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.
The optical characteristics of an advanced glazing system are presented in this paper. The investigated glazing system is based on the incorporation of a paraffin-based Phase Change Material (PCM) into a transparent component, made of two extra-clear glass panes and a cavity where the PCM layer is placed. Due to the highly scattering property of the system (when the PCM is in solid state), the use of a large integrating sphere equipment (75 cm diameter) is necessary to obtain reliable results. The spectral transmission, reflection and absorption coefficients of the PCM glazing system are measured between 400 and 2000 nanometers, and the integrated values are calculated according to the relevant standards. The optical properties are determined with a maximum relative error of 4% (on the sum of the transmission, reflection and absorption coefficients), when the PCM layer is either in complete solid state or liquid state. The average error for all the optical properties is 2%. Different thicknesses of the PCM layer are used in order to assess the dependency of the optical properties on the PCM layer thickness. The angular dependency is also investigated for beam angle up to 45 deg
Transparent 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.
The introduction of dynamic envelope components and systems can have a significant reduction effect on heating and cooling demands. In addition, it can contribute to reduce the energy demand for artificial lighting by better utilization of the daylight. One of these promising technologies is Phase Change Materials (PCM). Here, the latent heat storage potential of the transition between solid and liquid state of a material is exploited to increase the thermal mass of the component. A PCM layer incorporated in a transparent component can increase the possibilities to harvest energy from solar radiation by reducing the heating/cooling demand and still allowing the utilization of daylight. Measurements have been performed on a state-of-the-art window that integrates PCM using a large scale climate simulator. The glazing unit consists of a four-pane glazing with an integrated layer that dynamically controls the solar transmittance (prismatic glass) in the outer glazing cavity. The innermost cavity is filled with a PCM, contained into transparent plastic containers. The introduction of dynamic components in the building envelope makes the characterization of static performance (e.g. the thermal transmittance, U-value; the solar heat gain coefficient) insufficient in giving the full picture regarding the performance of the component in question. This article presents a series of measurements, and the related methodologies, carried out on a window with incorporated PCM. The tests have been carried out using several test cycles comprised of temperature and solar radiation cycling, where the aim has been to delve deeper into the possibilities for characterization of dynamic building envelope components by full scale testing in a climate simulator.
The 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.
The building enclosure plays a relevant role in the management of the energy flows in buildings and in the exploitation of the solar energy at 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 the energy demand for artificial lighting is often not considered, especially during the first stage of the design process. A global approach (i.e. including heating, cooling and artificial lighting energy demand) is instead necessary to reduce the total energy need of the building. When considering the total energy use in building, the optimization of a façade configuration becomes not straightforward, because non-linear relationships often occur. The paper presents a methodology and the results of the search of the optimal transparent percentage of a façade module for office buildings. The investigation is carried out for the four main orientations, on three "average" office buildings (with different surface-area-to-volume ratio), and with different HVAC system's efficiency, located in Frankfurt. The results show that the optimal configuration, regardless of the orientations and the surface-area-to-volume ratio, is achieved in an "average" office building when the transparent component of the façade module is between 35% and 45% of the total façade module surface. The north-exposed façade is the one that presents the highest difference between the "optimal configuration" and the worst one, while the south-exposed façade is the one which suffers less in case of the "worst" configuration.
