Performance evaluation of electrochromic windows on a sample of office building in Istanbul

Searching for solutions for the reduction of energy consumption, depending on the depletion of energy resources, has become a major issue in our days. In this era with problems like global warming and climate changes, energy conservation has become one of the most important subjects. Nowadays, 93 % of the energy that we use is obtained from nonrenewable sources. Therefore, energy efficient design is one of the most important responsibilities in the building design process. For this issue, energy conservation in buildings is gaining priority and designing to reduce energy consumption becomes of importance. Energy flows in buildings occur in different ways. The highest energy flow occurs through windows which are transparent elements of the building envelope. Due to this, windows play an important role in the energy consumption of buildings which must be considered in their design stage. Window systems are the most important components of building façades. They are indispensable components because of their functional and esthetical properties. Windows have to fulfill many requirements in the building system. They should have the required properties to cover physical, energy and occupancy needs. Today, especially with high transparency preference in high-rise office buildings, significant research is being done to improve the performance of window systems, which are the elements with the most energy loss, and new technologies are observed in the architectural field. With the increasing importance of the developing technology and sustainability issues, it has become increasingly important to design energy efficient buildings in harmony with the environment of the building envelope. The anticipation of façade systems that adapt to the surroundings has given rise to the development of "innovative window systems" that can actively work in harmony with external conditions. For this reason, it is expected that window systems will act as an energy efficient mechanical system that can adapt to the external conditions of the building. In recent years, many studies about window technologies were carried out which aim to reduce the energy consumption of windows while providing the required functions. With window systems' basic functions like daylighting, providing view and natural ventilation, providing thermal comfort, solar control, sound control and glare control safety, maintenance and aesthetical, economical and sustainable needs should be taken into consideration in the designing of efficient windows. 'High Performance Window System Technology' has been improved considering all these parameters. On the purpose of improving the energy performance of window systems, by using tinted, reflective and low emissivity (Low-E) or spectral selective low-emissivity (SS Low-E) coated glasses, filling the spaces between glasses with low thermal conductive gasses like argon and krypton, multi layered 'insulating glazing units'(IGU) have been developed. Although tinted windows reduce cooling energy of buildings in summer, they cause an increase in heating energy winter months and also a decrease in outdoor views and increase in energy usage due to artificial lighting because of lower daylight transmittance values. The spectral-selective film-coated glass technology (SS Low-E), which reflects the invisible spectrum of sunlight and allows the visible spectrum to enter the interior, can meet the performance requirements for solar control, thermal insulation and natural lighting at the same time. Spectral selective low-emission glasses (SS Low-E) are the second step in Low-E glasses which regulate the daylight level of the interior. These technologies can not react to sun and cloud changes during the day, and they cannot meet the system expectation of adapting to the environment. However, the innovations in window systems are capable of providing energy efficiency by adapting to environmental conditions without sacrificing visual connection. The last point reached in innovative window technology is the development of dynamic window systems that can respond to sun and cloud conditions by changing their optical properties with the changes in sun and cloud conditions. The major advancement in smart window technologies that show dynamic properties is "electrochromic (EC) window technologies", which are already widespread in the US and the European countries and is aimed to have more widespread use in the future. Electrochromic (EC) windows promise to be the next major advance in emerging, energy-efficient window technologies because of their capability to change state from a clear to a colored tint without loss of view. This technology provides an opportunity to improve and optimize both the energy efficiency and comfort aspects of a building through dynamic control and integration with automated lighting controls designed to respond to daylight. Although EC windows can provide considerable energy savings and relatively stable daylight levels, they cannot block direct sunlight, which may result in unwanted glare and reduced computer display visibility in office environments. Since the mid 90's, there are research and simulation studies on electrochromic window systems conducted by LBNL (Lawrence Berkeley National Laboratories). These systems, which have proven their performance but have not been implemented due to high costs, have started to be produced and applied within the last 10 years. However, despite all these developments, there are not any applications or conducted studies about electrochromic window systems in our country, and there are not enough Turkish resources in the literature. In