T. Li, L. Hu
University of Maryland, College Park,
Keywords: energy efficient building materials, thermal insulation, light haversting
Summary:More than $430 billion each year is spent each year to power our buildings, which constitutes 70% of the all electricity use in United States and contributes to almost 40% of nation’s CO2 emission. Among the energy and money used, lighting and heating contributes more than 50% of the total energy consumed and over 30% on average is wasted through inefficient windows. Due to the high thermal conductivity of most commercial single pane window glass (around 1 W/mK), windows act as thermal leak between the interior building space and outer environment. Conventional windows also cannot uniformly harvest sunlight throughout the day which leads to increased use of daytime lighting. Consequently, there exists an urgent need for low-cost energy-efficient windows. Our solution is a scalable, environmentally-friendly, and transparent wood composite to cut the large heat and energy losses inherent in other single-pane glass windows. For the first time, wood has been used as light harvesting constructional material. Among many other requirements, energy efficient building materials require effective daylight harvesting and thermal insulation to reduce electricity usage and weatherization cost. The most commonly used daylight harvesting material, glass, has limited light management capability and poor thermal insulation. We have invented a transparent wood composite to efficiently harvest sunlight and provide uniform indoor lighting to yield substantial energy savings with improved thermal insulation over corresponding single-pane glass windows to help reduce energy consumption for heating and air conditioning of residential, industrial, and government buildings. We used the vertically aligned transparent fibers in natural wood to create an efficient visible light guiding effect. This light guiding effect has been engineered and enhanced by a large forward-to-back scattering ratio. When used as building material for windows or roof, the transparent wood can effectively guide sunlight into the house. Unique optical properties of transparent wood lead to a uniform and comfortable indoor ambient lighting without the glare effects experienced by most glass materials. The transparent wood composite has much better thermal insulation than glass and a higher impact strength that eliminates the significant safety concerns inherent in glass. Greenhouse gas emission from residential and commercial sectors can mainly be attributed to the energy use of buildings. The application of our energy efficient transparent wood building material can yield substantial energy savings with associated reductions in greenhouse gas emission. Our transparent wood can reduce artificial light usage during the day to yield substantial energy savings with improved thermal insulation over corresponding single-pane glass windows to help reduce energy consumption for heating and air conditioning of residential, industrial, and government buildings. Our transparent wood composite thus exhibits great promise as a scalable future building material.