In recent years, Thermal Energy Storage (TES) is becoming more and more important in different engineering applications. As far as the building sector is concerned, TES is considered a crucial feature to reach the net-Zero Energy Building (nZEB) goal. Commonly, TES in building is obtained using the sensible heat property of conventional building materials (building thermal inertia). The drawbacks of this strategy are: the low amount of thermal energy that can be stored; the overheating of the indoor environment that may occur if elevate amount of heat is collected by a conventional building material. On the contrary, the exploitation of the latent heat of dedicate materials (the so-called Phase Change Materials - PCMs) for TES purpose (Latent Heat Thermal Energy Storage - LHTES) presents different advantages: it allows a much higher energy storage density; it allows "temperature selective" thermal energy absorption and release (by choosing the melting temperature range of the PCM). Moreover, since the storage is done at almost isothermal conditions, it is easier to match the energy demand of the building, with the requirements posed by indoor thermal comfort conditions. An exhaustive collection of both laboratory and commercial grade PCMs of different nature and for different purposes can be found in . The exploitation of LHTES is now gaining popularity : different applications of PCMs in construction are currently under investigation [3-5] and, sometimes, commercially available. The most common applications concern the incorporation of PCMs into opaque elements for indoor partitions, structural components and insulation layers. The adoption of PCMs may also occur in combination with active systems (e.g. air-based heating systems, floor heating). Furthermore, because of the ability of certain PCMs to transmit (part of) the visible spectrum of the solar radiation, some transparent/semi-transparent building envelope elements filled with PCMs have been also investigated [6-9]. Some systems based on PCMs integration into transparent components have also appeared on the market and have been adopted in some buildings too. The chemical stability and thermal reliability of PCMs and their live spam are key features to ensure the economic feasibility of exploiting LHTES. The requirements on the stability of the PCMs' thermal properties may depend on the different application of PCMs. However, as a general rule, it is mandatory that no relevant changes occur in the melting temperature and in the latent heat of fusion due to the thermal cycles the PCM undergoes. In common applications, such as in gypsum wallboard, thermal cycles are mostly caused by energy absorption and release by conduction and convection. If radiative transfers occur, only the long-wavelength infrared region is involved. On the contrary, in the case of PCMs contained into transparent elements and directly exposed to the solar radiation, the entire electromagnetic solar spectrum passes through and heats the materials. Thus, it may occur that the high energy radiation contained in the UV-VIS range negatively affects the thermal stability of PCMs. Thermal reliability of PCMs has been investigated since time. Accelerated thermal cycle test is usually adopted to simulate the ageing of the material. This technique consists in multi melt/freeze cycles (up to some thousands of cycles) conducted in laboratory by means of dedicated devices, under controlled and fixed conditions. The evolution of the thermal properties of the materials (i.e. the melting temperature and the latent heat of fusion) is then evaluated by means of Differential Scanning Calorimetry (DSC) on different samples of the material, which correspond to different ageing times. Following this procedure, several studies have been conducted to assess the thermal reliability of different PCMs. The literature survey reveals the lack of dedicated investigations that concern the chemical stability and thermal reliability of PCMs which are supposed to be directly exposed to the solar radiation. Although this application is not one of the main popular and developed, the use of PCMs in transparent components is under evaluation since time [6-9] and some solutions are already commercially available . As mentioned above, this type of application may cause chemical instability and degradation. In fact, PCMs can be damaged by the combined action of the UV-VIS electromagnetic radiation and oxidative processes. The aim of this research is to characterize and analyze the evolution of the thermal properties, and to evaluate the thermal reliability, of a paraffin wax exposed to the solar radiation. The analysis is conducted on four samples of the same PCM collected at regular interval during an on-field experimental campaign on a PCM glazing , that was exposed to operative conditions in a test cell equipment for more than one year.
Responsive Building Elements (RBEs) are technologies for the exploiting at the building scale renewable energy sources and the opportunities offered by the environment. Among the RBE concepts identified by the IEA-ECBCS Annex 44, Advanced Integrated Façades (AIFs) is probably one of the most promising technologies. Important players in the field of the façade have started to develop integrated modular façade systems (Multifunctional Façade Modules - MFMs), with a dynamic behaviour and interacting with the other building services, in order to reduce the building energy consumption and maximize the indoor comfort conditions. In the frame of a research activity aimed at the development of solar and active building skin, a MFM has been conceived and a prototype realized for experimental evaluation. The work presented in this paper illustrates the first results of the experimental campaign on the RBE-MFM called ACTRESS (ACTive, RESponsive and Solar). The ACTRESS façade module is being tested by means of a Test Cell apparatus. The main physical quantities (e.g. heat fluxes, temperatures, transmitted irradiances, PV power, air flows, etc.) are continuously measured by means of more than 70 sensors placed on the mock-up. A detailed picture of the monitoring system is given with the description of the measurement procedures. Preliminary results concerning the behaviour of the system during summer and mid season are illustrated and discussed.
Responsive Building Elements (RBEs) and energy storage within the building are considered as a crucial development towards the nearly Zero Energy/Emission Building target. The exploitation at the building scale of renewable energy sources and the opportunities offered by the environment is achieved by the ability of the RBEs to dynamically adapt to changing environmental conditions. Among these concepts, Advanced Integrated Façades (AIFs) are probably one the most promising technologies, due to the important role that the building envelope plays in controlling the energy and mass flows between the building and the outdoor environment. In the framework of a decade-long research activity on AIFs, a new Multifunctional Façade Module (MFM) has been conceived and a prototype realized for the experimental assessment of its performance. The work herewith presented illustrates the results of the experimental campaign on the RBE-MFM called ACTRESS (ACTive, RESponsive and Solar)
The 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 is 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) is 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 simulations on different configurations of PCM glazing systems.