L’émission électronique par effet de champ est un domaine qui concerne de nombreuses applications techniques. Dans ce travail, nous avons réalisé une étude essentiellement expérimentale des différents paramètres susceptibles d’avoir une influence sur l’émission électronique. En première partie, nous exposons les résultats obtenus pour un champ électrique homogène correspondant aux faibles intensités de courant. Le rôle de la distance inter-électrodes à champ constant et l’influence de la rugosité de surface sur l’émission électronique ont été étudiés. Nous discutons la méthode classique de Fowler-Nordheim utilisée pour le dépouillement des mesures en y portant un regard critique. Un modèle simple visant à prendre en compte l’échauffement des sites émetteurs est proposé. La seconde partie concerne l’effet de l’injection de gaz sur l’émission électronique, effet qui se traduit par une diminution du courant émis quand on augmente la pression de 10⁻⁶ Pa à 10⁻² Pa à champ macroscopique constant. Nous exposons des résultats montrant un effet de seuil concernant l’apparition de l’effet du gaz sur l’émission électronique. Nous présentons également des résultats pour différents matériaux de cathode et pour différents gaz (He, H₂, N₂, Ar). Une réversibilité de cet effet est montrée après le pompage pour redescendre à 10⁻⁵ Pa. La décroissance de courant par effet de gaz est interprétée par la diminution de la valeur du facteur d’accroissement local du champ électrique (β) au niveau des émetteurs à cause du bombardement de ces sites par les ions créés à leur proximité. Un calcul du flux d’ions bombardant un site émissif a permis d’estimer le temps nécessaire pour modifier un émetteur de façon cohérente avec les observations expérimentales. La théorie de la migration des atomes en surface de l’électrode en présence d’un champ électrique est proposée pour expliquer la réversibilité de l’effet de gaz observée qui est, selon cette théorie, liée à l’augmentation de la valeur de β au niveau des émetteurs. / Field electronic emission is a domain which concerns numerous different technical applications. In this work, we have taken an essentially experimental approach to study various parameters having influence on field emission. In the first part of the thesis, we have described the results obtained with a homogeneous electric field with relatively weak field emission. The role of the inter-electrode distance at constants field as well as that of the cathode surface roughness on field emission are studied. The classical method of Fowler-Norheim was then used for the analysis of the measurements. A simple model aiming to take into account the effect of the heating of the emission sites is then proposed. The second part of the theses concerns the effect of the injection of gas on the field emission; this effect being to significantly reduce emission intensity when the gas pressure is raised from 10⁻⁶ to 10⁻² Pa at constant field. A threshold value of emission intensity is shown to be necessary for the observation of this gas effect. The effect of different gas types (He, H₂, N₂, Ar) and cathode materials are also described. The gas effect is shown to be reversible upon lowering of the gas pressure to 10⁻⁵ Pa. The reduction in current is interpreted by a lowering of the field enhancement factor (β) of emission sites by ionic bombardment by ions created locally (within distances on the order of microns) near the cathode surface. A calculation of the flux of bombarding ions is used to estimate the time necessary to modify an emission site in a way corresponding to the observations. The phenomenon of surface migration in the presence of intense electric field is then proposed to explain the reversibility of the gas effect, increasing the local field enhancement factor.

