A NATURALLY VENTILATED GREENHOUSE FOR TEMPERATE VEGETABLE PRODUCTION IN THE TROPICS

A naturally ventilated tropical greenhouse (NVTGS) has been developed for high value temperate vegetable production in the lowlands of Malaysia. The structure has a simple frame, transparent roof and insect screen sides. Several NVTGS have been designed, constructed and their performance evaluated. The design criteria, material selection, construction cost, maintenance and in-house environments were developed and evaluated. The structure was found to be stable, durable, reliable and required minimal maintenance, while providing an environment conducive for good vegetable production, with high quality, early harvests and higher yields compared to open field crops. Proper design and choice of covering material could control problems of extreme solar radiation, high rainfall, insects, diseases, weeds, high temperature, high humidity and reduce labor requirements. Studies on covering materials and natural ventilation inside a full scale NVTGS were conducted. Natural ventilation models were developed and verified. The ventilation was by the stack effect (temperature difference), wind effect or a combination of both effects. The natural ventilation rates that could reduce in-house air temperature, humidity and maintain carbon dioxide concentration are discussed. The importance of the physical properties of covering materials is also discussed.