L-SOL : Heizungssystem mit PVT als Quelle für eine Wärmepumpe

Schlussbericht BFE Projekt L-SolWith the use of PVT collectors, (photovoltaic) electricity as well as (solar) heat can be produced within the same area. This allows for a better utilization of a given roof area. In the L-Sol project, a novel system that uses PVT collectors to produce heat for single-family houses was investigated The PVT collectors deliver both electricity and heat for the operation of a heat pump. A main characteristic of the system is a thermal storage tank (“cold water storage”) between the PVT collectors and the heat pump. This storage tank acts as the source for the heat pump. It was shown that the L-Sol concept makes sense in ecologic as well as in economic terms. For new buildings and old, energetically renovated ones, electricity consumption is 5 to 30 % lower than with the use of an air-water heat pump. During winter, grid purchase is 3 to 11 % below that of an air-water heat pump system combined with PV modules. However, it is difficult to achieve the low costs of an air-water heat pump system. In the L-Sol system, the investment costs for the PVT system (collectors and installation) are the main cost component. Through savings on the collector costs – mainly by using collectors that consist of “normal” PV modules with a retrofitted heat exchanger on the rear side – total life-cycle costs over 20 years can be reduced to a level similar to that of an air-water heat pump system while maintaining the ecological advantages. On top of the improved system efficiency, the L-Sol system’s main advantage over an air-water heat pump system is the lack of noise emissions on the outside of the building. Compared to systems that are using a combination of PVT collectors and either a geothermal storage (2-Sol) or an ice storage, the L-Sol system offers reduced life-cycle costs. Furthermore, it requires no extensive ground works or special building permits. It is therefore also well suited for replacing fossil heating systems in existing buildings. In an in-depth simulation study, main influence factors on the system efficiency were identified and possibilities to reduce the amount of electricity purchased from the grid were shown. The controls of the heat pump were adapted such that the heat pump is purposefully switched on to heat up und overheat the thermal storage for space heating and domestic warm water when there is surplus electricity from the PVT system. Another possibility to reduce grid purchase is to do the heating-up of the space heating buffer mainly during daytime and disable it at night as long as the comfort requirements are not neglected. A combination of these two control approaches can lead to an electricity self-consumption ratio of 45 %, compared to around 20 % when using standard controls. On top of these adaptations of the control system, adding a battery storage can further increase the level of self-sufficiency. With a battery storage of 10 kWh capacity, the self-consumption ratio can be increased to 55 %. In certain summer months, 100 % self-sufficiency is possible. The high energy demand and the low energy production during phases of bad weather can be buffered by a well-dimensioned thermal storage between the PVT collectors and the heat pump. By adding an additional hydraulic circuit, this storage can be used to cool down the building during summer. The heat that is extracted from the building is either used for domestic hot water generation or it is given off to the environment via the PVT collectors at night. For easy system dimensioning, so-called dimensioning matrices were created. An interested party can use them to estimate a useful system dimensioning for their house and quickly decide whether the L-Sol system could be an option that is worth a more detailed consideration. Depending on the heating energy demand and the flow temperature of the heating circuit, a typical system for a single-family house consists of 15 to 30 uncovered PVT collector modules and a cold water storage with a volume of 1’000 to 2’000 l. Furthermore, it includes a heat pump as well as a warm storage, e.g. a 600-l combined storage.Mit PVT-Kollektoren wird auf derselben Fläche sowohl (PV-)Strom als auch (solare) Wärme gewonnen. Dies erlaubt eine bessere Ausnutzung der Dachflächen. Im Projekt L-Sol wurde ein neuartiges System untersucht, welches die Wärme für Einfamilienhäuser aus PVT-Kollektoren erzeugt. Die PVT-Kollektoren liefern dabei sowohl Strom als auch Wärme für die Wärmepumpe. Charakteristisch für das System ist ein Pufferspeicher («Kaltwasser-Speicher») zwischen den PVT-Kollektoren und der Wärmepumpe, welcher als Quelle für die Wärmepumpe dient. Es zeigte sich, dass das Konzept L-Sol sowohl ökologisch als auch ökonomisch sinnvoll ist. Der Strombedarf ist bei Neubauten und energetisch sanierten Einfamilienhäusern jeweils 5 bis 30 % geringer als beim Einsatz einer Luft-Wasser-Wärmepumpe. In den Wintermonaten liegt der Netzbezug 3 bis 11 % unter dem eines Luft-Wasser-Wärmepumpensystem kombiniert mit einer PV-Anlage. Es ist jedoch schwierig, die tiefen Kosten eines Luft-Wasser-Wärmepumpensystems zu erreichen. Im L-Sol-System stellen die Investitionskosten für die PVT-Anlage (Kollektoren inklusive Installation) den grössten Posten dar. Durch Einsparungen bei den Kollektorkosten – insbesondere durch den Einsatz von mit Wärmetauschern nachgerüsteten «normalen» PV-Modulen - lassen sich die Gesamtkosten über 20 Jahre unter Beibehaltung der ökologischen Vorteile auf das Niveau eines Luft-Wasser-Wärmepumpensystems senken. Neben der höheren Systemeffizienz besteht der Hauptvorteil des L-Sol-Systems gegenüber einem System mit einer Luft-Wasser-Wärmepumpe in den wegfallenden Lärmemissionen im Aussenbereich. Verglichen mit Systemen, die PVT-Kollektoren in Kombination mit einer Erdwärmesonde (2-Sol) oder einem Eisspeicher verwenden, weist das L-Sol-System geringere Lebenszykluskosten auf. Ausserdem erfordert es keine umfassenden Bodenarbeiten oder besondere Bewilligungen. Es eignet sich deshalb auch gut für den Ersatz von fossilen Heizungssystemen in bestehenden Gebäuden. In einer vertieften Simulationsstudie wurden wesentliche Einflussfaktoren auf die Systemeffizienz identifiziert und Möglichkeiten aufgezeigt, wie der Strombezug aus dem Netz verringert werden kann. Die Steuerung der Wärmepumpe wurde so angepasst, dass sie bei einem Stromüberschuss aus der PVT-Anlage gezielt eingeschaltet wird, um die Speicher für Warmwasser und Heizung aufzuheizen oder zu überhitzen. Eine weitere Möglichkeit zur Reduktion des Netzbezugs besteht darin, die Beladung des Heizpufferspeichers überwiegend am Tag durchzuführen und in der Nacht zu sperren, sofern keine Komfortanforderungen verletzt werden. Durch Kombination dieser beiden Steuerstrategien kann der Eigenverbrauchsanteil des Stromes auf rund 45 % gesteigert werden, verglichen mit rund 20 % bei Verwendung einer Standardsteuerung. Zusätzlich zu diesen Steuerungsanpassungen lässt sich durch die Einbindung eines Batteriespeichers der Autarkiegrad weiter steigern. Mit einem Batteriespeicher von 10 kWh Kapazität kann ein Autarkiegrad von 55 % erreicht werden. In einzelnen Sommermonaten ist damit eine 100-prozentige Autarkie möglich. Der hohe Energiebedarf und der geringe Energieertrag während kurzen Schlechtwetterphasen können durch eine entsprechende Grösse des Speichers zwischen PVT-Kollektoren und Wärmepumpe gepuffert werden. Durch das Hinzufügen eines zusätzlichen hydraulischen Kreislaufs kann derselbe Speicher im Sommer verwendet werden um das Gebäude zu kühlen. Die dem Gebäude entnommene Wärme wird dabei zum einen für die Brauchwarmwasser-Erwärmung verwendet und zum anderen nachts über die PVT-Kollektoren an die Umgebung abgegeben. Zur einfachen System-Dimensionierung wurde eine Dimensionierungsmatrix erstellt. Anhand dieser Matrix können Interessenten für ihre Häuser sinnvolle Systemdimensionierungen abschätzen und somit beurteilen, ob das System L-Sol im betrachteten Fall für eine genauere Betrachtung in Frage kommt. Je nach Heizwärmebedarf und Heizkreis-Vorlauftemperatur besteht ein typisches System für ein Einfamilienhaus aus 15 bis 30 unabgedeckten PVT-Kollektor-Modulen und einem Kaltwasser-Speicher von 1'000 bis 2'000 l Volumen. Weiter beinhaltet es eine Wärmepumpe und einen warmen Speicher, z.B. einen 600-l-Kombispeicher

