UC Berkeley

The last decade has witnessed a heightened interest in making buildings more sustainable, which has been fueled largely by the relative increase in energy costs and advancements in manufacturing technology. Lighting consumes a substantial amount of the building energy consumption, making it necessary to look for alternative technology that depends more on natural lighting. A structural element for facades called the Translucent Concrete (TC) panel has been developed for capturing and delivering daylight into buildings that could reduce our dependence on artificial lighting and save energy. It consists of optical fibers embedded in concrete that can channel diffused sunlight into the office building workspace. The transmission of light is analyzed using a newly developed ray tracing software that is coupled with an open source software RADIANCE to compute the spatial illumination in a room. The information on distribution of illumination is applied to occupancy profiles generated from Markov chain models and is finally combined with light switching models to estimate the energy saved from using daylighting as an alternative to artificial lighting. It is observed from calculations on a studied windowless room example that using TC panels with a practical optical fiber volumetric ratio from constructibility view point can save at least 44% of lighting energy, spent between 8 am - 6 pm annually. These results have been presented for a place like Berkeley that due to its proximity to the Pacific Ocean experiences a Mediterranean type of climate.

The utility of a south-facing wall consisting of TC panels would be enhanced if it can also reduce the heating and cooling requirements of a room. Using the solar radiation channeled by optical fibers can offset some of the heating requirements of the room. On the other hand, if the optical fiber density in the TC panels is high, solar radiation leads to overheating and in this case cooling loads consume large portion of the building energy. Also, the use of natural daylight in illuminating the office work space reduces heat dissipation from lighting installations and positively impacts cooling loads. Moreover, conduction through the walls allows heat to be removed from the room during the morning but transmits heat from the ambient environment into the room later in the afternoon and evening. A thermal analysis algorithm is developed to calculate the heat transfer due to solar radiation, conduction through walls and heat dissipation from lighting installations. The thermal analysis is coupled with lighting analysis to search for an optimal optical fiber volumetric ratio for the TC panels that would reduce the energy expenditure on lighting, heating and cooling with respect to energy spent in a daylight-deprived room with opaque walls. The TC panels are able to cut down energy expenditure by as much as 18% for a fiber volumetric ratio of 5.6% which is also consistent with the objective of maintaining structural integrity and making the fabrication process practical for the construction case of the TC panels by having fewer embedded optical fibers.