Under the Healthy Greenhouse project, Wageningen UR Greenhouse Horticulture has for the first time controlled the greenhouse climate based on several wireless sensors for temperature and humidity. The goal was to control the climate based on the spot in the greenhouse with the lowest vapour deficit. Because the climate from place to place and over time may vary, this place will not always be the same. The climate computer performs as if the climate box may roam, and can intervene immediately as somewhere the moisture deficit falls below the threshold.
Growers can now prevent that condensation will occur at a local cold spot. The climate is more homogeneous, and a more humid level can be kept, which means less energy is required for dehumidification. For a tomato crop in the period 2014-2015, with an increase of the RH by 5%, windows kept close longer, and up to 10% of energy could be saved.
Growers look for opportunities to realize a more homogeneous climate, lower energy consumption and lesser diseases. The results are encouraging, and the tests have shown that the principle works. However, if there is already a homogeneous climate, no extra energy can be saved with this strategy. However, the controller can continue to respond quickly to local wet spots.
To see if the results are achievable for a whole year, under different growing conditions and in other crops, further research should be carried out. Also, growers still have many questions: "How much humidity can we allow to save energy safely, and to what extend does opening of windows and doors and switching of fans influence the working of the controller?"
The roaming measuring box controller is not yet available. However, companies are interested to sell it as an option for their climate computer. The wireless sensors are already on the market, and can be deployed. With these, growers can all learn a lot about the homogeneity of their climate.