New Model for Smart Windows with Movable Plane Mirror-Arrays as a Basis for Energy Minimizing Control
Abstract
The energy demand of buildings maintains one of the highest shares of the primary energy demand in Germany. It is used mainly for heating, cooling and for lighting. Controllable windows with solar-redirecting mirror systems can greatly influence the solar energy flows and distribution to the inside. The development of Micro-Mirror-Arrays (Viereck, 2011) within smart windows as such a device inspired this work by providing various possibilities to controllable windows, e.g. separate angular settings of different areas within the window, variable orientation of the mirror structures relative to the window and variable structure geometry. The control of smart windows meets different situations resulting in different set points. In high temperature conditions solar heat sources lead to higher cooling loads of a building resulting in a higher energy demand, and vice versa for cold temperatures. The need to illuminate a room and to provide a glare shield and a good view outside is related to the presence of people (Fig. 1). The functionality of the window is strongly linked to the changing outside conditions like sky radiance distribution and temperature. These examples show the high necessity of an automatic controlled window in terms of energy minimisation. A key part of developing an energy minimizing control strategy is having a valid model of the mirror structures as solar-redirecting system within the window. Some requirements to such a model are as follows: it should enable an integral approach evaluating solar heat sources and daylight distribution. The integral algorithm should make it possible to examine the system control. The use of an adapted programme basis, which makes control analysis possible, is preferable. Even for whole year runs the simulation times should be manageable. It is beneficial to have a limited number of input parameters.