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Article Excerpt
Abstract: Energy efficient design strategies should be finalised in the early stages of the building design process. Running costs can be reduced and the occupants' comfort and therefore productivity can increase. Evaluations of different facade systems should be carried out during the design stage in terms of energy demand in order to optimize the project. These evaluations need building simulations predicting the energy consumption. The present work covers a proposed approach to design the facade system and a case study to give an example of application, which is carried out by DAYSIM simulations. Such an approach would enable the design of an optimum facade system providing the visual comfort conditions and reducing electric energy consumption.
Keywords: Daylight simulations, Electricity, Energy consumption, Facade design, Lighting energy efficiency, Visual comfort
Introduction
Efficient use of energy sources is the most important subject in building design. Various aspects are affected including the reduction of C[O.sub.2] emissions and decreasing high-energy costs. It is estimated that between 2008 and 2012, greenhouse gas emissions will increase 20% of the 1990 levels in IEA Countries (Lebot & Nilsson, 2000). Energy efficient lighting requires facades that can control solar gain and glare while enhancing daylight. Glare-free daylight should be enhanced inside the spaces, so that the daylight availability increases. The innovative daylighting systems on the facade can provide this enhancement. When electric lighting and shading elements are controlled by daylight-responsive control systems, the electric lighting consumption is decreased, electric costs are reduced and so efficient lighting can be achieved.
Energy efficiency and sustainability are concepts that can be applied to the overall design of buildings. Design strategies related to energy efficiency should be decided in the early stages of the design process. efficient lighting concepts reduce energy consumption while providing a comfortable working environment. In order to optimize the project, evaluations of lighting system alternatives, including the control systems, should be carried out during the design stage in terms of the energy demand. These evaluations need precise simulations predicting the energy consumption of the building. The present work covers a proposed approach to design an energy efficient lighting system and a case study to give an example of application.
Energy Efficient Lighting Approach for Offices
Minimizing the lighting energy consumption in office spaces while providing the visual comfort conditions is very important in terms of reducing the total energy demand of office buildings. The main principles of office lighting, which should be provided in order to achieve the visual comfort conditions, are given in several standards and guidelines. In offices, the workplane illuminance should be satisfactory, the glare should be well controlled and the brightness of the room surfaces should be acceptable (Simons & Bean, 2001). The International Commission on Illumination (CIE) Lighting of Indoor Work Places Standard (2001) declares lighting design criteria on office lighting like luminance distribution, illuminance and glare. The luminances of all surfaces are important and determined by the reflectance of the surfaces. The ranges of useful reflectances for the major interior surfaces are 60%-90% for ceiling, 30%-80% for wall, 20%-60% for workplane and 10%-50% for floor. For office spaces where writing, typing, reading and data processing take place, 500 lux is the maintained illuminance on the reference surface for the task. The glare rating of the lighting installation that causes discomfort is determined by the CIE Unified Glare Rating (UGR) method and the UGR value of the lighting installation shall not exceed the value of 19 based on the UGR scale for office spaces where tasks explained above take place (CIE, 1986; CIE-S-008/E, 2001). High brightness produced by windows in the field of view can cause glare, which should be controlled by using shading devices (IESNA, 2000).
The above given requirements are considered in the proposed approach for energy efficient office lighting design. The steps are following:
Development of Design Alternatives
Design alternatives for office lighting systems can be grouped as discussed below:
Daylighting systems. Designing daylighting systems for office spaces require special attention in order to provide occupant comfort and energy efficiency. The main objectives of daylighting systems in offices are:
* Efficient use of daylight,
* Prevention of glare condition,
* Visual contact with exterior environment,
* Optimum integration of artificial lighting with daylighting in order to reduce the lighting energy consumption and
* Optimization of lighting, heating and cooling loads.
These objectives should be fulfilled by considering various parameters, i.e., geographical location, climatical characteristics, site specifications, orientation of the building and occupation time. Usually, side windows are used in office buildings for daylight penetration and view to the exterior environment. Location, amount and size of windows for a space should be designed in order to create an environment with maximum glare-free daylight penetration and minimum heating loss or overheating problems.
Solar control systems. A solar control system is needed to obstruct the direct sunlight and direct solar radiation in order to provide visual and thermal comfort conditions while reducing the energy consumption. Meanwhile, shading elements should minimize the reduction in daylight entrance. Geographical location, direction of the window and occupation time are the main factors affecting solar control system design. Light shelves and venetian blinds are used in side-lit office spaces to prevent the direct sunlight and optimize the light distribution in the space. Venetian blind systems contain a multiple series of horizontal or vertical slats exterior, interior or between the windowpanes. In order to reduce overheat and glare problem, the slats of the venetian blinds can be adjustable instead of being...
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