparison shows that the use of bikes has a lower impact than cars.

On-bill schemes are innovative financial frameworks for supporting energy renovation based on private capital. Direct intervention of public authorities may not be necessary. The pivotal role is assumed by energy utilities which are the originators of the business and act as market aggregators. On-bill schemes are based on a simple principle, namely the utility supports the energy renovation of final users by providing the upfront capital to repay on the utility bill. This implies that energy supply and renovation services are provided by the same company. This could be a limitation since the user may be obliged to stay with the same energy supplier for all the duration of the on-bill scheme. Even more complications can arise when the dwelling is sold or rent to another tenant. For such a reason it is important to find solutions for the possible decoupling of energy supply and energy renovation services. The present paper introduces an innovative business model which involves Distribution System Operators or other designated entities acting as market facilitators supporting the decoupling between energy supply and building energy renovation services. To characterise precisely the business ecosystem and the relations among the different actors, the Value Flow Model is employed.

Abstract The present paper reports a numerical investigation of a double-circuit Ranque–Hilsch vortex tube. Different turbulence models, namely k – e , k – e RNG, SAS-SST, RSM-LRR and LES, have been tested, in order to understand which is the most suitable for the considered problem. The analysis is conducted on a full three-dimensional model and the results show that LES turbulence model provides the best accuracy of temperature separation prediction, standard k – e and k – e RNG have the worst accuracy, whereas RSM-LRR and SAS-SST turbulence models take an intermediate position. On the contrary, LES model is the most expensive in terms of computational time and resources. The results obtained with LES highlight very high radial velocity values, which result in the enhancement of the turbulent heat and mass transfer, which implies a more accurate prediction of the temperature separation effect. The present study concludes that LES model provides the best accuracy for the simulation of a double-circuit Ranque–Hilsch vortex tube, but at the same time RSM-LRR and SAS-SST models are a good compromise between computational efficiency and accuracy.

Abstract This paper investigates possible scenarios of electric cars introduction and their impact on the Italian electricity system. Given the foreseen increased number of cars until the year 2030, three different scenarios in terms of penetration of electric vehicles have been considered, namely 10%, 20% and 40%. A detailed bottom up energy model of the Italian car fleet has been developed. The car fleet is analyzed in terms of energy consumption, carbon emissions and externalities costs. The scenarios analysis suggests that the introduction of electric cars would always lead to primary energy savings. In particular, the increase of the penetration corresponds to a decrease of primary energy consumption, carbon emissions and externalities costs.

Abstract Degree days represent a versatile climatic indicator which is commonly used in building energy performance analysis. In this context, the present paper proposes a simple dynamic model to simulate heating/cooling energy consumption in buildings. The model consists of several transient energy balance equations for external walls and internal air according to a lumped-capacitance approach and it has been implemented utilizing the Matlab/Simulink® platform. Results are validated by comparison to the outcomes of leading software packages, TRNSYS and Energy Plus. By using the above mentioned model, energy consumption for heating/cooling is analyzed in different locations, showing that for low degree days the inertia effect assumes a paramount importance, affecting the common linear behavior of the building consumption against the standard degree days, especially for cooling energy demand. Cooling energy demand at low cooling degree days (CDDs) is deeply analyzed, highlighting that in this situation other factors, such as solar irradiation, have an important role. To take into account these effects, a correction to CDD is proposed, demonstrating that by considering all the contributions the linear relationship between energy consumption and degree days is maintained.

Abstract The method of entropy generation analysis has been implemented with the aim to investigate a double-circuit vortex tube thermodynamics. The value of the enthalpy growth rate was utilized as an indicator of the useful work done by the system. Post-processing of the numerical simulation results was carried out in order to determine the irreversible energy transformations within the computational domain. Particular attention was paid to comparative analysis of the standard k-e and SAS-SST turbulence models from thermodynamic point of view. The near main nozzle area was mentioned as a source of irreversible energy losses because of active production of turbulence dissipation due to high local values of mean rate of strain tensor modulus. Existence of the negative work area, designated as a parasitic zone, was found in the center of the vortex tube in the close proximity to the additional flow inlet. Its formation can be explained by insufficient turbulent interactions between central and peripheral flows. It was shown that this area contributes significantly to the irreversibility and should be eliminated. The integral characteristics were developed on the ground of the three dimensional distribution of both entropy generation and enthalpy growth rate. The given characteristics are suggested to be used as objectives for the optimization studies. The vortex tube diameter, main nozzle geometry and the turbulization of the additional flow were suggested to be optimized.

Abstract The present paper analyzes the turbulent convection of Al 2 O 3 -water nanofluid inside a circular section tube subjected to constant wall temperature. The analysis is developed numerically by using the mixture model, which has been proved to be a convenient method to simulate nanofluids behavior. The numerical model is successfully validated by means of analytical equations and experimental correlations. The study is focused on the analysis of the performance of Al 2 O 3 -water nanofluid within the considered device. Performance indicators based on the first and second law of thermodynamics are taken into account and analyzed. At the increase of nanofluid concentration, the Nusselt number increases, but entropy generation and pumping power also increase, therefore the penalties overcome the benefits. The results reported in the present paper are believed to be useful for the thermal optimization of nanofluids flow inside tubes.