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Direct-expansion solar-assisted heat pump (DX-SAHP) system has proven to be an effective energy-saving application. In view of the low output temperature and large radiant heat loss in the conventional flat plate type DX-SAHP, this paper proposed an evacuated tube type DX-SAHP system to realize performance enhancement. Then, an experimental prototype of the proposed system was originally designed and constructed in laboratory. Moreover, the thermodynamic performance of the system was thoroughly investigated and analyzed under different operating conditions. The results indicate that the thermodynamic performance of the proposed system is sensitive to the solar radiation intensity and collector area. About every 100 W m−2 increase of solar radiation intensity, the COP increases nearly 1.70% and the heat collection efficiency decreases nearly 8.44%. Increasing collector area (from 1.5 m2 to 3 m2) results in 8.81% increase of COP and 22.47% reduction of the system exergy efficiency. A higher circulating water temperature can effectively improve its exergy performance and higher ambient temperature can enhance its energetic performance. Additionally, the optimization of the evacuated tube collector-evaporator should be preferential to improve the system due to large exergy destruction and low exergy efficiency. [ABSTRACT FROM AUTHOR]

The integration in a district heating network of renewable energies, waste heat or cogenerated heat is one of the key point of the 2012/27/EU Energy Efficiency Directive issued by the European Union (EU), to contribute to lower primary energy consumptions in final energy uses. The availability of an adequate set of indices that can efficaciously be used to evaluate the performance of hybrid district heating systems, in which traditional, cogenerative and renewable energy sources are integrated, becomes therefore a key aspect to assess the effectiveness of these systems. The aim of this paper is presenting a comparative analysis of different performance indices, applied to a real small-scale district heating network in operation in Turin, Italy, fed by a natural gas cogeneration plant and some boilers. All calculations are based on the experimental data of the real plant and show as the commonly employed indices for the assessment of performance of CHP units can overestimate to a great extent the real performance of the whole system, as do not take into account the heat transportation losses and the pumping electrical requirements. The results of these analyses are presented in detail in the paper. [ABSTRACT FROM AUTHOR]

Abstract: In the last two decades many scientific papers and reports have been published in the field of the application of the carbon dioxide as a refrigerant for refrigeration (heat pump) systems. A simple transcritical CO2 refrigeration machine is evaluated from the perspectives of energetic, exergetic, economic and exergoeconomic analyses. Special attention has been paid to the transcritical cycle under hot climatic conditions. The main goal of this paper is to define the energy and cost efficient transcritical CO2 refrigeration machine, therefore the options for the structure and parametric improvements are discussed. Introducing the economizer as an auxiliary component for one-stage transcritical CO2 refrigeration machine helps us to decrease the total cost of the final product by approximately 14%. [Copyright &y& Elsevier]

Abstract: Water desalination using capacitive deionization (CDI) has been a recent topic of intense research as a novel technique for water desalination, capable of returning a fraction of the input energy during the regeneration of nanoporous electrodes used for ion adsorption. Usually, a set of consecutive and alternating desalination–regeneration processes is conducted to evaluate the performance of this type of systems under different operational conditions (applied electric potential, flow rate, and initial solution concentration). However, the effect of timing for desalination and regeneration processes on the performance of a capacitive deionization system has not been explored yet. This paper analyzes the effect of varying the duration of desalination and regeneration processes on overall system performance for three different salinity levels and three different CDI system sizes. More specifically, the variation in energy recovery ratio, thermodynamic efficiency, and net energy required per moles of salt adsorbed per unit of volume treated are evaluated. To optimize the timing for transient operation, one desalination test was performed until total saturation, which is identified by the outlet concentration returning to inlet concentration. From this experiment, three characteristic times were obtained: one that minimizes the outlet solution concentration, one that gives the highest adsorbed ions per energy input and one that corresponds to maximum average adsorption rate. The results obtained from testing these three timing strategies in an alternating desalination–regeneration process suggest the existence of different optimal operational points, depending on the specific needs, such as maximum desalination rate or maximum energy efficiency. The methodology presented in this paper can be extended to other operational conditions/systems to optimize their energetic performance. [Copyright &y& Elsevier]

