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Low-temperature District Heating: Various Aspects of Fourth-generation Systems
Halmstad University, School of Business, Engineering and Science, The Rydberg Laboratory for Applied Sciences (RLAS). Department of Energy Sciences, Lund University, Lund, Sweden.ORCID iD: 0000-0003-2885-0923
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With decreasing heat demand and less availability of high-temperature heat supply in future energy systems, the current district heating systems may experience increased competition on the heat market. A viable option to mitigate increasing competition is to operate systems with lower temperature levels, and the most conceivable way to achieve lower temperature levels is to decrease return temperatures.In this thesis, aspects of improvements in district heating systems are assessed. Three aspects, in particular, have been analysed. These are integration between energy systems, improvements in heat distribution technology, and economic benefits of low-temperature district heating systems.An increasing interest in integrating different energy systems has been prompted by the rapid introduction of intermittent renewable electricity supply in the energy system. Large-scale conversion of power to heat in electric boilers and heat pumps is a feasible alternative to achieve the balancing capacities required to maintain system functioning. Analysis of the unique Swedish experience using large heat-pump installations connected to district heating systems shows that, since the 1980s, 1527 MW of heat power has been installed, and about 80% of the capacity was still in use in 2013. Thus, a cumulative value of over three decades of operation and maintenance exists within Swedish district heating systems.Increased competition prompted by changes in the operation environment necessitates improved heat distribution. This thesis focuses on three system-embedded temperature errors: 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 lower heat transfer than is possible in heat exchangers (i.e. too-short thermal length). To address these temperature errors, three technology changes have been proposed (i) a three-pipe distribution network to separate the recirculation return flow from the delivery return flow, (ii) apartment substations to eliminate hot-water circulation use, and (iii) improved heat exchangers for lower return temperatures. The analysis of the proposed changes indicates annual average return temperatures between 17°C and 21°C.The final analysed aspect is the economic benefits of low-temperature district heating. It was identified that strong economic motives for lower operating temperatures in future heat supply exist, whereas the economic motives are significantly weaker for the traditional heat supply.The five 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 on 4GDH.

Place, publisher, year, edition, pages
Lund: Lund University , 2019. , p. 31
Keywords [en]
District heating, low temperature, three-pipe systems, 4GDH-3P
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:hh:diva-41080Libris ID: cpbmkkdh94clrdq5ISBN: 978-91-7895-316-5 (print)ISBN: 978-91-7895-317-2 (electronic)OAI: oai:DiVA.org:hh-41080DiVA, id: diva2:1374841
Public defence
2019-12-11, M:B, M-huset, Ole Römers väg 1, Lund, 13:15 (English)
Opponent
Supervisors
Note

ISRN: LUTMDN/TMHP-19/1153-SE. I publikationen felaktigt: ISSN 0282-1990

Available from: 2020-02-18 Created: 2019-12-03 Last updated: 2020-02-18
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: 2020-05-11Bibliographically 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)000426413400045 ()2-s2.0-85040108589 (Scopus ID)
Available from: 2018-11-18 Created: 2018-11-18 Last updated: 2020-02-18Bibliographically approved
3. Pipe Sizing for Novel Heat Distribution Technology
Open this publication in new window or tab >>Pipe Sizing for Novel Heat Distribution Technology
2019 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 12, no 7, article id 1276Article in journal (Refereed) Published
Abstract [en]

This paper assesses pipe sizing aspects for previously proposed, novel, low heat distribution technology with three pipes. Assessment issues include heat loss, pressure loss, and pipe sizing for different typical pipe configurations. This assessment has been provided by the analysis of a case area with single-family houses. Concerning heat loss, the proposed three-pipe solutions have the same magnitude of heat loss as conventional twin pipes, since lower return temperatures compensate for the larger heat loss area from the third pipe. Regarding pressure loss, the main restriction on the size of the third pipe is limited to the pressure loss in the third pipe. Thermostatic valves to manage the flow rate of the third pipe are advocated, since alternative small pumps have not been found to be commercially available. The pipe sizing recommendation is that the third pipe for recirculation purposes can be two to three standard pipe sizes smaller than the corresponding supply and return pipe, if no prosumer is connected in the heat distribution network.

Place, publisher, year, edition, pages
Basel: MDPI, 2019
Keywords
low temperature, district heating, pressure gradients, three-pipe system, 4GDH-3P
National Category
Energy Engineering
Identifiers
urn:nbn:se:hh:diva-39198 (URN)10.3390/en12071276 (DOI)000465561400093 ()2-s2.0-85065515173 (Scopus ID)
Projects
TEMPO
Funder
EU, Horizon 2020, 768936
Available from: 2019-04-04 Created: 2019-04-04 Last updated: 2020-02-18Bibliographically approved
4. Economic benefits of fourth generation district heating
Open this publication in new window or tab >>Economic benefits of fourth generation district heating
2020 (English)In: Energy, ISSN 0360-5442, E-ISSN 1873-6785, Vol. 193, article id 116727Article in journal (Refereed) Published
Abstract [en]

The main impetus for lower distribution temperatures in district heating systems is the lower heat supply costs obtained by these lower temperatures. In this paper, the differences in heat supply costs for two different temperature levels have been estimated for various future heat supply options. The estimations were obtained by modelling a district heating system characterised by typical climate conditions for Central Europe. High sensitivity to lower supply costs from lower temperatures was found for geothermal heat, industrial excess heat, and heat pumps, whereas low cost sensitivity was estimated for combined heat and power plants using waste or biomass. Lower heat distribution loss constitutes a minor component of the total cost reductions. The current use of high heat distribution temperatures was identified as an important barrier for the transition to renewable and recycled heat supply in district heating systems. Hence, lower distribution temperatures would facilitate this required transition because lower distribution temperatures provide higher profitability for these renewable and recycled heat sources. © 2019 The Authors. Published by Elsevier Ltd.

Place, publisher, year, edition, pages
London, UK: Elsevier, 2020
Keywords
Low temperature, district heating, cost reduction gradients, 4GDH, economic motivation
National Category
Energy Engineering
Identifiers
urn:nbn:se:hh:diva-41287 (URN)10.1016/j.energy.2019.116727 (DOI)2-s2.0-85076847499 (Scopus ID)
Funder
EU, Horizon 2020, 768936
Note

Other funding: International Energy Agency Technology Collaboration Programme on District Heating and Cooling including Combined Heat and Power, IEA-DHC|CHP Annex TS2 Implementation of low-temperature district heating systems.

Available from: 2019-12-20 Created: 2019-12-20 Last updated: 2020-02-25Bibliographically approved

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