1,721,004 research outputs found
PCMs based thermal storage devices for enhancing energy efficiency
No full textTo improve the integration of thermal renewables in buildings, the utilization of thermal storage is of fundamental importance. The timing mismatch between thermal energy generation (e.g., for domestic hot water) and utilization is usually a limiting factor in the spread of thermal renewables, such as solar thermal panels. Traditionally water based thermal storage devices are used for accumulating the generated thermal energy to use it during the day. Such a solution has the advantage to be easy and cost-efficient, but in terms of effectiveness, it is not optimal. In the last years, new materials appeared on the market and they can be efficiently employed in thermal energy storage systems. Among these phase change materials (PCMs) can be certainly included. The present contribution aims to quantitatively evaluate the impact that the utilization of PCMs within thermal storage can achieve. A practical case on a domestic application for the city of Genoa (Italy) is proposed. Specific attention will be also devoted to the Life Cycle Analysis of the proposed case with particular attention to the impact that the embodied energy may have on the system. Based on the results obtained, a generalization is proposed and an overall analysis of PCMs along different dimensions (e.g., technical effectiveness, economics, environmental impact, circularity, etc.) is developed to evaluate their potential for large scale applications
Financial and energy performance analysis of efficiency measures in residential buildings. A probabilistic approach
No full textThe present paper presents a methodology to effectively address the evaluation of building energy retrofitting projects in a highly uncertain context. Buildings are modelled in terms of archetypes which are characterized by specific features, e.g., U-values, heating plant typology, surface to volume ratio, etc. By using the Monte Carlo approach, the proposed method can address the influence of more than thirty important parameters on the final result in terms of energy savings, Net Present Value and other indices aimed to quantify the level of risk associated to complex energy efficiency interventions, e.g., energy saving at risk. The methodology is tested on a case study related to a building built in the ‘60s and located in Rome, Italy. However, the method is applicable irrespectively of the location, climatic conditions, and typology of the building. Results highlight that a retrofitting intervention consisting in wall insulation has a risk to be unprofitable equal to 47%. This can be ascribed to the mild climatic conditions of the location
Rotary magnetic regenerator design and assembly
No full textMagnetic refrigeration is an emerging technology that exploits a particular feature of some materials, called "magneto caloric effect" to obtain a cooling effect. In recent years, several research groups have deepened studies on this innovative cooling method, showing its potential mainly through the development of various prototypes. The Augere Research Team (ART) at University of Genoa started the design that will lead to the realization of a magnetic refrigeration machine, based on the AMR cycle, with fixed magnetic structure and continuous rotating motion of the magnetocaloric material. The salient feature of this new refrigerator is the total absence of valves and dedicated ducts; it is the structure itself, extremely compact, of rotor and stator to provide a flow-guide to the heat transfer fluid. In the present work the functional plan for the construction and assembly of this promising configuration is presented, along with the simulation tests performed during the design stage. © 2016, International Institute of Refrigeration. All rights reserved
Investigating the Impact of Water-Glycol Mixture Ratios as Heat Transfer Fluid on the Performance of a Rotary Magnetic Refrigerator
No full textMagnetic refrigeration offers an eco-friendly and sustainable alternative for cooling applications. The selection of an appropriate working fluid is critical for heat removal and regeneration efficiency in Active Magnetic Regenerators (AMRs). This study evaluates various working fluids, focusing on water mixed with an antifreeze agent, glycol, to extend the temperature range and prevent corrosion. The thermophysical properties of such mixtures differ from pure water, influencing the refrigerator's performance. A parametric investigation using a numerical model of a rotative magnetic refrigerator was conducted to analyze the effects of varying the water-glycol mixture ratios. The study systematically varied operational parameters, such as rotation frequency and mass flowrate, to determine optimal performance conditions. Results indicate that the performance, measured by the Coefficient of Performance (COP), cooling load, and efficiency, declines with increasing glycol content, particularly at lower temperature spans. Increased viscosity in the mixture necessitates higher pumping power and torque for optimal operation, affecting the optimal rotational frequency. This study underscores the importance of balancing the mixture composition to enhance temperature range while minimizing negative impacts on performance, advocating for mixtures with lower glycol content
Improving the performance of room temperature rotary magnetic refrigerators via magnet shape optimization
