Anyone with thick brick or stone walls has probably noticed that their home takes a long time to heat or cool during the day. This is because for years architects have employed high mass materials, which slow the flow of temperature, as a means to build passive, eco-friendly buildings. While these materials work well at regulating temperature fluctuations, they can be expensive, require additional structure and eat up building square footage. Thankfully, scientists have been working hard on developing the same technology, but on a microscopic level, in the form of phase change materials. The basic idea of passive buildings and thermal mass, is building materials with a high mass (water, stone or concrete) collect and store heat throughout the day, and then slowly release it as the temperature drops. Ideally this design technique is used in climates who have extreme temperature fluctuations from day to night, or season to season. The thermal mass aides in a building's efficiency, reduces the need for heating and cooling equipment — and is done so without any moving parts.
Phase change materials (PCM) provide thermal mass, but on a much smaller scale. PCMs work by melting and solidifying at a specific temperature — heat is absorbed at the solid state, and when the material reaches a predetermined temperature, it changes to a liquid and releases the stored energy (heat). When the temperature falls below a predetermined degree, the PCM re-solidifys and the process repeats. The most common PCMs come in the form of paraffin, fatty acids and salt hydrates, each with their own advantages and disadvantages. Most PCMs must be encapsulated to be stored and prevent evaporation and absorption.
There are several sectors in building industry that are looking to incorporate PCMs into their materials and products — some examples of this include drywall, windows, concrete and insulation. For example, when PCMs are embedded into drywall, an entire building is capable of storing energy, rather than just it's exterior walls (where masonry is typically used). All walls that are sheathed with PCM embedded drywall are able to absorb and release heat around-the-clock to maintain a predetermined and desired temperature. By using drywall embedded with PCMs as thermal mass, instead of masonry or concrete, the building gains square footage that typically would've been lost to thick walls, and needs less structural support, which can get very expensive.
Other current PCM applications include:
- BioPCM: BioPCM can be integrated into new construction or retrofitted into existing. It is a rolled mat that contains PCM; the mat is installed between insulation and drywall layers and can be located in walls and ceiling.
- GlassX: GlassX is an insulated glazing unit that can be used as full glass walls and windows. The unit has an outer pane of glass that reflects high-angle sun and allows low-angle sunlight to pass. Sunlight that is transmitted through this outer pane of glass passes through inner polycarbonate channels that are embedded with salt-hydrate PCMs. These PCMs store the heat from the sunlight, and release the heat to the interior of the building as the temperature cools.
- ThermalCORE: Made by National Gypsum/BASF Corporation, ThermalCORE is a drywall panel embedded with paraffin PCM. The microscopic paraffin capsules absorb and distribute heat as the wax melts and solidifies with temperature fluctuations. ThermalCORE is not currently commercially available for purchase and is still undergoing testing.
Many PCM materials are undergoing testing as it is very difficult to fine tune each product to be aplicable for a variety of climates and desired temperature ranges. However, many PCM products are already being integrated into the construction industry in Europe and were seen as recently as last year in some of the Solar Decathlon entries. This seems like such an innovative, yet simple idea, and we're eager to see how it evolves within the building industry.
(Images: Greenlite Glass, BioPCM, ThermalCORE, BASF)