Jan Vincent Thue

Aging effects on thermal properties and service life of vacuum insulation panels

Vacuum insulation panels (VIPs) represent a high-performance thermal insulation material solution offering an alternative to thick wall sections and large amounts of traditional insulation in modern buildings. Thermal performance over time is one of the most important properties of VIPs to be addressed, and thus the aging effects on the thermal properties have been explored in this article. Laboratory studies of aging effects are conducted over a relatively limited time frame. To be able to effectively evaluate aging effects on thermal conductivity, accelerated aging experiments are necessary. As of today, no complete standardized methods for accelerated aging of VIPs exist. By studying the theoretical relationships between VIP properties and external environmental exposures, various possible factors for accelerated aging are proposed. The factors that are found theoretically to contribute most to aging of VIPs are elevated temperature, moisture, and pressure. By varying these factors, it is assumed that a substantial accelerated aging of VIPs can be achieved. Four different accelerated aging experiments have been performed to study whether the theoretical relationship may be replicated in practice. To evaluate the thermal performance of VIPs, thermal conductivity measurements have been applied. The different experiments gave a varying degree of aging effects. Generally, the changes in thermal performance were small. Results indicated that the acceleration effect was within what could be expected from theoretical relationships, but any definite conclusion is difficult to draw due to the small changes. Some physical changes were observed on the VIPs, i.e., swelling and curving. This might be an effect of the severe conditions experienced by the VIPs during testing, and too much emphasis on these should be avoided.

Improving thermal insulation of timber frame walls by retrofitting with vacuum insulation panels – experimental and theoretical investigations:

Many of the Norwegian buildings from the 1960s–1980s with timber frame walls are ready for retrofitting. Retrofitting of these buildings with vacuum insulation panels (VIPs) may be performed without significant changes to the buildings, e.g., extension of the roof protruding and fitting of windows. Effectively, U-values low enough to fulfill passive house or zero energy requirements may be achieved; thus, contributing to a reduction of the energy use and CO2 emissions within the building sector. Retrofitting with VIPs on the exterior side is normally considered as a better solution; however, it may cause condensation in the wall. To investigate this and the interior option, four different wall fields were tested. One of them was a reference wall field built according to Norwegian building regulations from the 1970s, and three other fields represent different ways of increasing the thermal insulation level. In addition to the experiments, numerical simulations were performed where temperature, relative humidity, and surface wetness were measured. In total, the results from the experiments, simulations, and condensation controls conclude that timber frame buildings insulated with 100 mm mineral wool, might be retrofitted at the outside by adding 30 mm VIPs. However, this method for retrofitting provides limits to outdoor temperature, indoor moisture excess, and indoor temperature.

An approach to impact assessments of buildings in a changing climate

Future climate change caused by global warming could have dramatic consequences for the built environment. An approach is presented to understand and assess these impacts on the Norwegian building stock in a changing climate. The approach is tested using calculations for the decay potential in timber structures (possessing wood cladding, timber frames or both). First, building data and climate data are compiled in a Geographic Information System (GIS). Second, the computer model calculates the number of buildings that could be affected by a particular climate parameter for historical climate data (1961–1990) and a future climate scenario (2071–2100). The results show that today approximately 615 000 buildings are situated in areas with a high potential risk of rot-decay. In 2100 this number could increase to roughly 2.4 million. The large current amount of wooden buildings and a high number of building defects indicates that future new and refurbished buildings need to be built more robustly to meet the future impacts of climate change. Other climate parameters, e.g. sea level rise, changes in permafrost, the risk of frost decay, temperature change and changes in the amount of wet winter precipitation – are under investigation for their effect on the Norwegian building stock. Les changements climatiques futurs causés par le réchauffement planétaire pourraient avoir des conséquences dramatiques sur l’environnement bâti. Il est présenté une approche visant à comprendre et évaluer ces impacts sur le parc bâti norvégien sous un climat en évolution. Cette approche est testée en utilisant des calculs relatifs aux possibilités de pourrissement des structures en bois de construction (possédant des bardages en bois, des ossatures bois, voire les deux). Dans un premier temps, les données relatives aux bâtiments et les données relatives aux climats sont compilées dans un Système d’Information Géographique (SIG). Dans un second temps, le modèle informatique calcule le nombre de bâtiments qui pourraient être affectés par un paramètre climatique particulier dans le cadre des données climatiques historiques (1961–1990) et d’un scénario climatique futur (2071–2100). Les résultats montrent qu’aujourd’hui environ 615 000 bâtiments se situent dans des régions présentant un risque potentiel élevé de pourrissement. En 2100, ce nombre pourrait s’accroître jusqu’à atteindre environ 2,4 millions. La grande quantité actuelle de bâtiments en bois et un nombre élevé de défauts de construction indiquent qu’il faudrait que les futurs bâtiments neufs et rénovés soient construits de manière plus solide afin de répondre aux impacts futurs du changement climatique. D’autres paramètres climatiques – tels que par exemple l’élévation du niveau de la mer, les modifications du permafrost, le risque de pourrissement par le gel, les changements de température et les changements dans la quantité de précipitations des hivers humides – sont étudiés sous l’angle de leur effet sur le parc bâti norvégien. Mots clés: mesures d’adaptation, parc bâti, changement climatique, études d’impact, bâtiments solides, risque de pourrissement, bâtiments en bois, Norvège

