Design and experimental investigation of a thermally managed solar latent heat storage system using hydrogenated palm stearin as a sustainable phase change material under high-altitude Andean conditions

This paper describes the design, construction, and performance analysis of a solar thermal system for space heating and hot water production. The system was integrated into one of the hotel’s guest houses and tested over twelve months in high-mountain conditions in the Colombian Andean region, with very contrasting day and nighttime temperatures. The system includes several modules of evacuated-tube solar thermal collectors, latent heat thermal storage with a phase-change material, and a control system to govern the system’s operation. The design of the latent heat thermal storage is based on a shell-and-coil configuration: the phase change material storage is a box with two coaxial rectangular copper coils installed inside and used as heat exchangers. As a novelty, the system deploys hydrogenated palm stearin as a sustainable phase change material with predefined thermophysical properties, namely the melting temperature and heat of fusion, that satisfy the application requirements. This new phase change material was produced from a sustainable source: waste generated by the local palm oil production industry. Utilising this agricultural waste, abundant in Colombia and other Latin American countries, to produce a new type of phase change material, rather than hydrocarbon-derived ones, noticeably reduces its negative environmental impact and improves the technical and economic feasibility of the solar energy system. The measured thermophysical properties of this new phase change material, relevant to heat storage, are presented for the first time. The system was tested over 12 months, and the paper highlights test results from two nine-day periods that represent typical seasonal weather in Colombia’s mountain regions. These results feature the daily dynamics in the overall system’s energy balance, with the control system providing an automatic operation by switching on and off the water flow from the solar thermal collectors to heat exchangers in the latent heat thermal energy storage and preventing its overheating and freezing during high solar radiation periods and low temperature conditions during nights, typical for the Andean Regions. The specific design of the prototype system demonstrated its capability to meet, on average, 54% of the overall thermal energy demand of the dwelling over the field test period. Six-monthly measurements of the thermophysical properties of the newly deployed phase change material demonstrated that these remained stable throughout the tests. The first experimental study on the performance of the developed solar heating system with a novel PCM for thermal energy storage over a 12-month period under high-mountain climatic conditions in the Andes Region in Colombia was conducted, yielding original test results.