Optimization of trigeneration systems by Mathematical Programming: influence of plant scheme and boundary conditions

The large potential for energy saving by cogeneration and trigeneration in the building sector is scarcely exploited due to a number of obstacles in making the investment attractive. The analyst often encounters difficulties in identifying optimal design and operation strategies, since a number of factors, either endogenous (i.e. related with the energy load profiles) and exogenous (i.e. related with external conditions like energy prices and support mechanisms), influence the economic viability. In this paper a decision tool is presented, that simultaneously optimizes the plant lay-out, the sizes of the main components and their operation strategy. For a specific building in the hotel sect…

Optimization of trigeneration systems by Mathematical Programming: Influence of plant scheme and boundary conditions

Abstract The large potential for energy saving by cogeneration and trigeneration in the building sector is scarcely exploited due to a number of obstacles in making the investments attractive. The analyst often encounters difficulties in identifying optimal design and operation strategies, since a number of factors, either endogenous (i.e. related with the energy load profiles) and exogenous (i.e. related with external conditions like energy prices and support mechanisms), influence the economic viability. In this paper a decision tool is adopted, which represents an upgrade of a software analyzed in previous papers; the tool simultaneously optimizes the plant lay-out, the sizes of the main…

Energy saving in airports by trigeneration. Part I: Assessing economic and technical potential

Airports are very energy-intensive areas, because of the large buildings (both terminals and non-passengers areas) equipped with heating and air-conditioning systems, the high power demand for lighting and electric equipment and the energy requests from many facilities within the airport area. The contemporaneous and high demand for power and heat makes cogeneration to represent a viable solution for energy saving; in southern climate zones, however, combined heating, cooling and power (CHCP) systems can lead to even better results. This paper constitutes the first part of a work in two parts; starting from an analysis of typical energy demand profiles in airports, economical and technical …

Risk reduction by Thermoeconomics for energy systems with probabilistic boundary conditions

Formation structure of optimality by thermoeconomics: disassembling thermodynamic and external influences in energy systems’ design

In this paper an original thermoeconomic approach for the optimization of complex energy systems is presented, based on a revitalized concept of “scope”, and therefore indicated as Scope Oriented Thermoeconomics (SOT). In plants including dissipative components, it allows to formulate non-arbitrary allocation criteria as concerns marginal costs; consequently, the optimization process is disassembled to recognize the Formation Structure of Optimality, i.e. the specific influences of thermodynamic and economic parameters in the path toward the optimal design. The method is applied to a very didascalic example, that is the optimization of the condensation temperature in a vapour compression ch…

Promotion of polygeneration for buildings applications through sector- and user-oriented “high efficiency CHP” eligibility criteria

Abstract The eligibility criteria adopted to assess polygeneration plants as “highly efficient” can play a determinant role in favouring or discouraging the market growth of polygeneration systems, especially for buildings applications where economic viability is often more difficult to achieve. Based on the current European framework, in this paper the opportunity to adopt sector- and user-oriented criteria is discussed. After having identified three buildings with different uses (a large hotel, a hospital and an office building), the optimal lay-out and operation strategy of a polygeneration plant serving each building is determined; then, ex-post processing of economic and energetic resu…

Matching Economical, Energetic and Environmental Benefits: An Analysis for Hybrid CHCP-Heat Pumps Systems

Abstract The optimization of design and operation of combined heat, cooling and power systems usually leads to select different plant lay-outs and size of components, depending on the adopted optimization criterion (maximum profit or energy saving or minimum environmental impact). This occurs when the current energy prices and the normative provisions supporting cogeneration are not able to coincide with the specific customer’s interest and the overall “social interest” for a reduction in energy consumption and in pollutants’ emissions. At EU level, polygeneration is considered to have a large potential for residential and commercial buildings district network, for the tertiary sector and f…

Optimization of Wave Energy Converter: DEIM Point Absorber II

The paper presents a possible solution to optimize a wave energy converter, device able to exploit the wave energy resource. The utilization of this technology shows also positive aspects, thanks to the limited visual and environmental impacts. This system could be also installed in reserved areas, being similar to signal buoys, simplifying the problem of energy supply in small islands. In order to exploit the wave energy potential in the Mediterranean Sea, the department of Energy of Palermo University realized a first prototype of the electrical linear generator, that is the main component of the wave energy converter. This electrical machine can be operated by a two-floating buoys system…

