Multi-objective Optimization of Sustainable Single-Effect Water/Lithium Bromide Absorption Cycle

A rigorous mathematical approach is developed for optimization of sustainable single-effect water/ Lithium Bromide (LiBr) absorption cooling cycles. The multi-objective formulation accounts for minimization of the chiller area as well as the environmental impact associated with the operation of the absorption cycle. The environmental impact is quantified based on the global warming potential and the Eco-indicator 99, both of which follow principles of life cycle assessment. The design task is formulated as a bi-criterion non-linear programming problem, the solution of which is defined by a set of Pareto points that represent the optimal compromise between the total area of the chiller and global warming potential. These Pareto sets are obtained via the epsilon constraint method. A set of design alternatives are provided for the absorption cycles rather than a single design; the best design can be chosen from this set based on the major constraints and benefits in a given application. The proposed approach is illustrated design of a typical absorption cooling cycle

Optimization of environmentally friendly solar assisted absorption cooling systems

La optimización de los sistemas de conversión de energía gana cada vez más importancia debido a su impacto ambiental y los limitados recursos de combustibles fósiles. Entre estos sistemas los de refrigeración tienen una contribución creciente en el consumo total de energía y en las emisiones de CO2. Los sistemas de absorción operados con energía solar son una de las alternativas más sostenibles frente a los sistemas de refrigeración convencionales. Por lo tanto, este trabajo se centra en su mejora siguiendo los métodos de optimización termo-económica y de programación matemática. El análisis exergético y la optimización termo-económica basada en el método estructural se han realizado para distintas configuraciones de ciclos de refrigeración por absorción con las mezclas de trabajo agua-LiBr y amoniaco-agua. En la sección de programación matemática se incluye la optimización multi-objetivo (frontera de Pareto), la optimización bajo incertidumbre de los precios de la energía, el uso de varios indicadores de impacto ambiental y el efecto del impuesto sobre las emisiones de CO2. Los resultados demuestran que se pueden obtener reducciones importantes del impacto ambiental frente a los sistemas convencionales. Los sistemas de refrigeración solar no sólo son atractivos para reducir el impacto ambiental, sino también pueden ser económicamente competitivos. Su implantación dependerá, en gran medida, del impuesto sobre las emisiones de CO2 y del coste de la energía.Optimizations of energy conversion systems become more important because of their environmental impact and the limitations of the fossil fuel resources. Among these systems cooling and refrigeration machines have an increasing share in the total energy consumption and contribution to CO2 emissions. Solar assisted absorption cooling systems are sustainable alternatives compared to the conventional cooling systems. Hence, this work is focused on improving the sustainability of cooling systems following the thermoeconomic optimization and mathematical programming approaches. In the first approach the energy, exergy and structural analysis are performed for different configurations of water/LiBr and ammonia/water absorption cooling cycles. In the second approach multi-objective optimization (Pareto frontier), optimization under uncertainty of energy prices, different environmental impact indicators, and the effect of CO2 emissions tax to reduce the global warming are discussed. The results of the multi-objective optimization show that a significant environmental impact reduction can be obtained. Results indicate that these systems are attractive not only to reduce the environmental impact but also in incurring the economic benefits. However, its practical impact largely depends on the CO2 emissions tax and the increase in the energy price

A comprehensive comparative investigation on solar heating and cooling technologies from a thermo-economic viewpoint—A dynamic simulation

© 2020 The Authors. Energy Science & Engineering published by the Society of Chemical Industry and John Wiley & Sons Ltd. The yearly thermo-economic performance is dynamically investigated for three solar heating and cooling systems: solar heating and absorption cooling (SHAC), solar heating and ejector cooling (SHEC), and heating and solar vapor compression cooling (HSVC). First, the effects of important design parameters on the thermo-economic performance of the systems to supply the heating and cooling loads of the building are evaluated. The systems are parametrically analyzed with the weather conditions of Tehran, Iran. The results show that the life cycle costs (LCC) of the SHAC and HSVC systems are alike and much lower than those of the SHEC system. The HSVC system exhibits the best performance from exergetic and solar fraction viewpoints. The comparative analysis shows that the energy efficiencies of the SHAC and SHEC systems are higher in colder climatic conditions. However, the collector efficiency of the HSVC system declines in colder climates, mainly due to the lower solar intensities relative to in hotter climates. Further, the solar fraction of the SHAC system is higher than the SHEC technology under all climatic conditions. Moreover, higher values of solar fractions are obtained under colder weather conditions for the SHEC and HSVC systems. The best economic performance is observed for the SHAC and HSVC technologies, having significantly lower LCCs than the SHEC system. These lower LCCs under colder climatic conditions are due to the lower cost of supplying the heating load compared to the cooling load. Furthermore, all systems exhibit enhanced exergetic performance in colder weather conditions. The yearly thermo-economic performance is dynamically investigated for three solar heating and cooling systems: SHAC, SHEC, and HSVC. In addition, the effects of important design parameters on the thermo-economic performance of the systems to supply the heating and cooling loads of the building are evaluated

