Physiological consideration in the development of a crop protection structure in the tropics
2000
Rezuwan Kamaruddin
Some temperate vegetable can be grown in the tropical lowlands. However, existing conventional open field farming system faces high risks due to extreme solar radiation, high rainfall, hot and humid. In addition, damages by insects and diseases are also very crucial. These problems have been addressed by introducing a crop protection structure incorporated with natural ventilation system. The structure has a simple structural frame, transparent roofing sheet and insect screen sidewall that modifies an open field environment. Transparent roofing protects crop against rainfall, transmits short wave radiation for photosynthesis and filters long wave radiation, which is detrimental for the crop. The screen excludes insects from entering and provides an opening for ventilation. High ventilation is essential in the enclosed structure. It reduces in-house air temperature, humidity and maintains carbon dioxide level. Natural ventilation model has been developed and tested on a full-scale crop protection structure. The study found that the calculated and measured ventilation rates were in a good agreement. The temperature, humidity, light intensity and carbon dioxide differences between inside and outside of the structure were found 2-4°C (inside is higher), 5-10 %, 15 -40% and 10-40 ppm in the afternoon respectively. The ventilation driving forces were due to the stack effect or temperature different between inside and outside, wind effect and a combination of both stack and wind effects.
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