Niedrigemittierende Außenoberflächen bei Wärmedämmverbundsystemen – ein Studie zur Vermeidung von Algenwuchs

Algae growth on the outside surface of thermal insulating composite systems (TICS) occurs because of long‐lasting wetting. The present techniques for its avoidance are without long‐term effect. Especially, dew and frost are an essential reason for its occurrence because of the highly thermal insulation of the TICSs. In the following report, it will be investigated by an algorithm on the basis of a worst case scenario for outside condensation whether outside condensation on TICSs can be counteracted by a low‐emissivity outside surface as it is well‐proven on highly insulating window glazing. The calculations showed that outside condensation on TICSs with heat transfer coefficients (U) values from 0.1 to 0.2 W/(m² K) cannot be avoided theoretically by thermal emissivity values ε in the range of 0.05 till 0.1. However, because the most critical scenario conditions for outside condensation are very stringent and, in addition, the calculations have shown that outside condensation is only possible for relative outdoor humidity rH_o ≥ 95%, it can be deduced that the occurrence of outside condensation will be very improbably in praxis for TICSs with U values from 0.1 to 0.2 W/(m² K) and ε values from 0.05 to 0.1. A weathering and soiling resistant surface with ε ≤ 0.1 can be realized by aluminum which may be additionally passivated by a titanium dioxide coating. Because of the hydrophilic property, this coating shows also self‐cleaning effect and quickly drying of the surface after rain. The latter may counteract algae growth, too.     

Entwicklung von hybriden Wärmedämmsteinen aus LAC

Die aktuell oftmals diskutierte Notwendigkeit der nachhaltigen Reduktion des Verbrauchs an Heizenergie bzw. der Reduktion des CO2‐Austoßes und die damit immer stärker werdende Forderung nach einem baulichen Wärmeschutz führten an der Universität Luxembourg dazu, ein Projekt auf den Weg zu bringen, welches das Ziel verfolgt, mittels hybrider Mauersteinkonstruktionen die Transmissionswärmeverluste durch die Außenwand weiter zu begrenzen. Mit der Energieeinsparverordnung (EnEV) in Deutschland und dem “règlement grand‐ducal Performance Energétique des b?timents d?habitation” [1] in Luxemburg bestehen neben der Anforderungsgröße des Jahresprimärenergiebedarfs auch über maximal festgesetzte Wärmedurchgangskoeffizienten U Anforderungen an die Transmissionswärmeverluste durch die Gebäudehülle. In Luxemburg beträgt der aktuelle Grenzwert zur Erfüllung des Mindestwärmeschutzes für Außenwände zur Zeit 0,32 W/m2K. Um den aktuellen Stand der Technik auf dem freien Markt festzuhalten, wurde zu Beginn des Projektes mit einer Marktstudie an 12 unterschiedlichen Wärmedämmsteinen aus verschiedenen europäischen Ländern begonnen. Dabei fiel das große Optimierungspotential der klassischen Wärmedämmblöcke aus haufwerksporigem Leichtbeton (LAC) in thermischer und statischer Hinsicht auf. Wie die Marktstudie zeigt, können mit klassischen monolithischen Wärmedämmblöcken (Vbl SW, Hbl) die deklarierten bzw. angestrebten Grenzwerte der Wärmeleitfähigkeit bei gleichzeitiger Einhaltung der Rohdichteklasse und Druckfestigkeit nicht immer gezielt erreicht werden. Es ist daher ratsam, eine Funktionstrennung der statisch und thermisch wirksamen Schichten im Steinquerschnitt vorzunehmen. Ein Weg zur Entwicklung von Mauersteinen mit Funktionstrennung der Trag‐ und Dämmschichten wird in diesem Beitrag aufgezeigt. Development of new heat‐insulating masonry blocks made of LAC. The actual discussion of the necessity of sustainable reduction of primary energy for heating of housing structures and of the reduction of CO2‐emissions led the University of Luxembourg to issue a project aimed to develop hybrid lightweight concrete blocks with high heat‐insulating properties. The progressing Energy Saving Regulation (EnEV) in Germany and the grand‐ducal Regulation in Luxembourg [1] are limiting the annual primary energy consumption for housing structures and office buildings. Supplementary, these regulations are also limiting the heat transfer coefficient U for the transmission of the heat flow through the outer walls. In Luxembourg e.g. the actual U‐value is limited to maximal 0,32 W/m2K. Based on the measured values, the static and thermal properties of the materials themselves (e.g. lightweight concrete with open structure) as well as the whole masonry bricks and blocks, taken from the European free market, were tested and simulated by the finite element method to study their weak spot and to use this experience for the construction of new prototypes. It was revealed that it is suggestive to separate the load bearing from a thermal construction part in the masonry block. The market study showed, that is only possible to reach certainly the declared limit values of the thermal and mechanical properties of the masonry block by separating the load‐bearing from the thermal function of the block.     

