Mirko Filipponi

An energy-balanced analytic model for urban heat canyons: comparison with experimental data

The climate of high-density urban areas is often affected by the air temperature increase with respect to the neighbouring country-side. This phenomenon, known as the urban heat island (UHI) effect, is strongly influenced by the solar reflectance of building envelope and coating materials, and it is enhanced in the presence of built patterns that trap the solar and anthropogenic energy, usually referred to as urban heat canyons. An original method to quantify the urban heat canyon effect as a function of meteorological conditions, geometry, and surface properties is proposed. The goal is to provide a reliable tool to estimate the effect of the reflective properties of the canyon surfaces on the urban environment, in order to guide the choice of effective solution towards the UHI mitigation. An energy-balanced analytic model, specifically set-up to predict surface temperatures inside an urban canyon, is applied to a scale test facility located at the University of Perugia, Italy. The test facility is made of two twin arrays resembling urban canyons with different aspect ratios. Each canyon can be equipped with reflective films to quantify the radiative exchange variation. Preliminary results from the experimental facility monitoring and the analytic model validation are presented.

Cool roofs as a strategy to tackle global warming: economical and technical opportunities

There is a growing consensus within the scientific community that the Earths climate system is unequivocally warming and it is very likely (according to the formal uncertainty language used in the AR4, the term “very likely” refers to >90% assessed probability of occurrence) due to the increase in anthropogenic greenhouse gas concentrations. Urgent solutions need to be adopted, which are environmentally sustainable, in order to tackle global warming in the short term. At present, the most accredited global warming mitigation methods are represented by the emissions reduction technologies. Such technologies include energy from renewable sources such as solar and wind. A potential alternative is to modify the Earths albedo by reflective surfaces (pavements and roofs), which are already employed to reduce building energy consumption and to mitigate heat island effects. In this paper a procedure is proposed which evaluates the influence of changes in the Earths albedo on the Earths temperature and, as a consequence, quantifies the high albedo surface size required to compensate or offset global warming from changes in CO2. Additionally, a technical-economical comparison is carried out here between the proposed albedo system and the main technologies for the production of electric and thermal energy from renewable sources in order to evaluate its effectiveness in terms of cost of carbon dioxide equivalent (CO2eq) emission reduction.

A Cylindrical Molten Carbonate Fuel Cell Supplied with Landfill Biogas

A small size cylindrical Molten Carbonate Fuel Cell stack was installed at Giugliano landfill in Italy. The stack was constituted by 16-cells with a 300 W nominal power. Preliminary tests were performed in order to verify the possibility to supply the stack by the landfill biogas, characterized by low methane content (32%). Results showed that the proposed plant is able to correctly operate also when supplied with low methane content biogas.

Use of Molten Carbonate Fuel Cell for CO2 Capture

The adoption of technologies for the separation, capture and subsequent storage of CO2 for geological time periods through injection into the subsoil (CCS, Carbon Dioxide Capture & Storage), has emerged as a key approach to reduce CO2 emissions from upstream emitting sources, to comply with EU-ETS directives on emissions control, which force polluting industries to reduce their CO2 emissions below given limits. However, the significant investments required, and the energy intensive nature of conventional capture processes, have fuelled the ongoing debate on the effectiveness of this means of reducing CO2 emissions. This thesis considers, as an alternative to conventional CCS, non-conventional systems to capture and concentrate emissions, through the use of both a Molten-carbonate fuel cell (MCFC) configured as an electrical power generator, and the same fuel cell configured as an electrolyser (MCEC), therefore absorbing a limited amount of electrical power. These systems will be set up in a cascade in settings which reproduce typical conditions of large scale high- CO2 emission environments, and compared through a technical-economic analysis.

Control of Noise from a Fan in a Wall Gas Boiler

Methods for reducing noise emissions from a fan in a wall gas boiler are investigated. Sound power and vibration measurements are conducted in order to identify the effect of noise reduction treatments. Numerical simulations and measurements of volume flow and temperature, before and after the installation of noise treatments, were conducted. A 3.5 dB reduction in the acoustic power and a 5.0 dB reduction in the vibration levels are achieved. The performance of the boiler was not affected by the noise control treatments.

Energetic Analysis of Solar-Supplied Processes for Methane, Biogas and Wood Chip Production

An interesting application of solar energy for methane production is here analysed in terms of energetic efficiency. The application (called Solargas) is constituted by photovoltaic (PV) panels, an electrolyser and a Sabatier reactor. PV panels pick up the solar energy to supply the electrolyser. The electrolyser produces hydrogen from water; the produced hydrogen is used in a Sabatier reactor to obtain methane. Solargas system is here compared to typical biogas and wood chip production systems in terms of the ratio between the output fuel energy and the input solar energy.

Use of phase change materials during compressed air expansion for isothermal CAES plants

Compressed air energy storage (CAES) plants are designed to store compressed air into a vessel or in an underground cavern and to expand it in an expansion turbine when energy demand is high. An innovative CAES configuration recently proposed is the isothermal process. Several methods to implement isothermal CAES configuration are under investigation. In this framework, the present paper deals with the experimental testing of phase change materials (PCM) during compressed air expansion phase. The experimental investigation was carried out by means of an apparatus constituted by a compression section, a steel pressure vessel, to which an expansion valve is connected. The initial internal absolute pressure was equal to 5 bar to avoid moisture condensation and the experimental tests were carried out with two paraffin-based PCM amounts (0.05 kg and 0.1 kg). Results show that the temperature change during air expansion decreases with increasing the PCM amount inside the vessel. With the use of PCM during expansions an increase of the expansion work occurs. The increase is included in the range from 9.3% to 18.2%. In every test there is an approach to the isothermal values, which represent the maximum theoretical value of the obtainable expansion work.