Optimization of ventilation opening area of a naturally ventilated net greenhouse in a humid tropical environment.

摘要

A study was conducted to evaluate the performance of a naturally ventilated net greenhouse designed for humid tropical conditions having a large vent ratio of 1.05. The greenhouse had a size of 10 m by 20 m. An ultraviolet (UV)-stabilized plastic film was used to cover the roof, gables and lower parts of the walls. The ventilation openings in the roof and side wall were covered by UV-absorbing insect-proof screen (52-mesh). Maintaining a very large ventilation opening, however, is not always advantageous when the cost of nets and the possible migration of smaller pests into the greenhouse via the net are taken into consideration. The main objective of the study was to determine the minimum size of ventilation opening area of the greenhouse. Five levels of 100, 80, 60, 40 and 20% of total ventilation openings area were tested. The experiment was carried out with a full crop (FC) and an empty condition (EC). Temperature rise, humidity difference, transpiration rate and air exchange rate were used to evaluate the greenhouse performance. The results revealed that internal temperature was increased by 1.5 degrees C (FC) and 4.5 degrees C (EC), respectively when the ventilation opening was reduced to 20% of total ventilation area or a ratio of opening to floor area of 0.2. The internal humidity was also increased by 37.5% while the air exchange rate was reduced by 40%. The study revealed that the ratio of ventilation opening to surface floor area of 0.6 was the minimum requirement in order to maintain a favourable microclimate in a tropical greenhouse..