Search

A new concept of a system for Combined Heat and Power generation is presented. The concept is based on hybrid use of two renewable energy sources, direct solar (thermodynamic solar) and biomass (indirect solar energy). Biomass combustion is conducted using a fluidized bed combustor. A second source of energy, given by the direct irradiation of the bed with a concentrated solar radiation, is integrated in the same system, using the fluidized bed as solar receiver. A Stirling engine converts heat into mechanical power. A Scheffler type mirror is adopted to allow irradiation of the system in a fixed focal point. Advantages of the proposed solution are illustrated and some preliminary results on the performance of the system, obtained with a simple model, are presented. The principal improvements with respect to existing systems of similar size and primary energy source are illustrated. The most important are the enhanced heat transfer processes that are realized with the help of the fluidized bed, and the possibility of continuous cogeneration during the day. Different working conditions are considered to estimate the contribution given by the burning of fuel, in presence as well as in absence of sun irradiation (as during the night). The distribution of energy shares among the different flux contributes is reported versus the amount of biomass burned per unit time. The results clearly demonstrate the advantage of coupling, in the same system, two sources for heat generation, thus maintaining the option of producing electricity without the supply of biomass fuel.

During last years, air conditioning demand has spread, both in the commercial and the residential sector. This caused a sensible increase in primary energy consumption. The innovative desiccant-based air handling units are a very interesting solution for air conditioning of buildings as they operate with low temperature thermal energy, such as waste heat recovered from a microcogenerator or especially solar energy. Solar radiation is widely available in summer and simultaneously there are the greatest demands for cooling, but solar energy can be used advantageously also to balance the winter thermal load. In the most common configuration, desiccant cooling system are equipped with a desiccant wheel, in which moist air is dehumidified by the adsorbent material and then cooled down by the evaporation of water and/or through an electric chiller (hybrid plants). A hybrid air conditioning device with silica-gel desiccant wheel is installed in the laboratories of the Università degli Studi del Sannio (Benevento, Italy), and currently operate coupled with a microcogenerator and a natural gas boiler. The system in its actual configuration can operate only in cooling mode. In this thesis the operation of the experimental air handling unit, considering the coupling of the innovative air handling unit with different solar collectors types (flat plate, evacuated tube, concentrated photovoltaic and thermal collectors), is analyzed through dynamic simulations performed with the commercial software TRNSYS 17. In order to allow the system operation even in winter mode, suitable modifications have been identified and implemented in the model. Furthermore the influence of climatic conditions on the performance of the system is assessed, and also modifications to the air handling unit layout are considered. Finally, for completeness, the system constituted by the desiccant-based air handling unit and the microcogenerator is studied. The innovative air conditioning systems were used to balance the sensible and latent load of a 63.5 m2 university classroom. Moreover, during the intermediate period, in the weekends and whenever there is a surplus of thermal energy the possibility of exploiting this energy in excess for further heating purpose is considered. TRNSYS models were used to simulate the operation of the innovative system and that of a conventional system in order to evaluate operational data and performance parameters. Primary energy saving, equivalent CO2 avoided emission and simple pay back period were evaluated. The performed analyzes showed that the desiccant-based air handling unit fed with a renewable energy source such as solar energy can advantageously replace a conventional air conditioning systems equipped with electrically-driven vapor compression cooling units if only energy and environmental performance are taken into account. However economic feasibility is still hard to obtain. For the considered application economic benefits do not occur together with the advantages mentioned above, although one considers incentives for the production of thermal energy from a renewable source. Only if the use of solar thermal is maximized considering other low temperature heating purposes (for example domestic hot water or swimming pools heating) in addition to the air conditioning economic advantages can take place.

Buildings are responsible for about 35-40% of energy demand and greenhouse gas emissions, and it implies that improvements of local and global climate, containment of urban heats islands, saving targets, and environmental goals cannot be achieved without high-efficient new buildings and a deep energy renovation of the existing building stock. This work analyses three possible case studies to fulfill the goals of policies in energy-matter and considers real case studies of new construction and the energy refurbishment of existing buildings. This is only a small part of a wider study that provides an overview of evolution, achieved goals, criticalities, and perspectives of twenty years of policies in the matter of energy performance of buildings. The new construction of a single-story dwelling, the refurbishment of a historical building, and a 70s cement-based building are the three exemplary case studies that will be proposed, as a part of a larger investigation.

