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Abstract:Urban waste management is one of the most challenging issues in energy planning of medium and large cities. In addition to the traditional landfill method, many studies are investigating energy harvesting from waste, not as a panacea but as a foreseeable solution. Thermo-chemical conversion to biogas, or even bio-methane under certain conditions, could be an option to address this challenge. This study focuses on municipal solid waste conversion to biogas as a local energy supply for the cities. Three urban models and their subdivision into urban areas were identified along with a typical Organic Fraction of Municipal Solid Waste (OFMSW) matrix for each urban area. Then, an energy analysis was carried out to provide an optimization map for an informed choice by urban policy-makers and stakeholders. The results highlighted how the urban context and its use could affect the opportunity to produce energy from waste or to convert it in fuel. So, in this case, sustainability means waste turning from a problem to a renewable resource.

Stationary and dynamic heat and mass transfer analyses of building components are an essential part of energy efficient design of new and retrofitted buildings. Generally, a single constant thermal conductivity value is assumed for each material layer in construction components. However, the variability of thermal conductivity may depend on many factors; temperature and moisture content are among the most relevant ones. A linear temperature dependence of thermal conductivity has been found experimentally for materials made of inorganic fibers such as rockwool or fiberglass, showing lower thermal conductivities at lower temperatures. On the contrary, a nonlinear temperature dependence has been found for foamed insulation materials like polyisocyanurate, with a significant deviation from linear behavior. For this reason, thermal conductivity assumptions used in thermal calculations of construction components and in whole-building performance simulations have to be critically questioned. This study aims to evaluate how temperature affects thermal conductivity of materials in building components such as exterior walls and flat roofs in different climate conditions. Therefore, experimental conductivities measured for four common insulation materials have been used as a basis to simulate the behavior of typical construction components in three different Italian climate conditions, corresponding to the cities of Turin, Rome, and Palermo.Energies 2018, 11, 872 2 of 17 new EU economy [6] since the finance of energy efficiency can be unlocked by public and private partnership and not rely only on EU funds [7]. Considering the problem of space heating demand reduction, heat losses can be decreased by improving envelope performance with increased levels of insulation. This measure is the most effective way to drastically reduce heating demand, considering, of course, dependence on climate conditions [8]. However, in the existing building stock, this measure is much more costly than the replacement of boilers in heating systems [9,10]. Nonetheless, there are evident synergies between building envelope performance enhancement and sizing and operation of technical systems [11], even in the case of advanced energy conversion systems [12]. Following this evidence, many research efforts have been concentrated on the definition of methodologies [13] for the determination of cost-optimal levels of energy performance [13] in new and retrofitted buildings [14,15], and the impact of insulation can be extremely relevant in modelling [16]. Clearly, a reasonably robust performance estimate [17] is necessary to evaluate project feasibility. In this sense, uncertainty of energy performance represents an issue in techno-economic assessment methodologies and relevant sources of uncertainty have to be considered to limit as much as possible the "performance gap" [18], or side effects such as "re-bound" [19], "pre-bound" [20], and overheating risk [21]. These effects could potentially undermine the credibility of energy efficiency practices and...

The present paper aims at assessing the carbon and energy footprint of an innovative process for carbon dioxide recycling, with flue gas as feedstock of nitrogen and carbon dioxide. Nitrogen is converted into ammonia through the Haber-Bosch process and carbon dioxide into methane via Sabatier reaction using hydrogen produced by renewable electricity excess. Carbon and energy footprint analysis of the process was assessed based on experimental data related to hydrogen production by electrolysis, methane synthesis via Sabatier reaction, energy consumption and energy output of the process units for flue gas separation, carbon dioxide methanation and ammonia synthesis. A Life Cycle Assessment method is applied, based on the experimental and computational data, both in case of renewable electricity excess and electricity from the grid. Results show that in case of renewable electricity excess, for a functional unit of 1 kg of treated flue gas, the specific carbon footprint is 0.7819 kg CO2eq and energy footprint is 50.73 MJ, which correspond to 4.012 kg and 260.3 MJ per 1 kg of produced hydrogen. In case of electricity from the grid, the specific carbon footprint is 1.550 kg CO2eq and energy footprint is 59.12 MJ per flue gas mass unit. If the carbon footprint is positive, the process indirectly leads to avoided emissions, ranging from 0.673 to 0.844 kg CO2eq kg −1 fluegas , thus proving the sustainability of the proposed pathway.

Electrification of the built environment is foreseen as a main driver for energy transition for more effective, electric renewable capacity firming. Direct and on-time use of electricity is the best way to integrate them, but the current energy demand of residential building stock is often mainly fuel-based. Switching from fuel to electric-driven heating systems could play a key role. Yet, it implies modifications in the building stock due to the change in the temperature of the supplied heat by new heat pumps compared to existing boilers and in power demand to the electricity meter. Conventional energy retrofitting scenarios are usually evaluated in terms of cost-effective energy saving, while the effects on the electrification and flexibility are neglected. In this paper, the improvement of the building envelope and the installations of electric-driven space heating and domestic hot water production systems is analyzed for 419 dwellings. The dwellings database was built by means of a survey among the students attending the Faculty of Architecture at Sapienza University of Rome. A set of key performance indicators were selected for energy and environmental performance. The changes in the energy flexibility led to the viable participation of all the dwellings to a demand response programme.

EU targets for sustainable development call for strong changes in the current energy systems as well as committed protection of environmental resources. This target conflicts if a policy is not going to promote the compatible solutions to both the issues. This is the case of the additional renewable energy sources to be exploited for increasing the share in the electricity mix and in the gross final energy consumption. Solar energy is, currently, the cheapest solution in Southern European Countries, like Italy. In this paper, thanks to the availability of three open databases provided by National Institutions, the authors compared the historic trends and policy scenarios for soil consumption, electricity consumption, and renewable electricity production to check correlations. The provincial scale was chosen as resolution of the analysis. The deviations from the policy scenarios was then addressed to identify the demand for policy recommendations and pathways to promote in order to achieve the target for renewable electricity share as well as the reduction in soli consumption trend in 2030. The role of renewables integrated in the existing contexts, such as building integrated photovoltaics, is considered a key driver for solving this issue.