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­Multistage Latent Heat Cold Thermal Energy Storage Design Analysis
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. (Thermal Energy Storage, Energy Technology)ORCID iD: 0000-0001-6982-2879
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology. (Thermal Energy Storage, Energy Technology)ORCID iD: 0000-0001-9556-552X
2013 (English)In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, no SI, 1438-1445 p.Article in journal (Refereed) Published
Abstract [en]

Thermal energy storage in cooling applications contributes to improvements in overall system efficiency as well as to better energy quality management. Latent heat thermal energy storage (LHTES) is used to provide load shifted thermal energy at small temperature swing with high storage density, hence an overall more compact energy system. However, the low thermal conductivity of the majority of the phase change materials (PCMs) necessitates delicate design of the active storage unit to meet power demand (high enough energy extraction/storage per amount of time).

A performance analysis of two LHTES configurations is carried out in this work. Thermal charge and discharge rate of single PCM is compared with multistage LHTES using a cascade design of multiple PCMs at various phase change temperatures in a submerged finned pipe heat exchanger design. The work is conducted with a validated finite element based numerical simulation for evaluation of both full charge/discharge cycle and continuous half charge/discharge cycles.

The results show that in full charge/discharge mode, the thermal performance of a multi-PCM LHTES may be improved by 10% to 40% as compared to that of a homogeneous­­ single-PCM storage unit in terms of thermal charge/discharge rate. This is due to the capability of the multistage LHTES to maintain a higher driving temperature difference for the heat transfer process in the charging and discharging processes. In half charge/discharge cycling mode, however, the thermal power rating performance of multi-PCM storage converges towards that of the single-PCM storage in melting process, reducing thus the multi-PCM enhancement. This work provides preliminary insights to multistage latent heat cold thermal energy storage design with finned pipe heat exchanger.

Place, publisher, year, edition, pages
2013. Vol. 112, no SI, 1438-1445 p.
Keyword [en]
Thermal energy storage, Phase change material, Multistage storage design
National Category
Energy Engineering Energy Systems
Identifiers
URN: urn:nbn:se:kth:diva-117698DOI: 10.1016/j.apenergy.2013.01.054ISI: 000329377800156Scopus ID: 2-s2.0-84884210408OAI: oai:DiVA.org:kth-117698DiVA: diva2:602620
Conference
4th International Conference on Applied Energy (ICAE),July 01-04, 2012, Suzhou, China
Note

QC 20140210

Available from: 2013-02-01 Created: 2013-02-01 Last updated: 2017-12-06Bibliographically approved
In thesis
1. Latent Heat Thermal Energy Storage for Indoor Comfort Control
Open this publication in new window or tab >>Latent Heat Thermal Energy Storage for Indoor Comfort Control
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Equating Earth’s existence to 24 hours, we, the Homo sapiens, came about in the last four seconds. Fossil fuel came to our knowledge with mass extraction dating from the Industrial Revolution two centuries ago, in other words 4 milliseconds out of Earth’s 24-hour equivalent lifetime. With the unruly use of fossil fuel based resources, global temperature increase due to anthropogenic emission is projected by the Intergovernmental Panel on Climate Change (IPCC) to increase between 2 °C and 6 °C by 2100. The expected results are unprecedented climatic phenomena, such as intense tropical cyclones, extreme heat waves, and heavy precipitation among others. Limiting climate change has become one of the most discerning issues in our highly energy dependent society.

Ever-increasing energy demand goes in hand with improved living standard due to technologic and economic progress. Behavioral change is one of the ultimate solutions to reduce energy demand through adequate life style change; however such approach requires societal paradigm shift. In this thesis, we look into using energy storage technology to peak shave and to load shift energy so as to attain increased renewable energy source utilization, improved system’s energy efficiency, and reduced Greenhouse Gas (GHG) emission without compromising living comfort.

High energy density thermal energy storage (TES) systems utilize phase change materials as storage mediums where thermal energy is principally stored in the form of latent heat (LH). Advantages of such systems are compact components and small storage temperature swing. However, challenges remain in implementing LHTES to the built environment, namely lack of understanding of system dynamics, uncertainty in component design, and non-documented material property are to be addressed.