A New Solution for Sea Wave Energy Harvesting, the Proposal of an Ironless Linear Generator

The paper investigates an innovative ironless linear generator, installable inside a wave energy converter, in order to produce electricity from sea waves. This energy source is considered strategic for the future, especially in small islands

Criteri e metodi per l'ottimizzazione di sistemi di poligenerazione di piccola e media taglia - Criteria and methodologies for the optimization of small/medium scale polygeneration systems

L'Unione Europea ha individuato nella produzione combinata di energia elettrica e calore una delle tecnologie ad alta efficienza di maggior interesse, fissando per il 2010 il target del 18% della produzione elettrica totale dell'Unione da sistemi cogenerativi (COM/97/0514). Dati recenti rivelano la non attualità di tale target (al 2005 si è raggiunto il 12% di penetrazione); rimane tuttavia evidente la volontà, esistente sia a livello comunitario che in molti Stati Membri, di perseguire la via della promozione della poligenerazione. Le ragioni di questo interesse sono evidenti: l'elevata efficienza di conversione garantita dal recupero dei cascami termici di un ciclo diretto consente, a par…

On the Efficacy of PCM to Shave Peak Temperature of Crystalline Photovoltaic Panels: An FDM Model and Field Validation

The exploitation of renewable energy sources and specifically photovoltaic (PV) devices have been showing significant growth; however, for a more effective development of this technology it is essential to have higher energy conversion performances. PV producers often declare a higher efficiency respect to real conditions and this deviation is mainly due to the difference between nominal and real temperature conditions of the PV. In order to improve the solar cell energy conversion efficiency many authors have proposed a methodology to keep the temperature of a PV system lower: a modified crystalline PV system built with a normal PV panel coupled with a Phase Change Material (PCM) heat stor…

Analisi degli effetti delle opzioni tariffarie regionali sull'ottimizzazione di μ-grids energetiche alimentate da impianti poligenerativi

L'ottimizzazione di sistemi energetici complessi per la produzione e la distribuzione di fluidi caldi e freddi per utenti civili è un problema molto complesso; due possibili configurazioni possono essere prese in considerazione, ovvero le piccole unità singole per singoli edifici ed i grandi impianti integrati con reti di teleriscaldamento. Affrontare un problema così complesso, che coinvolge un numero molto elevato di variabili, richiede algoritmi e tecniche di risoluzione efficienti. La ricerca svolta ha consentito di sviluppare nuovi metodi di mathematical programming, ed in particolare tecniche di Mixed Integer Linear Programming (MILP), per quanto concerne l’ottimizzazione di sistemi p…

ANALYSIS OF A RECIPROCATE ENGINE–BASED COGENERATION PLANT WITH HIGH TEMPERATURE HEAT RECOVERY FOR INDUSTRIAL USES

In consequence of the increasing awareness on the future scarcity of fossil energy sources and the global warming impact of energy conversion processes, the European Union has been planning several actions to enhance the efficiency of energy use and reduce the environmental impact. The declared goals of EU actions are synthetized in the 20-20-20 formula, consisting of an expected 20% increase of energy efficiency, a 20% contribution to the total energy supply by renewable sources and a 20% abatement of pollutant emissions. Applications of cogeneration in process industry can significantly contribute to achieve these targets. In this paper a reciprocate engine-based Combined Heat and Power (…

Experimental characterization of PEM fuel cells by micro-models for the prediction of on-site performance

This paper presents the results of an experimental analysis performed on a miniaturized, 6 We Proton Exchange Membrane Fuel Cell (PEMFC) system, integrated with on-site hydrogen production by electrolysis; in particular, the effects of environmental parameters such as the external temperature and the humidity on the performance of fuel cells are investigated. PEMFC systems are zero-emissions power technologies when they are fed with pure hydrogen (at concentration higher than 97%); also, being the only results of system operation the produced electricity and some pure water, when produced by renewable sources hydrogen can be considered an attractive alternative to fossil fuels and may concu…

Scope-Oriented Thermoeconomic analysis of energy systems. Part I: Looking for a non-postulated cost accounting for the dissipative devices of a vapour compression chiller. Is it feasible?

