Enhancing cold storage efficiency: Sustainable apple pre-cooling utilizing polyethylene glycol and waste coconut oil as phase change materials for chilled energy recovery from air-conditioning condensate

Abstract

Thermal energy systems can be upgraded by integrating them into thermal energy storage systems. Furthermore, reliability can be increased by using locally available waste materials. In this study, waste coconut oil (WCO) from a nearby bake shop and polyethylene glycol (PEG) were used as phase change materials (PCMs) in thermal energy storage systems for pre-cooling apples in cold-storage plants. Field assessments of cold-storage plants and energy, exergy, economic, and environmental analyses were conducted to determine the system feasibility. The exergy efficiency increased from 11 to 90 % for the condensate flow rates from 2.5 to 8.3 L/h at 11 ± 1 °C, achieving 3 °C pre-cooling. Similarly, a 13–21 % reduction in the WCO solidification time was found. PCM-apple direct contact discharging experiments attained pre-cooling through natural and forced convection of 3.4 and 4.1 °C and 2.5 and 3.2 °C for PEG and WCO, respectively. Effective condensate utilization at 11 ± 1 °C obtained 75 % energy savings. The life cycle cost favored WCO over PEG 600, resulting in savings of $168 and a payback period of less than 6 months. Environmental assessments highlighted the energy-saving potential of air-conditioning condensates and efficiency of WCO in recovering condensate chilled energy for optimal apple pre-cooling in cold storage facilities.