Design, Manufacturing, Testing, and Mathematical Modeling of Concentrating Solar Systems: a Study Applied to Prototypes of Parabolic Trough Collector and Solar Box Cooker

L'utilizzo di energia solare termica deve essere sostenuto per ridurre il consumo di fonti fossili climalteranti. Nel presente studio si sono progettati e realizzati due sistemi solari a concentrazione: un collettore parabolico assiale (PTC) ed un forno solare a scatola. Il PTC ha un angolo di bordo di 90° ed un rapporto di concentrazione di 19,89. Sul concentratore, realizzato in sandwich composito, sono state applicate pellicole in alluminio ad elevata riflettanza. Il ricevitore è un tubo di acciaio rivestito da una vernice selettiva. Il sistema di inseguimento è governato da un algoritmo solare. I test sperimentali sono stati condotti con acqua ad una temperatura massima di 85 °C. Il PTC è stato caratterizzato ottenendo curve di efficienza termica, modificatore dell'angolo di incidenza e costante di tempo. I risultati mostrano che l'equazione dell'efficienza termica è confrontabile con quella di collettori simili. I dati sperimentali sono stati utilizzati per validare un ambiente di simulazione della resa annuale di PTC. Si è determinata la convenienza nell'adozione di nanofluidi a base di metalli rispetto al fluido di base (acqua). Sono state analizzate 5 temperature del fluido in ingresso e 3 portate in massa. I risultati mostrano che solo le nanoparticelle di Au, TiO2, ZnO e Al2O3 alle più basse concentrazioni presentano ridotti miglioramenti. Il forno solare a scatola ha un rapporto di concentrazione di 11,57, ed è costituito da una camera di cottura, un coperchio superiore vetrato e una doppia fila di specchi riflettenti. Il prototipo consente un allineamento solare manuale sia azimutale che zenitale. La temperatura massima del forno è stata determinata attraverso prove a vuoto. Sono state inoltre svolte prove a carico inserendo nel forno una o due pentole di alluminio, verniciate o meno in nero, riempite con acqua o olio di arachidi. In quest’ultimo caso, si è giunti a temperature superiori a 200 °C e a risultati confrontabili con quelli in letteratura.Use of solar thermal energy has to be sustained to reduce consumption of climate-changing fossil fuels. Thus, in this study two concentrating solar prototypes were designed and manufactured: a parabolic trough collector (PTC) and a solar box cooker. The PTC has a 90° rim angle and a concentration ratio of 19.89. The concentrator is a sandwich composite structure with high-reflectance aluminum foils applied on it. The receiver is a steel pipe painted with a selective coating. The tracking system is based on a solar-position computer program. Experimental tests were carried out with water and temperatures up to 85 °C. Thermal efficiency, incident angle modifier, and time constant curves were found. Results show that the thermal efficiency equation is comparable with that of other PTCs in literature. Experimental data were utilized to validate a simulation environment able to determine the yearly yield of PTCs. The simulation was carried out to evaluate the convenience in adopting metal-based nanofluids respect to the base fluid (water). Five inlet fluid temperatures and three mass flow rates were analyzed. Results show that only Au, TiO2, ZnO, and Al2O3 nanoparticles, at the lowest concentrations, present reduced improvements respect to water. The solar box cooker is a high concentration ratio prototype (11.57). The cooker has a cooking chamber with a glass cover on the top and is composed by two rows of booster mirrors. The prototype allows both an azimuth and a zenith manual orientation. Tests without load were carried out to evaluate the maximum cooker temperature. Tests with load, conduced using aluminum vessels containing a certain amount of water, were accomplished both with non-painted vessels and black-coated ones, and with one or two vessels. Additional tests were carried out with peanut oil. Using this fluid, temperatures higher than the water ones were achieved (> 200 °C) and results exhibited values comparable to those in literature

Lignocellulosic Biomass Feeding in Biogas Pathway: State of the Art and Plant Layouts☆

