Research in semi-closed greenhouses has shown that during the night local differences in temperature and humidity can be up to 8 degrees and 30%. With a single climate box per compartment, condensation on leaves cannot be recognized in all parts of the greenhouse. To prevent disease, a wider VD margin should be set to the climate computer, and any extra energy should be taken for granted.
Within the project ‘The Healthy Greenhouse’ a study is undertaken to see if climate control based on multiple sensing points is possible. The goal is to avoid condensation by controlling on the spot with the lowest moisture deficit, and save energy at possible moments by using a smaller margin.
Because the climate may vary locally, and the lowest deficit spot may not always be at the same place, the climate computer performs as if the climate box may roam, and can intervene immediately and anywhere the moisture deficit falls below the threshold.
New controller with homogeneous climate and less energy use
At Straelen (D), in the spring of 2014, researchers from Wageningen UR Greenhouse Horticulture for the first time controlled the climate based on multiple wireless sensors for temperature and humidity. The operation of the new controller (with 8 sensors), has been compared with that of the single climate box in a tomato greenhouse of 250 m2, at two wider humidity margins of 3% and 5%, in two periods of a month. In both situations, the roaming monitoring box gave a more homogeneous climate, and there was less energy used, sometimes up to 10%.
These results are encouraging. Further research in other seasons and for other crops is needed to see whether these results are truly achievable under all circumstances.
The roaming monitoring box will be presented at the Demo Day Healthy Greenhouse 2014 in October.