Air Conditioning Systems from a 2nd Law Perspective

In this paper exergy analysis is used to assess the performance of the three most common air conditioning plant schemes: all-air, dual-duct and fan-coil systems. The results are presented in terms of flow diagrams to provide a clear picture of the exergy flow across the systems. The most relevant outcomes are that the air cooling and dehumidification is the process most responsible for the exergy loss and that the exergy efficiency of the overall systems is rather lo

The Effectiveness of PCM Wallboards for the Energy Refurbishment of Lightweight Buildings

Abstract In order to compensate for the small storage capacity of lightweight buildings, that usually suffer from pronounced overheating in summer, the incorporation of Phase Change Materials (PCMs) into the opaque envelope can be an effective way to enhance thermal inertia and to improve the thermal comfort. In particular, PCM wallboards are recommended during refurbishment, as they have a small thickness and can be easily applied on the inner surface of both the walls and the ceiling. In this paper, a comprehensive study is presented about the effectiveness of PCM wallboards for improving summer thermal comfort in existing lightweight buildings. The study is based on dynamic simulations carried out with the software EnergyPlus on a sample office building. The analysis is repeated in four different locations, ranging from Southern Europe (Catania, Italy) to Northern Europe (Paris, France). The results of the simulations may help designers to make the correct choices in terms of position of the PCM wallboards, scheduled rate of nighttime ventilation and value of the peak melting temperature for the specific PCM

Sensitivity analysis for room thermal response

The sensitivity theory is a suitable approach for assessing the room thermal response. It results in the 'sensitivity coefficients' (SCs) which, as derived here, evaluate the variation of the thermal load due to a fluctuation in a given design parameter around its nominal value. In this paper the general method is presented and a number of SCs are derived to evaluate the sensitivity of the building energy demand to the window surface area, to the overall transmittance and mass thermal capacity of a given wall, and to other structural data

The role of shading devices to improve thermal and visual comfort in existing glazed buildings

Abstract Buildings with large glazed surfaces may show severe thermal and visual discomfort issues, as an effect of the large incoming direct solar radiation. In order to avoid excessive solar gains and glare issues to the occupants, it is necessary to adopt suitable solutions that limit the incoming solar radiation, such as highly reflective coatings or movable shading devices. However, such devices must be accurately selected, according to the building location and to the exposure of the glazed facades, while also taking into account possible regulatory measures. This paper evaluates the effectiveness of a series of shading devices applied to an existing office building in Southern Italy. The building shows large glazed surfaces and has no overhangs, thus significant thermal discomfort is perceived in summer by the occupants. The aim is to identify those solutions that allow to improve thermal comfort while also keeping a sufficient illuminance level indoors, without disregarding the compliance with Italian regulations about the installation of shading devices and, of course, the need to keep costs on a reasonable level. The analyses are repeated for different building orientations, in order to provide general information

Assessment of thermal discomfortin non-uniformly heated enclosures: Two indices in the time-space domain

In this paper two indices are proposed to assess the thermal discomfort in not-uniformly heated enclosures in the time-space domain. The discussion of some meaningful cases reveals that living spaces are subject to significant non-uniform radiant heat fields, resulting in thermal discomfort. In order to quantify such effects, the concept of 'uniform equivalent temperature' is invoked. This allows two indices i+ and i− to be developed for assessing the thermal discomfort in intensity and duration. Such indices have a clear physical meaning and therefore may provide substantial help in detecting causes and/or locations of thermal unpleasantness. On this basis a necessary but not sufficient condition for thermal comfort is stated in the form: i+ = i− = 0, to be sought everywhere within the room. Further examples illustrate the value of the procedure in thermal comfort conscious design

Wear effects in retrieved acetabular UHMW-PE cups

There is an increasing awareness of the clinical problems associated with ultra-high-molecular-weight polyethylene (UHMW-PE) wear and failure in orthopaedics. This disadvantage is certainly promoted from the various oxidation process that can occur during prosthesis life. Scanning electron microscopy, IR-spectroscopy, and X-ray-photoelectron spectroscopy were employed to investigate the mechanism of polymer degradation. In particular, comparison among the spectra of starting and retrieved UHMW-PE components shows that the polymer oxidizes mainly in vivo. The data indicate that hydroxyl radicals are likely to be a major factor in degradation of the surface of this polymer, these groups are produced in vivo during the implantation time. Several other chemical groups, produced in the different steps of the prosthesis life, are contained in the material

