Thermal fluctuations, changing seasons, intense sunlight: many things can make a building hotter. The largest factor, however, is also the simplest: the building itself. In the US, modern construction overwhelmingly relies on lightweight materials such as wood, steel and glass, all marked by poor heat storage capacities. Instead of blocking the heat, they only absorb a small portion of it, leaving the rest free to reach the building interior - and by extension, its occupants. As the temperature rises, those occupants turn to energy-intensive air conditioning, wasting electricity and increasing CO2 emissions in the process. Solid building materials like brick and stone perform better in this regard, but have difficulty compensating for sudden spikes in temperature.
Enter Fraunhofer
Seeing increasing consumer demand for energy efficiency and carbon reduction, BASF turned to the Fraunhofer Institute for Solar Energy Systems (ISE) in 1999 to develop a latent heat storage material that could be integrated in lightweight and solid building materials. BASF had experience in microencapsulation, ISE knowledge of latent heat storage. Soon, phase change materials (PCM) became the focus of their research activities.
After investigating a variety of materials, researchers at ISE and BASF eventually settled on paraffin wax formed into small droplets encapsulated by acrylic glass. The result was a fine-particle granulate that could be added directly to drywall powder or dried out and incorporated into other construction materials, including concrete and plasters. Once integrated into a building, the wax inside the capsules keeps a room cool in much the same way that ice chills a drink: by absorbing heat as it melts. When it cools down at night, the paraffin wax inside the capsules solidifies, releasing the heat it has stored during the day.
Small Capsules, Big Results
"The thermal capacity of a one-half-inch thick plaster layer with 30 percent [capsules] is roughly equivalent to that of a six-inch thick brick wall,” says Michael Guibault, Marketing Manager for BASF's Construction Polymers business in North America. The end result: buildings constructed or retrofitted with wall panels or porous concrete blocks that incorporate PCM require less energy, are more cost-effective, and help to preserve the environment. More importantly, the PCM can be easily integrated into existing construction processes, requiring little additional effort to deploy.
BASF has since acquired a patent for this new material, which is now being marketed as Micronal® in Europe and North America.