No full textA magnetic structure intended for use in a room-temperature rotary active magnetic regenerator (AMR) is presented, under construction at the University of Genoa. Given the overall size of the regenerator and the thickness of the gap, the magnet design is optimized to produce the highest possible magnetic field difference between two adjacent regions. Magnet shape optimization is obtained by introducing a geometry with four degrees of freedom corresponding to the position of the edges of each magnet, plus the remanence angle. This approach serves two main purposes: the primary is to increase the magnetic induction and, to follow, some effort is made to minimize the volume and weight of the expensive NdFeB magnets, while preserving the cooling performance. So, a balance between these two goals must be achieved. After a rough preliminary sizing, a parametric investigation is performed toward these targets and some shapes are presented. The magnetic flux density in the gap, and other consolidated and novel performance indices, are evaluated and compared to those found in the literature for similar devices. The final design achieves, in the air gap, a maximum induction value of 1.045 T, and an average flux density of 0.83 T in a volume per unit length of 0.00268 m3/m in the high induction region. This is accomplished by using 0.00606 m3/m of magnetic material (N50, NdFeB). The magnet designs presented here exhibit a well-balanced performance (in terms of greater cooling for the same magnet weight) compared to earlier designs for similar AMR devices
Port Energy Supply through An LNG-Powered Integrated Grid
No full textPorts are primary importance infrastructures when considering the transportation of people and goods across the planet. Two of the biggest issues linked to harbor areas are the pollutant emissions from moored ships, as well as the huge energy demand coming from ships and other activities that take place inside of the port boundaries. To tackle these challenges, the effort on the ship-side is to promote the transition to Liquefied Natural Gas (LNG) propulsion, while on the harbor-side is to implement electrical ship feeding. In general, using LNG for bunkering purposes implies its storage onshore using dedicated tanks. The regasification of LNG in situ can be exploited to cool down a water-brine flow (i.e. ethyl-alcohol and water). The cold brine can be used to increase the efficiency of a standard inverse cycle to produce cold (i.e.-30°C) used for refrigeration purposes inside ports. Then, the NG flow can be used to produce electrical energy with a standard turbogas cycle with energy recovery from flue gases. The generated electricity directly runs the standard inverse cycle with ethyl-alcohol and water brine to completely fulfill the energy demand for cold thermal power. The electricity still available is then used to supply the onboard systems of moored ships, or otherwise is sold to the users operating in the port. The flue gas coming from the turbogas plant can be used to provide both heating and process heat, through a dedicated heat exchanger and a natural gas boiler. The new envisaged plant can exploit all possible useful effects coming from the regasification process, helping to push towards a greener energy management system in harbor areas, through smart operative integration of the several available energy systems and the implementation of efficient energy smart grids
The effect of dead volumes on the performance of magnetic refrigerators
No full textRegenerative magnetic refrigeration at room temperature has the potential to overcome various problems affecting vapor compression devices while providing competitive performance, but the effects of several loss mechanisms must be evaluated and accounted for. In actual devices, inactive sections in the regenerator originate dead volumes leading to possible non-optimal exploitation of the magnetocaloric material and the associated loss mechanism. While magnetic refrigeration gained attention, few studies have systematically investigated the effects of dead volume on system performance. In this work, a one-dimensional model valid for a generic magnetic refrigerator device (either linearly reciprocating or with continuous, or discontinuous, rotary motion) is used to study the effect of the dead volume. The device performance was assessed by comparing the characteristic curves (cooling power, and COP) of an ideal device (zero dead volume) to the corresponding characteristic curves for different dead volume ratios. The performance is negatively affected if the device is operated under the same working conditions and control parameter settings used in the ideal device. This effect is higher for higher temperature spans. Nevertheless, the device could approximate the ideal performance by adjusting its control parameters. The main measures to mitigate the negative effects of dead volumes can be summarized in the necessity to operate at lower frequencies, higher fluid mass flow rates, and higher torque. The results of this study prove that the proper control of such operative parameters is able to maximize the device performance and mitigate the performance losses due to the dead volume effects
The impact of e-mobility on the Italian electricity system
No full textThis 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
Electrification of the residential heat demand: An analysis of the power market potential to accommodate heat pumps
No full textThe share of renewables in the electric power generation is rapidly increasing and shifting the buildings heating demand to electricity represents a sustainable solution to decrease the fossil fuel dependency. In this paper, the maximum share of heating demand that can be switched to electricity by using heat pumps, according to the power market capacity, is estimated. By determining market price, plants generation and fuel consumption, the optimal share is calculated in terms of carbon emissions minimization. The methodology is developed with the support of a bid stack model (BISM) that performs an hourly simulation of the electricity market. Firstly, the analysis is led considering values of the heat pumps coefficient of performance, COP, in the range between 2 and 4. Then a focus is made on the COP dependence on local climatic conditions. In addition, three different time schedules of heat pumps activity are modelled to simulate the final users’ habits. Italy is considered as a case study to test the model. Italian market conditions are particularly favourable for the heat pumps utilization. The analysis is developed ex-post for the year 2019 as well as an outlook for the 2030 is provided. For the 2019 results show that the Italian electricity market allows a penetration of heat pumps in the range of 10%–56% for COP values between 2 and 4. In 2030 switching rates in the order of 5%–10% are estimated due to tighter market conditions
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