Instrumented Indentation of Super-Insulating Silica Compacts

International audienceHighly porous silica compacts for superinsulation were characterized by instrumented indentation. Samples showed a multi-scale stacking of silica particles with a total porous fraction of 90 vol %. The two main sources of silica available for the superinsulation market were considered: fumed silica and precipitated silica. The compacts processed with these two silica displayed different mechanical properties at a similar porosity fraction, thus leading to different usage properties, as the superinsulation market requires sufficient mechanical properties at the lowest density. The measurement of Young's modulus and hardness was possible with spherical indentation, which is an efficient method for characterizing highly porous structures. Comparison of the mechanical parameters measured on silica compacts and silica aerogels available from the literature was made. Differences in mechanical properties between fumed and precipitated compacts were explained by structural organization

Annex 65, Long-Term Performance of Super-Insulating-Materials in Building Components and Systems. Report of Subtask II: Scientific Information for Standardization Bodies dealing with Hygro-Thermo-Mechanical Properties and Ageing

This subtask is divided in two actions:Action 2A: Materials Assessment & Ageing Procedures (Experiments & Simulation)Action 2B: Components & Systems Assessment (Experiments & Simulation)As their structures and microstructures are completely different, Super-Insulating Materials (SIMs) cannot be compared directly to traditional insulating materials. Worldwide acceptance of these materials will be improved if the hygro-thermal and mechanical properties of SIM can be clearly articulated and reproduced. In particular, nano-structured materials used to manufacture a SIM are characterized by a high specific area (m\ub2/g) and narrow pores (smaller than 1 μm) which make them very sensitive to gas adsorption and condensation, especially in contact with water molecules.Therefore, methods of characterization must be adapted, or new methods developed to measure the microstructural, hygro-thermal and mechanical properties of these materials and their barrier films.In parallel, modelling methods to describe heat, moisture and air transfer through nano-structured materials and films will have to be developed (adsorption and desorption models, diffusion models, freeze-thawing …).Of course, a few methods will be common to all SIMs, but due to their structural differences some specific modelling methods have to be developed.SIMs can offer considerable advantages (low thickness, low Uvalue) ; however potential drawback effects should be considered in the planning process in order to optimise the development of these extraordinary properties (very low thermal conductivity) and to prevent negative publicity which could be detrimental to this sector of emerging products. This is why ageing tests will be set according to realistic conditions (temperature, moisture, pressure, load …) as set out in SubTask 3A. One objective of artificial ageing is to understand potential degradation processes that could occur. The durability of hydrophobic treatment is one of these processes and will also be subject to discussion and investigation.At the component scale, additional characterizations are needed as panels or rolls are sold by manufacturers. In particular, thermal bridges will be carefully investigated, as the extraordinary thermal performance of SIMs are sensitive to the influence of thermal bridges

Annex 65, Long-Term Performance of Super-Insulating-Materials in Building Components and Systems. Report of Subtask I: State of the Art and Case Studies

The objective of this subtask I is to present the main characteristic of SIM (Super Insulating Materials) compared to traditional materials.Two main SIM are considered:- VIP (Vacuum Insulation Panel)- APM (Advanced Porous Materials).Moreover, the present report provides an up-to-date catalogue of commercially available materials & components with technical description and data of each product and information about the application domains and the implementation rules.An overview on all the application areas such as external & internal wall insulation, roofs, floors, ceilings …are investigated through a few case studies.Finally, preliminary results about Life Cycle Assessment of SIM are presented at the end of the report

Annex 65, Long-Term Performance of Super-Insulating-Materials in Building Components and Systems. Report of Subtask III: Practical Applications – Retrofitting at the Building Scale – Field scale

