• Energy Research

The simulation of the energy consumptions in an hourly regime is necessary in order to perform calculations on residential buildings of particular relevance for volume or for architectural features. In such cases, the simplified methodology provided by the regulations may be inadequate, and the use of software like EnergyPlus is needed. To obtain reliable results, usually, significant time is spent on the meticulous insertion of the geometrical inputs of the building, together with the properties of the envelope materials and systems. Less attention is paid to the climate database. The databases available on the EnergyPlus website refer to airports located in rural areas near major cities. If the building to be simulated is located in a metropolitan area, it may be affected by the local heat island, and the database used as input to the software should take this phenomenon into account. To this end, it is useful to use a meteorological model such as the Weather Research and Forecasting (WRF) model to construct an appropriate input climate file. A case study based on a building located in the city center of Rome (Italy) shows that, if the climatic forcing linked to the heat island is not considered, the estimated consumption due to the cooling is underestimated by 35–50%. In particular, the analysis and the seasonal comparison between the energy needs of the building simulated by EnergyPlus, with the climatic inputs related to two airports in the rural area of Rome and with the inputs provided by the WRF model related to the center of Rome, show discrepancies of about (i) WRF vs. Fiumicino (FCO): Δ = −3.48% for heating, Δ = 49.25% for cooling; (ii) WRF vs. Ciampino (CIA): Δ = −7.38% for heating, Δ = +35.52% for cooling.

Abstract When water-ammonia absorption machines are used as heat pumps, the main problems can be found in the components operating at a high pressure (generator-condenser); the increase in temperature with respect to the exertion as refrigerator generates particular conditions that might unbalance the decomposition of ammonia into nitrogen. A decrease in the rate of the refrigerating fluid NH 3 in the condenser and evaporator occurs, hence of the performance coefficient of the heat pump with an increased risk of the potential generation of explosive mixtures due to the presence of the hydrogen. The aim of this study is to examine the reaction of ammonia during the dissociation process from a thermodynamic and thermokinetic point of view, focusing on the temperatures and pressures of a heat transformer. With the generator at a temperature of 170 °C it is necessary to reach a degree of dissociation at 1% a time period of the order of 1.013 seconds which is 100 times higher than the one of maximum permanence of the fluid in the components of the machines functioning at high temperatures. This is not a problem that might prevent the realization of high temperature absorption heat pumps.

Building energy need simulations are usually performed using input files that contain information about the averaged weather data based on historical patterns. Therefore, the simulations performed are not able to provide information about possible future scenarios due to climate change. In this work, future trends of building energy demands due to the climate change across Europe were studied by comparing three time steps (present, 2050, and -2080) in three different European cities, characterized by different Köppen-Geiger climatic classes. A residential building with modern architectural features was taken into consideration for the simulations. Future climate conditions were reached by applying the effects of climate changes to current hourly meteorological data though the climate change tool world weather file generator (CCWorldWeatherGen) tool, according to the guidelines established by the Intergovernmental Panel on Climate Change. In order to examine the resilience of the building, the simulations carried out were compared with respect to: peak power, median values of the power, and energy consumed by heating and cooling system. The observed trend shows a general reduction in the energy needs for heating (–46% for Aberdeen, –80% for Palermo, –36% for Prague in 2080 compared to the present) and increase (occurrence for Aberdeen) in cooling requirements. These results imply a revaluation of system size.

AbstractIn the engineering field there are many applications where it is important to evaluate the heat exchange between cylindrical surfaces and the surrounding ground (horizontal geothermal exchangers for heat pumps, underground pipelines, underground electric cables, etc...). For these reasons, there is an increased interest in the correct analysis of the soil thermal resistance. In this study different types of soils with linear heat sources were considered and, through a physical model reproduced in laboratory, the thermal field was evaluated. The model reproduced an “undisturbed” portion of soil and the influence of different thermal conditions of the linear heat sources and of the environmental parameters were evaluated. This paper will be extended through the implementation of the experimental device into a numerical model by applying a calculation software to the finite volumes; the result is a predictive model of the soil resistance able to furnish accurate information of the real mean radial thermal resistivity surrounding the geothermal exchanger.

