Elena Morini

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.

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.