Energieausweis: ein Beispiel für ein wenig genutztes Potential

Ungefähr 40 Prozent des gesamten Endenergieverbrauchs in Deutschland entfallen auf den Gebäudesektor. Gleichzeitig gilt die Steigerung der Gebäudeenergieeffizienz als eine der kosteneffektivsten Optionen zur Einsparung von Treibhausgasen. Um dieses Potential auszuschöpfen, wurde der Energieausweis als neues Instrument in der Europäischen Union (EU) eingeführt. Er soll Käufern, Eigentümern und Mietern klare Informationen über den energetischen Zustand von Wohn- und Nichtwohngebäuden vermitteln. Die Studie untersucht, inwiefern Energieausweise Käufern von Eigenheimen dabei geholfen haben, die Energieeffizienz der Gebäude in ihre Kaufentscheidung einzubeziehen. Die Ergebnisse weisen darauf hin, dass der Energieausweis bisher nur eine geringe Wirkung hat. Hauptgründe dafür sind, dass der Ausweis erstens nicht hilfreich für das Verständnis von Nebenkosten ist. Zweitens wird der Energieausweis aufgrund des derzeitigen rechtlichen Status nur selten genutzt. Drittens ist Energieeffizienz nur ein untergeordnetes Immobilienmerkmal beim Eigenheimkauf. Die Ergebnisse der Studie weisen allerdings auch auf das Potential des Energieausweises hin, da die Hindernisse überwindbar sind. So wird ab 2013 die Nutzung des Energieausweises durch die neue EU-Gebäuderichtlinie erhöht. Änderungen an der Darstellung - die durch Pilotstudien erprobt werden müssten - könnten zudem die Bedeutung des Energieausweises und der Energieeffizienz verbessern.Energy Performance Certificate (EPC), information instrument, energy efficiency

Characterization of Single Quantum Dot Blinking: Dwell Time Statistics and Electrochemical Control

This thesis addresses the observed fluorescence intermittency of single semiconductor nanocrystals, so called Quantum Dots (QDs), which is also referred to as blinking. Despite continuous excitation their fluorescence is randomly interrupted by dark periods that can last over several minutes. Especially the extraction of power law dwell time statistics in bright and dark states indicates very complex underlying processes that are not fully understood to date. Here two approaches are followed to reveal the nature of the blinking mechanism. One addresses the common threshold method for extraction of power law dwell times. Its performance is tested with simulations to a broad range of experimentally determined parameters. Strong deviations are found between input and extracted statistics dependent on input parameters themselves. A comparison with experimental data does not support the assignment of power law statistics for the bright state and indicates the existence of distinct blinking mechanisms. The second approach directly aims at the nature of the dark state, which is mostly attributed to charges in the QD or trap states in its vicinity. A method is developed to detect charging processes on single QDs with their fluorescence. Electrochemistry is combined with confocal microscopy also allowing evaluations of excited state lifetimes and emission spectra. Reduction and oxidation of the QD bands are successfully observed as a quenching of QD fluorescence. Single QD observations identify two independent blinking mechanisms, that are assigned to positive and negative charging. Positive charging is not only observed after hole injection but also the extraction of excited electrons. Three additional quenching mechanisms are identified, two of which are assigned to trap relaxation. Differences between two substrate electrodes demonstrate the importance of the substrate material

Distortion of power law blinking with binning and thresholding

Fluorescence intermittency is a random switching between emitting (on) and non-emitting (off) periods found for many single chromophores such as semiconductor quantum dots and organic molecules. The statistics of the duration of on- and off-periods are commonly determined by thresholding the emission time trace of a single chromophore and appear to be power law distributed. Here we test with the help of simulations if the experimentally determined power law distributions can actually reflect the underlying statistics. We find that with the experimentally limited time resolution real power law statistics with exponents αon/off ≳ 1.6, especially if αon ≠ αoff would not be observed as such in the experimental data after binning and thresholding. Instead, a power law appearance could simply be obtained from the continuous distribution of intermediate intensity levels. This challenges much of the obtained data and the models describing the so-called power law blinking

