Miguel A. Lozano

CGAM Problem: Definition and Conventional Solution

Note: (idem 93.31). Reference LENI-ARTICLE-1994-026 Record created on 2005-08-08, modified on 2017-05-10

Synthesis of Trigeneration Systems: Sensitivity Analyses and Resilience

This paper presents sensitivity and resilience analyses for a trigeneration system designed for a hospital. The following information is utilized to formulate an integer linear programming model: (1) energy service demands of the hospital, (2) technical and economical characteristics of the potential technologies for installation, (3) prices of the available utilities interchanged, and (4) financial parameters of the project. The solution of the model, minimizing the annual total cost, provides the optimal configuration of the system (technologies installed and number of pieces of equipment) and the optimal operation mode (operational load of equipment, interchange of utilities with the environment, convenience of wasting cogenerated heat, etc.) at each temporal interval defining the demand. The broad range of technical, economic, and institutional uncertainties throughout the life cycle of energy supply systems for buildings makes it necessary to delve more deeply into the fundamental properties of resilient systems: feasibility, flexibility and robustness. The resilience of the obtained solution is tested by varying, within reasonable limits, selected parameters: energy demand, amortization and maintenance factor, natural gas price, self-consumption of electricity, and time-of-delivery feed-in tariffs.

THERMOECONOMIC COST ANALYSIS OF CENTRAL SOLAR HEATING PLANTS COMBINED WITH SEASONAL STORAGE

The European Union and its Member States have committed themselves to achieving a 20% share of renewable energy by 2020. If the focus remains solely on solar thermal systems for domestic hot water (DHW) preparation, as in Spain, then the solar contribution will be very limited. Central Solar Heating Plants combined with Seasonal Storage (CSHPSS) systems enable high solar fractions of 50% and more. Most CSHPSS demonstration plants in Europe have been built in Central and North Europe, mainly in Denmark, Germany and Sweden. South Europe has little experience. This article presents a thermoeconomic cost analysis of CSHPSS systems. The objective of thermoeconomics is to explain the cost formation process of internal flows and products of energy systems. The costs obtained with thermoeconomics can be used to optimize the design of new plants and to control the production of existing plants. A simulation study on solar assisted district heating systems with high solar fractions and seasonal thermal energy storage was carried out with TRNSYS taking into consideration the meteorological conditions in Zaragoza (Spain). A CSHPSS plant was designed for a district of 500 dwellings with an annual thermal energy demand of 2,905 MWh/year. The process of cost formation has been analyzed considering the very specific features of the CSHPSS designed system: free solar energy, seasonal and DHW thermal energy storage, continuous variation of the operation due to highly variations of solar radiation and energy demands (hourly and seasonal). These features impose important difficulties in the calculation of the costs of internal flows and products in this type of systems.© 2010 ASME

Thermodynamic and Economic Analysis for Simple Cogeneration Systems

ABSTRACT Many countries in Europe promote cogeneration as a way to meet energy needs in residential and commercial buildings. They do this to save primary energy and reduce CO2 emissions. This article presents an energy and economic analysis approach for cogeneration plants hosted by such buildings. The plants use gas-fired internal combustion engines as prime movers. Technical criteria to characterize annual operation for cogeneration systems with seasonally and daily variable heat demand are defined. The focus is on determining the total engine size or output by considering different operational strategies. The methodology is illustrated by applying it to a cogeneration plant that meets domestic hot water and heating demand in a residential complex in Spain. The resulting graphical analysis allows one to compare various operational strategies.

Control del Rendimiento y Diagnóstico Termoeconómico de Centrales Termoeléctricas

This paper outlines how thermoeconomic diagnosis helps plant personnel to detect possible malfunctions that affect the efficiency of a thermal power plant, to identify the components where these malfunctions have occurred and to calculate their impact on fuel consumption. Two methods of evaluating the contribution of the plant components to overall performance deviation are presented. The theoretical background on which both methods are based is given first, followed by a description of how the deviations caused by each component can be isolated in each method. The proposed methods have been applied to a thermal power plant allowing to diagnose the operation of the plant as well as to evaluate the validity of the performed analysis taking into account the uncertainties of the measured data.

Análisis Energético y Económico de Sistemas Simples de Cogeneración

This paper investigates energy savings and economic aspects related to the use of internal combustion engines in cogeneration plants for buildings. Technical criteria that characterize the operation of simple cogeneration systems with variable thermal energy demands are defined. Also, the problem of finding the annual operational strategies for the variations of load demands and determining the sizes of cogeneration plants is analyzed. The proposed methodology is applied to the analysis of a plant that satisfies the requirements of hot water and heating of a residential area. The results allow to compare different operating strategies.

