• Energy Research

The EPBD, together with other acts and funding programs, strongly promotes the passive strategies in order to achieve, above all in summer, indoor comfort conditions, reducing or avoiding the active air-conditioning. The adoption and the design of these strategies are not indifferent to the specific boundary conditions. In this paper, the performances achievable adopting an earth-to-air heat exchanger for an air-conditioned building are evaluated for winter and summer. The analysis has been carried out on varying the main boundary conditions related to the environmental context, the soil, the tube properties and connected behaviours of the airflow crossing it. Several control strategies have been simulated too, in order to propose the most suitable design criteria for each climate. The fan electrical energy represents a design critical aspect, requiring an accurate evaluation, in order to achieve the maximum thermal exchange and limiting the pressure drops inside the buried pipes. Otherwise, the use of an EAHX can be also penalizing.

Abstract Nowadays the study of Net Zero Energy Buildings (NZEBs) is fundamental, because they are the main strategy to reduce the building energy demand and CO2-equivalent emissions. This paper analyses a case study concerning a multipurpose building located in Palermo (Southern Italy), and evaluates the benefits related to the use of an earth-to-air heat exchanger in a NZEB, in terms of energy saving and reduction of CO2-equivalent emissions, for a Mediterranean climate. The chosen building envelope is thermally performing. The HVAC system consists in fan-coil units connected to an air-to-water heat pump, and mechanical ventilation. The energy demand is reduced by an earth-to-air heat exchanger that pre-heats the ventilation outside air in winter and cools it in summer. The optimization of the heat exchange with the ground is a key-element to reduce the primary energy requirements and CO2-equivalent emissions, especially during summer. Moreover, this paper assesses the possibility to obtain a NZEB using only on-site renewable energy (on the roof of the building), with and without the earth-to-air heat exchanger. The energy analysis is carried out by means of a dynamic building simulation engine, namely EnergyPlus. In addition, a thermal performance and an environmental analysis are performed.

Abstract In order to deliver the European energy and climate objectives to 2050, significant changes are essential in the building sector, especially regarding the existing stock. Indeed, there is a huge potential for action, also regarding historic buildings. In this regard, today the question is: how to combine the building protection requirements and the application of energy efficiency measures? This paper tries to answer, evaluating if the refurbishment of historic architectures, in order to achieve very low energy need, is possible and economically feasible. More in detail, the applicability of the cost-optimal methodology (EPBD Recast 2010/31/EU) for historic buildings is discussed, by adopting the macroeconomic perspective, in order to take into account of the energy, environmental and economic impacts of about 60 packages of energy efficiency measures. The study is aimed to introduce a methodological approach to define reference buildings for historic architectures, through in-situ investigation of structural and energy peculiarities and, as real case study, the refurbishment of an Italian building of the XV century is presented. Moreover, guidelines are proposed to properly select energy efficiency measures, according to a point of view of cost-optimality. Conservation, aesthetical requirements, structural and energy issues are considered, as well as the incidence of all economic factors.

Abstract The advantages of desiccant-based air conditioning systems, compared to conventional ones based on the dehumidification by cooling, have been highlighted in many research papers. The energy saving and the reduction of the environmental impact are higher when the desiccant material is regenerated by using “free” thermal energy (for example, waste heat from cogenerators or solar energy). Further investigation on the performance of the desiccant wheel is useful: therefore, in this paper, an experimental analysis on this component is presented, with particular attention to the variation of the performance as a function of the process and regeneration air flow rates. The desiccant material is regenerated by means of low-temperature thermal energy (about 65 °C) from a microcogenerator. Both the experimental results obtained by the authors and the data provided by the manufacturer have been used to calculate some performance parameters, and a satisfactory agreement has been obtained. The performance parameters have been evaluated as a function of the regeneration temperature, the inlet process air humidity ratio and temperature and the ratio between the regeneration and process air flow rates, in both the cases of fixed regeneration temperature and fixed regeneration thermal power: the results show that higher influence on the dehumidification process is due to the regeneration temperature rather than to the regeneration air flow rate. Moreover, the process air humidity ratio and regeneration temperature influence the desiccant wheel performance more than the process air temperature.

The choice of thermal insulation technology for existing building retrofit can be a complex multi-criteria decision-making (MCDM) problem characterized by multiple stakeholders with conflicting interests. The conflicting interests of the building owners and the policymakers could negatively influence the adoption of low-carbon energy retrofit measures by building possessors, slowing down the progress toward sustainable development. The investigation of this issue is, therefore, crucial to support more informed decisions and offer policymakers useful insights to develop future economic incentives for energy refurbishment of buildings. Most of the existing MCDM studies on the subject do not emphasize the differences among different stakeholders nor consider the outcomes’ robustness. To overcome this gap, this paper integrates multi-stakeholder analyses and robustness assessments to provide broad-spectrum and reliable results. An innovative robust MCDM framework for building thermal insulation under conflicting stakeholder interests is proposed and tested on a real case study building (located in Southern Italy) using building dynamic energy simulation. Several alternatives of thermal insulation are evaluated under environmental, energy, and economic key performance indicators (KPIs). The Analytic Hierarchy Process is used to define criteria weights for conflicting decision-makers representing collectivity (policymakers) and private interests. TOPSIS, VIKOR, WASPAS, and MULTIMOORA methods are integrated to perform initial rankings of the alternatives. A rank similarity analysis is performed to evaluate the consensus between MCDM methods, and an ensemble ranking is obtained for each decision-maker using an approach based on the half-quadratic theory. A Confidence Index and a Trust Level are used to evaluate the agreement among the MCDM approaches, verifying the reliability of the final ensemble ranking. The robustness of the framework is attained by complying with well-established literature guidance. The hybrid MCDM analysis showed that porous materials like expanded clay and expanded perlite lead to better results under the KPIs investigated. The worst performances are attained by vacuum insulation panels and aerogel, mainly due to high values of embodied CO2 emissions and long payback periods. Insights upon the performance of different thermal insulating alternatives are also highlighted by the study and a stakeholder comparative analysis demonstrates that global rankings obtained for the different decision-makers show some similarities, but also important deviations, and a full compromise solution is not achieved.