CdSe/CdS dot-in-rods nanocrystals fast blinking dynamics

The blinking dynamics of colloidal core-shell CdSe/CdS dot-in-rods is studied in detail at the single particle level. Analyzing the autocorrelation function of the fluorescence intensity, we demonstrate that these nanoemitters are characterized by a short value of the mean duration of bright periods (ten to a few hundreds of microseconds). The comparison of the results obtained for samples with different geometries shows that not only the shell thickness is crucial but also the shape of the dot- in-rods. Increasing the shell aspect ratio results in shorter bright periods suggesting that surface traps impact the stability of the fluorescence intensity

Identification of Different Donor-Acceptor Structures via Förster Resonance Energy Transfer (FRET) in Quantum-Dot-Perylene Bisimide Assemblies

Nanoassemblies are formed via self-assembly of ZnS capped CdSe quantum dots (QD) and perylene bisimide (PBI) dyes. Upon assembly formation the QD photoluminescence is quenched, as can be detected both via single particle detection and ensemble experiments in solution. Quenching has been assigned to FRET and NON-FRET processes. Analysis of FRET allows for a distinction between different geometries of the QD dye assemblies. Time-resolved single molecule spectroscopy reveals intrinsic fluctuations of the PBI fluorescence lifetime and spectrum, caused by rearrangement of the phenoxy side groups. The distribution of such molecular conformations and their changed dynamics upon assembly formation are discussed in the scope of FRET efficiency and surface ligand density

Near-field strong coupling of single quantum dots

Strong coupling and resultant mixing of light and matter states is an important asset for future quantum technologies. Here we demonstrate deterministic room-temperature strong coupling of a mesoscopic colloidal quantum dot to a plasmonic nano resonator at the apex of a scanning probe. Enormous Rabi splittings of up to 110meV are accomplished by nanometer– precise positioning of the quantum dot with respect to the nanoresonator probe. We find that in addition to a small mode volume of the nanoresonator, collective coherent coupling of quantum dot band-edge states and near-field proximity interaction are vital ingredients for the realization of near-field strong coupling of mesoscopic quantum dots. The broadband nature of the interaction paves the road towards ultrafast coherent manipulation of the coupled quantum dot-plasmon system at ambient conditions

Understanding China’s past and future energy demand: an exergy efficiency and decomposition analysis

There are very few useful work and exergy analysis studies for China, and fewer still that consider how the results inform drivers of past and future energy consumption. This is surprising: China is the world’s largest energy consumer, whilst exergy analysis provides a robust thermodynamic framework for analysing the technical efficiency of energy use. In response, we develop three novel sub-analyses. First we perform a long-term whole economy time-series exergy analysis for China (1971–2010). We find a 10-fold growth in China’s useful work since 1971, which is supplied by a 4-fold increase in primary energy coupled to a 2.5-fold gain in aggregate exergy conversion efficiency to useful work: from 5% to 12.5%. Second, using index decomposition we expose the key driver of efficiency growth as not ‘technological leapfrogging’ but structural change: i.e. increasing reliance on thermodynamically efficient (but very energy intensive) heavy industrial activities. Third, we extend our useful work analysis to estimate China’s future primary energy demand, and find values for 2030 that are significantly above mainstream projections

Estimating a threshold price for CO2 emissions of buildings to improve their energy performance level. Case study of a new Spanish home

Energy consumption in homes produces CO2. In many countries, building regulations are being set to enable energy efficiency performance levels to be issued. In Spain, there is a regulated procedure to certify the energy performance of buildings according to their CO2 emissions. Consequently, some software tools have been design to simulate buildings and to obtain their energy consumption and CO2 emissions. In this paper the investment, maintenance and energy consumption costs are calculated for different energy performance levels and for various climatic zones, in a single-family home. According to the results, more energy efficient buildings imply higher construction and maintenance costs, which are not compensated by lower energy costs. Therefore, under current conditions, economic criteria do not support the improvement of the energy efficiency of a dwelling. 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