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Optimization of Microencapsulated Phase Change Materials in Gypsum Wall Boards

Conference Name: 49th Annual Technical Meeting of the Society of Engineering Science
Location: Atlanta, Georgia
Date: October 10-12, 2012

List of Authors:
Perrella, M., M. Moeini Sedeh, , J. M. Khodadadi


Phase change materials (PCM) have been utilized extensively for thermal energy storage and insulation due to their high latent heat and variable melting temperatures. Currently, the most promising work being conducted with PCM involves the encapsulation of the phase change materials with a polymer or resin coating, which helps to protect the PCM from the surrounding environment and also increases the exposed surface area. Micro-encapsulated phase change materials (MEPCM) offer a distinct advantage over larger PCM capsules because they can be mixed or dispersed into almost any medium with little concern of physical damage or reactivity. For this reason, they have gained popularity as an additive to common building materials to increase their thermal storage capacity and reduce energy consumption during daily cooling and heating cycles. In this experiment, commercial microencapsulated paraffin wax was used to enhance the thermal storage capacity of gypsum tiles. Four (4) tiles of different compositions were made to serve as analogues for common sheetrock or drywall building material. The first tile was pure gypsum plaster with no PCM enhancement. The second tile contained 10% PCM by total weight evenly dispersed throughout the plaster matrix. The third contained 20% PCM by total weight also evenly dispersed. The fourth tile consisted of two layers. The first layer was pure gypsum plaster, and the second contained 10% PCM by total weight. Both layers were of uniform thickness and together made a single tile of the same thickness as the other samples. A small control volume with an internal heating source was used to simulate hot, outdoor conditions, while the conditioned lab space simulated a conditioned space. Each tile was fitted onto one side of the control volume and subjected to a temperature gradient of approximately 22 to 37˚C. The double-layered tile was tested twice with each side facing the heat source and the conditioned space. Surface and ambient temperature measurements were taken as each sample was allowed to warm steadily until reaching a steady state. The temperature measurements from each sample were then compared to see what effect the PCM enhancement had on the gypsum tiles’ thermal performance (Figure 1). Figure 1: Conditioned Space Surface Temp When assessing the performance of a MEPCM-enhanced wallboard, two characteristics are of particular importance, namely the decrement factor and the time lag. The decrement factor is the ratio of the maximum surface temperature adjacent to the conditioned space of the non-enhanced wallboard to the enhanced wallboard. The time lag is the difference in time between when the enhanced and non-enhanced wallboards reach their maximum conditioned surface temperature. A high decrement factor and time lag indicates that the PCM was successful in absorbing enough thermal energy to reduce the total heat infiltration into the conditioned space. The analysis of experimental results showed that for each MEPCM- enhanced configuration, the addition of MEPCM was effective at delaying the plaster tile from attaining its maximum surface temperature, but did not greatly reduce the maximum surface temperature. This is likely due to the fact that wallboards were only exposed to a maximum air temperature to simulate hot weather conditions, but they were not subjected to a complete daytime/nighttime heating and cooling cycle. Experimental data also indicated that a plateau in surface temperature occurs at the melting point of the PCM. This further indicates that the MEPCM incorporated in the wall board is absorbing thermal energy as it is passing through the gypsum plaster. These results indicate that MEPCM holds significant promise as an energy saving implement in passive heating/cooling applications. With further investigation, it would be possible to determine the exact amount of heat that can be absorbed by a particular configuration and further specialize PCM-enhanced wallboard for energy saving applications.

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