Chemical giant DuPont also makes encapsulated phase-change materials and has incorporated them into heat-absorbing panels that it markets in Europe. BASF’s strategy is a little different: the company sells the capsules to other companies to incorporate into a range of building materials, including ceiling panels, aerated concrete blocks, and drywall. Based on German electricity prices and climate conditions, a study conducted by BASF estimated that a family home made with plaster that incorporated 360 grams of the phase-change material (at a cost of $4,883) would save enough electricity to recoup the cost within five years.
National Gypsum is working with the National Renewable Energy Laboratory and California’s Emerging Technologies Coordinating Council to field-test its heat-absorbing panels, which will be marketed under the name Thermalcore. The panels are made by mixing the BASF microcapsule-water solution with gypsum, the mineral used to make drywall. The paraffins used by BASF can be tailored to melt at different temperatures; those in National Gypsum’s panels liquefy at 22.8 ºC (about 73 ºF). According to the company, the panels can store 22 British thermal units per square foot.
National Gypsum will take at least a year to test the panels’ performance through all four seasons before bringing them to market. A spokesperson says the company may reformulate the panels to include more or less of the capsules, depending on how they perform in the climate of the western United States. Data from the field trials will also be used to model how much the panels help reduce energy consumption.
So far, the heat-absorbing capsules have only been tested in passive systems. But they could also be used in active systems in warmer climates, says MIT’s Glicksman. “In commercial buildings, you could run the air conditioner at night when electricity is cheaper and use the phase-change materials to maintain lower temperatures during the day,” he says. Schossig says his research group and BASF are gathering data from experimental active systems.