Sensor networks offer low-cost monitoring option

Horti Fair seminar explores how wireless sensor networks have made cost of monitoring in glasshouses more affordable.

With the trend towards bigger and more closed glasshouses, growers need to monitor constantly the different temperatures and relative humidity across the whole growing area to ensure uniformity and reduce disease pressure.

But a seminar at last week's Horti Fair heard how this has become more affordable with the advent of low-cost wireless sensor networks.

Researcher Jos Balendonck has led a project investigating the practical application of these networks on crops of tomatoes, cucumbers and flowers at Wageningen UR. "Cold and damp spots in your glasshouse lead to variability in crop quality and quantity. There can be differences of up to 7 degsC and 32 per cent relative humidity in the one glasshouse," he said.

But whereas climate monitors previously cost EUR1,000-EUR2,000, modern small lightweight wireless models sell for EUR300 and can be repositioned easily, making sensor arrays a realistic option, Balendonck added.

He suggested a minimum density of 10 sensors per hectare. A base station, typically under the glasshouse roof, relays signals from individual sensors to the main climate-control computer. Repeaters may be needed to boost signals from outlying sensors.

Jouke Miedema of Wireless Value, a consortium that has developed the equipment and software for this, said: "You can have real-time charts showing the distribution of temperature, relative humidity and vapour deficit. Over time, you can locate hot and cold spots. It can also be expanded with soil moisture and light sensors."

Explaining the importance of this, Marc Vergeldt of horticultural expertise group GreenQ added: "The relationship between plant development and temperature is pretty linear. Typically the better performing plants are in the middle of the glasshouse. Also, for every 1 degsC drop in temperature, humidity goes up five per cent, increasing the likelihood of fungal diseases. It's always at the edges or by the doors where problems start."

Climate inequalities - Reduction techniques

Rob Wientjens of Climeco Engineering concluded with suggestions to address glasshouse climate inequalities.

"Relatively cheap fixes include insulating heating pipes, adjusting your air input, repairing cracks in screens, correcting air vents, moving your main climate box and resetting your climate computer," he said.

"Beyond that, you need to look at moving the air around - with horizontal and vertical fans or air sleeves that can move air longer distances or which can be perforated to distribute heated or cooled air."

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