Assessment of Energy Savings Using Run-Around Coil Heat Recovery in Air Conditioning Systems: A Fresh-Exhaust Air Analysis

Abstract

Medical laboratories, chemical facilities, and hospitals require large volumes of conditioned fresh air, creating substantial annual cooling loads. Because these spaces operate at high ventilation air-change rates, exhaust-air heat recovery has become essential for reducing energy use and greenhouse gas emissions. Among available HVAC strategies, the run-around coil is widely adopted to transfer thermal energy between two independent fluid circuits and recover heat from supply and exhaust airflows. This study experimentally evaluates a run-around coil system that precools fresh air using cooled return air. The effects of fresh-air inlet temperature, cooled-air inlet temperature, mass-flow-rate ratio, and coil diameter on temperature reduction and heat-exchanger effectiveness were investigated. Results show that fresh-air inlet temperature is the dominant factor: higher inlet temperatures consistently increase the fresh-air temperature difference and enhance heat-exchanger effectiveness. Effectiveness peaks when the exhaust-to-fresh mass-flow-rate ratio is near or slightly greater than unity, whereas lower ratios reduce the temperature difference or limit heat transfer. Coil geometry also plays a critical role. A larger fresh-air coil paired with a smaller exhaust-side coil produces the greatest temperature change, whereas reversing these sizes yields the smallest. These findings demonstrate that maintaining a warm, fresh-air inlet, balancing flow rates, and selecting coil diameters to match flow capacity can substantially improve system efficiency. The results confirm the run-around coil as an effective approach for reducing energy consumption and environmental impact in high-load ventilation environments.