1,721,108 research outputs found
Dynamic Building Envelope Components and nearly Zero Energy Buildings
No full textDue to the significant impact of the building sector on greenhouse gas emissions, newer and stricter regulations aimed at reducing total energy use in buildings have appeared in the last few years. In the European context, all the new constructions will thus soon be asked to be nearly Zero Energy Buildings (nZEB). In order to reach this target, new concepts and technologies capable of further improving buildings' energy efficiency need to be developed. A very promising strategy to overcome current technologylimitations is represented by revisiting the conventional approach that considers the building as a staticobject and moves towards the vision where the building is a responsive and dynamic system. The main feature of this concept is the possibility of continuously changingthe interaction between the building elementsand the outdoor/indoor environment in order to reduce the energy demands and enhance the exploitation of "environmental" and low-exergy energies. In this framework, the building skin isprobably that element of the construction which shows the largest potential, especially if its properties can be continuously tuned so that the best response to different dynamic indoor and outdoor boundary conditions can be achieved. Although it is not possible to state that the dynamic building envelope alone could represent the only solution to achieving the nZEB target, great expectations are placed on advanced integrated façade systems. The aim of this research is therefore to evaluate to what extent dynamic and active building skins can reduce operational energy demand in buildings. In order to find an answer to such a wide (and general) question, the research activity is organized using a multi-level structure. Each segment of the investigation is thus dedicated to assessing the impact of such a vision on different scales: from a whole building skin approach (concept level) to an intermediate scale (system level) and further down to a very detailed and specific class of components (material-technology level). In the concept level, an ideal dynamic building skin is assumed and modelled. The performance of such a theoretical configuration is then numerically assessed and compared with that of a more conventional reference envelope solution. In the system level, an integrated multifunctional façade module, characterized by a high degree of adaptability and responsiveness, is presented, and its energy and thermo-physical behaviour evaluated by means of an experimental analysis. Finally, in the material-technology level, the implication of glazing systems integrating phase change materials on the energy performance and on thermal comfort are evaluated by means of experimental, numerical and laboratory analyses. The findings demonstrate that improvements in energy efficiency and comfort performance can be achieved when dynamic concepts, systems and technologies are applied. In every level, the dynamic component often provides a very good performance and, when compared to a conventional solution, advantages are shown.However, it is important that dynamic components are coherently employed in the framework of an integrated building design vision and properly managed. Further, the simple adoption of such systems without a global approach and optimal control strategies is often not enough to reach a significant improvement in energy efficiency and IEQ. The results also show that, sometimes, the advantages achieved by the investigated configurations may be lower than expected, though an optimization of their performance is probably still possible. Limitations in the analyses and possible solutions for future development of the research activity are also discussed, pointing out that, if from the one hand, considerable efforts are still needed in research and development before a completely adaptable building skin can be effectively employed on a large scale, on the other hand the large potentials that this vision has are worthy of further investigatio
Thermo-physical behaviour and energy performance assessment of PCM glazing system configurations: A numerical analysis
Full text linkAbstractThe 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
Physical-chemical properties evolution and thermal properties reliability of a paraffin wax under solar radiation exposure in a real-scale PCM window system
No full textExperimental analysis of the energy performance of a full-scale PCM glazing prototype
No full textThis paper deals with the development and use of innovative glazing systems that utilize Phase Change Material (PCM) to achieve dynamic and responsive behaviour. The coupling of a PCM and glass panes could be a way of improving the low thermal inertia of fenestrations and could be an effective way of collecting, storing and exploiting solar energy at a building scale. In the present work, a simple prototype of a PCM glazing system has been proposed and its energy performance has been analysed and compared with a conventional fenestration. The two glazing technologies were installed on an south facing outdoor test cell, in a temperate sub-continental climate. The surface temperatures, transmitted irradiances and heat fluxes of both the PCM glazing and the reference fenestration were measured during an extensive experimental campaign. Summer, Mid-season and Winter days were considered during the analysis, in both sunny and cloudy weather conditions, in order to assess the energy performance of the PCM glazing under different boundary conditions. The experimental results have highlighted a good ability of the PCM glazing to store solar energy and to smooth and delay peak values of the total heat flux. In summer the PCM prototype allows the energy gain to be lowered by more than 50%, compared to the traditional fenestration. In winter, a suitable reduction in the heat loss during the day can be observed, but the direct solar gain is also drastically reduced and the application of this technology for passive solar heating purpose might not always be effective. The obtained results have pointed out the promising performance of PCM glazing, even though a careful integration of the PCM glazing component with the control strategies of the indoor air temperature (e.g. night cooling) is necessar
