Phase Change Materials

The science before the engineering

AEI is monitoring research conducted by leading chemical companies to develop the next generation of high-performance phase change materials (PCMs), gauging PCMs’ projected capacities in cooling load absorption applications.


UW Molecular Engineering Building - Natural Ventilation

We’re projecting the performance of materials in development that combine advantages of existing organic and inorganic PCMs (e.g., large temperature range, congruent melting, self-nucleating, chemically stable, recyclable, compatible with conventional construction materials, low cost, low volume change), while eliminating disadvantages, most specifically flammability.

 

While thermal energy storage using water is a strategy of long standing to reduce energy costs by shifting cooling loads to off-peak hours when cheaper electricity is available, water stores energy as sensible heat. Meanwhile, PCMs store energy as latent heat, absorbing large amounts of heat at the nearly constant temperature where they change phase from solid to liquid. They continue to absorb or release heat without significant increase or decrease in temperature until all of the material changes phase. PCMs can absorb an order of magnitude more heat per unit volume than water or thermal mass and have been incorporated in systems in which the thermal storage water tank or ice storage system is replaced by a PCM tank. The PCM media can be tuned to the required use, storing energy for later use at an appropriate temperature. In one such use, the PCM stores energy at approximately 59F for use in chilled ceilings during the day, with the PCM being recharged overnight by cooling towers, operating during cool weather or otherwise under off-peak electrical rates.

 

Similarly, PCMs are currently being incorporated into building materials, such as wallboard and CMU (or materials that can be applied to wallboard and ceiling tiles), to increase the thermal mass of otherwise lightweight structures. Many materials are available at a selection of melting temperatures across the comfort range. The increased effective thermal mass can be used as a means of peak load reduction in mechanically ventilated space, or as an enhancement to naturally ventilated spaces – one that is particularly useful where a night ventilation strategy is employed.

 

AEI is currently specifying one such material, derived from soy, for use in the University of Washington Molecular Engineering & Sciences Building. The material will be applied to ceiling tiles and select walls in naturally ventilated office space to improve temperature stability and the ability of the night ventilation cycle to allow the building to ride through spikes in heat gain.