Messtechnische Ermittlung der U-Werte von Altbaufassaden im Vergleich mit Typologiewerten für den Gebäudebestand

in Bauphysik (2015)

Die Wirtschaftlichkeit von Renovierungsvorhaben an Altbauten hängt im Wesentlichen von der erwarteten Wertsteigerung, der Miethöhe und den zu erreichenden Energieeinsparungen ab. Um diese Einsparungen zu ... [more ▼]

Die Wirtschaftlichkeit von Renovierungsvorhaben an Altbauten hängt im Wesentlichen von der erwarteten Wertsteigerung, der Miethöhe und den zu erreichenden Energieeinsparungen ab. Um diese Einsparungen zu berechnen, wird ein rechnerischer Vergleich zwischen dem aktuellen Verbrauch und dem Verbrauch nach der Sanierung angestrebt. Zahlreiche Studien zeigen auf, dass der rechnerische Energiebedarf von Gebäuden häufig von dem tatsächlichen Verbrauch abweicht. Dies gilt vor allem für vor 1970 errichtete Altbauten. Ein wichtiger Eingangsparameter der Berechnungsmethodik sind die U-Werte der Aussenwände, welche typischerweise vom Energieexperten vor Ort aus Typologien des Gesetzgebers für die jeweilige Wandkonstruktion ausgewählt werden. In dieser Veröffentlichung werden Mess- und Simulationsergebnisse von verschiedenen Wandtypen präsentiert. Die ermittelten Werte lagen zwischen 0.9 und 1,2 W/(m2K) und somit deutlich unter den in Luxemburg angenommenen Typologiewerten von 1,4 bis 2,1 W/(m2K). Die beschriebenen Abweichungen zwischen Energiebedarfsberechnung und tatsächlichem Energieverbrauch können somit zum Teil auf fehlerhafte Annahmen des ausstellenden Experten vor Ort zurückgeführt werden, welche sich an Typologiewerten orientieren. [less ▲]

Biomechanical properties of five different currently used implants for open-wedge high tibial osteotomy

in Journal of Experimental Orthopaedics (2015), 2(14),

Background: As several new tibial osteotomy plates recently appeared on the market, the aim of the present study was to compare mechanical static and fatigue strength of three newly designed plates with ... [more ▼]

Background: As several new tibial osteotomy plates recently appeared on the market, the aim of the present study was to compare mechanical static and fatigue strength of three newly designed plates with gold standard plates for the treatment of medial knee joint osteoarthritis. Methods: Sixteen fourth-generation tibial bone composites underwent a medial open-wedge high tibial osteotomyn(HTO) according to standard techniques, using five TomoFix standard plates, five PEEKPower plates and six iBalance implants. Static compression load to failure and load-controlled cyclic fatigue failure tests were performed. Forces, horizontal and vertical displacements were measured; rotational permanent plastic deformations, maximal displacement ranges in the hysteresis loops of the cyclic loading responses and dynamic stiffness were determined. Results: Static compression load to failure tests revealed that all plates showed sufficient stability up to 2400 N without any signs of opposite cortex fracture, which occurred above this load in all constructs at different load levels. During the fatigue failure tests, screw breakage in the iBalance group and opposite cortex fractures in all constructs occurred only under physiological loading conditions (<2400 N). The highest fatigue strength in terms of maximal load and number of cycles performed prior to failure was observed for the ContourLock group followed by the iBalance implants, the TomoFix standard (std) and small stature (sm) plates. The PEEKPower group showed the lowest fatigue strength. Conclusions: All plates showed sufficient stability under static loading. Compared to the TomoFix and the PEEKPower plates, the ContourLock plate and iBalance implant showed a higher mechanical fatigue strength during cyclic fatigue testing. These data suggest that both mechanical static and fatigue strength increase with a wider proximal T-shaped plate design together with diverging proximal screws as used in the ContourLock plate or a closed-wedge construction as in the iBalance design. Mechanical strength of the bone-implant constructs decreases with a narrow T-shaped proximal end design and converging proximal screws (TomoFix) or a short vertical plate design (PEEKPower Plate). Whenever high mechanical strength is required, a ContourLock or iBalance plate should be selected. [less ▲]

A semi-centralized, valveless and demand controlled ventilation system in comparison to other concepts in field tests

in Building and Environment (2015), 93(21-26),

The idea of adapting the air supply rate to the actual demand in a building is not a new one. In commercial buildings it is already state-of-the-art to establish a demand controlled ventilation, where the ... [more ▼]

