Polymer-based CO2 sensors can be integrated together with other sensors such as humidity sensor, temperature sensor, light sensor, etc. to form multi sensor arrays in greenhouse.
Arrays of chemiresistors with different chemically active layers have already been proposed to increase the selectivity for specific gases [74] so that other gases (such as NH3, NO2)can be monitored at the same time with CO2. With proper algorithms for calibration and/or addition of a filter to prevent CO2 and other gases, the signal for interfering gases, such as humidity can be compensated. For using in wireless sensor networks (WSN) these gas sensors may communicate spatially separated with readout/display components [74]. The advantages of a WSN do include high nodal density and low installation costs without the need for extensive wiring. In addition, a WSN provides simultaneous measurements of different parameters (gas concentrations, temperature) for a large area such as in greenhouses and office buildings. The challenges of WSNs for gas sensing are power consumption of individual sensors and handling of the massive data coming from the WSN [74]. Moreover, long-term stability of the polymers should be considered because inadequate long-term stability of many research prototypes of gas sensors prevents their reliable applications in WSNs [74]. Therefore, the stability of the PEI-based sensors developed in this work should be tested further for a long time before they can be used in WSNs for greenhouses. Furthermore, these WSNs with PEI- based sensors can have various potential other applications, such as in-door air quality monitoring in office buildings, food storage/packaging, healthcare.
For the controlled cultivation (photo-synthesis) of plants in greenhouses monitoring of the following parameters are of importance:
• Light
• Temperature
• Humidity
• CO2 concentration.
With about 50 to 100 nodes distributed over a greenhouse area of about 1,000 to 10,000 m2 a good number of nodes is present to monitor appropriate and varying climate conditions.
Especially the climate conditions and related growth parameters covering a long period in a specific area of the greenhouse can be obtained. For a specific crop optimal growth conditions can be extracted from the obtained data on light, temperature, humidity and CO2 stored for the
136
full growing period of the crop. Furthermore, the total energy input needed to grow a specific crop can be extracted and minimized for the three energy consuming parameters including heat, CO2 and (electric) light within the greenhouse. In this way energy efficient cultivation of the crop is enabled by the controlled steering of light, temperature, humidity and CO2
concentration in the greenhouse during the day and during the full growth period.
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143 Supplementary Information for Chapter 2