High Tech Windows Utilize Phase Change Materials

by ‐ Tags: alternative energy, building science

Windows are often the bane of high performance buildings.  With low R-values and need for significant quality control to ensure proper installation, building gurus have long desired high efficiency glazing.  However, a remarkable new product has recently been developed in Europe and is now being brought to the North American market. The high tech GlassX window is an insulated glass assembly that incorporates a phase-change material (PCM) between two of the glass panes.  Read on to learn more!

The Technology

Phase change materials are compounds that are solid at room temperature but when they are warmed to a specific temperature range become liquid and absorb and store heat, thus cooling the building they’re used in. Conversely, when the temperature drops, the material will solidify and give off its stored heat, warming the building. PCMs reduce heating or cooling loads by smoothing daily temperature fluctuations, resulting in energy savings.

PCM Windows

GlassX windows have another important feature in addition to a phase change material.  The assembly incorporates a prismatic plane that deflects high-angle sunlight in the summertime, rather than transmitting it, to help keep the building cool. Lower-angle winter light is transmitted through this prism and into the PCM.  As a solid, the phase change material still transmits about 25% of visible light, and more than 40% is transmitted when it is in liquid state, so daylighting is not compromised.  From an aesthetic standpoint, polycarbonate spacers used between the panes to segregate the PCM give the windows a venetian blind appearance.  See what they look like in this slideshow.

Energy Savings

According to GlassX, its PCM layer will store as much heat as a nine-inch (24 cm) layer of concrete, essentially acting as a Trombe wall.  Initial studies have shown heating and cooling energy savings of about 20 percent for PCM wallboard.  Other studies showed air conditioning savings of 40 percent.

Though an incredible advance in glazing technology, these windows are likely not yet ready to replace those in your home. GlassX windows are over 3 inches thick and weigh nearly 20 pounds per square foot. They are very expensive at $60-90 per square foot, but the company projects payback to be between 5 and 10 years. In Europe there are dozens of GlassX installations, most of them fairly large--on multi-family housing, office buildings, and retirement homes.  There are currently limited examples in North America, but it likely won’t be long before more projects incorporate GlassX for its impressive thermal properties.