Etienne Chantoiseau

A DEHUMIDIFICATION STRATEGY TO AVOID CONDENSATION ON PLANTS AND SPARE ENERGY IN GREENHOUSE

The increase of fossil energy costs in the past years led producers to use more and more airtight greenhouses (air-inflated double-layer greenhouse) to reduce heat loss. Limiting air renewal however induces higher air moisture content and risks of condensation. Under such conditions, which may enhance fungal development (e.g., Botrytis), growing moisture-sensitive ornamental species may become tedious or even impossible (e.g., for cyclamen). Dehumidification may be undertaken through ventilation-heating which is however energy consuming and limits the benefits of modern greenhouses. In order to reduce energy costs, a dehumidification heat pump was set up inside a 2,350 m 2 plastic production greenhouse near Angers (West of France) to extract excess water vapour content from the inside air. This device was mainly used as a curative tool to avoid condensation according to the water vapour pressure deficit evolution. It was designed in such a way to compensate night plant transpiration and its power was only 4 W.m -2 to prevent dew point during the night. During the experiment, it was checked that no condensation occurred on the plants. Moreover, results revealed that the experimental thermodynamic and dehumidification efficiencies were high, and in agreement with values predicted by a simple model. The total energy consumption was only 120 kWh.m -2 for gas, and 14 kWh.m -2 for electricity from November to April 2011 for a 16°C set point temperature. In average, the heat pump brought 30% of the total heat input. Moreover, it was shown that the energy required by the heat pump was four to five times less than that corresponding to the ventilation-heating technique. This device thus makes it possible to grow plants that are very sensitive to humidity and fungal diseases, while reducing energy consumption as well as fungicide uses.