Abstract
Algorithmic optimization of visual comfort and view out in office buildings
Sandra Mende, Karlsruher Institut für Technologie
Being in a high position on the agenda for all European countries, climate protection, sustainability and energy efficiency are just three of the major keywords dominating international politics. In the Kyoto Protocol, industrialized countries agreed to reduce their collective greenhouse gas emissions by 5.2 % below the level of 1990 by 2012. Many countries are still looking for ways to achieve the ambitious objectives. Increasing costs and finite natural energy resources show the dependence of imported energy resources and the need for alternatives.High percentage of primary energy consumption is used for heating, cooling and lighting. For example, more than 104 million tons of coal equivalent (VDEW 2003) are required for room heating supply in Germany every year, which amounts to 32.8 % of the annual energy consumption. This fact illustrates the influence of the construction sector (i.e., the quality of buildings and their technical equipment).
Prototype buildings have achieved up to 94 % energy savings compared to the US market average, and 83 % compared to the most efficient buildings on the market (Cunningham and Saigo, 1992). In addition to an infrastructural optimization of a building, the utilization of natural and human design conditions, for example topography, surrounding build environment or optimal usage of daylight, affects the energy consumption of a building significantly.
According to the IESNA Lighting Handbook (Rea, 2000, p. 26-1), 20–25 % of all electricity in US buildings, or 5 % of the national energy consumption, is used for lighting. The heat generated in this way represents between 15–20 % of a building’s cooling load. Additionally, façades adjust the daylight distribution in the building by controlling solar gains. Thus, innovative control algorithms for shading systems could represent the key to decrease the lighting and cooling energy use. Therefore, it is necessary to develop control algorithms that minimize the use of energy for lighting according to the light distribution actually needed.
The handbook mentioned above quotes field studies (Rea, 1984a) according to which 40 % of energy savings can be achieved by means of elementary control systems such as predictable scheduling where lighting elements are connected to timers. Moreover, unpredictable scheduling (i.e., relying on occupancy sensors) has achieved up to 60 % savings of lighting energy in some areas, or even up to 80 % in extreme cases (Rubinstein et al., 1984). In addition, simulations of Bourgeois (Bourgeois et al. 2006) show that occupants using daylight in an active way can reduce the total primary energy consumption by more than 40 %.
Nevertheless, the implementation of the results of these studies in new controllers usually fails due to users rejecting automatic control algorithms that do not allow for individual regulation of sun and glare protection. According to Reinhart (2004), users in general adjust shading devices in a way that they are just not glared while having best available view out at the same time. In summer, however, this behavior leads for example to the phenomenon that shading systems are merely lowered down to eye level. Thus, solar gains and the cooling loads increase. This indicates once again that the saving potentials by user-friendly control systems are high. Furthermore, individual preferences interfere with the definition of control algorithms that are both energy-efficient and acceptable by user. Analogously to Fanger’s quantification of thermal comfort (Fanger 1970) with acceptance limits of 90-95 % satisfied and only 5-10 % dissatisfied users, similar values for visual comfort are expected. However, current lighting strategies, as for example investigated in the US, reach visual comfort rating limits of about 70 % of the users, implying that today’s strategies typically dissatisfy the remaining about 30 % (Lindelöf 2007).
Motivated by the elucidations above, the objective of this thesis comprises the development of new rating metrics including acceptance limits of users and energy-saving control algorithms, their implementation into commercial controllers as well as their testing under real conditions. Only if a high user acceptance is met, energy-saving controls of shading devices really can effect their purpose.
HYPOTHESES AND METHODOLOGY
Although the psychological relevance of the topic view out and visual contact has been examined several times, a quantification method of this factor, i.e. a definition of limit values like how much view out has to be ensured or an investigation of the interaction with other interference factors and their influence is missing so far.
Therefore the first hypothesis of this work is the connection of the variable “view out” with visual comfort as a subjective evaluation of user assessments in office space through empirical proof. This will analyze the relevance of the decisive acceptance parameters also on a perception-psychological level. A goal is to obtain new results supplying characteristics for further investigations, integrated into standard regulations and/or planning processes. In addition, the user assessments are to be accomplished in two identical test rooms on the roof of the Fraunhofer Institute for Solar Energy Systems (ISE) in Freiburg, which are variably adjustable for the position of the sun. Therefore the test rooms can be rotated according to get similar solar angles and two different view possibilities (view of a neighboring wall on the roof and a versatile, green, urban environment) in the morning and afternoon.
In a second part, the gained knowledge and results become a basis for the second hypothesis - the development of an index, rating visual comfort and/or the view out with consideration of the maximum satisfaction possible for users.
In the third part, the implementation of past scientifically validated indices will be the foundation for the optimization of control algorithms for sun and glare protection devices. They will be merged in new control algorithms and/or controllers. So the control algorithms used in commercial controllers are extended by new user-oriented functions. By imbedding the controllers into existing offices at the Fraunhofer ISE in Freiburg in the context of the verification of the third hypothesis - a higher acceptance by users within optimized energy savings - user studies with coworkers of the ISE are accomplished in their test offices. Additionally energetic simulations shall state the dimension of gained saving potentials.