Abstract: This paper analyses the viability of Brassica napus as an energy crop cultivated for producing biodiesel in southern Europe. The proposed methodology assessment combines physical variables such as grain production and agroclimate conditions with environmental analysis (LCA) in order to determine the Mediterranean agroclimates areas that could be cultivated for non-food purposes. The results obtained in a local production and distribution scenario (25 km) demonstrate that the biodiesel systems analysed have a better energy balance than diesel. Biodiesel obtained a net energy benefit of 16.25 MJ kg−1 of biodiesel or 35.10 MJ kg−1 of biodiesel when the avoided impacts from coproducts (glycerine and rapemeal) are considered in comparison with conventional diesel. In terms of environmental performance, the biodiesel system also has less impact compared with diesel in three categories Abiotic Depletion (AD), Photochemical Oxidation (PO) and Global Warming Potential (GWP). The estimated impact reduction in the GWP category when is compared with diesel reached a minimum of 1.76 kg CO2 eq. per kg of biodiesel when emissions of the use phase are included. The paper also demonstrates that agroclimates called “e”, “b” and “d” that ensure grain productions higher than 2000 kg ha−1 the biodiesel commercialization from B. napus energy crop is suitable in environmental terms for an energy local and regional production and distribution strategy. [Copyright &y& Elsevier]

In this paper, the performances of a vapour compression refrigeration plant using as working fluids R22 and its substitute R417A (R125/R134a/R600, 46.6/50/3.4% in mass) are experimentally studied. This type of plant is applied to a commercially available cold store, generally adopted for preservation of foodstuff. Its working is regulated by on/off cycles of the compressor, operating at the nominal frequency of 50 Hz, imposed by the classical thermostatic control. The problems related to the replacement of the fully halogenated chlorofluorcarbons (CFCs) and of the partially halogenated (HCFCs) have been only partially solved. As for R22, there is no unanimous solution for its substitution. In this paper, the refrigerant fluid experimentally tested as a substitute for R22 is the non-azeotropic mixture R417A. R417A is a non-ozone depleting long term replacement for R22, which can be used in new and existing direct expansion systems using traditional R22 lubricants. R417A provides an easy solution to the legislation requirement, since it presents an ozone depletion potential equal to zero, and it does not require a change of lubricant type, equipment redesign or significant modifications. The experimental analysis has allowed the determination of the best energetic performances of R22 in comparison with those of R417A in terms of the coefficient of performance, exergetic efficiency, exergy destroyed in the plant components and other variables characterizing the refrigeration plant performance. [Copyright &y& Elsevier]

In this paper, the energy and exergy performance of several polygeneration arrangements driven by low and medium temperature geothermal resource is investigated. The aim is to assess and compare different coupling schemes, identifying suitable thermally driven technologies for each type of arrangement. The polygeneration system is intended to produce power, cooling and heat for direct uses by considering variations of series and parallel coupling schemes along with different alternatives of ORC and absorption cooling machines. The study was conducted considering a temperature range of low-to-medium geothermal resource from 80 °C to 150 °C. Mathematical models are developed based on first and second law of thermodynamics and solved by means of an equation solver. The results show a threshold temperature that makes a shift between feasible polygeneration arrangements and the type of thermally driven technologies adopted, resulting in two different polygeneration arrangements with highest energetic and exergetic performance. The first arrangement correspond to a temperature range that lies between 80 °C and 110 °C, and the second one between 110 °C and 150 °C. The polygeneration arrangement with highest exergetic performance for the first range of temperatures was the hybrid parallel-series cascade arrangement (HPS2) having exergy efficiencies between 42.82% and 50.11%, while the one corresponding to the second temperature range was the series cascade arrangement (SC1) presenting exergy efficiencies from 51.44% to 52.9%. This effect is a consequence of the available temperature of the geothermal resource and the intrinsic energy performance of the different technologies considered. In regard to thermally driven technologies, arrangements where ORC and TDC subsystems are placed at the first thermal level, are the ones with the highest energetic and exergetic performance. Arrangements that have those components at the last level, present lowest performances. [ABSTRACT FROM AUTHOR]

Sun trackers allow the energy yield of photovoltaic systems to be increased. Among the different types of sun tracking strategies, North-South horizontal single-axis sun trackers are of big interest nowadays, especially for their implementation in utility-scale photovoltaic plants. It is important to find concepts which simplify as much as possible these sun trackers. In this paper, an energetic analysis of two very simple tracking strategies, based on a 2-position or 3-position rotatory movement for the North-South horizontal single-axis tracker, is carried out for latitudes up to 50°. The tracker positions (morning/afternoon for 2-positions, or morning/noon/afternoon for 3-positions) change at pre-defined daily schedules and the tilt angle at the morning and afternoon periods is fixed. However, both the daily schedules and the tilt angles can be adjusted in the installation process, to maximize the annual irradiation capture in a given location. Such simple tracking concepts can be implemented without the need of illumination sensors, complex sun position calculations or continuous control of the motion. The energetic analysis was carried out over a set of 22 locations worldwide and the captured irradiation was compared to that of equator-pointed optimally tilted fixed systems and to that of the best energetically efficient North-South horizontal single-axis tracker, i.e. the continuous sun tracker. Results indicate that, depending on the analysed location, the 2-position tracker can provide between 41% and 74%, and the 3-position tracker can provide between 68% and 87% of the annual irradiation gains that the North-South horizontal single-axis continuous sun tracker achieves with respect to an optimally tilted fixed system. Therefore, these types of simplified tracking concepts, especially the 3-position tracker, can be seen as alternatives to existing North-South horizontal single-axis continuous sun trackers, providing significant energy gains with respect to fixed photovoltaic systems. [ABSTRACT FROM AUTHOR]

