Background

Latent Heat and PCMs

 ​ ​Phase change materials use their respective latent heat capacities to absorb or release energy during phase transition (Fig. 1). This heat released or absorbed occurs when the surrounding air temperature is equal to the phase change material's (PCM) melting point or solidification point.

PCMs are categorized into three primary categories: organics, inorganics and eutectics (Fig. 2). Organic phase change materials range from paraffins (wax-like substances derived from oil refining process) to commonly found substances like glycerin and beeswax. Inorganic PCMs include salt hydrates, various sulfates in addition to metals like mercury, copper and gold. Eutectics are compounded or hybridized from distinct organic or inorganic materials. The most accessible PCMs are either in the organic or inorganic category, therefore eutectics will not be addressed during experimentation.

Phase change materials used in building applications require specific encapsulation methods, either macro-encapsulation or micro-encapsulation. Micro-encapsulated PCMs, often delivered as amalgamated mixture or power incorporated with a coating that preserves the integrity of the PCM material. Gypsum board and concrete are both capable of incorporating micro-encapsulated PCMs.  Macro-encapsulated PCMs are contained in a distinct tube or enclosed volume and experience the phase transition as a collected volume rather than dispersed particles. Both macro and micro encapsulated PCMs are integrated into building envelopes to reduce heating and cooling loads through latent heat storage.
Picture
Fig. 1 Phase transition cycle for latent heat materials. https://www.microteklabs.com/hubfs/Frames_Aligned_Artboards_V2_10.png
Picture
Fig. 2 PCMs vary in substance and origin. https://ars.els-cdn.com/content/image/1-s2.0-S1364032112005643-gr1.jpg
Picture
Fig. 3 Typically, PCMs are oriented on the interior face of an exterior wall.

Sources

1. Kalnæs, Simen Edsjø, and Bjørn Petter Jelle. "Phase change materials and products for building applications: A state-of-the-art review and future research opportunities." Energy and Buildings 94 (2015): 150-176.

​2.