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Thermal emissivity of coated glazing - simulation versus measurements
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.
2005 (English)In: Optical materials (Amsterdam), ISSN 0925-3467, Vol. 27, no 4, 705-712 p.Article in journal (Refereed) Published
Abstract [en]

A large variety of coated glazing products are available on the market today. These are used in energy efficient low emissivity (low-e) or solar control windows. Not only the solar optical properties, but also the thermal emissivity of these coated glazing materials are of importance for the performance of such energy efficient windows. The thermal emissivity is calculated from the IR reflectance. A problem is that for accurate determination of the emissivity according to international standards, the reflectance needs to be known between 2000 and 200 cm−1, and many FTIR spectrophotometers cannot measure below 400 cm−1. In this paper some different strategies for the extrapolation to 200 cm−1 are discussed. A sensitivity analysis for different types of materials is presented for a few different extrapolation algorithms. The simplest extrapolation procedure assumes a constant reflectance value throughout the extrapolation interval. This appears to work well for surfaces with high reflectance values. A procedure based on a linear relation between the values at a starting wavelength and at the end point of the extrapolation interval or one using a simple second-degree polynomial function can be used when coatings on glass having medium or low reflectance values are evaluated. A guide on how to extrapolate the spectra, according to the different strategies, is included in the Appendix.

Place, publisher, year, edition, pages
2005. Vol. 27, no 4, 705-712 p.
National Category
Natural Sciences
URN: urn:nbn:se:uu:diva-91555DOI: 10.1016/j.optmat.2004.09.007OAI: oai:DiVA.org:uu-91555DiVA: diva2:164327
Available from: 2004-04-14 Created: 2004-04-14 Last updated: 2014-01-28Bibliographically approved
In thesis
1. Preparation and Characterization of Sputter Deposited Spectrally Selective Solar Absorbers
Open this publication in new window or tab >>Preparation and Characterization of Sputter Deposited Spectrally Selective Solar Absorbers
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The optical efficiency of a commercially available sputter deposited spectrally selective solar absorber was improved. The main purposes were to decrease the thermal emittance, increase the solar absorbtance of the absorber and to protect the substrate from degradation due to environmental influence. The adhesion properties between the corrosion-protecting barrier and the substrate were also studied. This project was focused on process improvements that are realistic to implement in industrial production.

The thermal emittance of the absorber was decreased from 0.12 to 0.06 by changing the material of the corrosion-protecting layer from nickel-chromium to copper-nickel. Copper-nickel was less sensitive to variations in the sputter parameters than nickel-chromium. A novel method that could simplify the search for alternative corrosion resistant materials with a low thermal emittance has been purposed. Since resistivity data usually exist or can easily be measured and infrared measurements require more sophisticated measurements, the Hagen-Rubens relation was investigated for copper-nickel and nickel-chromium alloys. The dc-resistivity was found to be related to the infrared emittance or the integrated thermal emittance for alloys in their solid soluble fcc phase.

The solar absorbtance was increased when a graded index absorbing coating was tailored for a crossover of the reflectance from low to high reflectance at about 2.5 µm. The solar absorber graded index coating was optimized for nickel metal content in nickel oxide and a solar absorptance of 0.89-0.91 was achieved. The solar absorptance was further increased to 0.97 when an antireflection coating was added on top of the absorbing layer.

Finally, extrapolation algorithms were developed to assure correct determination of the thermal emittance for coatings on glass since modern spectrometers that do not cover the complete wavelength interval required to calculate the thermal emittance of surfaces at room temperatures accurately. The error arising from the extrapolation algorithms were smaller than the noise from the optical measurements. Similar strategies can be used for other surfaces.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2004. 71 p.
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 958
Engineering physics, spectrally selective solar absorber, thermal emittance, solar absorptance, sputter deposition, infrared reflectance, Teknisk fysik
National Category
Other Engineering and Technologies
urn:nbn:se:uu:diva-4145 (URN)91-554-5924-2 (ISBN)
Public defence
2004-05-07, Häggsalen, Ångströmlaboratoriet, Box 534 / Lägerhyddsvägen 1, Uppsala, 13:00
Available from: 2004-04-14 Created: 2004-04-14Bibliographically approved

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