Polytube Ventilation Air Heat Exchanger: Performance of One Design

Acounterflow air-to-air heat exchanger proposed for ventilation heat recovery in greenhouses or animal shelters was tested in the laboratory. The exchanger was constructed with 10.2 m (33.5 ft) long, 200 mm (8.0 in.) diameter polyethylene film tubes installed along one side of a 530 mm (21 in.) wide, 2.4 m (8.0 ft) high hallway; the cold fresh ventilation air flowed through the tubes while the hot exhaust ventilation air flowed down the hallway along the outside of the tubes. Heat transfer characteristics were determined over a matrix of warm air inlet configurations, air flows, cold air inlet temperatures, and warm air inlet relative humidities. Typical values for overall heat transfer coefficient, temperature-based effectiveness, and enthalpy-based effectiveness were 3.62 W nr2 C1 (0.64 Btu h1 ft2 F1), 0.240 and 0.148, respectively. The performance of this exchanger was better than for a wall surface heat exchanger of similar design tested earlier and reported in the literature. Example design calculations are presented.