Life cycle assessment of two biologically produced phase change materials and their related products

PURPOSE: Phase change materials (PCMs) hold considerable promise for thermal energy storage and reduction of temperature swings in building space, and can reduce reliance on fossil fuel sources for both heating and cooling. Previous studies have evaluated the use of PCMs for energy storage and provided some limited information on the embodied energy of the PCM; however, an important factor that has not fully been addressed until now is the environmental impact of preparation of organic PCMs. This study presents life cycle assessments (LCAs) of two organic, biosourced PCMs for their applications, focusing on embodied energy and CO₂emissions. METHODS: Dodecanoic acid produced from palm kernel oil was considered as a PCM for use in a solar thermal water heating application, and ethyl hexadecanoate produced from algae was considered for thermal buffering. The functional units were defined as 1 t of dodecanoic acid PCM and 1 kg of encapsulated ethyl hexadecanoate PCM, respectively. The LCA encompasses all phases in the PCM production: growth and harvesting of the feedstocks, extraction of the oil, treatment of the oil, and separation of singular components. The two PCMs were evaluated in terms of the payback times for their embodied energies and embodied CO₂under a modeled use phase. RESULTS AND DISCUSSION: The energy payback time for dodecanoic acid in a solar thermal application was found to be less than 2 years. Although production of dodecanoic acid is a net CO₂emitter, use of this PCM in a solar thermal system can recoup the CO₂of production in less than a year. Ethyl hexadecanoate produced from algae, considered for use in a thermal buffering wallboard product, would require at least 30 years of use before its energy savings would match its embodied energy, mostly due to the drying step in the production of the PCM. However, ethyl hexadecanoate is a strong sequester of CO₂at 7.6 t per ton of ethyl hexadecanoate. CONCLUSIONS: Dodecanoic acid produced from palm kernel oil for use in a solar thermal hot water system appears to be a viable PCM. Its payback time, both for energy and carbon emissions, is under 3 years. On the other hand, the high embodied energy of ethyl hexadecanoate produced from algae gives a prohibitively long payback time for use in domestic thermal buffering applications.