Papers by Massimiliano Renzi
Energy Procedia, 2015
In this paper building integ of 4 groups (Ga 0.5 In 0.5 P, G consists of a p pitch; the latte the... more In this paper building integ of 4 groups (Ga 0.5 In 0.5 P, G consists of a p pitch; the latte the cell area, ratio. The ove three stepper sunrays is gu Engineering F present the pe effect of the d different solu Direct Bonde system using therefore also
Cogeneration using solar dish Stirling engine is a proven technology showing good energy conversi... more Cogeneration using solar dish Stirling engine is a proven technology showing good energy conversion performance in those Countries where the solar resource is particularly high. Many international agencies report that in the regions where the direct solar radiation is higher than 1900 kWh/(m2 year), the solar concentration technologies for the production of electrical power will be a valuable solution for the greenhouse gases emission mitigation and the reduction of the fossil fuel use. However, up to now, the production cost of a solar dish system showed a lack of economic competitiveness if compared to other solar technologies. In order to reduce cost, economies of scale must be achieved, standardization of the components must be adopted and very cheap but effective solutions must be introduced. In this work, an innovative, cheap and performing solution to reduce the cost of a free piston Stirling engine (FPSE) solar receiver system is proposed. The receiver was studied to suite t...
In this paper the construction of a compact and small scale heliostat solar concentration plant i... more In this paper the construction of a compact and small scale heliostat solar concentration plant is presented and the first experimental measurements are reported. The prototype plant uses 25 heliostats for a total reflective area of 4.4 m2; the mirrors are moved by a two-axis tracking mechanisms to reflect the sun’s rays onto a fixed target, in which a transfer fluid flows. The thermal performance of the system are reported.
The aim of this work is the energy efficiency assessment of a urban settlement supplied by a dist... more The aim of this work is the energy efficiency assessment of a urban settlement supplied by a district heating system based on biomass located in Renon (Bolzano, Italy). The study investigates the energy performance of a 1 MW el Organic Rankine Cycle (i.e., ORC) connected to a district heating network that provides heat to several domestic users. A wood chip boiler, fed by wood waste and forest residues, provides thermal energy to the ORC system. The electricity produced is delivered to the electric grid and the heat recovered in the condenser is delivered to domestic users. A monitoring activity has been carried out to evaluate the energetic performance in different operating conditions; the system involves both the power plant, the distribution network and the users. Furthermore, a thermodynamic model that simulates the system operation has been developed in Matlab-Simulink environment using REFPROP 9. A preliminary test of the model has been carried out comparing the numerical res...
Applied Thermal Engineering, 2015
ABSTRACT More than seventy district heating (DH) plants based on biomass are operating in South T... more ABSTRACT More than seventy district heating (DH) plants based on biomass are operating in South Tyrol (Italy) and most of them supply heat to residential districts. Almost 20% of them are cogenerative systems, thus enabling primary energy savings with respect to the separate production of heat and power. However, the actual performance of these systems in real operation can considerably differ from the nominal one. The main objectives of this work are the assessment of the energy performance of a biomass boiler coupled with an Organic Rankine Cycle (i.e. ORC) generator under real operating conditions and the identification of its potential improvements. The fluxes of energy and mass of the plant have been measured onsite. This experimental evaluation has been supplemented with a thermodynamic model of the ORC generator, calibrated with the experimental data, which is capable to predict the system per- formance under different management strategies of the system. The results have highlighted that a decrease of the DH network temperature of 10 °C can improve the electric efficiency of the ORC generator of one percentage point. Moreover, a DH temperature reduction could decrease the main losses of the boiler, namely the exhaust latent thermal loss and the exhaust sensible thermal loss, which account for 9% and 16% of the boiler input power, respectively. The analysis of the plant has pointed out that the ORC pump, the flue gases extractor, the thermal oil pump and the condensation section fan are the main responsible of the electric self-consumption. Finally, the negative effect of the subsidisation on the performance of the plant has been discussed.
