• Energy Research

To address the increasing demand for ancillary services, new demand response strategies (DR) are being developed that involve the building sector to provide flexibility to the transmission system operator (TSO). In this respect, commercial buildings have great potential to become key players in providing flexibility to the TSO by changing their load profiles for heating, ventilation and air conditioning. This study presents a case study of a Mediterranean shopping centre heated and cooled by a heat pump and participating in the ancillary services market according to the specific rules of the Italian pilot project UVAM. The analyses start from the daily consumption profile assuming conventional operation for the HVAC system (baseline) during cooling and heating periods. Then two DR strategies are investigated, the first of which is to change the indoor set point temperature and the second is to reduce the electricity power to the HVAC systems, without introducing precooling or pre-heating periods. The results show that the studied flexibility strategies allow to obtain, for each DR event, over 60 kW of downward flexibility power and a reduction of energy consumption between 128 and 160 kWh during summer, and over 50 kW of downward flexibility power and a reduction of energy consumption between 40 and 160 kWh. This study identifies opportunities and barriers for commercial buildings to participate in the ancillary services market. However, the proposed DR strategies may lead to an unacceptable percentage of dissatisfaction (PPD), especially during the cooling season.

Abstract The main benefit attributed to opaque ventilated facades (OVF) is the reduction of cooling load for the building Heating Ventilation and Cooling (HVAC) achieved through ventilation led by natural convection in the ventilated chamber and the protection from solar radiation given by the outer layer of the facade. This research investigates the thermal behavior of an opaque naturally ventilated facade through Computation Fluid Dynamics (CFD) simulations during summer days. The CFD simulations have been performed in order to analyze the behavior of DSF components under different wind conditions in the summer period, utilizing the weather data of Catania city (Italy). For the different investigated scenarios, the authors have calculated the temperature and air velocity profiles inside the air gap of the facade, highlighting the different effects of buoyancy and wind forces. The results show that the wind forces in conjunction with the buoyancy forces affect significantly the performance of OVF components. Further, the reduction of the heat flux during the summer period has been evaluated by comparing the thermodynamic performance of a naturally ventilated and an unventilated facade with the same geometry and thermo-physical characteristics. The behavior of the naturally ventilated facade is an improvement in terms of passive cooling of the building compared to the non-ventilated facade since it allows the peak load to be shifted whilst offering energy savings in the range of 47% to 51% depending on climate.

Abstract The main objectives of the present paper are to describe a pilot cogenerative PV/T plant and discuss its preliminary electrical and thermal experimental data. The PV/T plant is installed in the campus of the University of Catania, (Catania, Italy) on the eastern coast of Sicily, right in the centre of the Mediterranean area. The operative conditions of the experimental PV/T plant can be modified to implement parallel and series electrical and hydronic connections to the PV/T modules. The electrical and thermal load supplied by the PV/T plant can also be managed in order to simulate different energy demand scenarios. This study reports the main thermal and electrical operating parameters of the PV/T plant on the basis of experimental measurements, with the PV/T modules connected in series. A good level of correspondence was found between the measurements and the simulations obtained from a model of the system, particularly as regards electrical features.

This paper presents a numerical study of a photovoltaic thermal plant that uses coolant fluid water nanofluids. The thermal properties of several investigated water nanofluids are derived from literature data. In particular, Al2O3–water (2–4% particle volume fraction) and TiO2–water (2–6% particle volume fraction) are investigated in this study. The effect of different working fluids on the performances of real PVT plants is simulated through “TRNSYS” software. First, several limitations and constraints needed to be resolved to develop a trustworthy simulation environment within the TRNSYS framework. The great sensitivity to particle volume fraction and temperature of the thermal conductivity of the nanofluid has to be taken into account. The performance in terms of thermal energy produced increases using nanofluids by up to 11%, making the use of nanofluids a promising technology. However, the annual energy benefit in a complete PVT system serving a home is only 2.5% greater than that of using water alone.

