Thermo-physical behaviour and energy performance assessment of PCM glazing system configurations: A numerical analysis

The adoption of Phase Change Materials (PCMs) in glazing systems was proposed to increase the heat capacity of the fenestration, being some PCMs partially transparent to visible radiation. The aim of the PCM glazing concept was to let (part) of the visible spectrum of the solar radiation enter the indoor environment, providing daylighting, while absorbing (the largest part of) the infrared radiation. In this paper, the influence of the PCM glazing configuration is investigated by means of numerical simulations carried out with a validated numerical model. Various triple glazing configurations, where one of the two cavities is filled with a PCM, are simulated, and PCM melting temperatures are investigated. The investigation is carried out in a humid subtropical climate (Cfa according to Köppen climate classifi-cation), and "typical days" for each season are used. The results show that the position of the PCM layer (inside the outer or the inner cavity) has a relevant influence on the thermo-physical behaviour of the PCM glazing system. PCM glazing systems (especially those with the PCM layer inside the outermost cavity) can be beneficial in terms of thermal comfort. The assessment of the energy performance and efficiency is instead more complex and sometimes controversial. All the configurations are able to reduce the solar gain during the daytime, but sometimes the behaviour of the PCM glazing is less efficient than the reference one. ©2012. Higher Education Press Limited Company. Production and hosting by Elsevier B.V. Open access underCC BY-NC-ND license

Numerical investigation of a diffuse ventilation ceiling system for buildings with natural and hybrid ventilation

The need to meet requirements, both in terms of ventilation and thermal comfort in modern buildings, has led to the development of different concepts for ventilation, among which the so-called Diffuse Ceiling Ventilation (DCV). This system makes use of the space between the ceiling slabs and the suspended ceiling as a plenum for fresh air, while the suspended ceiling itself becomes an air diffuser element. If compared to traditional solutions, this allows a higher amount of ventilation air to be injected in the room at lower speed, and a more even distribution of the fresh air within the room. Furthermore, it allows an easy integration with sound-absorbing perforated ceiling panels, since their typical design makes them particularly fit to be used as air diffusers. This paper builds upon a previous work by the authors where CFD simulations were used to optimise the dimension and the distribution of the perforation pattern in the panels to achieve an even air speed distribution. In this work, the performance of the perforated ceiling is investigated in a more comprehensive way, evaluating the thermal comfort in the room when varying the outdoor temperature. This solution is in fact meant to work in combination with natural or hybrid ventilation strategies, where the fresh air flow is supplied from the façade. Numerical simulations were performed on a typical office room, considering both the winter and the summer season, for different inlet air temperatures. This solution demonstrated a positive impact on the indoor conditions and on the thermal comfort inside the room in most of the cases but the most extreme ones. The thermal stratification in the room demonstrated to remain within a satisfactory level

Optimizing the configuration of a façade module for office buildings by means of integrated thermal and lighting simulations in a total energy perspective

The building enclosure plays a relevant role in the management of the energy flows in buildings and in the exploitation of solar energy at a building scale. An optimized configuration of the façade can contribute to reduce the total energy demand of the building. Traditionally, the search for the optimal façade configuration is obtained by analyzing the heating demand and/or the cooling demand only, while the implication of the façade configuration on artificial lighting energy demand is often not addressed. A comprehensive approach (i.e. including heating, cooling and artificial lighting energy demand) is instead necessary to reduce the total energy need of the building and the optimization of the façade configuration becomes no longer straightforward, because non-linear relationships are often disclosed. The paper presents a methodology and the results of the search for the optimal transparent percentage in a façade module for low energy office buildings. The investigation is carried out in a temperate oceanic climate, on the four main orientations, on three versions of the office building and with different HVAC system’s efficiency. The results show that, regardless of the orientations and of the façade area of the building, the optimal configuration is achieved when the transparent percentage is between 35% and 45% of the total façade module area. The highest difference between the optimal configuration and the worst one occurs in the north-exposed façade, while the south-exposed façade is the one that shows the smallest difference between the optimal and the worst configuration.© 2013 Elsevier B.V. All rights reserved. This is the authors' accepted and refereed manuscript to the article, post-print. Released with a Creative Commons Attribution Non-Commercial No Derivatives License. The final publication is available at https://doi.org/10.1016/j.apenergy.2013.02.063acceptedVersio

Solar efficiency index of building envelopes and load matching in low energy buildings

