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The cogeneration is the combined production of electric and/or mechanical and thermal energy starting by a single energy source; in particular in this paper the analysis will be focused on a cogeneration system with electric power lower than 15 kW (micro-cogeneration). The paper analyzes a system consisting of a natural gas-fired micro-cogeneration unit (MCHP), a heat storage and a peak boiler. The system provides thermal and electric energy to two end-users, the former is a tertiary building (office), where the generation system is located, and the latter is a residential building connected to the former through a district heating micro-grid. In order to analyze the influence of climatic conditions, two different geographical locations in Italy (Benevento and Milano) are considered, that are also characterized by different natural gas and electricity tariffs. Particular attention is paid to the choice of the users, in order to obtain more stable and continuous electric and thermal loads (load sharing approach) and to increase the operating hours per year of the MCHP unit. The operation of the MCHP is governed by a control system, aimed to optimize a thermo-economic objective function. The models representing the components, the thermo-economic objective function and the buildings have been implemented in a widely used commercial software for building simulations. The models are calibrated and validated through data obtained from experimental tests carried out in the laboratory of the University of Sannio (Benevento). The results of the simulations highlight the potential benefits of the thermal load sharing approach. In particular, this study shows that an MCHP unit connected by means of a thermal micro-grid to different users in “load sharing mode” can obtain a high number of operating hours as well as significant energy (Primary Energy Saving) and environmental (avoided CO 2 equivalent emissions) benefits with respect to an appropriate reference system, even in Mediterranean areas, where the climatic conditions are not always suitable for cogeneration.

The Directive 2004/8/EC on the promotion of cogeneration proposes a comparative indicator based on primary energy savings, neglecting some important thermodynamic aspects, such as exergy. This study aims to compare and discuss the usefulness of a set of complementary indicators for performance assessments of cogeneration systems, concerning thermodynamic principles based on first and second law (the exergy approach). As case study, a 6 kW electric output micro-combined heat and power unit was experimentally tested and a model of the unit was developed in TRNSYS. Considering as reference a set of different heat and electricity scenarios, including the actual electric mixes of Portugal and Italy, the indicators case incon (PES) and Primary and Total Irreversibilities Savings (PIS and TIS), as well as energy and exergy renewability ratios were assessed and discussed. The results show that the use of MCHP has higher advantages for the Italian electric grid, than an equivalent scenario considering the Portuguese electric network as reference. As result, for a particular scenario analysed, PES and PIS have 3% and 6% for Portugal, and 10% and 18% for Italy, respectively. Furthermore, for one particular scenario evaluated, the indicators energetic and exergetic renewability ratios have 23% and 14%, respectively for the Portuguese electric grid, and 19% and 10% for the Italian electric system.

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.

Micro-cogeneration is a well-established technology and its deployment has been considered by the European Community as one of the most effective measure to save primary energy and to reduce greenhouse gas emissions. Micro-trigeneration systems are also gaining an increasing interest thanks to the availability of small thermally driven cooling systems and the increasing demand for space cooling during the warm season. At the Built Environment Control Laboratory of Seconda Universita degli Studi di Napoli, a micro-cogenerator based on natural gas fuelled reciprocating internal combustion engine that can be coupled with a thermal-chemical absorption system has been set-up in order to experimentally investigate the on-site performances of both micro-cogeneration system and micro-trigeneration system under real operating conditions. This paper deals with the description of experimental plant and the results of first experimental tests. The analysis of the measured data is carried out from an energy, economic and environmental point of view, by comparing the performances of the proposed system with those of the conventional system and the best available technology.

Hybrid desiccant HVAC systems have shown several advantages, compared to conventional cooling and dehumidification systems. Therefore, their use is also spreading for tertiary and residential buildings, especially when the regeneration of the desiccant can be obtained by using available waste heat. In this paper, an experimental analysis is presented on the performances of a silica-gel desiccant wheel, inserted in a test facility characterized by an advanced desiccant air handling unit, coupled to an electric chiller, a natural gas-fired boiler and a small scale cogenerator. The desiccant wheel is regenerated by using low temperature thermal energy recovered from the microcogenerator. The effects of the main thermal-hygrometric parameters (outdoor air humidity ratio and temperature, regeneration air temperature) on the desiccant wheel performances have been experimentally evaluated; in particular, the thermal-hygrometric properties of the process air exiting the rotor and the desiccant wheel effectiveness values have been obtained. Finally, fixing the regeneration temperature at its maximum available value (65 °C), ventilation and internal latent loads that the desiccant wheel can handle have been evaluated and compared to the required values, both for a set of cities all over the world and as a function of the thermal-hygrometric outdoor conditions.