More than 80% of the energy consumption will be influenced by the existing building stock. Accordingly, building renovation has a high priority in many countries. Furthermore, several studies have shown that the most efficient way to curb the energy consumption in the building sector (new & existing) remain the reduction of the heat loss by improving the insulation of the building envelope (roof, floor, wall & windows). All since the first oil crisis in 1973-1974, the national building regulations require improvement of the thermal performance of the building envelope to significantly reduce the energy use for space heating. Following the regulations, the energy efficiency of new buildings has improved. In Europe, targeting to an average U-value close to 0.2 W/m2\ub7K is optimal. Using traditional insulation materials this means an insulation thickness of about 20 cm. Thus, the thickness of internal and/or external insulation layers becomes a major issue of concern for retrofitting projects and even for new building projects in cities. Therefore, there is a growing interest in the so-called super-insulating materials (SIM). The scope of the present work covers two different types of SIMs:• Advanced Porous Materials (APM), where the gaseous heat transfer is hindered significantly by the fine structure in the sub-micrometre range, and• Vacuum Insulation Panels (VIP), where the contribution of gaseous conductivity to the total heat transfer is suppressed by evacuation.For Advanced Porous Materials (APM) one might distinguish between• porous silica e.g. based on fumed silica, and• aerogels.For Vacuum Insulation Panels (VIP) one might distinguish between:• different core materials: fumed silica, glass fibre, PU, EPS, others;• different envelopes: metalized film, aluminium laminate, stainless steel, glass, or combinations;• with or without a getter and/or a desiccant.The objective of this Annex 65 Subtask 3 report is to define the application areas of SIM and to describe the conditions of the intended use of the products. Indeed, it’s clear that the requested performance of the SIM will strongly depend on the temperature, humidity and load conditions. For building applications, storage, handling and implementation requirements are also described. Common and specific numerical calculations will be performed at the building scale to assess the impact of SIM on the performance of the building envelope.SIM was used in almost all building components with different environmental condition (boundary condition) and in different climate zone. The moisture and temperature conditions in building components can cause moisture/temperature induced stresses and the stresses can cause damage in sensitive super insulation material e.g. VIPs. Thus, to convince the conservative market of construction, it needs, in addition to laboratory measurements, real condition/environmental measurements of commercially realized objects (new buildings as well as refurbishments) under several years of operation.The long-term performance of super insulation materials has to be determined based on case studies in field and laboratory. Full scale experiments provide knowledge of practical and technical difficulties as well as data for service life estimation. For certain conclusions to be drawn from the case studies, monitoring is essential. Unfortunately, monitoring is only performed in few case studies. In this report these experiences are gathered and evaluated from a long-term performance perspective.APMs have been commercially successful in the building industry in niche applications typically with space restrictions since the early 2000s. Therefore, over the last years, a number of state-of-the-art reviews have focused on applications of advanced porous materials, such as aerogels, used as thermal insulation in buildings. VIPs, on the other hand, have also been used in other applications than buildings, such as refrigerators and transport boxes. The different applications areas have been identified by numerous researchers. However, in most studies of VIPs available in the literature, it was only the thermal performance of the assembly that was investigated. However, also the moisture performance is important to consider since changes to existing structures will influence the risk for moisture damages.In the Annex, the gathered case studies cover a wider range of SIM i.e. aerogel blankets, AB, (7 case studies), silica-based boards, SB, (3 case studies) and VIP (22 case studies). The aim was to gather information from projects where SIMs were used in different assemblies. Some of the projects have been monitored, i.e. sensors were installed to monitor the temperature, relative humidity or heat flux through the assemblies, while only three have been followed up, i.e. where a third party have analysed the results of the monitoring. The case studies are presented and specific and general conclusions from each application are made.The case studies showed that aerogel blankets are possible to install in up to five layers (50 mm) without too much difficulty. The evaluations showed that the performance of the aerogel blankets was maintained over the evaluation period. For VIPs, it is difficult to evaluate the performance when installed in the wall. In one of the case studies in the report, the external air space made it impossible to identify the different panels by thermography. Only indirect methods, like evaluation of the measured temperatures in the wall, can be used to follow the long-term performance of the panels. In another case study, hybrid insulated district heating pipes were installed at two locations in a district heating system with temperatures up to 90\ub0C. Measurements during the period 2012 to 2015 showed no sign of deterioration of the VIPs and the temperature profile over the pipes was constant. An existing masonry wall was insulated with VIP-foam sandwich (XPS-VIP-XPS). It showed satisfactory and promising performance for a period of six years (2011-present). The analysis of the data obtained from continuous temperature monitoring across each insulation layer indicated the aging of VIP remains insignificant.In the framework of IEA EBC Annex 65 a common simulation-based procedure was introduced with the scope to identify potential critical hygrothermal working conditions of the SIM, which were identified as main drivers of the ageing effect. The study highlights that some physical phenomena (such as thermal bridging effects, the influence of temperature on the thermal conductivity and the decay of performance over time depending on the severity of the boundaryconditions) should be carefully evaluated during the design phase in order to prevent the mismatch between expected/predicted and the actual thermal performance.As general guidelines to mitigate the severity of the operating conditions of VIP, a list of recommendation are in the following summarised:• For the external wall insulation with VIP in solar exposed fa\ue7ade, the adoption of ventilated air layer could dramatically reduce the severity of the VIP operating conditions. Alternatively, light finishing colour are warmly encouraged to mitigate the surface temperature.• The protection of VIP with thin traditional insulation layer is always encouraged.• The application of VIP behind heater determines high value of surface temperature field which could potentially lead to a fast degradation of the panel. A possible solution to mitigate the severity of the boundary conditions could be the coupling of VIP with a radiant barrier, or the protection of VIP with thin insulation layer when it is possible.• In roof application, light colour (cool roof), performant water proof membrane, ventilated airspace and gravel covering layer (flat roof) represent effective solutions to mitigate the severe exposure.• In presence of wall subjected to high driving rain, it is preferable to adopt ventilated fa\ue7ade working as rain-screen to prevent the water absorption.Furthermore, to provide designers, engineers, contractors and builders with guidelines for the applications of vacuum insulation panels (VIPs) and Advanced Porous Materials (APMs) examples are given of methods that may be used to verify the quality and thermal performance of SIMs after installation. A comprehensive account of transport, handling, installation and quality check precures are presented. The main purpose of the descriptions is to promote safe transport, handling and installation. In the case of VIPs the primary issue is that of protecting the panels whereas the main concern for APMs is the safety in handling of the material.During the work of the Annex several questions regarding the long-term performance of SIMs on the building scale have been identified and discussed. Four main challenges were identified:• Knowledge and awareness among designers concerning using SIM• Conservative construction market• Cost versus performance• Long-term performance of SIMsFinally, SIMs for building applications have been developed in the recent decades. Theoretical considerations and first practical tests showed that VIP, especially those with fumed silica core, are expected to fulfil the requirements on durability in building applications for more than 25 years. Both VIPs and APMs have been successfully installed over the past 15 years in buildings. However, real experience from practical applications exceeding 15 years is still lacking, especially when considering third-party monitoring and follow up of demonstrations

Determination of the fracture energy in polymeric films by in situ photoelasticimetry on double edge notch specimen

International audienc

Water Vapor Sorption Properties of Polyethylene Terephthalate over a Wide Range of Humidity and Temperature

International audienc

The hygrothermal degradation of PET in laminated multilayer

International audienc

Dimensional instabilities of polyester and polyolefin films as origin of delamination in laminated multilayer

International audienc

Predictive durability of polyethylene terephthalate toward hydrolysis over large temperature and relative humidity ranges

International audienc