Molecular characterization and genetic structure of the Nero Siciliano pig breed

Nero Siciliano is an autochthonous pig breed that is reared mainly in semi-extensive systems in northeastern Sicily. Despite its economic importance and well-appreciated meat products, this breed is currently endangered. Consequently, an analysis of intra-breed variability is a fundamental step in preserving this genetic resource and its breeding system. In this work, we used 25 microsatellite markers to examine the genetic composition of 147 unrelated Nero Siciliano pigs. The total number of alleles detected (249, 9.96 per locus) and the expected heterozygosity (0.708) indicated that this breed had a high level of genetic variability. Bayesian cluster analysis showed that the most likely number of groups into which the sample could be partitioned was nine. Based on the proportion of each individuals genome derived from ancestry, pigs with at least 70% of their genome belonging to one cluster were assigned to that cluster. The cluster size ranged from 7 to 17 (n = 108). Genetic variability in this sub-population was slightly lower than in the whole sample, genetic differentiation among clusters was moderate (FST 0.125) and the FIS value was 0.011. NeighborNet and correspondence analysis revealed two clusters as the most divergent. Molecular coancestry analysis confirmed the good within-breed variability and highlighted the clusters that retained the highest genetic diversity

application of a mapping tool to plan energy saving at a neighborhood scale

Abstract This study proposes the application of a model for the evaluation of the overall energy demand of existing urban neighborhoods, which can be useful when planning energy enhancement strategies at urban scale. The application of this model can be interconnected with the use of a GIS software tool, thus providing the opportunity to perform the energy mapping of city neighborhoods. In the proposed model, the overall energy demand of existing urban neighborhoods is evaluated by considering the three most energy intensive sectors: buildings, transport and urban lighting. However, in this paper the application of the model is only focused on the assessment of the energy demand in the building sector. The proposed methodology is applied to a neighborhood of the municipality of Catania in Southern Italy. The preliminary results are reported in this study: first, the existing energy consumption for space heating and electric appliances is assessed, then the effectiveness of a series of energy-saving strategies is considered, thus providing a tool to implement effective energy planning policies at urban scale

uhi effects and strategies to improve outdoor thermal comfort in dense and old neighbourhoods

Abstract Modelling techniques have received growing attention as a tool to investigate the thermal comfort within a city, on the basis of which decision makers can set-up appropriate mitigation strategies. This research aims at studying the effectiveness of strategies for reducing the urban heat island-associated effects in dense and old neighborhoods considering, in particular, green roofs, cool roofs, cool pavements, green areas and urban renewal actions. Computer simulation was selected as the major methodology in this research; ENVI-met software was used under different scenarios for a case study consisting in an old neighborhood in the city of Avola. The investigation focused on evaluating the efficacy of each strategy for a condition corresponding to a typical summer heat wave. The results highlight that the cool pavements allow relevant improvements at the height of 1.50 m, with a temperature decrease up 1.15°C, whereas the other scenarios, given the relatively high density of the buildings, are able to improve outdoor conditions only at higher elevations. Reported results represent a guideline for the choice of UHI mitigation method that can help stakeholders involved in new urban assessment of old neighborhoods in Mediterranean climate

Refurbishing an existing apartment block in Mediterranean climate: towards the Passivhaus standard

The Passivhaus standard, although widely appreciated in cold regions, is seldom regarded as a reference in the energy renovation of existing buildings in warm countries. This paper evaluates the effectiveness of a series of strategies for the energy refurbishment of an existing apartment block in Southern Italy, based on dynamic energy simulations. The paper aims to show that, in warm Mediterranean areas, a building refurbishment must not be oriented towards an excessive insulation level. Conversely, if aimed to comply with the Passivhaus standard, the renovation must look above all at those strategies that mitigate the energy needs for space cooling and improve thermal comfort in summer