How can dynamic glass and geothermal technology work together to create an ultra-modern, ultra-efficient heating/cooling system for commercial buildings? Experts at SageGlass and geothermal company GEOptimize wanted to find out. They designed a first-of-its-kind dual system—using SageGlass’s electrochromic window technology to supplement an existing geothermal system—that the designers hope will be a model for energy-efficient buildings around the world.
Arvig, a Minnesota-based internet service provider, planned a large renovation of its office building, from 5 000 to 7 000 square meters. It enlisted the help of The Design Group to evaluate the current ground coupled heat pump (GCHP) system. A local electric utility, Otter Tail Power Company, saw an opportunity to improve the efficiency of its electrical grid with the renovation of the Arvig building, and partners with geothermal company GEOptimize for some GHCP projects. GEOptimize’s Ed Lohrenz had a novel idea.
Instead of pairing the GCHP system with a supplemental energy source to manage the heating/cooling loads (the way most GCHP systems are set up traditionally), the Arvig project team would use dynamic glass as a building load management device. “The new renovated building is expected to increase its window-to-wall ratio to 30%,” explains GEOptimize’s Connor Dacquay. “This large increase in windows creates a larger impact by the solar heat gains.”
Essentially, the system takes advantage of a source already available—sunlight coming through the windows—to lower the building’s demand for heat. And when the smart glass windows are tinted, they help lower the demand for cooling, too. The result is a renewable, low-carbon project that also delivers a comfortable workspace for the building’s occupants.
Connor Dacquay says, “The challenge with incorporating this type of [dual] system is that it has never been done before.” To accurately predict how well the smart glass would impact heating/cooling needs in the building, Dacquay and his colleagues developed a building energy model and ran simulations.
The researchers developed four building energy models with different solar heat gain coefficients, and ran simulations that analyzed 20-year temperature trends and system efficiencies (summarized in a paper that recently appeared in the Journal of Building Engineering1). They accounted for weather patterns, climate-change scenarios, office room usage scenarios, and other factors. The results of the modelling showed that the building’s annual cooling demand decreased by 32% when the dynamic windows were fully tinted (compared to clear glass). The integrated system also reduced carbon dioxide emissions by 30%, and made financial sense, too: The 30-year net present value of the system, compared to a conventional system, was $142,273 cheaper. Capital costs for the geothermal system were also reduced—no new ground boreholes were needed, despite the large increase in the building’s square footage.
The Arvig project is set to be completed in 2022, and the system is fully automated: Temperature sensors and flow meters on the ground heat exchanger collect data, and the client’s building automation system uses that information to set the tint level of the smart glass windows.
“As the concern of climate change and awareness of greenhouse gas emissions increases, commercial building owners will be forced to design energy-efficient buildings,” says Dacquay. “A building with a high window-to-wall ratio allows for a symbiotic relationship between a geothermal system and dynamic glass.” Dacquay thinks this kind of dual system will quickly become prevalent in commercial building design. “It’s not a matter of if, but when.”