The aim of this work is the energy efficiency assessment of a power plant located in Renon (Bolza... more The aim of this work is the energy efficiency assessment of a power plant located in Renon (Bolzano, Italy) integrated with a district heating system using a multistage modeling approach. The study investigates the energy performance of a 1 M W el ORC generator connected to a district heating network. A wood chip boiler, fed by wood waste and forest residues, provides thermal energy to an Organic Rankine Cycle with regenerative section. The electricity produced is delivered to the electric grid and the heat recovered in the condenser is delivered to domestic users by means of a district heating network. A monitoring activity has been carried out to evaluate the energetic performance in different operating conditions; the system involves both the power plant and the distribution network. Furthermore, a thermodynamic model that simulates the system operation has been developed in M atlab-Simulink environment using REFPROP 9. A preliminary test of the model has been carried out comparing the numerical results with the experimental data.
This work refers to an innovative integrated system for the simultaneous production of fresh wate... more This work refers to an innovative integrated system for the simultaneous production of fresh water and electricity. In particular, a 1 kWe Stirling engine coupled with a thermal desalination plant has been considered for the purpose. The prototype, which refers to the distributed micro cogeneration field, has the final aim of building and testing a single effect distillation plant with a fresh water production of about 150 L/d.
Firstly, thermodynamic theories and numerical analysis have been carried out to define the final prototype configuration. Then, an experimental test phase has been carried out to evaluate the actual plant performance.
The experimental analysis has been in good agreement with the predicted results. In particular, at nominal operating conditions (@50 °C) the maximum heat transfer rate was higher than the evaporator heat exchanger designed condition (5.5 kWt). Despite the non-ideal plant thermal insulation, fresh water production reached a maximum of about 7 L/h at best operating conditions, proving a good process efficiency. According to the behavior predicted by the model, fresh water production is strongly dependent on the temperature difference between the heating fluid and the salt water in the evaporator tank while it is weakly influenced by the salt content of the treated water. Moreover, the apparatus
exhibited a very good response to varying thermal power input thus confirming the opportunity to feed the desalination plant also with different forms of waste heat. More precisely, the plant average efficiency was about 1.3 L/kWh of energy input with minimum and maximum values equal to 1.16 and 1.42 L/kWh.
Definitely the proposed solution, studied for a coupling with a 1 kWe Stirling engine, can be easily applied also to the other micro-CHP technologies.
Applied Thermal Engineering, 2011
This paper presents the experimental results of a test-bed developed to analyze a 100 kW cogenera... more This paper presents the experimental results of a test-bed developed to analyze a 100 kW cogeneration micro gas turbine (MGT). Its main feature, flexibility, allows MGT testing in nearly all the conditions that final use may entail, in particular simulation of operating conditions and thermal loads in broadly different electrical power, flow rate and temperature conditions of the cogeneration circuit. The
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In this paper, a small non-imaging focusing heliostat is presented, and an analytical model for a... more In this paper, a small non-imaging focusing heliostat is presented, and an analytical model for assessing its performance is described. The main novelty of the system lies in the tracking mechanism and the mirror mount, which are based on off-the-shelf components and allow a good trade-off between accuracy and costs. The concentrator mirrors are moved by this two-axis tracking machinery to reflect the sun's rays onto a fixed target, the dimensions of which can be varied to suit the user's needs. A prototype plant to be located in central Italy was designed and simulated with a ray-tracing algorithm, and it comprises 90 heliostats for a total reflective area of 7.5 m 2 . The reflected solar rays are tracked taking the mechanical positioning errors of the tracking system into account. The total flux of radiation energy hitting the target was determined, and intensity distribution maps were drawn. Simulations showed that the system's optical efficiency can exceed 90% in summer, despite the tracking errors, mainly because of the smaller distance between the heliostats and the receiver. The solar concentration ratio over a receiver of 250 mm in diameter reached 80 suns with a very good uniformity. Over a 400-mm receiver, the concentrated radiation was less uniform, and the solar concentration ratio reached 50 suns, with a higher optical efficiency and collected solar radiation. The present concentration ratio is still suitable for many applications ranging from the electric power production, industrial process heat, and solar cooling.
