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DAYLIGHTING ESTIMATION FOR CONTROL USING HIGH DYNAMIC RANGE IMAGINGAuthor: SNEHA Jain Date: 2019-05-17 Report no: IIIT/TH/2019/56 Advisor:Vishal Garg AbstractThere are different aspects of daylight that has been proven to effect the human visual and non-visual system. Daylighting in buildings have a substantial impact on workers’ health, productivity, performance, and circadian system. It can enhance the overall experience of built spaces and benefit the inhabitants in many ways. However, it is necessary to control the daylight admission inside buildings to avoid visual and thermal discomfort. Automated shading and integrated lighting control systems are being used in buildings, for controlling the daylight either in closed loop or open loop system. A typical commercial closed loop system usually has a series of indoor photosensors integrated with dimmers to maintain desk illuminance levels. Unfortunately, these sensors are expensive to install at each desk, challenging to commission and difficult to calibrate therefore highly prone to errors. Whereas in open loop systems, sensors are mounted at external surface of façade to measure sky conditions and daylight availability. However, these devices are only capable of giving single specific measurements without accounting size, directionality, temporal and spatial dynamics of clouds. This leads to failure of the control system to respond in a timely fashion by inaccurately estimating visual discomfort parameters. A reliable estimation of sky conditions and indoor daylight metrics is crucial to open loop controls system. Currently, the daylighting and lighting design practices followed by architects and designers predominantly focuses on the visual characteristics of light. These characteristics include provision of sufficient work plane illuminance, colour rendition and appearance of lighting. There is little or no consideration imparted towards the circadian impacts of lighting and daylighting devices in design process. The impact of lighting in regulating the circadian rhythm in human body has been strengthen with the recent discovery of intrinsically photosensitive retinal ganglion cells (ipRGCs). However, there is lack of accessible instruments to measure the circadian lighting and therefore it’s difficult to monitor daylit spaces and incorporate circadian aspects of lighting in design process. To understand the impacts of lighting, it is essential to devise methods that can quantify both visual and non-visual parameters of daylighting. In this work, a system has been developed to operate a physical setup to calculate glare, illuminance, correlated colour temperature and circadian lighting in an indoor space using high dynamic range (HDR) imaging and control the window roller shades based on glare levels in an open loop system. This thesis gives the details of the system and its performance in various test beds. Following are the objectives: 1. Determine, validate and control simulation based indoor glare and illuminance levels using real time image-based sky maps. 2. Determine and validate correlated colour temperature and circadian lighting in two different experimental setups at two different locations:Results indicate that HDR image-based sky maps provide a good estimation of diffuse sky and take the surroundings, cloud dynamics into consideration as well. In the operational range, the errors observed are within 12% limit. However, larger errors are observed when lux is higher than 2000lux. These errors are of less importance since daylight control will be operational during that time. The circadian lighting measured in test setups vary significantly throughout the day. Lower daylight levels led to lower melanopic lux levels. The correlated colour temperature of the light provided by the tubular daylight device was generally found to be higher than that of the electric lights in test room. The HDR photography technique makes measuring circadian light accessible to all lighting professionals and facilitates field measurements of circadian lighting. Full thesis: pdf Centre for IT in Building Science |
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