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Thermoacoustic (TA) oscillations have been one of the most exciting discoveries of the physics of fluids in the 19th century. Since its inception, scientists have formulated a comprehensive theoretical explanation of the basic phenomenon which has later found several practical applications to engineering devices. The most common devices are the so-called TA engines (prime movers) and refrigerators (heat pumps). These devices are distinguished by the direction in which they perform energy conversion. While a traveling sound wave propagates through a TA regenerator with a positive temperature gradient, the gas parcels experience a Stirling-like thermodynamic cycle, so that thermal energy can be converted into acoustic power cyclically. The most fascinating feature of TA engines is its capability of utilizing low-grade external heat sources, such as industrial waste heat and solar thermal energy to produce acoustic power, which can be easily converted into electricity using piezoelectric elements. The absence of moving parts in TA engines is another advantage over conventional heat engines, which demonstrates the potential for developing low-cost and reliable power generators. To-date, significant research efforts have been made to develop TA coolers and electric generators, but all studies have concentrated on fluid media where this mechanism was exclusively believed to exist. This research extends the idea of thermoacoustic instability to solid media and lays the theoretical foundation of Solid-State Thermoacoustics (SSTA). This new paradigm uncovers the fundamental idea that a self-sustained TA response can be achieved also in solid media. Although the underlying physical mechanism exhibits interesting similarities with its counterpart in fluids, the theoretical framework highlights relevant differences that have important implications on the ability to trigger and sustain the TA response. This work shows both theoretically and numerically that TA instability can be achieved in solids in the form of both longitudinal standing and traveling waves, the most logical counterpart to pressure waves in gases. However, mechanical waves in solids are polarized, hence leading to multiple mode types unlike pressure waves in fluids. This research also reveals the existence of thermoacoustically excited flexural waves and presents theoretical and numerical analyses of flexural-mode thermoacoustic waves in a bilayer beam. Experimental investigations are conducted to confirm the thermo-mechanical energy conversion associated with the flexural motion. In contrast to conventional fluid-based thermoacoustics, SSTA systems offer the capability to leverage the tunable thermo-mechanical properties of engineered materials to improve thermoacoustic instabilities. Numerical evidence of using negative thermal expansion materials to intensify both axial-mode and flexural mode thermoacoustic intensities are shown in this work, which sheds light on the practical design and application of SSTA devices. This research opens a unique window on the use of solid materials as working substances to overcome the shortcomings of traditional thermoacoustic devices. Based on the fundamental theoretical and numerical explorations conducted in this research, it is believed that SSTA provides a promising path towards the development of more robust, more powerful, more cost-effective and more eco-friendly thermo-mechanical energy conversion devices, hence promoting practical applications and commercialization of thermoacoustic technologies.

To achieve an adequate quality of buildings it is necessary to consider a set of aspects that are interconnected and influence each other, not always in a favourable way. The selection of the most suitable construction solution for the building elements must consider its contribution to the thermal and acoustic comfort inside the buildings, the daylight conditions, its energy efficiency and sustainability, and also the weight of the solution and its effect on the structural project of the building. In this work, the use of a multi-criteria analysis, to balance all these aspects on the design phase, in order to assist the designer in the selection of construction solutions and materials, will be presented. The selection of the most adequate construction solutions will increase the buildings thermal and acoustic behaviour and also its energy performance and sustainability. (undefined)

The energy efficiency of buildings is nowadays one of the main concerns of the construction market. But, Indoor Environmental Quality of Buildings (IEQ) should not be disregarded. To achieve an adequate quality of buildings it is necessary to consider a set of aspects that are interconnected and influence each other, not always in a favourable way. The selection of the most suitable construction solution and materials for the building elements must consider its contribution for the IEQ (thermal and acoustic comfort, daylight conditions and the indoor air quality) inside the buildings, its energy efficiency and its environmental impact (considering the embodied energy, for example), but also the weight of the solution and its effect on the structural project of the building. The solutions adopted in buildings, usually, only optimize no more than one of the necessary comfort requirements. In many cases, the best solutions to accomplish different comfort requirements are not compatible, especially in what concerns natural ventilation and lighting strategies and the acoustic and thermal performance. So, it is necessary to have an integrated approach to ensure the best overall behaviour taking into account all of the, sometimes incompatible, comfort and energy efficiency requirements. In this work the use of a multi-criteria analysis, to balance all these aspects on the design phase, in order to assist the designer in the selection of construction solutions and materials will be presented. The selection of the most adequate construction solutions will increase the buildings IEQ, energy performance and also its environmental impact.