Pion-nucleon scattering in chiral perturbation theory II: Fourth order calculation

We analyse elastic-pion nucleon scattering to fourth order in heavy baryon chiral perturbation theory, extending the third order study published in Nucl. Phys. A640 (1998) 199. We use various partial wave analyses to pin down the low-energy constants from data in the physical region. The S-wave scattering lengths are consistent with recent determinations from pionic hydrogen and deuterium. We find an improved description of the P-waves. We also discuss the pion-nucleon sigma term and problems related to the prediction of the subthreshold parameters.Comment: 28 pp, LaTeX2e, uses epsf, 6 figs, better discussion of the convergence issues, accepted for publication in Nuclear Physics

Pion-nucleon scattering in an effective chiral field theory with explicit spin-3/2 fields

We analyze elastic-pion nucleon scattering to third order in the so-called small scale expansion. It is based on an effective Lagrangian including pions, nucleons and deltas as active degrees of freedom and counting external momenta, the pion mass and the nucleon-delta mass splitting as small parameters. The fermion fields are considered as very heavy. We present results for phase shifts, threshold parameters and the sigma term. We discuss the convergence of the approach. A detailed comparison with results obtained in heavy baryon chiral perturbation theory to third and fourth order is also given.Comment: 44 pp, LaTeX2e, uses epsf, 6 fig

Increased risk for thromboembolic events from combination of a gynecologic malignancy with severe acute respiratory syndrome coronavirus 2 infection: a case report

