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Thermal district networks are effective solutions to substitute fossil fuels with renewable energy sources for heating and cooling. Moreover, thermal networking of buildings allows energy efficiency to be further increased. The waste heat from cooling can be reused for heating in thermal district systems. Because of bidirectional energy flows between prosumers, thermal networks require new hydraulic concepts. In this work, we present a novel network topology for simultaneous heating and cooling: the reservoir network. The reservoir network is robust in operation due to hydraulic decoupling of transfer stations, integrates heat sources and heat sinks at various temperature levels and is flexible in terms of network expansion. We used Modelica simulations to compare the new single-pipe reservoir network to a basecase double-pipe network, taking yearly demand profiles of different building types for heating and cooling. The electric energy consumed by the heat pumps and circulations pumps differs between the reservoir and base case networks by less than 1%. However, if the reservoir network is operated with constant instead of variable mass flow rate, the total electrical consumption can increase by 48% compared to the base case. As with any other network topology, the design and control of such networks is crucial to achieving energy efficient operation. Investment costs for piping and trenching depend on the district layout and dimensioning of the network. If a ring layout is applied in a district, the reservoir network with its single-pipe configuration is more economical than other topologies. For a linear layout, the piping costs are slightly higher for the reservoir network than for the base case because of larger pipe diameters.

Thermal district networks are effective solutions to substitute fossil fuels with renewable energy sources for heating and cooling. Moreover, thermal networking of buildings allows energy efficiency to be further increased. The waste heat from cooling can be reused for heating in thermal district systems. Because of bidirectional energy flows between prosumers, thermal networks require new hydraulic concepts. In this work, we present a novel network topology for simultaneous heating and cooling: the reservoir network. The reservoir network is robust in operation due to hydraulic decoupling of transfer stations, integrates heat sources and heat sinks at various temperature levels and is flexible in terms of network expansion. We used Modelica simulations to compare the new single-pipe reservoir network to a basecase double-pipe network, taking yearly demand profiles of different building types for heating and cooling. The electric energy consumed by the heat pumps and circulations pumps differs between the reservoir and base case networks by less than 1%. However, if the reservoir network is operated with constant instead of variable mass flow rate, the total electrical consumption can increase by 48% compared to the base case. As with any other network topology, the design and control of such networks is crucial to achieving energy efficient operation. Investment costs for piping and trenching depend on the district layout and dimensioning of the network. If a ring layout is applied in a district, the reservoir network with its single-pipe configuration is more economical than other topologies. For a linear layout, the piping costs are slightly higher for the reservoir network than for the base case because of larger pipe diameters.

Abstract Low-temperature district heating and cooling networks, operated at water temperatures below 20 °C, substitute fossil-based heating systems with environmental heat or waste heat from industrial processes and additionally provide a source of direct cooling during the warmer months. These networks have the potential to reduce carbon emissions and are a key future technology in the strategy to combat climate change. However, large initial investments limit the diffusion of such networks. A large fraction of those investments, apart from trenching, goes to piping. Piping costs are highly dependent on pipe diameter, material and pressure rating. In this work, we focus on reducing costs by reducing the pressure in the system; thus allowing a reduced pressure rating. To reduce the maximum pressure in a hydraulic system, we present a novel technique based on alternating the connection of the expansion vessel. We explain our concept in a lab experiment and subsequently apply our method to the large-scale network at ETH Zurich, Switzerland. At ETH Zurich, we predict a pressure reduction of 8% from 6 to 5.5 bar. Lowering the pressure increases the economic viability and may thus promote the market dissemination of low-temperature district heating and cooling networks. Highlights • Low-temperature networks allow for simultaneous heating and cooling. • Low-temperature networks replace fossil-based heating by environmental heat. • A variable connection of the expansion vessel lowers the pressure in such networks. • Pressure reduction reduces piping costs and promotes market dissemination. • A novel valve automatically switches the connection of the expansion vessel. [ABSTRACT FROM AUTHOR]