Additively Manufactured Polymer-Encapsulated Phase-Change Material Heat Exchangers for Residential Thermal Energy Storage

Thermal energy storage, in the form of chilled water or ice-based phase-change systems, has been used in commercial buildings for over 30 years. These systems take advantage of off-peak electricity rates to cool water or ice at night, which provides cooling power during the day when the electricity prices are at their peak. Although these systems work well for commercial buildings, they are not feasible for residential applications, mainly due to the fact that a residential system supplies air at 55 degrees F (12.8 degrees C)-a temperature that is too high to take advantage of the latent heat of water which freezes and melts at 32 degrees F (0 degrees C); therefore, alternative phase-change materials are needed. The direct implementation of phase-change materials becomes problematic due to the very nature of these materials cycling between solid and liquid states during normal operating temperatures. Therefore, encapsulation of the phase-change material, typically in a polymer, is necessary to maintain structural shape stability during the melting and solidification of the material. Polymers used for encapsulation help maintain the shape of the material as well as retain the phase-change material within the polymer during the phase change. Coincidentally, polymer heat exchangers and additive manufacturing are also of rising interest. Polymer heat exchangers boast a number of benefits including weight reduction, natural corrosion resistance, and anti-fouling when exposed to typical process fluids. The goal of the study is to explore the implementation of a novel, functional encapsulated phase-change material as the primary structure in a polymer heat exchanger, which can be additively manufactured, for residential thermal energy storage. The work presented includes an exploratory thermodynamic analysis on the effectiveness of the novel polymer phase-change material thermal energy storage heat exchanger on reducing the load on a residential HVAC unit.