Examination of the technical potential of near-infrared switching thermochromic windows for commercial building applications
Title | Examination of the technical potential of near-infrared switching thermochromic windows for commercial building applications |
Publication Type | Journal Article |
Year of Publication | 2014 |
Authors | Sabine Hoffmann, Eleanor S Lee, César Clavero |
Journal | Solar Energy Materials and Solar Cells |
Volume | 123 |
Start Page | 65 |
Pagination | 65-80 |
Date Published | 04/2014 |
Keywords | Building energy efficiency, daylighting, Solar control, Thermochromic, windows |
Abstract | Current thermochromic windows modulate solar transmission primarily within the visible range, resulting in reduced space-conditioning energy use but also reduced daylight, thereby increasing lighting energy use compared to conventional static, near-infrared selective, low-emittance windows. To better understand the energy savings potential of improved thermochromic devices, a hypothetical near-infrared switching thermochromic glazing was defined based on guidelines provided by the material science community. EnergyPlus simulations were conducted on a prototypical large office building and a detailed analysis was performed showing the progression from switching characteristics to net window heat flow and perimeter zone loads and then to perimeter zone heating, ventilation, and air-conditioning (HVAC) and lighting energy use for a mixed hot/cold climate and a hot, humid climate in the US. When a relatively high daylight transmission is maintained when switched (Tsol=0.10–0.50 and Tvis=0.30–0.60) and if coupled with a low-e inboard glazing layer (e=0.04), the hypothetical thermochromic window with a low critical switching temperature range (14–20 °C) achieved reductions in total site annual energy use of 14.0–21.1 kW h/m2-floor-yr or 12–14% for moderate- to large-area windows (WWR≥0.30) in Chicago and 9.8–18.6 kW h/m2-floor-yr or 10–17% for WWR≥0.45 in Houston compared to an unshaded spectrally-selective, low-e window (window E1) in south-, east-, and west-facing perimeter zones. If this hypothetical thermochromic window can be offered at costs that are competitive to conventional low-e windows and meet esthetic requirements defined by the building industry and end users, then the technology is likely to be a viable energy-efficiency option for internal load dominated commercial buildings. |
DOI | 10.1016/j.solmat.2013.12.017 |
LBNL Report Number | LBNL-187530 |