Applied Thermal Engineering, 2015
The importance of optimal sizing of renewable microgeneration systems is addressed. A hybrid syst... more The importance of optimal sizing of renewable microgeneration systems is addressed. A hybrid system made up of solar and micro-CHP devices is considered. Both Photovoltaic and high concentration PV technologies are analysed. Optimal sizing enhances savings in dwelling sector applications. Electricity grid constraints can have the potential CO 2 emissions reduction.
The recovery of energy content of combustion flue gas in biogas-fed Stirling co-generators is stu... more The recovery of energy content of combustion flue gas in biogas-fed Stirling co-generators is studied. A spiral gasegas heat exchanger is used. Electric efficiency can be raised up to 22.5%. The system is applied to a residential case study following optimal management criteria. The extra-cost of the recuperator is paid back in less than two years.
Applied Thermal Engineering, 2013
The paper addresses a hybrid renewable system that consists of a micro-CCHP unit and a solar ener... more The paper addresses a hybrid renewable system that consists of a micro-CCHP unit and a solar energy conversion device. Both PV and High Concentrator Photovoltaic (HCPV) systems have been modelled and embedded in the hybrid system. The work identifies the optimal management strategies for variable electricity prices. Hybrid renewable systems provide a yearly primary energy reduction of between 20% and 30% compared to separate production. When the level of solar radiation is high, HCPV becomes competitive with the PV technology.
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Papers by Massimiliano Renzi
Firstly, thermodynamic theories and numerical analysis have been carried out to define the final prototype configuration. Then, an experimental test phase has been carried out to evaluate the actual plant performance.
The experimental analysis has been in good agreement with the predicted results. In particular, at nominal operating conditions (@50 °C) the maximum heat transfer rate was higher than the evaporator heat exchanger designed condition (5.5 kWt). Despite the non-ideal plant thermal insulation, fresh water production reached a maximum of about 7 L/h at best operating conditions, proving a good process efficiency. According to the behavior predicted by the model, fresh water production is strongly dependent on the temperature difference between the heating fluid and the salt water in the evaporator tank while it is weakly influenced by the salt content of the treated water. Moreover, the apparatus
exhibited a very good response to varying thermal power input thus confirming the opportunity to feed the desalination plant also with different forms of waste heat. More precisely, the plant average efficiency was about 1.3 L/kWh of energy input with minimum and maximum values equal to 1.16 and 1.42 L/kWh.
Definitely the proposed solution, studied for a coupling with a 1 kWe Stirling engine, can be easily applied also to the other micro-CHP technologies.
Firstly, thermodynamic theories and numerical analysis have been carried out to define the final prototype configuration. Then, an experimental test phase has been carried out to evaluate the actual plant performance.
The experimental analysis has been in good agreement with the predicted results. In particular, at nominal operating conditions (@50 °C) the maximum heat transfer rate was higher than the evaporator heat exchanger designed condition (5.5 kWt). Despite the non-ideal plant thermal insulation, fresh water production reached a maximum of about 7 L/h at best operating conditions, proving a good process efficiency. According to the behavior predicted by the model, fresh water production is strongly dependent on the temperature difference between the heating fluid and the salt water in the evaporator tank while it is weakly influenced by the salt content of the treated water. Moreover, the apparatus
exhibited a very good response to varying thermal power input thus confirming the opportunity to feed the desalination plant also with different forms of waste heat. More precisely, the plant average efficiency was about 1.3 L/kWh of energy input with minimum and maximum values equal to 1.16 and 1.42 L/kWh.
Definitely the proposed solution, studied for a coupling with a 1 kWe Stirling engine, can be easily applied also to the other micro-CHP technologies.