An empirical study of a full-scale polymer thermochromic window and its implications on material science development objectives

TitleAn empirical study of a full-scale polymer thermochromic window and its implications on material science development objectives
Publication TypeJournal Article
LBNL Report NumberLBNL-6376E
Year of Publication2013
AuthorsLee, Eleanor S., Xiufeng Pang, Sabine Hoffmann, Howdy Goudey, and Anothai Thanachareonkit
JournalSolar Energy Materials and Solar Cells
Volume116
Start Page14
Pagination14-26
Date Published09/2013
Keywordsbuildings energy efficiency, Solar control, Thermochromic, windows
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°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.

DOI10.1016/j.solmat.2013.03.043
AttachmentSize
PDF2.17 MB