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This paper investigates the energy performance and sizing criteria of 5th generation district heating and cooling (5GDHC) networks as a function of the heat distribution temperature in the building systems connected to the district network. An energy simulation model of a 5GDHC network was developed in Modelica for a case study located in Denmark. Calculations were carried out for four different building heating systems. Simulation results show that reducing the heat distribution temperatures from 70 ◦C to 23 ◦C leads to around 40% annual electric energy savings (from 10.4 kWh/m2 to 6.2 kWh/m2) for the operation of the heat pumps. Heat distribution temperatures of 23 ◦C cause higher water mass flow rates through the network, leading to annual electric energy consumption for the circulation pumps that are almost doubled (from 0.16 kWh/m2 to 0.3 kWh/m2) compared to the reference case at 70 ◦C. Furthermore, the paper discusses how the results obtained from the Danish case study can be generalized and applied to other cases using a simplified mathematical approach. It is found that about 1.5% of electric energy savings can be achieved for each temperature degree reduction in the heat distribution system.

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.

Two types of simulation software TRNSYS and Polysun are studied to check their suitability for solar district heating system planning. A reference case, a part of the Vallda Heberg district heating system is modelled in both tools and results are compared with available measured data and with each other. Models are successfully calibrated. TRNSYS and Polysun models have deviations in main key figures compared to the reference case less than 2% and less than 8% respectively. A sensitivity analysis of key parameters shows that the two tools give similar results.

Low-temperature thermal networks enable simultaneous heating and cooling of buildings and reduce CO2 emissions by substituting fossil fuels by environmental heat sources. In this work, we compare two different network topologies, the traditional lowtemperature network (TLTN) and the new reservoir low-temperature network (RLTN). We show that the volume flow in the RLTN can be adjusted to increase the efficiency of heat pumps and to reduce hydraulic power losses in the supply lines without compromising heat demands., + ID der Publikation: hslu_60968 + Art des Beitrages: Wissenschaftliche Medien + Jahrgang: 1343 + Sprache: Deutsch + Letzte Aktualisierung: 2019-12-03 14:14:29

The Solar Heat Integration NEtwork (SHINE) is a European research school in which 13 PhD students in solar thermal technologies are funded by the EU Marie-Curie program. It has five PhD course modu ...