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PCM mats helped lift Virginia Tech to first place in Solar Decathlon

Ben Welter - Monday, February 18, 2019

FutureHAUS, front elevation

The Virginia Tech team that won first place in the 2018 Solar Decathlon Middle East credits a good share of its success to the deft use of phase change material donated by Insolcorp LLC of New London, N.C.

FutureHAUS, the lone U.S. entry, topped 13 other finalists and more than 60 total entrants in the competition organized by the U.S. Department of Energy and the United Arab Emirates’ Dubai Electricity & Water Authority. Australia's University of Wollongong finished second. The finals took place in November in the desert heat of Dubai.

Insolcorp donated 400 square feet of two types of Infinite R PCM mats. Both are salt hydrates, one with a melt point of 21 degrees Celsius, the other a melt point of 22 degrees C. The phase change material acts as a thermal battery, absorbing and releasing thermal energy as it solidifies and melts.

The Virginia Tech team deployed the mats in the plenum of its 900-square-foot solar-powered house. The PCM allowed the team to take advantage of a rule that limited the use of solar energy to 8kw at any one time, with one exception: Unlimited use of solar energy for air conditioning was allowed during daily inspection periods to assure visitor comfort. The PCM mats, solidified during those periods, helped keep the house comfortable at other times. That helped the FutureHAUS achieve the highest score in net energy use, a key metric in the competition.

Joseph Wheeler, AIA"Every team struggled with the 8kw limit," said Joseph Wheeler, right, lead faculty on FutureHAUS and co-director of Virginia Tech's Center for Design Research. "Typically, during peak energy, you would be generating lots and lots of power, which you could easily charge your batteries with, which you could easily run all your tasks, and you could feed the grid, and build up quite a bit of surplus so that you would remain energy positive throughout the two weeks of competition.

"But, since they limited inverter use at any one time to 8kw, it really put a limit to what our energy budget was. We saw phase change as batteries. A massive ton of batteries. ... It's more of a strategy for a competition than it is for a realized situation. But in a realized situation, we know the value of the PCM. Heat energy, cost of power being cheaper at night than during the day where you can charge your systems and load shift. Practically, PCMs make a lot of sense. And we wanted to have the PCMs in this house for practical reasons, not just for competition reasons. ...

"In simple terms, we eased the demand for the HVAC every afternoon. It was the hottest time of the day and it was also the time when we were getting less power from the solar panels because the sun was moving down. It was a critical time because we knew that once the sun went down, we had to survive on battery. And we had a limit. They limited every house to 15kw of battery."

FutureHAUS, kitchenThe FutureHAUS team finished in the top three in eight of the competition's 10 categories: first place in Architecture, House Functioning and Sustainable Transportation; second place in Sustainability and Innovation; and third place in Engineering/Construction, Energy Efficiency and Comfort Conditions.

The FutureHAUS entry was a two-year university-wide effort. More than 100 Virginia Tech students helped design and build the structure, with help from faculty members in architecture, urban studies, science, engineering and other departments.

The house consists of 18 modular  "cartridges" built inside a Virginia Tech research facility. It was first assembled on campus in Blacksburg, Va., last summer. After testing, it was disassembled, shipped to Dubai and then reassembled at the competition site in just two days. It has since been shipped back to Blacksburg, where it will undergo testing to measure its various energy-saving components.

"We now have a system in place where we can collect data and can truly test the performance," Wheeler said. "We know the PCM worked for us during the competition because we did have some temperature sensors in the ceiling. And so we were able to prove that we were reaching the pre-state when those PCMs were being charged. But we really want to collect a lot more data and look at it in real-world situations."

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