Liquefied natural gas (LNG) will contribute in future significantly to the overall energy supply in the world. During the last two decades the effectiveness of the technologies associated with the chain “natural gas – LNG – natural gas” has increased. However, the regasification systems, which use approximately 1.5% of the LNG energy, have not been considerably improved. The objective of this paper is to demonstrate the potential for generating electricity while regasifying LNG, and to compare some novel concepts developed for this purpose. The concepts are based on combination of the open- and closed-cycle gas-turbine systems with combustion of natural gas as the heat source and regasification of LNG as the heat sink. The comparisons are conducted from the thermodynamic, economic and ecological points of view. The complications introduced to the Base Case in order to maximize the utilization of useful energy (transferred to the environment from the open-cycle gas-turbine system) have the following consequences: The overall energetic efficiency increases from 68% to 86%, the overall exergetic efficiency increases from 52.6% to 54.3% while the specific fixed capital investment is approximately 1.0 mil US$/MW for all schematics. The specific CO 2 emissions (per unit of generated electricity) increase from 0.145 to 0.19 kg CO 2 /kWh while per kg of regasifyed LNG, the specific CO 2 emissions decrease significantly from 0.09 to 0.067 kg CO 2 /kg LNG. [ABSTRACT FROM AUTHOR]

This paper presents the results of the first energetic and carbon footprint analysis in the manufacturing process of bamboo boards in Colombia. The energetic analysis was performed using energetic management tools, with the objective of estimating the energy consumption and the Consumption Index that characterizes the process. Life Cycle Assessment was used for carbon footprint analysis, taking into account the impact category of global warming following IPCC 2007, 100 years and having defined one bamboo board as the functional unit. The energetic analysis indicates an electricity value of 3456.6 kWh non-associated to the boards manufacturing, and a Consumption Index that recommends a minimum monthly production of 400 boards. The environmental analysis considered the avoided emissions due to prevention of remaining waste decomposition on the farming fields. The sum of generated and avoided emissions yields a negative value of – 117 kg of CO 2-eq . This result is due to the use of bamboo waste as a fuel for the boilers. We evaluated an alternative scenario of using natural gas as fuel. This alternative scenario also showed a high sensibility to the variation of critical supplies such as the fuel for the boilers. Which validates the environmental model. [ABSTRACT FROM AUTHOR]

The aims of this paper are (1) to evaluate the geothermal resources in Tunisia and (2) to test the deployment of the surface geothermal energy for cooling application. The experiment consists of installing a ground source heat pump (GSHP) system, was carried out in the ‘Centre de Recherches et des Technologies de l’Energie’ (CRTEn) at Borj Cédria, northern Tunisia. The GSHP is composed with horizontal ground heat exchanger (GHE) connected to a reversible geothermal heat pump (GHP), which is connected to a chilled ceiling panel (CCP) system installed in a climate test room. The status of geothermal energy and its utilization are pointed out, the test of the direct use of surface geothermal is examined as well as the evaluation of the GSHP system for air conditioning. The important findings of this study are: (1) Tunisia benefits from important geothermal resources, but its use remains very limited, (2) the only use of the (GHE) has reduced the average temperature inside the climate test room of about 2 °C during 1 day. (3) The test of the GSHP system proves that it is a profitable solution in Tunisia, the coefficient of the performance of the GHP and the whole system are found to be 4.46 and 3.02, respectively. [ABSTRACT FROM AUTHOR]

In this communication, detailed review of the solar thermal power plants based on the available solar concentrator systems like parabolic trough, parabolic dish, central tower, linear Fresnel reflector system are reported. The aim of the paper is to summarize overall research work being carried out worldwide on the thermodynamic performance evaluation of solar and other thermal power generation systems using different thermodynamic cycles. An attempt has also been made to assess as well as compare the energetic and exergetic performance of such thermal power generation systems. It has been observed that the efficiencies of the solar concentrator aided coal fired thermal power plant, and combined-cycle power plants are higher as compared to a solar alone thermal power plants. Furthermore, there is much scope in the areas of solar aided thermal power generation for further research with the aim of quantifying energy and exergy losses, and exergy destructions in the components of the solar thermal power generation systems. [ABSTRACT FROM AUTHOR]