Abstract The authors of the main thermoeconomic methodologies developed in the last two decades have recently focused their efforts on the analysis of dissipative devices, i.e. those components whose productive purpose is neither intuitive nor easy to define. Coherent and unanimously accepted cost structures have been identified for dissipative components, while ambiguities still exist as concerns the cost allocation principles to be adopted. Being this aspect evidently cost-influencing, accurate analyses focused on the subjectivity of results are needed. This paper is structured in two parts. In the Part I an in-depth study of some critical issues arising from the thermoeconomic analysis o…

Optimal sizing and operation of thermal energy storage devices for trigeneration systems

Analisi sperimentale dell’influenza delle condizioni ambientali sulle prestazioni di un sistema PEMFC di bassa potenza

Analitic prediction of spread scenarios for small-scale CHP systems

Robust optimization of trigeneration systems based on linear programming

Non-uniform doping concentration CIGS absorber profile for highefficiency solar cells

The quaternary chalcopyrite semiconductor alloy Cu(In,Ga)Se2 (CIGS) is nowadays commonly considered one of the most suitable materials to fabricate cost-effective and high-efficiency photovoltaic cells. Thanks to the optical and structural properties of the absorber layer and to the tunable bandgap, thin-film CIGS cells have reached efficiencies around 20%, not far from the maximum values of traditional crystalline silicon cells. This high efficiency, together with the conceivable low fabrication costs, makes CIGS cells a promising alternative to silicon technology for large-scale production. In order to further improve the cells performance, in a previous work we have already proposed a si…

OPTIMIZATION OF COGENERATION PLANT FOR APPLICATIONS IN FOOD INDUSTRY

Cogeneration systems represent an effective solution for optimizing energy performance of users with contemporary thermal and electrical energy demand. An energy audit of an industrial pasta factory equipped with a cogeneration system natural gas fuelled has carried out along last two years. This CHP plant, with a 650 kWe capacity, currently covers a relevant fraction of the electric and high-temperature heat loads during peak hours, while it is switched off during off-peak hours because of the much lower electricity price. Heat content of flue gases is recovered by two cascaded gas-diathermic oil and diathermic oil- water heat exchangers; the superheated water obtained is then supplied to …

Indagine tecnica ed economica per lo sfruttamento ai fini energetici dei tralci di potatura della vite

Ottimizzazione di impianti poligenerativi con accumulo termico tramite algoritmi ibridi basati su programmazione lineare ed analisi energetica

USER- AND CONTEXT-ORIENTED CRITERIA FOR ASSESMENT OF HIGH EFFICIENCY POLYGENERATION PLANTS FOR BUILDINGS APPLICATIONS

The eligibility criteria adopted to assess polygeneration plants as “highly efficient” can play a determinant role in favouring or discouraging the market growth of polygeneration systems, especially for buildings applications where economic viability is often more difficult to achieve. Basing on the current European framework, in this paper the opportunity to adopt user- and context-oriented criteria is discussed. After having identified three buildings with different uses (a large hotel, a hospital and an office building), the optimal layout and operation strategy of a polygeneration plant serving each building is determined; then, ex-post processing of economic and energetic results is u…

Finite difference thermal model of a latent heat storage system coupled with a photovoltaic device: Description and experimental validation

Abstract The use of photovoltaic (PV) systems has been showing a significant growth trend but for a more effective development of this technology it is essential to have higher energy conversion performances. Producers of PV often declare an higher efficiency respect to real conditions and this deviation is mainly due to the difference between nominal and real temperature conditions of the PV. To improve the solar cell energy conversion efficiency many authors have proposed a methodology to keep lower the temperature of a PV system: a modified PV system built with a normal PV panel coupled with a Phase Change Material (PCM) heat storage device. In this paper is described a thermal model ana…

Brief description of current research activities on energy saving by cogeneration and thermoeconomic analysis and diagnosis of energy systems

