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The Application of Nanofluids, Bio-Based PCMs, Hydrates, and Natural Refrigerants in Renewable Energies

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Dear Colleagues,

Nanofluids, bio-based phase change materials (PCMs), hydrates, and natural refrigerants are emerging technologies that play a key role in renewable energy systems. Nanofluids enhance heat transfer performance, improving the efficiency of solar collectors and thermal storage systems. Bio-based PCMs allow sustainable thermal energy storage by storing and releasing heat with minimal environmental impact. Gas hydrates offer high energy density storage potential, especially for cooling and gas transportation applications. Natural refrigerants such as CO₂, ammonia, and hydrocarbons reduce greenhouse gas emissions compared to synthetic alternatives. These solutions support more efficient, eco-friendly, and resilient renewable energy applications.

This Special Issue aims to investigate the most recent advances related to the theory, design, and application of nanofluids, bio-based PCMs, hydrates, and natural refrigerants in the field of renewable energies.

The Special Issue welcomes review papers, in addition to theoretical, numerical, and experimental research with technical applications in, but not limited to, the following topics:

Nanofluids;

Heat transfer enhancement using nanofluids;

Thermodynamic and fluid dynamic analysis of energy systems;

Hydrogen production, storage, and utilization;

Hydrates;

Bio-based PCMs for thermal storage technologies;

Compact and micro-scale energy storage devices;

Natural refrigerants;

System integration and optimization techniques;

High-performance heat exchangers and cooling systems;

All of the above topics—along with emerging challenges and innovations in thermodynamics and fluid mechanics for renewable energy sources—are welcome for this Special Issue. We look forward to your contributions.

Dr. Eugenia Rossi Di Schio
Dr. Paolo Valdiserri
Guest Editors

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29 pages, 16754 KB

Open AccessArticle

Thermodynamic Comparison of Two- and Three-Stage Cascade Refrigeration Systems: A Dynamic Energy Assessment in Hospital Environments

by Eugenia Rossi di Schio, Oğuzhan Pektezel and Paolo Valdiserri

Energies 2026, 19(15), 3598; https://doi.org/10.3390/en19153598 - 31 Jul 2026

Viewed by 407

Abstract

The design of ultra-low-temperature refrigeration systems has gained increasing importance in recent years, driven by the growing demand for very-low-temperature storage cabinets for many applications, such as the preservation of vaccines and biological materials. In the first part of this study, the thermal design of both two-stage and three-stage cascade refrigeration systems was developed using the Engineering Equation Solver (EES). The systems were evaluated under evaporator temperatures of −85 °C, −80 °C, and −75 °C and ambient temperatures ranging from −5 °C to 40 °C. For the two-stage configuration, the R170/R161 refrigerant pair was assessed as an alternative to the conventional R170/R290 combination. In the three-stage configuration, the performance of the R1150/R170/R290 and R1150/R170/R161 refrigerant combinations was analyzed. The results indicate that under identical operating conditions, the three-stage system demonstrated lower compressor power consumption and reduced exergy destruction compared to the two-stage configuration, while achieving higher coefficients of performance (COPs) and exergy efficiency. In the second part of the study, long-term dynamic simulations of energy consumption for both two-stage and three-stage systems were carried out using TRNSYS 18 under varying ambient temperature conditions. The simulations were performed for hospital installation rooms located in three different cities: Muğla (Turkey), Milan (Italy), and Warsaw (Poland). The results of the dynamic simulations indicate that the use of R161 leads to significant energy savings compared to R290. Specifically, when comparing the three-stage cascade system using R1150/R170/R161 with the conventional two-stage R170/R290 system, energy consumption reductions of 20.5% in Warsaw, 23.6% in Milan, and 26.6% in Muğla were achieved. Full article

(This article belongs to the Special Issue The Application of Nanofluids, Bio-Based PCMs, Hydrates, and Natural Refrigerants in Renewable Energies)

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