Robustness Classification of Materials, Assemblies and Buildings

Reliable methods are needed for classifying the robustness of buildings and building materials for many reasons, including ensuring that constructions can withstand the climate conditions resulting from global warming, which might be more severe than was assumed in an existing building’s design. Evaluating the robustness of buildings is also important for reducing process-induced building defects. We describe and demonstrate a flexible framework for classifying the robustness of building materials, building assemblies, and whole buildings that incorporates climate and service life considerations.

Numerical Simulation of Natural Convection in Three-dimensional Cavities with a High Vertical Aspect Ratio and a Low Horizontal Aspect Ratio

In this article a commercial computational fluid dynamic program is used to study the effect of the horizontal aspect ratio on heat flow through cavities with a high vertical aspect ratio (cavities typically found in vertical window frames with internal cavities). The cavities studied have two opposite isothermal vertical walls separated by four adiabatic walls. The vertical aspect ratios are 20, 40, and 80 and the horizontal aspect ratios range from 0.2 to 5. Simulations of two-dimensional cavities are also included. The simulations show that three-dimensional cavities with a horizontal aspect ratio larger than five can be considered as being two-dimensional cavities to within 4% when considering heat transfer rates. Nusselt number correlations for the different horizontal aspect ratios are included. Complex multicellular flow is presented for one of the three-dimensional cavities.

High-performance weather-protective flashings

The lifetime of the built environment depends strongly on the severity of local climatic conditions. A well-functioning and reliable infrastructure is a precondition for economic growth and social development. The climate and topography of Norway puts great demands on the design and localization of buildings. The relationship between materials, structures and climatic impact is highly complex; illustrating the need for new and improved methods for vulnerability assessment of building envelope performance in relation to externally imposed climatic strains. Historically, major variations in climatic impact have led to corresponding large variations in building practice throughout the country - often well suited to local conditions. Today it is fair to say that sound building traditions and practice to some extent are being rejected in the quest for cost-effective solutions. Furthermore, projected changes in climatic conditions due to global warming will enhance the vulnerability within the built environment.The primary objectives of the present dissertation are to increase the knowledge about possible impacts of climate change on building envelope performance, and to analyse and update methods for the planning and design of external envelopes in relation to climatic impact. This is accomplished through the development of integrated approaches and improved methods for assessing impacts of external climatic parameters on building envelopes, combining knowledge on materials, structures and relevant climate data, applicable for both historical data and scenarios for climate change. The results will contribute to more accurate building physics design guidelines, promoting high-performance building envelopes in harsh climates.Approaches to assessments of the risks associated with climate change and buildings are suggested, identifying main areas of vulnerability in the construction industry. It is shown that there are benefits to be gained from the introduction of risk management strategies within a greater extent of the construction industry. A way of analysing the building economics of climate change is also proposed Analyses of building defects are necessary in order to further develop tools, solutions and preventive measures ensuring high-performance building envelopes. To illuminate the vulnerability of different building envelope elements under varying climatic exposure, a comprehensive analysis of empirical data gathered from process induced building defect assignments is carried out. The amount of building defects in Norway clearly illustrates that it is not only the extreme weather events that need to be studied as a foundation for adaptation towards a changing climate. Furthermore, the analyses of defects reveal a fundamental need for climate differentiated design guidelines.New and improved methods for geographically dependent design of building envelopes are proposed:- A method for assessing the relative potential of frost decay or frost damage of porous, mineral building materials exposed to a given climate is developed.- A national map of the potential for decay in wood structures is developed. Detailed scenarios for climate change for selected locations in Norway are used to provide an indication of the possible future development of decay rates.- A method for assessing driving rain exposures based on multi-year records of synoptic observations of present weather, wind speed and direction is also presented.These climate indices can be used as a tool for evaluation of changes in performance requirements or decay rates due to climate change under global warming incorporating data from regional- and local-level climate change scenarios. Historical records of climate data have finally been used to illuminate challenges arising when introducing international standards at the national level, without considering the need for adjustments to reflect varying local climatic conditions.At present, building standards and design guidelines presuppose use of historic weather data. Historically, location-specific climate data have only to a very limited extent been applied systematically for design purposes, life cycle assessments, and climate differentiation of the suitability of a given technical solution in a given climate. The work is a first step towards methods and approaches allowing for geographically dependent climate considerations to be made in the development of design guidelines for high-performance building envelopes, and also approaches to assess the risks associated with the future performance of building envelopes due to climate change.The dissertation focuses on methods for assessing impacts of external climatic parameters on a local scale, but with the use of daily and monthly averages of climate data. The reliability of climate indices or climate differentiated design guidelines is strongly dependent on the geographical spreading of the observing station network. The Norwegian network is not optimally distributed to fully embrace local variations, but provides a solid platform for the development of methods for geographically dependent design and guidelines on the appropriateness of different solutions in different climates.Climate indices (using geographic information systems technology)allowing for quantitative assessment of building envelope performance or decay potential may be an important element in the development of adaptation measures to meet the future risks of climate change in different parts of the world. Finally, the work offers a conceptual point of departure for the development of a vintage model of the robustness of the Norwegian building stock.

