Question: Could you describe the topic of your WP?
Answer Dr. Pierre Hollmuller: While reducing temperatures in district heating networks (DHN) is a priority for integrating renewable heat, it is conditioned by the temperature level of the individual substations. This issue is of particular concern for existing buildings, where distribution temperatures are known to be high and where corrective actions within inhabited spaces are of a certain complexity. Several techniques for temperature reductions at the substation level have been proposed or are currently under investigation, but their actual implementation on existing DH substations depends, to a large extent, on pre-existing conditions. Furthermore, specific case studies need to analyze the real benefit of temperature reduction at the DH network level and the interaction between temperature reduction strategies and other energy policy measures. Within this WP, these issues will be tackled using case studies on existing DH systems in an urban and rural context, requiring close collaboration with our cooperation partners.
Question: How does it relate to DeCarbCH?
P. Hollmuller: In the case of existing 2nd generation DH networks (with nominal 120 °C supply/70 °C return temperatures), integration of low-temperature resources by way of heat pumps (with production at 90 °C) is intrinsically limited to around 50% share of the annual delivered heat. On the contrary, temperature reduction of such DH (nominal 100 °C supply/60 °C return) could increase this share to 90%. The WP07 is in direct link with the overall DeCarbCH project, which addresses the colossal challenge of decarbonization of heating and cooling in Switzerland by facilitating, speeding up, and de-risk the implementation of renewables for heating and cooling in the residential sector.
Question: What are the main objectives?
P. Hollmuller: Based on actual case studies, in relation to cooperation partners, we strive to gain a solid understanding of i) Strategies/actions to lower temperature levels on existing substations; ii) the impact of such strategies at the level of the DHN network in terms of integration of renewable heat; iii) Interaction between temperature reduction strategies and other energy policy measures; iv) socio-technical dynamics of the implementation of temperature reduction measures; v) suitable socio-economic and policy measures to accelerate the diffusion of such solutions.
Question: What are the main research questions?
P. Hollmuller: Task 1 tackles the issue of temperature reduction techniques at the substation level: optimization/control of flowrates and heat exchanger sizes, cascade production of SH and DHW, instantaneous DHW production (without storage) for suppression of legionella issues, etc.
Task 2 focuses on the impact of the technologies mentioned above on the operating temperatures of the DHN itself. It is foreseen that two case studies will be selected, one in an urban setting and one in a rural/semi-urban setting. The selection will be based on the existence of detailed monitoring at the substation level combined with motivated utility partners.
Task 3 deals with the interaction between temperature reduction strategies and other energy policy measures, like i) the expected impact of different refurbishment policies on the possible lowering of DHN temperatures; ii) the relation between foreseeable DHN temperatures and the achievement of renewable energy policies at municipal/regional level; iii) the impact of solar energy strategies on DHN temperatures.
Task 4 analyses the relation between temperature reduction measures and governance arrangements in terms of the nature and intensity of economic relationships between the different actors (e.g., modified energy sales, delivery guarantees and contractual obligations, terms for the sale of heat from renewable energy sources).
Question: What are the main expected outcomes of your WP?
P. Hollmuller: Most of the existing DHN networks in Switzerland have not been optimized in terms of forward/return temperature. The cooperation partners of WP07 have expressed keen interest in implementing possible temperature reduction strategies on their existing DH networks. Once properly identified, implemented, and validated, such strategies should be transposable to other existing DH networks.
Preliminary calculation shows that in the case of existing 2nd generation DH networks (with nominal 120 °C supply/70 °C return), integration of low-temperature resources by way of heat pumps (with production at 90 °C) is intrinsically limited to a 50% share of the annual delivered heat. However, temperature reduction of such DH (nominal 100 °C supply/60 °C return) could increase this share to 90%.
Question: Could you provide some examples to illustrate the specialty of your WP?
P. Hollmuller: The short News contributions illustrate some ongoing tasks, covering aspects such as data collection on used case studies, audit of existing DHN and substations, and numerical simulation models.
Question: A final word for our readers?
P. Hollmuller: In the energy field, as elsewhere, efficiency is the fruit of an iterative process of innovation, observation, and training: it’s not because a technology is efficient that is being used, it’s because it is being used that it becomes efficient!
