University of Massachusetts, Lowell,
Keywords: phase change materials, building, energy storage
Summary:Phase change materials (PCMs) are high latent heat materials that can be used to store thermal energy and/or regulate application temperature. In buildings, PCMs can be used in many active and passive applications. The best-known uses include mitigation and time-shifting of thermal load peaks by absorbing (a part) of heat gain during warmer daytime via melting and releasing the stored thermal energy during cooler nighttime when PCMs solidify. Building applications of inorganic PCMs in buildings have a long history. The first reported demonstration of PCM in a North American building utilized inorganic salt based PCM system (Maria Telkes PCM/solar house built in Dover, MA in 1940s ). Also, Los Alamos National Laboratory experimented, in early 1980’s, with an application of Glauber’s salt in concrete . Today, however, a great majority of PCM-enhanced building products are using variety of organic based compounds, including paraffins and biobased fatty acids and esters. Unfortunately, these commercialized products have been unsuccessful in gaining a serious traction in the building market, because of a host of issues associated with organic PCMs: 1) high cost of raw organic compounds, 2) flammability, 3) relatively low energy storage density because organic compounds usually have low density, below or close to 1000 kg/m3, 4) low thermal conductivity (<0.3 W/m-K) which often causes incomplete phase cycling in building applications, 5) high environmental impact of petroleum based PCMs, and 6) toxicity and odor concerns associated with several organic PCMs. In contrast, inorganic salt hydrates are non-toxic, nonflammable, and significantly less expensive than organic PCMs. Because of their higher density (~1500–2500 kg/m3), they have a potential of reaching volumetric energy density close to 100 kWh/m3 in a cost-effective way. This creates a unique opportunity for wide market adoption of new PCM technologies utilizing inorganic PCM formulations. However, inorganic PCMs also have a long list of their performance problems. This presentation will discuss, examples of these problems and their solutions, which may help with wide-ranging implementations of this technology in future buildings.