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.1
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. We spent a lot of time reading proposals from other students that tested phase change materials. The first one outlined in this paper involves the testing of phase change materials in a warm summer humid continental climate. In the introduction, Maris talks about how the construction industry is one of the largest consumers of energy, as well as a major source of CO2 emissions globally.2 Lightweight structures are being applied to counter emissions and save energy. One option for accomplishing this is through the use of phase change materials. There is proof from scientific data that phase change materials can be used passively in order to improve the thermal mass of lightweight structures. This also increases thermal comfort and reduces peak cooling and heating loads. This translates into energy savings thereby driving down cost. At this current time, when a phase change material is present in a building, it is typically being used experimentally and tested in hot climates. They have not been studied extensively in cooler regions such as those with a humid continental climate. This experiment involves five test sites and two types of phase change materials to study the performance of these materials as well as their capacity to assist in heating, ventilation, and HVAC systems. The main goal of this experiment was to see if phase change materials can increase thermal mass when passively applied to lightweight buildings. The study found phase change materials to be most effective in this regard when combined with the use of capillary ceiling cooling, which reduces the temperature inside by three to four degrees Celsius over the course of the day. The experiment also confirmed that phase change materials have a heating application that increases building thermal inertia. This helps to minimize temperature fluctuations during the winter, thereby increasing thermal comfort. There is more potential in cooling applications. When phase change materials are cooled they can be regenerated. Maris used a capillary ceiling cooling system to run cold water between two layers of phase change material. The results showed that this cooling method can significantly improve regeneration. This in turn reduced peak temperature by three to four degrees celsius and reduced daily temperature fluctuations by one to two degrees celsius. It was concluded that further tests would be needed to measure the cumulative energy input and output. |
Fig. 1 Phase transition cycle for latent heat materials. https://www.microteklabs.com/hubfs/Frames_Aligned_Artboards_V2_10.png
Fig. 2 PCMs vary in substance and origin.
https://ars.els-cdn.com/content/image/1-s2.0-S1364032112005643-gr1.jpg
Fig. 3 Typically, PCMs are oriented on the interior face of an exterior wall.
Fig. 4 Five experimental test buildings (lower) with different external walls (upper).
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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. Sinka, Maris, Diana Bajare, Andris Jakovics, Janis Ratnieks, Stanislavs Gendelis, and Jelena Tihana. "Experimental testing of phase change materials in a warm-summer humid continental climate." Energy and Buildings 195 (2019): 205-215.
2. Sinka, Maris, Diana Bajare, Andris Jakovics, Janis Ratnieks, Stanislavs Gendelis, and Jelena Tihana. "Experimental testing of phase change materials in a warm-summer humid continental climate." Energy and Buildings 195 (2019): 205-215.