Low-cost, Highly Transparent Flexible Low-e Coating Film to Enable Electrochromic Windows with Increased Energy Savings PDF Download

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Languages : en
Pages : 33

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Book Description
Five Quads of energy are lost through windows annually in the U.S. Low-e coatings are increasingly employed to reduce the wasted energy. Most commonly, the low-e coating is an oxide material applied directly to the glass at high temperature. With over 100,000,000 existing homes, a retrofit product is crucial to achieve widespread energy savings. Low-e films, i.e. coatings on polymeric substrates, are now also available to meet this need. However, the traditional oxide materials and process is incompatible with low temperature plastics. Alternate high performing low-e films typically incorporate materials that limit visible transmission to 35% or less. Further, the cost is high. The objective of this award was to develop a retrofit, integrated low-e/electrochromic window film to dramatically reduce energy lost through windows. While field testing of state-of-the-art electrochromic (EC) windows show the energy savings are maximized if a low-e coating is used in conjunction with the EC, available low-e films have a low visible transmission (~70% or less) that limits the achievable clear state and therefore, appearance and energy savings potential. Comprehensive energy savings models were completed at Lawrence Berkeley National Lab (LBNL). A parametric approach was used to project energy usage for windows with a large range of low-e properties across all U.S. climate zones, without limiting the study to materials that had already been produced commercially or made in a lab. The model enables projection of energy savings for low-e films as well as integrated low-e/EC products. This project developed a novel low-e film, optimized for compatibility with EC windows, using low temperature, high deposition rate processes for the growth of low-e coatings on plastic films by microwave plasma enhanced chemical vapor deposition. Silica films with good density and optical properties were demonstrated at deposition rates as high as 130Å/sec. A simple bi-layer low-e stack of silica and a transparent conductive oxide demonstrated 90% visible transmission with high thermal infrared reflectivity characteristic of conventional low-e coatings. A slightly more complex stack provided high solar infrared reflection without sacrificing visible transmission or thermal infrared reflection. Successful completion of the effort produced a prototype integrated low-e, dynamic window film with characterized energy saving potential. Cost modeling for the passive bi-layer, low-e film projects a manufacturing cost of ~$0.50/ft2 for a plant with 10M ft2/yr capacity. The novel thin film processes developed here enable high deposition rate (low cost), optical quality oxide coatings at low temperatures. When combined with engineered materials, ITN's coating will result in low-cost, low-e films that reflect a high degree of infrared radiation without substantially reducing the visible transmission. The resultant window film will improve the U-value and achieve SHGC improvements over bare glass. The new low-e coating will be particularly attractive when combined with an electrochromic film. Low-e coating design guided by energy savings modeling allows customization of the product for different climate zones.