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

Comparison of different heating generator systems to reduce energy consumption in social housing in a Mediterranean climate

This study analyses the energy consumption of a social housing built in the 80's. This building typology is deteriorating over time with increased energy consumption for air conditioning and indoor comfort that is well below the standard. This typology is also widely diffused in the city's building stock, especially in its suburbs. Thus, the energy efficiency of public social housing represents a major concern for the Italian national scene, and its improvement represents an effort of critical importance. However, public funding is significantly reduced compared to the past and. In addition, it is often difficult to act on passive systems, such as installing thermal insulation, or replacing terminal units inside apartments. In these cases, as an energy retrofit, it may be appropriate to evaluate the possibility of preserving as much of the existing distribution and supply system as possible, while modifying the thermal energy generation system. 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 main goal of the present work was to evaluate through dynamic analysis different HVAC scenarios, to assess the optimal configuration of the system for residential use. The results show that a hybrid system can lower the primary energy consumption up to 28%, thus allowing the employment of renewable energies within the social housing building stock

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

Construction and demolition waste as a road construction material for flexible pavements

This research is focuses on evaluating the physical properties and durability characteristics of both demolition and process waste for flexible pavement construction. The initial results showed that there is a possibility to replace aggregate base course using crushed concrete material of demolition waste Possibility to replace soil using construction and demolition waste as a stabilization agent are to be studied. This study included extensive laboratory and field testing. California bearing ratio (CBR), moisture susceptibility and abrasion evaluations tests are conducted. Effects of repeated load over the constructed pavement are evaluated using Nondestructive testing (falling weight deflectometer) on accelerated pavement testing facility

Validation of the Coupled Heat and Moisture in the Soil for Underground Thermal Energy Storage Systems

The Renewable Energy System for Residential Building Heating and Electricity Production (RESHeat ) system is a typical application of the utilisation of sun-tracked Photovoltaic Thermal (PVT) panels and underground heat storage units. This work introduces a MATLAB simulation model coupled with moisture and heat transfer processes. Validation of the proposed model from experimental measurements was conducted. The simulations were performed for a single year of RESHeat system operation for demo sites located in Cracow City. Results showed that the relative error between calculation and measurement varies from 0.258 % to 5.829 %, along with the same temperature trend. A Control Volume method is used to simulate coupled heat transfer in the ground

Verification of applicability of the two-equation turbulence models for temperature distribution in transitional flow in an elliptical tube

To increase the efficiency, elliptical tubes are often used in cross-flow heat exchangers. For these kinds of heat exchangers the flow field in the tubes exhibits irregularities. Therefore, various flow regimes can be observed: the turbulent, the transitional, and even the laminar one. Therefore, applying typical turbulence models for numerical calculations may cause significant errors, when flow in the heat exchanger tubes is in the transitional or laminar regime. Hence, the average values of flow velocities and temperature in heat exchanger tubes can be calculated incorrectly. The paper presents empirical verification of applying the basic two-equation turbulence models for a transitional flow of water in an elliptical pipe of a heat exchanger.</jats:p