greenhouse temperature
How to meet the temperature requirements for crop growth in greenhouses
The indoor air design temperature is usually set by greenhouse construction companies based on the design requirements of the greenhouse-temperature. It is derived from the type, variety, growth stage (or growth period) of the crops to be planted in the greenhouse, as well as the cultivation season (the time of the entire crop cycle in a year). For example, tomatoes have different greenhouse-temperature requirements at different growth stages: the suitable temperature for seed germination is 25 to 30°C, with 28°C being the optimal temperature. Most varieties have a low germination rate above 35°C and germination is difficult above 40°C. The temperature requirements during the seedling stage are different. They have strong adaptability. The suitable temperature during the day is 23 to 28°C. If the temperature is too high, the seedlings will grow easily. The flowering stage requires a higher and stricter greenhouse-temperature. Generally, 25 to 28°C is appropriate. If it is higher than 33°C, it will cause flower drop. The temperature during the fruiting stage is generally 25 to 28°C during the day. There are strict temperature requirements for fruit coloring. 19 to 24°C is conducive to the formation of lycopene, while temperatures above 30°C are not conducive to coloring.
Although the maximum cooling load must be estimated during ventilation design, for the suitable temperature range of 25 to 28°C for tomato cultivation, it is not necessary to determine the design value based on the lower limit, as other parameter values are considered in the calculation to meet the minimum requirements. Therefore, the cooling load estimated based on the upper limit of 28°C can already meet the temperature requirements throughout the entire growth period of the crop. However, considering the economy of equipment configuration and greenhouse construction, the upper limit of the suitable greenhouse-temperature is not the only option. According to cultivation practices, as long as the nighttime temperature can be lowered and the average daytime temperature can be controlled at 21°C, the temperature requirements for tomatoes can be met. For example, the daily maximum temperature control target can be set at 30 to 32°C, as long as the nighttime temperature can be reduced to keep the average daytimegreenhouse-temperature at 21°C, the temperature requirements for tomatoes can still be met. Therefore, for regions with large diurnal temperature differences and good lighting conditions, the indoor air design temperature can be higher than the upper limit of the suitable greenhouse-temperature, but should not exceed the maximum temperature limit.
