R744-R717 Cascade Refrigeration System: Performance Evaluation compared with a HFC Two-Stage System

Abstract In this study is presented a thermodynamic analysis of a cascade refrigeration system using as refrigerant carbon dioxide in low-temperature circuit and ammonia in high-temperature circuit. The operating parameters considered in this paper include condensing, evaporating, superheating and subcooling temperatures in the ammonia (R717) hightemperature circuit and in the carbon dioxide (R744) low-temperature circuit. Diagrams of COP versus operating parameters have been obtained. In addition, values for R744-R717 cascade refrigeration system are compared with the values obtained for a partial injection two-stage refrigeration system using the synthetic refrigerant R404A, a nearly azeotropic blend, specially used for commercial refrigeration. Results show that a carbon dioxide-ammonia cascade refrigeration system is an interesting alternative to R404A two-stage refrigeration system for low evaporating temperatures (–30 °C ÷ –50 °C) in commercial refrigeration for energy, security and environmental reasons

Using Recurrent Artificial Neural Networks to Forecast Household Electricity Consumption

Abstract The electricity consumption related to the civil sector (residential and tertiary) in the most developed countries has considerably increased during the last years, especially in the summer season. One of the reasons for this rise can be found in the drastic growth of the sales of mono and multi-split systems for air-conditioning. In this context is very important to assess the correlation between electricity demand and utilization of electric appliances (especially airconditioners). This paper describes a model based on an Elman Artificial Neural Network (ANN) for the short-time forecasting (1 hour ahead) of the household electric consumption related to a suburban area in the neighbours of the town of Palermo (Italy). One of the aims of the study is the assessment of the influence of the use of air-conditioning equipments on the electricity demand

Potential applications using LNG cold energy in Sicily

According to previsions, natural gas could be the main energy source worldwide, inducing relevant geopolitical changes. Most likely, such problems will be solved with the development of a gas transportation mode alternative to traditional pipelines: liquefied natural gas (LNG). The global LNG trade has increased rapidly during recent years. A significant amount of energy is consumed to produce low-temperature LNG, which has plenty of cryogenic exergy/ energy. Therefore, the effective utilization of the cryogenic energy associated with LNG vaporization is very important. Sicily, with more than five million inhabitants, is the second biggest region of Italy and in this region will be realized two of the 11 gasification plants planned in Italy according to the regional energy master-plan. This paper shows some interesting applications for the cold produced in gasification plants, e.g. for seawater desalination and for fresh and frozen food production and conservation. These applications seem very interesting for Sicilian situation and also can contribute to energy saving and greenhouse gases reduction to match Kyoto Protocol targets.According to previsions, natural gas could be the main energy source worldwide, inducing relevant geopolitical changes. Most likely, such problems will be solved with the development of a gas transportation mode alternative to traditional pipelines: liquefied natural gas (LNG). The global LNG trade has increased rapidly during recent years. A significant amount of energy is consumed to produce low-temperature LNG, which has plenty of cryogenic exergy/ energy. Therefore, the effective utilization of the cryogenic energy associated with LNG vaporization is very important. Sicily, with more than five million inhabitants, is the second biggest region of Italy and in this region will be realized two of the 11 gasification plants planned in Italy according to the regional energy master-plan. This paper shows some interesting applications for the cold produced in gasification plants, e.g. for seawater desalination and for fresh and frozen food production and conservation. These applications seem very interesting for Sicilian situation and also can contribute to energy saving and greenhouse gases reduction to match Kyoto Protocol targets. Copyright # 2008 John Wiley & Sons, Ltd

Evaluating the performances of small wind turbines: a case study in the south of Italy

AbstractAmong renewable energy resources, wind energy became more attractive in the last decade. Wind farms installations dramatically increased in areas where climatic conditions, topography and environment have allowed their development. The installation of wind turbines, usually carried out in remote areas, recently began to cover areas identified by a complex terrain such as urban and suburban zones. Although these new sites' choices are characterized by lower productivity there is increasing interest in wind energy production in both urban and suburban area. In this work the authors have carried out an energy analysis developed from a sample of small wind turbines available on the market. This study shows how variable can be the energy production of a small wind turbine according to many design and context parameter: wind profiles, installation height, land use, characteristics of the turbine

Evaluation of Net Energy Obtainable from Combustion of Stabilised Olive Mill By-Products

This work is aimed at calculating the energy content of the residues from olive oil production. Olive pulp, olive husk and sludge (a mixture of olive pulp and husk) have been analyzed separately. Olive Mill Effluents (OME) are normally a problem for olive mill farms, yet they may be used as feedstock for biomass-fuelled power plants. Nonetheless, OMEs are characterized by a relatively high humidity content and are produced only during the olive season. Thus, OME need a stabilization process to be employed as a solid biofuel throughout the year. The analyses conducted attempt an evaluation of the energy consumption of a three-stage stabilization process: drying, milling and pelletising. The net electrical energy available from OME is then calculated as a difference between gross energy available and energy consumed for stabilization. The gross available electrical energy was calculated based on direct energy conversion of the stabilized feedstock on a small scale direct combustion and Organic Rankine Cycle (ORC) turbine. Results show that OME are suitable for energy production. Approximately 4500 kJ/kg of net electrical energy may be obtained out of olive sludge or olive pulp, while olive husk shows a potential gross energy of 3400 kJ/kg

On the Evaluation of Solar Greenhouse Efficiency in Building Simulation during the Heating Period

a flat equipped with a sunspace, recently built thanks to public contributions provided by the Umbria Region in Italy to widespread bio-climatic architecture, was used as case-study. Simulations were carried out for the examined flat, both with a steady-state tool and with a dynamic on