Roberto de Lieto Vollaro

Buildings Energy Efficiency: Interventions Analysis under a Smart Cities Approach

Most of the world’s population lives in urban areas and in inefficient buildings under the energy point of view. Starting from these assumptions, there is the need to identify methodologies and innovations able to improve social development and the quality of life of people living in cities. Smart cities can be a viable solution. The methodology traditionally adopted to evaluate building energy efficiency starts from the structure’s energy demands analysis and the demands reduction evaluation. Consequently, the energy savings is assessed through a cascade of interventions. Regarding the building envelope, the first intervention is usually related to the reduction of the thermal transmittance value, but there is also the need to emphasize the building energy savings through other parameters, such as the solar gain factor and dye solar absorbance coefficients. In this contribution, a standard building has been modeled by means of the well-known dynamic software, TRNSYS. This study shows a parametrical analysis through which it is possible to evaluate the effect of each single intervention and, consequently, its influence on the building energy demand. Through this analysis, an intervention chart has been carried out, aiming to assess the intervention efficiency starting from the percentage variation of energy demands.

Accuracy of lumped-parameter representations for heat conduction modeling in multilayer slabs

Heat conduction in homogeneous solids can be studied by resorting to one-dimensional schemes, as is often done, e.g., for building construction elements. In such situations, a simple model often employed makes use of an electrical analogy between temperature and heat flux, on one side, and voltage and electrical current on the other side. Within this framework, a few lumped-parameter representations have been described in literature to describe the thermal behavior of a single homogeneous slab or of multilayer slabs. Such models have the advantage of providing some physical insight into the phenomenon of one-dimensional heat conduction, by conveying the concepts of thermal resistance and thermal capacitance, the latter related to heat storage ability. There is, however, a certain degree of approximation in such models. The simplifying assumptions and approximations underlying these approaches will be reviewed and discussed in this contribution.The accuracy of some lumped-parameter model will be analyzed in order to show under which circumstances the approximate solutions can be satisfactorily employed. In particular, the focus will be on the comparison of the predictions that approximate and accurate methods provide when studying the influence of layer order and distribution on the thermal performance of multilayer structures.

Predictive Models for Evaluating Mobility Buses Thermal Performance

Every day, in every city, many buses are moving, carrying a lot of citizens. During the year, especially during the summer, buses become uncomfortable places because of both environmental and internal conditions. Due to the rising of the mobility needs, time that people spend in vehicles has strongly grown. Moreover, also the thermal environment in urban buses changes greatly, in fact passengers onboard are exposed to local heating and/or cooling due to vertical temperature gradients, radiant asymmetry and local unexpected airflow. This study aims to optimize the energy performance of a bus envelope, identifying practical solutions. The analysis was carried out numerically, considering a hot day during July and passengers on board during the 24 hours per day.

Natural Convection of Nanofluids in Enclosures Heated Laterally and Underneath

A two-phase mixture model is used to study natural convection in a square cavity filled with CuO+H2O nanofluids, in the hypothesis of temperature-dependent physical properties, assuming that Brownian diffusion and thermophoresis are the primary slip mechanisms between solid and liquid phases. The cavity is heated at one side and cooled at the opposite side, whereas the horizontal walls are assumed either both adiabatic, or the bottom heated and the top cooled. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. It is found that, owing to the effects of the slip motion occurring between solid and liquid phases, the rate of heat transferred across the cavity by the nanofluid in the heating-from-below configuration is remarkably higher than that transferred by the pure base liquid. Moreover, in this particular configuration the addition of nanoparticles to the base liquid generates periodicity in heat transfer. Additionally, the heat transfer enhancement is discovered to increase as the imposed temperature difference is increased, showing a smooth maximum at an optimal particle loading.

Dimensionless correlating-equations for predicting the optimal tilting angle of water-filled square and shallow enclosures differentially heated at sides

Laminar natural convection heat transfer inside water-filled, tilted square and shallow cavities heated at one side and cooled at the opposite side, is studied numerically. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. Simulations are performed using the Rayleigh number based on the length of the heated and cooled sides, the height-to-width aspect ratio of the enclosure, and the positive tilting angle with respect to the gravity vector (which corresponds to configurations with the heated wall facing upwards), as independent variables. It is found that the heat transfer performance has a peak at an optimal tilting angle which increases as the Rayleigh number is decreased and the aspect ratio is increased. On the basis of the results obtained, a set of dimensionless correlations is developed.

Buoyancy-Induced Convection in a Square Enclosure Discretely Heated at One Side and Cooled either at the Top or at the Bottom Using both Gases and Liquids as Working Fluids

Laminar natural convection heat and momentum transfer in fluid-filled, square enclosures partially heated at one side and cooled either at the top or at the bottom, is studied numerically. A computational code based on the SIMPLE-C algorithm is used to solve the system of the mass, momentum and energy transfer governing equations. Simulations are performed using the Rayleigh number based on the cavity width, the thermally-active fraction of the partially heated sidewall, and the Prandtl number of the working fluid, as independent variables. It is found that the top cooling is definitely more efficient than the bottom cooling. In both cooling configurations the average Nusselt number of the cavity increases as each controlling parameter is increased. On the basis of the results obtained, a set of dimensionless correlations is developed.