Advanced Daylighting

The California Lighting Technology Center (CLTC), in collaboration with Southern California Edison (SCE), developed and evaluated advanced daylight harvesting strategies (ADHS) for commercial buildings, aimed at maximizing comfort and energy efficiency. Efforts focused on use of dynamic fenestration systems and the integration of automated controls for electric lighting, fenestration and HVAC systems. This approach to daylight harvesting is an energy-savings strategy not yet required by California Building Energy Efficiency Regulations (Title 24, Part 6) and is therefore being researched by the Emerging Technologies group. In order to understand the market and incorporate best-in-class devices into the ADHS, a market assessment was conducted for each technology to be incorporated into the Advanced Daylighting System (ADS) i.e., dimmable electric lighting, dynamic fenestration components, HVAC, sensors, controllers, communication and Building Management Systems (BMS). A technology specification was then developed, which integrates all components in terms of controls into an ADHS. The technology specification includes a product-specific deployment scenario consisting of a suite of commercially available components and systems. This scenario is just one combination of products that can be utilized as part of an ADHS. For dynamic fenestration components, it includes a venting skylight with motorized roller shade, a window with two electrochromic (EC) glazing units, and a venting window with a motorized roller shade between glazings. The deployment scenario includes four LED luminaires, an HVAC system and motion, temperature and photo sensors to determine environmental conditions for automated operation. The ADHS components were selected based on their compatibility with JACE, a commercial control hardware platform that supports development of custom control algorithms for integrated operation that can communicate with other devices over many communication devices, namely the BACNET MT/SP protocol. Custom control algorithms were developed for ADHS that improve on the control of electric lighting and optimize fenestration controls for comfort and energy efficiency. The algorithms for automating electric lighting and HVAC output are based on traditional criteria, such as occupancy, light levels and indoor temperature, as both electric lighting and HVAC can be autonomous without any knowledge of each-other’s status or the status of any other building system. The algorithms for automating fenestration operation were focused on controlling visible light transmittance (VLT), solar heat gain coefficient (SHGC) and venting, for natural ventilation and cooling. Fenestration automation requires knowledge of the status of both electric lighting and HVAC systems as well as means to determine potential for daylight glare. The research team installed the ADS in the CLTC Advanced Daylighting Laboratory (ADL) to test and evaluate the effectiveness of the control algorithms and the overall performance of the system. Results from testing show that commercially available products are able to be connected and communicate with JACE. The testing and demonstration of the algorithms were focused on the control of the electric lighting and the EC glazing panes, using a new, dual-loop sensing approach (a combination of open- and closed-loop sensing), which resolves the key daylighting controls issue of reliably detecting if the closed loop photosensor signal changes are due to true daylight changes or changes in the geometry and reflectance of interior surfaces. The operation of the control algorithms was tested for daylight changes during sunrise, sunset and partly cloudy sky conditions, which were simulated using the Sky Wall of the CLTC integrated controls laboratory, which illuminates the façade with the two windows and the skylight. The results of the testing and demonstration showed that the operational logic of the control algorithms is effective at reducing power consumption of the electric lights in the room, while maintaining a desired light level. The electric lighting controls worked very well in adjusting electric lighting levels following daylight changes, verifying the effectiveness of the dual-loop sensing approach in reliably sensing daylight changes. The EC glazing tint control was challenging for three reasons: -There are only four states that the EC glazing can stabilize tint level (2%, 6%, 21% and 62%). -It takes significant time (about 5 minutes) for the EC glazing to change states. -The EC glazing controller provides limited information about tint state. These issues were temporarily resolved for the laboratory setup by mapping EC states to closed-loop sensor signals through experimentation, and repeated calls to the electric lighting control during the EC glazing tint switching periods. A more permanent resolution is being considered, using a photo sensor that looks to the outdoors through the EC glazing. This sensor, originally intended for determination of glare potential, can be used in combination with the open-loop photosensor to provide an estimate of the tint state of the EC glazing. While the algorithms proved to be accurate and effective, the speed of execution could not be made as fast as desired. The communications between JACE and the controllers of the lighting and fenestration systems were not reliable at polling speeds of less than one second, which resulted in several seconds before the lighting and the fenestration would reach desired states. Polling speeds of traditional controllers, are at the level of milliseconds, which result in very short times to reach steady states, faster than occupants can perceive the fluctuations towards steady state. This issue is being addressed at three levels: the JACE hardware, the BACnet MT/SP protocol, and the status export of the TWS room controller, which is also polling the signals of the occupancy and photo-sensors. The development of the control algorithms for the ADS is continuing, leveraging funding from the California Energy Commission, under a cost-sharing activity. Key findings presented in this report are being evaluated and issues are being addressed for successful resolution.