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Judges Notebook:

“Greenlite Glass Systems’ GlassX is a much needed push forward in glazing technology.”

Game Changer

GlassX from Greenlite Glass Systems triple-glazed insulating unit uses phase change change material (Crystalline PCM) to absorb, store and release solar and thermal energy. This passive energy storage system activates when solar/thermal gains reach 70 to 86 F. Solar envelopes designed within GlassX can reduce heating and cooling energy cost by 50%.

According to Dennett, GlassX not only meets but exceeds the requirements of current building-energycode standards. ”People thought at one stage that glass buildings would be a thing of the past because you were going to have to have a concrete building with little punch-out windows in it. GlassX allows you to still have that glass facade and include visionless, spandrel areas that will still let light through but will meet the new standards for heat loss in buildings.” As it is translucent and not transparent, in either its solid or liquid state, the glazing is better suited for spandrel and lower transom applications.

An ice cube that doesn’t melt The salt hydrate in the PCM is specifically formulated for the building market to melt and freeze within a narrow range that is close to room temperature. The 0.8-inch-thick section of the PCM can store as much heat as 9 inches of concrete; it will then release that constant heat at a rate of 16 to 30 BTU s over a 20-hour cycle. Depending on the usage and the amount in the building, interior temperatures can be reduced by 4 to 6 degrees in Celsius in the summer months. “You can think of the PCM as an ice cube for a building that doesn’t melt,” says Dennett.

Developed in Switzerland over a decade ago and used in many European buildings, the glazing is now being considered for projects in North America. In comparison to $20 to $30 a square foot for typical triple glazed IGUs, GlassX costs about three times as much, averaging $60 to $90 per square foot. “But you are looking at a payback time of five to 10 years given your up-front savings in HVAC systems and longterm energy savings,” says Dennett.

One of the architecture firms currently considering GlassX for an upcoming project is SRG Partnership in Seattle. According to project designer Christopher Colley, SRG is possibly using the glazing for a new nursing and health-science building for Everett Community College in Washington state. While the product’s newness and cost may be hurdles, particularly for publicly bid projects, Colley thinks it is an intriguing new option for spandrel glass as his firm starts to design buildings for The 2030 Challenge. “This is a product that can potentially allow us to have more design freedom and still have a very high-performing building.” Greenlite Glass Systems Inc., Vancouver, B.C. www.greenliteglass.com

While GlassX is available in various configurations (at least in Europe), here’s how the version with all the bells and whistles (GlassX Crystal), which is being marketed in North America, works:

An outer insulated glazing unit (IGU) has a suspended prismatic filter (like a Fresnel lens) between the panes of glass that reflects higher-angle sunlight back out while transmitting low-angle sunlight. This offers a “passive” solar-control mechanism for south-facing glass to keep out most of the high summer sun, while benefiting from the lower-angle winter sun.

Sunlight that makes it through this outer IGU passes into an inner IGU that is filled with sealed polycarbonate channels into which a translucent salt-hydrate PCM is encapsulated. PCMs store a lot of heat as they change phase from solid to liquid (melt) over a narrow temperature range, then they release that heat as they cool off. The salt hydrate used in GlassX melts and freezes in the temperature range of 79-86 degrees F (26-30 degrees C).

Two separate low-emissivity (low-e) coatings and low-conductivity gas fill in the outer two sealed spaces glass help to push heat from the PCM inward while slowing outward heat loss. The U-factor is about 0.08 Btu/hr-ft2-F (0.48 W/m2-K). The direct-beam light transmission (assuming the sunlight isn’t blocked by the prism layer) is up to 45% when the PCM is liquid and up to 28% when the PCM has crystallized.

Along with doing a remarkably good job at blocking heat loss, the glazing stores heat like a Trombe wall (or thermal storage wall)–offering a heat storage capacity of 376 Btu/ft2 (1,185 Wh/m2). According to GlassX, the PCM will store as much heat as a nine-inch (24 cm) layer of concrete–though I haven’t been able to dig into the technical literature enough to figure out exactly what the assumptions are for coming up with that comparison. If that proves to be the case and if the phase-change efficiency is retained after hundreds or thousands of cycles, this will be a remarkable product indeed!

Overall, this glazing assembly is slightly over three inches thick (79 mm) and weighs 19.5 lb/ft2 (95 kg/m2). Glazing modules are available in a maximum height of 110 inches (280 cm) and a maximum width of 59 inches (150 cm).

Not surprisingly, it’s also fairly expensive: $60-90/ft2 ($560-$970/m2), according to Ryan Dennett, president and CEO of the exclusive North American distributor, Greenlite Glass Systems, near Vancouver, British Columbia. Given the performance, Dennett said he expects a fairly rapid economic return. “We’re looking at payback periods of five to ten years,” he claims.

GlassX was introduced to the North American market at the AIA convention in Miami earlier this month. Dennett tells me that, while there aren’t yet any installations of the product in North America, that should change fairly soon, as the glazing has been specified on several projects. “There’s a lot of excitement about it,” he says.

In Europe there are at least 25 installations of GlassX, most of them fairly large–on multi-family housing, office buildings, and retirement homes, for example.

Along with vacuum glazings and electrochromic glazings, GlassX is one of a number of a emerging high-tech glazing options that could revolutionize building design in the years ahead–and perhaps make the all-glass building a truly green option. (The upcoming July issue of Environmental Building News has a feature article, “Rethinking the All-Glass Building.”) I’ll keep you posted on these and other developments.

The retirement apartments are located on the edge of a housing development within a new row of detached residential houses to south of the historic centre of the village. A total of twenty small apartments have been built next to each other over four floors and facing south-west. To the north-east, wide windows overlook an adjoining arbour. Encompassing the apartments is a generous arrangement of cascade staircases and wide forecourts which the kitchens look out onto through large-sized windows. Living rooms and bedrooms, together with the recessed balconies, form another series of clearly bounded areas that are connected via sliding partitions and which together create a dynamic and interactive connection between the interior and exterior.

The bedroom facade elements, i.e. floorheight translucent glass panels, contain prism glass in order to prevent overheating in summer, with the steep insolation being completely reflected. In winter the flat insolation enters through the prism glass and is absorbed by the salt-hydrate-filled elements behind it, which serve as a storage medium. Salt crystals dissolve at room temperature and at the same time absorb energy which can be released later on. The dissolving process results in the glass panel becoming more translucent, i.e. heat absorption can be both seen and felt. The facade unites both windows and walls by allowing sunshine to pass through it and at the same time storing the energy.