Dynamic Parameters to Characterize the Thermal Behaviour of a Layer Subject to Periodic Phase Changes

Abstract The paper addresses the issue of the dynamic characterization of a layer subject to phase change (PCM) with non-sinusoidal periodic boundary conditions, which are typical of the external walls of air-conditioned building. The dynamic parameters used to characterize a monophase layer are not sufficient to describe how the temperature and heat flux trends in transfer through a layer subject to phase change are modified. Furthermore, a PCM due to the effect of latent heat associated with the phase change significantly modifies the heat storage capacity of the wall. The proposed parameters are determined by means of an explicit finite difference numerical model, considering PCM with different melting temperatures and thermophysical properties. The boundary conditions are such that one or more bi-phase interfaces originate in the layer. These parameters can be used for the thermal design of innovative walls in air-conditioned buildings with the aim of reducing power peaks entering the indoor environment, or to reduce thermal requirements, or to improve the thermal comfort within the building

A multilayer panel in cork and natural phase change materials: thermal and energy analysis

This paper presents thermal and energy analysis of a multilayer panel in bio-based cork material and natural phase change materials (PCMs) for the development of prefabricated, recyclable and energy-efficient and autonomous building modules. For this purpose, a calculation tool is developed for the dynamic simulation of the thermal and energy behaviour of the sandwich panel. In particular, through an extensive parametric survey, the panel is sized with the identification of the arrangement of the layers, PCM temperature, and layer thicknesses to optimize the insulating and damping properties, considering typical climatic conditions of the Mediterranean climates of Southern Italy. From the conducted simulations, the types of sandwich panels that have the best insulating and storage characteristics for the building module construction were chosen. The results of these simulations will be used in future research for the preliminary design of tests to be carried out in a climatic chamber and to build a building module in real conditions to be constantly monitored through the automatic instrumental survey of internal and external physical quantities such as temperature, humidity and radiant temperature

Paper-based electroanalytical devices for accessible diagnostic testing

Microfluidic paper-based analytical devices (μPADs) use the passive capillary-driven flow of aqueous solutions through patterned paper channels to transport a sample fluid into distinct detection zones that contain the reagents for a chemical assay. These devices are simple, affordable, portable, and disposable; they are, thus, well suited for diagnostic applications in resource-limited environments. Adding screen-printed electrodes to the detection zones of a μPAD yields a device capable of performing electrochemical assays (an EμPAD). Electrochemical detection has the advantage over colorimetric detection that it is not affected by interferences from the color of the sample, and can be quantified with simple electronics. The accessibility of EμPADs is, however, limited by the requirement for an external potentiostat to power and interpret the electrochemical measurement. New developments in paper-based electronics may help loosen some of this requirement. This review discusses the current capabilities and limitations of EμPADs and paper-based electronics, and sketches the ways in which these technologies can be combined to provide new devices for diagnostic testing.Chemistry and Chemical Biolog

Characterization of Bifacial Photovoltaic Modules Based on I-V Curves Outdoor Measurement

Photovoltaic (PV) systems are well known for their simplicity of design, environmental friendliness, and low maintenance. Among the PV technologies, the behaviour of bifacial PV modules was studied in this research. Measurements of the I-V curves were carried out in the SolarTechLAB test facility at the Department of Energy of Politecnico di Milano, Italy, to detect the bifacial PV module behaviour, mainly in terms of power performance. In particular, I-V and power-voltage curves were measured at different tilt angles to consider several irradiance and cell temperature levels with both sides uncovered as well as with the back side covered. This last configuration was tested to evaluate the contribution of the rear face in the overall photoelectric conversion process. The comparison between the bifacial and monofacial operations highlighted that the power at the maximum power point of the bifacial operation can increase up to 13%. At the same time, leaving the rear face free allows for reducing the bifacial cell temperature up to about 6°C

Informed assessment of structural health conditions of bridges based on free-vibration tests

consolidated procedure for the evaluation of current structural health con-ditions in bridges consists in the comparison between estimated modal features from in-situ tests and numerical values. This strategy allows making informed decisions for existing bridge structures to ensure structural safety or serviceability. Free vibration tests are common in bridges monitoring since they allow a quick and cost-effective determination of dynamic infor-mation about the structure, using a sparse network of few sensors and avoid long-lasting monitoring campaigns. Exploiting an identification method based on a tuned version of Vari-ational Mode Decomposition and an area-ratio based approach, modal parameters are deter-mined from free vibration tests. This technique is applied to the dynamic identification of cables in a stay-cabled bridge assumed as case study: the obtained results prove reliability of the adopted method as a useful tool for objective dynamic identification purposes, with focus on the structural health conditions of bridges

Energy Independence of a Small Office Community Powered by Photovoltaic-Wind Hybrid Systems in Widely Different Climates

Hybrid renewable energy systems are an optimal solution for small energy communities’ energy supply. One of the critical issues is the strong correlation of these systems with outdoor climatic conditions. The goal is to make local communities increasingly energy independent. To this end, an in-depth analysis of the behaviour of hybrid photovoltaic (PV)–wind systems powering small office communities in 48 locations around the world characterized by widely varying climates was conducted. System sizes, assumed to be stand-alone or grid-connected, were varied, for a total of 343 system power configurations. Highest satisfied load fraction (SLF) values are obtained with a significant predominance of PV over wind; the trend is more pronounced in dry and continental climates (zones B and D according to the Köppen climate classification). The utilization factor (UF) values of 1 are rarely reached and never in the wind-only or PV-only configurations. In all climates, the grid energy interaction factor (GEIF) values of zero are never reached but come very close. The benefit-cost ratio (BCR) of grid-connected systems is significantly higher than stand-alone systems

Dynamic Thermal Characteristics of Opaque Building Components. A Proposal for the Extension of EN ISO 13786

Abstract In order to dynamically characterise the opaque components of a building envelope subject to sinusoidal loadings in steady periodic regime conditions, the use of nondimensional periodic thermal transmittance is proposed. Such a parameter allows for the evaluation of the decrement factor and time lag that the heat flux undergoes while crossing the wall and the efficiency of the heat storage. For non-sinusoidal loadings, dynamic characterisation is obtained by the decrement factor, defined as the ratio between energy in a semi period entering the indoor environment and entering the wall and as the ratio between maximum heat fluxes entering the environment and the wall, and as the ratio between the minimum heat fluxes. These parameters allow to determine the heat storage capacity of the component, the maximum heat flux in summer and winter conditions and their time lags. The defined dynamic properties were calculated considering two commonly used walls and surrounding conditions that are representative of the effective operative conditions