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Simulations of coatings to avoid external condensation on low U-value windows
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Physics.
2008 (English)In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 30, no 6, 968-978 p.Article in journal (Refereed) Published
Abstract [en]

Well-insulated windows, windows with a low U-value, become more and more common. On well-insulated windows, in contrast to on traditional, poorly insulated windows, dew easily forms on the outer side of the outer pane. This external water condensation usually happens during clear and humid nights with no or little wind. It sometimes remains till the morning and obstructs the view to the outside for the house occupants. The characteristics of the outer surface of the window affects the annual number of hours with condensation and how good the visibility is through the water layer. The spectra of two commercial glass pane coatings which have proved to have a dampening effect on how much the view through the window is obstructed by external water condensation were simulated; a low-emissivity coating and a self-cleaning coating. Optical constants were used as input. Furthermore, a new glazing was simulated with a layer combination which consists of both a low-emissivity coating and a self-cleaning coating. The simulations gave spectra similar to measured ones on real coated glass samples of the three kinds. When designing the window, it should be optimized so that the visual transmittance is high, the thermal transmittance low and the occurrence of external water condensation rare. In this article, after a discussion on different window functionalities, it is suggested that 50-100 nm of the low-emissivity coating and 10 nm of the self-cleaning coating would give a surface emissivity of 0.3-0.5. If used as the external surface of a well-insulated window this would substantially decrease how often the view through the window is obstructed by external water condensation. Simulations were performed on two well-insulated windows with and without this external surface. The effects of the surface on the light transmittance, U-value and the total solar energy transmittance, the g-value, are discussed here.

Place, publisher, year, edition, pages
2008. Vol. 30, no 6, 968-978 p.
Keyword [en]
External water condensation, Hydrophilic glazing, Low-e glazing, Radiant cooling, Radiative cooling, Thin film coatings
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-95595DOI: 10.1016/j.optmat.2007.05.030ISI: 000253612500026OAI: oai:DiVA.org:uu-95595DiVA: diva2:169878
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2016-04-13Bibliographically approved
In thesis
1. External Water Condensation and Angular Solar Absorptance: Theoretical Analysis and Practical Experience of Modern Windows
Open this publication in new window or tab >>External Water Condensation and Angular Solar Absorptance: Theoretical Analysis and Practical Experience of Modern Windows
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Part I of this thesis is a theoretical background to parts II and III.

Part II treats the phenomenon of decreased visibility through a glazing due to external water condensation, dew, on the external surface. Some simulations are presented where it is shown that under certain circumstances condensation can be expected. A combination of coatings on the external surface is suggested to overcome the problem of external condesation. It consists of both a coating which decreases the emissivity of the surface and a hydrophilic coating which reduces the detrimental effects to the view through the window.

Fresnel calculations of the optical properties are used to discuss the feasibility of using different coatings. A new test box was used to verify that the proposed window coatings perform as expected.

Part III is a study on the angular dependence of solar absorptance in windows. Optical properties vary with the angle of incidence of the incoming light. The variation is different from one window pane to another.

A model is proposed to approximate the angular variation of the solar absorptance in window panes. The model is semi-empirical and involves dividing the wide range of windows into nine groups. To which group a window belongs, depends on how many panes it has and on the features of the outer pane. The strength of the model is that it can be used without knowing the exact optical properties of each pane of the window. This makes it useful in the many cases when these data are not given by the manufacturer and Fresnel calculations to get the optical properties of the window are not feasible. The model is simple and can be added as an appendix to existing standards for measuring optical properties of windows.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 132 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 283
Keyword
Engineering physics, Windows, External condensation, Radiative cooling, Optical properties, Coated glass, External condensation, Radiant cooling, Teknisk fysik
Identifiers
urn:nbn:se:uu:diva-7744 (URN)978-91-554-6830-9 (ISBN)
Public defence
2007-04-13, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15
Opponent
Supervisors
Available from: 2007-03-23 Created: 2007-03-23 Last updated: 2011-03-23Bibliographically approved

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