Ein neues Wärmedämmsystem für Architekturglass

Vacuum coated glass plays an outstanding role for the energy saving of buildings. The basis of such low emissivity coatings is a 10 nm thick silver layer causing an effective reflexion of room temperature radiation. With conventional coatings k‐values of 1,3 W/m²K are realized. In the frame of a research project funded by the BMBF reactive mid frequency sputtering (Leybold TwinMag®) has been introduced for manufacturing of low e glass. The new developed system glass — TiO₂ — ZnO — Ag — NiCrO_x — Si₃N₄ enables a k‐value of 1,1 W/m²K and an improvement of optical properties.     

Schubtragfähigkeit von Mauerwerk aus Wärmedämmziegeln

Der Beitrag berichtet über zentrische und exzentrische Schubversuche an Mauerwerk aus Wärmedämmziegeln. Die Ergebnisse werden mit den aktuell gültigen Bemessungsansätzen in DIN 1053‐1 verglichen. Es wird gezeigt, dass die Versuchsergebnisse immer eine ausreichende Sicherheit gegenüber den Bemessungswerten nach DIN 1053‐1 aufweisen. Auch für Mauerwerk aus Wärmedämmziegeln mit allgemeiner bauaufsichtlicher Zulassung können somit die vereinfachten Bemessungsregeln der DIN 4149 ohne Abminderungen angewendet werden. In plane shear resistance of thermal insulating vertically perforated clay brick masonry. In plane shear tests on thermal insulating vertically perforated clay brick masonry are presented. The results are compared with the design rules from DIN 1053‐1. The test results exceeded the design predictions of DIN 1053‐1 by a significant safety margin. The simplified design rules from the German earthquake standard DIN 4149 can be applied to thermal insulating clay unit masonry with technical approvals without any reduction.     

Entwicklung von Oxid – Keramik zur Anwendung als Wärmedämmschichten

Development of Oxide Ceramics for an Application as TBC The standard thermal barrier coating material yttria stabilised zirconia (YSZ) is limited in long term operation to a maximum temperature of about 1200°C. As a result further increase of the gas inlet temperature and hence the efficiency of gas turbines are hardly to achieve with YSZ coatings. In a screening procedure especially perowskite (ABO₃, A = Sr,Ba, B = Zr) and pyrochlore (A₂B₂O₇, e.g. A = La and other rare earth elements, B = e.g. Zr) materials have been identified as possible candidates for thermal barrier coatings. Basic physical properties (e.g. thermal expansion coefficient, thermal diffusivity and conductivity) of several candidates have been determined using sintered, dense samples. The possibility of optimization of the properties by using specific compositions will be discussed. From promising materials powders which are suitable for plasma‐spraying have been produced by spray‐drying. New TBC systems consisting of new materials (BaZrO₃, La₂Zr₂O₇) deposited by atmospheric plasma spraying and vacuum plasma sprayed MCrAlY bondcoats were tested in a gas burner facility. Especially La₂Zr₂O₇ coatings gave promising results. A further improvements could be achieved by the use of layered or graded coatings with a YSZ coating at the bondcoat interface and on top a layer of the new TBC material. First results of thermal cycling tests with 1250 and 1350°C surface temperature will be presented.     

Röntgenografische Eigenspannungsmessungen an plasmagespritzten Wärmedämmschichten aus Zirkonoxid vor und nach thermischer und mechanischer Beanspruchung

X-Ray Stress Measurements on Plasma Sprayed Zirkonia Thermal Barrier Coatings Turbine blades for aero engines with plasma sprayed zirconia thermal barrier coatings were subjected to typical component loads as thermal fatigue and creep. Before and after testing residual surface stresses in the coatings were determined by X-ray stress measurements. Different substrate temperatures during the plasma spraying process caused tensile or compressive stresses on the surfaces of the thermal barrier coatings. Coatings with compressive stresses failed after only a few thermal cycles whereas those with tensile stresses sustained 700 to 1500 cycles without visible damage. Thermal fatigue and creep tests lead to stress changes reducing tensile stresses and increasing compressive stresses.     