Energy performance assessment of advanced glazed façades in office buildings
No full textThe adoption of glazed façades in commercial building is becoming more and more widespread. The main limits of conventional transparent façades related to energy efficiency and IEQ aspects have been overcome developing a new generation of transparent building envelope components called Advanced Integrated Façades This paper evaluates if the thermal behaviour of this kind of technologies can be correctly assessed by means of conventional performance parameters. Data from experimental campaigns on a reflective double glazed unit and on a Climate Façade under actual operating conditions have been used to estimate the correspondent equivalent U-value and g-value. Subsequently, these parameters have been employed to calculate the energy balance of the same glazed façades. The validation of the parameters is then carried out through the comparison between experimental and simulated specific total hourly heat flux and specific total daily energy. The result shows that it is still acceptable to use conventional performance parameters for “simple” glazing technology (e.g. reflective double glazing unit). On the contrary, the adoption of such parameters in case of more advanced façade technologies leads to considerable inaccuracies and makes the predictions based on these metrics not reliable
A numerical model to evaluate the thermal behaviour of PCM glazing systems
No full textThe adoption of Phase Change Materials (PCMs) in building components is an up-to-date topic and a relevant number of research activities on this issue are currently on the way. A particular application of PCMs in the building envelope focuses on the integration of such a kind of material into transparent envelope components. A numerical model that describes the thermo-physical behaviour of a PCM layer in combination with other transparent materials (i.e. glass panes) has been developed to perform numerical analyses on various PCM glazing systems configurations. The paper illustrates the structure of the model, the main equations implemented and the hypotheses adopted for the model development. The comparison between numerical simulations and experimental data of a simple PCM glazing configuration is also presented to show the potentials and the limitations of the numerical model. While a good agreement between simulations and experimental data can be shown for the surface temperature of the glazing, the comparison between simulated and measured transmitted irradiances and heat fluxes does not always reach the desired accuracy. However, the numerical tool seems to predict well the thermo-physical behaviour of the system and may therefore represent a good starting point for further simulations on PCM glazing system configurations
Modeling and experimental validation of an algorithm for simulation of hysteresis effects in phase change materials for building components
Full text linkThe use of Phase Change Materials (PCM) in different building applications is a hot topic in today's R&D activities. Numerical simulations of PCM-based components are often used both for research activities and as a design tool, although present-day codes for building performance simulation (BPS) present some shortcomings that limit their reliability. One of these limitations is the limited possibility of replicating the effects given by thermal hysteresis – a characteristic of several PCMs.
In this paper, an original algorithm that allows hysteresis effects to be accounted for is described and the results from simulations are compared against experimental data. The algorithm is implemented in EnergyPlusTM and makes use of the Energy Management System (EMS) group, one of the high-level control methods available in EnergyPlusTM. The algorithm enables the replication of PCM's different heating/cooling enthalpy curves in this BPS tool, which just recently was equipped with an integrated module for the replication of the effects of thermal hysteresis.
A comparison between numerical results from the proposed model and from other methods implemented in BPS tools, and the experimental data provided, shows the impact of the algorithm in the simulation of heat transfer in a PCM layer intent for opaque walls. In general, it is shown that the proposed method presents a better agreement with experimental data than alternative modelling approaches, but it is also seen that all the tested numerical models are not fully able to replicating the behaviour of PCM layers if the PCM does not melt or resolidify completely (i.e. it remains in the phase change) during the charge/discharge cycle. A local sensitivity analysis complements this study and highlights the most relevant parameters that influence the results of a simulation carried out with the proposed model.