We are coming to realize that there is an urgent need to reduce energy usage in buildings and it has to be done in a sustainable way. This thesis focuses on the performance of the building envelope; more precisely thermal performance of walls and super insulation material in the form of vacuum insulation. However, the building envelope is just one part of the whole building system, and super insulators have one major flaw: they are easily adversely affected by other problems in the built environment.  Vacuum Insulation Panels are one fresh addition to the arsenal of insulation materials available to the building industry. They are composite material with a core and an enclosure which, as a composite, can reach thermal conductivities as low as 0.004 W/(mK). However, the exceptional performance relies on the barrier material preventing gas permeation, maintaining a near vacuum into the core and a minimized thermal bridge effect from the wrapping of barrier material round the edge of a panel. A serpentine edge is proposed to decrease the heat loss at the edge. Modeling and testing shows a reduction of 60% if a reasonable serpentine edge is used. A diffusion model of permeation through multilayered barrier films with metallization coatings was developed to predict ultimate service life. The model combines numerical calculations with analytical field theory allowing for more precise determination than current models. The results using the proposed model indicate that it is possible to manufacture panels with lifetimes exceeding 50 years with existing manufacturing. Switching from the component scale to the building scale; an approach of integrated testing and modeling is proposed. Four wall types have been tested in a large range of environments with the aim to assess the hygrothermal nature and significance of thermal bridges and air leakages. The test procedure was also examined as a means for a more representative performance indicator than R-value (in USA). The procedure incorporates specific steps exposing the wall to different climate conditions, ranging from cold and dry to hot and humid, with and without a pressure gradient. This study showed that air infiltration alone might decrease the thermal resistance of a residential wall by 15%, more for industrial walls. Results from the research underpin a discussion concerning the importance of a holistic approach to building design if we are to meet the challenge of energy savings and sustainability. Thermal insulation efficiency is a main concept used throughout, and since it measures utilization it is a partial measure of sustainability. It is therefore proposed as a necessary design parameter in addition to a performance indicator when designing building envelopes. The thermal insulation efficiency ranges from below 50% for a wood stud wall poorly designed with incorporated VIP, while an optimized design with VIP placed in an uninterrupted external layer shows an efficiency of 99%, almost perfect. Thermal insulation efficiency reflects the measured wall performance full scale test, thus indicating efficiency under varied environmental loads: heat, moisture and pressure. The building design must be as a system, integrating all the subsystems together to function in concert. New design methodologies must be created along with new, more reliable and comprehensive measuring, testing and integrating procedures. New super insulators are capable of reducing energy usage below zero energy in buildings. It would be a shame to waste them by not taking care of the rest of the system. This thesis details the steps that went into this study and shows how this can be done. / QC 20120228

The motivation for development of energy efficiency and implementation of novel advanced materials applied in buildings can be traced to increasing energy costs in conjunction with an enhanced environmental awareness among people. This doctoral dissertation presents contributions towards sustainable building, where factors such as building technology, energy efficiency in buildings, workers' health issues during construction measures, and certain economic considerations for renovation of buildings have been considered. The research study aims to provide a knowledge base for motivating building owners to renovate buildings based on energy efficiency and improved indoor environment. The initial phase of the research study identifies a detailed description of common drivers, expected in renovation projects by building owners. In the second phase, an information base is identified which may facilitate the bidding processes for decision makers by means of technological, social and economic aspects. The aforementioned information base can also contribute to attentive decisions regarding sustainable renovation and energy saving measures. A strategy was developed within the Renovation Workshop of Riksbyggen, in order to promote energy saving measures concurrent with major renovations in residential buildings. This operational decision support process was applied in a tenant owners' cooperative in Sweden. The objective of this process was to showcase and more importantly to implement energy saving measures, based on knowledge transfer between different parties involved in the renovation project. For the conducted case study, this process was shown to be of great importance when decisions regarding energy saving measures in conjunction with scheduled renovations are being planned. A unique case study was conducted on two of the most commonly used environmental certification programs for buildings in Sweden; Environmental Building (Miljöbyggnad) and GreenBuilding. Following a granted access to a limited database of submitted applications to Sweden Green Building Council, the most common mistakes in these were identified and categorized. This study contributed to further understanding about the level of ability among building consultants, comprehension of environmental certification, and enhancement of the ability to produce high-quality calculations concerning building-related energy usage. In addition, this