Abstract The traditional pathway for biogas production consists in the anaerobic digestion of starchy and sugar biomass mainly from dedicated energy crops, needing agricultural land and heavy irrigation. A retrofitting of the existing biogas plants is proposed in order to reduce competition with food crops and to increase the sustainability of the whole chain in terms of land and water consumption; moreover the use of the lignocellulosic biomass is evaluated. The biomass after physical, chemical or biological pretreatment can be digested in a biogas plant to reduce the current diet without affecting the biogas production. The present study analyzes the state of the art in the lignocellulosic biomass feeding into biogas plants and describes a preliminary techno-economical study of the pathway and the layout to be adopted, including the efficiencies and energy yields of the involved processes

Energy flexibility as additional energy source in multi-energy systems with district cooling

none4The integration of multi-energy systems to meet the energy demand of buildings represents one of the most promising solutions for improving the energy performance of the sector. The energy flexibility provided by the building is paramount to allowing optimal management of the different available resources. The objective of this work is to highlight the effectiveness of exploiting building energy flexibility provided by thermostatically controlled loads (TCLs) in order to manage multienergy systems (MES) through model predictive control (MPC), such that energy flexibility can be regarded as an additional energy source in MESs. Considering the growing demand for space cooling, a case study in which the MPC is used to satisfy the cooling demand of a reference building is tested. The multi-energy sources include electricity from the power grid and photovoltaic modules (both of which are used to feed a variable-load heat pump), and a district cooling network. To evaluate the varying contributions of energy flexibility in resource management, different objective functions- namely, the minimization of the withdrawal of energy from the grid, of the total energy cost and of the total primary energy consumption-are tested in the MPC. The results highlight that using energy flexibility as an additional energy source makes it possible to achieve improvements in the energy performance of an MES building based on the objective function implemented, i.e., a reduction of 53% for the use of electricity taken from the grid, a 43% cost reduction, and a 17% primary energy reduction. This paper also reflects on the impact that the individual optimization of a building with a multi-energy system could have on other users sharing the same energy sources.openMugnini A.; Coccia G.; Polonara F.; Arteconi A.Mugnini, A.; Coccia, G.; Polonara, F.; Arteconi, A

vapor liquid equilibrium of binary systems containing low gwp refrigerants with cubic equations of state

Abstract Different Cubic Equations of State (CESs) were used to represent Vapor-Liquid Equilibrium (VLE) of binary systems containing low Global Warming Potential (GWP) refrigerants. The calculated VLE data from some of the widely used CESs were compared with the experimental data collected from the literature. To extend CESs to binary systems, van der Waals one-fluid mixing rules with a single binary interaction parameter were used. Although the deviations between the experimental and calculated values are generally low, a comparison of the results was performed to find the most accurate CES for VLE of the studied binary systems

An Innovative Tool for Technical, Environmental and Economic Design of Building Energy Plants: A Case Study in Umbria

Abstract The European goals on environmental sustainability and carbon footprint reduction should be reached by the installation of Renewable Energy Sources (RES) plants. However, the massive development of RES plants has inevitably caused new relevant problems and critical situations due to their low energy density, their social acceptance and the non-programmability of some sources. A smart tool is proposed to evaluate the integration feasibility of different energy plants; this tool is also able to estimate the environmental impacts caused by the several proposed plants for building energy production in terms of land usage, carbon footprint and water consumption. A case study, a rural tower shaped building in Umbria, is analyzed to validate the innovative tool: environmental, energy and economic parameters are calculated to allow the designer to define the best energy plant configuration

Proposal of a non-linear curve for reporting the performance of solar cookers

Performance parameters of solar cookers have conventionally been determined by assuming a linear trend between the cooker power and the difference between load temperature and ambient air temperature. This approach may not be convenient for some solar cooker designs. In the present work, the suitability of a non-linear regression derived from fitting the measured load temperature to a second order exponential polynomial was investigated and compared with the linear regression. Both regressions were compared with the corresponding experimental curves of a panel cooker and a box cooker. In the case of the panel cooker, the linear trend of the experimental plot was confirmed over a large period of the conducted test. Minor deviations from the experimental data were observed only at the beginning and at the end of the test. On the contrary, in the box solar cooker, significant deviations between the linear regression plot and the experimental points were observed, while smaller deviations were obtained using the non-linear regression. Thus, the proposed method can be seen as a promising approach that should be considered when updating the existing procedures for testing and reporting the performance of solar cookers.info:eu-repo/semantics/publishedVersio

