Novel control of run-around heat recovery system: Evaluation of the novel control method’s performance through laboratory experiments

Abstract

Run-around coil (RAC) systems are particularly well-suited for applications requiring complete separation between supply and exhaust airflows, such as hospitals, laboratories, and other facilities with stringent hygiene or contamination control requirements. Unlike rotary or plate type heat exchangers, RAC systems ensure full airstream separation while offering design flexibility and modular installation, making them appropriate for complex and specialized ventilation scenarios. However, their efficient operation critically depends on the accurate control of the circulating liquid flow rate to achieve optimal heat recovery performance. Traditional control strategies regulate liquid flow based on balancing the heat capacity flow rates of air and liquid media, which requires accurate real-time knowledge of their thermophysical properties. This approach becomes challenging in dynamic operational environments, especially under demand-controlled ventilation (DCV) conditions, where airflows fluctuate in response to changing occupancy. Moreover, accurately measuring flow rates and properties in real-time often increases system complexity, limiting the practicality of such control strategies. To address these challenges, a novel temperature-based control method was developed and evaluated through laboratory experiments. This new approach relies on temperature measurements, rather than flow measurements or thermophysical property estimations, to regulate the system. The method aims to enhance system adaptability, reduce measurement uncertainties, and maintain stable heat recovery performance across a wide range of ventilation demands and external conditions. The experimental evaluation focused on testing this strategy's effectiveness, robustness, and responsiveness compared to conventional flow-based control methods. The results demonstrate that the temperature-based control method (Xt) offers a reliable and efficient alternative, particularly in applications where fluid properties are variable or where accurate flow sensors are impractical. With appropriate tuning of control parameters, specifically the proportional and integral settings, the method achieved consistently high effectiveness and system stability across variable conditions. The findings suggest strong potential for integrating this novel control approach into both new and existing RAC installations, supporting improved energy efficiency and simplified operation in real-world DCV systems.