International Workshop on Energy Performance and Environmental 1 Quality of Buildings, July 2006, Milos island, Greece A single sensor system for whole building daylight linking S. Stravoravdis Cardiff University, United Kingdom ABSTRACT Linking artificial lighting with daylight requires the presence of controls and censors for each room. Apart from the energy saving produced though, this can have significant initial cost im- plications for the user. This paper presents a method for linking artificial lighting with day- light over a whole building in real time, through a single sensor system. By placing a camera on the top of a building, it is possible to capture a digital image of the sky at regular intervals. Post processing that image can give us an accurate representation of the sky conditions at any given moment. Using that in- formation we can reconstruct any sky condition and predict/simulate the amount of available daylight at any point within a building. By util- izing a database management system, where all the simulation information is stored, we can ob- tain the simulated daylight levels for each point within a building, for the current sky conditions. This is turn, allows us to control artificial light levels for all the building from a central loca- tion. 1. INTRODUCTION Artificial lighting can account for a significant part of the electrical energy demand of build- ings. Studies have shown more than 20% can be attributed to lighting in the case of non-domestic buildings (Li et al., 2002). By incorporating daylight into the design of buildings, significant energy savings can be achieved (Atif et al., 2003). In order to achieve these savings though, the presence of controls is required, so that on/off switching or dimming is possible, as well as the presence of sensors that can detect the amount of daylight available and thus inform the controls through a BMS system, how much light they need to provide, if any, at any given time to supplement the available day- light. The presence of controls is a necessity and a financial burden that cannot easily be avoided, if the integration of daylight with artificial light- ing is to be achieved. The presence of photosen- sors though, although desirable so that daylight levels can be determined, can add a significant initial cost to the whole artificial lighting system budget of a building. This is due to the number of sensors that need to be installed so that the variation in daylight levels within every room can be accurately represented, the additional in- stallation costs and maintenance/replacement costs. All these costs, prevent many building owners from installing photosensors even though over time there is a payback on their in- vestment. To this end, a method is proposed where the use of photosensors is not required to achieve dynamic daylight linking. Instead, a single sen- sor system is proposed where the variations in daylight availability due to changing sky condi- tions are accounted for and a range of other technologies are implemented to provide real- time daylight linking for a whole building. 2. SINGLE SENSOR SYSTEM 2.1 Background In order for the system to provide the maximum possible savings of electrical energy, it needs to be able to take account of the changing sky con-