The rating performance of a run-around heat recovery system using a two-phase gas-liquid as the coupling fluid is investigated. A laboratory test facility is used to measure the thermal and flow behaviour of the run-around system with the supply coil inside an environmental chamber and an exhaust coil supplied by room air. This two-phase, gas-liquid flow, with a bubbly flow pattern, was supplied to a run-around system composed of two single-row coils, a pump, a phase separator, and a supply of compressed air. Data were measured over a range of operating conditions to develop pressure drop and heat transfer correlations for the gas-liquid coupling fluid. The overall effectiveness of the run-around system is simulated using previously developed correlations of the heat transfer coefficients on both the coupling fluid and air sides of the heat exchangers and pressure drop for the coupling fluid. These simulation results agreed well with experimentally determined overall effectiveness, which is typically 20% higher when the gas-liquid coupling fluid is used than the same system without gas injection.

KEYWORDS: performance, heat recovery, run around coils, heat exchangers, ventilation, testing, climate chambers, measuring, heat flow, pressure drop, heat transfer coefficient, experiment, exhaust air