this study, the physical properties of electrochromic window systems and the control strategies will be explained together with innovative window technologies and the energy performance of the electrochromic windows will be evaluated in comparison with traditional windows in a simulation study on a sample office building in Istanbul. This thesis examines the performance parameters expected from innovative windows and the steps involved in describing the properties of these systems, examining the properties of the EC windows in detail and introducing control strategies, explaining evaluation criteria with sample building specifications, and the results of the simulations. Within the scope of this thesis, the evaluation of the energy performance of electrochromic windows is performed comparatively with the different window systems in the context of Istanbul climatic conditions. A reference building for energy performance assessment was designed and modeled in the Design Builder program which is an Energy Plus-based software tool developed to measure and control the performance of building designs according to the issues of energy, carbon, lighting and comfort. In the computer model, necessary parameters related to environment, building structure and users are defined according to ASHRAE and TS-825 standards. For the study, a square shaped and south oriented reference office building has been designed and a simulation for a south oriented middle floor office unit has been studied. In order to compare the energy performances of electrochromic windows and traditional windows, four types of window systems as uncoated glass, Low-E, SS low-E and electrochromic windows were modeled, and three different control strategies were modeled for electrochromic windows. The building was modeled with %40 and %60 window-to-wall ratios separately to compare the effect of window-to-wall ratio. Simulations were performed for each window type and heating, cooling and lighting loads were calculated for each option. Simulation results are evaluated on a daily and yearly basis. For the daily evaluations, 21 July, the hottest day of the year, and 21 January, the coldest day of the year, were taken as the basis. The daily assessments were designed to understand how the windows fit into the sun and cloud movements and to determine the accuracy of the simulation tool; yearly evaluations gain importance in determining the performance of windows. The evaluation of the data obtained as a result of the simulation study was made by comparing the window performances with the performance of the most commonly used uncoated double glazing system. First of all, the way window types affect the energy loads has been observed. It was determined that SS Low and EC window systems affect the heating and lighting loads adversely while the Low-E windows do not affect the heating and lighting loads, while the Low-E, SS Low-E and EC window types all have a positive effect on the cooling load. When we observe the effects of the EC windows control strategies, the lighting control strategy (light load ≥ 0 W/m²) and the solar light intensity control strategies (solar radiation ≥ 200 W/m²) have a positive effect on the cooling loads. The lighting level control strategy (brightness level ≥ 500 lux), which is supposed to reduce the lighting loads, has not affected the lighting loads but has affected the heating loads in the negative direction. Cooling load control strategy (cooling load ≥ 0,1 W/m²) negatively affects lighting loads while not affecting heating loads. Solar radiation intensity control strategies (solar radiation ≥ 200 W/m²) affected heating and lighting loads negatively. As a result of the evaluations, the window system providing the best energy performance due to the reduction of the total energy consumption per year compared to the uncoated window for Istanbul has been the SS Low-E window system with 60% transparency. The SS Low-E window system reduces annual cooling loads by 32% and saves 18% on a yearly basis. The EC windows, which are expected to exhibit higher energy performance, have not been able to outperform the SS Low-E. The EC window system, which is controlled only by the lighting control strategy (brightness level ≥ 500 lux), has almost the same performance as the SS Low-E window system. As a result of these studies, it can be said that the EC windows will not solve the glare problem and as a result of the other studies done so far, the use of EC systems which are more expensive system with foreign production instead of the SS Low-E window systems which are already widely used by the domestic companies in Istanbul climate will be beneficial. Instead, the choice of SS Low-E systems used in conjunction with solar shredders may result in more positive results in terms of cost and performance. This thesis will be shaped as follows: In the second chapter, innovative window types and working principles are explained. Then the expectations of energy and comfort performance expected from the innovative windows are explained. In the third chapter, definition, working principle and physical properties of electrochromic windows are explained and control strategies are introduced. Furthermore, the section contains examples of exercises and practices related to EC windows. In the fourth chapter, information about the simulation program to be used will be given first. The location of the sample building, climate characteristics, user information and structural features will be explained. Finally, the evaluation criteria will be determined in the fifth chapter, the data obtained as a result of the simulation study will be explained with graphs and discussed under the determined evaluation criteria.