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Effects of the District Heating Supply Temperature on the Efficiency of Borehole Thermal Energy Storage Systems

Formhals, J. and Welsch, B. and Schulte, D. O. and Sass, I. :
Effects of the District Heating Supply Temperature on the Efficiency of Borehole Thermal Energy Storage Systems.
In: 3rd International Conference on Smart Energy Systems and 4th Generation District Heating, 12.-13.9.2017, Kopenhagen.
[Conference or Workshop Item] , (2017)

Abstract

The mismatch of high heat demand in winter and high solar heat supply in summer can be compensated by solar district heating (SDH) with borehole thermal energy storage (BTES) systems. Transient simulations are imperative to attain a good understanding of the system behavior and to determine an optimized system design. In this context, the models of SDH systems and BTES pose very different requirements on their simulation environments. Taking this into account, a coupled simulation, in which both models can be realized in separate and specialized simulation environments becomes favorable. In the presented work, a SDH modeled in SimulationX (Modelica) and a BTES modeled in FEFLOW (Finite Element subsurface FLOW system) were simulated simultaneously and coupled via a TCP/IP connection. An adaptive communication step size control was implemented, to minimize both the error in transmitted energy and the computational effort.

Recent studies have shown that the performances of the single components of SDH with integrated BTES – and thus the whole system – strongly depend on design parameters like size, system architecture and control strategy. With the aforementioned method the strong interdependencies and the complex system behavior can be simulated in high detail, which allows for a comprehensive analysis and subsequent identification of energetic inefficiencies. The temperature level of the district heating flow proves to be a parameter, which has a strong effect on the storage performance as well as on the system efficiency. A case study is carried out, to illustrate the difference in efficiency of BTES integrated into district heating grids with different flow temperatures. It analyzes the potentials of an integration of a BTES into the existing district heating grid of the TU Darmstadt with and without a reduction of the grid flow temperature. During summer, a solar thermal collector field and buffer storages are used to the charge of the BTES system, whereas a heat pump was added for discharging it in winter.

The results support the general opinion that low district heating flow temperatures and respectively low return temperatures are crucial for an efficient operation of SDH systems with integrated BTES. The storage, the solar thermal collectors and the heat pump can be operated in an energetically much more favorable way. As a consequence it can be said that not only district heating systems profit from the integration of seasonal BTES, but the efficient operation of the storage itself is highly dependent on the shift to 4th generation district heating.

Item Type: Conference or Workshop Item
Erschienen: 2017
Creators: Formhals, J. and Welsch, B. and Schulte, D. O. and Sass, I.
Title: Effects of the District Heating Supply Temperature on the Efficiency of Borehole Thermal Energy Storage Systems
Language: English
Abstract:

The mismatch of high heat demand in winter and high solar heat supply in summer can be compensated by solar district heating (SDH) with borehole thermal energy storage (BTES) systems. Transient simulations are imperative to attain a good understanding of the system behavior and to determine an optimized system design. In this context, the models of SDH systems and BTES pose very different requirements on their simulation environments. Taking this into account, a coupled simulation, in which both models can be realized in separate and specialized simulation environments becomes favorable. In the presented work, a SDH modeled in SimulationX (Modelica) and a BTES modeled in FEFLOW (Finite Element subsurface FLOW system) were simulated simultaneously and coupled via a TCP/IP connection. An adaptive communication step size control was implemented, to minimize both the error in transmitted energy and the computational effort.

Recent studies have shown that the performances of the single components of SDH with integrated BTES – and thus the whole system – strongly depend on design parameters like size, system architecture and control strategy. With the aforementioned method the strong interdependencies and the complex system behavior can be simulated in high detail, which allows for a comprehensive analysis and subsequent identification of energetic inefficiencies. The temperature level of the district heating flow proves to be a parameter, which has a strong effect on the storage performance as well as on the system efficiency. A case study is carried out, to illustrate the difference in efficiency of BTES integrated into district heating grids with different flow temperatures. It analyzes the potentials of an integration of a BTES into the existing district heating grid of the TU Darmstadt with and without a reduction of the grid flow temperature. During summer, a solar thermal collector field and buffer storages are used to the charge of the BTES system, whereas a heat pump was added for discharging it in winter.

The results support the general opinion that low district heating flow temperatures and respectively low return temperatures are crucial for an efficient operation of SDH systems with integrated BTES. The storage, the solar thermal collectors and the heat pump can be operated in an energetically much more favorable way. As a consequence it can be said that not only district heating systems profit from the integration of seasonal BTES, but the efficient operation of the storage itself is highly dependent on the shift to 4th generation district heating.

Divisions: 11 Department of Materials and Earth Sciences > Earth Science > Geothermal Science and Technology
11 Department of Materials and Earth Sciences > Earth Science
11 Department of Materials and Earth Sciences
Event Title: 3rd International Conference on Smart Energy Systems and 4th Generation District Heating
Event Location: Kopenhagen
Event Dates: 12.-13.9.2017
Date Deposited: 19 Sep 2017 05:48
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