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Phase Change Materials

When the temperature becomes warmer, PCMs liquefy and absorb and store heat, thus cooling the house.

Phase change materials look like little white pellets.

Phase change materials (PCMs), currently under research and development, 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.

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. However, more research is needed before the technology can be marketed.

A private company, with the help of the U.S. Department of Energy's (DOE) Oak Ridge National Laboratory, also developed another building envelope application. It tested an attic insulation that absorbs daytime heat, releasing it at night. The insulation consists of perlite embedded with hydrated calcium chloride. Perlite is a naturally occurring siliceous rock, that when heated to a suitable point in its softening range, it expands from four to twenty times its original volume. The resulting PCM, changes phases from solid to liquid at 82°F (28°C), at that point absorbing heat from a hot attic during the day, before it can penetrate into the home. When attic temperatures cool at night, the phase change material solidifies and releases heat back into the attic, moderating outdoor temperatures.

Energy Efficiency

Phase change materials have the ability to reduce mechanical heating and cooling needs and to moderate indoor temperature.


Although installing phase change materials is not technologically complex, the limited availability of PCMs and the limited number of people with design or installation experience make the materials difficult to incorporate into a residential building at this time.

Not Applicable

PCMs will reduce heating and cooling costs in a typical home. Initial studies have shown house heating and cooling energy savings of about 20 percent for PCM wallboard. Other studies showed air conditioning savings of 40 percent.

Currently there are no code or regulatory requirements pertaining to PCMs.

Not Applicable

PCM attic insulation would normally be installed between two layers of another insulation material, such as extruded or expanded polystyrene, urethane or cellulose.

Not Applicable

Claims are that the PCM wallboard being developed could save up to 20 percent of house space-conditioning costs. Computer model laboratory tests of attic PCM insulation showed that it reduced the total heat flow by 22 percent, and the peak heat flow was 42 percent lower than an equal thickness of fiberglass insulation. It reduced the air conditioning load by 40 percent, and shifted the peak load up to eight hours, depending on climate. PCM insulation is most effective in climates that have large variations between day and night temperatures. The technology should result in reductions of peak-hour energy use.

Disclaimer: The information on the system, product or material presented herein is provided for informational purposes only. The technical descriptions, details, requirements, and limitations expressed do not constitute an endorsement, approval, or acceptance of the subject matter by the NAHB Research Center. There are no warranties, either expressed or implied, regarding the accuracy or completeness of this information. Full reproduction, without modification, is permissible.