Mass and Energy Flows of Cardoon Oil in a Prototype System for Seeds Milling and Vegetable Oil Treatment and Cogeneration

Abstract The experimentation was carried out in a prototype for the production of vegetable oil from seeds. The system consists of seeds storage, mill, filtration system, oil tanks and diesel engine for combined heat and power production. The vegetable oil tested is cardoon oil; cardoon biomass is the main topic of BIT3G project, that aims to develop biorefineries integrated in the territory through the use of biomass residues or sustainable energy crops (cardoon, black locust, miscanthus) in marginal lands. In this study the milling step was monitored in order to evaluate mass and energy flows; input biomass was separated into biomass residues and seeds, and each part was evaluated in terms of mass, moisture, low heating value. The milling products, vegetable oil and solid panel, were evaluated in terms of mass, moisture and energy content, estimating oil efficiency in the press and main characteristics. Finally an energy balance was performed monitoring the process energy consumption and energy potential using all obtained products, oil, panel and residues for power, heat and cooling purposes

Influence of the aperture area on the performance of a solar funnel cooker operating at high sun elevations using glycerine as load

Five funnel solar cookers have been tested to investigate the influence of the aperture area on their performance. The largest cooker had an aperture area of 0.5 m(2) and it was tested side by side with two other two smaller cookers. Each cooker was tested with the same amount of glycerine. The linear performance curves relating the efficiency with the specific temperature difference was determined. Then, the determined regressions of the cooker opto-thermal ratio and the reference time on the aperture area were used to predict: i) the influence of the solar irradiance and the aperture area on the maximum temperature achieved by the load, ii) the time duration required for achieving load temperature from 65 to 140 degrees C, and iii) the power of the cooker. It was found that for a solar irradiance range of 600-1100 W m (2), the pasteurization temperature can be achieved even by the smallest cooker, and the efficiency of the largest cooker is close to the efficiency of a cooker with optimum aperture area. Moreover, when using the largest cooker, under an irradiance of 1100 W m (2) and ambient temperature 20 degrees C, the load can achieve 180 degrees C, implying that frying is possible.info:eu-repo/semantics/publishedVersio

Demand side management analysis of a supermarket integrated HVAC, refrigeration and water loop heat pump system

Supermarkets are intensive energy consumers because of a high electricity demand, mainly due to refrigeration utilities. Thus, in this work a supermarket integrated HVAC, refrigeration and water loop heat pump (WLHP) system was analyzed according to a demand side management approach, adopting a demand response strategy coupled with real-time pricing predictive rule based controls. The system was modeled with TRNSYS and several DR strategies were applied to both the space heating/cooling and the WLHP to determine the plant configuration with the most effective electricity cost saving. It was found that two setups guarantee the highest economic savings. The first consists of a predictive rule based control applied to the space heating/cooling only, which is basically inexpensive and allows an annual cost saving of 4.06% respect to the baseline configuration. The second, instead, combines predictive rule based controls applied to both the space heating/cooling and the WLHP auxiliary heater, and shows the best performance with the adoption of a 200\u202fm3 water-based thermal energy storage. Respect to the baseline, this configuration provides an annual cost saving of 4.67%

Correction Procedures for Temperature and Irradiance of Photovoltaic Modules: Determination of Series Resistance and Temperature Coefficients by Means of an Indoor Solar Flash Test Device

none5openLuciani, Silvia; Coccia, Gianluca; Tomassetti, Sebastiano; Pierantozzi, Mariano; Di Nicola, GiovanniLuciani, Silvia; Coccia, Gianluca; Tomassetti, Sebastiano; Pierantozzi, Mariano; Di Nicola, Giovann