insight can provide a basis for planning of continuing education of consultants within the field of building technology. For a church building, a study was conducted subsequent to an exchange of an existing electric coil heating system to a hydronic ground source heat pump system. Analyses of the energy demand and energy signature, prior to and after installation were carried out. The replacement of the original heating system with a ground source heat pump system for the church building constitutes a reduced energy consumption level of approximately 66%, at the average outside temperature of -2.30 °C. This study demonstrated that data from a detailed electric bill can be utilized in order to obtain the energy signature of the building and henceforth assess the energy savings. One aspect of the research, examined the decision making process related to sustainable renovation and refurbishment in buildings. The utilized methodology identified three distinct phases in order to instigate an engagement in sustainable renovation, by means of questionnaires and semi-structured interviews. In particular, the attitudes of stakeholders in Sweden, Denmark and Cyprus to sustainable building were studied through three separate case studies. Within the framework of this study, it was identified that building physics and durability are among the most important drivers for energy renovation. The results provided an insight into the renovation process in the aforementioned countries and identified that drivers such as improvement of indoor air quality and elimination of moisture in the building envelope are also of crucial importance. Another aspect of the conducted research highlights workplace accidents occurring within the Swedish construction sector. The purpose of this study was to serve as a useful tool to track the working environments of construction workers in order to reduce health and safety issues within the construction sector. The findings of this research suggest that despite laws, regulations or additional factors that seek to ensure a safe and healthy environment for construction workers, the Swedish construction work force still faces challenges. Moreover, it is identified that construction workers participating in the study call for additional measures to ensure occupational health and safety. Improved knowledge of economic performance and technical results of renovations can contribute to a snowball effect, with more property owners recognizing the value of energy aspects and thus provide an increased level of energy savings. / <p>QC 20140127</p> / A Concept for promotion of sustainable retrofitting and renovation in Early Stages (ACES)

Today’s buildings are responsible for 40% of the world’s energy use and also a substantial share of the Global Warming Potential (GWP). In Sweden, about 21% of the energy use can be related to the heat losses through the climatic envelope. The “Million Program” (Swedish: Miljonprogrammet) is a common name for about one million housing units, erected between 1965 and 1974 and many of these buildings suffer from poor energy performance. An important aim of this study was to access the possibilities of using Vacuum Insulation Panels (VIPs) in buildings with emphasis on the use of VIPs for improving the thermal efficiency of the “Million Program” buildings. The VIPs have a thermal resistance of about 8-10 times better than conventional insulations and offer unique opportunities to reduce the thickness of the thermal insulation. This thesis is divided into three main subjects. The first subject aims to investigate new alternative VIP cores that may reduce the market price of VIPs. Three newly developed nanoporous silica were tested using different steady-state and transient methods. A new self-designed device, connected to a Transient Plane Source (TPS) instrument was used to determine the thermal conductivity of granular powders at different gaseous pressure combined with different mechanical loads. The conclusion was that the TPS technique is less suitable for conducting thermal conductivity measurements on low-density nanoporous silica powders. However, deviations in the results are minimal for densities above a limit at which the pure conduction becomes dominant compared to heat transfer by radiation. The second subject of this work was to propose a new and robust VIP mounting system, with minimized thermal bridges, for improving the thermal efficiency of the “Million Program” buildings. On the basis of the parametric analysis and dynamic simulations, a new VIP mounting system was proposed and evaluated through full scale measurements in a climatic chamber. The in situ measurements showed that the suggested new VIP technical solution, consisting of 20mm thick VIPs, can improve the thermal transmittance of the wall, up to a level of 56%. An improved thermal transmittance of the wall at centre-of-panel coordinate of 0.118 to 0.132 W m-2K-1 and a measured centre-of-panel thermal conductivity (λcentre-of-panel) of 7 mW m-1K-1 were reached. Furthermore, this thesis includes a new approach to measure the thermal bridge impacts due to the VIP joints and laminates, through conducting infrared thermography investigations. An effective thermal conductivity of 10.9 mW m-1K-1 was measured. The higher measured centre-of-panel and effective thermal conductivities than the published centre-of-panel thermal conductivity of 4.2 mW m-1K-1 from the VIP manufacturer, suggest that the real thermal performance of VIPs, when are mounted in construction, is comparatively worse than of the measured performance in the laboratory. An effective thermal conductivity of 10.9 mW m-1K-1 will, however, provide an excellent thermal performance to the construction. The third subject of this thesis aims to assess the environmental impacts of production and operation of VIP-insulated buildings, since there is a lack of life cycle analysis of whole buildings with vacuum panels. It was concluded that VIPs have a greater environmental impact than conventional insulation, in all categories except Ozone Depilation Potential. The