Net-zero energy buildings oftentimes rely on solar-based building integrated technologies to offset energy use and achieve their goals. However, the value of a particular system is difficult to assess given that these technologies often bring about complex interactions with the indoor environment, and building energy management systems. The approach chosen in this study was to propose and test a simple index called the Solar Efficiency index (SE index), which makes it possible to characterize the performance of building envelopes with integrated solar systems. The index was used to investigate the effect of different configurations of a PV integrated shading device on an office building in Norway. The results provided by the index allowed estimating how much solar energy was converted and how useful that energy was to the building in terms of load matching. This provided a picture of the building’s energy autonomy

Laboratory testbed and methods for flexible characterization of thermal and fluid dynamic behaviour of double skin facades

publishedVersio

Characterization and energy performance of a slurry PCM-based solar thermal collector: a numerical analysis

Flat plate solar thermal collector is the most common technology for solar energy conversion at the building scale. This technology has been established since long time and continuous developments have been achieved as time passed by; significant improvements of flat plate solar thermal collectors are thus now limited. A novel approach to increase further the performance of this technology is based on the exploitation of the latent heat of the heat carrier fluid. In order to assess this strategy, a previously developed numerical model of flat plate solar thermal collector with slurry PCM as heat carrier is herewith used to simulate the technology. The characterization and energy performance of such a system are herewith presented, based on the outcome of the numerical analysis. The results demonstrate that the novel approach is able to improve the performance of the system under different boundary conditions and in different climates: the improvement in the instantaneous efficiency is in the range 5-10%, while during the winter season the converted heat by the slurry PCM-based system is 20-40% higher than that of a conventional water based solar collector, depending on the climates – the colder the climate, the larger the improvement

A Methodological Approach to Assess the Climatic Potential of Natural Ventilation Through Façades

Due to the rapid development of super insulated and airtight buildings, the energy requirement for mechanical ventilation is becoming more and more dominant in today’s highly efficient buildings. In this scenario, natural ventilation has the potential to reduce energy use for buildings while maintaining ventilation rates that are consistent with acceptable indoor air quality. The increase in air temperature and frequency of extreme weather events (e.g. heavy rains, heat and cold waves) due to climate change will alter future outdoor boundary conditions and consequently the potential for natural ventilation in buildings. Therefore, to respond to the fluctuations in outdoor boundary conditions, the building envelope should become more and more dynamically responsive. In that sense, the façade plays an important role by regulating indoor comfort based on outdoor environmental conditions. This paper presents a methodological approach to investigate the potential of natural ventilation through the façade in office buildings in present and future climate conditions. It reviews technologies and strategies that maximise the use of natural ventilation in office buildings located in six selected different European climates. Numerical analyses were conducted, considering outdoor air temperature and humidity. Integrated façades with hybrid systems and strategies is one of the key solutions for increasing the potential of natural ventilation. The results showed that a hybrid solution with low-pressure drop heat recovery had the greatest potential to maximise the possibilities of low energy façade integrated ventilation

Thermal and Optical Properties of a Thermotropic Glass Pane: Laboratory and In-Field Characterization

Switchable windows are glazing technologies that exhibit dynamic optical properties and may thus be used to improve the energy performance of buildings. A window system based on a thermotropic glass pane was tested both in the laboratory and by means of an outdoor test cell facility. In this paper the full optical and thermal characterization of this glazing technology is presented. Experiments and data analysis led to the characterization of the behaviour of the thermotropic glazing both when this technology is used alone (single glass pane) and when it is integrated in a multilayer fenestration (a triple glazed unit)

Experimental Analysis of an Advanced Dynamic Glazing Prototype Integrating PCM and Thermotropic Layers

Glazing components are the most challenging element of the building envelope system. The insertion of a Phase Change Material coupled with a thermotropic layer is herewith proposed as an innovative solution aimed at improving the energy performance of the fenestration. The intention is to increase the dynamic features of glazing systems and to enhance their capability of exploiting solar energy – a crucial feature in nearly Zero Energy Buildings. The paper presents the experimental analysis of two prototypes of such a glazing concept and the assessment of their energy performance during the warm season. The samples are installed on an outdoor thermostatic cell facing south, together with a reference triple glazed unit, and continuous measurements of temperatures, irradiances and heat fluxes are performed. In the summer season, when the aim of the glazing system is to reduce the solar gain and to allow daylighting the energy performance is very promising. When compared to the reference technology, both the prototypes are able to reduce to a great extend the direct transmitted solar energy, as well as to smooth the peak indoor surface temperature of the glazing. In particular, one of the two configurations lowers down the solar energy gain under all boundary conditions, while the other configuration presents a slightly worse performance than the other prototype when high solar irradiation occurs. An attempt to measure the thermal transmittance was also carried out and it is shown that the insertion of PCM does not increase the U-value of the component