Waste materials as the potential phase change material substitute in thermal energy storage system: a review

Energy and environmental analysis of a condensate recovery thermal energy storage for the building cooling system

In the pursuit of sustainability and reduced environmental impact, waste-to-energy conversion methods are gaining importance. This study investigates the untapped potential of air-conditioning (AC) condensate as a source of chilled energy in AC systems of varying cooling capacities expressed in tons of refrigeration (TR) including 10 TR, 25 TR, and 50 TR. Field assessments revealed daily condensate generation of 37-148 L at 15 ± 1 °C, indicating significant cooling potential for energy recovery. Waste coconut oil (WCO) is proposed as a phase change material (PCM) for this purpose, aiming to examine its thermal characteristics and effectiveness for energy storage. Characterization of WCO reveals a latent heat of 101 J/g and a phase transition temperature of 22.1 °C. Thermal degradation occurs between 346 and 462 °C, while stability is maintained below 60 °C. WCO exhibits solid thermal conductivity of 0.181 W/mK at 10 °C and liquid conductivity of 0.175 W/mK at 30 °C, with specific heat capacities of 1.19 J/g K (solid) and 2.43 J/g K (liquid), ensuring efficient heat transfer during phase change. A pilot experiment examines the charging and discharging dynamics of WCO. It achieves complete solidification in 160 min at a freezing temperature of 21.3 °C, with 1.1 °C supercooling. During melting at ambient conditions (32 ± 1 °C), it takes 92 min, with a melting temperature of 21.9 °C. The study extends to evaluate the reduction in environmental impact through life cycle assessment (LCA). The significant impact values such as acidification, eutrophication, ozone depletion, fossil depletion, climate change, and metal depletion are calculated using the ecoinvent database. Overall, our study underscores the promise of WCO-based energy recovery systems in advancing sustainability efforts within the realm of air conditioning.

A comprehensive review of critical analysis of biodegradable waste PCM for thermal energy storage systems using machine learning and deep learning to predict dynamic behavior

This article explores the use of phase change materials (PCMs) derived from waste, in energy storage systems. It emphasizes the potential of these PCMs in addressing concerns related to fossil fuel usage and environmental impact. This article also highlights the aspects of these PCMs including reduced reliance on renewable resources minimized greenhouse gas emissions and waste reduction. The study also discusses approaches such as integrating nanotechnology to enhance thermal conductivity and utilizing machine learning and deep learning techniques for predicting dynamic behavior. The article provides an overall view of research on biodegradable waste-based PCMs and how they can play a promising role in achieving energy-efficient and sustainable thermal storage systems. However, specific conclusions drawn from the presented results are not explicitly outlined, leaving room, for investigation and exploration in this evolving field. Artificial neural network (ANN) predictive models for thermal energy storage devices perform differently. With a 4% adjusted mean absolute error, the Gaussian radial basis function kernel Support Vector Regression (SVR) model captured heat-related charging and discharging issues. The ANN model predicted finned tube heat and heat flux better than the numerical model. SVM models outperformed ANN and ANFIS in some datasets. Material property predictions favored gradient boosting, but Linear Regression and SVR models performed better, emphasizing application- and dataset-specific model selection. These predictive models provide insights into the complex thermal performance of building structures, aiding in the design and operation of energy-efficient systems. Biodegradable waste-based PCMs' sustainability includes carbon footprint, waste reduction, biodegradability, and circular economy alignment. Nanotechnology, machine learning, and deep learning improve thermal conductivity and prediction. Circular economy principles include waste reduction and carbon footprint reduction. Specific results-based conclusions are not stated. Presenting a comprehensive overview of current research highlights biodegradable waste-based PCMs' potential for energy-efficient and sustainable thermal storage systems.

Phase Change Materials for Renewable Energy Storage at Intermediate Temperatures

Thermal energy storage technologies utilizing phase change materials (PCMs) that melt in the intermediate temperature range, between 100 and 220 °C, have the potential to mitigate the intermittency issues of wind and solar energy. This technology can take thermal or electrical energy from renewable sources and store it in the form of heat. This is of particular utility when the end use of the energy is also as heat. For this purpose, the material should have a phase change between 100 and 220 °C with a high latent heat of fusion. Although a range of PCMs are known for this temperature range, many of these materials are not practically viable for stability and safety reasons, a perspective not often clear in the primary literature. This review examines the recent development of thermal energy storage materials for application with renewables, the different material classes, their physicochemical properties, and the chemical structural origins of their advantageous thermal properties. Perspectives on further research directions needed to reach the goal of large scale, highly efficient, inexpensive, and reliable intermediate temperature thermal energy storage technologies are also presented.