The idea of adapting the air supply rate to the actual demand in a building is not a new one. In commercial buildings it is already state-of-the-art to establish a demand controlled ventilation, where the level of air ow is based on sensors or time control. In residential buildings however, mechanical ventilation systems, whether centralized or decentralized, are in most cases operated in a constant modus, providing fresh air regardless if the fresh air is needed or not, even though the technology and the components needed for demand controlled ventilation exist and can be purchased at reasonable prices. In this article, results of eld tests with a semi-centralized demand feedback-controlled ventilation system are shown and compared to outcomes with other demand controlled systems. The semi-centralized prototype includes decentralized fans per ventilation zone, making a room-wise ventilation possible and valves to balance the system hydraulically unnecessary. It is shown that each presented concept of demand controlled ventilation can save energy by decreasing the operational time or the mean airflow rate without compromising air quality. Concepts which make a zone- or even a room-wise control of air ow possible, showed the highest energy saving potential of up to two-thirds compared to a system operating at constant flow rates. In addition to the energy savings due to decreased operational time, the maintenance and lter costs are decreased while the user comfort is increased, as natural ventilation in spring, summer and autumn may easily be added when delta T between inside and outside is small. [less ▲]

Use of recycled concrete in construction in Luxembourg

in Cahier Scientifique - Revue Technique Luxembourgeoise (2015)

Construction and demolition waste constitutes a major portion of total waste production in the world, and most of it is used in landfills. The re-use of concrete rubble collected from demolished ... [more ▼]

Construction and demolition waste constitutes a major portion of total waste production in the world, and most of it is used in landfills. The re-use of concrete rubble collected from demolished structures is an important issue. After crushing and screening, there is the possibility of appropriately treating and reusing such waste as aggregate in new concrete, especially in lower level applications. Different aspects of the topic beginning with a brief review of the European initiatives and definition in terms of C&D waste generated and recycled aggregates produced from C&D waste are given. Along with a brief overview of C&D waste, a summary of the situation in Luxembourg in use of recycled aggregate is discussed. This writing concludes by identifying some of the major barriers in more use of recycled aggregate concrete, including lack of awareness, lack of knowledge, barriers of specifications/codes for reusing these aggregates in new concrete. [less ▲]

Fatigue in the Core of Aluminium Honeycomb Panels: Lifetime Prediction compared to Fatigue Tests

in International Journal of Damage Mechanics (2014), 23 no.5

In comparison to their weight, honeycomb composite structures have a high bending stiffness, which makes them very suited for every application where little weight is important, like airplanes, railway ... [more ▼]

In comparison to their weight, honeycomb composite structures have a high bending stiffness, which makes them very suited for every application where little weight is important, like airplanes, railway-cars and vehicles. The sandwich panels consist of two thin and stiff aluminium face sheets , which are bonded to a thick and lightweight aluminium honeycomb core. These structures are subjected to dynamic loading. However, in literature, there are hardly any fatigue properties of the honeycomb core described. The fatigue properties of the core are investigated using the finite element method and experiments. Depending on the load application, the honeycomb core fails either through core indentation or shear failure. For a fatigue prediction, both failure modes have to be investigated. Additionally the physical behavior of the honeycomb core is depending on the orientation of the core. Hence, fatigue tests were conducted in three directions of the core: the stiffest direction, the most compliant direction and the direction with the highest stresses. A three-point bending test setup was built to study the fatigue properties of the honeycomb core. Several fatigue tests were carried out with a load ratio of R=0.1 (maximum load 10 times bigger than minimum load) and the fatigue diagrams being illustrated. Additionally, Food-Cart Roller Tests (wheels of a cart rolling in a circle on a floor panel) were done to dynamically test the panels in every angle. The sandwich structures were modeled with the ANSYS finite element software. The simulations, which were used to determine the stress amplitudes in the specimens, are described in the following pages. In addition, buckling analyses were used to examine core indentation failure. Based on these simulations, failure predictions can be made. The fatigue life of the examined specimens is successfully approximated in this manuscript, with the lifetime analysis being based on the FKM-guideline (error less than 14% in load amplitude). [less ▲]

Wie genau sind unsere Energiepässe?

in Bauphysik (2014), 1(2014), 40-43

Member States of the European Union are obliged to present a calculation method and certificate for the energy performance for buildings according to the guidelines 2002/91/EG und 2010/31/EU. In ... [more ▼]