Micro-cogeneration is a developed technology aiming to produce electricity and heat close to the final users, with the potential, if designed and operated correctly, to reduce both the primary energy consumption as well as the associated greenhouse gas emissions when compared to traditional energy supply systems based on separate energy production. The distributed nature of this generation technology has the additional advantages of (i) reducing electrical transmission and distribution losses, (ii) alleviating the peak demands on the central power plants, and (iii) diversifying the electrical energy production, thus improving the security of energy supply. Micro-cogeneration devices are used to meet both electrical requirements and heat demands (for space heating and/or hot water production) of a building; they can be also combined with small-scale thermally fed or mechanically/electrically driven cooling systems. Many micro-cogeneration units are already commercialized in different countries (such as Japan, Germany, United Kingdom, etc.) and in recent years several researches have been carried out in order to advance the design, operation, and analysis of this technology. Currently the use of commercial micro-cogeneration units in applications such as hospitals, leisure facilities, hotels, or institutional buildings is well established. The residential cogeneration industry is in a rapid state of development; the market remains not fully mature, but interest in the technology from manufacturers, energy utilities, and government agencies remains strong.

Desiccant-based air handling units can achieve reductions in greenhouse gas emissions and energy savings with respect to conventional air conditioning systems. Benefits are maximized when they interact with renewable energy technologies, such as solar collectors. In this work, experimental tests and data derived from scientific and technical literature are used to implement a model of a solar desiccant cooling system, considering three different collector technologies (air, flat-plate and evacuated collectors). Simulations were then performed to compare the energy, environmental and economic performance of the system with those of a desiccant-based unit where regeneration thermal energy is supplied by a natural gas boiler, and with those of a conventional air-handling unit. The only solution that allows achieving the economic feasibility of the solar desiccant cooling unit consists of 16 m 2 of evacuated solar collectors. This is able to obtain, with respect to the reference system, a reduction of primary energy consumption and of the equivalent CO 2 emissions of 50.2% and 49.8%, respectively, but with a payback time of 20 years.

Desiccant-based air handling units allow significant reductions in greenhouse gas emissions and energy savings with respect to conventional air conditioning systems. Benefits are maximized when they interact with renewable energy technologies, such as solar collectors. Due to the high requirements of humidifiers, water consumption is a major issue for desiccant cooling technology. Therefore, a water consumption analysis should be also performed.In this work, experimental tests and data derived from scientific and technical literature are used to implement a model of a solar desiccant cooling system, considering three different solar caption technologies (air, flat plate and evacuated collectors). Simulations were then performed to compare the energy, environmental and economic performance and water consumption of the system with those of a desiccant-based unit in which regeneration thermal energy is supplied by a natural gas boiler, and with a conventional air handling device. A trade-off solution is chosen, consisting of 16 m2 of flat-plate solar collectors. This solution allows to obtain, with respect to the reference system, a reduction of primary energy consumption and of the equivalent CO2 emissions of 24.2% and 27.1%, respectively, with an acceptable pay-back time of 4.81 years, and a water consumption very similar to that of the reference system.

A new concept of a system based on a Stirling engine for the combined production of heat and electric power is presented. The system uses two renewable energy sources, direct solar (thermodynamic solar) and biomass (indirect solar energy). Biomass combustion is conducted using a fluidized bed combustor. A second source of energy, given by the direct irradiation of the bed with a concentrated solar radiation, is integrated in the same system, using the fluidized bed as solar receiver. A Scheffler type mirror is adopted to allow irradiation of the system in a fixed focal point. A Stirling engine, integrated into the fluidized bed, converts heat into electricity. Advantages of the proposed solution are illustrated and some preliminary results on the performance of the system, obtained with a simple model, are presented.