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In this paper a simulation tool for simulating and comparing windows have been further developed so that the software also can simulate smart windows with the ability to vary the g-value or the solar heat gain coefficient. The g-value can be controlled using different control strategies, which can be based on time control, user control and different types of daylight control. The software is basically a simulation tool to calculate the energy for heating and cooling caused by the windows as a building component. Due to the simplicity of the program, it is suitable as a tool for selecting the right type of window for a certain building. Six different control strategies have been developed to show different approaches for controlling smart windows. Some results are shown as examples of how the new functionality is working. This new functionality of the software makes it easy to compare smart windows between themselves and also to make fair comparisons with static windows.

Several studies have shown that the use of switchable windows could lower the energy consumption of buildings. Since the main function of windows is to provide daylight and visual contact with the external world, high visible transmittance is needed. From an energy perspective it is always best to have the windows in their low-transparent state whenever there are cooling needs, but this is generally not preferable from a daylight and visual contact point of view. Therefore a control system, which can be based on user presence, is needed in connection with switchable windows. In this study the heating and cooling needs of the building, using different control mechanisms were evaluated. This was done for different locations and for different combinations of switchable windows, using electrochromic glazing in combination with either low-e or solar control glazing. Four control mechanisms were investigated; one that only optimizes the window to lower the need for heating and cooling, one that assumes that the office is in use during the daytime, one based on user presence and one limiting the perpendicular component of the incident solar irradiation to avoid glare and too strong daylight. The control mechanisms were compared using computer simulations. A simplified approach based on the balance temperature concept was used instead of performing complete building simulations. The results show that an occupancy-based control system is clearly beneficial and also that the best way to combine the panes in the switchable window differs depending on the balance temperature of the building and on the climate. It is also shown that it can be beneficial to have different window combinations for different orientations.

The aim of this project was to investigate how the visual appearance and energy performance of switchable or smart windows can be improved by using antireflective coatings. For this study clear float glass, low-e glass and electrochromic glass were treated with antireflection (AR) coatings. Such a coating considerably increases the transmittance of solar radiation in general and the visible transmittance in particular. For switchable glazing based on absorptive electrochromic layers in their dark state it is necessary to use a low-emissivity coating on the inner pane of a double glazed window in order to reject the absorbed heat. In principle all surfaces can be coated with AR coatings, and it was shown that a thin AR coating on the low-e surface neither influences the thermal emissivity nor the U-value of the glazing. The study showed that the use of AR coatings in switchable glazing significantly increases the light transmittance in the transparent state. It is believed that this is important for a high level of user acceptance of such windows.

High visible transmittance values are interesting for windows in general and for the bleached state of smart windows in particular. For smart windows it is always possible to darken them and therefore the transparency of the bleached state can never become too high. One way of achieving a higher transmittance could be the use of antireflective coatings on the surfaces of the smart window. In this project the use of dip coating for putting antireflective coatings on window surfaces has been studied. The effect on transmittance and surface light scattering has been investigated and the results show that antireflective coatings on windows can have a positive impact on both.

Fritted glass is commonly used as a light diffusing element in modern buildings. Traditionally it has been used for aesthetic purposes but it can also be used for energy savings by incorporating it in novel daylighting systems? To answer such questions the light scattering properties must be properly characterized.

This paper contains measurements of different varieties of fritted glass, ranging from the simplest direct-hemispherical measurements to angle-resolved goniometer measurements. Modeling the light scattering to obtain the full bidirectional scattering distribution function (BSDF) extends the measured data, making it useful in simulation programs such as Window 6 and Radiance. Surface profilometry results and SEM micrographs are included to demonstrate the surface properties of the samples studied.

Light scattering materials are frequently used in solar energy applications, for instance as cover glass in solar thermal absorbers or to increase the path length of photons in solar cells. Knowing the transmittance of such materials is essential to modeling, designing or characterizing a system with these materials as components. The transmittance is traditionally obtained using an integrating sphere spectrophotometer. However, it is known that most commercial spectrophotometers might underestimate the true transmittance of surface scattering samples. Some of the scattered light might hit the edge and escape out of the sample. Thereby the transmitted light exits the sample in such a fashion, that it is not collected by the integrating sphere. The detected signal from the light entering the sphere then underestimates the real transmittance or reflectance of the sample. In this paper this side shift and edge losses of surface scattering samples have been studied and the results show that this might have a significant impact on measured values. Several different techniques have been used to quantify the influence on measurements.