Electrochromic properties of WO 3

Tungsten oxide (WO3) thin films with various thicknesses of approximately 36, 72, 108, and 180 nm were prepared using radio frequency sputtering method. Film thickness can be controlled at nanoscale. In addition, X‐ray diffraction, scanning electron microscopy, and Fourier transform infrared spectroscopy were utilized for investigating morphologies and microstructures of as‐prepared WO3 thin films. Moreover, optical properties of the WO3 nanofilms were characterized using ultraviolet‐visible‐near infrared spectroscopy. Transmittance of WO3 films changed during the electrochemical cycles. WO3 films with various thicknesses give various transmittance modulation between colored and bleached states. WO3 films with a thickness of approximately 108 nm had the largest transmittance modulation among various film thicknesses, about 66% measured at 550 nm. Results showed that the value of transmittance of colored samples decreased with increasing film thickness. However, transmittance of bleached samples was not influenced significantly by their thickness.publishedVersio

Operating hardware impact on the heat transfer properties of windows

Despite significant advancements in fenestration technology in the last two decades, the thermal transmittance of fenestration products is still significantly higher than that of walls. This corresponds to 60% of the total energy loss of a modern building envelope through the windows. Hence, further development and improvements of fenestration products are necessary. Increasingly stringent codes and standards for fenestration stimulate industry to work on improved solutions. Thus, it is crucial that assessment techniques are able to account for innovations accurately. The thermal effects of non-continuous hardware in window frames are currently ignored by international rating procedures. A preliminary investigation conducted by our team showed significant performance degradation in two of the three out-opening casement profiles caused by the presence of operating hardware. Frames with the structure made of vinyl and fiberglass consist of many air cavities that are penetrated by operating hardware made of highly conductive materials. In these frames, in order to have an accurate assessment, it may be required to employ three-dimensional modeling due to the convective nature of heat transfer within the cavities. However, in this study, we demonstrate that the three-dimensional (3D) effects of non-continuous hardware can be approximated accurately with simpler two-dimensional (2D) simulations. We then develop a simplified model based on weighted average capable of replacing the time-and computation-intensive 3D simulations with 2D simulations and validate it against market available frames and their corresponding hardware. Validation results show that our approximation technique results in discrepancies lower than 0.05 W/(m2K), or 3% of the total thermal transmittance. Thus, we conclude that simplified 2D simulation models may be used for predicting hardware impact in window frames with reasonable accuracy. As windows and glazing structures are becoming ever better thermally insulated, it is becoming even more important to be able to model the impact of the operating hardware on the total thermal performance in order to design the best windows possible and not let the operating hardware ruin an otherwise well-proven design, which is hence addressed in this study

Comparison of the energy saving potential of adaptive and controllable smart windows: A state-of-the-art review and simulation studies of thermochromic, photochromic and electrochromic technologies

Windows play a huge role in today's buildings, allowing for outside view and providing occupants with daylight. However, windows are also often considered to be one of the weakest building components with respect to high thermal losses and are in addition often the reason for overheating and glare issues. In comparison to traditional static windows, dynamic solutions like adaptive and controllable smart windows have the ability to adjust their optical properties in response to changing boundary conditions and hence have the potential to improve the energy performance and the user comfort of buildings. The objective of this work is twofold: (1) To collect and present the state-of-the-art of commercially available smart windows from manufacturers, both adaptive and controllable products, i.e. thermochromic, photochromic and electrochromic smart windows. This collection provides the reader with valuable information about window properties such as the U-value, g-value, solar transmittance (Tsol) and visible solar transmittance (Tvis). However, it is currently difficult to obtain all the desired information about the products from the manufacturers' websites and other open channels. (2) To conduct building energy performance simulations on selected products from each technology. These products are also simulated using the same U-values as the reference window, and in addition, two theoretical cases have been simulated to investigate the theoretical potential of different smart windows. Here, the optical parameters take on fictitious values between 10 and 90% and between 0 and 100% transmittance, respectively. All cases are simulated at three different locations, i.e. Trondheim (Norway), Madrid (Spain) and Nairobi (Kenya), and are compared to a reference static window. In total, 63 cases are simulated using the simulation software package IDA Indoor Climate and Energy (IDA ICE). The results shows that the electrochromic window controlled by operative temperature has the highest potential in lowering the energy demand for all cases and locations. The study also highlights the importance of having the right control strategy and control levels for each specific case

A dataset of wind-driven rain measurements on a low-rise test building in Norway

Semi-empirical models and especially numerical simulation models based on Computational Fluid Dynamics (CFD) are increasingly being used to calculate wind-driven rain (WDR) on building facades. The development, verification and validation of these models require accurate and complete WDR measurement datasets. Although many WDR measurement campaigns have been conducted in the past, few reports of these contain enough information for model development and model validation. This paper presents a complete dataset of WDR measurements for a low-rise test building in Trondheim, Norway. It contains a detailed description of the building, its surroundings and the meteorological station, as well as WDR measurements in free-field conditions and on the building facades, measurements of wind speed, wind direction, horizontal rainfall intensity, temperature, relative humidity and error estimates for the WDR measurements. The paper also provides the link to a website from which the full set of data can be downloade

Open Packing for Facade-Layout Synthesis Under a General Purpose Solver

International audienceFacade-layout synthesis occurs when renovating buildings to improve their thermal insulation and reduce the impact of heating on the environment. This interesting problem involves to cover a facade with a set of disjoint and configurable insulating panels. Therefore, it can be seen as a constrained rectangle packing problem, but for which the number of rectangles to be used and their size are not known a priori. This paper proposes an efficient way of solving this problem using constraint programming. The model is based on an open variant of the DiffN global constraint in order to deal with an unfixed number of rectangles, as well as a simple but efficient search procedure to solve this problem. An empirical evaluation shows the practical impact of every choice in the design of our model. A prototype implemented in the general purpose solver Choco is intended to assist architect decision-making in the context of building thermal retrofit