Abstract

Oncidium are planted in open protected culture or under shading nets in subtropical regions. Because of the lack of cooling techniques for the inside microclimates, the production period is limited, and the quantity and quality of flowers is unstable. Without ventilating, high humidity and temperature induces severe growth problems. In this study, mechanical ventilation fans with intermittent misting were applied to modify the internal microclimate of the Oncidium greenhouse. Nine experimental setting of misting intervals were tested. The misting efficiency is defined and served as the performance index. The misting intervals of 3 min on to 3 min off or 5 min on to 5 min off had the higher efficiency. The cooling technique can keep the interior air temperature lower than that of outside air temperature. The temperature of plants could be maintained close to the greenhouse air temperature. The intermittent misting function with the best evaporative cooling efficiency was controlled with interval operation. This technique can be applied to other protected structures of Oncidiumand other orchids.

Key words: Shading nets, misting cooling, tunnel greenhouse, Oncidium.

Abbreviation

Nomenclature: ME, Misting efficiency (decimal); RH_in, relative humidity of the greenhouse (%); RH_out, relative humidity of the ambient air (%); T_db,a, dry bulb temperature of the ambient air (°C); T_i, dry bulb temperature of the greenhouse (°C);T_leaf, leaf temperature (°C); T_medium, medium temperature (°C); T_out, temperature of outside air (°C); T_stem, stem temperature (°C); T_wb,a, wet bulb temperature of the ambient air (°C); t_ri, recording interval (s); V, air velocity (ms^-1).