The goal of this thesis is to address the issues on material property characterization, on component heat transfer study and on system integration. A methodology in measuring material’s thermo physical property through T-History setup is defined. Caveats of existing methodology are presented and improvements are proposed. The second part of this thesis consists of establishing valid numerical models of LHTES component for both shape stabilized and free flowing PCMs. Experimental verifications were performed and models were validated. Improvement to the thermal power performance was studied and was reached with multistage multi-PCM storage design. Techno-economic optimization and parametric study were carried out for transient TES integrated system study. Finally, an estimation of the Swedish peak energy demand reduction was performed through study of TES implementation to the existing energy systems. The peak energy shave attained through TES implementation determines the amount of fossil fuel based marginal energy that can be reduced for a greener environment.

Abstract [sv]

Om vi låter jordens livstid motsvaras av 24 timmar, har mänskligheten endast existerat under de sista fyra sekunderna. Fossila bränslen med utvinning i stor skala kom till vår kännedom under den industriella revolutionen för två sekel sedan, med andra ord fyra millisekunder av jordens dygnslånga livstid. På grund av ohämmad fossilbränsleanvändning förutspår FN:s klimatpanel (IPCC) att den av människor orsakade globala uppvärmningen blir mellan 2°C och 6°C till år 2100. Onormala klimatfenomen förväntas som resultat, till exempel starka tropiska cykloner, extrema värmeböljor, och kraftig nederbörd. Att begränsa klimatförändringarna har blivit en av de viktigaste frågorna i vårt starkt energiberoende samhälle.

Ständigt ökande efterfrågan på energi går hand i hand med förbättrad levnadsstandard på grund av teknologiska och ekonomiska framsteg under det senaste århundradet. Beteendeförändringar, att anpassa vår livsstil, har betraktats som den slutgiltiga lösningen, men en sådan strategi kräver långsiktig utbildning och vilja. I denna avhandling undersöks en ny energiteknik: energilagring, för att minska topplaster och skifta belastningen så att vi kan gå mot ett paradigmskifte i form av ökat nyttjande av förnybara energikällor, förbättrad energieffektivitet och minskade utsläpp av växthusgaser utan att ge avkall på boendekomfort.

System för termisk energilagring med hög densitet (TES) använder fasändringsmaterial som lagringsmedia, där värmeenergi huvudsakligen lagras i form av latent värme (LH). Fördelarna är kompakta komponenter och små variationer i lagringstemperatur. Utmaningar återstår i att integrera LHTES i fastigheter: bristande förståelse för systemdynamiken, osäkerhet i komponentdesign och odokumenterade materialegenskaper.

Målet med denna avhandling är att ta itu med frågor kring materialkarakterisering, studier av värmeöverföring för komponenter och om systemintegration. En metod för att mäta materials entalpi genom Temperature-History definieras genom att identifiera brister i existerande metoder, och implementera förbättringar. Den andra aspekten består i att upprätta gångbara numeriska modellerna för LHTES, där experimentell verifiering har genomförts. Förbättring av den termiska effekten erhålls med flerstegs-fasändringsmaterial-lagring. Känslighetsanalys och teknisk-ekonomisk optimering utförs för integrerad systemdesign med TES. Slutligen görs en uppskattning av hur mycket Sveriges topplast i energisystemet kan minskas genom att studera implementering av TES. Minskningen i topplast som uppnås genom implementation av TES bestämmer mängden marginalenergi från fossila bränslen som kan reduceras för att nå ett mer uthålligt samhälle.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. xvii, 77 p.
Series
Trita-KRV, ISSN 1100-7990 ; 13:02
Keyword
Thermal Energy Storage, Phase Change Material, Indoor Comfort, Heat Transfer, Termisk Energilagring; Fasändringsmaterial; Inomhuskomfort; Värmeöverföring
National Category
Energy Engineering Energy Systems
Identifiers
urn:nbn:se:kth:diva-119275 (URN)978-91-7501-679-5 (ISBN)
Public defence
2013-04-09, F3, Lindstedtsvägen 26, KTH, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20130312

Available from: 2013-03-12 Created: 2013-03-11 Last updated: 2013-03-12Bibliographically approved

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