Moisture Robustness During Retrofitting of Timber Frame Walls with Vacuum Insulation Panels: Experimental and Theoretical Studies

A large amount of the buildings in Norway is from the 1960s–1980s. Many of these buildings have timber frame walls and are now ready for retrofitting. Application of vacuum insulation panels (VIPs) may make it easier to improve the thermal insulation in timber frame walls with a minimal additional thickness. Retrofitting of timber frame walls using VIPs may therefore be performed without large changes to the building, e.g. extension of the roof protruding and fitting of windows. Additionally, U-values low enough to fulfil passive house standards or zero energy building requirements may be achieved, thus contributing to a reduction of the energy use and CO2 emissions within the building sector. This work investigates different ways of retrofitting timber frame walls with VIPs on the exterior or the interior side. Timber frame walls retrofitted with VIPs on the exterior side is interesting because it allows for a continuous layer of VIPs over the building envelope, and it is also considered as a more robust solution than VIPs at the interior side (less risk of puncture). However, application of VIPs on the exterior side may cause condensation in the wall. To investigate this, a wall module containing four different wall fields was built between two climate rooms with indoor and outdoor climate, respectively. One field represents a reference wall built according to Norwegian building regulations from the 1970s. The three other fields represent different ways of improving the thermal insulation of the reference field, with VIPs at the interior or the exterior side. To minimize the size of the thermal bridge caused by traditional methods of fastening VIPs, a tailor-made VIP fastening bracket was applied in the build-up of the fields. Temperature, relative humidity (RH), and surface wetness was measured during the experiment. The surface wetness was measured on the wind barrier with a tailor-made surface wetness sensor consisting of double-sided tape, metal electrodes and paper sheets. In addition to the experimental investigations, numerical simulations and condensation control calculations were performed for the same wall fields with hygrothermal robustness performance as the main objective. In overall, the results from the experiments, simulations, and condensation controls conclude that timber frame buildings insulated with 100 mm mineral wool, might be retrofitted at the outside by adding 30 mm VIPs. However, this method for retrofitting provide limits to outdoor temperature, indoor moisture excess and indoor temperature.

Measurement of the convective moisture transfer coefficient from porous building material surfaces applying a wind tunnel method

This article presents results for the average convective moisture transfer coefficients of several porous building material samples exposed to airflow. The experimental measurements explore the effect of the various air velocities, air temperatures and local positions on the average convective moisture transfer coefficients. Selected building materials were soaked in distilled water at least 2 weeks before the measurements. A thin building specimen with moisture content close to the saturation point was mounted in level with the bottom wind tunnel surface. A stable airflow regime was measured over the thin samples placed in the specimen holder. Water from the sample holder was absorbed from the bottom side of the building materials and evaporated from the upper side of the specimen during the airflow exposure. Two different membranes were fixed over the water cup as reference materials for comparison. The measurements were carried out at a relative humidity of 50% ± 3%, air temperatures of 23.6°C ± 0.5°C, 26.5°C ± 0.5°C and 30.0°C ± 0.5°C, and air velocities of 1.1, 3.0 and 5.5 m/s. The experimental data show that the convective moisture transfer coefficient is a function of velocity, temperature difference between the ambient air and material surface, local position as well as of the material type. The experimental results from water surfaces were compared to the expressions for the convective moisture transfer coefficients from the literature.