EXPERIMENTAL ANALYSIS OF INFLUENCE OF AIR TEMPERATURE, VENTILATION AND SHADING ON COOLING LOAD AND CO₂ CONCENTRATION IN ZONE COOLING SYSTEM IN GREENHOUSE

A zone cooling system was constructed in a greenhouse (glasshouse) in Ehime University. Tomato plants were grown by hydroponics on a bench. Growing space of the tomato plants, that is, cooled space was surrounded by transparent vinyl film. An air-to-water heat exchanger with fans was installed in the cooled space. A heat pump system supplied the heat exchanger with cold water. Air in the cooled space was circulated by the fans and was cooled and dehumidified by the heat exchanger. A width, a length and a height of the cooled space were 153cm, 196cm and 110cm, respectively. Shading material which covered over the cooled space was equipped.

Ten cooling experiments were carried out for different combinations of air temperature (22, 25 or 28°C), ventilation rate (1.2, 11.8 or 23.5mh^-1) and shading ratio (0 or 53%) on sunny days in summer of 1994.

The results were as follows. Influence of the ventilation rate on the total cooling load became large according as the air temperature in the cooled space became low. Little influence of the ventilation rate on the total cooling load was observed in case of air temperature of 28°C. Average CO₂ concentration between 10:00 and 14:00 in case of ventilation rate of 11.8mh^-1 was about 200ppm, while that in case of ventilation rate of 1.2mh^-1 was below 60ppm. The results of these experiments showed the same tendency as the results of the simulation by the authors (Nishina et al., 1995).

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