1987 年 43 巻 1 号 p. 15-20
This paper describes climatic factors in the greenhouses ventilated with two different systems; forced ventilation and natural roof ventilation. The author discusses 1) the profile of inside air temperature related to that of solar radiation, 2) horizontal distribution of inside air flow velocity and carbon dioxide concentration, and 3) photosynthetic rate of a tomato crop.
Air temperature varied according to the height from the floor surface. Since the amount of solar radiation at the lower part in the plant canopy was smaller than that at the upper part, the air temperature decreased at the lower part. This decrease in temperature became larger with the increase in LAI. In the naturally ventilated greenhouse, a low temperature spot was observed close to the roof ventilators, through which the outside air came into the inside. The temperature in the spot was lower than that at the same position in the greenhouse ventilated with fans.
Horizontal patterns of inside air flow velocity was similar to those of carbon dioxide concentration. The air flow velocity was large at the early stage of crops, but was reduced at the later stage in the naturally ventilated greenhouse. In the fan ventilated greenhouse, the incoming air descended to the floor surface at the early stage of crops, and thus carbon dioxide was supplied to the crops. As the crop stage became later, the area with large air flow velocity expanded in the whole greenhouse. Under such a condition a clear decline of carbon dioxide was observed from the inlet to the outlet of the air.
The author estimated the reduction of photosynthetic rate due to the drop in carbon dioxide concentration. The percent reduction was 7-15% (LAI=1.0) and 22-32% (LAI=3.5) in the naturally ventilated greenhouse; about 10% (LAI=1.0) and about 25% (LAI=3.5) in the fan ventilated greenhouse.