• Energy Research

Abstract A mathematical model for ammonia–water bubble absorbers was developed and compared with experimental data using a plate heat exchanger. The analysis was performed carrying out a sensitive study of selected operation parameters on the absorber thermal load and mass absorption flux. Regarding the experimental data, the values obtained for the solution heat transfer were in the range 0.51–1.21 kW m−2 K−1 and those of the mass absorption flux in the range 2.5–5.0 × 10−3 kg m−2 s−1. The comparison between experimental and simulation results was acceptable being the maximum difference of 11.1% and 28.4% for the absorber thermal load and the mass absorption flux, respectively.

Abstract In the absorbers of air-cooled water–lithium bromide absorption chillers, the absorption process usually takes place inside vertical tubes with external fins. In this paper we have carried out an experimental study of the absorption of water vapour over a wavy laminar falling film of water–lithium bromide on the inner wall of a smooth vertical tube. The control variables for the experimental study were; absorber pressure, solution mass flow rate, solution concentration and cooling water temperature. Relatively high cooling water temperatures were selected to simulate air-cooling thermal conditions. The parameters considered to assess the performance of the absorber were; the mass absorption flux, the outlet solution degree of subcooling and the falling film heat transfer coefficient. The results indicate that in water cooling thermal conditions the mass absorption fluxes are in the range 0.001–0.0015 kg·m−2·s−1, whereas in air-cooling thermal conditions the range of mass absorption values decreases to 0.00030–0.00075 kg·m−2·s−1.

Global environmental concerns and the escalating demand for energy, coupled with steady progress in renewable energy technologies, are opening up new opportunities for utilization of renewable energy resources. Hybrid energy (solar and wind) are the most abundant, inexhaustible and clean of all the renewable energy resources till date. Hybrid power generation system combines a renewable energy source (PV in this case) with other forms of generation, usually a conventional generator powered by diesel or even another renewable form of energy like wind. Such hybrid systems serve to reduce the consumption of non renewable fuel, we analyze long-term data of solar radiation and wind speed, spanning a period of 23 years, of the town of Adrar located in south of Algeria to evaluate technical- economic feasibility of using a hybrid system. The aim is to answer at load demand of a typical residential house with the annual electric energy demand of 8000kWh, an average calculated according to a study made by the Algerian government and to limit carbon emissions. Simulation results using the Hybrid Optimization Model for Electric Renewable (HOMER) software is proposed. The optimization modelling demonstrates that 100% of power demand can be supplied by hybrid configuration composed of 3 kW PV and 2 wind turbine of 2.6 KW and 18 batteries with no diesel generator. The Hybrid penetration PV and wind and the cost of generating energy from the renewable energy are analyzed. The cost of generating energy from system has been found 1.07 $/kWh. It is shown that with the proposed

Abstract Monthly averages of hourly irradiances upon a surface tilted toward the south in Barcelona, Spain, have been calculated from the global and diffuse average hourly solar irradiance on a horizontal surface computed over a period of three years (1973–1975). Similarly, daily irradiation on a monthly average and total annual irradiation for several inclinations were computed. Optimum slopes corresponding to a maximum incident energy were calculated from the annual average of daily solar irradiation, summer and winter, in the same way as the values of the inclination for which annual irradiation is maximum and minimum.

Optimisation models are commonly used in analysing and selecting the optimal configuration of a cogeneration or trigeneration system. Due to the high variability of energy demand in the residential and tertiary sector, hourly demand data is needed in order to accurately analyse and optimise energy supply systems, but a very high number of hours leads to very high or unfeasible computational time expenses. To overcome this problem, the most common practice is to reduce the number of days used in the optimisation model working only with typical days, but there are no guidelines on how to select these days and it is not clear if these typical days properly represent the whole year in the optimisation model. This study proposes a method for the selection of typical days of hourly energy demand for a whole year and analyses the influence of the results on an optimisation model for a trigeneration system. Heating and cooling energy demand data has been obtained from energy simulation software for buildings and an optimisation model for a trigeneration system has been developed. The optimisation of the whole year is then compared with the optimisation of the selected typical days. The results using typical days are very similar to the results of the whole year.

Abstract The use of waste heat or low-exergy heat sources represents a strategic opportunity to reduce the environmental footprint and operation cost of industrial processes. The absorption heat transformer, also known as absorption heat pump type II, is a thermal machine which can boost the temperature of a heat flow by using a negligible amount of electrical power. However, owing to the lack of established technical knowledge and the absence of comprehensive recordings of successful heat transformer applications, the feasibility and reliability of absorption heat transformers have been questioned and the diffusion of this technology remained limited. Therefore, in this paper, all the industrial applications of the absorption heat transformer that are recorded in previous literature and yet unpublished reports are presented and discussed. In addition to literature research, intense knowledge exchange with three leading manufacturers of absorption heat transformers gave an accurate perspective on the technological level of commercial products and operative installations. It is shown that between 1981 and 2019, 48 absorption heat transformers have been installed in 42 plants with a total capacity of ≈ 134 MW . Two main implementation periods, separated by 25 years of infrequent heat transformer installations, have been recognised. More than 74% of the installations were in Asia. Approximately 61 % of the heat transformer installations were applied into the chemical industry. Therefore, through the analysis of the technical challenges and their solutions, along with related economical aspects of heat transformer installations, the effective state-of-the-art of this technology is presented and discussed.

10.1016/j.applthermaleng.2011.12.005 The high energy consumption in buildings in Mediterranean countries, especially in the spring and summer months due to the extensive use of air conditioning, requires immediate actions to minimise energy costs and environmental impact given the current energy crisis. Solar cooling systems offer an attractive solution, but the main drawbacks of this type of systems are the low efficiency of the currently used single-effect absorption chillers and the large areas of thermal collectors needed to produce the thermal energy. These large solar installations make difficult their building integration. A way to overcome these difficulties is the use of high efficient integrated solar concentrator systems able to achieve temperatures around 150 °C that could be used to activate the more energy efficient double-effect absorption chillers. In the frame of this concept, in the present work a comparison between two cooling systems for a specific three-floor building, with and without solar concentration, is performed. The first is a conventional system which consists of evacuated tube collectors feeding a single-effect absorption chiller. On the other hand, a Fresnel reflective solar concentrating system, integrated on the building façade, is coupled to a double-effect absorption chiller. The results show an important reduction of the solar collectors absorber area in the concentrating system compared with the standard solar thermal installation. However, the solar concentrating system requires a large aperture area. In addition, the rejected heat in the double-effect chiller is lower, implying that the investment and operation costs of the solar concentrating cooling system can be reduced significantly

10.1016/j.applthermaleng.2012.10.027 In this paper data reconciliation is applied to the steady-state operational data of a single-effect ammonia/water absorption chiller. The methodology includes the detection of steady-state, the application of systematic degrees of freedom analysis (in order to determine a suitable set of measured input variables for the absorption chiller model), and data reconciliation of the measurements (which included the treatment of gross errors). The reconciliation problem was solved using a two stage sequential approach in which the objective function is minimized in Matlab and the absorption chiller is simulated in the Engineering Equation Solver (EES). The Modified Iterative Measurement Test was used to detect the measurements that contain gross errors. This methodology makes it possible to identify and eliminate the sources of gross errors, and to obtain performance calculations that are in agreement with the laws of conservation.