Member States of the European Union are obliged to present a calculation method and certificate for the energy performance for buildings according to the guidelines 2002/91/EG und 2010/31/EU. In Luxembourg it is obligatory to add the real final energy consumption to the certificate after 3 years. The measured real final energy consumptions and the calculated ones were compared for 125 single-family homes and 105 multi-family homes with 870 dwellings in total. The mean calculated values for single-family homes were 74 % higher, the mean calculated values for multi-family homes 103 % higher than the actual measured data. The older the buildings, the higher the deviations, as the input parameters, which were partly assumed and partly predefined, diverge between calculations and reality. Sensitive parameters of interest are the indoor room temperature, the U-values, the used assessment for thermal bridges and the air exchange rate. [less ▲]

VOLUME FLOW UNBALANCES AND SHORTCUTS IN DECENTRALIZED AND CENTRALIZED VENTILATION UNITS – FIELD TESTS IN RESIDENTIAL BUILDINGS

Scientific Conference (2014)

Centralized and decentralized mechanical ventilation have become state-of-the-art in modern energy-efficient residential buildings. Calculations for the energy demand of buildings are done with nominal ... [more ▼]

Centralized and decentralized mechanical ventilation have become state-of-the-art in modern energy-efficient residential buildings. Calculations for the energy demand of buildings are done with nominal values of the ventilation units, assuming a proper function of the devices. The used ventilation concepts may be divided into two main categories- centralized and decentralized units and both come with advantages and disadvantages in terms of energy efficiency. In Luxembourg, a comprehensive field test has been performed in order to evaluate and compare their performance in practice. It could be shown that ventilation systems often do not meet the expectations. High unbalances in volume flows, high sensitivity to pressure differences and recirculation were measured in several cases. Only a proper installation and balancing of the systems can ensure an energy efficient function. [less ▲]

Modern damage detection by using static assessment methods for efficient rehabilitation

in Proceedings (2012, September)

Evaluation of the bridge Champangshiel by using static assessment methods

in KIT Scientific Publishing, No. 026a, p. 323-329 (2012, July)

WIE VIEL ENERGIE VERBRAUCHEN NEUE UNTERRICHTS- UND BÜROGEBÄUDE IN LUXEMBURG?

in Cahier Scientifique - Revue Technique Luxembourgeoise (2012)

In Luxemburg hat sich in den vergangenen Jahren der nationale Energieverbrauch ebenfalls verstärkt zum Gebäudesektor hin verändert. Während 1990 noch 71 % des gesamten Energieverbrauches auf den ... [more ▼]

In Luxemburg hat sich in den vergangenen Jahren der nationale Energieverbrauch ebenfalls verstärkt zum Gebäudesektor hin verändert. Während 1990 noch 71 % des gesamten Energieverbrauches auf den Industriesektor zurückzuführen waren und nur 20 % auf die Gebäude, hat sich dies bis zum Jahr 2009 deutlich verändert. Demzufolge entfallen nur noch 30 % auf den Industriesektor, 25 % auf Verkehr (nach Abzug der Treibstoffexporte) und 45 % auf den Verbrauch des Tertiären Sektors3, welcher sowohl die privaten und die öffentlichen Haushalte, als auch Dienstleistungsgebäude beinhaltet. Die Direktive 2010/31/EG2 fordert von den Mitgliedstaaten die nationalen Normen weiterhin zu verschärfen und Pläne zu erstellen, um die Anzahl an Niedrigstenergiegebäuden weiter zu erhöhen. Um die Energieströme in Gebäuden besser zu verstehen, Sparmaßnahmen zu erarbeiten und mögliche Bewertungen über das Energieeinsparpotential für Gebäude durchführen zu können, sind jedoch aussagekräftige Verbrauchsdatenanalysen notwendig, die leider oftmals noch nicht in verlässlicher Qualität vorliegen. In der Direktive wird zudem empfohlen für die Berechnung eine Unterteilung aller Gebäude in angemessene Kategorien vorzunehmen, welche von Einfamilienhäusern (EFH), über Bürogebäude und Unterrichtsgebäude bis hin zu Krankenhäuser, Hotels und Sportanlagen reicht. In einer ersten Studie der Universität Luxemburg4 wurden bereits neuere EFH in Luxemburg hinsichtlich ihres realen Energieverbrauches untersucht und ausgewertet. [less ▲]