Beatrice Castellani

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.

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.

Carbon and energy footprint of the hydrate-based biogas upgrading process integrated with CO2 valorization

The present paper aims at assessing the carbon and energy footprint of an energy process, in which the energy excess from intermittent renewable sources is used to produce hydrogen which reacts with the CO2 previously separated from an innovative biogas upgrading process. The process integrates a hydrate-based biogas upgrading section and a CO2 methanation section, to produce biomethane from the biogas enrichment and synthetic methane from the CO2 methanation. Clathrate hydrates are crystalline compounds, formed by gas enclathrated in cages of water molecules and are applied to the selective separation of CO2 from biogas mixtures. Data from the experimental setup were analyzed in order to evaluate the green-house gas emissions (carbon footprint CF) and the primary energy consumption (energy footprint EF) associated to the two sections of the process. The biosynthetic methane production during a single-stage process was 0.962Nm3, obtained mixing 0.830Nm3 of methane-enriched biogas and 0.132Nm3 of synthetic methane. The final volume composition was: 73.82% CH4, 19.47% CO2, 0.67% H2, 1.98% O2, 4.06% N2 and the energy content was 28.0MJ/Nm3. The functional unit is the unitary amount of produced biosynthetic methane in Nm3. Carbon and energy footprints are 0.7081kgCO2eq/Nm3 and 28.55MJ/Nm3, respectively, when the electric energy required by the process is provided by photovoltaic panels. In this scenario, the overall energy efficiency is about 0.82, higher than the worldwide average energy efficiency for fossil methane, which is 0.75.

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.