Finally, the paper hypothesises that the general discrepancy between simulations and experimental data seen in the case of incomplete melting of the PCM layer can be due to unsuitable data for the thermophysical behaviour of the PCM, which are obtained through conventional characterisation procedures far from the physics of the PCM layer when in real building structures
Numerical model and simulation of a solar thermal collector with slurry Phase Change Material (PCM) as the heat transfer fluid
No full textThe performance of conventional, water based, solar thermal collectors is limited by some intrinsic limitations, such as the need for high irradiation levels and the heat loss due to the relatively high temperature of the heat transfer fluid. In order to overcome these limitations and to improve the performance of solar thermal collectors, a different kind of heat transfer fluid can be proposed. This fluid is based on the exploitation of the latent heat of fusion/solidification of suspended particles, which change their state of aggregation at a micron scale, but keep/maintain the liquid state of the fluid at a macroscopic scale. An example of an already existing material that shows this feature is the so-called slurry phase change material or PCS. OR The so-called slurry phase materials, or PCS, are examples of this kind of material.
In order to evaluate the effectiveness of such a concept, a numerical model of a PCS-based flat-plate solar thermal collector has been developed, presented and discussed. This model has been derived from the well-known Hottel–Whillier model, but several changes have been implemented so that a phase change of the heat transfer fluid can be handled, as well as the thermophysical properties of a non-Newtonian fluid, such as those of a PCS. The paper presents the main and auxiliary equations necessary/?that have been introduced to modify the Hottel–Whillier model.
A numerical analysis conducted with the newly developed model, is also presented in the paper. The aim of these simulations was to test the code and obtain a preliminary evaluation of the performance of the novel concept. Different (dynamic) boundary conditions (location, orientation, PCM concentration) were adopted to evaluate the performance of the PCS-based technology and compare it with that of a conventional solar thermal collector.
The outcomes of the simulations have proved model robustness and the possibility of using it/OR the model is robust and that it can be used for preliminary analysis. It was also shown that the adoption of the PCS as a heat transfer fluid can lead to an increase in solar energy exploitation, with different magnitudes, (DO YOU MEAN- of different magnitude) according to the climate. The greatest benefit can be achieved for cold climates. The limitations of the analysis (e.g. fixed, non-optimal flow rate) are also discussed
Impact on thermal comfort of conventional and advanced glazed façades in office buildings
No full textTransparent façades are often used to increase the aesthetic value of the building and to provide visual contact with the outdoor. However, together with several positive features, it should be mentioned that glass façades may reduce the quality of the indoor thermal environment, causing thermal discomfort especially due to overheating in the summer season.
The aim of this paper is to compare the implications on thermal comfort of different glazed façades, whose surface temperatures have been monitored during several experimental campaigns. The analyzed glazing systems were double skin façades and non conventional single skin façades integrating different materials (i.e. phase change material, areogel). Starting from the measured internal surface temperatures, a fictitious office room was simulated in order to assess the thermal comfort performance through the calculation of the PMV index.
Results show that the choice of the glazing system can strongly affect the thermal comfort of an office
Analysis of a non-calorimetric method for assessment of in-situ thermal transmittance and solar factor of glazed systems
Full text linkThe performance of glazing systems is usually assessed through the thermal transmittance and the solar factor, two metrics characterised either through calorimetric laboratory tests or calculations. In this paper, the analysis of the performance of a non-calorimetric method for obtaining the in-situ thermal transmittance and solar factor of glazing systems is presented. This method, developed as a trade-off between accurate (and expensive) laboratory tests (which characterise the systems under standardised, “averaged” conditions), and easy and less expensive tests on systems installed in real buildings (under real operative conditions), has been previously adopted for the characterisation of different glazed systems, but never presented and discussed in full detail. The method, suitable for full-scale glazing systems installed in buildings or in test cells, is based on the acquisition of temperature, heat flux, and solar irradiance values. Experimental data are then processed through simple equations and linear regressions to determine the thermal transmittance and the solar factor under real boundary conditions. In this paper, a detailed description of the method, the experimental test rig, and the related expected accuracy is reported. The method is then applied to a case study (a conventional double glazed unit) to give an example of the proposed procedure and to validate it. The results of the case study show the capability of the assessed in-situ thermal transmittance and solar factor to replicate the thermophysical behaviour of the glazing system within a satisfactory degree of accuracy. An in-depth discussion on the observed outcomes from the case study deepens the understanding of the method’s performance and the results’ significance
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