Impact of heating location and mechanical ventilation on climate distribution inside a greenhouse cucumber crop

Abstract

Cucumbers grown in heated greenhouses represent an important economic activity in western France (Loire Atlantique). Heating makes it possible to crop three times a year, but with high energy consumption, corresponding to 20-40% of the total cost. It is therefore necessary to improve energy efficiency while maintaining the productivity and quality of cucumbers. With this in mind, two heating treatments were tested inside a greenhouse compartment (307 m(2)): one with heating tubes at a low position inside the canopy and the second one with heating tubes at the upper limit of the canopy. Considering a second, identical greenhouse compartment, the impact of adding mechanical ventilation (5 volumes h(-1)) was also tested. These compartments were equipped with sensor chains (temperature and humidity probes). Each chain consisted of four series of sensors placed at different heights. Additional thermocouples measured leaf and fruit temperatures. The results indicate that a lower location of the heating pipes reduced the vertical temperature gradient and also increased the temperature at the bottom of the plants. Ventilation also contributed to homogenization of the vertical distribution of temperature and humidity and favoured higher temperatures at the bottom of the canopy. It is therefore expected that heating pipes at the bottom of the canopy combined with ventilation could increase the energy efficiency of the greenhouse. Assessment of fruit and leaf temperatures also showed that the risk of reaching the dew point on fruits and leaves was reduced when heating was at the lowest position and when ventilators were running.