Exergy and Thermoeconomic Analysis of a Solar Air Heating Plant

The aim of this work is to present the energy, exergy and thermoeconomic analysis of a hypothetical solar air heating plant located in Zaragoza, Spain. The plant consists mainly of four parts: 1) a field of solar collectors, 2) a water tank storage, 3) a heat exchanger where heat energy is transferred from the collectors to the water storage tank, and 4) a water to air heater heat exchanger. Circulating pumps, pipes and fan have also been considered. In a previous work of the authors the design variables of the system were optimally determined from a conventional economic approach.In this paper, a productive structure for the plant has been proposed and energy losses and exergy destructions (or irreversibility) have been calculated. Energy and exergy efficiencies have also been determined for each of the components and the whole system. Moreover, the costs of internal flows have been dynamically calculated for the time period under consideration. The very specific features of solar heating systems: thermal energy storage as well as continuous variation of solar radiation and energy demand (seasonal and throughout the day) impose important difficulties, which in our opinion have not been deeply studied yet in current methodologies.The major conclusions are: i) energy, exergy and thermoeconomic analyses following a dynamic approach is very sensitive to the reference environment (ambient air temperature), ii) the same productive structure can and must be used for all of them, iii) solar energy should be considered as a high quality source and thermodynamic efficiency of solar heating plants is very low (2.5% in our case), and iv) a dynamic analysis of the process of cost formation through the different components reveals interesting and valuable information about the physics and economics of solar energy conversion systems.Copyright

Erratum to: Tackling environmental impacts in simple trigeneration systems operating under variable conditions

Purpose Environmental concerns have been a growing issue when planning energy supply systems for buildings, as the energy demands (presenting seasonal and daily variations) represent one of the most energy-intensive consumptions in industrialized societies. The optimal operation corresponding to different energy demands of a trigeneration system was analyzed by an integrated methodology combining Thermoeconomic analysis and life cycle assessment, in order to adequately allocate the energy resources and the generated environmental loads to the different energy services produced. Methods Thermoeconomic analysis, which is usually used to allocate energy and economic costs, is herein applied to the evaluation of environmental costs and distribution of resources throughout the trigeneration system. Attention is focused on the correct allocation of energy resources and environmental loads to internal flows and final products. Appropriate rules were established to calculate energy and environmental costs. Results and discussion Operation of the system considered the possibilities that surplus electricity could be exported to the national grid and part of the cogenerated heat could be wasted if this resulted in a decrease of operation costs and/or environmental loads. The results obtained show a low-cost and low-emission production with respect to the separate production in different operation modes. It was observed that, in specific periods, the trigeneration system operates wasting part of the cogenerated heat, and, in other periods, part of the electricity produced is exported to the electric grid. The trigeneration system operates in these modes because it results beneficial from environmental or economic viewpoints, achieving a lower economic cost or fewer CO2 emissions. Conclusions The methodology presented as well as the allocation method proposal were congruent with the objectives of installing trigeneration systems that supplied energy services with fewer emissions than those of separate production and of equally benefitting the consumers of heat, coolth (“coolth” is used as the noun form of “cool”; opposite of warmth. Not to be confused with cooling, which is the opposite of heating.) (alias cooling energy), and electricity.

Evaluation of Environmental Loads for the Synthesis of a Trigeneration System

This paper details the calculation of the environmental loads associated with the construction of each piece of equipment (considering that the materials were not reused at the end of the equipment’s lifetime, which is the worst case scenario) and operation of a trigeneration system. The purpose of a trigeneration system is to meet the demands of a consumer center — in this case, a medium-sized hospital located in Zaragoza, Spain. The evaluation extended over a period of one year, considering previously specified energy service demands (electricity, heat - sanitary hot water and heating -, and cooling). The system interacted with the economic environment (market) through the purchase of natural gas and electricity from the grid, and also through the sale of autogenerated electricity to the grid, according to Spanish regulations. Therefore, the environmental loads regarding the operation of the system were associated with the consumption of natural gas and electricity purchased/sold from/to the grid. Technical information on each piece of equipment was obtained from catalogs and from consultation with manufacturers. Regarding natural gas, special care was taken to correctly identify the natural gas supplied to a user in Spain (it was considered that the gas comes from Algeria, transported in Liquefied Natural Gas (LNG) carriers, including pipeline transportation to the user and controlled burning). The electricity supplied by the Spanish electric grid was also properly specified and characterized. The environmental loads were calculated utilizing SimaPro, a specialized Life Cycle Assessment tool, and then incorporated into a linear programming model, solved by LINGO optimization software. Environmental criteria were used to obtain the optimal configuration and operation of the system simultaneously.Copyright