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Case Studies in Low-Energy District Heating Systems: Determination of Dimensioning Methods for Planning the Future Heating Infrastructure

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Hakan İbrahim Tol, Svend Svendsen
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The climate crisis and the new technological possibilities for building the low energy buildings give the opportunity to transform the municipal heating systems from high temperature, and high demand systems to low temperature, and low demand systems. The heating demand will be reduced significantly in the future and renewable energy has to be integrated in the design of district heating systems in proper with the non-fossil fuel based future. The paper suggests a plan for an energy efficient District Heating (DH) system with low operating temperatures, such as 55 °C in terms of supply and 25 °C in terms of return. Different case studies could be the rational basis for the integrated planning of the future’s sustainable and energy efficient heating infrastructure.

Firstly, consideration was given to define an optimal dimensioning method for a new settlement where low-energy houses are planned to be constructed within a case study in collaboration with Roskilde Municipality, Denmark. In this case study focus was given to the determination of the optimal substation configuration equipped at each house and optimal network layout to prevent excessive supply temperature drop occurring in summer months. The use of optimization method yielded in energy savings of 14% in terms of heat loss from the DH network, in comparison to mostly used traditional dimensioning method based on pressure gradient. Also, considering a storage tank at each substation of the houses at the low-energy DH network resulted in energy savings of 8% in preventing the heat loss from the DH network in comparison to the use of substation without storage tank. The use of by-passes at the end-users in a branched DH network could save significant energy in the point of heat loss from the DH network in comparison to forming the low-energy DH network with looped layout.

Second consideration was given to define an optimal dimensioning of low-energy DH network in connection with existing settlement and with existing citywide heating system. The technical aspect of using low-temperature at existing inhouse heating systems was also investigated in collaboration with Gladsaxe Municipality, Denmark. This case is used to form the operational planning. The peak-demand conditions were defined to be supplied with boosted temperature, allowing further reduction of pipe dimensions at the design stage. The existing houses in the case area were considered to be renovated to low-energy class. Dimensioning the low-energy DH network with consideration given to current heat demand situation yielded in 41% higher pipe investment cost in comparison to the pipe dimensions achieved by use of boosted supply temperature at peak-demand conditions. Thus overdimensioned DH network for the future situation could be avoided by considering current and future heat demand situations together with boosting the supply temperature in some certain peak situations.