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Among cellular materials, Triply-Periodic Minimal Surfaces are promising for thermal management applications because of their high specific surface area, tortuosity, and effective thermal conductivity. In very recent years, additive manufacturing techniques are being employed in designing and printing customized 3D cellular structures, which allow to maximize their heat transfer performance. In applications where convection plays a significant role, monitoring pressure drop is important because of its contrasting role to convective heat transfer enhancement. A CFD analysis of pressure drop in air flowing through gyroid-type structures with different porosities and cell sizes is carried out and presented. Governing equations with appropriate boundary conditions are solved with a finite element commercial code. Velocity and pressure fields as well as correlations to predict the permeability and the Forchheimer coefficient, useful to designers of gyroid-type structures, are presented.

This work experimentally and numerically investigates the thermal performance of a vertical shell-and-tube heat exchanger, filled with a biological phase change material (PCM), linked to a water-chiller system for cold thermal energy storage. The system provides the cooling service to a 150 m2 single-family house. An experimental apparatus has been designed to collect the PCM temperature data through the employment of multiple thermocouples located at different heights of the heat exchanger. Starting from the experiment, a comprehensive 3D numerical model of the system has been developed based on the enthalpy-porosity method using COMSOL Multiphysics®. The PCM temperature profiles and the evolution of the solid-liquid interface location at various time instants are used as performance indicators of the model reliability and accuracy. The numerical agreement with the experimental findings is proved using statistical indices, e.g., maximum values of mean absolute error (MAE) and root mean square error (RMSE) equal to 1.18 °C and 1.33 °C, respectively, with regards to central thermocouples. The results reveal that natural convection highly affects the PCM charging/discharging processes, as proved by the PCM liquid fraction, which moves from full to 51 %, between two levels spaced by 0.78 m. The developed 3D model, based on the enthalpy-porosity method, allows to consider boundary conditions variability with both angle and height, which are not usually covered by simplified 2D models. Hence, this model confirms that only 39 % of the PCM mass experiences the complete phase change process, proving that the current design does not allow the PCM to totally exploit the thermal storage potential, thereby making optimization pivotal and challenging.

Thanks to their high effective thermal conductivity, specific surface area, and tortuosity, open-cell foams are well-known for their capability to enhance heat transfer in applications like heat exchangers or volumetric solar air receivers. In the very recent years, innovative manufacturing techniques, including 3D designing and printing, have been looked very helpful to find foam morphologies that allow to maximize heat transfer with an eye on reducing pressure drop. Optimal foam structures can be obtained by means of pore-scale simulations, employing a brute-force search with a bearable computational effort. A multi-objective optimization of convective heat transfer and pressure drop in 3D designed Kelvin foams with air is presented in this paper. A pore-scale numerical model, with a uniform heat flux solid/fluid interface boundary condition, is used to predict the interfacial convective heat transfer coefficient, h, and pressure drop, Dp, in the foam. The cell size, porosity, cell anisotropy stretching factor, as well as the inlet velocity and the direction of the air flow are assumed as the design variables for the optimization model, while the interfacial convective heat transfer coefficient and pressure drop are chosen as the objective function to be maximized and minimized, respectively. Pareto fronts ranging from h = 110 W/m 2 K and Dp = 0.766 Pa to h = 460 W/m 2 K and Dp = 51.1 Pa are predicted, within which the optimum point for the chosen foam morphology and air velocity and direction can be selected, according to the chosen criterion.

Ever-increasing heat fluxes of electronic components ask for higher performance of devices responsible for their cooling. Against that background, PCM-based heat sinks – because of their compactness, and effectiveness – are well-established solutions for thermal management issues. Even though solutions for the thermal enhancement of PCM devices have been widely presented, new ways to optimize such systems are emerging. Among them, this work investigates the application of density-based topology optimization to define innovative heat sinks design able to minimize thermal resistance under constant wall temperature. A 2D numerical model is developed by means of a finite element tool. The heat equation is solved for the topology optimization problem with the objective of minimizing the average temperature, considering further manufacturing restrictions. Solid-isotropic-material-with-penalization (SIMP) method is applied to link the design variable to material properties. Parameterization of Helmholtz filter’s minimum feature size and projection based on the hyperbolic tangent function is performed, showing improved performance as well as feature size decrease. The optimized prototype – with PCM – is then simulated with the enthalpy-porosity model to assess the benefits, i.e., reduction in the melting time, with respect to the baseline. Results show the potential of optimizing heat sinks via a topology-based approach and confirm it as a promising tool for finding new heat sink geometry, whatever the application.

The national and international building stock – representing one of the most intensive energy-consuming sectors worldwide – is characterized by a large share of old constructions, designed without following any energy criteria. This scenario has promoted the rising of powerful technologies, e.g., Additive Manufacturing (AM), which despite its recent rise is leading the innovation process involving both the industrial and civil sectors. 3D printing techniques are going to outperform current production techniques because of their various advantages, i.e., design of complex forms, uniform materials, reduced production steps and costs. The aim of the present work is to combine the accuracy of computer-aided design (CAD) for AM structures with the benefits of the computational thermo-fluid dynamic simulation (CFD) to perform thermal and moisture performance analysis of innovative building walls. Natural convection and radiation problem – involving buoyancy-driven flow in a cavity – is investigated and solved under appropriate boundary conditions defined in a finite element commercial code. After validation with international guidelines and literature data, the model is simulated in Napoli (Italy) under winter design conditions. Moreover, this work provides a comparison between a simplified procedure for the condensation risk detection, i.e., the Glaser method, and an advanced one – based on the steady-state diffusion theory – which considers latent heat effect and capillary transport of moisture liquid. The results show that the radiative heat transfer mechanism has a significant influence on thermal transmittance. On the other hand – with reference to the case study – here we present the discrepancy between the prediction of the condensation effect during the winter months by adopting the present method with respect to the Glaser one

