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Enhanced District Heating Technology: Maintaining Future System Feasibility
Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS). Lund University, Lund, Sweden.ORCID iD: 0000-0003-2885-0923
2017 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

When heat demand and high temperature heat supply gradually decreases in the future, then it will effect district heating systems ability to compete on the heat market. A good way to mitigate less district heating feasibility is to operate systems with lower temperature levels and the most conceivable way to achieve lower temperature levels is to decrease return temperatures.

Thus, this thesis emphasise temperature errors embedded in district heating systems. Only a selection of temperature errors are analysed in this thesis. First, the temperature error that occurs due to recirculation in distribution networks at low heat demands. Second, the temperature error that occurs due to hot water circulation in multi-family buildings. Third, the temperature error that occurs due to less than possible heat transfer in heat exchangers, i.e. too short thermal lengths.

In order to address these temperature errors three technology changes have been proposed (i) three-pipe distribution network to separate the recirculation return flow from the delivery return flow, (ii) apartment substations to eliminate hot water circulation utilisation, and (iii) improved heat exchangers for lower return temperatures at a constant scenario. Analysis of proposed changes has resulted in annual average return temperatures between 17-21 °C.

Furthermore, rapid introduction of intermittent renewable electricity supply in the energy system has prompted an increased necessity of power system balancing capacities. Large-scale conversion of power-to-heat in electric boilers and heat pumps is a feasible alternative to achieve such balancing capacities. Analysis of the unique Swedish experience with utilisation of large heat pumps installations connected to district heating systems show that since the 1980s 1527 MW of heat power has been installed, about 80 % of the capacity was still in use by 2013. Thus, a cumulative value of over three decades of operation and maintenance exists within Swedish district heating systems.

The two papers presented in this thesis are related to future district heating systems through the five abilities of fourth generation district heating (4GDH), which are documented in the definition paper of 4GDH.

Place, publisher, year, edition, pages
Lund: Lund University Open Access, 2017. , p. 75
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:hh:diva-39199Libris ID: 22509321ISBN: 978-91-7753-507-2 (print)ISBN: 978-91-7753-508-9 (electronic)OAI: oai:DiVA.org:hh-39199DiVA, id: diva2:1302301
Presentation
2017-12-18, M:B (M-huset), Ole Römers väg 1, Lund, 13:15 (English)
Opponent
Supervisors
Note

Med populärvetenskaplig sammanfattning på svenska. I publikationen felaktigt: ISSN 0282-1990

Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2019-04-04Bibliographically approved
List of papers
1. Large heat pumps in Swedish district heating systems
Open this publication in new window or tab >>Large heat pumps in Swedish district heating systems
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2017 (English)In: Renewable & sustainable energy reviews, ISSN 1364-0321, E-ISSN 1879-0690, Vol. 79, p. 1275-1284Article in journal (Refereed) Published
Abstract [en]

Power-to-heat solutions like heat pumps and electric boilers are foreseen to be possible future tools to stabilise international power markets with high proportions of variable power supply. Temporary low cost electricity can be used for heat generation at times with high availability of wind and solar power through substitution of ordinary heat supply, hence contributing to increased energy system sustainability. Power-to-heat installations in district heating systems are competitive due to low specific investment and installation costs for large electric boilers, heat pumps, and heat storages. Several large-scale heat pumps were installed in Swedish district heating systems during the 1980s, since a national electricity surplus from new nuclear power existed for some years. The aim of this paper is to summarise the accumulated operation experiences from these large Swedish heat pumps to support and facilitate planning of future power-to-heat solutions with heat pumps in district heating systems. Gained experiences consider; installed capacities, capacity utilisation, heat sources used, refrigerant replacements, refrigerant leakages, and wear of mechanical components. The major conclusion is that many of the large thirty-year-old heat pumps are still in operation, but with reduced capacity utilisation due to internal competition from waste and biomass cogeneration plants in the district heating systems.

Place, publisher, year, edition, pages
Kidlington: Pergamon Press, 2017
Keywords
Power-to-heat, Heat pumps, District heating, District cooling, Integrated energy systems
National Category
Energy Systems
Identifiers
urn:nbn:se:hh:diva-34097 (URN)10.1016/j.rser.2017.05.135 (DOI)000410011500091 ()2-s2.0-85019691543 (Scopus ID)
Available from: 2017-06-13 Created: 2017-06-13 Last updated: 2019-04-04Bibliographically approved
2. Novel low temperature heat distribution technology
Open this publication in new window or tab >>Novel low temperature heat distribution technology
2018 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 145, p. 526-539Article in journal (Refereed) Published
Abstract [en]

Lower future heat demands and lower availability of non-fossil high temperature heat supply are expected future market conditions that restrain the long-term viability of contemporary district heating systems. Hence, current district heating technology should be enhanced to increase system performance in new heat distribution areas. This paper aims to outline a proposal for technical improvements required to achieve lower annual average return temperatures in new residential buildings to improve viability in future market conditions. The proposed technical solution consists of three principle changes: three-pipe distribution networks, apartment substations, and longer thermal lengths for heat exchangers. The three technical modifications aims at addressing system embedded temperature errors. Furthermore, a simulation model was developed to assess the proposed technical solution concerning different energy performances of buildings and different thermal lengths in heat exchangers. The results show that implementation of the three technical modifications reaches time-weighted annual average return temperatures of 17–21 °C with supply temperatures of about 50 °C. The results also verify the increased necessity to separate the network return flows into delivery and recirculation flows in residential substations as energy performance in buildings increase.

Place, publisher, year, edition, pages
London: Elsevier, 2018
Keywords
Low temperature, District heating, Three-pipe system, Recirculation, 4GDH-3P
National Category
Energy Engineering
Identifiers
urn:nbn:se:hh:diva-38360 (URN)10.1016/j.energy.2017.12.157 (DOI)
Available from: 2018-11-18 Created: 2018-11-18 Last updated: 2019-04-04Bibliographically approved

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