Wireless measuring system identifies cold and wet spots in greenhouses

Horizontal and vertical climate differences in greenhouses are unwanted. In current practice the number of measuring boxes is too low to detect such differences. SmartDust is the wireless system of sensors developed by Wageningen UR Greenhouse Horticulture that gives growers better insight in the greenhouse climate. This information enables optimisation of climate control, which leads to energy savings.

Wet and cold spots are unwanted in a greenhouse. Horizontal and vertical temperature differences, however, can hardly be avoided as result of greenhouse construction, irradiation, wind, or other natural forces. `Heat drying´ is a common measure to avoid damp spots in the greenhouse. But each degree of extra heating, however, costs up to ten per cent energy.

Accurate information about horizontal and vertical climate differences is required to avoid unnecessary ´heat drying´. In current practice the number of measuring boxes per compartment is usually too low for taking adequate measures. Wageningen UR Greenhouse is therefore working on the development of a cheap and practical wireless measuring system. This SmartDust system will much more accurately then has been possible until now collect information about wet and cold spots in the greenhouse. Such a system can lead to energy saving and better crop quality because it gives growers a better tool for reacting to climate differences.

Ten sensors per ha
The wireless measuring system has been tested in practice in the 2008-2009 season. The sensors have been tested in the cultivation of tomato, cucumber, gerbera and Matricaria with a density ranging from 60 to 128 sensors per hectare. The way in which cool-wet spots manifest themselves under different conditions such as day/night, open/closed screen, and seasons has been investigated.
The wireless system was found to perform well and the sensors do under normal conditions serve their purpose. During daytime, however, strong irradiation can still cause inaccuracies and the sensors are less reliable during the night, at air humidities close to 100%. Structural deviations can be detected by averaging the recorded data over a longer period of time – at least one daily period.
The researchers conclude that around ten sensors are required per hectare to make sure that no cold-wet spots are missed. The use of wireless sensors is not only useful for occasional characterisation of the greenhouse but also for permanent monitoring. The obtained information then enables structural modification of the greenhouse or application of specific climate control to homogenise the climate and to achieve further energy savings.