This case study analyzes a cryogenic air separation unit (ASU) with a production of ${\dot{V}}_{O_2}=\mathrm{58,300} \left[\frac{m^{3}N}{h}\right]$ of gaseous oxygen with a concentration greater than 98.5%, operating in Romania on a steel plant platform. The goal of the paper is to provide an extensive model of exergetic analysis that could be used in an optimization procedure when decisional parameters are changed or structural design modifications are implemented. For each key part of the Air Separation Unit, an exergetic product and fuel were defined and, based on their definition, the coefficient of performance of each functional zone was calculated. The information about the magnitude of the exergetic losses offers solutions for their future recovery. The analysis of the exergy destructions suggests when it is worth making a larger investment. The exergetic analysis of the compression area of the ASU points out an exergy destruction and loss of 37% from the total plant’s electrical energy input. The exergy loss with the heat transferred to the cooling system of compressors can be recovered; for the exergy destruction portion, the challenge between investment and operating costs should be considered. The exergy destruction of the air separation columns found the High Pressure Column (HPC) to be more destructive than the Low Pressure Column. The share of the exergy destruction in the total plant’s electrical energy input is 8.3% for the HPC. The local COP of the HPC, calculated depending on the total exergy of the local product and fuel, is 62.66%. The calculus of the air separation column is performed with the ChemSep simulator.

The use of organic Rankine cycles (ORCs) is a viable solution for the recovery of waste heat. For an air separation unit (ASU) with a production of ${\dot{\mathrm{V}}}_{{\mathrm{O}}_2}={58300}^{}\left[{\mathrm{m}}_{\mathrm{N}}^3/\mathrm{h}\right]$ operating in Romania, the value of utilization of the heat transferred to the cooling system of the compression area represents 21% of the global system electrical energy input. To recover this thermal energy and transform it into mechanical energy, an ORC system was proposed. To maximize the production of mechanical power, an exergy analysis was performed. Exergy analysis was used to choose the most suitable organic fluid and find the optimum constructive structure of the Rankine cycle. The calculation of the exergy destruction in the key apparatuses of the system allowed investigation into the optimization search procedure. The large exergy destruction in the liquid preheater suggested the decrease in the temperature difference in this part of the evaporator by increasing the inlet temperature of the liquid; and an internal recuperative heat exchanger was used for this purpose. When permitted, the overheating of the vapors also reduced the temperature difference between the heat source and the organic fluid during the heat transfer process. The analysis was comparatively performed for several organic fluids such as R-245fa, R123, n-pentane and R717. The use of ammonia, that offered the possibility of superheating the vapors at the turbine inlet, brought a gain of mechanical power corresponding to 6% economy in the electrical energy input of the global plant.

The paper identifies and describes the possibilities for heat and mechanical energy recovery within refrigeration systems using CO₂ as a working fluid, employed in commercial and industrial applications. The heat and mechanical energy recovery methods that can be utilized for beneficial purposes are taken into consideration. These methods could increase the energy efficiency of the refrigeration system or the building in which it operates. This paper summarizes various configurations and recovery methods and critically compares and evaluates them (COP improvements, exergy performance, and system integration complexity) based on the data available in the literature. As a result, the internal heat exchangers can be used as a superheater, in which case the COP can increase to 35%. If the internal heat exchanger is used as a subcooler, it could lead to a COP increase of 17% compared to a CO₂ refrigeration system without subcooling for an evaporating temperature of −10 °C and the temperature of the gas cooler outlet of 30 °C. The heat and mechanical energy recovery possibilities are presented using the available scientific literature.

This study investigates steady-state conductive heat transfer and water-vapor diffusion through the external wall of a refrigerated warehouse with a specified load-bearing wall assembly. The formal analogy between heat conduction and mass diffusion is stated and used to establish a practical calculation framework for estimating heat and moisture ingress through multilayer cold-store walls. Calculation routines are presented to determine the temperature field and the corresponding water-vapor saturation and partial-pressure distributions across (and within) the insulation layer, enabling the identification of regions prone to interstitial condensation. The analysis highlights the roles of (i) the vapor diffusion resistance of the vapor barrier layer, (ii) the thermal resistance of the insulation, and (iii) key outdoor boundary conditions in governing condensation risk. Increasing insulation thermal resistance reduces external heat gains; however, it may also increase the likelihood of condensation in layers close to the cold side by lowering local temperatures and saturation pressures. Among external parameters, outdoor relative humidity exerts the strongest influence on interstitial condensation risk. For the investigated wall assembly, increasing outdoor relative humidity by 50% shifts the condensation onset location within the insulation toward mid-thickness. The effects of vapor barrier diffusion resistance, insulation thermal resistance, and changes in outdoor conditions (relative humidity, temperature, and wind speed) are reported in tabulated form and illustrated through pressure–position and temperature–position profiles.