Abstract
In Japanese greenhouses, hot air generated by oil heaters or heat pumps generally is used for heating. Hot air heating is more likely to result in non-uniform temperatures in the greenhouses than heating with hot water pipes, so extra energy is used and uneven crop growth occurs. However, the details of the degree and mechanism of temperature non-uniformity caused by hot air are not well understood. To clarify them, it is effective to use a wireless sensor network (WSN) that can simultaneously measure the temperature at multiple points in the greenhouse for a long time. In this study, we developed a sensor node that measures the temperature distribution of greenhouses at multiple points simultaneously, considering the communication environment and power supply in the greenhouse. Further, WSN was evaluated by measuring the room temperature in a commercial greenhouse. TWELITE, which consumes less power during communication, was used as a communication method. TWELITE is one of the wireless systems that use 2.4 GHz band. Solar cells and capacitors were used as a power supply to eliminate the need for battery replacement. The developed WSN secured a communication distance of 100m in field measurement. The solar cells sufficiently generated electric power even in a greenhouse, and successfully transmitted radio waves from the sensor node for at least half a year or more. Seventy sensor nodes installed in a 0.5 ha tomato cultivation greenhouse showed the change over time of room temperature in detail, indicating that WSN functions effectively.