In the last decades the severe issues related with fossil fuels depletion, increasing energy prices and global warming impact of energy conversion systems have attracted the efforts of scientists toward efficient technologies and methodological improvements for a rational use of energy both in the civil and the industry sectors. Among the numerous research lines developed, the combined production of multiple energy vectors and the process integration are widely considered very promising solutions to achieve more sustainable scenarios as concerns the use of energy. While polygeneration in industry represents a well-established practice to reduce the production cost of energy and material str…

Characterization of cooling loads in the wine industry and novel seasonal indicator for reliable assessment of energy saving through retrofit of chillers

Abstract The food sector is a major consumer of energy and growing efforts are being made in the search for solutions that will guarantee the efficient and sustainable use of energy resources. Among the different sectors, wineries are attracting particular interest due to the continuous growth of the global market and production. Surveys conducted in the winemaking sector have highlighted the importance of performing accurate energy audits and have identified the installation of efficient refrigeration systems as a promising solution in a variety of cases. Unfortunately, the savings achievable by efficient cooling technologies are often estimated using simplified approaches which do not tak…

Penetration Scenarios of Cogeneration in the Liberalised Energy Market

Il progetto SAVE-DABASI, parte II Ottimizzazione di impianti CHCP mediante simulazione oraria

Modello energetico ed aspetti critici nell’analisi termoeconomica di un impianto di dissalazione ad effetti multipli (MEE)

Advanced energetics of a Multiple Effects Evaporation (MEE) desalination plant Part I: 2nd principle analysis by a zooming representation at single-effect level

This paper represents the Part I of a paper in two parts, aimed at proposing a 2nd principle and thermoeconomic analysis for a Multiple Effects Evaporation (MEE) process and discussing solutions for optimization and energy saving. After a brief analysis of the thermochemical fundamentals of desalination, the minimum theoretical work of separation is introduced to represent a reference condition for the assessment of plants' efficiency. A forward feed MEE configuration is then analysed, abandoning the conventional approach to “at overall plant-level”-analysis; a zooming strategy, based on focusing on the physical model of a generic stage (i.e. effect), is preferred to best recognize the marg…

Experimental characterization of regenerative PV-PEMFC systems by micro-models for performance preliminary analysis

On the Reliability of Optimization Results for Trigeneration Systems in Buildings, in the Presence of Price Uncertainties and Erroneous Load Estimation

Cogeneration and trigeneration plants are widely recognized as promising technologies for increasing energy efficiency in buildings. However, their overall potential is scarcely exploited, due to the difficulties in achieving economic viability and the risk of investment related to uncertainties in future energy loads and prices. Several stochastic optimization models have been proposed in the literature to account for uncertainties, but these instruments share in a common reliance on user-defined probability functions for each stochastic parameter. Being such functions hard to predict, in this paper an analysis of the influence of erroneous estimation of the uncertain energy loads and pric…

Impianti di trigenerazione per il risparmio energetico nel settore alberghiero in aree mediterranee

Il settore alberghiero presenta prospettive particolarmente favorevoli alla diffusione degli impianti di cogenerazione, grazie alla simultanea presenza di una domanda elettrica e di una termica a bassa temperatura, che consentono, in particolare per gli alberghi che funzionano durante tutto l’anno, significativi risparmi di energia primaria e notevoli benefici sia economici che ambientali. Nei paesi del bacino Mediterraneo, in particolare, la diffusione dei frigoriferi ad assorbimento presenta grandi vantaggi per l’opportunità di integrare, nei cosiddetti impianti di trigenerazione o CHCP, la domanda di energia frigorifera all’interno del processo di “sfruttamento in cascata” del potenziale…

Advanced energetics of a Multiple Effects Evaporation (MEE) desalination plant

This paper represents the Part I of a paper in two parts, aimed at proposing a 2nd principle and thermoeconomic analysis for a Multiple Effects Evaporation (MEE) process and discussing solutions for optimization and energy saving. After a brief analysis of the thermochemical fundamentals of desalination, the minimum theoretical work of separation is introduced to represent a reference condition for the assessment of plants' efficiency. A forward feed MEE configuration is then analysed, abandoning the conventional approach to “at overall plant-level”-analysis; a zooming strategy, based on focusing on the physical model of a generic stage (i.e. effect), is preferred to best recognize the marg…

