The research topic aims to address the urgent need for enhanced energy efficiency in HVAC systems by developing and optimizing efficient heat transfer fluids. Despite the significant attention given to single-component nanofluids, there is a lack of systematic study on the performance of Al2O3-CuO hybrid nanofluids in a double-pipe heat exchanger for HVAC system applications. A comprehensive experimental investigation was done on the various hybrid nanofluid concentrations (0.05%, 0.1%, 0.15%) under different Al₂O₃:CuO ratios (70:30, 60:40, 50:50) at Reynolds number 3,000-12,000. Results show that 60: 40 Al2O3:CuO hybrid nanofluid of 0.1% concentration exhibits a 42.3% enhancement in Nusselt number, 38.7% increase in heat transfer coefficient and 28.4% improvement in thermal effectiveness over that of pure water, with tolerable friction penalties (15-22%). The obtained performance shows a remarkable increase when compared with other published works. The current correlation has 42.3% higher increase with 13.8% reported by Suresh et al. for Al2O3-Cu and 31% with Madhesh et al. for Cu-TiO2 hybrid nanofluids. The hybrid shows a 35.5% improvement over the single Al2O3 nanofluids and 13.5% improvement over CuO. A significant increase is shown in this work of 18-25 % as compared to single nanoparticles by using a hybrid system. It can be concluded that in the current research work, the experimental correlations were developed and validated which could be used to implement the hybrid nanofluids in the advanced energy-efficient HVAC systems. Finally, the study has developed validated experimental correlations which enable the implementation of hybrid nanofluids in advanced HVAC systems to achieve higher energy efficiency.