Energetical analysis of two different configurations of a liquid-gas compressed energy storage

In order to enhance the spreading of renewable energy sources in the Italian electric power market, as well as to promote self-production and to decrease the phase delay between energy production and consumption, energy storage solutions are catching on. Nowadays, in general, small size electric storage batteries represent a quite diffuse technology, while air liquid-compressed energy storage solutions are used for high size. The goal of this paper is the development of a numerical model for small size storage, environmentally sustainable, to exploit the higher efficiency of the liquid pumping to compress air. Two different solutions were analyzed, to improve the system efficiency and to exploit the heat produced by the compression phase of the gas. The study was performed with a numerical model implemented in Matlab, by analyzing the variation of hermodynamical parameters during the compression and the expansion phases, making an energetic assessment for the whole system. The results show a good global efficiency, thus making the system competitive with the smallest size storage batteries

The wind test on heat loss from three coil cavity receiver for a parabolic dish collector

The heat loss from cavity receiver in parabolic dish system determines the efficiency and cost effectiveness of the system. A modified three coil solar cavity receiver of inner wall area approximately three times of single coil receiver, is experimentally investigated to study the effect of fluid inlet temperature (Tfi=50 degrees C to 75 degrees C) and cavity inclination angle (theta = 0 degrees to 90 degrees) on the heat loss from receiver under wind condition for head on wind and side on wind velocity at 3 m/s. Overall it was found that the natural and forced convection total heat loss increases with increase in mean fluid temperature. The combined heat loss decreases sharply with the increase in cavity inclination and observed to be maximum for horizontal position of receiver and minimum with the receiver facing vertically downward for all investigations. The maximum heat loss in wind test (V=3m/s) is 1045 W at theta=0 degrees cavity inclination at mean fluid temperature 68 degrees C and minimum at 173 W theta=90 degrees at 53 degrees C. Total heat loss from the receiver under wind condition (V=3m/s) is up to 25% higher (1.25 times at 0 degrees inclination) than without wind at mean fluid temperature similar to 70 degrees C and minimum 19.64 % (1.2 times at 90 degrees inclination) in mean temperature similar to 50 degrees C. In horizontal position of the receiver (theta=0 degrees), the total heat loss by head on wind is about 1.23 times (18% higher ) as compared to side on wind (at fluid mean temperature similar to 70 degrees C). For receiver facing downward (theta=90 degrees), for head-on wind, total heat loss is approximately the same as that for side-on wind

Efficient energy storage in residential buildings integrated with RESHeat system

The Renewable Energy System for Residential Building Heating and Electricity Production (RESHeat) system has been realized for heating and cooling residential buildings. The main components of the RESHeat system are a heat pump, photovoltaic modules, sun-tracking solar collectors and photovoltaic/thermal modules, an under-ground thermal energy storage unit, and a ground heat exchanger. One of the main novelties of the RESHeat system is efficient ground regeneration due to the underground energy storage unit. During a heating season, a large amount of heat is taken from the ground. The underground energy storage unit allows the restoration of ground heating capability and the heat pump's coefficient of performance (COP) to be kept high as possible for consecutive years. The paper presents an energy analysis for a residential building that is a RESHeat system demo site, along with integrating the RESHeat system with the building. The experimentally validated components coupled with the building model to achieve the system performance in TRNSYS software. The results show that the yearly average COP of the heat pump is 4.85 due to the underground energy storage unit. The RESHeat system is able to fully cover the heating demand of the building using renewable energy sources and an efficient underground energy storage system

Numerical investigation of semiempirical relations representing the local Nusselt number magnitude of a pin fin heat sink

Heat transfer augmentation study using air jet impingement has recently attained great interest toward electronic packaging systems and material processing industries. The present study aims at developing a nondimensional semiempirical relation, which represents the cooling rate (Nu) in terms of different geometric and impinging parameters. The spacing of the fin (S/dp) and the fin heights (H/dp) are the geometric parameters, while the impinging Reynolds number (Re) and nozzle‐target spacing (Z/d) are the impinging parameters. During the plot of the Nusselt profile, three vital secondary peaks are observed due to local turbulence of air over the heat sink. To incorporate this nonlinear behavior of the Nusselt profile in developing nondimensional empirical relations, the Nusselt profiles are divided into different regions of secondary rise and fall. Four different sets of the semiempirical relation using regression analysis are proposed for Z/d ≤ 6, H/dp ≤ 4.8 with S/dp ≤ 1.58, S/dp > 1.58 and for Z/d > 6, H/dp > 4.8 with S/dp ≤ 1.58, S/dp > 1.58. These empirical relations benefit the evaluation of the cooling rate (Nu) without any experimentation or simulation

Experimental and analytical evaluation of a gas-liquid energy storage (GLES) prototype

In this paper, a novel gas-liquid compressed air energy storage prototype, installed in the laboratory of DIAEE Department of Sapienza University of Rome, is studied. Similar to the Compressed-Air Energy Storage (CAES), the Gas-Liquid Energy Storage (GLES) technology is based on gas compression/expansion, where the liquid-piston compression and expansion are utilized. This paper reports on the experimental performance of the first GLES prototype and presents the results from a validated mathematical model. The results show that the proposed system has a high energy efficiency (indicated) over 90%, and then to achieve high values of round trip efficiency (RTE), it is important to improve and optimize the efficiency of the auxiliaries (Motor/Pump and Turbine/Generator). Two different Test, with two different speed of charging phase were done. From the results of the experimental measurements done with the prototype built in the laboratory of the DIAEE Department of Sapienza University of Rome, it can be seen that for slow compression the RTE of the system is around 72%, instead for the fast compression phase, the RTE is around 70%. A mathematical model was implemented and tested with the experimental measurements. From results it can be seen a good agreement between the experimental and numerical analysis, with a maximum error in the Test B (slow compression) equal to 2.5% and 1% respectively for charging and discharging phase. From the parametric analysis it can be seen that only the volume of the tank and the pressure ratio are needed to predict the round trip efficiency of the system.(c) 2021 Published by Elsevier Ltd