In the Mediterranean area, the increasing demand of summer cooling in residential and tertiary sectors is usually satisfied by electrically-driven units; this often determines electric load peaks and black-outs. Thus, a wide interest is spreading in small scale natural gas-fired polygeneration systems: a prime mover drives (mechanically, electrically, thermally) electric generators and/or heat pumps, desiccant wheels, etc., matching thermal (heating and cooling) and electric end-user requirements. In this paper, laboratory tests have been considered to experimentally evaluate a small scale polygeneration system based on a natural gas-fired Micro-CHP and a desiccant-based HVAC system. Cogenerated thermal power is used for the desiccant wheel regeneration, while electric power for auxiliaries, chiller and external units. The HVAC system can also interact with electric and thermal separate “production” systems. The main results of the experimental tests are shown, stating the increase of the COP of the chiller in desiccant-based HVAC systems. Then the paper identifies the operating conditions (outdoor and supply air thermal-hygrometric conditions, electric grid efficiency and partial load operation of the MCHP) which guarantee significant primary energy savings (up to around 30%) and CO2 equivalent emission reductions (up to around 40%) of the polygeneration system compared to the conventional HVAC system.

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.

The increasing diffusion of micro-cogeneration systems is raising the need for studying their environmental impact in order to assess their sustainability. The adoption of the systems for the combined production of heat and power may provide a significant reduction of global impact in terms of carbon dioxide emissions with respect to the separate production of electricity and heat. However, a comprehensive environmental evaluation of this technology should take into account as well the impact due to the presence of plants spread over the territory that could increase the local pollution, in particular due to nitrogen oxides and carbon monoxide, and thus could worsen the local air quality. In this paper the nitrogen oxides and carbon monoxide emissions of a residential building-integrated micro-cogeneration system were evaluated; a 6.0 kWel natural gas fuelled internal combustion engine-based micro-cogeneration unit was coupled with a multi-family house compliant with the transmittance values suggested by the Italian Law. The analyses were carried out by using the whole building simulation software TRNSYS upon varying the city where the building is located (four Italian cities representative of different climatic regions were considered) as well as the control logic of cogeneration device (electric and thermal load-following strategies). The simulated performance of the proposed system was compared with those of a conventional system composed of a natural gas-fired boiler (for thermal energy production) and a power plant mix connected to the central electric grid (for electricity production) in order to assess the suitability of the cogeneration-based system in reducing the local emissions.

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.

The advantages of desiccant-based air conditioning systems, compared to conventional ones based on the dehumidification by cooling, have been highlighted in many research papers. The energy saving and the reduction of the environmental impact are higher when the desiccant material is regenerated by using “free” thermal energy (for example, waste heat from cogenerators or solar energy). Further investigation on the performance of the desiccant wheel is useful: therefore, in this paper, an experimental analysis on this component is presented, with particular attention to the variation of the performance as a function of the process and regeneration air flow rates. The desiccant material is regenerated by means of low-temperature thermal energy (about 65 °C) from a microcogenerator. Both the experimental results obtained by the authors and the data provided by the manufacturer have been used to calculate some performance parameters, and a satisfactory agreement has been obtained. The performance parameters have been evaluated as a function of the regeneration temperature, the inlet process air humidity ratio and temperature and the ratio between the regeneration and process air flow rates, in both the cases of fixed regeneration temperature and fixed regeneration thermal power: the results show that higher influence on the dehumidification process is due to the regeneration temperature rather than to the regeneration air flow rate. Moreover, the process air humidity ratio and regeneration temperature influence the desiccant wheel performance more than the process air temperature.

In the Mediterranean area, there is increase in demand for summer cooling satisfied by electrically driven units in domestic and small commercial sectors; this involves electric peak loads and black-outs. Consequently, there is an increasing interest in small scale polygeneration systems fuelled by natural gas. In this paper, attention is paid to a test facility, located in Southern Italy, to carry out experimental analysis on a small scale polygeneration system based on a natural gas-fired Micro-CHP and a desiccant HVAC system. The MCHP provides thermal power, recovered from engine cooling and exhaust gas, for the regeneration of the desiccant wheel and electric power for the chiller, the auxiliaries and the external units (computers, lights, etc.). The HVAC system can also operate in traditional way, by interacting with electric grid and gas-fired boiler. An overview of the main experimental results is shown, considering both the desiccant wheel and the global polygeneration system. The experimental results confirm that the performances of the desiccant wheel are strongly influenced by outdoor thermal-hygrometric air properties and regeneration temperature. The polygeneration system guarantees primary energy savings up to 21.2% and greenhouse-gas emissions reductions up to 38.6% with respect to conventional HVAC systems based on separate energy “production”.