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"A Comparative Analysis of Automatic Lighting Control Strategies in Buildings"
Rosinda Duarte
INESC Coimbra
A. Gomes Martins
INESC Coimbra
FCT- Universidade de Coimbra
Abstract
This paper deals with the use of daylight as a mean of avoiding electricity consumption for lighting in buildings, with application to a case study school building, which is provided with an automatic lighting control system. This building is also provided with passive solar devices for improving daylight availability and glare avoidance inside the rooms, such as external overhangs above the glazing, light shelves, light ducts and rooflights. Two alternative automatic control strategies of artificial lighting are compared in order to assess the performance differences of the two strategies from the point of view of daylight use and energy savings. The strategies considered are selective switching and dimming. The building has been simulated based on a detailed description of daylight penetration devices and of the lighting system and components. Climatic data have been used to perform year-round simulations.
Simulations have been carried out using the powerful software package RADIANCE to model all the space and components' geometry, surfaces' characteristics and light sources in every season and weather conditions.
The CONTROLITE program was also needed to model the two lighting control strategies mentioned above. On/off control strategies are considered in the simulations as they are actually implemented in the school. Dimming control simulation is based on a ballast regulation curve and energy consumption is a function of the light output.
RADIANCE generates standard CIE sky models which should be calibrated in order to calculate daylight availability in a room, as close as possible to actual values. To calibrate the sky models it was necessary to get illuminance level measurements from real skies. The illuminance values calculated by RADIANCE were used as input to CONTROLITE to predict the savings of energy spent in lighting. The study was aimed at performing a cost/benefit analysis of two lighting control strategies in order to determine which one would be more appropriate for application in new buildings.
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