Applicability of forced-air and ridge ventilation for cooling of side net-covered tropical greenhouses.

摘要

This experiment was conducted to evaluate the effectiveness of the prevailing static ventilation methods and selected alternative methods for greenhouse cooling under variable wind speeds and directions in the central highlands of Sri Lanka using single span side net-covered venlo-type greenhouses. Two static ventilation methods with equal opening areas (two directional alternate ridge vents and single directional continuous ridge vent) were compared with forced-air intake and exhaust ventilation methods. Replicated climatic data were collected using an automatic data acquisition system. Wind direction was inconsistent while the mean wind speed was 0.5 m second-1 during the experiment. Alternate ridge and continuous ridge ventilation together with side nets could reduce the temperature difference up to 1.1-0.9 and 1.3-1.1 degrees C, respectively at the mean external temperature of 31-1.2 degrees C. Further reduction of the temperature difference by 0.34-0.21 degrees C was possible when forced-air intake was combined with the continuous ridge and side net ventilation. The effectiveness of forced-air exhaust and side net ventilation (without ridge vents) as a cooling mechanism was much lower than the static ventilation method. Regarding the cost-effectiveness, static ventilation appeared to be more applicable for cooling of single-span greenhouses under tropical conditions. Alternate ridge vent is more efficient and user-friendly due to its relatively stable cooling effect under variable wind directions. Meanwhile, forced-air intake system can be used for situations with low winds and in situations where more accurate temperature control is needed. Further improvements of the forced-air exhaust ventilation can also be suggested, considering its special attribute of complete protection against the entry of pests..