Bauweise mit Zukunft: Durch und durch mineralisch —Wärmedämmendes Mauerwerk mit mineralischem Putz

Hat Mauerwerk eine Zukunft? Oder dienen Wände bald nur noch als Trägermaterial für Dämmschichten? Dabei ist gerade wärmedämmendes Mauerwerk aus gutem Grund im Wohnungsbau nach wie vor die Nummer Eins — und wird es nach Einschätzung der Fachleute auch bleiben. Dieser Beitrag schildert aktuelle Entwicklungen und beleuchtet Hintergründe. Construction with a future — theral insulating brick with mineral plaster. Does brickwork has a future? Couldn’t it be that walls will soon only serve as backing material for insulation layer? However, there are good reasons that heat insulating brickwork is still the number one in domestic constructions — according to experts this will remain so. The following article will characterize current developments und backgrounds.     

Installing windows in composite thermal insulation systems / Fenstermontage in Wärmedämm‐Verbundsystemen

According to the German Association for Composite Thermal Insulation Systems, about 780 million m² of composite thermal insulation systems (ETICS) have up to now been installed in both existing and new buildings in Germany ? a trend that is set to continue. Correct window installation in ETICS with a permanent and functional connection to the building fabric requires architects, engineers and contractors to be familiar with the special details of this external wall system [1], [2]. However, experience from expert witness reporting has shown that this is frequently not so and that eliminating any defects subsequently is only possible at great expense.     

Der Einfluß von thermozyklischer Beanspruchung auf den Eigenspannungszustand in elektronenstrahlgedampften Wärmedämmschichten aus Zirkonoxid

Influence of Thermal Cycling on Residual Stresses in Zirconia Thermal Barrier Coatings Produced by Electron Beam – Physical Vapor Deposition. Flat specimens and aircraft turbine engine blades were coated with partially stabilized zirconia by electron beam - physical vapor deposition. Residual stresses of these thermal barrier coatings were measured before and after thermal cycling by x-ray stress analysis. All flat specimens and blades showed compressive residual stresses. Stress values in the longitudinal direction were significantly greater than those measured in the transverse direction. No changes of stress states and line widths were observed after thermal cycling. The specimens showed considerable differences in texture which made evaluation of the stress measurements difficult and which may have influenced degradation behaviour during thermal cycling.     

Einfluss einer PVD‐Al‐Zwischenschicht auf die Eigenschaften eines thermisch gespritzten Wärmedämmschichtsystems nach Temperaturwechselbelastung

Thermal barrier coatings (TBC) generally consist of a metallic bond coat (BC) and a ceramic top coat (TC). Co–Ni–Cr–Al–Y metallic super alloys and Yttria stabilised zirconia (YSZ) have been widely used as bond coat and top coat for thermal barrier coatings systems, respectively. As a result of long‐term exposure of thermal barrier coatings systems to oxygen‐containing atmospheres at high temperatures, a diffusion of oxygen through the porous ceramic layer occurs and consequently an oxidation zone is formed in the interface between ceramic top coat and metallic bond coat. Alloying components of the BC layer create a so‐called thermally grown oxides layer (TGO). One included oxide type is α‐Al₂O₃. α‐Al₂O₃ lowers oxygen diffusion and thus slows down the oxidation process of the bond coat and consequently affects the service life of the coating system positively. The distribution of the alloying elements in the bond coat layer, however, generally causes the formation of mixed oxide phases. The different oxide phases have different growth rates, which cause local stresses, micro‐cracking and, finally, delamination and failure of the ceramic top coat layer. In the present study, a thin Al inter‐layer was deposited by DC‐Magnetron Sputtering on top of the Co–Ni–Cr–Al–Y metallic bond coat, followed by thermal spraying of yttria‐stabilised zirconia (YSZ) as a top coat layer. The deposited Al inter‐layer is meant to transform under operating conditions into a closed layer with high share of α‐Al₂O₃ that slows down the growth rate of the resulting thermally grown oxides layer. Surface morphology and microstructure characteristics as well as thermal cycling behaviour were investigated to study the effect of the intermediate Al layer on the oxidation of the bond coat compared to standard system. The system with Al inter‐layer shows a smaller thermally grown oxides layer thickness compared to standard system after thermal cycling under same conditions.     

Die Kalibrierung von Wärmeleitungsvakuummetern. The Calibration of Thermal Conductivity Vacuum Gauges

In many applications in the rough and fine vacuum thermal conductivity gauges are utilized. In order to determine the accuracy of the measuring values modern quality assurance systems require a regular calibration. The calibration laboratory of the German Calibration Service (DKD) at VACUUBRAND GMBH + CO KG features calibration equipment and procedures to calibrate vacuum gauges in the pressure range from 10^‐3 to 1000 mbar. The measuring techniques and calibration procedures are explained for thermal conductivity gauges with digital readouts. Besides general information on the calibration, particularities on thermal conductivity gauges and their effects on the calibration procedure are pointed out. The meaning of measuring deviation and measuring uncertainty and the interpretation of the calibration certificate for the user are discussed.