@article{MalzKrenkelSteffens, author = {Malz, Sebastian and Krenkel, Walter and Steffens, Oliver}, title = {Infrared Reflective Wall Paint in Buildings: Energy Saving Potentials and Thermal Comfort}, series = {Energy and Buildings}, volume = {224}, journal = {Energy and Buildings}, number = {October}, publisher = {Elsevier}, issn = {0378-7788}, doi = {10.1016/j.enbuild.2020.110212}, abstract = {The reduction of the energy demand of existing buildings is the main objective of building refurbishment. Managing the heat radiation properties of the wall construction is a possible way to develop highly effective and resource efficient insulation materials and concepts. The application of infrared reflective wall paints and coatings has been studied since the latter half of the 20th century. A brief review of the literature gives an account of the current research status. One has to realise that the conclusions are not uniformly consistent but depend strongly on the specific boundary conditions and investigated parameters. The study presented here discusses the usage of infrared reflective wall paint in conjunction with heat insulation for historic brick masonry. The possible energy savings are linked to the resulting thermal comfort. We identify critical parameters that must be taken into account when using infrared reflective wall paint and derive recommended design rules for the refurbishment of such building types. The findings prove that infrared reflective wall paint can decrease heat losses by 18\% and up to 22\% if comfort conditions are considered. Increasing energy savings can also cause the negative effect of high radiative asymmetry. Thus, each configuration must be observed in detail.}, language = {en} } @article{HaugSteffens, author = {Haug, Sonja and Steffens, Oliver}, title = {Die Akzeptanz von Baumaßnahmen im Planungsstadium}, series = {Deutsches Ingenieurblatt}, journal = {Deutsches Ingenieurblatt}, number = {3}, publisher = {Schiele \& Sch{\"o}n}, address = {Berlin}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-16499}, pages = {20 -- 27}, abstract = {Der kontinuierliche Sanierungs- und Modernisierungsprozess im Geb{\"a}udebestand in Deutschland, verst{\"a}rkt durch den Mangel an bezahlbarem Wohnraum, l{\"a}sst das gesellschaftliche Interesse an klimafreundlichen und ressourcenschonenden Technologien stetig wachsen. Modernisierungsmaßnahmen betreffen h{\"a}ufig Geb{\"a}ude (auch aus der j{\"u}ngeren Vergangenheit), deren historischer und architektonischer Wert oft {\"u}bersehen wird und der unter einer modernen W{\"a}rmed{\"a}mmverbundfassade zu verschwinden droht. Infolge einer intensiven bauhistorischen Besch{\"a}ftigung mit dem genossenschaftlichen Wohnungsbestand der Zwischenkriegszeit in der Stadt Regensburg hat sich ein interdisziplin{\"a}res Team aus Bauforschung, Architektur, Planung, Bauphysik und Geb{\"a}udetechnik zusammengefunden, um nachhaltige L{\"o}sungskonzepte f{\"u}r die energetische Modernisierung und Restaurierung historischer Quartiere zu erforschen. Dieser Beitrag widmet sich den Erkenntnissen einer sozialwissenschaftliche Studie, die als Erg{\"a}nzung und Hintergrundinformation zu den technischen und bauhistorischen Untersuchungen durchgef{\"u}hrt wurde.}, subject = {Altbaumodernisierung}, language = {de} } @article{StierstorferWellnitzSteffens, author = {Stierstorfer, Johannes and Wellnitz, Felix and Steffens, Oliver}, title = {Integrale Bauforschung und simulationsgest{\"u}tzte Analysen zur Wahrung historischer Bausubstanz am Beispiel der Asamkirche St. Georg zu Weltenburg}, series = {Bauphysik}, volume = {39}, journal = {Bauphysik}, number = {2}, issn = {0171-5445}, doi = {10.1002/bapi.201710016}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-20540}, pages = {135 -- 143}, abstract = {Die Klosterkirche St. Georg zu Weltenburg an der Donau, sp{\"a}tbarockes Hauptwerk der Br{\"u}der Asam und bayerische Welterbest{\"a}tte, musste sich aufgrund ihrer topographisch, geologisch und klimatisch exponierten Lage in der Vergangenheit tiefgreifenden Instandsetzungsmaßnahmen unterziehen. Um der hygrischen Problematik im Inneren des Kirchenraumes zu begegnen, wurde ein außergew{\"o}hnlicher Sanierungsansatz verfolgt, dessen bauphysikalische und raumklimatische Verifizierung im Rahmen dieses Forschungsprojektes durchgef{\"u}hrt wird. Dabei steht die Optimierung des Raumklimas im Zentrum der Untersuchungen. Ganzheitlich betrachtet stellt sich die Frage: Welche Maßnahmen d{\"u}rfen - bei Bewahrung der denkmalgesch{\"u}tzten Bausubstanz - ergriffen werden, um eine nachhaltige Nutzung historischer Bauwerke zu erm{\"o}glichen und dabei die Anforderungen der heutigen Zeit zu erf{\"u}llen?