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Phase Change Materials

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Phase change materials (PCMs) can smooth daily fluctuations in room temperature by lowering the peak temperatures resulting from extreme external daily temperature changes. PCMs reduce home heating or cooling loads, thereby producing energy savings for the consumer, and ultimately reducing the need for new utility power plants. Building materials that absorb heat during the day and release it at night can eliminate the need for air-conditioning in some climates. This doesn’t help much where the difference in day and night temperatures is small, but desert areas get very cool at night and hot during the day, and therefore can be appropriate areas for the use of PCMs.

PCMs are solid at room temperature. When the temperature becomes warmer, PCMs liquefy and absorb and store heat, thus cooling the house. Conversely, when the temperature drops, the material will solidify and give off heat, warming the house. By incorporating PCMs in the building envelope, they absorb the higher exterior temperature during the day, and dissipate the heat to the interior at night when it is cooler.

Properties of PCM that are desirable for residential use include: (1) A melting temperature above 25°C (77°F), (2) material is low cost, (3) not toxic, corrosive, or hydroscopic, and (4) commercially available in sufficient quantities for producers to incorporate into ordinary building materials.

Researchers have identified a number of materials that meet most of the specifications. For example, paraffin compounds (linear crystalline alkyl hydrocarbons) are commercially available from petroleum refining or polymerization. Some manufacturers have demonstrated processes that successfully incorporate paraffin beads into wallboard.

One successful project in Park City, Utah, utilizes PCM in a large, mass wall. Known as the Sungazing House in Park City, this zero energy Passive House was built with tubes of paraffin wax embedded in the concrete thermal mass wall that runs approximately 100 feet along the east/west axis of the home with a height of 18 feet. The one-and-a-half-inch-diameter PVC pipes are spaced every 16 inches, closer to the interior surface, and filled with paraffin wax that melts at a desired room temperature.

BASF’s Micronal® PCM phase change materials have been incorporated into CelBloc Plus aerated cement blocks and gypsum wall board. This substantially increases the heat storage capacity of both building materials. Thanks to the porous structure of the blocks, the aerated cement has excellent thermal and acoustic insulating as well as fire resistant properties. Incorporating the PCM Micronal® enhances the heat storage capacity of the aerated cement and hence of the structures built with it. The result is that buildings based on modern light construction principles can have a significantly improved indoor climate.

BASF’s Micronal® PCM is a microencapsulated latent heat storer that works according to the following principle in the wall board: microscopically small polymer capsules containing a pure wax storage medium at their core, so-called phase-change materials, are inserted into the gypsum wall boards during production. In rooms walled with this material, if the room temperature exceeds the switching temperature of 26 degrees Celsius set during production, the wax inside the microcapsules melts and absorbs the excess heat. If on the other hand it falls, the wax becomes solid and the capsules release their heat again. The temperature differences between night and day ensure the alternating sequence of melting and solidifying. In this way, Micronal® PCM helps to absorb daytime temperature peaks.

 

Phase Change Materials

The zero energy, passive, Sungazing House in Park City, was built with tubes of paraffin wax embedded in its concrete thermal mass wall that runs approximately 100 feet along the east/west axis of the home with a height of 18 feet. The one-and-a-half-inch-diameter PVC pipes are spaced every 16 inches, closer to the interior surface, and filled with the "phase change material" wax that melts at a desired room temperature. ©2011 O'Meara Sungazing House


Documents

  Phase Change Materials in Building Applications 2007 (4,097 kb)

  Phase Change Benefit Explanation (40 kb)

  Phase Change Wallboard Experiment (294 kb)