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Energetic and exergetic analysis of alternative low-temperature based district heating substation arrangements
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. École des Mines de Nantes - EMN, Energy Systems and Environment - DSEE. (Thermal Energy Storage)ORCID iD: 0000-0002-0194-8317
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. (Thermal Energy Storage)ORCID iD: 0000-0001-6982-2879
École des Mines de Nantes - EMN, Energy Systems and Environment - DSEE.
École des Mines de Nantes - EMN, Energy Systems and Environment - DSEE.
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2016 (English)In: International Journal of Thermodynamics, ISSN 1301-9724, Vol. 19, no 2, p. 71-80Article in journal (Refereed) Published
Abstract [en]

District Heating (DH) technology is an efficient and cost-effective solution to provide heating services to the built environment. However, the existing DH technology may not be technically and economically effective to service buildings with low energy demands. Here, low-temperature based district heating (LTDH) can provide a better match between supply and demand in terms of energy quality and quantity. This paper deals with the energy and exergy analyses of a LTDH substation supplying a secondary LTDH network as a subnet of the existing DH system. In order to improve the temperature match, a mix of supply and return streams from the main DH network are used to supply the substation. Based on modelling and simulation, an energy and exergy analysis is employed to compare the performance of two proposed substation configurations to that of a conventional DH substation operating at low temperatures. The results of this analysis show that the proposed LTDH substation reduced the share of energy demand covered by the main DH supply by 20% to 25%. Likewise, by using the flow from the main DH return pipe, the final exergy efficiency of the overall system increased by 5% on average. The exergy destruction occurring at the system components was also identified and compared: during high heat demands the substation heat exchanger is responsible for the largest share of exergy destruction, whereas for low heat demands, it is due to the pumping effort. Based on these results, the proposed system is seen as an effective approach to increase the quality and quantity match between the low-temperature network and the conventional supply.

Place, publisher, year, edition, pages
2016. Vol. 19, no 2, p. 71-80
Keyword [en]
Low-Temperature District Heating; Substation; Performance; Exergy; Temperature Cascading
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
URN: urn:nbn:se:kth:diva-190005DOI: 10.5541/ijot.5000148882ISI: 000382970100002Scopus ID: 2-s2.0-84973322315OAI: oai:DiVA.org:kth-190005DiVA, id: diva2:950154
Projects
SELECT+
Note

QC 20160809

Available from: 2016-07-28 Created: 2016-07-28 Last updated: 2018-06-12Bibliographically approved
In thesis
1. Low-temperature based thermal micro-grids: operation and performance assessments
Open this publication in new window or tab >>Low-temperature based thermal micro-grids: operation and performance assessments
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Alternative title[fr]
Micro-réseaux de chaleur urbains basse température : évaluation du fonctionnement et de la performance
Abstract [en]

Energy use in the urban environment is vital for the proper functioning of our society, and in particular, comfort heating –or cooling– is a central element of our energy system often taken for granted. Within this context, district energy systems and especially, district heating (DH) systems must evolve to adapt to the upcoming decades-long transition towards a sustainable energy system. This dissertation seeks to introduce, discuss, and assess from a techno-economic perspective the concept of low-temperature (LT) based thermal micro-grids (subnets) as active distribution thermal networks. It explores the role of the subnet at the system distribution level supervised by an active agent (DH substation), performing tasks of heat supply and demand management (storage and dispatch), as well as coordinating bidirectional flows.

 

Here, a mixed methodological approach based on analytical simulation for the assessment of alternatives to evaluate a set of technologies is developed and discussed. This approach covers: the identification of knowledge gaps through the state-of-the-art analysis; a collection of incremental technical and/or economic performance assessments; and the analysis of a measurement data set from an existing LTDH demonstration project.

 

Key findings of this work include: an updated and improved model of aggregated heat loads; identification of differences in load and temperature patterns for certain LT subnets; analysis of benefits and drawbacks of active substations with distributed heat sources and/or storage; and the impact on the reduction of the primary network return temperature as a consequence of the increase in the share of LT subnets, leading to lower generation and operating costs.

 

These outcomes reveal that the integrated design and operation of the active thermal micro-grid have the potential to improve both the performance of the subnet, and that of the primary network. It further enhances the capability of the overall system to integrate unconventional and distributed heat sources together with energy efficient buildings by increasing the system’s flexibility and controllability. Active thermal distribution networks will likely become a subsequent step in the technological development of DH technologies, to address the matter of providing comfort heating in an effective and cost-efficient manner. This work advances the current DH knowledge by identifying synergies and challenges that arise with these new developments, in order for DH technology to play a key role in the future smart and sustainable energy system.