}, language = {de} } @article{SteffensSuhrke, author = {Steffens, Oliver and Suhrke, Michael}, title = {Novel spin features in Raman spectra of few-electron quantum dots}, series = {Physical Review Letters}, volume = {82}, journal = {Physical Review Letters}, number = {19}, publisher = {American Physical Society}, doi = {10.1103/PhysRevLett.82.3891}, pages = {3891 -- 3894}, abstract = {We employ a self-consistent, dynamic spin-density functional concept beyond the dipole approximation in order to calculate the collective modes of few-electron quantum dots with partial spin polarization. Because of Hund's rule in a magnetic field the mode energies exhibit characteristic discontinuities in their magnetic-field dependence, which is a manifestation of ground-state transitions between different spin configurations. A finite ground-state spin density couples collective charge- and spin-density excitations. We predict their observability in state-of-the-art Raman experiments.}, language = {en} } @article{StierstorferWellnitzSteffens, author = {Stierstorfer, Johannes and Wellnitz, Felix and Steffens, Oliver}, title = {Conservation of historic building fabric through integrated building research and digital simulation}, series = {Bauphysik}, volume = {39}, journal = {Bauphysik}, number = {2}, publisher = {ERNST \& SOHN}, doi = {10.1002/bapi.201710016}, pages = {135 -- 143}, abstract = {The abbey of Weltenburg monastery, a late baroque icon, designed by the Asam brothers and today's world heritage, has been subject to a constant need for repair and restoration due to its geological, climatological, and exposed location on the banks of the river Danube. To solve the hygric problems within the church, an exceptional restoration concept has been executed in the last decade. This research project analyses and verifies the building-physical and indoor climatic effects of the restoration measures with focus on the improvement of the central space climate. With this case study the question is raised whether appropriate measures exist that allow a contemporary and sustainable usage of historic buildings with respect to the preservation of the historic building fabric.}, language = {en} } @article{SteiningerGadererSteffensetal., author = {Steininger, Peter and Gaderer, Matthias and Steffens, Oliver and Dawoud, Belal}, title = {Experimental and Numerical Study on the Heat Transfer Characteristics of a Newly-Developed Solar Active Thermal Insulation System}, series = {Buildings}, volume = {11}, journal = {Buildings}, number = {3}, publisher = {MDPI}, doi = {10.3390/buildings11030123}, pages = {1 -- 22}, abstract = {A newly-developed solar active thermal insulation system (SATIS) is introduced with the main objective to accomplish a highly-dependent total solar transmittance on the irradiation angle. SATIS is also designed to obtain the maximum transmittance at a prescribed design irradiation angle and to reduce it remarkably at higher irradiation angles. A purely mineral thermal insulation plaster with micro hollow glass spheres is applied to manufacture the investigated SATIS prototype. Light-conducting elements (LCEs) have been introduced into SATIS and suitable closing elements have been applied. The SATIS prototype has been investigated both experimentally and numerically. It turned out that the contributions of conduction, radiation and convection to the effective thermal conductivity of SATIS, without the closing elements (49 mWmK), amount to 86.2\%, 13.2\% and 0.6\%, respectively. The angle-dependent short-wave radiation exchange within the LCE has been investigated via ray tracing. At the incidence angle of 19\% (design angle), 27\% of the radiation within the LCE is absorbed by the absorber plate, resulting in measured and computed total solar energy transmittances of 11.2\%/11.7\%, respectively. For a typical summer irradiation angle of 60\%, 98\% of the incident radiation is absorbed by the surfaces at the entrance of the LCE. The corresponding total solar energy transmittance amounts to 2.9\%.