Abstract In many emerging countries over the past few years some phenomena, such as a better welfare state, industrial growth and a development in agriculture, led to a significant increasing of the demand concerning fresh water. In order to face this ever-growing demand, one of the possible solutions to counterbalance the lack of water resources, is the desalination of sea water. For this specific goal solar energy, as a resource, is the process which has more reliance since it allows a low-cost production of desalted water (without using any valuable energy resources such as fossil fuels) and in a complete respect of the environment. This first study has the purpose to analyze from an energetic perspective whether it is possible or not to reach process temperatures over 100 °C, through the use of solar ponds and heat transformers, in order to produce desalinated water. The final aim of this work is to quantify the surface of solar ponds needed to a production (expressed in cubic meters) of desalinated water. An absorption heat transformer is a thermal machine that while extracting heat from a source (at an available temperature) is able to ennoble a portion of the heat collected/obtained, making it available at higher temperatures. This process occurs at the expenses of the remaining portion of heat whose temperature degrades by lowering its values. The portion of heat will be then transferred to a thermal well. Hence an absorption heat transformer can use the solar energy stored in solar ponds as an energy source at an average temperature. Process temperatures which are higher than 100 °C for a whole year can take place only under certain chained conditions such as: source temperature with steady values during the entire season obtainable through solar ponds; condensation process occurring at sufficiently low temperatures through the use of sea water; exertion of heat transformers. The heat which is usually available at these temperatures could be used for common thermal processes during the desalination of seawater. In this work we want to demonstrate that it is possible, energetically speaking, to produce desalinated water by exploiting the solar energy stored in solar ponds and the technology of absorption heat transformers. We can notice how for every m3 of desalinated water produced in one day we need ponds with an area ranging between 1000 and 4000 m2, this depends on the amount of heat flux drawn. The analysis we carried out represents a first attempt to face this kind of problem. In future studies we will examine both technical and economic feasibility.

The energy requalification of existing buildings entails the fulfillment of different, often conflicting, criteria, such as the reduction of the specific annual energy demand, the containment of the construction costs, the decrease in the annual energy operating cost and the reduction of climate-change gas emissions. Therefore, optimization methods based on the application of computational algorithms are essential to determine solutions that meet multi-objective criteria and so highly optimized to be on the Pareto frontier. In this work, a procedure for the optimization of existing buildings using genetic algorithms is presented. Building energy simulations conducted in the dynamic regime using EnergyPlus are coupled with an Active Archive Non-dominated Sorting Genetic Algorithm (aNSGA-II type). Using a residential building as a benchmark, this procedure is employed to evaluate the best retrofitting interventions for 19 European cities with different climates. The criteria taken into account in the optimization procedure are: the reduction in the annual specific energy demand, the decrease in the construction and installation costs, the reduction in the annual energy operating costs and the reduction in the greenhouse gas emissions. The results show the most advantageous energy retrofitting interventions fulfilling the criteria for the different geographical sites.

Outdoor thermal comfort is an essential factor of people’s everyday life and deeply affects the habitability of outdoor spaces. However the indices used for its evaluation were usually developed for indoor environments assuming still air conditions and absence of solar radiation and were only later adapted to outdoor spaces. For this reason, in a previous study the Mediterranean Outdoor Comfort Index (MOCI) was developed, which is an empirical index able to estimate the thermal perception of people living in the Mediterranean area. In this study it was compared numerically (by using the data obtained through a field survey) with other selected thermal indices. This comparison, performed in terms of Spearman’s rho correlation coefficient, association Gamma, percentage of correct predictions and cross-tabulation analysis, led to identify the MOCI as the most suitable index to examine outdoor thermal comfort in the interested area. As a matter of fact it showed a total percentage of correct predictions of 35.5%. Good performances were reported even in thermophysiological indices as the Physiological Equivalent Temperature (PET) and Predicted Mean Vote (PMV). Moreover it was revealed that adaptation and acclimatization phenomena tend to have a certain influence as well.