Master's Thesis Lukas Kivilip


Optimal design and operation of bidirectional low temperature networks

Holistic approach Copyright: EBC Holistic approach for the optimization of bidirectional low temperature networks

Bidirectional low temperature networks are a novel concept for providing district heating and cooling. The buildings connected to the network act as prosumers of thermal energy. Thus, the thermal demands of the connected buildings can be balanced out to some extent. The remaining residual load is supplied by a central energy hub. In this thesis, a novel approach for designing bidirectional low temperature networks by means of mathematical optimization is presented.

The optimization model is formulated using linear programming (LP). The objective of the optimization is to minimize the annual costs for covering the heating and cooling demands. The energy systems of all buildings including the energy hub are designed simultaneously within one optimization model. The LP formulation comprises different technologies for heating, cooling and power generation as well as thermal and electrical energy storages.

Within a case study, the optimization model is applied to a district with 17 buildings. The optimal design and operation of the bidirectional low temperature network is compared to two alternative concepts: an individual supply of each building on the one hand, and conventional district heating and cooling on the other hand. The bidirectional network leads to a cost reduction of 14 % compared to conventional district heating and cooling and up to 42 % compared to an individual building supply. Moreover, the carbon dioxide emissions are reduced by 34 % compared to conventional DHC and up to 56 % compared to the individual supply.

In a second case study, synthetic demand profiles are used to investigate the influence of the demand structure on the economic, ecological and thermodynamic performance indicators. A strong correlation between the system’s performance and the simultaneity of heating and cooling demands is observed.