Optofluidic Device for Controlling the Exchange of Radiation Between a Building and the Environment

Student’s name: Megan Santamore Home Institution: Princeton University NNCI Site: CNS @ Harvard University REU Principal Investigator: Dr. Joanna Aizenberg REU Mentor: Raphael Kays Abstract: Buildings are responsible for approximately a third of all energy usage worldwide, with a significant amount of this energy usage dedicated entirely to simply maintaining a desired temperature and brightness level indoors [1]. Building infrastructure, from HVACs to blinds and indoor lighting, has been developed and implemented in buildings to maintain the comfort levels of those inside. Windows, as the least insulating part of most buildings, are often viewed as the most active region of energy exchange between a building and its surroundings. However, much of this exchange results in wasted energy, with recent estimates suggesting that windows account for 40% of total building energy costs [2]. Thus, recent research efforts have investigated the fabrication of different materials that exhibit control over light and heat independently. However, while these optical and thermal systems operate well separately, most are incapable of operating synergistically within the same building design. In order to develop a single platform that will allow for the achievement of optical and thermal control over energy exchange between buildings and their external environment, we propose looking at a new class of materials: fluids. Other studies conducted in this field have investigated approaches such as electrochromic windows, liquid crystal window designs, and even more complex optical filters. However, all of these methods require the use of unconventional window materials or complex fabrication processes that prevent them from being easily scalable. Our proposed solution is simple: by pumping fluids, with precisely tuned optical properties, through two layers of a larger window, certain bands of electromagnetic radiation can be tunably transmitted, reflected, or absorbed in a desirable fashion. Fluids of varying particle size and visible color were fabricated and shown to selectively transmit or reflect visible and near-infrared radiation. To aid the optical efforts of these fluids, additional ITO-based thin films and titanium dioxide and silver dielectric/metal/dielectric (D/M/D) stacks were fabricated on the interior glass window pane and were proven to selectively reflect mid-infrared light, representative of the black body radiation most commonly transmitted between nearby buildings. Together the use of these specially designed microparticle solutions and optical thin films was proven to save energy compared to the typical energy levels required to maintain a comfortable room temperature and brightness level by selectively and independently controlling when mid-infrared light is absorbed or reflected, when near-infrared light is reflected or transmitted, and when visible light is reflected or transmitted into a building.