Abstract Energy consumption for heating and cooling of Italian office buildings is growing. In particular, there is an increase in the demand for electricity for cooling in the summer. Thermal insulation on the external side of the buildings is a very usual strategy to reduce energy demand for air-conditioning systems. However, a too high thickness of insulating material, even if complying with current legislative requirements, can be disadvantageous in buildings characterized by great internal thermal loads and/or located in climatic contexts with mild winters and hot summers. In this paper, the energetic and economic influence of external thermal insulation is evaluated by using energy simulations under dynamic conditions (DesignBuilder software) for a case study. The analysis is performed for various cities (Palermo, Milan and Cairo) and for different values (10, 20, 30 W/m2) of internal thermal loads. According to the recent and innovative “cost-optimal” methodology, optimal insulation thicknesses are derived, and the results demonstrate the need to avoid excessive insulation of buildings to obtain the highest energy saving. Finally, an integration of the “cost-optimal” methodology is proposed considering also the topic of thermal comfort; this modification allows to obtain other optimal solutions compared to the basic calculation procedure.

The energy needs of a Net Zero Energy Building (NZEB) are fully met by renewable energy sources. Nevertheless, the time span of the energy balance can affect the effective energy self-sufficiency of the building. The aim of this paper is to demonstrate the lack of reliability that a yearly energy balance has in characterizing an NZEB. At this scope, comparisons between two different photovoltaic systems (fixed and tracking) and two kinds of energy balance (yearly and monthly) are made for a real NZEB building located in South-Italy. The investigation was carried out through dynamic energy simulations after validating the building model. The results show that the PV surface which attains the NZEB target on yearly basis not always achieves the same objective as the monthly balance. Furthermore, considering a monthly balance, the size of the photovoltaic system with biaxial solar tracking is 50% minor than the fixed one, thanks to a steadier energy production. Also, solar tracking systems show a significantly lower reduction of operational and embodied CO2 emissions. A final technical-economic analysis shows, however, that design solutions that satisfy NZEB target not always can meet the financial interest of the private stakeholder, showing a high discounted payback period.

The implementation of strategies for the decarbonization of the existing buildings by 2050 and the reduction of polluting emissions is urgent, for energy, economic and environmental reasons. Moreover, the built heritage undergoes structural deterioration for which restoration in terventions are required. Seismic and energy improvement strategies are usually treated sepa rately. Conversely, this paper proposes a holistic approach to improve both structural and energy efficiency of existing buildings. The innovative aspect is to obtain a dual objective by exploiting a single element, i.e., the exoskeleton. This component is an external self-supporting structural system connected to the existing building structure for improving strength, stiffness, and/or dissipation capacity under seismic actions. Contemporarily, it defines a new building envelope with different functions, such as ventilated wall, solar greenhouse, shields, and support for insulating panels or solar panels. This approach is applied to a case study, a reinforced concrete building in central Italy. The exoskeleton is rigidly connected to the existing building and designed to absorb the seismic loads and prevent damage to the structure under seismic excita tion. The exoskeleton is also used for energy retrofit, by combining active and passive solutions. A design procedure is illustrated step-by-step for the case study. The results show a significant improvement of thermal characteristics of the building envelope, with a relevant reduction of primary energy, and of the seismic capacity of the existing structure that preserves its elastic behaviour. Moreover, this approach is also convenient from an economic point of view compared to a total demolition and reconstruction.

The energy retrofit of a partial recirculation all-air HVAC system serving a university lecture room located in southern Italy is analysed. Mmulti-objective optimization and multi-criteria decision-making are used to find optimal design alternatives and rank them considering two different decision-makers, i.e., public and private stakeholders. The results show that, in the post-pandemic era, baseline retrofit scenarios for infection reduction that do not involve installation of inverter devices and automatic dampers cause energy consumption increase from negligible values up to 59%. Contrariwise, baseline retrofit scenarios involving the installation of inverter and automatic dampers cause energy consumption decrease between 5% and 38%. In this last scenario, for the implementation of further deep retrofit intervention solutions, there is no agreement between decision-makers on the preferable retrofit solution. In the case of operation of the system with 100% outdoor air + inverter and automatic dampers, both stakeholders agree on the same deep retrofit solution.