Simulation and Analysis of Biogas operated Double Effect GAX Absorption Refrigeration System

A thermodynamic simulation of a double effect generator heat exchanger absorption refrigeration cycle using biogas as source of energy has been carried out. The binary mixture considered in the present investigation was NH3 – H2O (Ammonia - Water). This simulation was performed in order to investigate the effect of the temperature and pressure of the high temperature generator and the pressure of evaporator have over the Coefficient of Performance (COP) for a constant condenser and absorber temperatures. The basic parameters at various state points of the cycle was computed using standard correlations. The solution circulation rates and volume of biogas required for operation of the cycle are analysed for the variations in operating parameters at the high temperature generator and evaporator

Thermodynamic Limits of the Use of Solar Energy for Cold Production

Permiso obtenido de la institución para subir este documetnoThe paper quantifies the thermodynamic limits on the energy and exergy use that would result from the use of PCM in photovoltaic BIPV modules versus not using PCM, by limiting module temperature to 298 K and the thermal energy use in buildings according to a set of hypotheses. The results obtained have been extended to six different climates. The results show that the maximum use of PCM depends heavily on the climate, therefore in hot climates as Seville, Cairo and Nairobi, the improvements in energy efficiency are very important (multiplied from 6 to 9 times), while in cold climates as London and Helsinki, the improvements are not that significant (multiplied from 1.5 to 2 times). The exergetic efficiency improvements range of about 5% for all climates, due to the low operating temperature of the PCM. These materials requirements are significant, ranging between 31 and 193 kg/m2, with thicknesses between 3.9 and 24.2 cm/m

Analysis of heat and mass transfer in membrane-based absorbers with new working fluid mixtures for absorption cooling systems

Absorption refrigeration technology, which has the ability to utilize heat directly for cooling purposes, has been one of the most widely used technologies for refrigeration and cooling applications since the early stages of refrigeration technology. Working fluid mixtures employed in the absorption cooling systems are environmental friendly and do not contribute in green house gas emission when compared to vapour compression systems which also use costly mechanical energy input. However, high initial costs and bigger size are some of the main obstacles that impede their wide use in small scale residential buildings and transport sector. In order to overcome these obstacles, design and configuration of the system and its components need to be reinvestigated in order to achieve compact components and reduce the size of the system. Use of membrane contactors in the form of hollow fiber membrane module or plate-and-frame membrane module is one of the alternatives to achieve compact components. Absorber is an important component of the absorption refrigeration system and plays a critical role in the overall performance, size, and capital cost of the system. In this study, numerical analyses are performed to evaluate the performance of a plate-and-frame membrane contactor based absorber employing water/(LiBr + LiI + LiNO3 + LiCl) and water/(LiNO3+KNO3+NaNO3) working fluid mixtures for air cooled absorption cooling systems and multi-stage high temperature heat sources applications, respectively. CFD tool ANSYS/FLUENT 14.0 is used to perform the simulation and investigate in detail the heat and mass transfer mechanisms and the fluid dynamics behaviour at local levels in the channels. Moreover, a MATLAB code is developed to investigate the effect of membrane material characteristics and operating conditions on the absorption performance of the absorber. This study recommends optimum operating and design parameters to effectively utilize the membrane based absorber

An analytical and experimental investigation of a 1.8 by 3.7 meter Fresnel lens solar concentrator

Line-focusing acrylic Fresnel lenses with application potential in the 200 to 370 C range are being analytically and experimentally evaluated. Investigations previously conducted with a 56 cm wide lens have been extended by the present study to experimentation/analyses with a 1.8 by 3.7 m lens. A measured peak concentration ratio of 64 with 90 percent of the transmitted energy focused into a 5.0 cm width was achieved. A peak concentration of 61 and a 90 percent target width of 4.5 cm were analytically computed. The experimental and analytical lens transmittance was 81 percent and 86 percent, respectively. The lens also was interfaced with a receiver assembly and operated in the collection mode. The collection efficiency ranged from 42 percent at 100 C to 26 percent at 300 C