Abstract: In the present paper, the nominal design data and the experimental data of eleven industrial cogeneration power plants, based on different prime mover technologies and actually in operation in Italy, have been compared. The aim of the study is to compare the expected energetic and economic results with the real performance and economic profitability of the plants in operation: the analyses have highlighted that, in the design phase, the simple payback time is usually underestimated. An assessment of the European incentives policy on cogeneration has also been undertaken, focusing on Italian legislation, which foresees a tax reduction for fuel and Tradable White Certificate support mechanisms: these incentives allow an average SPB (Simple PayBack) reduction of about 15–20%. A sensitivity analysis on the SPB has also been performed, changing the fuel and maintenance costs, and the thermal and electrical energy prices, and the particular features of the different CHP (Combined Heat and Power) technologies have been pointed out. [Copyright &y& Elsevier]

Abstract: The cogeneration, or the combined production of electric and/or mechanical and thermal energy, is a well-established technology now, which has important environmental benefits and has been noted by the European Community as one of the first elements to save primary energy, to avoid network losses and to reduce the greenhouse gas emissions. In particular, our interest will be focused on the micro-cogeneration, MCHP (electric power ≤15kW), which represents a valid and interesting application of this technology which refers, above all, to residential and light commercial users [M. Dentice d’Accadia, M. Sasso, S. Sibilio, Cogeneration for energy saving in household applications, in: P. Bertoldi, A. Ricci, A. de Almeida (Eds.), Energy Efficiency in Household Appliances and Lighting, Springer, Berlin, 2001, pp. 210–221; Directive 2004/8/EC of the European Parliament and of the Council of the 11 February 2004 on the promotion of cogeneration based on the useful heat demand in the internal energy market and amending Directive 92/42/EEC, Official Journal of the European Union (2004)]. In particular, our work group started a R&D programme on micro-cogeneration in 1995: a laboratory, equipped with the most common appliances (washing-machine, dishwasher, storage water heater, …), has been built and some MCHP prototypes have been tested too. In this article, the results of an intense experimental activity on three different micro-cogenerators, one of them made in Japan and in a pre-selling phase, are reported. In a previous paper a detailed analysis of the test facility, with the description of the equipments and the data acquisition systems, can be found [M. Dentice d’Accadia, M. Sasso, S. Sibilio, R. Vanoli, Micro-combined heat and power in residential and light commercial applications, Applied Thermal Engineering 23 (2003) 1247–1259]. A typical 3-E (Energetic, Economic and Environmental) approach has been performed to compare the proposed energy system, MCHP, to the conventional one based on separate “production”. In the energetic analysis the amount of primary energy savings provided by micro-cogeneration unit has been evaluated for different types of MCHP units and at various working conditions. Furthermore the evaluation of the equivalent CO2 emissions of the compared systems, MCHP and conventional systems, allows to calculate the MCHP potentials to reduce greenhouse gas emissions. Finally the Simple Pay Back approach has been considered to define the economic feasibility of cogeneration in small size applications with the varying of some economic variables (first cost, gas price, operating hours per year …). [Copyright &y& Elsevier]

• Mixed integer linear programming for optimal management of solar assisted heat pump. • Energetic and economic analyses on a yearly basis are carried out. • Parametric analysis of the solar modules number and battery size. • Dual-source solar assisted heat pump achieves the highest energetic performance. • Conventional air-to-water heat pump achieves the lowest operating cost. This paper presents a yearly energetic and economic assessment of three different solar assisted heat pump concepts integrated with electrical and thermal storages and applied to a single-family house. The three heat pump-based systems are (i) a conventional air-to-water heat pump plus photovoltaic solar modules, (ii) a water-to-water heat pump coupled to hybrid photovoltaic-thermal solar modules and (iii) a dual source heat pump integrated with hybrid photovoltaic-thermal solar modules. The energetic and economic analysis is performed using physically-based models of each component for different numbers of solar modules and sizes of the electric storage. The maximum economic saving of these highly integrated systems is determined through an optimization algorithm based on the mixed integer linear programming technique. The results show that the dual source heat pump system with the largest battery size is the system that achieves the highest energetic performance, i.e. 77% primary energy saving with respect to traditional boiler-based system, whereas the lowest operating cost and the highest economic saving are obtained using the conventional air-to-water heat pump without any electric storage since it achieves 31% economic saving compared with the baseline system. [ABSTRACT FROM AUTHOR]