To reach the EU 2030 goal of reducing greenhouse gas emissions targets, many apartments within residential buildings can be equipped with rooftop or building-integrated PV systems. However, as non-programmable renewable energy sources (solar, wind) are characterized by uncertainty and fluctuation, it is very difficult to match the supply with the demand for the building's energy needs. Thermal and electric energy storage play a fundamental role in maximizing self-consumption, reducing the difference between peaks and valleys of the energy demand, and improving the electrical system's flexibility. In this study, the performances of an energy system composed of an electric heat pump (HP) fed by a PV plant and both thermal and electric storage are investigated. An innovative logic of the charge and discharge of the two storages as a function of energy generation and demand has been developed with the aim to optimize the energetic self-sufficiency of typical residential buildings. The results of the analyses carried out evidence that the system configurations with a thermal storage of about 1.000 L and an electrical storage of 5.0 kWh allow achieving rates of self-consumption and self-sufficiency of about 80%, which are 3 times higher than that one achievable by an energy system without storage. Moreover, this system configuration reduces dramatically the power exchange with the grid. The outcomes of this study are useful to provide indications for the design of the storage in combination with a solar-assisted heat pump system avoiding the recurrent praxis of oversizing of more than 100% of the electric storage.

Abstract Nowadays, there is continuing worrying about energy efficiency and the reduction of GHG emissions in the building sector. It has been claimed that ventilated building envelopes help to reduce energy use in buildings and improve occupant comfort. This study proposes a comprehensive comparison of the thermal behaviour between an Opaque Ventilated Facade (OVF) and a conventional unventilated Facade (UF) considering two reference days for the winter and summer period. The analysis is developed investigating different facade orientations and two states of windiness, which are a state of calm wind and a state with wind velocity higher than zero (i.e. 5.0 m/s at 10 m of height) are taken into account. These analyses were developed utilizing fluid-dynamic calculation under dynamic conditions. Thus for the two facades were calculated: (I) the hourly surface temperatures of the most external, (II) the temperature profiles for all the facade’s layers; (III) the airflow profiles inside the cavity and near the facade; (IV) the hourly thermal fluxes that cross the facade. Finally, the daily energy fluxes and the energy-saving, achievable through the adoption of the OVF, is calculated for the different facade exposures and the conditions of windiness. The outcomes of this study highlight that the OVF guarantees an energy-saving ranging from 20 to 55%, with the highest rate during the summer day for the facade facing East/West.

This study systematically explores and compares the performance of various artificial-intelligence (AI)-based models to predict the electrical and thermal efficiency of photovoltaic–thermal systems (PVTs) cooled by nanofluids. Employing extreme gradient boosting (XGB), extra tree regression (ETR), and k-nearest-neighbor (KNN) regression models, their accuracy is quantitatively evaluated, and their effectiveness measured. The results demonstrate that both XGB and ETR models consistently outperform KNN in accurately predicting both electrical and thermal efficiency. Specifically, the XGB model achieves remarkable correlation coefficient (R2) values of approximately 0.99999, signifying its superior predictive capabilities. Notably, the XGB model exhibits a slightly superior performance compared to ETR in estimating electrical efficiency. Furthermore, when predicting thermal efficiency, both XGB and ETR models demonstrate excellence, with the XGB model showing a slight edge based on R2 values. Validation against new data points reveals outstanding predictive performance, with the XGB model attaining R2 values of 0.99997 for electrical efficiency and 0.99995 for thermal efficiency. These quantitative findings underscore the accuracy and reliability of the XGB and ETR models in predicting the electrical and thermal efficiency of PVT systems when cooled by nanofluids. The study’s implications are significant for PVT system designers and industry professionals, as the incorporation of AI-based models offers improved accuracy, faster prediction times, and the ability to handle large datasets. The models presented in this study contribute to system optimization, performance evaluation, and decision-making in the field. Additionally, robust validation against new data enhances the credibility of these models, advancing the overall understanding and applicability of AI in PVT systems.

Abstract The installation of solar collectors applied or integrated into the building envelope may represent an interesting opportunity to increase the fraction of the building energy demands supplied through solar energy. In particular, building solar thermal facades (BSTFs) could be very useful in high-rise buildings, which do not have sufficient spaces where to install a solar plant. This paper aims to evaluate the energy performances of building solar thermal facades (BSTFs), constructed with two distinct types of solar collectors, flat plate (FPC) and evacuated solar collectors (ETC), through transient simulations, carried out with TRNSYS software, under different climate conditions. Moreover, an economic and LCA analysis on the two types of examined BSTFs were developed. Additionally, this study presents a preliminary investigation on a prototype of ventilated building solar thermal facade (v-BSTF) built in Ragusa. The results of such analysis highlight that BSTFs can represent suitable systems for the DHW production with great environmental and economic conveniences due to the short energy and CO2 payback times.