}, language = {en} } @article{SchloplocherEttengruberSteffens, author = {Schloplocher, Paul Dragos and Ettengruber, Stefan and Steffens, Oliver}, title = {Improvements for building-performance simulations by a comparative finite-element method analysis}, series = {Energy and Buildings}, volume = {278}, journal = {Energy and Buildings}, publisher = {Elsevier}, doi = {10.1016/j.enbuild.2022.112563}, pages = {1 -- 12}, abstract = {This paper presents a method to improve building-performance simulations (BPS) by the comparison and analysis of different approaches based on finite-element method (FEM) models. The lumped parameter method (LPM) is used in several BPS programs and tools. It has the advantage of fast computing times and comparably good accuracy for thermal and energy loads. With the help of detailed FEM simulations, it is possible to further improve the degree of detail and accuracy while maintaining the high simulation speed. In this work, we compare time-dependent results for local temperatures in a generic reference room within a given periode of time. In a second step, the differences between the models with respect to various physical effects are analyzed and used to introduce additional equations into the LPM model in order to improve its accuracy. Thus, we discuss potentials for improvement for BPS and demonstrate a method of a practical implementation. The results show minor differences of less than 0.1 K for radiation and heat transfer, so their level of detail in BPS is appropriate. In these terms, no improvements were pursued within the work. However, the FEM simulation is capable of calculating the internal convective heat transfer and thermal bridges more accurately due to the use of computational fluid dynamics (CFD) and the geometrically precise representation of the FEM model. Here, deviations of up to 1 K in room temperature (convective heat transfer) and up to 0.5 K in wall temperatures (thermal bridges) were pointed out. By improving the LPM with equations obtained from the FEM, these deviations can be reduced to less than 0.2 K, which is a considerable improvement in accuracy.}, language = {en} } @article{SteffensSchloesserRotteretal., author = {Steffens, Oliver and Schl{\"o}sser, Tilman and Rotter, Peter and Ensslin, Klaus and Suhrke, Michael and Kotthaus, J{\"o}rg and R{\"o}ssler, Ulrich and Holland, M.}, title = {From the two-dimensional electron gas to antidot superlattices: Magnetoresistance effects in the transition regime}, series = {Journal of Physics: Condensed Matter}, volume = {10}, journal = {Journal of Physics: Condensed Matter}, number = {17}, issn = {0953-8984}, doi = {10.1088/0953-8984/10/17/016}, pages = {3859 -- 3872}, abstract = {Magnetoresistance measurements and theoretical calculations for two-dimensional electron systems under a perpendicular magnetic field are presented which illuminate transport effects due to a periodic electrostatic potential modulation. We focus on features arising from the resolution of the magnetic miniband structure which are beyond the perturbative regime governed by the dispersion of Landau bands. Our non-perturbative quantum-mechanical calculations reveal that the dispersion of individual minibands is responsible for the complicated behaviour of the magnetoresistance in the regime of intermediate modulation strength. In particular, the interplay between miniband and scattering contributions to the conductivity leads to an almost structureless magnetoresistance in this regime followed by the formation of antidot peaks due to the miniband conductivity.}, language = {en} } @article{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Shell structure and exchange-related spin effects for quantum dots in a magnetic field}, series = {Physica B}, volume = {256-258}, journal = {Physica B}, doi = {10.1016/S0921-4526(98)00557-2}, pages = {147 -- 151}, abstract = {Ground-state calculations based on current spin density-functional theory for circular parabolic quantum dots are presented which reveal interesting spin effects in dependence on an external magnetic field: Hund's first rule (well-known from atomic physics for zero magnetic field) is related to the level occupancy near the Fermi energy and determines the spin configuration of the ground state in finite magnetic field. Consequently, the addition spectrum of the quantum dot exhibits a specific non-monotonous dependence on magnetic field, which is visible in recent quantum transport experiments.