Effect of mutual radiative exchange between the surfaces of a street canyon on the building thermal energy demand

In this paper, a building energy simulation tool is exploited to study the impact of multiple radiative inter-reflections exchanges in an urban environment. The aim is to evaluate their influence on the thermal energy demand of buildings. A street canyon model validated in a previous work is used in TRNSYS to investigate the effects of the related urban radiative trapping. Due to multiple shortwave and longwave reflections, the actual radiation exchanged by the buildings facades is different if compared to a street canyon building, where only shadowing phenomena due to canyon geometry are considered. Buildings energy simulation commercial codes do not take in account inter-reflections inside urban canyons. The objective of this study is to evaluate how multiple shortwave and longwave reflections affect thermal energy demand (cooling and heating) of a street canyon building depending on its orientation, its transparent/opaque surfaces ratio and on the solar absorption factor of the envelope surfaces. Increases in cooling demand up to 50% and decreases in heating demand up to 20% are found

Retrofit Analysis of a Historical Building in an Architectural Constrained Area: A Case Study in Rome, Italy

A significant portion of Europe’s historical buildings have significant potential for energy efficiency. Social policy is typically opposed to energy retrofits because it is concerned about damaging historical or cultural sites. Contrarily, there are several approaches to energy efficiency that may be used with historic structures while also retaining the region’s architectural constraints. The findings of this study demonstrate that historical structures, which are typically not targets of energy efficiency technology because of architectural constraints on the building or in the neighbourhood, may also achieve a meaningful decrease in energy usage and GHG emissions. The significant energy-saving capability of this type of building is emphasized in the historical structure taken into consideration. The historical building object of the present study was built in the beginning of the 1900s and it was selected by the Ministry of Culture for energy efficiency improvements

Experimental investigation about the adoption of high reflectance materials on the envelope cladding on a scaled street canyon

In the last years innovative building envelope materials were studied in order to mitigate the urban heat island phenomenon in cities. Among them, cool materials represent a valid solution to achieve this goal. These materials are characterized by high solar reflectance and high thermal emittance. Another way to reduce the urban heat island effect is the adoption of retroreflective materials on the building facades, in order to reduce the amount of solar radiation entrapped within the urban fabric. The retroreflective materials have a particular surface conformation that allows to reflect the solar radiation back in the same direction of the incident radiation. In this case, the temperature of the surfaces inside an urban canyon should have lower values compared with the case with common construction materials. Consequently, also the air temperature inside the urban canyon has low values with significant advantages on outdoor thermal comfort and on building thermal energy demands. In this work the solar reflectance directional dependence was investigated with a Goniophotometer. Furthermore, experimental measurements of retroreflective materials effects on a scaled urban canyon were performed. It was found that the albedo of the RR material increases with the incident angle of the light beam from 38.2% to 42.3% with an angle of 8 degrees and 60 degrees respectively. An increase of the reflected radiation to the sky in the case of the use RR materials despite of a commercial Lambertian paint with same albedo at 8 degrees of incident light beam was evaluated. In particular, the measurement brings to assess a maximum average percentage canyon albedo difference of 2.03%. (C) 2021 Elsevier Ltd. All rights reserved

Energy analysis of a thermal system composed by a heat pump coupled with a PVT solar collector

The development of heat pump technology in the tertiary sector can lead to a reduction in greenhouse emissions and enhanced exploitation of renewable energy sources, including solar energy. The present paper investigates the potentiality of an energy system equipped with photovoltaic thermal (PV) hybrid solar collectors, a storage tanks for the heat source and a heat pump for the space heating of a small office located in three different European cities. The behaviour of the heat pump according to the heat taken from the photovoltaic panels and stored in the tank has been analysed. An energy analysis was performed according to the efficiency of the heat pump and then the thermodynamic parameters of the system were evaluated. The analytical model of each subsystem of the thermal plant was developed in Matlab where hourly simulation during the period of heating season were performed. Therefore, a comparison between the results obtained for Rome, Milan and Cracow provided the heating energy demand covering rate for each of the cities in different subsystem efficiency conditions. When thermal and electrical efficiency of PVT are set respectively to 0.6 and 0.15 and the efficiency of storage unit heat exchanger is considered equal to 0.9 the heating demand covered for Rome is 70%, for Milan is 62%, while for Cracow is 47%. Those values show a good potential for supporting heat-pump based PV-T heating systems

Energy retrofit optimization for social building in temperate climate zone

This study analyses the energy consumption of a social housing built in the 80's. This typology is widely diffused in the building stock of Rome and of the city's suburbs and for this its improvement represents a dutiful effort for the Italian national scene, where the energy efficiency of public social housing is a major concern. Public funding is significantly reduced compared to the past and the conditions of the buildings are deteriorating over time, resulting in an increase in energy consumption for air conditioning and in indoor comfort conditions very far from the standards. Often it is also very difficult to act on the passive system, with the insertion of a thermal insulation, as well as inside the apartments, with the replacement of terminal units. For this reason a good way is to evaluate the possibility of modifying the thermal energy generation system, preserving as much as possible the distribution and supply system inside the apartments. In general, where the boiler is not obsolescent, the idea is to propose a hybrid generation system with the inclusion of a heat pump (HHP), which could be implemented with renewable energy equipment, properly installed in the building. The results show that a hybrid system can lower the pri-mary energy consumption up to 28%, thus allowing the employment of renewable energies within the social housing building stock.(c) 2023 Elsevier B.V. All rights reserved