Economic analysis of the daylight-linked lighting control system in office buildings
Introduction
Recently, intelligent building is rapidly increasing with the development of information-oriented technology and telecommunication environment. The lighting environment of the office has, therefore, also been responding to these changes and aims to improve the quality and creation of a comfortable lighting environment (Fontoynont, 2002). Also, the requirement of reducing energy consumption has become more important in Korea like the other countries because of a rise in the oil prices, a high dependence on foreign energy resources and a global warming problem due to using fossil energy. Moreover, heat gain due to electric lighting represents significant proportion of the total building cooling load (Li and Lam, 2001). In Korea, approximately 24% of the total energy is consumed in buildings, and approximately 35.8% of the building energy is consumed by lighting systems and electric outlet (Korea Energy Management Corporation). The detailed rate of energy consumption is shown in Fig. 1. Therefore, methods for reducing the energy consumption of the lighting systems in the buildings are highly required.
One of the methods is to exploit the daylight coming into indoor areas more effectively. If the lighting can be automatically turned off according to the level of daylight flowing indoors, the amount of electrical energy consumed for artificial lighting can be thereby reduced. And owing to the decrease of heat gain caused by artificial lighting, cooling energy can be also reduced in office buildings (Aries and Newsham, 2008, Athienitis and Tzempelikos, 2002, Ihm, 2004, Li et al., 2006, Onaygil and Guler, 2003). In other words, the effect would be to reduce an annual total energy consumption through the application of lighting control system (Roison et al., 2008, Lah et al., 2006). This also helps the occupants to increase working efficiency, satisfaction and productivity (Park and Athienitis, 2003) by exploiting radiant energy and the color rendition that characterizes daylight (Song et al., 2003). Thus, the introduction of an electric lighting control system (Lawrence Berkeley National Laboratory (LBNL), 2000) is necessary because correct passive control, which uses natural daylight effectively, is not possible (Cho, 2007). Designers, however, need to make a decision as to whether it is feasible to introduce the electric lighting control system because this incurs additional initial costs.
In this study, in order to analyze the economics of such a lighting control system, an example building was selected, and the control range was determined by employing a daylight analysis simulation using 3Ds Max 8.0 Radiosity that was performed according to a grazing ratio that gives the most information regarding incoming daylight. Following this, when the artificial lights were turned off, the amount of reduction in electrical energy was calculated. In addition, the amount of cooling energy reduction based on the electric lighting control was calculated by using the building energy analysis simulation. Moreover, the initial cost of introducing the electric lighting control system was calculated according to the number of building floors. And, in order to analyze an economics of the electric lighting control systems, a payback period method was used. The payback period was calculated by comparing the initial cost of introducing the electric lighting control system with the cost of the annual energy reduction based on the above values. This economic evaluation was analyzed based on the office building in Korea. This paper will also present the reference data that designers can determine whether they choose the automatic on/off lighting control system, by presenting adequacy of introduction of electric lighting control system through quantitative analysis such as the payback period method. The flow chart for this study is illustrated in Fig. 2.
Section snippets
Outline of the simulation
In order to establish the lighting control range and evaluate the performance of indoor lighting environment that involves artificial lighting and daylight which changes according to various conditions, an example building was chosen as a simulation model at first stage. And it is a typical office building which is located near Seoul. An envelope of this model building is covered with glass, except for the core space which is located in north, and it is rectangular in shape. By considering a
An outline of a building energy analysis simulation
First of all, the amount of energy used by the artificial lighting and air-conditioning (HVAC; Heating, Ventilation and Air-Conditioning) system should be calculated for economic analysis of the electric lighting control system.
In the case that the lighting control using the daylight was applied to a building, the effects on energy consumption of lighting control were analyzed using a DOE-2.1E program (Lawrence Berkeley National Laboratory (LBNL), 1980) developed by the Lawrence Berkeley
Computation of the initial cost of the electric lighting control system
Architecture of the electric lighting control system is shown in Fig. 11. CCMS (Central Control & Monitoring System), UPS (Uninterruptible Power Supply) and a printer were installed at the central control and monitoring room, G/W (gateway) and DDC (Direct Digital Controller) on each floor, and a photo sensor in each zones were separately installed. The CCMS has an input/output function, such as an input for settings regarding the lighting control, condition monitoring and control information.
Conclusion
The purpose of this paper is to present the reference data that designers can determine whether they choose the daylight-linked automatic on/off lighting control system or not, by presenting adequacy of introduction of the electric lighting control system through employing a quantitative analysis e.g., a payback period. In order to achieve this, an example building was chosen, and both the daylight analysis and building energy analysis simulation were accomplished according to the conditions
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