Abstract [sv]

Energianvändning i stadsmiljö är avgörande för att vårt samhälle ska fungera väl, och i synnerhet är komfortvärme eller -kylning centrala element i vårt energisystem som ofta tas för givet. I detta sammanhang måste distributionsnätverk för energi och i synnerhet fjärrvärmesystem utvecklas för att anpassa sig till de kommande årtiondenas övergång till ett hållbart energisystem. Denna doktorsavhandling syftar till att analysera och diskutera koncept med lågtemperaturbaserade termiska mikronät, sekundära nät och deras roll som aktiva termiska distributionsnätverk. Såväl driftsstrategier som systemprestanda undersöks. Det sekundära nätets inverkan på det övergripande distributionsnätet utforskas med särskilt fokus på smarta undercentraler (fjärrvärmecentraler) som hanterar flödesreglering i två riktningar, lagring samt behovsuppfyllelse.

 

Studien är baserad på ett metodiskt tillvägagångssätt där analytisk simulering har använts för utvärdering av alternativa tekniklösningar. Utgångspunkten är en kunskapssammanställning där viktiga frågeställningar som behöver svar har identifierats. Därefter har simuleringar utförts så att tekniska och/eller ekonomiska prestationer kunnat undersökas stegvis. Vidare har mätdata från en befintlig installation av lågtemperaturbaserad fjärrvärme analyserats, och delvis använts för att verifiera resultat från simuleringen.

 

Viktiga resultat av detta arbete är: en uppdaterad och förbättrad modell av aggregerade värmebelastningar; identifiering av skillnader i belastnings- och temperaturmönster för vissa lågtemperatur fjärrvärmenät; analys av fördelar och nackdelar med aktiva fjärrvärmecentraler där distribuerade värmekällor och/eller lagring hanteras; samt effekten av minskningen av primärnätets returtemperatur som en följd av ökningen av andelen lågtemperaturnät, vilket leder till lägre produktion- och driftskostnader.

 

Dessa resultat visar att den integrerade utformningen och driften av det aktiva termiska mikronätet har potential att förbättra både prestanda hos delnätet och det primära nätverket. Det ökar dessutom det övergripande systemets potential för att integrera okonventionella och distribuerade värmekällor tillsammans med energieffektiva byggnader genom att öka systemets flexibilitet och styrbarhet. Aktiva termiska distributionsnät visar sig vara en intressant del av framtida fjärrvärmesystem där komfortvärme erbjuds på ett resurs- och kostnadseffektivt sätt. Detta arbete fördjupar befintlig kunskap kring lågtemperaturbaserad fjärrvärme i det att synergier och utmaningar har identifierats. Därmed bidrar avhandlingen till att fjärrvärmeteknik kan utvecklas för att fortsatt spela en nyckelroll i smarta och hållbara energisystem.

Abstract [fr]

L’utilisation d'énergie en milieu urbain est essentielle pour le bon fonctionnement de notre société, en particulier pour les besoins de chauffage qui est un élément central de notre système énergétique souvent considéré comme allant de soi. Dans ce cadre, les systèmes énergétiques urbains et en particulier les réseaux de chaleur urbains ont besoin d’évoluer pour s'adapter à la transition à venir vers un système énergétique durable.

 

Ce travail de recherche a pour objectif de présenter, de discuter et d’évaluer, du point de vue technico-économique, le concept de micro-réseaux de chaleur urbains basse température comme réseaux secondaires de distribution de chaleur actifs. Dans cette thèse, une approche méthodologique mixte basée sur la simulation analytique pour l'évaluation des alternatives est développée et discutée pour étudier une combinaison de technologies associées aux sous-stations basse température.

 

Les principaux résultats de ce travail couvrent : le développement d’un modèle amélioré de charges thermiques agrégées ; la comparaison des performances des réseaux basse température ; l’analyse des avantages et des inconvénients des sous-stations actives couplées à des sources de chaleur ou du stockage distribuées ; et les effets d’une température de retour du réseau primaire plus basse.

 

Les conclusions révèlent que la conception et le fonctionnement intégrés du micro-réseau de chaleur urbain actif ont le potentiel d'améliorer les performances de l'ensemble du système, afin de relever ses défis d'une manière efficace et rentable. Ce travail fait progresser les connaissances actuelles sur le chauffage urbain en identifiant les synergies et les enjeux associés, en vue de que ces technologies jouent un rôle clé dans le futur système énergétique intelligent et durable.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2018. p. 278
Series
TRITA-ITM-AVL ; 2018:36
Keyword
low-temperature district heating; active thermal micro-grid; substation operation; performance assessment; distributed heat resources, chauffage urbain basse température; micro-réseaux de chaleur urbains actifs; fonctionnement de la sous-station; évaluation de la performance; sources de chaleur distribuées, lågtemperatur fjärrvärme; aktiv fjärrvärmemikronät; fjärrvärmecentral operation; prestationsbedömning; distribuerada värmekällor
National Category
Energy Engineering
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-228607 (URN)978-91-7729-847-2 (ISBN)
Public defence
2018-07-04, F3, Lindstedtsvägen 26, KTH Campus, Stockholm, 10:00 (English)
Opponent
Supervisors
Projects
Erasmus Mundus Joint Doctorate SELECT+ ‘Environomical Pathways for Sustainable Energy Services’
Available from: 2018-06-13 Created: 2018-06-12 Last updated: 2018-06-13Bibliographically approved

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