Advanced Control of Electrochromic Windows
In our research we use the technology of electrochromic (EC) glazing to maximize the use of daylight and minimize the energy consumption in buildings while preserving visual and thermal comfort of the users. We propose an advanced automatic control of EC windows coupled with an anidolic daylighting system (ADS), blinds and dimmable fluorescent lights. EC windows with a visible transmittance range (Tv) of 0.15 – 0.50 were installed on the southern façade of an office room of the LESO experimental building (EPFL campus in Lausanne, Switzerland). The system is divided in two independent zones: The lower zone is equipped with EC windows and blinds while the upper zone features in addition the ADS, which facilitates the even distribution of daylight across the room. Electric lighting is used only complementary when daylight is not sufficient. Data regarding instantaneous weather conditions, room conditions, as well as user wishes is collected and recorded in the database of the building's central management system (KNX/EIB). To address visual comfort requirements, a novel sky-scanner approach is implemented into a predictive control strategy to take into account the time the EC glazing requires to switch between different transmission states (up to 15 minutes). For the thermal comfort, we consider a wider time horizon, taking under consideration also the time, day and season. User has always the possibility of manually overriding the automatic control system. Adaptive fuzzy logic algorithms are implemented allowing the system to learn from users' wishes. Simulations showed that the elaborated algorithms for the automatic control of EC windows can provide better thermal and visual comfort conditions when compared to standard glazing coupled with blinds and still exhibit acceptable levels of energy consumption for space heating and electric lighting. Field study results showed that workplane illuminances were mostly kept inside acceptable visual comfort levels (at around 450-1000 lx). Field survey results regarding the acceptance of the system by the users are also presented along with a discussion on the efficacy of an EC windows system to handle glare issues without the use of blinds.