The energy retrofit of the building stock is a central issue in the view of reduction of energy consumption and climate change. The energy efficiency measure proposed in this study provides first the application of a double skin facade and the evaluation of the positive and negative effects due to this measure; then, in a second phase, to counteract the possible negative effects, a control logic for opening windows of the double skin facade is defined. These windows respond dynamically to variation of external conditions by allowing an air flow from the cavity to the internal environment in winter period and from the cavity to the external environment in summer period. The building under investigation belongs to the University of Naples Federico II and it is dedicated to offices. The building geometry and the characterization of building envelope and systems installed are realized with the graphical software DesignBuilder®, while EnergyPlus software is used for the dynamic simulation of the building thermal and energy performance. The control logic for the opening of the windows is defined through the module Airflow Network of EnergyPlus. The energy benefit in terms of reduction of primary energy demand for the space heating and cooling reaches values of 44.4% and 8.4%, respectively. Finally, semi-transparent a-Si photovoltaic modules (efficiency of 4 %) are integrated into the facade. When they cover the half area of the external facade, there is a production of 5120 kWh/year and a saving of 11.2% in electricity consumption.

The redevelopment of the existing building stock is essential to reach sustainability goals, worldwide. The energy retrofit measure analyzed in the study is based on the installation of a double skin facade with the integration of transparent photovoltaic on a structural exoskeleton that has the function of providing the building with a higher level of structural and seismic safety. The examined building is an Italian typical building construction of the 60s and 70s, i.e., it represents an archetype building and not a real building. After carefully collecting the input data, the graphical software DesignBuilder® is used to model the building geometry and the HVAC systems, while EnergyPlus software is used for dynamic energy simulation. The model is validated against the energy need for the type of reference buildings. Initially, the effect related to the double skin façade is assessed, and then a gradual inclusion of the transparent photovoltaic is implemented. Therefore, the energy benefit, in terms of primary energy consumption, due to the combined use of the two technologies is evaluated. When PV panels cover the entire area of the external facade, a saving of 55% in primary energy consumption is achieved.

The current World situation is particularly complex and heavy, from many points of view, among which energy and socio-economic ones. The COVID-19 pandemic, besides causing a health crisis, has brought out, even more, the need to reduce emissions for a healthier environment. The role played by the existing building stock is fundamental, as it is responsible for 36% of CO2 emissions in Europe. The proposed work aims to define some energy refurbishment interventions, for a residential building in south Italy, regarding the building envelope, the heating and cooling systems, and the addition of systems from renewable energy sources in order to improve its energy labeling. The methodological approach has followed the guidelines for the energy certification of buildings in Italy. It was possible to evaluate the improvement in building energy labels according to the proposed efficiency measures, highlighting those which allow for a tax relief recently introduced by the Government. Finally, the addition of photovoltaic and solar collector systems was evaluated to allow even the fulfillment of nZEB standard.

Environmental problems have offered new challenges to the energy production sector, starting from the need of increasing the efficiency of thermodynamic systems to preserve fuel consumption. Accordingly, multi-energy generation systems are among the most efficient generation systems, and Heat Recovery Steam Generators (HRSGs) represent key components of such systems. In this regard, this paper shows a comprehensive approach to optimize a HRSG by using a multi-objective Genetic Algorithm (GA). The aim is to highlight how to determine the optimal values of geometrical and thermodynamic design variables according to two objective functions: the global costs to be minimized and the steam turbine output power to be maximized. Starting from a reference HRSG design, thermodynamic modeling and simulations as well as the optimization procedure are performed in MATLAB®. A validation is carried out to show the accuracy of the modeling approach. Latin Hypercube Sampling is applied to create a uniform sample to select the design variables based on a global sensitivity analysis, producing a significant reduction of computational efforts. Then, the GA optimization is performed to achieve the Pareto front, collecting the best trade-off design solutions. Economic savings up to 20% are achieved limiting the HRSG size.

The paper proposes a multi-objective optimization approach to address the energy design of the building envelope. A genetic algorithm (GA) is implemented by means of the coupling between MATLAB® and EnergyPlus to minimize primary energy consumption (PEC), energy-related global cost (GC) and discomfort hours (DH). The design variables concern the set point temperatures, the radiative properties of plasters, the thermo-physical properties of envelope components, the window type, the building orientation. The GA performs a Pareto optimization and finally two optimal solutions are recommended: the nZEB (nearly zero energy building) optimal solution, which minimizes PEC, and the cost-optimal solution, which minimizes GC. These solutions provide the optimal design strategies for the public and private stakeholders, respectively, which represent the main actors involved in building design. The approach is applied for the design of a new typical Italian residential building. Four locations are considered to investigate the typical Italian climates. The outcomes can give precious indications to rebuild the Italian residential stock with a view to energy-efficiency and cost-optimality, given that the optimal solutions provide low values of PEC – between 62.0 and 91.9 kWhp/m2a – and of GC – between 456 and 665 €/m2 – depending on the location.

Hospitals are complex structures that require the highest energy intensity of the building sector. Thus, in both cases of new construction and retrofit, their proper energy design and management are a critical issue, because these must consider all levers of energy performance, from the building envelope to the operation and efficiency of energy systems. Furthermore, different objective functions to minimize can be pursued, for example, energy consumption, thermal discomfort, lifecycle costs, and polluting emissions. Definitely, comprehensive approaches are required to address the aforementioned issues. The chapter provides an overview of these approaches by showing the application to different case studies.