Building rehabilitation is essential to achieve the targets defined by the EPBD recast regarding energy efficiency, reduction of carbon emissions and use of on-site renewable energy sources. Besides the energy efficiency the Indoor Environmental Quality of Buildings (IEQ) and environmental impact must also be considered when planning a refurbishment project. Thus to propose an effective building rehabilitation is necessary select the adequate construction solutions taking into account their impact on the energy performance, thermal and acoustic comfort, indoor air quality and environmental impact of the building. In this work a multi-criteria decision analysis method, ELECTRE III, is applied to balance all these aspect, during the design phase of a refurbishment project, in order to assist the design team on the selection of construction solutions. Throughout the multi-criteria analysis performed, it was possible to verify that the rehabilitation solutions with lower embodied energy were the best refurbishment options.

Due to buildings high energy consumption their refurbishment is essential to achieve the targets defined by the EPBD-recast regarding energy efficiency and reduction of carbon emissions. Besides the energy efficiency, the sustainability and the Indoor Environmental Quality (IEQ) of Buildings must also be considered when planning a refurbishment project. Thus, to propose an effective building refurbishment it is necessary to select the adequate construction solutions taking into account their impact on the energy performance, thermal and acoustic comfort, indoor air quality and environmental impact of the building. In this work a multi-criteria decision analysis method is applied to balance all these aspects in a refurbishment project, in order to assist the design team on the selection of the construction solutions. Throughout the multi-criteria analysis performed, it was possible to verify that the rehabilitation solutions with lower embodied energy were the best refurbishment options.

Abstract Sound absorption materials structure is generally based on porous synthetic media (rock wool, glass wool, polyurethane, polyester, ect.): they have expensive production processes, important energy consumptions, and high environmental impact. Recycled materials are becoming an interesting alternative, due to their good acoustic behavior, similar to traditional porous materials; they also allow low impact production costs, thanks to the use of wastes derived from other production cycles. This work focuses on the evaluation of the acoustic absorption properties of new panels made of recycled paper and other scrap materials, as wool and nonwoven polyester fabric: different samples were produced and tested by means of impedance tube, according to ISO 10534-2. In order to present the environmental benefits, Life Cycle Assessment was carried out in terms of primary embodied energy and greenhouse gas emissions, considering a “cradle-to-gate” approach. Furthermore, the behavior of innovative absorption materials was investigated in order to improve the acoustic performance of a lecture room, by means of an acoustic simulation software. A comparison with traditional materials was also carried out for both acoustic and environmental aspects. In the simulation model, calibrated by an in-situ experimental campaign of the main acoustic quality indexes (Reverberation Time, Clarity and Definition Indexes, Speech Transmission Index), different acoustic correction solutions were implemented: both the new recycled and traditional panels were applied as wall and ceiling absorbers. The analysis of the acoustic absorption trends, in 100 - 5000 Hz frequencies range, shows that the new materials are suitable as acoustic correction systems, especially the panel composed by waste paper and wool fibers. The LCA analysis results show that, considering the same acoustic performance, the recycled panels allow to reduce the environmental effects and the global production costs.

AbstractAn implementation of the sustainable development idea in the building sector stimulates search for materials and structures providing better heat insulation. Because the acoustical expectations and requirements also rise, a need for harmonization of both parameters increases. The article demonstrates differences between thermal and acoustical behavior of various building elements. The analysis of measurement results obtained for different structures demonstrates that finding a simple relationship between acoustical and thermal insulations is quite difficult. Tendencies observed in each case are rather opposite than parallel and materials or technical solutions that improve thermal resistance of a building partition often deteriorate its acoustic performance.

At the present time, buildings technologies for residential constructions are essentially divided into two groups. The first one is associated to conventional techniques using concrete, masonry or in general heavyweight structures, while the second one is associated to timber, e.g., sustainable glulam, crosslam, etc. (lightweight structures). Technicians, scientist, designers and non-expert people have their own stereotyped ideas and attitudes, related to thermal and sound insulation, structural stability, fire resistance, service equipment, heating and cooling systems, etc. Nevertheless, for people who is not strongly related to both construction procedure studies, analysis, experiences or focuses, timber structures appear to be more comfortable, reliable and insulated. The need of investigating the role of non-physical and non-measurable parameters in affecting future inhabitants’ overall preconceptions related to new sustainable buildings is thus of paramount importance. The hypothesis that behavioral, physiological, past experiences and psychological factors can have a non-negligible role in determining the final user perception, interaction and adaptation to timber buildings has to be verified. For these reasons, an international survey was realized in order to investigate what individuals expect from these two different construction technologies. After focused statistical analysis, it could be demonstrated how geographical difference could influence results and that, for indoor comfort, stereotypes do exist for lightweight buildings in comparison to heavyweight ones, highlighting how timber construction are associated to thermal comfort and sensed as innovative even if there is no complete distrust in conventional ones. The influence of non-physical and non-measurable parameters is correlated to people’s attitudes.