}, language = {en} } @article{SteffensRoesslerSuhrke, author = {Steffens, Oliver and R{\"o}ssler, Ulrich and Suhrke, Michael}, title = {Generalized Hund's rule in the addition spectrum of a quantum dot}, series = {EPL (Europhysics Letters)}, volume = {42}, journal = {EPL (Europhysics Letters)}, number = {5}, doi = {10.1209/epl/i1998-00276-4}, pages = {529 -- 534}, abstract = {We report on ground-state calculations based on current-spin density-functional theory for circular parabolic quantum dots. Hund's first rule, well-known from atomic physics, applies not only at zero magnetic field; analogous rules, related to the level occupancy near the Fermi energy, determine the spin configuration of the ground state in finite magnetic field. Consequently, the addition spectrum of the quantum dot exhibits a specific non-monotonous dependence on magnetic field. We discuss our results with focus on recent experiments which may already contain indications of this new feature.}, language = {en} } @article{SteffensSuhrkeRoessler, author = {Steffens, Oliver and Suhrke, Michael and R{\"o}ssler, Ulrich}, title = {Spontaneously-broken time-reversal symmetry in quantum dots}, series = {EPL (Europhysics Letters)}, volume = {44}, journal = {EPL (Europhysics Letters)}, issn = {1286-4854}, doi = {10.1209/EPL/I1998-00460-0}, pages = {222 -- 228}, abstract = {We present current-spin density-functional calculations for circular parabolic quantum dots in zero magnetic field. We find the possibility for broken time-reversal symmetry via exchange correlation with spontaneously induced orbital currents. For certain electron numbers, this results in new current textures which give rise to a finite magnetization even for ground states with vanishing total angular momentum.}, language = {en} } @article{ReutherSteffens, author = {Reuther, Maike and Steffens, Oliver}, title = {Evaluation der Bauteiltemperierung f{\"u}r den Herzogskasten Abensberg}, series = {Bauphysik}, volume = {37}, journal = {Bauphysik}, number = {2}, publisher = {Ernst \& Sohn, a Wiley Brand}, doi = {10.1002/bapi.201510010}, pages = {96 -- 99}, abstract = {Die These, dass die Methode der direkten Temperierung von erdber{\"u}hrten oder anderweitig feuchtebelasteten Bauteilen zur Beseitigung von Feuchtesch{\"a}den in Bestandsgeb{\"a}uden auch die Energieeffizienz des Geb{\"a}udes erh{\"o}hen und sogar ohne weitere energetische Sanierungsmaßnahmen die Anforderungen der Energieeinsparverordnung (EnEV) erf{\"u}llen kann, wird anhand des als Museum genutzten Herzogskastens in Abensberg {\"u}berpr{\"u}ft. In Verbindung mit einer Evaluation der Trocknungswirkung wird die Geb{\"a}ude-Energieeffizienz durch Vergleich von Bedarfsberechnungen auf Basis der DIN V 18599 mit realen Verbrauchszahlen {\"u}berpr{\"u}ft und diskutiert.}, language = {de} } @article{MalzSteiningerDawoudetal., author = {Malz, Sebastian and Steininger, Peter and Dawoud, Belal and Krenkel, Walter and Steffens, Oliver}, title = {On the Development of a Building Insulation using Air Layers with Highly Reflective Interfaces}, series = {Energy and Buildings}, journal = {Energy and Buildings}, number = {236, April}, publisher = {Elsevier}, doi = {10.1016/j.enbuild.2021.110779}, abstract = {In this work, a novel building insulation system implying wooden fiberboards and intermediate air layers with highly reflective interfaces for the reflection of longwave IR radiation is introduced. A wall test sample with a double air insulation layer has been built and experimentally investigated in a dedicated setup, which consists of a differential climatic chamber to simulate different indoor and outdoor conditions. The test results have been utilized in validating the developed simulation model. In addition, a thorough numerical parameter study has been conducted, through which the general design rules of the introduced insulation system for realizing the lowest possible effective thermal conductivity have been defined. Furthermore, a multi-air-layer-insulation concept is developed, and the energy saving potential is evaluated. It turned out that, emissivity, object size and air layer thickness are the most dominant design parameters which influence the thermal conductivity of the introduced insulation. A thermal conductivity of 0.033 W/(mK) has been estimated for a multi-air-layer insulation with 7 layers. The obtained results prove the high insulation potential of the introduced building insulation system compared with insulating materials available in the market while outlining their limitations.}, language = {en} }