The building sector is a major global energy consumer, particularly in Lebanon, where heating and air conditioning demand remains high. Integrating Phase Change Material (PCM) into building envelopes presents a promising solution for latent heat storage and enhanced energy efficiency. This study investigates the optimal wall configurations for improved thermal performance using PCM in two Lebanese regions: Beirut and Bekaa. Using ANSYS Fluent, various wall configurations were analyzed to determine the most effective placement of PCM. The optimal configurations were then evaluated in DesignBuilder to estimate energy savings. Results indicate that in Bekaa, external PCM and insulation provide the best performance due to strong dependence on external conditions, whereas in Beirut, internal PCM and insulation are more effective. PCM implementation in both regions significantly reduces energy consumption, with Bekaa proving more advantageous as it does not require additional cooling mechanisms. This research underscores the potential of PCM as a viable strategy for enhancing energy efficiency in building envelopes, with relevance to the climatic conditions of Beirut and Bekaa.

Modern HVAC decarbonization demands working fluids that can operate efficiently with low-grade thermal energy, reducing reliance on compressor-driven, high-GWP vapor compression systems. This work investigates a single-effect absorption chiller using a hybrid refrigerant–absorbent system, 1-ethyl-3-methylimidazolium ethyl sulfate (LiBr + [EMIM][ESO ₄ ]/ethanol), benchmarked against conventional LiBr/H ₂ O absorption and an R410A vapor-compression baseline, each designed for the same cooling capacity. Unlike the traditional LiBr/H ₂ O pair, which typically requires generator temperatures (Tg) of 80°C–90°C, the proposed ternary mixture achieves stable operation at substantially lower driving temperatures (50°C–65°C) while sustaining superior performance. At Tg = 50 °C, the system attains a COP about 15% higher than LiBr/H ₂ O. Over a 30-year lifetime, the elimination of compressor electricity demand relative to R410A translates into nearly half the total climate impact, with the Life Cycle Climate Performance (LCCP) cut by 47%. Sensitivity analysis indicates an optimal operating window of Tg 45°C–55°C with weak-solution concentrations of 52.7%–55%. These results highlight the novelty of the LiBr + [EMIM][ESO ₄ ]/ethanol pair: enabling absorption cooling to transition from high-grade thermal input to low-grade sources such as solar thermal or industrial waste heat, while achieving higher COPs than conventional refrigerants. Although simulation-based, the findings motivate experimental studies to verify vapor–liquid equilibrium, viscosity, and stability of the mixture, as well as safety protocols addressing ethanol flammability. The techno-economic analysis indicates that competitive payback is achievable only when both abundant low-grade heat is available and electricity tariffs are elevated; outside these conditions, the economic viability remains limited. Collectively, this positions the proposed ternary pair as a promising pathway for low-temperature, low-carbon cooling, contingent on experimental validation.

The intermittent nature of renewables has increased the reliance on energy storage technologies to boost the efficiency and stability of power systems. Adiabatic Compressed Air Energy Storage (A-CAES) systems, which recover and reuse the heat generated during compression, have attracted significant attention in recent years. While A-CAES combined with thermal energy storage (TES) systems show promising potential, especially in renewable-integrated power systems, their commercial implementation remains limited, with only a few A-CAES power plants operating and which rely solely on sensible heat storage. The relatively low energy density of sensible heat storage opens the door to exploring latent heat storage (LHS) systems using Phase Change Materials (PCM’s), which could play a significant role in enhancing the performance of A-CAES systems. Although high-temperature PCM’s have demonstrated efficiency benefits in concentrated solar plants and energy-intensive industries, their integration into A-CAES systems requires further exploration. Accordingly, this paper aimed at simulating and assessing the performance of a combined A-CAES and PCM-based LHS system coupled to a gas turbine and an air turbine, alongside a wind farm. The simulations were conducted for charging durations ranging between 2 and 10 hours, with a fixed 2-hour discharge operation. The resulting fuel-saving efficiency in the gas turbine configuration improved with extended charging durations, ranging between 63.8 % and 66.1%. Furthermore, the exergetic roundtrip efficiency remains higher in the gas turbine configuration for charging durations shorter than 7 hours. Beyond this threshold, however, the air turbine configuration becomes more appealing when the combined CAES–LHS systems are coupled to it, exhibiting higher exergetic roundtrip performance under extended charging conditions. These findings, although theoretical in nature, could serve as a starting point for estimating the performance of the combined CAES-LHS systems and promoting their deployment into power generation applications in a renewable energy context.

The use of Latent Thermal Energy Storage (LTES) systems in Adiabatic Compressed Air Energy Storage (ACAES) systems is expected to significantly improve the performance of electricity-generating turbines. This improvement is particularly notable when medium- and high-temperature Phase Change Materials (PCM's) are employed as the storage medium. The relevant literature is abundant with analytical formulations that are intended to model the thermal behavior of large-scale PCM-based LTES systems. While these formulations offer valuable insights, they are mostly validated using experimental or theoretical studies conducted on reduced versions of the full-size storage systems. In an attempt to build on existing literature, this paper proposes an analytical model to simulate the thermal behavior of an industrial-scale PCM-based Shell-and-Tube Heat Exchanger (STHE). In this configuration, compressed air flowing in the shell exchanges heat with a medium- or high-temperature PCM stored in the tubes. The analytical model was validated using a series of Ansys^® Fluent^® Computational Fluid Dynamics (CFD) simulations conducted on a full-scale model using a variety of PCM's. It was demonstrated that the analytical model, which is based on the Kern method, can successfully predict the PCM phase change fraction evolution with a Root Mean Square Error (RMSE) of less than 0.05, and the compressed air outlet temperature with a Mean Absolute Percentage Error (MAPE) of less than 3%, for PCM Stefan numbers less than 2, at a speed 864 times faster than CFD simulations. Hence, the proposed model can serve as a quick remedy for resource-intensive CFD simulations and costly experiments, which further promotes the integration of PCM-based LTES systems into A-CAES systems.