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Research unit
SFOE
Project number
SI/501565
Project title
Exergetic and economical optimization of seasonal thermal energy storage systems

Texts for this project

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Short description
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Key words
(English)
Seasonal storage, thermal energy storage, sensible storage, thermal insulation, optimization
Short description
(German)
Das Projekt «Exergetische und ökonomische Optimierung saisonaler Wärmespeichersysteme» gewinnt Erkenntnis über das optimale Design der Wärmedämmung sensibler, saisonaler Wärme-speicher von Mehrfamilienhäuser. Dazu wird der Einsatz verschiedener Dämm-Materialien geprüft, eine optimale geometrische Anordnung der Dämmung untersucht und eine Kostenoptimierung unter Berücksichtigung des Raumbedarfs von Speicher- und Dämmvolumen erstellt.
Short description
(English)
The project «exergetic and economical optimization of seasonal thermal energy storage systems» gains knowledge about optimally designed thermal insulation of sensible, seasonal thermal energy storage of multi family houses. Therefore the application of various insulation materials is exam-ined, an optimal geometrical design of the instulation investigated and a cost optimization imple-mented considering the space need of storage and instulation volume.
Publications / Results
(German)
Auf Anhieb möchte man kaum glauben, dass ein einfacher Wassertank genügt, um die Wärme vom Sommer in den Winter zu bringen. Doch tatsächlich reicht ein Speicher ab 12 Kubikmeter Volumen, um eineWohnung den ganzenWinter mit Heizwärme und Warmwasser aus Sonnenkollektoren zu versorgen. Weil solche Speicherlösungen bisher relativ teuer sind, habenWissenschaftlerinnen undWissenschaftler der Hochschulen in Rapperswil und Luzern in zwei Forschungsprojekten nach wirtschaftlichen Konzepten gesucht. Eine Stossrichtung besteht darin, mit gezielten Optimierungen das Volumen der Speicher und damit ihre Kosten zu verringern.
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Publications / Results
(English)
At first glance, one would hardly believe that a simple water tank could be enough to bring heat from summer into winter. But in fact, a storage tank with a volume of 12 cubic meters or more is enough to supply an apartment with heat and hot water from solar collectors for the entire winter. Because such storage solutions have been relatively expensive up to now, scientists from the universities in Rapperswil and Lucerne have been searching for ways to make the technology more economical in two research projects. One approach is to reduce the volume of the storage tanks and thereby their costs through optimization.
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Final report
(English)
In combination with seasonal thermal energy storage (STES), solar energy offers a vast potential for the supply of space heating and domestic hot water. Today, increasing market diffusion of STES requires reducing the high investment costs. In this work, a parametric-based optimization is conducted to assess the potential of reducing the costs of hot-water STES through the use of alternative thermal insulation materials and an exergy-oriented control strategy of the solar collectors. The investigated configurations include: (1) a hot-water thermally stratified storage, (2) a solar thermal collector installation, and (3) a representative multifamily low-energy building with a solar fraction of 100%. The storage tank is either integrated inside the building (either new building or retrofit) or buried underground in direct vicinity of the building.  A simulation-based analysis shows that the required storage volume can be reduced by 30% by switching from a high-flow (baseline case) to a low-flow control strategy – this for a typical tilt angle of the solar collectors of 45°. If the tilt angle is increased to an optimum of 65°, the storage volume can be further reduced by round 10%. If the hot-water tank is integrated as part of a retrofitting inside an existing residential building – where the costs are primarily driven by the loss of living space –, maximizing the solar collector area is the best strategy to minimize the Levelized Cost of Energy Storage (LCOES100). In the retrofitting scenario, vacuum-insulation panels (VIP) – as an alternative to conventional glass wool – can lead to 20% savings in living space and a cost advantage of about 5%. At an LCOES100 of about 1.1 CHF/kWh, the integration of the storage inside an existing building is the most expensive option due to the high costs associated to the internal modification of the building and the loss of living space. The LCOES100 can be reduced by 50% if the storage is integrated inside a new building – mainly because of the high building reconstruction costs that are avoided. If the regulations would allow the storage to be removed from the calculation of the building footprint (in German the socalled 'Ausnützungsziffer'), the LCOES100 could be further reduced by 40%, reaching a minimum of 0.4 CHF/kWh. In spite of the high excavation costs and the increased heat losses, the concept of burying the STES underground – in direct vicinity of the building – represents a promising option (LCOES100 ∼0.6 CHF/kWh) to allow the integration of seasonal storage system in both new and existing residential buildings.  In this study, the focus was on residential buildings with solar fractions of 100%. It is envisaged that the economic optimum of future energy systems will be reached at lower autarky levels and bigger systems that include multiple buildings that make use of sector coupling strategies – e.g. by using photovoltaic installations in combination with heat pumps.
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