External Water Condensation and Angular Solar Absorptance : Theoretical Analysis and Practical Experience of Modern Windows

• Main Author: Werner, Anna
• Format: Doctoral Thesis
• Language: English
• Published: Uppsala universitet, Institutionen för teknikvetenskaper 2007
• Subjects: Engineering physics; Windows; External condensation; Radiative cooling; Optical properties; Coated glass; Radiant cooling; Teknisk fysik
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-7744; http://nbn-resolving.de/urn:isbn:978-91-554-6830-9

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.