Optimization of polygeneration plants and μ-grids for civil applications

The problem of combined energy production and distribution of warm and cold fluids is very complex because it includes two possible configurations, the small single unit for individual buildings and the large plant integrated with district heating networks. Dealing with such a complex problem, involving a very large number of variables, requires efficient algorithms and resolution techniques. The present study illustrates a MILP approach to the optimization of synthesis, design and operation for CHCP-based μ-grids including thermal energy storages. The proposed approach develops a method for designing and optimizing district energy systems, starting with the information available for the di…

Il progetto SAVE-DABASI. Parte I. Dimensionamento di impianti di trigenerazione

Application of Thermographic Techniques for the Detection of Failures on Photovoltaic Modules

The paper focuses on thermography as a useful investigation tool for diagnosis, detection and prevention of failures of photovoltaic modules. The paper describes the faults detectable by thermographic investigations and how to conduct these investigantions. Then the results of some analyses conducted on a photovoltaic field are presented. The investigations made possible to identify faulty modules with hot spots by measuring localized superheat due to the presence of concentrated deposits on the exposed surface of the module and the superheating due to the presence of sand/dust deposits distributed on a significant portion of the module surface. The thermographic investigations can be used …

An original indicator to predict spread scenarios for small scale poligeneration in the liberalised energy market

Exergoeconomic analysis as a tool for supporting the design and operation of multiple chiller systems in air conditioning applications.

Multiple-Chillers systems represent viable solutions for medium/large-scale air conditioning applications. In these systems, however, design and energy savings are highly affected by the configuration and operation strategies adopted. For instance, when considering multiple chillers of same size, “symmetric” or “sequential” load sharing strategies are two viable options. Conversely, when considering chillers of different sizes, a wide combination of chillers cooling capacities may be adopted. It is apparent that an integrated analysis of the design and operation of these systems should be carried out in order to achieve profitable energy saving. With this respect, Exergoeconomics, which res…

Electrical characterization of low power CIGSSe photovoltaic modules

This paper presents the electrical characterization of low power CIGSSe photovoltaic (PV) modules. Such investigation is achieved to perform a comparison of their performances with conventional silicon PV modules. For this purpose, a test bench, suitable for the characterization of both traditional and innovative low power modules, has been set-up and experimental results are accurately described and discussed.

A thermoeconomics-based approach to the integrated optimization of design and operation for decentralised energy systems and variable load conditions

The many comprehensive approaches formulated for the optimization of large industrial energy systems have been rarely applied to small and medium scale units, because of the difficulties in handling a continuously variable energy demand and of the lower margins for energy and emissions saving. Today, the growing interest for decentralised energy systems in the civil sector stimulates major efforts for the optimization of such plants, with a particular focus on the control system and on a management strategy able to exploit the opportunities existing in the free energy market. In this paper a methodology is proposed for the optimization of design and operation of variable demand systems supp…

OPTIMIZATION OF POLYGENERATION SYSTEMS SERVING A CLUSTER OF BUILDINGS

The optimization of combined energy systems for the production and distribution of warm and cold fluids to civil users is very complex; two possible configurations, i.e. the small single units for individual buildings and the large plants integrated with district heating networks, can be essentially considered, especially in cold climates. Dealing with such a complex problem, involving a very large number of variables, requires efficient algorithms and resolution techniques. The present chapter illustrates a Mixed Integer Linear Program (MILP)1 approach to the optimization of synthesis, design and operation for CHCP-based μ-grids including thermal energy storages. A novel approach is presen…

Exergoeconomic analysis as support in decision-making for the design and operation of multiple chiller systems in air conditioning applications

Abstract Multiple-chillers systems represent viable solutions for medium/large-scale air conditioning applications characterized by variable cooling demand. The energy efficiency of such systems is influenced by the number of chillers, the combination of cooling capacities, and the load-sharing among the units. Large efforts have been devoted to developing efficient operation strategies for these systems, but rules of thumb are usually adopted for selecting cooling capacities thus leaving room for energy and economic savings. In this paper, exergoeconomic analysis is proposed as a promising method to identify near-optimal design and operation strategies, due to the capability of exergoecono…

