A comparative analysis of multi-stage evaporative cooling and conventional chillers for office-scale cooling loads

The building sector accounts for a substantial share of global electricity consumption, with HVAC systems dominating energy use in large commercial buildings, particularly in developing countries. This study presents a comparative, climate-specific performance assessment of a hybrid multi-stage evaporative cooling-chiller system, with a specific focus on modifying an indirect evaporative cooling (IEC) unit by utilizing return air as the working air stream which is a configuration rarely evaluated for Indian climatic conditions. The methodology combines psychrometric analysis, real-time system modification, and detailed building heat-load calculations for a large office-scale building across multiple Indian climate zones under summer and monsoon conditions, and benchmarks three configurations: (i) stand-alone chiller, (ii) conventional IEC-chiller system, and (iii) modified IEC-chiller system. Results show that the conventional IEC configuration reduces chiller capacity by 50-60 TR, while the modified multi-stage IEC system achieves a chiller capacity reduction of 80-140 TR, depending on climate and seasonal load. For identical cooling demands, the conventional IEC system consumes 27.53% less electrical energy than a stand-alone chiller, whereas the modified IEC-return air configuration delivers a higher reduction of 34.97%. The modified system also demonstrates superior temperature reduction and wet-bulb effectiveness, particularly under humid monsoon conditions where conventional IEC performance is typically constrained. These findings demonstrate that return-air-assisted multi-stage evaporative cooling significantly enhances chiller load reduction and energy efficiency, offering a technically viable and scalable hybrid cooling solution for large buildings in diverse Indian climates.