VIPs have a measurable influence on the total Global Warming Potential and Primary Energy use of the buildings when both production and operation are taken into account. However, the environmental effect of using VIPs is positive when compared to the GWP of a standard building (a reduction of 6%) while the PE is increased by 20%. It was concluded that further promotion of VIPs will benefit from reduced energy use or alternative energy sources in the production of VIP cores while the use of alternative cores and recycling of VIP cores may also help reduce the environmental impact. Also, a sensitivity analysis of this study showed that the choice of VIPs has a significant effect on the environmental impacts, allowing for a reduction of the total PE of a building by 12% and the GWP can be reduced as much as 11% when considering both production and operation of 50 yes. Finally, it’s possible to conclude that the VIPs are very competitive alternative for insulating buildings from the Swedish “Million Program”. Nevertheless, further investigations require for minimizing the measurable environmental impacts that acquired in this LCA study for the VIP-insulated buildings. / Dagens byggnader ansvarar för omkring 40% av världens energianvändning och  står också för en väsentlig del av utsläppen av växthusgaser. I Sverige kan ca 21 % av energianvändningen relateras till förluster genom klimatskalet. Miljonprogrammet är ett namn för omkring en miljon bostäder som byggdes mellan 1965 och 1974, och många av dessa byggnader har en dålig energiprestanda efter dagens mått. Huvudsyftet med denna studie har varit att utforska möjligheterna att använda vakuumisoleringspaneler (VIP:ar) i byggnader med viss fokus på tillämpning i Miljonprogrammets byggnader. Med en värmeledningsförmåga som är ca 8 - 10 gånger bättre än för traditionell isolering erbjuder VIP:arna unika möjligheter till förbättrad termisk prestanda med minimal isolerings tjocklek. Denna avhandling hade tre huvudsyften. Det första var att undersöka nya alternativ för kärnmaterial som bland annat kan reducera kostnaden vid produktion av VIP:ar. Tre nyutvecklade nanoporösa kiselpulver har testats med olika stationära och transienta metoder. En inom projektet utvecklad testbädd som kan anslutas till TPS instrument (Transient Plane Source sensor), har använts för att mäta värmeledningsförmågan hos kärnmaterial för VIP:ar, vid varierande gastryck och olika mekaniska laster. Slutsatsen blev att transienta metoder är mindre lämpliga för utföra mätningar av värmeledningsförmåga för nanoporösa kiselpulver låg densitet. Avvikelsen i resultaten är dock minimal för densiteter ovan en gräns då värmeledningen genom fasta material blir dominerande jämfört med värmeöverföring genom strålning. Det andra syftet har varit att föreslå ett nytt monteringssystem för VIP:ar som kan användas för att förbättra energieffektiviteten i byggnader som är typiska för Miljonprogrammet. Genom parametrisk analys och dynamiska simuleringar har vi kommit fram till ett förslag på ett nytt monteringssystem för VIP:ar som har utvärderats genom fullskaleförsök i klimatkammare. Resultaten från fullskaleförsöken visar att den nya tekniska lösningen förbättrar väggens U-värde med upp till 56 %. En förbättrad värmegenomgångskoefficienten för väggen i mitten av en VIP blev mellan 0.118 till 0,132 W m-2K-1 och värmeledningstalet centre-av-panel 7 mW m-1K-1 uppnåddes. Detta arbete innehåller dessutom en ny metod för att mäta köldbryggor i anslutningar med hjälp av infraröd termografi. En effektiv värmeledningsförmåga för 10.9 mW m-1K-1 uppnåddes. Resultaten tyder även på att den verkliga termiska prestandan av VIP:ar i konstruktioner är något sämre än mätvärden för paneler i laboratorium. En effektiv värmeledningsförmåga av 10.9 mW m-1K-1 ger dock väggkonstruktionen en utmärkt termisk prestanda. Det tredje syftet har varit att bedöma miljöpåverkan av en VIP-isolerad byggnad, från produktion till drift, eftersom en livscykelanalys av hela byggnader som är isolerade med vakuumisoleringspaneler inte har gjorts tidigare. Slutsatsen var att VIP:ar har en större miljöpåverkan än traditionell isolering, i alla kategorier förutom ozonnedbrytande potential. VIP:ar har en mätbar påverkan på de totala utsläppen av växthusgaser och primärenergianvändningen i byggnader när både produktion och drift beaktas. Miljöpåverkan av de använda VIP:arna är dock positiv jämfört med GWP av en standardbyggnad (en minskning med 6 %) medan primärenergianvändningen ökade med 20 %. Slutsatsen var att ytterligare användning av VIP:ar gynnas av reducerad energiförbrukning och alternativa energikällor i produktionen av nanoporösa kiselpulver medan användningen av alternativa kärnmaterial och återvinning av VIP kärnor kan hjälpa till att minska miljöpåverkan. En känslighetsanalys visade att valet av VIP:ar har en betydande inverkan på miljöpåverkan, vilket ger möjlighet att reducera den totala användningen av primärenergi i en byggnad med 12 % och utsläppen av växthusgaser kan vara minska, så mycket som 11 % när det gäller både produktion och drift under 50 år. Avslutningsvis är det möjligt att dra slutsatsen att VIP:ar är ett mycket konkurrenskraftigt alternativ för att isolera byggnader som är typiska för Miljonprogrammet. Dock krävs ytterligare undersökningar för att minimera de mätbara miljöeffekter som förvärvats i denna LCA-studie för VIP-isolerade byggnader. / <p>QC 20151109</p> / Simulations of heat and moisture conditions in a retrofit wall construction with Vacuum Insulation Panels / Textural and thermal conductivity properties of a low density mesoporous silica material / A study of the thermal conductivity of granular silica materials for VIPs at different levels of gaseous pressure and external loads / Evaluation of the thermal conductivity of a new nanoporous silica material for VIPs – trends of thermal conductivity versus density / A comparative study of the environmental impact of Swedish residential buildings with vacuum insulation panels / ETICS with VIPs for improving buildings from the Swedish million unit program “Miljonprogrammet”