An original multi-objective criterion for the design of small-scale polygeneration systems based on realistic operating conditions

The optimal design and operation of cogeneration and trigeneration systems for buildings applications is a complex issue, which has been investigated by several different approaches. Both the two basic management strategies, namely heat-tracking and electricity-tracking, have advantages and drawbacks in terms of operating results and may lead the plant designer either to undersize or oversize the CHP unit with respect to the optimal lay-out. Experimental works have demonstrated how the actual on-site performance of small-scale polygeneration systems significantly differs from their expected operation, due to the need for a regular plant operation and the effects of outages for scheduled or …

EABOT – Energetic analysis as a basis for robust optimization of trigeneration systems by linear programming

Abstract The optimization of synthesis, design and operation in trigeneration systems for building applications is a quite complex task, due to the high number of decision variables, the presence of irregular heat, cooling and electric load profiles and the variable electricity price. Consequently, computer-aided techniques are usually adopted to achieve the optimal solution, based either on iterative techniques, linear or non-linear programming or evolutionary search. Large efforts have been made in improving algorithm efficiency, which have resulted in an increasingly rapid convergence to the optimal solution and in reduced calculation time; robust algorithm have also been formulated, ass…

Il progetto SAVE-DABASI: dimensionamento di impianti di trigenerazione, parte II

An Approach to Heuristic Optimitation of design and Operation for trigeneration Systems Based on Profit Formation Process

A comprehensive tool for efficient design and operation of polygeneration-based energy μgrids serving a cluster of buildings. Part I: Description of the method

Polygeneration systems with thermal energy storage represent promising solutions to achieve energy saving and emissions reduction in the civil sector. The definition of customer-oriented design and operation strategies represents a most challenging task, in order to maximize the profitability and make the investment attractive. A large potential is often recognized for the installation of centralized plants serving a cluster of buildings located over a small area; in such cases the design problem becomes extremely complex and the analyst needs reliable instruments to identify the optimal solution. This paper in two parts presents a scientific tool for the optimization of design and operatio…

Energy saving in airports by trigeneration. Part II: Short and long term planning for the Malpensa 2000 CHCP plant

With reference to the feasibility analysis for CHCP applications in airports performed in Part I of this work, the optimal strategy for repowering and operation of the Malpensa 2000 CHCP plant is here discussed. The analysis starts from experimental energy demand data, available on hourly basis for an entire operational year. After a description of the CHCP lay-out, the optimal management strategy was determined keeping into account the articulated energy tariff system and the technical characteristics of components. A profit-oriented optimization of the repowering actions to take up to 2010 is presented, based on the expected growth of energy consumption due to the scheduled increases in t…

Improving energy efficiency of commercial buildings by Combined Heat Cooling and Power plants

Abstract Commercial buildings play a key-role in the energy consumption of the building sectors. Recent statistics have shown that as the number of commercial buildings is continuously increasing, their effects on energy consumption are expected to grow. These buildings are characterized by high energy demand mainly due to lighting and HVAC requirements. Rooms of energy saving exist by considering that: (i) electricity demands and HVAC requirements occur simultaneously during the day and (ii) both demands are currently satisfied by using separate energy systems. It is apparent that the adoption of polygeneration systems could represent a valid solution to achieve energy savings. To this aim…

On thermoeconomics of energy systems at variable load conditions: integrated optimization of plant design and operation

Abstract Thermoeconomics has been assuming a growing role among the disciplines oriented to the analysis of energy systems, its different methodologies allowing solution of problems in the fields of cost accounting, plant design optimisation and diagnostic of malfunctions. However, the thermoeconomic methodologies as such are particularly appropriate to analyse large industrial systems at steady or quasi-steady operation, but they can be hardly applied to small to medium scale units operating in unsteady conditions to cover a variable energy demand. In this paper, the fundamentals of thermoeconomics for systems operated at variable load are discussed, examining the cost formation process an…