Purpose During the severe acute respiratory syndrome coronavirus 2 pandemic, several patient groups are at particular risk. Mortality is higher among cancer patients and may be increased further by thromboembolic events, which are more common in coronavirus 2019 patients according to recent publications. We discuss the association of gynecologic malignancies, Severe acute respiratory syndrome coronavirus 2, and thromboembolism by reporting a case study and summarizing available literature. Case report A 71-year-old Caucasian patient with ovarian cancer receiving first-line chemotherapy was diagnosed with deep vein thrombosis and pulmonary embolism. Routine screening revealed infection with severe acute respiratory syndrome coronavirus 2 in absence of specific symptoms. After uneventful recovery, oncologic treatment could be continued a few weeks later. Methods We performed a systematic review of the literature on PubMed following Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines. The search included articles ahead of print, published between 1 December 2019 and 1 June 2020. Cross-searches were conducted on all relevant articles. Results We identified five articles meeting the defined criteria, including two retrospective studies, a review, a position paper, as well as a letter to the editor. Conclusion Cancer patients infected with severe acute respiratory syndrome coronavirus 2 have a relatively poor outcome, which may partially be due to a higher rate of thromboembolic events. Thromboprophylaxis is recommended, and scoring systems are helpful in early detection. In cancer patients with severe acute respiratory syndrome coronavirus 2, individual risk for thromboembolic events should be taken into account when considering interruption versus continuation of antitumoral therapy. However, further data and studies are required

Towards an understanding of isospin violation in pion-nucleon scattering

We investigate isospin breaking in low-energy pion-nucleon scattering in the framework of chiral perturbation theory. This work extends the systematic analysis of [1] to the energy range above threshold. Various relations, which identically vanish in the limit of isospin symmetry, are used to quantify isospin breaking effects. We study the energy dependence of the S- and P-wave projections of these ratios and find dramatic effects in the S-waves of those two relations which are given in terms of isoscalar quantities only. This effect drops rather quickly with growing center-of-mass energy.Comment: 12 pp, REVTeX, 8 figs, FZJ-IKP(TH)-2000-2

On the size of isospin violation in low-energy pion-nucleon scattering

We present an analysis of isospin-breaking effects in threshold pion-nucleon scattering due to the light quark mass difference and the dominant virtual photon effects. We discuss the deviation from various relations, which are exact in the isospin limit. The size of the isospin-violating effects in the relations involving the isovector $\pi N$ amplitudes is typically of the order of one percent. We also find a new remarkably large effect $(\sim 40$ in an isoscalar triangle relation connecting the charged and neutral pion scattering off protons.Comment: 10 pp, LaTeX, uses epsf, 2 fig

Controlling Volatility and Nonvolatility of Memristive Devices by Sn Alloying

Memristive devices have attracted significant attention due to their downscaling potential, low power operation, and fast switching performance. Their inherent properties make them suitable for emerging applications such as neuromorphic computing, in-memory computing, and reservoir computing. However, the different applications demand either volatile or nonvolatile operation. In this study, we demonstrate how compliance current and specific material choices can be used to control the volatility and nonvolatility of memristive devices. Especially, by mixing different materials in the active electrode, we gain additional design parameters that allow us to tune the devices for different applications. We found that alloying Ag with Sn stabilizes the nonvolatile retention regime in a reproducible manner. Additionally, our alloying approach improves the reliability, endurance, and uniformity of the devices. We attribute these advances to stabilization of the filament inside the switching medium by the inclusion of Sn in the filament structure. These advantageous properties of alloying were found by investigating a choice of six electrode materials (Ag, Cu, AgCu-1, AgCu-2, AgSn-1, AgSn-2) and three switching layers (SiO$_2$, Al$_2$O$_3$, HfO$_2$)

Pion-nucleon scattering in chiral perturbation theory I: Isospin-symmetric case

We construct the complete effective chiral pion-nucleon Lagrangian to third order in small momenta based on relativistic chiral perturbation theory. We then perform the so-called heavy baryon limit and construct all terms up-to-and-including order $1/m^2$ with fixed and free coefficients. As an application, we discuss in detail pion-nucleon scattering. In particular, we show that the $1/m$ expansion of the Born graphs calculated relativistically can be recovered exactly in the heavy baryon approach without any additional momentum-dependent wave function renormalization. We fit various empirical phase shifts for pion laboratory momenta between 50 and 100 MeV. This leads to a satisfactory description of the phase shifts up to momenta of about 200 MeV. We also predict the threshold parameters, which turn out to be in good agreement with the dispersive analysis. In particular, we can sharpen the prediction for the isovector S-wave scattering length, $0.083 M_\pi^{-1} \leq a_{0+}^- \leq 0.093 M_\pi^{-1}$. We also consider the subthreshold parameters and give a short comparison to other calculations of $\pi N$ scattering in chiral perturbation theory or modifications thereof.Comment: 38 pp, LaTeX, uses epsf, 7 figs, additional remarks, one figure added, version to be published in Nucl.Phys.