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Predicting Electrochromic Smart Window Performance
KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Applied Electrochemistry.
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

The building sector is one of the largest consumers of energy, where the cooling of buildings accounts for a large portion of the total energy consumption.

Electrochromic (EC) smart windows have a great potential for increasing indoor comfort and saving large amounts of energy for buildings. An EC device can be viewed as a thin-film electrical battery whose charging state is manifested in optical absorption, i.e. the optical absorption increases with increased state-of-charge (SOC) and decreases with decreased state-of-charge. It is the EC technology's unique ability to control the absorption (transmittance) of solar energy and visible light in windows with small energy effort that can reduce buildings' cooling needs.

Today, the EC technology is used to produce small windows and car rearview mirrors, and to reach the construction market it is crucial to be able to produce large area EC devices with satisfactory performance. A challenge with up-scaling is to design the EC device system with a rapid and uniform coloration (charging) and bleaching (discharging). In addition, up-scaling the EC technology is a large economic risk due to its expensive production equipment, thus making the choice of EC material and system extremely critical. Although this is a well-known issue, little work has been done to address and solve these problems.

This thesis introduces a cost-efficient methodology, validated with experimental data, capable of predicting and optimizing EC device systems' performance in large area applications, such as EC smart windows. This methodology consists of an experimental set-up, experimental procedures and a twodimensional current distribution model. The experimental set-up, based on camera vision, is used in performing experimental procedures to develop and validate the model and methodology. The two-dimensional current distribution model takes secondary current distribution with charge transfer resistance, ohmic and time-dependent effects into account. Model simulations are done by numerically solving the model's differential equations using a finite element method. The methodology is validated with large area experiments.

To show the advantage of using a well-functioning current distribution model as a design tool, some EC window size coloration and bleaching predictions are also included. These predictions show that the transparent conductor resistance greatly affects the performance of EC smart windows.

Abstract [sv]

Byggnadssektorn är en av de största energiförbrukarna, där kylningen av byggnader står för en stor del av den totala energikonsumtionen.

Elektrokroma (EC) smarta fönster har en stor potential för att öka inomhuskomforten och spara stora mängder energi för byggnader. Ett elektrokromt fönster kan ses som ett tunnfilmsbatteri vars laddningsnivå yttrar sig i dess optiska absorption, d.v.s. den optiska absorptionen ökar med ökad laddningsnivå och vice versa. Det är EC-teknologins unika egenskaper att kunna kontrollera absorptionen (transmittansen) av solenergi och synligt ljus i fönster med liten energiinsats som kan minska byggnaders kylningsbehov.

EC-teknologin används idag till att producera små fönster och bilbackspeglar, men för att nå byggnadsmarknaden är det nödvändigt att kunna producera stora EC-anordningar med fullgod prestanda. En välkänd utmaning med uppskalning är att utforma EC-systemet med snabb och jämn infärgning (laddning) och urblekning (urladdning), vilket även innebär att uppskalning är en stor ekonomisk risk på grund av den dyra produktionsutrustningen. Trots att detta är välkända problem har lite arbete gjorts för att lösa dessa.

Denna avhandling introducerar ett kostnadseffektivt tillvägagångssätt, validerat med experimentella data, kapabelt till att förutsäga och optimera ECsystems prestanda för anordningar med stor area, såsom elektrokroma smarta fönster. Detta tillvägagångssätt består av en experimentell uppställning, experiment och en tvådimensionell strömfördelningsmodell. Den experimentella uppställningen, baserad på kamerateknik, används i de experimentella tillvägagångssätten så att modellen kan utvecklas och valideras. Den tvådimensionella strömfördelningsmodellen inkluderar sekundär strömfördelning med laddningsöverföringsmotstånd, ohmska och tidsberoende effekter. Modellsimuleringarna görs genom att numeriskt lösa en modells differentialekvationer med hjälp av en finita-element-metod. Tillvägagångssättet är validerat med experiment gjorda på stora EC anordningar.

För att visa fördelarna med att använda en väl fungerande strömfördelningsmodell som ett designverktyg, har några prediktioner av infärgning och urblekning av EC-fönster inkluderats. Dessa prediktioner visar att den transparenta strömtilledarresistansen har stor påverkan på EC-fönsters prestanda.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. , vii, 35 p.
Trita-CHE-Report, ISSN 1654-1081 ; 2012:24
Keyword [en]
Electrochromic, Electrooptics, Smart windows, Prediction model, Large Area Device model
National Category
Chemical Engineering
URN: urn:nbn:se:kth:diva-95167ISBN: 978-91-7501-356-5OAI: diva2:526802
2012-06-08, Sal K2, Teknikringen 28, entreplan, KTH, Stockholm, 14:00 (English)
Formas, C62318
Available from: 2012-05-22 Created: 2012-05-15 Last updated: 2012-05-22Bibliographically approved
List of papers
1. Methodology for measuring current distribution effects in electrochromic smart windows
Open this publication in new window or tab >>Methodology for measuring current distribution effects in electrochromic smart windows
2011 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, no 29, 5639-5646 p.Article in journal (Refereed) Published
Abstract [en]

Electrochromic (EC) devices for use as smart windows have a large energy-saving potential when used in the construction and transport industries. When upscaling EC devices to window size, a well-known challenge is to design the EC device with a rapid and uniform switching between colored (charged) and bleached (discharged) states. A well-defined current distribution model, validated with experimental data, is a suitable tool for optimizing the electrical system design for rapid and uniform switching. This paper introduces a methodology, based on camera vision, for experimentally validating EC current distribution models. The key is the methodology's capability to both measure and simulate current distribution effects as transmittance distribution. This paper also includes simple models for coloring (charging) and bleaching (discharging), taking into account secondary current distribution with charge transfer resistance and ohmic effects. Some window-size model predictions are included to show the potential for using a validated EC current distribution model as a design tool.

Bleaching, Charge transfer, Cleaning, Design, Electrochromic devices, Electrochromism, Systems analysis
National Category
Atom and Molecular Physics and Optics
urn:nbn:se:kth:diva-47978 (URN)10.1364/AO.50.005639 (DOI)000296066600005 ()2-s2.0-80053918306 (ScopusID)
Swedish Research CouncilStandUp

QC 20150716

Available from: 2011-11-17 Created: 2011-11-15 Last updated: 2015-07-16Bibliographically approved
2. Predicting Performance of Large Area Electrochromic Smart Windows
Open this publication in new window or tab >>Predicting Performance of Large Area Electrochromic Smart Windows
(English)Article in journal (Other academic) Submitted
National Category
Atom and Molecular Physics and Optics
urn:nbn:se:kth:diva-95309 (URN)
QS 2012Available from: 2012-05-22 Created: 2012-05-22 Last updated: 2012-05-22Bibliographically approved

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