@article {57039, title = {An empirical study of a full-scale polymer thermochromic window and its implications on material science development objectives}, journal = {Solar Energy Materials and Solar Cells}, volume = {116}, year = {2013}, month = {09/2013}, pages = {14-26}, chapter = {14}, abstract = {

Large-area polymer thermochromic (TC) laminated windows were evaluated in a full-scale testbed office. The TC interlayer film exhibited thermochromism through a ligand exchange process, producing a change in solar absorption primarily in the visible range while maintaining transparent, undistorted views through the material. The film had a broad switching temperature range and when combined to make an insulating window unit had center-of-glass properties of Tsol=0.12-0.03, Tvis=0.28-0.03 for a glass temperature range of 24-75{\textdegree}C. Field test measurements enabled characterization of switching as a function of incident solar irradiance and outdoor air temperature, illustrating how radiation influences glass temperature and thus effectively lowers the critical switching temperature of TC devices. This was further supported by EnergyPlus building energy simulations. Both empirical and simulation data were used to illustrate how the ideal critical switching temperature or temperature range for TC devices should be based on zone heat balance, not ambient air temperature. Annual energy use data are given to illustrate the energy savings potential of this type of thermochromic. Based on observations in the field,a broad switching temperature range was found to be useful in ensuring a uniform appearance when incident irradiance is non-uniform across the facade. As indicated in prior research, a high visible transmittance in both the switched and unswitched state is also desirable to enable reduction of lighting energy use and enhance indoor environmental quality.

}, keywords = {buildings energy efficiency, Solar control, Thermochromic, windows}, doi = {10.1016/j.solmat.2013.03.043}, author = {Eleanor S. Lee and Xiufeng Pang and Sabine Hoffmann and Howdy Goudey and Anothai Thanachareonkit} } @techreport {60935, title = {A Pilot Demonstration of Electrochromic and Thermochromic Windows in the Denver Federal Center, Building 41, Denver, Colorado}, year = {2013}, note = {

Completed September 30, 2012, released March 30, 2014.

}, month = {07/2013}, abstract = {

Chromogenic glazing materials are emerging technologies that tint reversibly from a clear to dark tinted state either passively in response to environmental conditions or actively in response to a command from a switch or building automation system. Switchable coatings on glass manage solar radiation and visible light while enabling unobstructed views to the outdoors. Building energy simulations estimate that actively controlled, near-term chromogenic glazings can reduce perimeter zone heating, ventilation, and air- conditioning (HVAC) and lighting energy use by 10-20\% and reduce peak electricity demand by 20-30\%, achieving energy use levels that are lower than an opaque, insulated wall.

This project demonstrates the use of two types of chromogenic windows: thermochromic and electrochromic windows. By 2013, these windows will begin production in the U.S. by multiple vendors at high-volume manufacturing plants, enabling lower cost and larger area window products to be specified. Both technologies are in the late R\&D stage of development, where cost reductions and performance improvements are underway. Electrochromic windows have been installed in numerous buildings over the past four years, but monitored energy-efficiency performance has been independently evaluated in very limited applications. Thermochromic windows have been installed in one other building with an independent evaluation, but results have not yet been made public.

}, keywords = {building controls, daylighting, Demand Side Management, electrochromic, energy-efficiency, Smart windows, switchable windows, Thermochromic, Window}, url = {http://gsa.gov/portal/content/187967}, author = {Eleanor S. Lee and Luis L. Fernandes and Howdy Goudey and Jacob C. Jonsson and Dragan C. Curcija and Xiufeng Pang and Dennis L. DiBartolomeo and Sabine Hoffmann} }