• Energy Research

Some simplified correlations of mean hourly global and diffuse luminous efficacy on the horizontal plane for all sky conditions have been obtained for Arcavacata di Rende (Italy) and have been compared with other literature models and other experimental data measured in Geneva (Switzerland), Vaulx-en-Velin (France), Bratislava (Slovakia) and Osaka (Japan). The comparisons show that, for global efficacy, the differences among the various models are not significant, and the use of a model with a constant value of efficacy gives good predictions of global illuminance. For the prediction of diffuse illuminance the differences among the models are larger, but the use of a constant diffuse efficacy provides a good first estimate of diffuse illuminance.

Abstract To analyse the behaviour of a parabolic trough operating with nanofluids, and compare its performance to the more traditional ones using oil, a model for the thermal analysis of the system has been developed and implemented in Matlab. The simulations have been performed for a suspension of Al2O3 in synthetic oil and its characteristics compared to the corresponding basic liquid used by itself. The string has been assumed to have a length of 100 m and a concentrating surface area of 550 m2. The simulations have been carried out for different DNI (Direct normal irradiance) and variable mass flow, ensuring a temperature at the collector outlet below 400C. For a proper comparison, the following variables and efficiency indicators have been checked: power output, pumping power, thermal efficiency and overall efficiency of the parabolic trough system.

Abstract Many correlations of mean hourly direct luminous efficacy for all sky, clear sky and intermediate sky conditions have been compared with experimental data measured in Arcavacata di Rende (Italy), Geneva (Switzerland), Vaulx-en-Velin (France), Bratislava (Slovakia) and Osaka (Japan). The comparisons show that, for all sky conditions, the correlations developed for one locality predict the luminous efficacy in the other localities with mean errors between −13% and 20% and root mean square errors between 15% and 35%; for clear sky conditions, the correlations developed for one locality predict the luminous efficacy in the other localities with mean errors between −7% and 14% and root mean square errors between 7% and 19%; for intermediate sky conditions, the correlations developed for one locality predict the luminous efficacy in the other localities with mean errors between −17% and 26% and root mean square errors between 20% and 41%. If the correlations with local coefficients are applied in each locality, the errors become considerably shorter. The paper gives indications on the values of the measured mean luminous efficacies and on the best models.

The energy transition represents an essential process necessary to drive a shift towards a sustainable and balanced human-environment interaction. Within the residential building sector, this obj ective can be pursued by promoting both the utilization of renewable sources and the energy efficiency improvement of technical systems and the building envelope. In this regard, this article conducts an energy analysis to assess the reduction in energy requirements achieved by installing two Trombe walls on the south-facing wall of the variable orientation test station at the University of Calabria. The two passive systems were symmetrically positioned on either side of the existing window system. The evaluation of monthly energy requirements during the heating period was performed using the dynamic simulation software DesignBuilder. To define the optimal configuration of the Trombe walls, the influence on energy requirements associated with the materials used to construct the support structure of the Trombe walls, the type and number of glass panels forming the solar space, the size of the solar space, and the dimensions of the vents were assessed. The results show that the installation of the two Trombe walls, each consisting of two vents with an area of 0.1 m 2 and a solar space depth of 0.20 m, supported by a PVC structure and vertically bounded by three glass walls with double low-emissivity glazing (two lateral and one frontal facing south), allows for a 60.62% reduction in winter energy requirements.

Abstract A calculation code, named INLUX, able to predict the average illuminance on the inside surfaces of a room with six walls and a window, is presented. The walls and the window are subdivided into a given number of small areas, identified by the coordinates of their centres. The code solves, at each desired instant, the system of the illuminance equations of each surface element, characterized by its reflection coefficient and its view factors toward the other elements. It is assumed that all surfaces reflect the light in a diffuse manner. The model belongs to the calculation models classified as “radiosity models” The code was validated by comparing the calculated values of illuminance with the experimental values measured inside a scale model (1:5) of a building room, located outdoors, in overcast sky conditions. The validation, performed using the sky luminance data measured by a sky scanner as input data, showed a good performance of the code.

The production of electricity from photovoltaic panels has experienced significant developments. To manage the energy flows introduced into the electricity grid, it is necessary to estimate the productivity of PV panels under the climatic conditions. In this study, a photovoltaic panel is modelled from thermal and electrical points of view to evaluate electrical performance and identify the temperature distribution in the layers. The analysis performed is time dependent and the problem is solved using the finite difference technique. A methodology is introduced to estimate the cloudiness of the sky, which affects radiative heat exchange. The calculation method is validated using experimental data recorded in a laboratory of the University of Calabria. Temperature and electrical power are predicted with RMSE of 1.5–2.0 °C and NRMSE of 1.2–2.1%, respectively. The evaluation of the temperature profile inside the panel is essential to understand how heat is dissipated. The results show that the top surface (glass) is almost always colder than the back of the panel, despite being exposed to radiation. In addition, the upper surface dissipates more heat power than the lower one. Cooling systems, such as spray cooling, work better if they are installed on the back of the panel.